Instructions / Assembly

62
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•
Weld metal ductility.
• Weld metal corrosion resistance.
• Weld metal shear strength in fillet and lap joints.
• Ease of welding (i.e., weldability).
• Wire electrode feedability.
• For applications requiring postweld anodizing, color matching
with parent metal.
There are a number of filler metal selection charts which take
these variables into account, and they provide recommendations
for filler metal selection. A composite of these charts covering
m
ost alloy combinations are shown on Table 24 on page 65.
In general, filler alloy recommendations for the various alloy
f
amilies of base materials can be summarized as follows
1XXX alloys – These base materials are usually used for their
electrical conductivity and/or corrosion resistance. Their tenden-
cy to hot cracking is very low. They are usually welded using
1100 or 1188 fillers, but matching filler metals are also available
for specialized alloys such as 1350. If electrical conductivity of
the finished weld joint is not of primary importance, then 4043
may be used
2XXX alloys – Many base materials in this series are not recom-
mended for arc welding. Those that are weldable include: 2219,
2014, 2519, 2008, and 2036. Alloy 2319 is a matching filler alloy
for 2219 and 2519 and can also be used on the other weldable
alloys. Alloys 4043 and 4145, which contain copper, can also
be used. 5XXX fillers should not be used to weld 2XXX parent
materials; otherwise weld cracking will result.
3XXX alloys – These moderate strength aluminum-manganese
base materials are relatively crack resistant and can be welded
easily using either 4043 or 5356 filler alloys.
4XXX alloys – These base materials are usually found as welding
or brazing fillers. In the rare event they are encountered as
parent materials, 4047 is usually the best choice as a filler metal
5XXX alloys – These higher strength aluminum-magnesium
base materials, are the most commonly found structural
aluminum sheet and plate alloys. The general rule, except for
5052, is to choose a 5XXX filler metal with slightly higher
magnesium content than the parent material being welded. For
all alloys except 5052, 5XXX alloys should not be welded using
4XXX filler alloys. The high Mg content of the parent material
when combined with the high silicon content of the 4XXX fillers
will result in a high level of Mg
2
Si (magnesium silicide), a brittle
intermetallic compound that will cause the weld to have very
poor ductility and toughness. In choosing filler alloys for 5XXX
alloys, there are several specific recommendations as follows:
• 5052 – The magnesium content of this alloy contributes to its
high crack sensitivity. If it is welded with 5052 filler alloy, it will
often crack. In order to avoid the tendency to crack, 5052 is
usually welded with a filler alloy of much higher Mg content,
such as 5356. The result is that the weld metal, which is an
alloy of the 5356 and 5052, has magnesium contents high
enough to be crack resistant. Additionally, the magnesium
content of 5052 is low enough so that it can be successfully
welded using 4043.
•
For high temperature applications the Al-Mg alloys with Mg
c
ontent over 3% are unsuitable for service temperatures over
150°F (66°C). They are susceptible to stress corrosion crack-
ing at higher temperatures. This is also true for the filler alloys,
and should be taken into account when selecting the proper
f
iller alloys
• 5454 – This alloy is a lower Mg alloy specifically developed to
b
e immune to the stress corrosion cracking noted above.
Filler alloy 5554 is designed as a matching filler alloy for the
5454 base alloy and it should be used whenever possible.
• 5083 and 5456 – These high Mg, high strength alloys can be
successfully welded using 5356. However, most structural
welding codes require that the tensile strength of these welds
have a minimum ultimate tensile strength of 40 ksi. When
welded using 5356, welds in these alloys often will not meet
this requirement. For this reason, 5183 or 5556 are the recom-
mended filler materials for these alloys
6XXX alloys – These Al-Mg-Si alloys are primarily used for
extrusion alloys, although they can also often be found as sheet
and plate. The chemistry of these alloys makes them very
sensitive to hot cracking. Autogenous welds (i.e., welds made
without adding filler metal) are susceptible to cracking. But,
these alloys are readily weldable using either 4043 or 5356 filler
metal. The chemistry of 4043, aluminum with 5% silicon, or
5356 aluminum with 5% magnesium, when combined with
6061, provide a crack resistant chemistry.
• The decision whether to use 4043 or 5356 depends upon a
number of factors. Below is a comparison of these two com-
mon filler metals and shows the advantages and disadvan-
tages of each:
Comparison of 4043 and 5356
ER4043 ER5356
• Smooth Bead, Good Wetting • Black Smut, Distinct Ripples
• Low Column Strength • Best Feedability
• Higher Penetration • Lower Penetration
• Lower Ductility • Higher Ductility
• Lower Tensile • Higher Tensile
•
Less Prone to Porosity
•
More Prone to Porosity
• Anodizes a Dark Gray • Anodizes w/good Colormatch
• Much Lower Shear Strength • Higher Cracking Sensitivity
•
Lower Cracking Sensitivity
• Higher Melting Point
• Lower Melting Point • Wider Melting Range
• Narrower Melting Range
To summarize, ER4043 is easier for the welder to use than
ER5356, it is more fluid and therefore it wets into the base
material better. It is also more crack resistant. ER5356 feeds
better and gives welds that are both stronger, especially in lap
welds and fillet welds, and more ductile. While 5356 should be
used to weld the 6XXX alloys to any of the 5XXX alloys, 4043
should be used to weld the 6XXX alloys to the common 3XXX
casting alloys.