Filler alloy ER4643

This filler alloy was developed for welding 6xxx series base alloys and developing high mechanical properties in the post-weld heat-treated condition. This alloy was produced by taking the well-known alloy 4043, reducing the silicon, and adding 0.10 to 0.30 percent magnesium, thus ensuring its ability to respond to post-weld heat treatment. This is a premium filler alloy that is priced for its specialized characteristics and would not normally be used unless post weld heat treating was being performed. As post weld heat treatment is not to be used, there is no reason to use this alloy.

Filler Alloy ER4043

While the 4043 filler alloy, a 5% Silicon alloy, is often used to weld 6061 base materials, it is not commonly used when the shear strength of the component is a predominant consideration. The 4043 filler alloy is a silicon-based filler alloy that is often used to take advantage of the element’s capability of promoting fluidity in aluminum. While groove welds can be made using this filler alloy that can characteristically pass minimum transverse tensile test requirements, this filler alloy has considerably lower shear strength when compared to the 5xxx series filler alloys.

Filler Alloy ER4047

Like the 4043 filler alloy, 4047 is a silicon-based alloy but has a much higher level of silicon, approximately 12%. The extra silicon within the alloy provides exceptional fluidity. This alloy, which is also registered as a brazing alloy, is most often used for leak-tight joints in thin-wall applications. The 4047 filler alloy has a very narrow freezing range and consequently is very resistant to solidification cracking. The 4043 and 4047 filler alloys have remarkably similar mechanical characteristics - 4047 having slightly higher tensile strength. Both 4043 and 4047 have lower ductility and lower shear strength properties than the 5xxx series filler alloys. They also possess lower column strength when compared to the 5xxx series filler alloys, and consequently, require extra care during feeding to minimize feedability problems.

Filler Alloy ER5554

The 5554 filler alloy was designed to provide the improved strength and ductility characteristics of a magnesium-based filler alloy that was also suitable for elevated temperature applications. It contains 2.4% to 3.0% magnesium thereby providing an alloy that is not susceptible to stress corrosion cracking but has improved shear strength and improved ductility when compared to the 4xxx series filler alloys. The typical transverse shear strength of 4043 and 4047 is 15.0 ksi and the typical transverse shear strength of 5554 is 23 ksi, an increase of 65% (see Fig 1).

In addition to the improved mechanical properties of 5554 on the completed weld, we see an increase in the column strength of the wire. This characteristic can distinctly improve the wire feedability. The 5554 filler alloy will typically produce a weld that is not as cosmetically appealing as the 4xxx series filler alloys and has a slightly greater potential for producing “smut” (a black deposit of metal oxides that is not harmful to the weld).

Filler wire 5356 or 4043

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.

Al4043 will be a better option. I have performed welding of Al6061T6 with this filler wire in the MIG process and it worked fine.