Final Report

Mg Science & Technology Workshop - Fundamental Research Issues

Held May 19-20, 2011

Arlington, VA

by

Sean R. Agnew, Organizer

Heinz and Doris Wilsdorf Research Chair and

Associate Professor of Materials Science and EngineeringUniversity of Virginia395 McCormick Rd

Charlottesville, VA 22904-4745Ph: 434-924-0605FAX: 434-982-5660

e-mail: agnew@virginia.edu

in consultation with the Workshop Steering Committee

Eric Nyberg, Pacific Northwest National Lab (Co-Organizer)Tresa Pollock, UC Santa Barbara

Robert Wagoner, the Ohio State UniversityBob Powell, General Motors

Ray Decker, Thixomat, Nanomag LLCDonald Shih, The Boeing Company

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Executive Summary

Workshop Overview: A 2-day workshop held on May 19 and 20 in Arlington, Virginia brought together a diverse group of 52 scientists and engineers from academia, government laboratories, industry, and funding agencies to i) identify the outstanding fundamental science issues which inhibit broader application of Magnesium (Mg) alloys in structural (including biomedical) applications and ii) to recommend research directions to address the outstanding issues. Notably, fellowships to attend the workshop were issued to four graduate students, who are interested in academic or research-intensive careers, providing them with a unique perspective of a part of the research process that students rarely see. Two other local graduate students were also able to attend and participate in all aspects of the workshop. This final report summarizes the deliberations and recommendations of the participants.

Workshop Commission: The current renaissance in Mg application and R&D was initiated by interest from the automotive industry, with the primary driver being vehicle mass reduction for improved vehicle efficiency and performance. Interest has expanded into the consumer goods sector with a large number of manufacturers selecting to die cast or semi-solid molding of Mg alloys for the cases of handheld tools and portable electronic goods. Now, the aerospace, defense, and biomedical sectors are all developing interest in strategies to exploit the lightest structural metal in the periodic table of elements. However, there are a variety of application areas which require either better alloy properties or better understanding of how to process and/or design with Mg alloys before broader application will be possible.

Workshop Agenda: 12 invited speakers presented 11 lectures designed to set the tone for the smaller group discussions (see Appendix A for a detailed schedule). The invited speakers represented a broad cross-section of industry, academia and national laboratories from across the globe. They described recent advances and highlighted remaining gaps in our understanding of Mg alloys as well as their personal perspectives regarding opportunities for scientific impact, given new advanced experimental techniques and computational methods. The subsequent break-out discussion sessions addressed 13 topical areas of research (see Appendix B).

The results of those discussions are synthesized into recommendations in eight sections of this final report: Casting and Solidification, Alloy Development, Coatings and Corrosion, Mechanical Performance, Deformation Processing, Joining and Fastening, Flammability and Aerospace Concerns, and Integrated Computational Materials Engineering (ICME). This document should help research sponsors and researchers alike to focus future efforts on those areas that are considered most important and/or appear to have the greatest promise. A short summary of the recommendations follows on the next page.

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Summary of RecommendationsMg alloys play an increasingly important role in structural applications, which demand the light weighting potential of the lowest density structural metal. This is most obvious in the recent, marked increase in the use of Mg alloy die castings for automotive interior parts and consumer products. More aggressive application of Mg alloys in situations demanding greater corrosion resistance, strength, workability, and tolerance for dynamic loading will require active research and development to overcome outstanding scientific and technical barriers.

The following list highlights the areas in greatest need of fundamental research:1. The poor corrosion resistance of Mg alloys demands a focus on slowing the kinetics of

dissolution. Improved fundamental understanding of the mechanisms of corrosion will enable the development of game-changing alloy compositions/surface modifications designed to promote better surface film properties and/or improved barriers (coatings) at the interface with the environment. These approaches should be pursued in parallel, in order to overcome what many view as the critical obstacle to broader application of Mg.

2. There is a need to enhance the mechanical behavior (formability, strength, fatigue, fracture, creep) relevant to deformation processing and application. The unifying theme is a need to improve the understanding of the fundamentals of anisotropic plasticity of hexagonal close packed crystals, including the roles of deformation twinning, shear localization, and the effects of alloying (solute and precipitates) on various deformation mechanisms. Without this understanding, alloy and microstructure design efforts will proceed in an empirical, data-driven manner at a pace too slow for incorporation into modern engineering applications.

3. The knowledge base of Mg alloy thermodynamics is developing quickly, yet that pertaining to kinetics lags. There is a need for more diffusion data and understanding of non-equilibrium phase transformations relevant to solidification, precipitation, and creep. Models of structure evolution during thermal processing and under service conditions are poorly developed, due to inadequate knowledge of system kinetics.

4. Finally, because there are more gaps in the fundamental scientific understanding of Mg based alloys, as compared to more heavily studied ferrous, aluminum, and nickel based alloy systems, they are considered ripe to benefit from increased computational modeling, including that relevant to corrosion, deformation mechanisms, alloy and microstructure design, processing (casting and forming), and performance (failure prediction & mitigation). Integrated approaches which span this entire spectrum and permit new design paradigms are viewed as optimal.

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Contents

Executive Summary.......................................................................................................................................2

Summary of Recommendations.....................................................................................................................3

Workshop Recommendations........................................................................................................................5

Introduction................................................................................................................................................5

Invited Presentations..............................................................................................................................5

Breakout Discussions.............................................................................................................................5

1. Casting and Solidification..................................................................................................................6

2. Alloy Development............................................................................................................................8

3. Coatings and Corrosion......................................................................................................................9

4. Mechanical Performance.................................................................................................................11

Deformation Mechanisms....................................................................................................................11

Dynamic Loading.................................................................................................................................13

Creep....................................................................................................................................................13

Fatigue and Fracture............................................................................................................................14

5. Deformation Processing (including Rolling, Extrusion, and Sheet Forming).................................15

Extrusion..............................................................................................................................................16

Plate and Sheet Rolling........................................................................................................................16

Sheet Formability.................................................................................................................................17

6. Joining and Fastening......................................................................................................................18

7. Flammability and Aerospace Issues.................................................................................................20

8. Integrated Computational Materials Engineering (ICME)..............................................................21

Acknowledgements......................................................................................................................................23

Appendix A: Workshop Schedule...............................................................................................................24

Appendix B: Discussion Group Assignments.............................................................................................26

Appendix C: List of Participants and E-mails.............................................................................................28

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Workshop RecommendationsIntroductionThe recommendations expressed in this report are the collective opinions of the workshop participants. The participants were not required to provide citation or attribution for the work upon which the opinions are based. Nevertheless, experts in the respective fields were present to refute unsubstantiated claims or ideas that have limited merit.

Invited Presentations12 invited speakers presented 11 lectures designed to set the tone for the smaller group discussions whose deliberations are summarized below. Full *.ppt or *.pdf presentation files containing their individual recommendations are available on-line via a password protected website: https://collab.itc.virginia.edu/portal/

1. Integrated Computational Materials Engineering (ICME) (John Allison, U. of Michigan)2. Casting, extrusion, rolling and international collaboration (Karl Kainer, Helmholz Center,

Geestacht, Germany)3. Alloy design & Applications of modern hi-res probes (J.F. Nie, Monash U., Melbourne,

Australia)4. Coatings and Corrosion (Guangling Song, GM, and Robert McCune, retired Ford)5. High strain rate performance (G.T. “Rusty” Gray, Los Alamos National Laboratory)6. Biomedical applications (Wim Sillekens, TNO, Netherlands)7. DoD perspective on Mg Applications: Past, Present & Future (Suveen Mathaudhu, Army

Research Office)8. Formability (Paul Krajewski, General Motors)9. Crystal plasticity modeling and formability (Surya Kalidindi, Drexel Univeristy)10. Ab initio modeling (Dallas Trinkle, University of Illinois, Urbana-Champaign)11. Alloy Design - CALPHAD, texture (Alan Lou, General Motors)

The key quote of the workshop: “Al alloys of incredible strength were developed by Edisonian trial and error, over the course of 80 years. The science and engineering community will only permit us 5-10 years to make similar improvements to Mg alloys.” --- J.F. Nie. There was a consensus that the necessary theoretical, computational, and characterization tools are now available to make this dream a reality.

Breakout DiscussionsWorkshop attendees were broken up into a number of discussion groups on Thursday and Friday afternoons (see Appendix B). The results of those discussions are synthesized in the following eight sections: Casting and Solidification, Alloy Development, Coatings and Corrosion, Mechanical Performance, Deformation Processing, Joining and Fastening, Flammability and Aerospace Concerns, and Integrated Computational Materials Engineering (ICME). The following sections provide detailed recommendations in each of these eight areas.

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Noteworthy absences in the list of topics are those of which explicitly deal with the price of Mg or life cycle analysis. It is true that Mg alloys can be expensive relative to competing alloys and polymers. Thus, their use must be justified in terms of lowered manufacturing cost (e.g. via part integration), lowered life cycle cost (e.g. lowered fuel consumption of a lighter vehicle), or a specific performance enhancement. During the workshop planning stages, it was decided that an explicit focus on these issues was outside the scope of the workshop objectives. For example, it is clear that political factors (including tariffs and other import controls) have a strong influence on the price of Mg alloy products, which can positively or negatively affect the prospects for more widespread application of Mg alloys. However, policy issues are not the immediate purview of the materials scientists and mechanical engineers who comprised the list of workshop participants. Two technical areas that have direct cost implications, which were not addressed, are magnesium extraction and recycling. On the other hand, we did address a number of technical barriers that have direct implications for the cost of using Mg alloys. For example:

Developing a better ability to predict macro/microstructure which results from the die casting processes would improve properties and foundry yields. This would enable the foundries to improve their margins or to lower the price for the end-user.

Exploring low cost methods of primary conversion, e.g. strip casting of Mg alloy sheet is also fruitful, particularly if it can be partnered with low-cost methods of sheet forming, such as a lower temperature forming.

Some of the alloy development strategies highlighted below target improving extrusion rates, which could affect the price of extrusions.

Finally, the entire subjects of coatings, corrosion, fatigue, and fracture all have a strong impact upon the longer term cost of use.

The details of these, and many other, strategies are more fully described in each of the breakout discussion summaries below.

1. Casting and SolidificationIt was noted that all magnesium products begin as liquid, whether die-cast, wrought, or even advanced composites and powder metallurgical concepts that have been proposed recently. It was further noted that the vast majority of current magnesium alloy products are die cast. The need to understand solidification effects on microstructure and properties, in that case, are obvious.

It was celebrated that the thermodynamics (free energies, phase diagrams, etc.) of many of the alloy systems of interest are in reasonable shape and are continuing to develop. Accordingly, we do not view this as an area of desperate need for increased support, but the present level should continue, since one may expect the continuing emergence of new alloy systems which will need further exploration. On the other hand, there are large gaps in our understanding of fundamental diffusion kinetics in both solids and liquids – more complete diffusion databases are needed and new simulation capabilities needed – first principles, cluster variation, and kinetic Monte Carlo

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techniques were mentioned. Additionally, we need to develop a better quantitative understanding of the properties of Mg alloy liquids (viscosity, thermal conductivity, diffusivity, and solution type, e.g. regular or other, etc.) With these properties in hand, simulations of liquid metal flow as well as solidification itself, will improve. Details of the nucleation of the solid within the liquid are still viewed as an area requiring further research. Finally, better models of porosity formation are needed for many metal systems and Mg alloys are no exception.

More broadly speaking, higher fidelity simulations of the entire casting process are required. For example, most casting simulations employ Scheil solidification models, which are inadequate to describe solidification during the typically high rates of cooling employed during most casting operations. New simulation models to more accurately simulate non-equilibrium cooling response are required. These models need to provide a means to link solidification paths to the final microstructure formation (e.g. solute distribution is critical for predicting subsequent age hardening response). It is also important to consider that as new casting and solidification processes develop, their needs will put further stress on the fidelity of existing simulation methodologies.

Producing fine grain microstructures is a goal of many metallurgical processes, and the properties of magnesium alloys appear to respond particularly favorably to grain size reduction. For instance, grain size reduction has been shown to improve the creep resistance of some magnesium alloys, which is unusual. (It is wondered if this result is restricted to alloys based upon the Mg-Al system.) The tremendous grain refining potential of Zr in Al-free Mg alloys is well-known. However, research into other inoculation strategies is still viewed as worthy of research. The potential of adding small (nano-sized) particles to improve the properties of cast Mg should be further explored. Questions arise concerning the grain refining possibilities associated with semisolid processing. In fact, there is a need for models for flow of semisolid material over the range conditions encountered in die casting, thixomolding, etc. Additionally, the possibility of hybrid cast-wrought processes (such as nanoMAG and twin roll casting) should not be overlooked. The grain sizes that are produced by these processes can be quite small and the potential of these processes has not been fully explored.

The potential of twin roll casting has been trumpeted for some years in the Mg community, based upon laboratory-scale results, but the process appears to be very technologically challenging during scale-up. Holistic engineering and simulation strategies are needed. The U.S. research community has played essentially no role in this area, which is dominated by Korean, Australian, Chinese, German, Turkish, and Canadian companies and research institutes. Furthermore, it has yet to be demonstrated that the investment costs for such sheet products has a reasonable return on investment.

The final area explored within the context of casting and solidification was the development of Mg-based metal matrix composites. A more rigorous microstructure design framework is

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needed: micro- and nano-composites do show promise, but less Edisonian approaches are needed. What is needed is modeling of in-situ phenomena (solid/liquid interfacial phenomena) and property prediction before making the composite. Use of new 3D characterization methods, such as synchrotron facilities to uncover a better understanding of liquid-solid phenomena should be encouraged. Dispersion control seriously inhibits the potential of many composite processing strategies, and techniques to prevent agglomeration, ranging from colloid-type approaches to agitation (ultrasonics) should be evaluated. Lower cost approaches aimed at selective reinforcement (e.g. for wear resistance) via local compositing should also be explored.

2. Alloy DevelopmentThe workshop participants agreed that new Mg alloys are needed which target specific property combinations, both to address existing limitations of Mg (susceptibility to corrosion), and to further enhance the advantages of Mg. Currently, there are a very limited number of Mg alloys commercially available from which design engineers must choose. Furthermore, there was a consensus that today’s pace of technology is such that non-Edisonian alloy development efforts need to take place within five-year periods, rather than the 80 years it took to develop the current suite of ultra-high strength aluminum alloys. Rapidly solidified Mg-Y-Zn alloys with tensile yield strengths of 600 MPa and elongation ~ 5% already exist. Developing compositions and processing strategies that make these such property achievements cost-competitive is a real goal.

Mg-Zn is viewed as perhaps the most promising binary system for developing high strength casting or wrought alloys because of the strong precipitation hardening response in this system. In addition, this system meets the need for low-cost alloys. To advance this and other promising alloy systems, principles or rules need to be established for selecting appropriate alloying additions and including micro-alloying additions; e.g., to further enhance age hardening response and mechanical properties. Some published work has already illustrated the great potential of micro-alloying strategies in the Mg-Zn system. There is a balancing point of view, however, since there are ranges of Zn content which suffer from poor hot cracking and corrosion resistance. These facts have historically limited the applicability to die casting and they have limited the application of high strength commercial alloys like ZK60.

Despite the fears surrounding the current high price of rare earth (RE) metals and the nearly sole-supplier status of China, it is suggested that Mg-rare earth systems still deserve more research. Rare earth additions to Mg have proven very potent for improving strength (numerous alloys), creep resistance (numerous alloys), resistance to flammability (e.g. WE43), and reduction in the texture strength of wrought products and subsequent improvement in formability. For one thing, developing alloys which retain these advantages at lower RE content could improve the weight and price competitiveness of Mg alloys. For another thing, the scientific knowledge which is developed through the study of RE alloys may be translated into alloy development strategies applicable to non-RE-containing systems. As an example, RE-containing AE44 was developed to enable the production of a lightweight engine cradle for the Corvette. Later, the AX alloys

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were developed on the basis that Ca was a low cost alternative to RE which forms similar precipitate phases.

At the risk of redundancy, it is again observed that the development of thermodynamic databases has progressed at a good pace in recent years. However, there continues to be a need for more accurate binary and multi-component phase diagrams. For example, the Mg-Nd binary is controversial. Perhaps more urgently, there is a great need for diffusivity data for alloy development. Interfacial energies are also important. This will take a combination of experimental measurements (e.g., using three dimensional EBSD measurements) and some calculations. Interfacial energy of precipitates is also needed for developing precipitation hardenable alloys. More modeling work is needed to support science-based alloy development, including first-principles calculations, molecular dynamics, monte carlo, phase-field, etc, to cover major issues on thermodynamics, kinetics, precipitation, crystal plasticity, strengthening, etc. The lecture by Dallas Trinkle illustrated the potential of first-principles atomistic calculations within a concurrent multiscale framework for predicting bulk alloy properties.

Finally, while many emphasized the need to develop alloys with high strength (in combination with various other properties such as corrosion resistance), some participants expressed the view that not all applications demand high strength. This contingent suggested an equally important focus should be placed on the development of high formability alloys through enhancements in: i) work hardening and ii) resistance to damage initiation.  Some suggested that damage initiation, especially at high strain rates, is linked to one of the deformation twinning modes. They suggest that twinning should be suppressed by alloying or grain size reduction. Evidence that such an approach will work is still lacking. In fact, some researchers point out the possibility of enhancing certain types of twinning in ultrafine grained Mg alloys. It would be beneficial if hard answers to these implied questions could be provided by the scientific community.

3. Coatings and CorrosionMany view corrosion as THE issue which prevents broader application of Mg alloys. The intrinsic problem is that elemental Mg is not thermodynamically stable. In fact, thermodynamically speaking, it is the most active structural metal, and unfortunately, it does not have a good inherent kinetic barrier to corrosion. What we can do to improve its corrosion resistance is try to slow down the kinetics of the dissolution reactions by applying a barrier (coating) at the interface with the environment, adding alloying additions which promote better surface film properties, or altering the environment (where possible).

The basic corrosion mechanisms for Mg are well established, and the common Mg alloys (AZ91, AM60, AZ31, etc.) have been extensively studied. However, there still are some phenomena that cannot be explained. Further studies are urgently required, since these will affect future developments and applications of Mg alloys. In short, there is still opportunity to develop high quality, quantitative corrosion data with correlation to microstructure and processing, even in commercial alloys. Given the commercial significance of these alloys, such research is valued by

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industry. Similarly, there is interest in developing standardized testing schemes that focus on standard environments, relevant to the applications. For example, existing ASTM standards often do not reflect the in-service environments encountered. Thus, there is also interest in developing better qualitative (corrosion damage morphology) and quantitative (corrosion damage evolution) correlations between laboratory tests and service experience.

The detailed roles of all possible alloying/coating elements are not established and must be. Further understanding of precise roles of major and minor alloying elements of passivity and on the details of anodic dissolution must be developed. Further, the role of major and minor alloying elements, intermetallic compounds, and microstructural heterogeneity on cathodic reactions must be better understood. The role of species in complex solutions in aiding in passivation, beyond mere oxides, should be determined. Examples include the possible formation of complex mineral scales.

Given the priority of improving the corrosion resistance of Mg alloys, all possible strategies should be pursued including the development of “game changing,” passivated “stainless” alloys, alloys with more resistant surface "skins,” traditional purification approaches that have proven successful in improving the corrosion resistance of AZ91C AZ91D AZ91E, and coating strategies based upon metals, oxides, and polymers. Concerning metallic coatings, some feel that amorphous coatings or surface modification may have a role to play in corrosion protection of Mg.

In parallel with alloy/coating development and in support of it, the development of a predictive Mg alloy corrosion modeling capability is viewed as critical. Although thermodynamic modeling (including first-principles modeling of Pourbaix diagrams) has some potential, due to the thermodynamic limitations mentioned above, we really need a broader modeling approach including gathering kinetic data and applying it to modeling. This kind of holistic, experimentally validated modeling is expensive, requires a team of investigators, and needs a long-term financial commitment, but the workshop participants view it as important. A roadmap for this modeling work can likely be gained from the recent corrosion modeling work on Al alloys (e.g., the work of Rob Kelly and John Scully at UVa, and Farrel Marin at NRL).

Macro-galvanic corrosion due to joining of dissimilar metals is understood and viewed as an engineering design problem, not requiring deeper mechanistic understanding. Micro-galvanic coupling between phases within an alloy is a significant issue in Mg alloys that deserves significant research attention. Further, coatings should be designed to optimize protection against galvanic corrosion.

Beyond corrosion, other environmental effects, such as stress corrosion cracking and environmentally affected fatigue cracking should be investigated as these are often life-limiting in practical applications in which the uniform and localized corrosion damage accumulation rates in the absence of stress would be acceptable. There does not appear to be nearly as much

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quantitative data available regarding the effect of the environment on the mechanical properties of Mg alloys, relative to Al alloys, steels, etc. Along these lines, alloying and surface treatment designed to minimize hydriding and ways of suppressing/poisoning the hydrogen evolution reaction should be explored.

A final issue related to the corrosion resistance of magnesium alloys is the possible application of bioabsorbable stents and orthopedic implants. In this case, the controlled, but reasonably rapid, corrosion of the implant is actually the goal. There are many issues to be addressed, including processing strategies, drug coatings, and possible unintended health effects of locally high Mg concentrations. Significant research in this area is being done in Europe, with new programs being proposed in Canada, and limited research on-going within U.S. institutions.

4. Mechanical Performance

Deformation Mechanisms

A great deal about the deformation mechanisms of magnesium and its alloys has been learned in the past decade. The basic roles of dislocation-based mechanisms of plasticity, including basal and non-basal slip of <a> type dislocations, and the significance of <c+a> non-basal dislocations are established. The basic role of mechanical twinning is understood as well, including {10.2} “extension” twinning, {10.1} “contraction” twinning and {10.1}-{10.2} double-twinning. EBSD has proven very effective in answering many of the previously unanswered questions. The plastic anisotropies (and asymmetries) that result from the operation of these mechanisms are basically understood and can be accounted for by existing crystal plasticity modeling approaches. The same can be said about the effect of crystallographic texture on macroscopic deformation. There are some inconsistencies in the literature, but consensus appears to be emerging on many of these aspects.

That said, there are many basic phenomena which require much more careful consideration of the various individual deformation mechanisms and of the crystallographic texture than is required for traditional cubic metals. For example, there currently is no widely accepted rule for grain size strengthening of Mg alloys, which can accurately account for all these factors, let alone the effect of grain size distribution. It is suggested by some that only crystal plasticity based approaches will suffice to accurately capture these details relevant to materials design, although this approach may not immediately solve the problems of component and process design. There are many other outstanding questions for which only vague answers exist today. There has been a great deal of confusion about the basal stacking fault energy. Experimental estimates published in the literature vary tremendously.  Some very long stacking faults have been observed, but recent experiments reveal solute segregated at such faults. (In fact, some argue these are precipitates.)  If there is no solute, then the faults tend to be very short.  The interrelation between chemistry and stacking fault energy should be clarified. Atomistic modeling may be helpful in such cases. Atomistic modeling is also demonstrating promise in the

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area of mechanical twinning. However, we still have a very incomplete understanding of the nucleation of twins. The effects of twinning are challenging to implement in continuum models, which are important for forming prediction. Existing continuum models are highly suspect.

It is generally observed that our understanding of the strain hardening behavior of Mg alloys is much less developed that that for fcc metals, for example. What are the interactions between various dislocation and twin types? Additionally, the effect of strain path changes on strain hardening behavior is much stronger than that in cubic metals, and must be accounted for in order to develop robust constitutive models. The effect of temperature (and strain rate) on the strength and activity of various deformation mechanisms has been heavily studied and a number of issues have become clear. The main twinning mode, {10.2} extension twinning, appears to be essentially athermal, while the {10.1} mode is thermally activated. Atomistic modeling has helped to explain distinctions like this, and the details of the twinning dislocation structure are becoming clearer.

Alloy designers, in particular, want to know the quantitative effects of alloy solute and precipitates on the individual deformation mechanisms. In this context, there is a need for control and characterization of tramp impurities.  Commercially available material is not of very high purity.  The role of Zr, for example, is not clear. Atomistic modeling is beginning to augment single crystal experiments in the area of solute effects on dislocation mobilities and stacking fault energies. There are good ideas about the relative impacts of particles: size, shape, and orientation on yield strength and various deformation mechanisms, but these are not well-tested and our ability to predict microstructure effects on strain hardening behavior are still at a relatively nascent state. Finally, there is great interest in better understanding the mechanism(s) of shear localization, which impacts plastic anisotropy, fracture during quasistatic and dynamic loading, and dynamic recrystallization during hot deformation processing. Our basic ability to predict shear banding in Mg is rudimentary.

Some researchers have proposed explanations for the poor multi-axial ductility, fracture toughness, and resistance to shear instability based upon mechanical twinning. Images of shear bands, cracking, and cavitation associated with twins have caused scientists to suggest that minimizing the occurrence of mechanical twinning would promote improved formability and improved dynamic loading response. However, hard evidence that this strategy would work is lacking. Current strategies for minimizing twinning are limited to grain size refinement. Even that notion has been challenged by some recent observations of twinning in a nano-grained Mg-Ti alloy. Our knowledge of the impact of solutes on mechanical twinning is limited. There have been some investigations of the effects of various precipitates on twinning, but this area is still considered open to investigation. The notion that twinning is detrimental to ductility must be tempered by the knowledge that pure Ti is ductile despite prolific twinning and Ti-alloys in which twinning is suppressed have much poorer ductility. Further, one study of the Mg-Cd solid solution alloys revealed that the ductility plummeted in the alloy in which the c/a ratio caused the

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{10.2} twinning mode to switch from an “extension” to a “contraction” twin, i.e. at that condition extension twinning did not occur.

There are various new characterization methods that have been successfully brought to bear on the problem of deformation mechanisms and these ought to be further exploited. These include, but are not limited to: neutron diffraction, 3D synchotron methods, nanoindentation, micro-pillar compression, X-ray tomography, high angle annular dark field imaging in the TEM. There is a need for mesoscale characterization, including grain size, grain orientation and grain boundary character distribution effects on mechanical response and on corrosion resistance. There also opportunities for efficient, statistical quantification of the details of the microstructure using a more rigorous framework such as the n-point statistics, since this approach has not been applied to Mg alloys. There was a discussion of FIB damage. Mg is easily damaged by Ga. This is a problem in preparing micro-compression samples, TEM specimens, and atom probe specimens.

Dynamic Loading

Mg alloys generally exhibit poor dynamic loading response. As suggested above, they have lower resistance to shear instability than many competing Al alloys and steels. Fundamental explanations and possible solutions must be sought. An explanation rooted in texture-based plastic anisotropy has been offered, however, this is countered by the fact that even randomly textured die castings suffer from this problem. There is still the possibility of a texture-softening effect during shear localization; this should be further explored. The poor resistance to shear instability may be connected with a low strain hardening rate, beyond an initial period of high strain hardening. Strategies to improve the strain hardening response should be explored. Similarly, higher strain rate hardening behavior is cited as beneficial. Finally, it would be very useful if there were models which could explain the relationships between strength/ductility and energy absorption/fragmentation.

Creep

Clarity has emerged in the area of creep deformation under service conditions, whereas there were significant inconsistencies in the recent past. For example, the role of grain boundary sliding has been disputed. Recent work has suggested that creep is dislocation accommodated in most of the alloys and stress/temperature regimes of interest for application. Emphasis has now been placed upon alloy systems which offer significant solid solution strengthening or stable precipitation strengthening, the two major avenues employed to achieve creep resistance in other alloy systems. Nevertheless, there is continued interest in understanding the role of grain boundary sliding type deformation at low temperatures and during high temperature forming. A few years ago, creep and bolt-load retention were the principal mechanical properties of interest, as researchers sought to develop new alloys for automotive powertrain applications. The

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successes achieved with the Mg-Al-RE and Mg-Al-Sr alloys within the engine cradle and engine block applications have demonstrated the feasibility of Mg alloys for powertrain applications.

Fatigue and Fracture

Discussion revealed that the understanding of Mg fatigue and fracture behavior is more nascent than our basic understanding of plastic anisotropy of textured alloys and creep behavior, for instance. The existing studies have been largely empirical and the models phenomenological, rather than mechanism based. Connections between microstructure and fatigue properties are not clear. One thing that is clear is that Mg alloys exhibit a very strong Bauschinger effect, at least part of which is due to the intrinsic plastic anisotropy of Mg single crystals and a phenomenon known as twinning-detwinning. The significance of the latter effect on the fatigue properties is only vaguely understood.

The state-of-the-art fatigue models are empirical and are not Mg-alloy specific, which does not provide sufficient information for modeling a broad class of cast and wrought Mg alloy developments. Cyclic plasticity modeling of pure HCP Mg and Mg alloys and understanding the interaction between the slip and twin during unloading should be viewed as a priority. Recent work on deformation and role of microstructure and texture, both experimental and modeling, needs to be extended to cyclic behavior and fatigue crack propagation. In order to achieve this goal, we would need to develop a physics-based understanding of the mechanisms of fatigue damage formation and small-crack growth. Toward this end, 3D microstructure data bases are needed for the modeling of fatigue in magnesium alloys. Such data bases have been developed for aluminum alloys of interest to the aerospace industry. Emerging physics based models for fatigue and fracture, based on 3D microstructure datasets are ready to be developed and applied for Mg-alloys. The computational, analytical, and characterization tools required to advance our understanding of Mg fatigue mechanisms and modeling are available. Applying such tools to Mg will in-turn contribute to improved Mg alloy design and optimization. In short, if we could develop sound, physics-based models for cyclic deformation, damage development and small crack propagation, more rapid alloy design and materials insertion into commercial applications would become a reality.

There is a similar need to educate the Mg research community regarding fracture mechanics and failure models/modes. While our collective knowledge of Mg fracture behavior is relatively limited, we do understand that Mg alloys do not fail by cleavage, despite the fact that many authors frequently misapply that term in their fractographic analyses. Things as basic as the impact of triaxiality, given the strong anisotropy, appear to be open questions. Some materials are more sensitive to imposed hydrostatic pressures than others. This ought to be further explored for Mg alloys. Quantitative understanding and modeling of the nucleation of cracks is needed. For example, are Gurson-type models applicable? Do they need to be modified to account for the greater tendency to localize? There have been very few systematic studies of

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environmental effects, such as the possibility of hydrogen embrittlement, stress corrosion cracking (which may become a bigger concern if higher strength alloys are developed), and environmentally enhanced fatigue.

5. Deformation Processing (including Rolling, Extrusion, and Sheet Forming) There is a need to develop improved constitutive laws (e.g., yield surface models) that take into account the effects of temperature, strain rate, and the various deformation mechanisms. These new constitutive laws are necessary for the construction of accurate models of deformation processes. Issues of anisotropy and tension/compression asymmetry and how to model them, reduce them, or take advantage of them were all discussed. In fact, there is significant overlap in the needs for Deformation Processing and those of the Alloy Development and Mechanical Performance; see these previous sections. It is emphasized that there is a difference between fundamental understanding of the deformation mechanism behavior and a constitutive model that can be employed for predicting the forming behavior or performance of an actual component. While the fundamental understanding of deformation mechanisms has been developing through the use of crystal plasticity modeling, the need remains for constitutive models which are relevant to engineering problems. Combined methods have been developed in other alloy classes, and these should be further explored for Mg alloys.

There is a need to better understand the interactions between the deformed state and that which evolves during recovery/recrystallization. Such issues have been heavily studied, in ferrous and aluminum alloys, but much less detail is available for Mg alloys. There is significant interest in developing a more quantitative understanding of dynamic recrystallization in Mg alloys, as this process may be the key to sustaining the large strains imparted during hot deformation processes, such as hot rolling and extraction. An improved general understanding of microstructure evolution during hot, and warm, deformation and its relation to recrystallization and grain growth is needed for the principal Mg alloy types. The purpose of this understanding is to apply it to the control of product microstructure, e.g., control the recrystallized grain size. The effects of Zr and rare-earth elements, particularly, must be understood. The need to understand the “rare earth effect” was noted specifically and emphatically, as well as our collective ignorance as to the specific mechanisms behind this effect. Other schemes of microstructure control based upon Hornbogen’s concept of “combined reactions,” e.g. recrystallization and phase transformation seem worthy of exploration.

Before moving on to the details individual deformation processing methods, it is mentioned that almost all metal forming processes, involve significant “friction.” The metal has a surface morphology and chemistry, which is distinct from the bulk, and interfacial mediation is applied in the form of liquids, solid particulate, films, etc. The tool/workpiece interface evolves (and hence can be described with suitable state variables) just like the bulk. It is suggested that we have put so much emphasis on modeling the bulk material, that when it comes time to actually simulate a forming process, it is absurd to appeal to an eighteenth century “Law” and use a single

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"friction coefficient." New research should be conducted to develop "interfacial constitutive models." This recommendation applies far beyond the present scope of Mg alloy processing, but is certainly relevant since the frictional behavior of Mg appears to be largely unknown, particularly at forming temperatures and conditions.

Extrusion

Extrusion offers the potential to be a high volume source of wrought magnesium products. The hydrostatic state of stress and elevated temperature present in deformation zone during extrusion allows achieving much higher strain than in many other technological processes. However, they have historically been plagued by low production rates due to limited workability and problems of hot-shortness (depending upon the alloy.) In any event the process window for Mg alloys tends to be smaller than for Al alloys. There is a need for better understanding of the required degree of homogenization of billet material. This is usually achieved by deformation processing. There is continued interest in developing alloys, which can be extruded at higher speeds, but have the desired physical properties in the finished product. Some felt that the Mg-Zn-RE alloy systems merit further investigation. Additionally, it was mentioned that the RE effect on texture was not fully understood, though there has been significant progress over the past five years. On the finished product side, there are problems associated with non-uniform grain size and texture-induced anisotropy.

Plate and Sheet Rolling

Final product should be fine grained, isotropic, and possess microstructural stability necessary for warm forming. There is also interest in developing age hardenable sheets, since the present mass-produced sheet alloy, AZ31, does not respond to heat treatment. Higher strength, heat treatable Mg alloy sheets would open up new application opportunities and are already under development by both US and Korean producers. The “Achilles heel” of many of the sheet/plate alloys applications, relative to die cast alloys, is corrosion. While the base corrosion rate of AZ31 is not significantly higher than AZ91D, thin sheets are much more sensitive to localized (particularly galvanic) corrosion than presently used die-castings, which are thick and most frequently employed in dry or oily environments.

There is interest in developing alternative rolling processes, such as asymmetric and high speed rolling, both of which have demonstrated potential in preliminary trials. In a more conventional sense, there is interest in comparisons of microstructures and sheet properties developed on reversing coil mills vs. unidirectional (e.g. tandem) rolling mills. As has been mentioned in many of the discussions above, there is a sense that fine grained materials may be part of the answer. In this regard, Mg grain refinement in casting, such as that provided by twin-roll casting (TRC) possibly combined with severe shear is of interest. An extreme angle endorsed by some participants was the exploration of rapidly solidified, powder metallurgical routes.

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Sheet Formability

Because of very limited cold formability, Mg alloys have not historically been used in sheet form to produce components with complex shapes. The hot formability of Mg alloys, however, can be outstanding, e.g., superplastic. This excellent hot formability is often attributed to the fine grain structure (relative to many Al alloys and steels) that can be readily developed during conventional wrought magnesium production. Plate applications are, for all practical purposes, presently limited to photo-engraving plate, which benefits from ease of machining and etching and tooling applications which benefit from stiffness combined with low inertia. There is current military interest in broadening the applications of plate, but concerns do exist regarding the mechanical properties at high strain rates.

There was a sense that novel hot- and warm-forming processes (non-isothermal, press quench, etc.), which overcome the difficulties of current technologies or take advantage of particular opportunities specific to Mg alloys, should be explored. There is interest in leveraging the significant current research into alloy and process development, as well as constitutive modeling relevant to warm and hot forming. A specific need to develop new and innovative “joining” processes, such as warm hemming, that take advantage of local heating was recognized. Friction and tribological issues influence all sorts of sheet forming operations, but there is very little knowledge of these phenomena with respect to Mg alloy sheet materials. The success of future forming technologies for Mg alloys will rely upon improved understanding of tribological interactions as a function of alloy, surface condition, temperature and surface deformation (strain rate of surface deformation, surface morphology changes, oxide breakage/formation, etc.)

A clearer answer regarding the optimal grain size for forming of various alloys needs to be provided. Many researchers are suggesting that a finer grain size may produce better forming behaviors (e.g., down to 1 or 2 um), but others suggest that a larger grain size can promote higher greater strain hardening to delay plastic instability. Additionally, questions concerning failure mechanisms abound. What are the failure initiation sites (are they inclusions, twins, shear bands, etc.?) Does void nucleation and growth or necking control ultimate failure during sheet forming? Is there a relationship between alloy content and the role of grain boundary sliding? As mentioned in the deformation processing section, there is a great need to develop our understanding of recrystallization, both static and dynamic. There is a need to better understand how to appropriately suppress or enhance recrystallization for different applications. Finally, an alloy which can be formed and subsequently aged to increase strength is viewed as desirable; perhaps a press-quenching process and an applicable alloy should be developed in parallel. The group feels that answers to these and many other questions about optimal microstructure and alloying may be specific to the target forming temperature and strain rate conditions. Hence, this section is divided into three sections: high temperature (frequently superplastic), warm, and room temperature.

High-temperature forming: Microstructure evolution during hot forming is still poorly understood. It has not been adequately quantified or modeled, for the purpose of prediction. The optimal alloy composition for hot forming is not known. It is known that texture plays a primary role in determining the behavior at low homologous temperatures. However, it is not known what role texture plays during hot deformation.

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Warm Forming (< 250ºC): The basics physics of warm deformation in Mg alloys is not well understood. For example, solute-drag creep in Mg is not understood, but solute-drag creep is recognized as critical for developing warm formability in Al alloys. The idea of press quenching merits further exploration. Multi-physics modeling to enable exploration of novel non-isothermal conditions is viewed as essential. For example, if one were to develop a press-quench process, questions arise concerning the relevant constitutive model to use when the temperature range in the material could span hundreds of degrees Kelvin. Understanding tribological effects and determination of the optimal lubricants for forming in this temperature regime are needed.

Room-temperature forming: All of the aforementioned issues relating to grain size, texture, etc. are pertinent here. A form-anneal-form, multi-step process may be a viable solution to forming somewhat complex shapes. However, limitations of such an approach, such as production speed, must be explored. It is emphasized that determining the stress exponent describing the hardening rate during uniaxial tension testing is not a standalone answer to the question of multiaxial formability. Multiaxial experiments and modeling are required, and this is also true for warm- and hot-forming applications. There is strong evidence that the “RE effect” can improve low-temperature formability. A better understanding of this effect is required. Can it be induced by alloying with other elements? Spring back is anticipated to be complicated in a magnesium alloy which can be formed at low temperatures, due to the low modulus and relatively high strength these alloys exhibit, in combination with the effects of twinning.

6. Joining and FasteningThe overall conclusion of this group is that joining and fastening should not be an afterthought. Rather, consideration of possible options and complications should be a part of initial material selection, manufacturing, and part design strategies. There are a variety of joining processes and options, including mechanical fastening that can be potentially applied to join Mg alloys. Multi-material solutions have great promise from a mechanical design perspective. However, in addition to concerns over galvanic corrosion, mentioned earlier, there are also significant challenges associated with joining Mg to other metals and/or polymer composites in a cost effective manner. The cost penalty associated with joining potentially challenging material combinations needs to be considered up front. Joint efficiency (i.e. the ratio of joint strength to the base-metal strength) also needs to be considered, as it can exceed 100% or be significantly lowered by a variety of metallurgical effects discussed below.

Fusion welding processes, such as gas metal arc welding (GMAW), resistance spot welding (RSW), and laser welding are attractive because of all the existing industrial knowhow and infrastructure. However, Mg weld quality can be poor. GMAW is a widely used mass production process for Al alloys, steels and stainless steels. It could also be widely useful for Mg alloys if the following fundamental issues can be solved: (1) spattering caused by high Mg vapor pressure, (2) gas porosity caused mainly by hydrogen dissolved into the weld pool, and (3) cracking caused by liquation (liquid formation and hence weakening along grain boundaries), which can occur easily because of the very low eutectic temperature (e.g., ~435oC) of many Mg alloys. Liquation cracking has been reported in fusion welding, resistance spot welding and even

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friction stir welding of Mg alloys. High vapor pressure, hydrogen porosity and liquation are problems that potentially can be solved by welding metallurgy approaches.

Dissimilar material joining between Mg alloys and other metals or polymer composites presents the greatest challenge. Solid state/cold processes such as friction stir welding (FSW), ultrasonic welding (UW), friction bit joining (FBJ), self-piecing riveting (SPR) are attractive, but require considerable research and development before they can be applied by the industry. For example, friction stir welding is not presently widely practiced in the automotive industry and it is difficult for certain applications. Most Mg alloys do not have sufficient high-strain rate ductility at ambient temperature required for SPR. Adhesive bonding does not appear to have been significantly investigated, but does have interest for multi-material joining where it may provide some electrical isolation to protect against galvanic corrosion.

There is also interest in developing hybrid solutions such as weld bonding and friction bit joining. There are questions regarding the compatibility of FSW with adhesives in weld bonding, and friction bit joining is only in its infancy of research and development. Different processes have different advantages and disadvantages depending on the application and materials. The optimal joining process for large-scale application of Mg is unknown. Current applications rely exclusively on mechanical fastening (bolting) coupled with galvanic isolation techniques. Science-based, systematic development and fundamental understanding of materials behavior before/during/after joining is critically needed to evaluate the other options. Although research publications on Mg joining have increased sharply recently, the main focus has been on the evaluation of various joining processes on Mg alloys. Much less has been done to understand and overcome the fundamental metallurgical issues. A widely useful process for joining Mg alloys is still not available, and this will hinder more widespread use of Mg alloys.

The effect of heat/deformation from joining processes on defects, microstructure evolution far from equilibrium, and related degradation of weld properties relative to base metal properties need to be determined. The sensitivity of the weld performance to base metal and weld crystallographic texture must be determined. There are indications that the strong texture developed during friction stir welding could render the weld vulnerable to shear loads. Finally, the interest in novel alloys, such as those containing rare earth elements raises questions regarding the effect these additions may have on alloy weldability and weld performance. Finally, there are not established protocols for inspection of Mg weld quality.

In the spirit of Integrated Computational Materials Science (other ICME topics are detailed below), it is suggested that advanced computer aided engineering (CAE) model tools must be developed and matured to accelerate the use of Mg alloys for automobile light-weighting. Such modeling tools are essential for body structure performance prediction (durability, crashworthiness, and rigidity), and body structure assembly dimensional tolerance control. These modeling tools must be able to capture the microstructure changes and inhomogeneity in the

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joints caused by different joining processes. Linking the desired joint properties with the underlying microstructure features by integration of joining process models with the structure performance CAE models would allow for intelligent design and optimization of the joint and joining processes for light-weighting, performance and cost-effectiveness. It is recommended that ICME needs to include material joining as an essential manufacturing technology in its future development.

7. Flammability and Aerospace Issues The drive for light weighting is even greater in aerospace than in automotive. Fuel accounts for 35-40% of the cost in aerospace applications. A 20% weight reduction saves 10% fuel. A 30% weight reduction would save 10% of the entire operating cost. Aircraft manufacturers currently employ Mg castings in helicopter transmission housings, jet engine auxiliary gearboxes, thrust reversers, and a number of cockpit and cabin door fittings. However, other applications are currently under consideration, including fuselage interior, particularly seat applications, which have been considered banned by the FAA under Paragraph 3.3.3 of SAE Standard AS8049. At this point, Mg alloys meet Federal Aviation Regulations (FAR) requirements as well as Joint Aviation Authorities Europe Regulations (JAR). There has been NO known case of aircraft or helicopter accident due to Mg ignition. Nevertheless, flammability is clearly a general concern for all of the payload materials and structures, e.g. polymers, composites, Al, and (potentially) Mg alloys.

Recent full-scale flammability tests of aircraft seat structures (leg assemblies, cross tubes, spreaders, seat back frames and baggage bars) by the FAA Technical Center reveal that Mg alloy WE43 performs better than Mg alloy AZ31, but even the latter performs similarly to Al alloy 2024. Other recently introduced Mg-based materials, such as the Korean ECO-Mg (which contains CaO), also appear to have good flammability resistance. Outstanding gaps are quantitative explanations for alloy chemistry effects on flammability resistance, including rare earth element and CaO effects. Standardized seat frame testing methodologies for the FAA to use in the qualification of materials are being developed. A report describing a new test method will be submitted by the FAA project researchers to the Transport Airplane Directorate by March 2012. The review process will take several months, but it is conceivable that a path to certification of magnesium in aircraft seats could be available by the middle of 2012.

The aerospace industry is also interested in formable wrought products (sheet and extrusion) which could compete with current Al alloys in an effort to reduce weight. A goal of any such alloy design strategy must be to remain cost competitive. Due to currently escalating costs of rare earths (RE) from China, minimizing RE alloying elements could be an important approach for future applications. Of course, the interplay with the new RE mining undertakings in the U.S., Malaysia and the newly discovered undersea RE resources near Hawaii has the potential to stabilize RE pricing at lower levels than today. Moreover, there may be applications where the

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improvement in creep strength, texture modification, and increased flammability resistance would merit the increased cost associated with rare earth alloying.

8. Integrated Computational Materials Engineering (ICME)Many of the individual topics above mentioned the need for a more developed modeling capability. The following recommendations reiterate some of those, but also include the implicit recommendation that an integrated approach, which has come to be known as ICME is meritorious. The ICME approach, as described in a recent National Research Council document has a number of ingredients which distinguish it, for example, from a stand-alone structure-property modeling effort. The approach seeks to promote competitiveness through the rapid insertion of materials innovations into industrial product design. Because there is not a great deal of experience-based empirical knowledge in industry, Mg is viewed as ripe to benefit from an ICME-based approach.

The ICME paradigm involves integration of “materials information” – whether digital data or computational models – into product performance analysis and manufacturing process simulation tools with the goal of promoting more rapid conversion of science-based information into viable engineering tools. Product design, process optimization, and material selection all need to be more closely married in order to develop the optimal product. It is generally recognized that the success of the ICME approach will required coordinated and sustained funding.

While the ICME approach offers a compelling framework, its application still requires a great deal of development work. Isolated researchers (in both academia and industry) will not quickly address these issues. Some feel that advancing the ICME approach will require focused, small team efforts targeting individual tough problems. Enlightened leadership will be required at the research team level as well as from the funding agencies. There are a number of successful demonstrations of modeling a property (in the spirit of the ICME approach) available in the literature. The development of a more comprehensive ICME capability would offer an important outlet and end use for the scientific understanding developed in traditional fundamental projects. In addition to the uses of ICME tools for engineering and alloy design, there are important scientific synergies to be gained by integrating fundamental research projects into an ICME framework.

A high-risk, high-payoff goal would be to develop an integrated composition-processing-microstructure-property modeling approach that would enable alloy optimization for a range of properties, within the next 5-10 years. If we could develop sound, physics-based models for the various properties of interest, more rapid alloy design and materials insertion into commercial applications would become a reality. The potential of Mg alloys to contribute substantially to the light weighting of a variety of transportation systems is great. However, the present knowledge base in the target application industries is limited. Providing them with ICME tools would greatly reduce reluctance on the part of design engineers to employ “unknown” solutions.

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The development of an ICME framework and capability for magnesium alloys would provide a means to conduct computationally the quantitative tradeoffs (between processing routes, alloying additions and properties) required to accelerate alloy design for complex engineering applications. In the context of an NSF program on Mg that explicitly includes ICME, there was discussion that novel funding mechanisms would be required to ensure that integration of the efforts of multiple PIs is accomplished. This could take the form of a call for one or more Focused Research Groups or proposals that explicitly linked PIs to efforts within industrial firms developing ICME capabilities (i.e. ICME GOALI proposals).

As the workshop proceeded, it became clear that many of the participants were not aware of what ICME meant as the acronym was frequently used as a placeholder for computational modeling. In fact, there was significant discussion over the terms “multi-scale” and “multi-temporal” modeling and some dispute over whether it was appropriate to use these terms as synonymous with ICME. Despite individual opinions, there was agreement that the following modeling needs and approaches merit further investigation.

More predictive capability for precipitation in Mg systems: For example, ab initio combined with phase field has been demonstrated as useful in modeling the processing of Al alloys and should be applied to Mg-based systems.  However, there were cautionary notes expressed about the ability of the models to predict certain important quantities and one should expect to have to measure certain aspects and impose them on the meso-scale models. One example concerns atomistic models, we do not have a single Mg embedded atom method (EAM) potential that is accepted by the community for predicting the structure and kinetics of both dislocations and twinning.

Thermomechanical process (TMP) modeling: There is plenty of evidence that microstructure (including texture, microtexture) is critical such that controlling it requires modeling of thermomechanical processing (TMP).  We need to understand how the various deformation mechanisms compete and especially how recrystallization nucleates and grows; again nucleation of damage (voiding, cracking) will probably have to be imposed on the models.  We need to model both the processing and the deformation involved in properties such as fatigue.  Such modeling may well have to include multiple scales such as continuum mechanics and dislocation dynamics.  Particles affect many of these processes (e.g. recrystallization).  Even before one can start a TMP model, one needs to model the solidification process so that, for example, one can quantify segregation of solutes. Obviously, these issues were mentioned in great detail earlier in the report. However, repetition should serve to emphasize their importance. In the context of development of an ICME capability for Mg, an important element of such developments is ensuring that the individual research activities are sufficient to provide a continuous stream of information in the form of constitutive and microstructural evolution models going from casting through wrought processing and heat treating and leading to models for predicting properties.

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Experimental Validation: Validation of modeling is,an important issue.  Some aspects of this are currently accessible.  Some, however, require 3D characterization, such as synchrotron-based methods, e.g. for solidification models or for plastic deformation models.  Also, there are only some aspects of microstructure that we know how to quantify (e.g. grain size) and plenty that we do not have robust tools for (e.g. grain shape). The ICME paradigm admits that models with sufficient fidelity do not exist to describe all the phenomena that must be described for complete process modeling. Therefore, implementation of an ICME capability requires state-of-the-art experimental capabilities to fill outstanding gaps with empirical relationships as well as providing validation of existing models.

AcknowledgementsThe organizers would like to thank the NSF Grant #1121133, with primary support from the Division of Civil, Mechanical, and Manufacturing Innovation (CMMI); Materials and Surface Engineering (MSE) Program; Clark Cooper, Program Manager; and the Division of Materials Research (DMR); Metals and Metallic Nanostructures (MMN); Alan Ardell, Program Manager, for sponsoring this event, the participants (listed in Appendix C) for their active engagement, and the steering committee for fielding an unending list of questions. We would specifically like to thank the many participants and committee members who read and re-read the proposal and this report during the editing phase.

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Appendix A: Workshop Schedule

May 19, 2011 Holiday Inn Arlington-Ballston, Arlington, VA

7:45 – 8:15 Ballston Room - Gathering and registration, light breakfast

8:15 – 8:30 Short Opening Remarks Sean Agnew (Overview, Schedule) Clark Cooper (NSF perspective) Will Joost (DOE perspective)

8:30-12:15 State of the Art in Mg Alloy Science and Technology

8:30 ICME (John Allison, U Mich)9:20 Casting, extrusion, rolling and international collaboration (Karl Kainer,

Helmholz Center, Geestacht, Germany)

10:10 Coffee Break

10:20 Alloy design & Applications of modern hi-res probes (J.F. Nie, Monash U, Melbourne, Australia)

11:10 Coatings and Corrosion (McCune, retired Ford and Song , GM)

12:15 – 13:30 Lunch break

13:30 – 15:10 State of the Art in Mg Alloy Science and Technology

13:30 High strain rate performance (G.T. “Rusty” Gray, LANL)14:20 Biomedical applications (Wim Sillekens, TNO, Netherlands)

15:15 Coffee Break

15:30 – 18:00 Breakout Session 1: commission (Eric Nyberg)

17:30 Breakout 1 group reports

19:00 – 20:30 Dinner and Stakeholder presentation, Arlington-Clarendon Room

Suveen Mathaudhu (Army Research Office, DoD perspective)

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May 20, 2011 – Holiday Inn Arlington-Ballston, Arlington, VA

8:00 – 8:30 Ballston Room, Gathering and registration, light breakfast

8:30 - 12:00 Focus Topics in Mg Alloys

8:30 Formability (Paul Krajewski, GM)9:20 Crystal plasticity modeling and formability (Surya Kalidindi, Drexel)

10:10 Coffee Break

10:20 Ab initio modeling (Dallas Trinkle, UIUC)11:10 Alloy Design - CALPHAD, texture (Alan Lou, GM)

12:00 – 13:15 Lunch

13:15 – 15:00 Breakout session 2: commission (Eric Nyberg)

14:45 Breakout 2 reports

15:15 Participant Coffee Break(Steering committee to quickly meet to discuss wrap-up)

15:30 – 16:00 Closing remarks

16:00 Adjourn

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Appendix B: Discussion Group Assignments

Thursday1. Integrated Computational Materials Engineering 1 (ICME1) (6)

a. Leader – Tony Rollett b. Secretary – Dongwon Shinc. Participants –Ibrahim Karaman, Dallas Trinkle, Surya Kalidindi

2. Characterization (8)a. Leader – J.F. Nieb. Secretary – Greg Rohrerc. Participants – Jim Fitz-Gerald, Yong-ho Sohn, Bin Li, Donald Stone, Cindy Byer,

Benjamin Anglin3. High stain rate deformation (8)

a. Leader – K.T. Rameshb. Secretary – Suveen Mathaudhuc. Participants – Will Joost, Jian Wang, Bob McCune, Rusty Gray, Paul Krajewski,

Neha Dixit4. Fatigue and fracture (8)

a. Leader – Wayne Jonesb. Secretary – Anna Xuec. Participants – John Allison, Mark Weaver, Somnath Ghosh, Rupalee Mulay,

Donald Shih, Dean Paxton5. Casting (8)

a. Leader - Tresa Pollockb. Secretary – Mike Dierksc. Participants – Karl Kainer, Anand Raghunathan, Eric Nyberg, Zhili Feng, Alan

Luo, Vince Hammond6. Deformation processing – rolling and extrusion (8)

a. Leader – Martyn Aldermanb. Secretary – Warren Poolec. Participants – Wojtek Misiolek, Rad Radhakrishnan, Eric Taleff, Yuri Hovanski,

Amanda Levinson, David Foley, Keith Wang7. Biomedical applications (6)

a. Leader – Michelle Manuelb. Secretary – Wim Sillekensc. Participants – Guangling Song, Barb Shaw, Clark Cooper, Ray Decker

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Friday

1. Integrated Computational Materials Engineering 2 (ICME2) (8)a. Leader – John Allisonb. Secretary – Rad Radhakrishnanc. Participants – Dallas Trinkle, Bin Li, Jian Wang, Somnath Ghosh, Yong-Ho

Sohn, Ben Anglin2. Alloy development (8)

a. Leader – Alan Luob. Secretary – J.F. Niec. Participants - Michelle Manuel, Tresa Pollock, Rupalee Mulay, Dongwon Shin,

Anna Xue3. Formability (8)

a. Leader – Eric Taleffb. Secretary – Eric Nybergc. Participants – Paul Krajewski, Amanda Levinson, Warren Poole, Mark Weaver,

Ibrahim Karaman4. Flammability, Aerospace, and Composites (8)

a. Leader - Donald Shihb. Secretary – Martyn Aldermanc. Participants - Ray Decker, Suveen Mathaudhu, Mike Dierks, David Foley, Karl

Kainer, Wayne Jones5. Joining and Fastening and Multi-material Solutions (6)

a. Leader – Dean Paxtonb. Secretary – Zhili Fengc. Participants – Jim Fitz-Gerald, Vince Hammond, Yuri Hovanski, Keith Wang

6. Corrosion and Coatings and Multi-material solutions (7)a. Leader – Barb Shawb. Secretary – Robert McCunec. Participants – Guangling Song, Wim Sillekens, Clark Cooper, Karl Kainer, Will

Joost7. Deformation and Fracture Mechanism (7)

a. Leader – Surya Kalidindib. Secretary – Bin Lic. Participants – Rusty Gray, Neha Dixit, Tony Rollett, Donald Stone, Cindy Byer

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Appendix C: List of Participants and E-mailsSpeakersJohn Allison johnea@umich.eduJian-Feng Nie Jianfeng.Nie@monash.eduKarl Kainer karl.kainer@hzg.deGuangling Song Guangling.song@gm.comBob McCune robert.mccune@sbcglobal.net “Rusty” Gray rusty@lanl.govWim Sillekens wim.sillekens@tno.nlSuveen Mathaudhu suveen.n.mathaudhu.civ@mail.milPaul Krajewski paul.e.krajewski@gm.comSurya Kalidindi skalidin@coe.drexel.eduDallas Trinkle dtrinkle@illinois.eduAlan Luo alan.luo@gm.com

ParticipantsAnna Xue anna.xue@usu.eduAnand Raghunathan araghunathan@energetics.com Bin Li binli@cavs.msstate.eduBarbara Shaw bas13@psu.eduDean Paxton dean.paxton@pnl.govZhili Feng fengz@ornl.govGreg Rohrer gr20@andrew.cmu.eduIbrahim Karaman ikaraman@tamu.eduWayne Jones jonesjwa@umich.eduJim Fitz-Gerald jmf8h@virginia.eduMartyn Aldreman martyn.alderman@magnesium-elektron.comMike Dierks mdierks@spartanlmp.comMichelle Manuel mmanuel@mse.ufl.eduMark Weaver mweaver@eng.ua.edu“Rad” Radhakrishnan radhakrishnb@ornl.govTony Rollett rollett@andrew.cmu.eduDongwon Shin shind@ornl.govEric Taleff taleff@mail.utexas.eduVince Hammond vincent.h.hammond@us.army.milWarren Poole warren.poole@ubc.ca“Wojtek” Misiolek wzm2@Lehigh.eduYongho Sohn ysohn@mail.ucf.eduYuri Hovanski yuri.hovanski@pnl.govJian Wang wangj6@lanl.govClark Cooper ccooper@nsf.govWill Joost William.Joost@ee.doe.govDonald Stone dsstone@wisc.edu

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Somnath Ghosh sghosh20@jhu.eduQi Yang Qi.Yang@hap.com

Steering CommitteeSean Agnew sra4p@virginia.eduEric Nyberg eric.nyberg@pnl.govTresa Pollock pollock@engineering.ucsb.eduRay Decker RDecker@Nanomag.usDonald Shih donald.s.shih@boeing.com*Bob Powell bob.r.powell@gm.com*Rob Wagoner wagoner@matsceng.ohio-state.edu* unable to attend workshop

Graduate Students:Rupalee Mulay rpm8g@virginia.eduBen Anglin anglin.ben@gmail.com David Foley tdfoley@tamu.eduAmanda Levinson amanda.j.levinson@gmail.comNeha Dixit dixitnehar@gmail.comCindy Byer cbyer1@jhu.edu

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