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 material
Joining several castings together
Build up a casting
Worn area or manufacturing
Join casting to other metal
Physical damage to old casting
Repair of superficial defect in a new casting
Repair of unavoidable shrinkage porosity in new casting
Note 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.

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

Aluminium Casting Designations Which alloy is which - Cast Alloy Designations
There 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 Other
1xx.x 2xx.x 3xx.x 4xx.x 5xx.x 7xx.x 8xx.x 9xx.x
Non-heat-treatable
Heat-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
A X XX .X Principle Alloying Element Alloy Number Form - 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-treatable
Heat-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
AC X X XXX Principle Alloying Element Alloy Groups (with principal element) Arbitrary Generally 0 0 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

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

Which castings are weldable ?
Process
Composition

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 Alloys
Non heat treatable
EN 44100 (LM6, AlSi12)
EN 44000 (AlSi11)
EN 43100 (LM9, AlSi10Mg)
EN 5100 (LM5)
Heat treatable
EN 42100 (AlSi7Mg0,3)

Which castings are weldable ? Composition
Based on aluminium silicon
Main elemental additions of Cu, Mg, Fe, Mn, Ni, Zn, Pb
Other elemental additions include a wide additional range.
Alloy elements modify casting characteristics
Also influence hardness, fluidity, machinability, weldability , castability

Aluminium 660 o C 231 o C- 327 o C Se, Sn, Bi, Cd, Pb, 97,7 o C Na 44.2 o C P- 650 o C Mg 630 o C Sb 420 o C Zn 1410 o C Si 1245 o C Mn 1150 o C Fe 1083 o C Cu 1852 o C – 2625 o C Zr, Ti, Cr, B, V, Mo Which castings are weldable ? Composition - What do we add - Summary 768 o C Sr hardeners Grain refiners (never melts) Free machining Grain modifiers (casting) affects micro porosity (early freeze c.f. Si) MgSi composition 6xxx

Which castings are weldable ? Composition – cf wrought alloys

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 c astings are weldable ? Compostion NOTE Log scale! l n Cu upper 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 )

Silicon
Si improves fluidity, feeding and hot tear resistance.
Si increases hardness, reduces ductility & machinability.
Si content is related to casting process
Sand casting 5 - 7% Si
Permanent mould 7 - 9% Si
Die casting 8 - 12% Si

Copper
Basis of heat treatable alloys
Improves strength, hardness, thermal conductivity
Decreases castability and hot tear resistance
Allows most hardening in 4 - 6% range
Copper base alloys above about a 0,4% limit weldability, corrosion resistance and suitability for decoration

Iron
Normally not added but picked up from furnace
Forms many intermetallic phases
Increases elevated temperature strength
Improves hot tear resistance
Reduces ductility
Too high reduces castability
Flowability and feeding characteristics

Magnesium
Strengthening in AlSi alloys
Premium grade alloys have 0,4 - 0,7%Mg
No benefit above 0,7%
High corrosion resistance

Lead
Added 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%

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

Designations of comparable casting alloys (unalloyed and aluminium silicon) CEN Chemical designat-ion UK BS1450/ AEA France NF A50 Germany DIN 1725 Italy UNI USA AA / ASTM Japan JIS 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) CEN Chemical designat-ion UK BS1450/ AEA France NF A50 Germany DIN 1725 Italy UNI USA AA / ASTM Japan JIS H5202 H5302 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) Note: Designations in brackets are considered fairly comparable For export purposes the LM series is not recognised CEN Chemical designat-ion UK BS1450/ AEA France NF A50 Germany DIN 1725 Italy UNI USA AA / ASTM Japan JIS H5202 H5302 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 Alloys 48100 AlSi18Cu1 Mg1Ni1 LM28 (KS 2811) A392.1 (AC9B) 48000 AlSi12Cu1 Mg1Ni1 LM13 A-S12UN (KS 1275) A336.0 AC8A

Alloys selection for weldability/ corrosion resistance
Generally 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
.

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

Alloys used in RSA
EN 44100 (LM6, AlSi12)
10,5 – 13,5%Si; 0,15%Cu
Widely used for sand and chill castings
Poor machinability
Good weldability
Not 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%Pb
High strength because of Cu and Fe
Good castability because of high Si
Not weldable because of Cu
Non heat treatable
.

Cast Alloys cont..
6,5 – 7,5%Si; 0,2%Cu
Larger castings ~ cylinder blocks etc.
High strength
Good castability
Heat treatable
Weldable

Cast Alloys cont..
EN 46100 (LM2, ADC12, AlSi11Cu2(Fe))
10,0 – 12,0%Si; 1,5 – 2,5%Cu
Pressure die casting alloy specifically
Good castability
Not weldable
Non heat treatable

Cast Alloys cont..
EN 44000 (ALSi11)
Very fluid permanent mould alloy
Traditionally used for alloy wheels
Good ductility, moderate strength
High impact strength
Non heat treatable
Weldable
.

Cast Alloys cont..
EN 42100 (AlSi7Mg0.3)
Used for alloy rims, premium aerospace castings, nuclear plant, marine parts
High strength, good ductility
Good corrosion resistance
Heat treatable
Weldable

Cast Alloys cont..
10,0 – 11,8%Si; 0,25 – 0,45%Mg
Most fluid permanent mould alloy available
Used for intricate castings ~ feedability
Non heat treatable
Good 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

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

Repair Welding
Casting is heat treatable and has been hardened
Welding will over age HAZ
Can do simple repairs in T6 or T7 temper
Better to weld in F or T2 condition
Large extensive repairs only in F or T2
Anneal before welding

Non Heat Treatable Castin g
Preheat 100  C up to 8 mm thick
340 - 400  C for heavy or intricate castings
Use 4043 (6%Si) or 4047 (12% Si) filler
Heat input 0,8 - 1,6 kJ/mm
Slow cool
Weld strength very close to base metal

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

Cosmetic Repair
Non heat treatable
Preheat as appropriate
Clean thoroughly
Weld with 4043 or 4047 filler
Slow cool <15°C per minute

Cosmetic Repair
Heat treatable alloy
Casting is in ‘as cast’ F temper
Preheat and clean thoroughly
Use 4043 filler
Low heat input minimises precipitation aging
Post weld aging enhances weld strength – but 4043 not heat treatable

Welding Multiple Castings
Preferably F or T2 condition
Lowest strength in base metal
Preheat and clean
Weld with 4043 or 4047 filler
Non heat treatable ~ slow cool
Heat treatable ~ Solution anneal and harden

Welding Cast to Wrought
Same principles as casting to casting
Wrought material will lose strength
Hot weld cracking is main problem
Caused by shrinkage & other stresses
Several techniques can be used

Build-up of Castings
Very similar to cosmetic repair procedure
Depends on alloy and temper
Preheat depends on casting size and complexity

Aluminium to Steel
Very difficult ~ intermetallic compounds, melting temperatures, expansion
Can 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 Copper
Used for electrical terminations
Can coat copper with silver or silver alloy
Then join with Al or Al/Si filler without penetrating the silver layer
Can use MIG spot welding
Usually use friction welding

Objectives:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

General Considerations
Avoid unnecessary stresses
No sudden thickness changes ~ use tapers
Ensure good fit up ~ 1 - 1,5 mm
Good alignment is essential
Use correct weld preparation ~ check drawing

Clean the joint properly
Aluminium very susceptible to contamination
(hydro carbons or oxides)
Solvent wipe to degrease 50 mm either side
Clean stainless steel wire brush
Do not use grinding disks
Tungsten carbide burrs are suitable
Weld within three hours of cleaning

Create 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)

Ensure consumables are suitable
Gas must be 99,995% pure minimum - normally Argon
Keep 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 gloves
Old MIG wire will become contaminated and cause oxide contamination

Cutting and Preparing Al
Cannot use oxy fuel
Aluminium is not fit up tolerant – cannot fill significant gaps
Plasma cutting widely used
Cut surface is rough, oxidised, must be dressed
HT alloys crack 2 - 3 mm into plate ~ finish cut
Non HT alloys just need mechanical dressing
Woodworking band saw works well
Circular saws and portable jig saws are useful
Mineral oil lubrication is needed

Cutting and Preparing Al cont..
Planers, routers and edge mills for edge preparation
Tungsten carbide burrs are suitable for final cleaning
Do not use (corundum) grinding disks for final cleaning

Welding problems Gas 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 problems Gas 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 problems Cracking in aluminium is always hot cracking
Strength of solidifying metal is too low to resist stresses during cooling
Reduce heat input
High travel speed, lowest weld parameters
Preheat base metal ~ reduce cooling rate
Change joint design to minimize dilution
Change restraining jigs or fixtures
Use correct depth to width ratio

Hot Cracking cont..
Weld bead chemistry - Select suitable filler metal
Higher alloy content allows for dilution
Hot crack sensitivity depends on alloy content.
Welding problems

Welding problems 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

Good Fair Poor Filler Alloy 5356 Parent Alloy 6061 Filler Alloy 4043 a b d c 1 2 3 4 5 6 Silicon in the Weld Bead (%) 0 1 2 3 4 5 6 7 8 Magnesium in the Weld Bead (%) Figure 1. Resistance to hot cracking

Topics covered:
What is a casting
Why weld a casting
Alloys used in RSA
Welding problems

The welding of aluminium castings Tony Paterson (082 602 4517) Questions??

Welding of aluminium castings - October 2011

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Welding of aluminium castings - October 2011 Presentation Transcript