Page 58 - Welding of Aluminium and its Alloys

Material standards, designations and alloys 49

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

Base Highest Best ductility Salt water Least cracking Best for
material strength corrosion tendency anodising
resistance
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 re-
commendations 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 recommenda-
tion 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 guid-
ance 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 magne-
sium silicide, Mg 3Si, is formed. This embrittles the joint and can lead to
failure in joints that are dynamically loaded. The converse is also true,
that Mg 3Si 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 Al 2Mg 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.