The welding of aluminium and its alloys

Filler metal selection

Filler metal specifications are to be found in BS 2019 Part 4, although this will be replaced in the near future by a CEN specification. The BS specifi­cation lists 11 filler metal types in the 1XXX, 3XXX, 4XXX and 5XXX series and details the delivery conditions. BS 2901 does not include any filler metals capable of being age hardened. The American Welding Society has

Table 3.1 General guidance on filler metal selection

Parent metal

Al-Si Castings

Al-Mg Castings

1XXX

2XXX

3XXX

4XXX

5XXX

6XXX

7XXX

Al-Si Castings

4XXX

NR

4XXX

NR

4XXX

4XXX

NR

4XXX

NR

NS

NR

NS

NR

NS

NS

NR

NS

NR

NS

NR

NS

NR

NS

NS

NR

NS

NR

Al-Mg Castings

NR

5XXX

5XXX

NR

5XXX

NR

5XXX

5XXX

5XXX

NR

NS

NS

NR

3XXX

NR

NS

NS

NS

NR

NS

NS

NR

NS

NR

NS

NS

NS

1XXX

4XXX

5XXX

4XXX

NR

4XXX

4XXX

5XXX

4XXX

5XXX

NS

NS

1XXX

NS

3XXX

1XXX

NS

NS

NS

NS

NS

NS

4047

NS

NS

NS

NS

NS

2XXX

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

4047

4047

4047

4047

NR

4047

NR

3XXX

4XXX

5XXX

4XXX

NR

4XXX

4XXX

5XXX

5XXX

5XXX

NS

3XXX

3XXX

NR

3XXX

3XXX

NS

NS

NS

NS

NS

NS

4047

NS

NS

NS

NS

NS

4XXX

4XXX

NR

4XXX

NR

4XXX

4XXX

NR

5XXX

5XXX

NS

NR

1XXX

NR

3XXX

NS

NR

4XXX

4XXX

NS

NR

NS

4047

NS

NS

NR

NS

NS

5XXX

NR

5XXX

5XXX

NR

5XXX

NR

5XXX

5XXX

5XXX

NR

NS

NS

NR

NS

NR

NS

NS

NS

NR

NS

NS

NR

NS

NR

NS

NS

NS

6XXX

4XXX

5XXX

4XXX

NR

5XXX

5XXX

5XXX

5XXX

5XXX

NS

NS

NS

NR

NS

4XXX

NS

NS

NS

NS

NS

NS

4047

NS

NS

NS

4XXX

NS

7XXX

NR

5XXX

5XXX

NR

5XXX

5XXX

5XXX

5XXX

5XXX

NR

NS

NS

NR

NS

4XXX

NS

NS

NS

NR

NS

NS

NR

NS

NS

NS

NS

NS

Table 3.2 Guidance on filler metal selection - dissimilar metal joints for specific alloys

Parent

1050

2219

3103

5005

6061

7005

8090

metal

1080

1200

3105

5083

5251

5454

6063

6082

7019

7019 7039

8090

5556

5556

7039

5556

5556

5356

5556

5556

7019

5356

5356

5356

5356

7020

5183

5183

5183

5183

7005

5039

6061

5356

4043

5356

5556

6063

NS

5356

5356

6082

4043

5183

5454

5356

5356

5356

5251

5356

5356

5056

5083

5356

5356

5005

5356

3103

5356

2319

5356

5356

5356

5556

5556

3105

4043

NS

4043

4043

5056

5356

2219

2319

4043

2319

1050

4043

2319

1080

1050

4043

1200

1080

published a similar specification, AWS A5.10 ‘Specification for Bare Alu­minium and Aluminium Alloy Welding Electrodes and Rods’, which fulfils a similar role. This specification includes 15 separate filler metal composi­tions, comprising alloys in the 1XXX, 2XXX, 4XXX and 5XXX series. In addition there are five age-hardening filler metals designed for use in the welding of castings. AWS A5.10 also includes delivery conditions and the testing requirements for usability and soundness.

As mentioned earlier, filler metal selection is crucial to producing crack - free, optimum strength welded joints but there are other considerations that may need to be included when making the choice. Unlike selecting consumables for welding steel, where the composition of the filler metal generally matches that of the parent metal with respect to composition, mechanical properties, corrosion resistance and appearance, aluminium alloys are often welded with filler metals that do not match the parent metal in some or all of these properties. This presents the engineer with some problems when it comes to deciding on the optimum filler metal composi­tion. In addition to strength and crack resistance the choice may also need to include colour match, corrosion resistance, response to anodising and

Table 3.3 Filler metal selection to achieve specific properties for the commoner structural alloys

Base

material

Highest

strength

Best ductility

Salt water

corrosion

resistance

Least cracking tendency

Best for anodising

1100

4043

1050

1050

4043

1100

2219

2319

2319

2319

2319

2319

3103

4043

1050

1050

4043

1050

5052

5356

5356

5554

5356

5356

5083

5183

5356

5183

5356

5356

5086

5356

5356

5183

5356

5356

5454

5356

5554

5554

5356

5554

5456

5556

5356

5556

5356

5556

6061

5356

5356

4043

4043

5654

6063

5356

5356

4043

4043

6356

6082

4043

4043

4043

4043

4043

7005

5556

5356

5356

5356

5356

7039

5556

5356

5356

5356

5356

creep strength. Guidance on suitable fillers can be found in Table 3.1, for specific alloys, in Table 3.2 and to achieve specific properties in some of the commoner structural alloys in Table 3.3. In Table 3.1 there are three re­commendations based on the best strength, the upper figure; the highest crack resistance, the middle figure; and an acceptable alternative, the lower figure. Note that the alloys are arranged in families - for a recommenda­tion on filler metal read directly across and down from the alloys of interest.

There are a number of specific points to be made to amplify the guid­ance given in Tables 3.1-3.3:

• When welding alloys containing more than 2% magnesium avoid the use of fillers containing silicon as the intermetallic compound magne­sium silicide, Mg3Si, is formed. This embrittles the joint and can lead to failure in joints that are dynamically loaded. The converse is also true, that Mg3Si will be formed when welding alloys containing more than 2% silicon with 5XXX fillers.

• 5XXX filler metals with more than 5% Mg should be avoided if the service temperature exceeds 65 °C as Al2Mg is formed, which makes the alloy susceptible to stress corrosion. Filler metals such as 5454 or 5554 containing less than 3% Mg should be used.

• High-purity 5654 is preferred for the welding of high-purity aluminium in hydrogen peroxide service.

• 4643 may be used to weld the 6XXX alloys as the small amount of magnesium improves the response to solution treatment.

• The pure aluminium 1XXX alloys are very soft and wire feeding prob­lems can be experienced.

• Low magnesium (<2%) 5XXX alloys such as 5251 may suffer hot crack­ing if matching composition fillers are used. Use Al-Mg5 type instead.

• When welding the 7XXX alloys 5039 filler metal may give more effec­tive age hardening in low-dilution applications.

• 6XXX alloys exhibit solidification cracking if welded autogenously.

• Titanium and zirconium are sometimes added to filler metals to reduce the risk of weld metal hot cracking by means of grain refinement.

• 4047 may be used to prevent weld metal cracking in joints involving high dilution or restraint but remember the first point above.

• The 2XXX series of copper containing alloys were generally regarded as unweldable until the higher (>4%) copper alloys such as 2219 became available. If it is necessary to weld the lower copper-containing alloys then 4047 is the best choice as a filler metal.

The welding of aluminium and its alloys

Alloy designations: wrought products

Table A.4 BS EN BS EN Old BS/DTD Temperature (°C) numerical chemical number designation designation Liquidus Solidus IVIdUng range Al 99.99 1 660 660 0 AW-1080A Al 99.8 1A AW-1070A …

Principal alloy designations: cast products

Table A.3 BS EN numerical designation BS EN chemical designation Old BS number ANSI designation Temperature (°C) Liquidus Solidus Melting range Al 99.5 LM0 640 658 18 AC-46100 Al Si10Cu2Fe …

Physical, mechanical and chemical properties at 20°C

Table A.2 Property Aluminium Iron Nickel Copper Titanium Crystal structure FCC BCC FCC FCC HCP Density (gm/cm3) 2.7 7.85 8.9 8.93 4.5 Melting point (°C) 660 1536 1455 1083 1670 …

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