Aluminum Workshop: An overview of 4XXX and 5XXX fillers

In the last issue we discussed 4043 and 5356 filler metals. It is a fact that these two filler alloys represent 80 percent of the worldwide consumption of aluminum filler metals. So it stands to reason that you should be using one of these filler alloys for roughly 80 percent of your applications.

But what about the other two dozen or so aluminum filler alloys? Let’s discuss some of them and where you should use them.

4XXX Fillers

4047 contains 12 percent silicon (Si). It has a narrower melting range than 4043, making it somewhat more crack-resistant, especially regarding crater cracking. It is significantly more expensive than 4043, and it doesn’t provide an advantage in most applications. However, the application where it has found its niche is heat exchanger fabrication, where the small melting range can result in lower leak rates in welding thin-wall tubing.

4145 contains 5 percent Si and 4 percent copper (Cu). It is designed to weld Cu-containing alloys such as 2219 and 6013. You should not use it to weld aluminum alloys that do not contain Cu, since the weld dilution can produce a weld chemistry containing about 2 percent Cu, which can be crack-sensitive.

356 and 357 alloys are designed to be matching filler alloys to the corresponding base material casting alloys. They are designed to repair aluminum castings before heat treatment. Subsequent heat treatment produces comparable properties in the repaired casting. They really have no other applications.

4008, 4009, 4010, 4943, and 4643 are alloys that are designed to be heat-treatable. They produce stronger welds in thicker applications where the weldment will be completely heat-treated after welding (that is, solution heat-treated, quenched, and aged). They display little to no advantage in applications where the weldment is used as-welded or even as-aged.

5XXX Filler Alloys

5556, 5183, and 5087 were designed as higher-strength versions of 5356. It certainly isn’t wrong to use them to weld alloys such as 6061-T6, but they have no real benefit over using 5356. However, you should use them when welding high-strength 5XXX alloys such as 5083, 5059, and 5456, where most fabrication codes specify a minimum weld strength of 40 KSI. Why? Because 5356 simply does not contain enough alloy to meet this value consistently, usually producing a strength of 38 or 39 KSI. It should be noted that 5087 is a matching filler to 5087 base material, which is a European alloy that is rarely seen in North America.

5554 was designed as a matching filler alloy for 5454, which is relatively low in magnesium (Mg). Any Al-Mg alloy with more than 3½ percent Mg is susceptible to stress corrosion cracking at long-term exposures of more than 150 degrees F. 5454, which has a lower amount of Mg, was designed for such applications along with some specific corrosive applications. Using filler with more Mg, such as 5356, can result in failure under these conditions.