October 3, 2006
Both are acceptable for welding 6061-T6, but each has advantages and disadvantages depending on the application.
An aluminum alloy containing 5 percent magnesium, 5356 generally is stronger and more ductile than 4043. But 4043, which contains 5 percent silicon, typically flows better, is more crack-resistant, easier to weld with, less prone to weld smut, and yields a more aesthetic weld.
You're probably wondering this: If 5356 is stronger, shouldn't I always use it? The answer is no. While 5356 is stronger than 4043, they're both stronger than the weakest area of the heat-affected zone (HAZ) in 6061-T6 butt welds. These butt welds fail in the HAZ—not in the weld metal—and the strength doesn't change, regardless of the filler metal.
This isn't the same with lap or fillet welds. These welds almost always are stressed in shear loading in real-world designs, not in tensile loading like butt welds. Lap and fillet welds usually fail in the weld metal, and 5356 has a shear strength almost 50 percent higher than 4043.
Again, 4043 is less crack-sensitive than 5356 and shows less tendency for crater cracking. If your component will be heat-treated after welding, use 4043; 5356 can be made susceptible to stress corrosion cracking after heat treatment. Similarly, if the component will operate at temperatures above 150 degrees F, use 4043 to avoid stress corrosion cracking.
But if the component will be anodized after welding, use 5356. The high silicon content of 4043 will cause the weld to turn black during anodizing, making the location of each weld obvious and unattractive; 5356 will anodize to a silver color.