It isn’t enough to know that you are welding aluminum plates . Welding professionals have to know which alloy is about to be welded, and they have to know the correct filler metal to use. The most common alloys used in shipbuilding are the Al-Mg 5XXX sheet alloys and the Al-Mg-Si 6XXX extrusion alloys, primarily because of their excellent resistance to corrosion.
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Most Aluminum Alloy plates are easily arc weldable. Virtually all of the alloys in the 1XXX, 3XXX, 4XXX, 5XXX and 6XXX series can be arc welded using GTAW and GMAW. However, most of the alloys plates in the 2XXX and 7XXX series cannot be arc welded. The only arc weldable alloys in the 2XXX series are 2219 and 2519. Almost all of the other 2XXX alloys will crack severely when welded. Similarly, the only alloys in the 7XXX family that can be arc welded are 7003, 7004, 7005 and 7039.
Specifically, be particularly wary of 2024 and 7075 aluminum plate. It is tempting to buy one of these alloys for repair welding because they are strong and commonly available, but they are crack-sensitive to arc welding.
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.
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