welding of aluminium castings - october 2011

The welding of aluminium castings

Tony Paterson

Welding of aluminium castings Objectives:

• What is a casting

• Why weld a casting

• Casting designations

• Which castings are weldable

Effect of casting processes

Effect of welding composition

• Alloys used in RSA

• Welding of selected casting alloys

• Specific applications

• Welding problems

What is a casting? three dimensional shape formed from the melt (highly

complex shapes possible)

cf wrought flats - one dimensional (thickness)

wrought extrusions – two dimensional

wrought forgings – simpler three dimensional

(hot or cold formed from solid or semi solid cast)Generally non homogenous structure due to directional

solidification Produced using various processes (sand, permanent mould

(gravity and low pressure – laminar flow), high pressure die casting

Why weld a Casting?Join a casting to wrought materialJoining several castings togetherBuild up a casting

Worn area or manufacturingJoin casting to other metalPhysical damage to old castingRepair of superficial defect in a new castingRepair of unavoidable shrinkage porosity in new

castingNote that not all castings are weldable

Why weld a Casting?Join a casting to wrought material

Welding compromises the strength of tempered aluminium because it reverses the temper effect

It is desirable to choose the position and nature of welds to limit the impact of this loss of strength.

From a structural point of view a casting forms a good corner stress transfer unit in three dimensional structural applications as it potentially displaces welds to low stress areas.

Whilst adhesive bonding is sometimes called for, some casting alloys are weldable.

Aluminium Casting Designations

Which alloy is which - Cast Alloy DesignationsThere is no single universally accepted designation system

Designations systems include: US 3 digit number, plus 1 decimal EN 5 digit number (RSA standard since 1990’s) Chemical designations (eg old DIN) UK discontinued LM series still commonly cited in RSA Others – eg old eastern Europe Others Far East – including Japan

Note: From a welding point of view we need to understand which alloy we are dealing with as not all are weldable – in particular most Cu (2xx.x)and ZnCu (7xx.x) alloys are practically unweldable. There are exceptions.

Aluminium Casting Designations

Cast Alloy Designation (US)

US 3 digit number, plus 1 decimal Al+

Cu Si/Cu/Mg Si Mg Zn Sn Other1xx.x 2xx.x 3xx.x 4xx.x 5xx.x 7xx.x 8xx.x 9xx.x

Non-heat-treatableHeat-treatable

Aluminium Casting Designations Cast Alloy Designation (US)

• Example 535.0 is an Al/Mg alloy, with no modification, assigned alloy number 35, for final casting

AXXX.XPrinciple Alloying ElementAlloy NumberForm - Final Casting (.0) or Ingot (.1 or .2)**Depending on Purity Limits

(Modifications (sometimes have a prefix [A,B,C])

depending on the element

Aluminium Casting Designations Cast Alloy Designation (EN)

EN 5 digit number Al+

Cu Si/Mg Si/Cu/Mg Si.12% Mg Zn/Mg Master 21xxx 41xxx 45xxx 44xxx 51xxx 71xxx 9xxxx 42xxx 46xxx 43xxx 47xxx

Non-heat-treatableHeat-treatable

Aluminium Casting Designations Cast Alloy Designation (EN)

• Examples: AC 42100 is an Al/Si/Mg alloy . AC 45100 is an Al/Si/Cu/Mg alloy

ACXXXXXPrinciple Alloying ElementAlloy Groups (with principal element)ArbitraryGenerally 00 except for aerospace

Aluminium Casting Designations Cast Alloy Designation (Chemical) – similar to wrought

Chemical designation (older German specifications)

First symbol: AB (billet) or AC (casting) or (A) or G (DIN)

Second symbol: Al

Third and following: Alpha numeric – Alpha - Main element or elements in order of decreasing nominal content (or, if equal, in alphabetical order – up to a maximum of four elements) followed by numbers. - Numeric - represent the mass percentage contents to the nearest 0,5%, or, if less than 1%, the nearest 0,1%)

Weldability: take care with alloys where Cu>0,25 -0,4%

Aluminium Casting Designations Cast Alloy Designation (BS now

superceded)

UK discontinued LM series (unsystematic – WW2 base) Still used in RSA and cited in reference literature

Al

Cu Si/Cu Si/Mg Mg Other (piston)LM0 LM2 LM6 LM5 LM28

LM4 LM9 LM13 LM20 LM25 LM21 LM22

LM24 Non-heat-treatable

Heat-treatable

Which castings are weldable?ProcessComposition

Which castings are weldable?Process

Alloys Processes

Wrought alloys All except > 0,25% copper addition - (some exceptions <0,4%) and free machining alloys

All - Rolling, extrusion, forging, etc

Cast alloys All except > 0,25% copper additions, and free machining alloys

Sand, gravity, permanent mould, low pressure.

Not standard high pressure die casting (i.e. unless vacuum cast.)

Weldable Cast AlloysNon heat treatable

EN 44100 (LM6, AlSi12)EN 44000 (AlSi11)EN 43100 (LM9, AlSi10Mg)EN 5100 (LM5)

Heat treatableEN 42000 (LM25, AlSi7Mg)EN 42100 (AlSi7Mg0,3)

Which castings are weldable?Composition

Based on aluminium siliconMain elemental additions of Cu, Mg, Fe, Mn, Ni, Zn, Pb

Other elemental additions include a wide additional range. Alloy elements modify casting characteristicsAlso influence hardness, fluidity, machinability,

weldability, castability

Aluminium 660oC

231oC- 327oC Se, Sn, Bi, Cd, Pb, 97,7oC Na 44.2oC P-

650oC Mg 630oC Sb 420oC Zn

1410oC Si1245oC Mn1150oC Fe 1083oC Cu

1852oC – 2625oC Zr, Ti, Cr, B, V, Mo

Which castings are weldable?Composition - What do we add - Summary

768oC Srhardeners

Grain refiners(never melts)

Free machining

Grain modifiers(casting) affectsmicro porosity(early freeze c.f. Si)

MgSi composition 6xxx

Which castings are weldable?Composition – cf wrought alloys

20

Which castings are weldable?Composition relationship between filler/parent metal and weld cracking –

(Note: long copper sensitivity above 0,25%)

Dilution by 4043 – thus choose 5356

Dilution by 4043 – avoid 5356

5xxx

6xxx

2xxx

Which castings are weldable?Compostion

22

NOTE Log scale! ln Cuupper limit% (wrought and cast alloys)

(Other alloy elements, eg silicon, also have a role)

Welding Rating

Excellent A

Very good B

Good C

Poor D

0.1 0.2 0.3 0.5 1 2 3 3+

****** (1xxx) ** ******* *** * ** * (3xxx, 5xxx, 51000 (LM0,LM5))

**** * * ** * (6xxx, LM25, LM6) ****

* *** ** *** ** ** ** (LM20)

* ******** ******** (2xxx, LM4, 21,22,24,26)

SiliconSi improves fluidity, feeding and hot tear resistance.Si increases hardness, reduces ductility &

machinability.Si content is related to casting process

Sand casting 5 - 7% SiPermanent mould 7 - 9% SiDie casting 8 - 12% Si

CopperBasis of heat treatable alloysImproves strength, hardness, thermal conductivityDecreases castability and hot tear resistanceAllows most hardening in 4 - 6% range

Copper base alloys above about a 0,4% limit weldability, corrosion resistance and suitability for decoration

IronNormally not added but picked up from furnace Forms many intermetallic phasesIncreases elevated temperature strengthImproves hot tear resistanceReduces ductilityToo high reduces castability

Flowability and feeding characteristics

MagnesiumStrengthening in AlSi alloysPremium grade alloys have 0,4 - 0,7%MgNo benefit above 0,7%High corrosion resistance

LeadAdded up to 0,35%Pb to improves machinability by

enhancing intergranular chip breaking

Not suited to food grade products as these limit lead to 0,05%

Designations of comparable casting alloys(unalloyed and aluminium silicon)

CEN Chemical designat-ion

UKBS1450/ AEA

France NF A50

Germany DIN 1725

Italy UNI

USAAA / ASTM

JapanJIS H5202 H5302

Unalloyed aluminium – generally weldable

Al 99,5 LM0 A5 Al99,5H 3950 150.1

Al 99,7 A7 Al99,7H 3950

Aluminium Silicon – generally weldable

42000 AlSi7Mg0,3 AEA 44525 (A –S7G03) (G AlSi7Mg)

42100 AlSi7Mg (Fe) LM25 A-S7G03 G- AlSi5Mg 3599 A356,1 AC4C

42200 AlSi7Mg(0,6) AEA 44530 (A-S7G06) (G -AlSi7Mg) A357

43100 AlSi10Mg LM9 A-S10G (G –AlSi10Mg)

3049 A360 AC4A

43200 AlSi10Mg(Cu) (LM9) (A-S9G) A360

44000 AlSi11 (LM9) A-S13 (G –AlSi12)

44100 AlSi12(Fe) LM6 A-S12U G –AlSi12 4514 A413 AC3A

44200 AlSi12 AEA46330 /LM6

A-S13 AC3A

44300 AlSi12(Fe) (LM20) A-S12 (G –AlSi12)

Designations of comparable casting alloys(aluminium silicon copper)


UKBS1450/ AEA

France NF A50

Germany DIN 1725

Italy UNI

USAAA / ASTM


Aluminium Silicon Copper – generally not weldable

45000 AlSi6Cu4Mn LM21 A-S5UZ G-AlSi6Cu4 7369/4 A308 AC2A

45100 AlSi5Cu3Mg (LM4) (LM22)

A-S5U3G (G-AlSi6Cu4)

45200 AlSi5Cu3Mn LM4 A-S5U3 (G-AlSi7Mg) 3052 A319.2 AC2A

45400 AlSi5Cu4Mn LM22 A-S5U G-AlSi6Cu4 3052 A319.2 AC2A

46000 AlSi9Cu3 (LM26) A-S10G A335 AC4B

46100 AlSi9Cu3 LM2 A-S10UG 5067 A384.1 ADC12

46200 AlSi9Cu3(Fe) (LM24) A-SGU3

46500 AlSi9Cu3(Fe)(Zn)

LM24 A-S9U3 G-AlSi8Cu3 5075/3601 A380.1 AC4B/ ADC10

47000 AlSi12(Cu) LM20 A-S12 G-AlSi12(Cu) 5079 A313.1

47100 AlSi12Cu1 (Fe)

(LM6)(LM20) A-S12 G-AlSi12(Cu)

Designations of comparable casting alloys(Aluminium copper/aluminium magnesium and piston alloys)


UKBS1450/ AEA

France NF A50

Germany DIN 1725

Italy UNI

USAAA / ASTM


Aluminium Copper – not weldable

21000 Al Cu4MgTi AEA 24850 A-U5GT A204.2 AC1B

Aluminium Magnesium – weldable

51000 AlMg3 LM5 A-G3T G-AlSiMg5 3059

Piston Alloys48100 AlSi18Cu1

Mg1Ni1LM28 (KS 2811) A392.1 (AC9B)

48000 AlSi12Cu1 Mg1Ni1

LM13 A-S12UN (KS 1275) A336.0 AC8A

Note: Designations in brackets are considered fairly comparable For export purposes the LM series is not recognised

Alloys selection for weldability/ corrosion resistanceGenerally corrosion resistance and weldability run in parallel

LM0, LM2, LM4, LM5, LM6, LM9, LM21, LM24, LM 25,LM31 (low Cu alloys) resistant to weathering attack

Other alloys require protection by anodising or organic finishes

LM0, LM5, LM6, LM9, LM20, LM25, LM31 suited to marine applications

LM5 best if bright finish to be maintained

.

Alloys used in RSAEN 44100 (LM6, AlSi12)10,5 – 13,5%Si; 0,15%Cu Widely used for sand and chill castingsPoor machinabilityGood weldabilityNot heat treatable

.

Cast Alloys cont..EN 46500 (LM24, AlSi9Cu3(Fe)(Zn))8,0 – 11,0%Si; 2,0 – 4,0%Cu; 1,3%Fe;

0,35%PbHigh strength because of Cu and FeGood castability because of high SiNot weldable because of CuNon heat treatable

.

Cast Alloys cont..EN 42000 (LM25, AlSi7Mg)6,5 – 7,5%Si; 0,2%CuLarger castings ~ cylinder blocks etc.High strengthGood castabilityHeat treatableWeldable

Cast Alloys cont..EN 46100 (LM2, ADC12, AlSi11Cu2(Fe))10,0 – 12,0%Si; 1,5 – 2,5%CuPressure die casting alloy specificallyGood castabilityNot weldableNon heat treatable

Cast Alloys cont..EN 44000 (ALSi11)Very fluid permanent mould alloyTraditionally used for alloy wheelsGood ductility, moderate strengthHigh impact strengthNon heat treatableWeldable

Cast Alloys cont..EN 42100 (AlSi7Mg0.3)Used for alloy rims, premium aerospace castings,

nuclear plant, marine partsHigh strength, good ductilityGood corrosion resistanceHeat treatableWeldable

Cast Alloys cont..EN 43100 (LM9, AlSi10Mg)10,0 – 11,8%Si; 0,25 – 0,45%MgMost fluid permanent mould alloy availableUsed for intricate castings ~ feedabilityNon heat treatableGood weldability ~ high ductility

Cast Alloys – filler alloy choice

Selection of filler rods and wires for MIG and TIG welding

Parent metal combination

LM25 LM20 LM9 LM6 LM5 LM4

1070, 1200, 1350, 5251, 5454, 6082, 6061, 6063,

4043 4043 4043 4043 5356 4043

5083 4043 NR 4043 NR 5356 4043

7020 NR NR NR NR 5356/5556 NR

LM4 4043 4043 4043 4043 NR 4043

LM5 NR NR NR NR 5356/5056 NR

LM6 4043/4047 4043/4047 4043/4047 4043/4047

LM9 4043/4047 4043/4047 4043/4047

LM20 4043/4047 4043/4047

LM25 4043/4047

Repair WeldingCasting is heat treatable and has been hardenedWelding will over age HAZCan do simple repairs in T6 or T7 temperBetter to weld in F or T2 conditionLarge extensive repairs only in F or T2Anneal before welding

Non Heat Treatable CastingPreheat 100C up to 8 mm thick

340 - 400C for heavy or intricate castings

Use 4043 (6%Si) or 4047 (12% Si) fillerHeat input 0,8 - 1,6 kJ/mmSlow coolWeld strength very close to base metal

Heat Treatable Alloy cont..Preheat 100 - 400°C (short period to avoid anneal)Use 4043 filler metalSolution anneal ~ also stress relieves weldHeat treat as required – but 4043 NHT

Cosmetic RepairNon heat treatablePreheat as appropriateClean thoroughlyWeld with 4043 or 4047 fillerSlow cool <15°C per minute

Cosmetic RepairHeat treatable alloyCasting is in ‘as cast’ F temperPreheat and clean thoroughlyUse 4043 fillerLow heat input minimises precipitation agingPost weld aging enhances weld strength – but 4043 not

heat treatable

Welding Multiple CastingsPreferably F or T2 condition

Lowest strength in base metalPreheat and cleanWeld with 4043 or 4047 fillerNon heat treatable ~ slow coolHeat treatable ~ Solution anneal and harden

Welding Cast to WroughtSame principles as casting to castingWrought material will lose strengthHot weld cracking is main problemCaused by shrinkage & other stressesSeveral techniques can be used

Build-up of CastingsVery similar to cosmetic repair procedureDepends on alloy and temperPreheat depends on casting size and complexity

Aluminium to SteelVery difficult ~ intermetallic compounds, melting

temperatures, expansionCan tin steel, then with tin/aluminium then use

aluminium with TIG welding (used for welding anode stems to steel anode inserts)

Usually use friction welding (not friction stir)

Aluminium to CopperUsed for electrical terminationsCan coat copper with silver or silver alloyThen join with Al or Al/Si filler without penetrating

the silver layerCan use MIG spot weldingUsually use friction welding

General ConsiderationsAvoid unnecessary stresses

No sudden thickness changes ~ use tapersEnsure good fit up ~ 1 - 1,5 mmGood alignment is essentialUse correct weld preparation ~ check drawing

General ConsiderationsClean the joint properly

Aluminium very susceptible to contamination

(hydro carbons or oxides)Solvent wipe to degrease 50 mm either sideClean stainless steel wire brushDo not use grinding disksTungsten carbide burrs are suitableWeld within three hours of cleaning

General ConsiderationsCreate the right conditions for welding - physical

Dry (RH<65%), warm, draught free conditions are best

(Be careful at coast or early on winter mornings on highveld)

Al very susceptible to hydrogen from moisture or oils – leads to porosity

Draughts can disrupt inert gas flow and cause oxide inclusions (Note - too high an inert gas flow disrupts the molten pool and causes porosity)

General ConsiderationsEnsure consumables are suitable

Gas must be 99,995% pure minimum - normally ArgonKeep wire and filler rods clean and dry (remove or

cover at night) Clean using stainless steel wire wool – never use

“Scotchbrite” as it leads to porosity.No greasy glovesOld MIG wire will become contaminated and cause

oxide contamination

Cutting and Preparing AlCannot use oxy fuelAluminium is not fit up tolerant – cannot fill significant gapsPlasma cutting widely used

Cut surface is rough, oxidised, must be dressedHT alloys crack 2 - 3 mm into plate ~ finish cutNon HT alloys just need mechanical dressing

Woodworking band saw works wellCircular saws and portable jig saws are usefulMineral oil lubrication is needed

Cutting and Preparing Al cont..Planers, routers and edge mills for edge

preparationTungsten carbide burrs are suitable for final

cleaningDo not use (corundum) grinding disks for final

cleaning

Welding problemsGas porosity in aluminium welds – always caused by hydrogen

• Low solubility in solid and high solubility in liquid aluminium

• Alloying elements Si, Cu, Mn and Zn lower hydrogen solubility

• Alloying elements Mg, Ni and Ti increase hydrogen solubility

• Some hydrogen in molten metal comes from disassociation of water vapour in the air, burner fuels or damp fluxes.

• To avoid hydrogen pick-up the oxide layer on the liquid aluminium should not be disturbed as if protects the metal.

Welding problemsGas porosity in aluminium welds – always caused by hydrogen(Low solubility in solid and high solubility in liquid aluminium)

Welding problems- Gas Porosity in welds

Welding problemsCracking in aluminium is always hot cracking

Strength of solidifying metal is too low to resist stresses during cooling

Reduce heat inputHigh travel speed, lowest weld parameters

Preheat base metal ~ reduce cooling rateChange joint design to minimize dilutionChange restraining jigs or fixturesUse correct depth to width ratio

Hot Cracking cont..Weld bead chemistry - Select suitable filler metalHigher alloy content allows for dilutionHot crack sensitivity depends on alloy content.

Welding problems

Welding problemsComposition relationship between filler/parent metal and weld cracking –

(Note: long copper sensitivity above 0,25%)

Dilution by 4043 – thus choose 5356

Dilution by 4043 – avoid 5356

5xxx

6xxx

2xxx

Good

Fair

Poor

Filler Alloy 5356

Parent Alloy 6061

Filler Alloy 4043

a

b

dc

1 2 3 4 5 6Silicon in the Weld Bead (%)

0

1

2

3

4

5

6

7

8

Mag

nesi

um in

the

Wel

d B

ead

(%)

Figure 1. Resistance to hot cracking

Welding of aluminium castings Topics covered:











The welding of aluminium castings

Tony Paterson (082 602 4517)

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welding of aluminium castings - october 2011

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