Different aluminum alloys require differing welding wires in order for successful welding to be achieved. Characteristics of the wire should match those of the specific alloy on which it will be welded, and the wire’s color-matching ability, strength and effect on HAZ should also be considered. Additionally, the welding wire must have a melting temperature similar to that of its base material in order for the most effective welding to occur.   For example, aluminum alloys with higher concentrations of magnesium should be welded with a filler alloy that also contains higher levels of magnesium. Each category of welding wire contains its own dynamic chemical makeup that will yield more efficient results with an aluminum alloy that has similar characteristics. In addition to increasing production efficiency, welding deformation should decrease.

Repair of production molds made of several of the 7000-series alloys are challenging because their susceptibility to hot cracking or stress-corrosion cracking makes these alloys unweldable using arc welding techniques. Exceptions to this rule are 7003 and 7005 extrusion alloys and 7039 plate alloy. Welding of qualifying 7000-series alloys can be done using 5356 or 2319 alloy welding wire, both of which can produce porosity-free welds of acceptable strength that can match the aluminum alloy’s integrity. The more commonly used of these welding wires is 5356, because it is rigid and offers acceptable strength and continuous feeding, while 2319 is heat-treatable and provides high strength and good ductility. The 5356 wires also have a 5-percent-magnesium content filler, which reduces the sensitivity to weld cracking. The higher the amount of magnesium, the lower the risk of cracking.

Two mills that produce 7000-series aluminum alloys have helped develop a proprietary alloy welding wire that is designed to work well with 7000-series alloys. These products are not widely available yet, but all early testing results show improved color matching over the 2319 and 5356 wires. The HAZ around the weld repair area that is common to all heat-treated alloys during repair remains an issue with these new wires, however.

The 2319 wire is best-suited for welding of molds made from 2000-series alloys. Wrought 2000-series alloys can be heat-treated to achieve their high tensile strength, which can range to as high as about 448 MPa. They are alloyed with copper, which helps produce much better welding characteristics. Testing has shown that 2319 wire yields outstanding weld quality and color matching, making it the most popular option when color match is of great importance. Alloys in the 2000 series, because of their high aging and tempering, are also more resistant to thermal fatigue than their 7000-series counterparts, meaning that the heat from the weld will not cause a loss in strength of the material being welded.

Alloys in the 6000 series are heat-treatable wrought alloys that show an HAZ around welded areas. The appropriate wire for welding 6000-series aluminum alloys is 4043, which is one of the most manageable, and has a lower melting point and better fluidity, making it less sensitive to weld cracking. This wire type is suited for applications in which strength of the welded area and color matching are most critical. If the parent material will be anodized after repair however, 5356 welding wire is a better option and will produce a much closer color match, because 4043 will turn dark gray after anodizing.

Because cast alloys offer a stronger grain structure while wrought alloys are more porous, they are more likely to exhibit stronger welding repair. A good choice for 5000-series aluminum alloys is 5356 welding wire, while 2319 wire is suited for 2000 series alloys. These wires produce the best color match with the alloys because they possess lower silicon content, maintaining a silver anodized color that blends in well, rather than a black color that is obvious and unattractive. As non-heat-treated products, cast alloys show no HAZ around the weld, so the welded area is not visible on the finished surface of the mold.