effect of multi-pass friction stir processing on ... · the samples were etched with keller’s...
TRANSCRIPT
http://www.iaeme.com/IJMET/index.asp 667 [email protected]
International Journal of Mechanical Engineering and Technology (IJMET)
Volume 9, Issue 6, June 2018, pp. 667–679, Article ID: IJMET_09_06_076
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=6
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
EFFECT OF MULTI-PASS FRICTION STIR
PROCESSING ON MECHANICAL PROPERTIES
OF AA6061-T6
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo
Department of Mechanical Engineering Science, University of Johannesburg, South Africa
Michael Agarana
Department of Mechanical Engineering Science, University of Johannesburg, South Africa
Department of Mathematics, Covenant University, Nigeria
ABSTRACT
Samples with one through five passes with 100% overlap were produced using
friction stir processing (FSP) technique to study the effect of multi-pass FSP on the
microstructure and mechanical properties of AA6061-T6 alloy. The evolving
microstructure and mechanical properties after each successive FSP pass were
studied in detail. Constant traverse and rotational speeds were used for processing.
The resulting microstructural evolution and the grain sizes after each FSP pass was
seen to be strongly dependent on the processing parameters, the thermal cycle and the
presence of second-phase precipitates. The base material was found to have better
mechanical properties than all processed samples.
Keywords: Aluminum alloy, mechanical properties, microstructure, multi-pass
friction stir processing.
Cite this Article: Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and
Michael Agarana, Effect of Multi-Pass Friction Stir Processing on Mechanical
Properties of AA6061-T6, International Journal of Mechanical Engineering and
Technology, 9(6), 2018, pp. 667–679
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=6
1. INTRODUCTION
Friction stir processing (FSP) is a technique developed to modify the properties of a metal
through severe plastic deformation. It entails passing a non-consumable rotating tool
containing a specifically designed pin and shoulder through a metal sheet or plate. FSP is
based on the same approach as friction stir welding (FSW), a solid-state joining technique,
developed by The Welding Institute (TWI) in the United Kingdom in 1991 [1]. Since its
invention, FSP has continually been improved to achieve desired mechanical properties. It has
been effectively applied to a variety of aluminum, magnesium, and copper alloys. Several
studies have shown that FSP is known to improve the mechanical properties of materials. Sun
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 668 [email protected]
and Apelian [2] reported that there was a high grain refinement and improved mechanical
properties in their study of the microstructural evolution during the single-pass FSP of
aluminum cast alloys. Hashim et al [3] applied a single-pass FSP on 2024-T3 aluminium alloy
and recorded an improvement in hardness and tensile strengths of the material. This was
reported to be as a result of a significant grain refinement of about 77% decrease in grain size.
Furthermore, a study of the effect of single-pass FSP on mechanical properties and the
microstructure of Al-Zn-Mg-Cu alloy by Salman [4] also revealed that FSP result in
significant grain refinement, elimination of casting defects, and an improvement in the
hardness, tensile strength, and ductility of the aluminum alloy. However, some studies
reported deterioration in the mechanical properties after the FSP process. An example is the
reduction in material hardness reported by Gan et al [5] in their study of the evolution of the
microstructure and hardness of rolled pure aluminum after FSP, even though equiaxed and
fully recrystallized grains was achieved. They observed a local material softening in the
friction processed zone (FPZ) and recorded that the decrease in hardness is due to the
dissolution of precipitates during FSP. There was also a similar report by Weglowski [6] on
the reduction in hardness when they applied a single FSP pass on AlSi9Mg aluminum alloy.
Few researchers have applied multi-pass FSP on aluminum materials to study its effect on
microstructural evolution. Chen et al [7] carried out a three-pass FSP with 100% overlap on
Al-5083 aluminum alloy sheet and recorded a refinement in grain size due to recrystallization
in the first pass, but no substantial change in grain size after subsequent overlapping passes.
All the multi-pass friction stir processed (FSPd) samples exhibited reduced hardness, yield
strength and tensile strength in the stir zone (SZ) compared to the base material and no
significant changes with subsequent multiple passes. El-Rayes and El-Danaf [8] studied the
influence of multi-pass FSP on the properties of thick commercial 6082-T651 AA plates.
They carried out one to three passes with 100% overlap and discovered that the single-pass
FSP caused dynamic recrystallization of the stir zone leading to equiaxed grains, but there
was a decrease in the hardness and tensile strength after subsequent multiple passes. The
hardness reduction was reported to be as a result of the SZ softening which accompanied the
increase in the number of passes. This softening was attributed to larger grain size after
subsequent FSP passes. It was also suggested that the reduction in tensile strength was due to
the over aging effect on the previous passes by the subsequent ones. Krishna and
Satyanarayana [9] also reported a reduction in yield strength, tensile strength, hardness, and
elongation with an increase in the number of passes when they carried out three-pass FSP
with 100% overlap on Al6331+SiC composite. There was a reduction in grain sizes and
silicon flakes after subsequent FSP passes. The deterioration in the mechanical properties was
attributed to the precipitate dissolution and the limited re-precipitation by the thermal cycles
of FSP. Yang et al [10] reported contrary results when they studied the effects of four-pass
FSP with 100% on the microstructure and mechanical properties of Al3Ti/A356. There was a
continuous significant reduction in grain size from base material to the fourth pass and the
yield strength, tensile strength, and ductility also improved after every subsequent pass
because of the grain refinement. The variety and inconsistency observed in the results showed
a strong dependency of FSPd materials mechanical properties distinctly on the workpiece
material and FSP processing parameters irrespective of the number of FSP passes.
In the present study, the effects of five-pass FSP on the microstructural evolution and
mechanical properties of AA6061-T6 were investigated. The alloy in its T6 condition is of
great interest because of its tendency to lose some strength in the weld region after
joining/welding - because its solution is heat-treated and artificially aged.
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 669 [email protected]
2. METHODS
The FSW machine used to produce the welds is a custom designed computer controlled 2-
Axis FSW machine with the tool in a horizontal position and the specimen held in vertical
position at the Indian Institute of Science (IISC), Bangalore, India. This machine was
developed with the help of ETA technologies, Bangalore, India. It has the capability to vary
the tool rotational speed, traverse speed and plunge depth during a process. This platform is
shown in Fig.1.
Figure 1 The FSW Platform
The parent material used in this research work was AA6061-T6. The dimension of the test
coupon for each plate was 250 x 210x 6 mm and the length of the welds produced was 200
mm. The chemical composition of the parent material was confirmed, using a spectrometer,
and these were found to conform to the standard AA6061-T6 specifications [11]. Table 1
shows the chemical composition of the parent material.
Table 1 Chemical composition of AA6061-T6 used in this study
Element Weight %
Si 068
Fe 0.49
Cu 0.21
Mn 0.08
Mg 0.84
Cr 0.06
Ni 0.01
Zn 0.07
Ti 0.07
Al 97.40
Ag Balance
The FSP tool used for this research was a High-Density Steel (HDS) tool, with a concave
shoulder diameter of 25mm and a cylindrical pin with tapered pin diameter 6-7mm, pin length
5mm (Fig. 2).
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 670 [email protected]
Figure 2 High-Density Steel (HDS) Tool
Among the various tool materials available, HDS was chosen due to its high strength,
hardness, availability and low cost. The tool geometry and parameters were also selected
based on the knowledge from the review of literature. A constant 3° tilting angle was applied
to the tool, and all FSP was performed in position control mode, with a plunge depth of
5.3mm. The plunge depth ensured that the necessary downward pressure is achieved, and the
tool fully penetrates the weld, while the tool tilt angle ensured that the rear of the tool is lower
than the front as reported in the literature review. A constant rotational and transverse speed
of 1600rpm and 40mm/min respectively was used throughout the FSP processes. These were
optimum process parameters earlier obtained for FSP of AA6061 [12]. Samples were
sectioned using a Concord Wire Electric Discharge Machine (EDM) employing a 0.2mm
diameter molybdenum cutting wire.
Optical microscopy was conducted using Olympus BX51M and Olympus SZX16 optical
microscopes. Olympus BX51M was used to observe the microstructures, while the Olympus
SZX16 was employed in observation of the samples macrograph. Digital output was captured
and processed using the Olympus Stream Essential software. The TESCAN VEGA3 Scanning
Electron Microscope (SEM) setup was used to study and compare the microstructures
observed in the base material. The Vega TC software was used in acquiring the image on the
SEM. The Vickers microhardness values were measured using the Time Vickers
Microhardness Hester TH713 by Beijing Cap High Technology Co. Ltd according to ASTM
384-16 standard [13]. The transverse tensile tests were performed using the servohydraulic
Instron tensile testing machine model 1195 to obtain the ultimate tensile strength and
elongation. The tensile samples were tested according to ASTM E8M-13 standard [14]. The
tensile properties of the materials were evaluated by testing three specimens in each condition
to quantify the tensile and yield strengths. The percentage of the elongation of the FSPd
samples was evaluated by measuring the final length of the failed specimens to determine the
ductility of the samples.
3. EXPERIMENTS
The FSW machine has an already installed customized program for the control of the FSW
process which provides the interface for inputting the process parameters to create and
execute the FSW/FSP process. 5 multi-pass FSP with 100% overlap were conducted with
increasing FSP passes conducted on different workpiece. The processed samples, in multi-
pass cases, were cooled down to room temperature before successive FSP passes were
conducted. For optical microscopy (OM), Samples of size 25 x 6 x 6 mm at the processed
zone were sectioned, and mounted in polyfast thermoplastic resin with a Struers hot mounting
machine and identified according to the number of FSP passes with an engraving tool. The
samples were then grinded and polished using a Struers polishing machine, and cleaned with
distilled water. The samples were mounted, grinded and polished with the advancing side of
the weld always to the right following the standard metallographic procedures [15]. After this,
samples were chemically etched to reveal microstructure. At the initial stage of the research,
the samples were etched with Keller’s reagent (190ml distilled H2O, 5ml HNO3, 3ml HCL,
and 2ml HF) but the grains were not visible, hence Weck’s reagent (100ml distilled H2O, 4g
KMnO4, 1g NaOH) was used. The samples were observed under the microscope for
microstructural characterization. Microstructures of FSP samples were obtained for the base
material (BM), SZ, thermo-mechanically affected zone (TMAZ), and heat affected zone
(HAZ) for comparison. The grain sizes of the different zones were carried out, according to
the standard test method for determining average grain size: ASTM E112 – 12[16]. For
microhardness, the samples were placed on the testing platform. When the hardness testing
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 671 [email protected]
machine is in operation, a pyramid-shaped diamond penetrates the surface of the material with
the set force, generating an indentation into the material. The dimension, D1, and D2, of the
indent are proportional to the depth penetrated by the diamond, and the depth reached is
directly related to the hardness of the material. The hardness profiles were obtained across the
process zones in the FSP samples, to investigate local variations in mechanical properties as a
functional of the experimental variables. The measurements were taken in the as-polished
conditions, across the cross-sections of the process zones with a load of 200g and a dwell time
of 15secs. The indentations were taken at 1.5mm intervals on the sample, with the
indentations manually focused and the hardness measurement digitally displayed. Before
beginning the tensile testing, the computer system connected to the machine was set up by
inputting the necessary information of gauge length and width of the specimen. The computer
system was then prepared to record data and output necessary load-deflection graphs. The test
was conducted at room temperature by gripping the ends of the samples in the tensile test
machine and then loaded until at a constant cross head speed until failure. An extensometer
was used to measure the strain of the samples during the experiment at an extension rate of 5
mm/min and a gauge length of 25 mm, with a maximum load of 100kN. The load-deflection
curve was shown on the computer screen as a visual representation, with the data collected
using the customized Instron Bluehill2 software. The tests were repeated 3 times to check for
consistency within the data to achieve better accuracy.
4. RESULTS
The average grain size in the base material was found to be 6.69 µm while the average size of
precipitates (Mg2Si) present was found to be 6.57 µm using the linear intercept method. The
microstructures of the various zones of the processed plates in this work are illustrated in Fig.
3 showing each zone and the various number of FSPd samples. It was observed that
microstructures of the FSPd regions are different from that of the base material. The FSPd
zones exhibited a much more distinct spherical grain morphology compared to the base
material. The BM had yield strength of ~311 MPa, ultimate tensile strength (UTS) of ~338
MPa and a ductility of 15%. It was clear that all the FSPd samples show a reduction in the
UTS and yield strength compared to BM samples. The samples average UTS and yield
strengths of all the FSPd samples are between the ranges of 170-200 MPa and 165-190 MPa
respectively. However, there was no significant change in the elongation percentages of the
processed samples compared to the BM. There was a range of 1-2% reduction in the
elongation percentage from the single-pass sample to the four-pass sample, while the five-
pass sample exhibit the same elongation percentage as the BM showing that FSP does not
have a significant effect on the ductility of the material using the processing parameters
employed in this study. A graphic representation of these properties is presented in Fig. 4.
Fig. 5 shows a graphic representation of the mean hardness values of all the processed
samples. The highest hardness values were seen in the BM, similar to the report by Al-
Fadhalah et al [17]. The microhardness profiles of the BM and the FSPd samples are
presented in Fig. 6 to fully understand the variation of the hardness values across the samples.
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 672 [email protected]
Figure 3 OM micrographs of FSPd samples (a) SZ (b) TMAZ (c) HAZ
Figure 4 Tensile Properties
Figure 5 Average Hardness Values
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 673 [email protected]
Figure 6 Microhardness Profile
5. DISCUSSION
The SZ of the single-pass sample consists of nearly equiaxed grains as a result of dynamic
recrystallization. Grain growth and a complete dissolution of the second-phase precipitate into
the matrix are also clearly visible in the micrograph. The complete dissolution of the second-
phase precipitates is attributed to the inability of the identified precipitates to withstand high
temperatures. El-Rayes and El-Danaf [8] reported that the precipitates are not temperature
resistant and rapidly dissolve when exposed to high temperatures resulting from FSP. Woo et
al [18] also reported that the frictional heating resulting from FSP causes the dissolution of
the precipitates. During FSP, the SZ experiences intense plastic deformation and thermal
exposure with peak temperatures almost up to the melting point of the alloy [7]. The size of
the grains in the TMAZ and HAZ in the single-pass samples seems to appear similar to the
grain size in the SZ. However, there are differences in grain size across the different zones.
The result shows almost 70% increase in the grain size of the SZ after a single FSP pass,
with 23% and 17% increases in the TMAZ and HAZ respectively, showing that the TMAZ
and HAZ of the base material have experienced lower strains and strain rates as well as lower
peak temperatures compared to the SZ. It is noteworthy that the consequential grain growth in
the SZ is defined by the factors impacting on the nucleation and growth of the dynamic
recrystallization. Mishra and Ma [19] reported that the FSP parameters, tool geometry,
material chemistry, workpiece temperature, vertical pressure, and active cooling significantly
impact on the size of the grains in the SZ. The grain growth observed in this sample can be
classified as abnormal grain growth (AGG), as the resulting microstructure is dominated by a
few very large grains which usually results from a subset of grains growing at a high rate at
the expense of their neighbours. AGG occurs when there is an inhibition in the normal growth
of the matrix grains, and when the temperature is high enough to allow a few special grains to
overcome the inhibiting force and to grow disproportionately. All two-pass sample
microstructural zones show a refinement in grain size. This could be attributed to dynamic
recrystallization after the second pass. A grain refinement of 25%, 11%, and 14% decrease in
grain size in the SZ, TMAZ, and HAZ respectively compared to the single-pass sample is
recorded. This dynamic recrystallization is usually attributed to the plastic deformation and
the high temperatures from FSP [8]. It is noteworthy that in the micrograph of the two-pass
sample SZ, it can be observed that there is a competition between the dynamic
recrystallization and concurrent recovery. Dynamic recrystallization also occurred in the
three-pass sample resulting in further refinement in the grain sizes. The various
microstructural zones show a 34%, 27%, and 18% reduction in size in the SZ, TMAZ, and
HAZ respectively compared to the two-pass sample. Platelet-shaped re-precipitation of the
second-phase precipitates is clearly visible in the HAZ of the sample. The precipitates were
more relatively homogenous in the HAZ with an average size of 9.76 µm, which is much
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 674 [email protected]
larger than those found in the base material. This limited re-precipitation could be attributed
to the thermal cycle [9]. A reduction in temperature because of reduced friction during the
third pass FSP is assumed to have favoured the re-precipitation. A similar two stage
mechanism involving full dissolution of the precipitates followed by re-precipitation was
reported during FSW on 6056 aluminum alloy by Cabibbo et al [20].
The four-pass sample shows grain growth in all the microstructural zones. There was a
47%, 32%, and 18% increase in grain sizes in the SZ, TMAZ, and HAZ respectively. There
was a complete dissolution of the second-phase precipitates observed in the three-pass
sample. The behavior in the transition from the three-pass sample to the four-pass sample is
similar to the transition of the base material to the single-pass sample with respect to second-
phase precipitates dissolution and increase in grain size. The four-pass sample also exhibited
nearly equiaxed distinct spherical grains in all the FPZ zones like the first sample. However,
in this case, it is believed that normal grain growth (NGG) has occurred, as the grain growth
seems to have occurred in a uniform manner. A significant coarsening and growth of the
grains is seen in all the five-pass sample FPZ zones; the SZ seems to be coarser than the
TMAZ and HAZ. This coarsening could be attributed to the additional/accumulated thermal
cycles which the plate has experienced. Sinhmar et al [21] stated a similar reason for grain
coarsening after multiple FSP passes. It is apparent that the various mechanisms acting at
different stages of the microstructure evolution after every successive multiple FSP pass are
related to the strain, strain rate, and thermal cycle which the material undergoes at each stage.
The significant high strength in the base material is attributed to the presence of the
second-phase precipitates. Shankar et al [22] reported that precipitation treatable aluminum
alloys such as Al6061-T6 which is peak aged (T6 temper) have an optimum distribution of
precipitates that ensures the greatest strength of the material. A similar high strength is
recorded in a study by Ravikumar et al [23] on the characterization of the mechanical
properties of Al6061-T6 after FSW. The yield strength is seen to decrease uniformly as the
UTS decreases. A significant reduction in the tensile properties after the first FSP pass could
be attributed to the dissolution of the precipitates resulting in softening which occurred in the
SZ, and a reduction in pre-existing dislocations. Al-Fadhalah et al [17] reported that age-
hardened aluminum alloys depend strongly on precipitate size and distributions rather than on
grain size. This is displayed in the tensile values of the second and third passes, where there
was a reduction in the grain size, and a reduction in the UTS and yield strength, against the
expected increment in the values according to Hall-Petch relation [24]. It could be concluded
that these reductions of UTS and yield strength are due to the overaging effect which the
subsequent passes cause to the previous one [8]. The re-precipitation seen in the three-pass
sample is ~1.5 times bigger than the precipitates in the base material. It is noteworthy that the
size of the precipitates has a major influence on how the precipitates influence the mechanical
properties of materials. There was no significant change in the UTS and yield strength after
the fourth FSP pass, but a sharp increase in these properties was observed after the fifth FSP
pass. This could be attributed to the completely homogenous FPZ microstructure obtained
after the pass.
The reduction in the hardness of the FSPd samples compared to the BM can be attributed
to softening from the complete dissolution of the second-phase precipitates. The BM has an
average hardness of ~99 ± 7.4 HV reaching a peak hardness value of 107 HV. This is
relatively high when compared to the 35% drop in hardness value to ~64 ± 2.6 HV after the
first FSP pass. The single-pass sample shows a relatively uniform microhardness distribution
with less scatter. An increase in the softening area in the sample after the second pass led to a
reduction in the microhardness value to an average value of ~59 ± 3.1 HV. The two-pass
sample show a distribution of hardness values lower in all regions when compared to the
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 675 [email protected]
hardness distribution of the single-pass sample. However, both samples’ peak hardness values
were observed to be on the AS. Jiang and Kovacecis [25] reported that this behavior was as a
result of the substantial fluctuation related to the heterogeneous constitution of the nugget.
Yadav and Buari [26] claimed that hardness variations may result from different
microstructural features at different locations in the FPZ. They explain that the flow of
material from the RS to the AS during FSW/FSP gives rise to gradients in temperature, strain
and strain rate in the stir zone.
There was no significant change in the average hardness values of the three-pass sample
compared with the two-pass sample. An average hardness value of ~59 ± 6.3 HV was
recorded. However, a significant peak hardness up to 60 HV is observed towards the AS
which could be attributed to the re-precipitation observed in the three-pass sample HAZ. Even
though the re-precipitation has a negligible effect on the tensile properties, this shows that it
has an effect on the hardness properties of the material. From this observation, it could be said
that the negligible effect of re-precipitation on the tensile properties of a material is not an
indication that the precipitates will not influence the hardness properties of the material. A
significant observation in the behavior of the microhardness values is its increase as the
samples near a homogenous FPZ. A 4.4% increase in the average hardness value is observed
in the four-pass sample, which further increased by an 8.8% increase in the five-pass sample.
The four-pass and five-pass samples have an average hardness value of ~61 ± 3.7 HV and ~67
± 8.7 HV respectively. The average hardness value, as well as the distribution of the hardness
values in the fifth pass as shown in Fig. 5 and 6 respectively can be seen to be higher than all
the values obtained from the preceding numbers of FSP passes. However, this is still far
below the hardness values obtained from the BM. From the observations, it could be said that
material flow and mixture have a strong effect on the hardness of the material making the
microstructural homogeneity of the FPZ a very important factor in determining the hardness
of a material. The increase in hardness after the fourth and fifth FSP passes could be
attributed to the re-precipitation of the second-phase strengthening precipitates.
6. CONCLUSIONS
FSP has been performed on 6061-T6 aluminum alloy by applying one through five 100%
overlapping passes with the main emphasis on the effects of the multi-pass on the evolving
microstructure and mechanical properties of the material. The BM has more improved
mechanical properties when compared to all FSPd samples, irrespective of the number of FSP
passes. This is attributed to the presence of unaltered second-phase precipitates and T6
condition (heat-treated and artificially aged).
The microstructural evolution and the resulting grain sizes are strongly dependent on the
processing parameters, the thermal cycle, and the presence of second-phase precipitates in the
matrix. Single-pass FSP led to a non-homogenous FPZ, decreased strength, hardness and
ductility, and abnormal grain growth while multi-pass FSP led to a completely homogenous
FPZ after the fifth FSP pass, attributed to accumulative plastic strain. This indicates that the
number of FSP passes have a significant effect on the homogeneity of FPZ in a material. The
homogenous FPZ led to improvements in previously reduced mechanical properties
(hardness, and tensile strength, and ductility) of AA6061-T6.
The thermal cycle has more influence on the mechanical properties than the grain size, the
increase in the number of FSP passes accumulates more heat which leads to a complete
dissolution of hardening second-phase precipitates. This dissolution impairs the mechanical
properties. An increase in the grain sizes is also observed after dissolution of the second-phase
precipitates (as observed after the first and fourth FSP passes).
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 676 [email protected]
ACKNOWLEDGEMENT
The authors would like to express their sincere appreciation to the Department of Mechanical
Engineering - Indian Institute of Science - India for supporting this work. The main author
will also like to acknowledge University of Johannesburg for the Global Excellence Stature
(GES) scholarship award. This work was supported by the University of Johannesburg
Research Committee (URC).
REFERENCES
[1] Dawes, C.J., Thomas, W.M. (1995). Friction stir joining of aluminium alloys. TWI
bulletin, vol. 6, p. 124-127.
[2] Sun, N., Apelian, D. (2009). Microstructural modification of A206 aluminium via friction
stir processing. Materials Science Forum, vol. 618, p. 361-364,
DOI:10.4028/www.scientific.net/MSF.618-619.361.
[3] Hashim, F.A., Salim, R.K., Khudair, B.H. (2015). Effect of friction stir processing on
(2024-T3) aluminum alloy. International Journal of Innovative Science Engineering and
Technology, vol. 4, no. 3, p. 1822-1828, DOI: 10.15680/ijirset.2015.0404003.
[4] Salman, J.M. (2014). Effect of friction stir processing on some mechanical properties and
microstructure of cast (Al-Zn-/mg-Cu) alloy. Journal of Babylon University Engineering
Sciences, vol. 22, no. 2, 10pp.
[5] Gan, W.Y., Zheng, Z., Zhang, H., Tao, P. (2014). Evolution of microstructure and
hardness of aluminum after friction stir processing. Transactions of Nonferrous Metals
Society of China, vol. 24, no. 4, p. 975-981.
[6] DOI: 10.1016/s1003-6326(14)63151-4.
[7] Węglowski, M.S. (2014). Microstructural characterisation of friction stir processed cast
AlSi9Mg aluminium alloy. Archives of Foundry Engineering, vol. 14, no. 3, p. 75-78.
[8] Chen, Y., Ding, H., Li, J., Cai, Z., Zhao, J., Yang, W. (2016). Influence of multi-pass
friction stir processing on the microstructure and mechanical properties of Al-5083 alloy.
Materials Science and Engineering: A, vol. 650, p. 281-289.
[9] DOI: 10.1016/j.msea.2015.10.057.
[10] El-Rayes, M.M., El-Danaf, E.A. (2012). The influence of multi-pass friction stir
processing on the microstructural and mechanical properties of Aluminum Alloy 6082.
Journal of Material Processing Technology, vol. 212, no. 5, p. 1157-1168, DOI:
10.1016/j.jmatprotec.2011.12.017.
[11] Krishna, V.V.M.G., Satyanarayana, K. (2015). Microstructure and mechanical properties
of multipass friction stir processed aluminum silicon carbide metal matrix. International
Journal of Scientific Engineering and Technology, vol. 4, no. 2, p. 88-90, DOI:
10.17950/ijset/v4s2/212.
[12] Yang, R., Zhang, Z., Zhao, Y., Chen, G., Guo, Y., Liu, M., Zhang, J. (2015). Effect of
multi-pass friction stir processing on microstructure and mechanical properties of
Al3Ti/A356 composites. Materials Characterization, vol. 106, p. 62-69. DOI:
10.1016/j.matchar.2015.05.019.
[13] Howard, E.B., Timothy, L.G. (1985). Metals handbook. American Society for Metals.
Materials Park, OH.
[14] Salehi, M., Saadatmand, M., Mohandesi, J.A. (2012) Optimization of process parameters
for producing AA6061/SiC nanocomposites by friction stir processing. Transactions of
Nonferrous Metals Society of China. Vol. 22, no. 5, p. 1055-1063, DOI: 10.1016/s1003-
6326(11)61283-1.
[15] ASTM E384-16: 2016. Standard test method for microindentation hardness of materials.
ASM International, USA.
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 677 [email protected]
[16] ASTM E8M-13: 2013. Standard test methods for tension testing of metallic materials.
ASM International, USA.
[17] Struers. Application notes on metallographic preparation of aluminium and aluminium
alloys, from www.struers.com, assessed on 2017 - 06 - 10.
[18] ASTM E112-11: 2013. Standard test methods for determining average grain size. ASM
International, USA.
[19] Al-Fadhalah, K.J., Almazrouee, A.I., Aloraier, A.S. (2014). Microstructure and
mechanical properties of multi-pass friction stir processed aluminum alloy 6063. Materials
& Design, vol. 53, p. 550-560, DOI: 10.1016/j.matdes.2013.07.062.
[20] Woo, W., Choo, H., Brown, D.W., Zhili, F. (2007). Influence of the tool pin and shoulder
on microstructure and natural aging kinetics in a friction-stir-processed 6061–T6
aluminum alloy. Metallurgical and Materials Transactions A, vol. 38, no. 1, p. 69-76,
DOI: 10.1007/s11661-006-9034-0.
[21] Mishra, R.S., Ma, Z.Y. (2005). Friction stir welding and processing. Materials Science
and Engineering: R: Reports, vol. 50, no. 1-2, p. 1-78, DOI: 10.1016/j.mser.2005.07.001.
[22] Cabibbo, M., McQueen, H.J., Evangelista, E., Spigarelli, S., Di Paola, M., Falchero, A.
(2007). Microstructure and mechanical property studies of AA6056 friction stir welded
plate. Materials Science and Engineering: A, vol. 460, p. 86-94, DOI:
10.1016/j.msea.2007.01.022.
[23] Sinhmar, S., Dwivedi, D.K., Pancholi, V. (2014). Friction stir processing of AA 7039
Alloy. International Conference on Production and Mechanical Engineering. Bangkok,
Thailand, p. 75-78.
[24] Shankar, M.R., Chandrasekar, S., Compton, W.D., King, A.H. (2005). Characteristics of
aluminum 6061-T6 deformed to large plastic strains by machining. Materials Science and
Engineering: A, vol. 410, p. 364-368, DOI: 10.1016/j.msea.2005.08.137.
[25] Ravikumar, E., Arunkumar, N., Sunnapa, G.S. (2013). Characterization of mechanical
properties of aluminium (AA 6061-T6) by friction welding. 3rd International Conference
on Mechanical, Automotive and Materials Engineering. Singapore, p. 127 - 131.
[26] Sato, Y.S., Urata, M., Kokawa, H., Ikeda, K. (2003). Hall–Petch relationship in friction
stir welds of equal channel angular-pressed aluminium alloys. Materials Science and
Engineering: A, vol. 354, no. 1-2, p. 298-305, DOI: 10.1016/s0921-5093(03)00008-x.
[27] Jiang, W.H., Kovacevic, R. (2004). Feasibility study of friction stir welding of 6061-T6
aluminium alloy with AISI 1018 steel. Proceedings of the Institution of Mechanical
Engineers, Part B: Journal of Engineering Manufacture. vol. 218, no. 10, p. 1323-1331,
DOI: 10.1243/0954405042323612.
[28] Yadav, D., Bauri, R. (2012). Effect of friction stir processing on microstructure and
mechanical properties of aluminium. Materials Science and Engineering: A, vol. 539, p.
85-92, DOI: 10.1016/j.msea.2012.01.055.
[29] Dawes, C.J., Thomas, W.M. (1995). Friction stir joining of aluminium alloys. TWI
bulletin, vol. 6, p. 124-127.
[30] Sun, N., Apelian, D. (2009). Microstructural modification of A206 aluminium via friction
stir processing. Materials Science Forum, vol. 618, p. 361-364,
DOI:10.4028/www.scientific.net/MSF.618-619.361.
[31] Hashim, F.A., Salim, R.K., Khudair, B.H. (2015). Effect of friction stir processing on
(2024-T3) aluminum alloy. International Journal of Innovative Science Engineering and
Technology, vol. 4, no. 3, p. 1822-1828, DOI: 10.15680/ijirset.2015.0404003.
[32] Salman, J.M. (2014). Effect of friction stir processing on some mechanical properties and
microstructure of cast (Al-Zn-/mg-Cu) alloy. Journal of Babylon University Engineering
Sciences, vol. 22, no. 2, 10pp.
Effect of Multi-Pass Friction Stir Processing on Mechanical Properties of AA6061-T6
http://www.iaeme.com/IJMET/index.asp 678 [email protected]
[33] Gan, W.Y., Zheng, Z., Zhang, H., Tao, P. (2014). Evolution of microstructure and
hardness of aluminum after friction stir processing. Transactions of Nonferrous Metals
Society of China, vol. 24, no. 4, p. 975-981.
[34] DOI:10.1016/s1003-6326(14)63151-4.
[35] Węglowski, M.S. (2014). Microstructural characterisation of friction stir processed cast
AlSi9Mg aluminium alloy. Archives of Foundry Engineering, vol. 14, no. 3, p. 75-78.
[36] Chen, Y., Ding, H., Li, J., Cai, Z., Zhao, J., Yang, W. (2016). Influence of multi-pass
friction stir processing on the microstructure and mechanical properties of Al-5083 alloy.
Materials Science and Engineering: A, vol. 650, p. 281-289.
[37] DOI: 10.1016/j.msea.2015.10.057.
[38] El-Rayes, M.M., El-Danaf, E.A. (2012). The influences of multi-pass friction stir
processing on the microstructural and mechanical properties of Aluminum Alloy 6082.
Journal of Material Processing Technology, vol. 212, no. 5, p. 1157-1168, DOI:
10.1016/j.jmatprotec.2011.12.017.
[39] Krishna, V.V.M.G., Satyanarayana, K. (2015). Microstructure and mechanical properties
of multipass friction stir processed aluminum silicon carbide metal matrix. International
Journal of Scientific Engineering and Technology, vol. 4, no. 2, p. 88-90, DOI:
10.17950/ijset/v4s2/212.
[40] Yang, R., Zhang, Z., Zhao, Y., Chen, G., Guo, Y., Liu, M., Zhang, J. (2015). Effect of
multi-pass friction stir processing on microstructure and mechanical properties of
Al3Ti/A356 composites. Materials Characterization, vol. 106, p. 62-69. DOI:
10.1016/j.matchar.2015.05.019.
[41] Howard, E.B., Timothy, L.G. (1985). Metals handbook. American Society for Metals.
Materials Park, OH.
[42] Salehi, M., Saadatmand, M., Mohandesi, J.A. (2012) Optimization of process parameters
for producing AA6061/SiC nanocomposites by friction stir processing. Transactions of
Nonferrous Metals Society of China. Vol. 22, no. 5, p. 1055-1063, DOI: 10.1016/s1003-
6326(11)61283-1.
[43] ASTM E384-16: 2016. Standard test method for microindentation hardness of materials.
ASM International, USA.
[44] ASTM E8M-13: 2013. Standard test methods for tension testing of metallic materials.
ASM International, USA.
[45] Struers. Application notes on metallographic preparation of aluminium and aluminium
alloys, from www.struers.com, assessed on 2017 - 06 - 10.
[46] ASTM E112-11: 2013. Standard test methods for determining average grain size. ASM
International, USA.
[47] Al-Fadhalah, K.J., Almazrouee, A.I., Aloraier, A.S. (2014). Microstructure and
mechanical properties of multi-pass friction stir processed aluminum alloy 6063. Materials
& Design, vol. 53, p. 550-560, DOI: 10.1016/j.matdes.2013.07.062.
[48] Woo, W., Choo, H., Brown, D.W., Zhili, F. (2007). Influence of the tool pin and shoulder
on microstructure and natural aging kinetics in a friction-stir-processed 6061–T6
aluminum alloy. Metallurgical and Materials Transactions A, vol. 38, no. 1, p. 69-76,
DOI: 10.1007/s11661-006-9034-0.
[49] Mishra, R.S., Ma, Z.Y. (2005). Friction stir welding and processing. Materials Science
and Engineering: R: Reports, vol. 50, no. 1-2, p. 1-78, DOI: 10.1016/j.mser.2005.07.001.
[50] Cabibbo, M., McQueen, H.J., Evangelista, E., Spigarelli, S., Di Paola, M., Falchero, A.
(2007). Microstructure and mechanical property studies of AA6056 friction stir welded
plate. Materials Science and Engineering: A, vol. 460, p. 86-94, DOI:
10.1016/j.msea.2007.01.022.
Esther Akinlabi, Kayode Oyindamola, Oluwole Olufayo and Michael Agarana
http://www.iaeme.com/IJMET/index.asp 679 [email protected]
[51] Sinhmar, S., Dwivedi, D.K., Pancholi, V. (2014). Frictions stir processing of AA 7039
Alloy. International Conference on Production and Mechanical Engineering. Bangkok,
Thailand, p. 75-78.
[52] Shankar, M.R., Chandrasekar, S., Compton, W.D., King, A.H. (2005). Characteristics of
aluminum 6061-T6 deformed to large plastic strains by machining. Materials Science and
Engineering: A, vol. 410, p. 364-368, DOI: 10.1016/j.msea.2005.08.137.
[53] Ravikumar, E., Arunkumar, N., Sunnapa, G.S. (2013). Characterization of mechanical
properties of aluminium (AA 6061-T6) by friction welding. 3rd International Conference
on Mechanical, Automotive and Materials Engineering. Singapore, p. 127 - 131.
[54] Sato, Y.S., Urata, M., Kokawa, H., Ikeda, K. (2003). Hall–Petch relationship in friction
stir welds of equal channel angular-pressed aluminium alloys. Materials Science and
Engineering: A, vol. 354, no. 1-2, p. 298-305, DOI: 10.1016/s0921-5093(03)00008-x.
[55] Jiang, W.H., Kovacevic, R. (2004). Feasibility study of friction stir welding of 6061-T6
aluminium alloy with AISI 1018 steel. Proceedings of the Institution of Mechanical
Engineers, Part B: Journal of Engineering Manufacture. vol. 218, no. 10, p. 1323-1331,
DOI: 10.1243/0954405042323612.
[56] Yadav, D., Bauri, R. (2012). Effect of friction stir processing on microstructure and
mechanical properties of aluminium. Materials Science and Engineering: A, vol. 539, p.
85-92, DOI: 10.1016/j.msea.2012.01.055.