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More and more welded assemblies are being made from aluminum alloys. While the alloy has a number of interesting characteristics, its light weight is largely responsible for an increase in use in the transportation industry.
Many experienced welding professionals mistakenly believe aluminum is a more difficult alloy to weld than steel. The perception is largely due to operators bringing their habits and experiences of welding steel to this material.
This article will examine common mistakes made when welding aluminum in the fabrication of trailers and how these mistakes can be corrected or avoided.
Know Your Alloy
Virtually all of the alloys in the 1XXX, 3XXX, 4XXX, 5XXX and 6XXX families are arc weldable using either the GTAW or GMAW process.
Most aluminum alloys in the 2XXX and 7XXX families are not weldable. The only weldable alloys in the 2XXX family are 2219 and 2519; in the 7XXX family, the only weldable alloys are 7003, 7004, 7005 and 7039.
Be particularly careful about 2024 and 7075. They are strong and commonly available, but unweldable.
Welding an "unweldable" alloy or using the wrong filler alloy can result in immediate cracking or a premature failure in service at a later time.
“Prior to welding, the correct alloy should always be identified and matched to the correct filler metal.”
Using the Correct Filler Alloy
The most common applications in the trailer industry are joining one of the 5XXX Al-Mg sheet/plate alloys – such as 5052, 5154 , 5454 or 5083 – to themselves or in the joining of a 6XXX extrusion alloy to one of the above mentioned 5XXX alloys.
- For joining a 5XXX sheet or plate to a 6XXX extrusion alloy
- For 6061-T6, the recommended filler alloys are 5356 or 5554
- For 4043, 5XXX can also be used
“A blockquote here that’s worth highlighting. Go on, I dare you to not read it.”
For joining the 5XXX alloys to themselves, the correct filler alloy is 5554 for welding 5154 or 5454; for welding 5052, either 4043, 5554 or 5356 should be used, although 5356 and 5554 are more commonly used so that one filler alloy can be used in the shop to avoid the possibility of mixing up filler alloys. For welding 5083, which has higher strength, 5556 or 5183 are recommended. 5356 does not quite match the strength of 5083. 4043 should not be used to weld 5XXX alloys, except for 5052, which has a low Magnesium content.
There is absolutely no advantage in using the higher strength fillers 5183 or 5556 in this application. Some suppliers will try to sell these alloys, but they give no benefit despite their higher cost.
