Aluminum welding wire ER4043 and ER5356 are two of the most widely used filler metals in the aluminum fabrication industry and have been in use for over 65 years. However, for most everyday welding applications, ER4043 or ER5356 wire will suffice. It is generally accepted that all arc weldable 6000 series aluminum alloys, such as 6005, 6061, 6063, 6082, 6351, and all 5000 series aluminum alloys, can be welded with ER5356 wire. In addition, all arc weldable 6000 series aluminum alloys, as well as 5000 series aluminum alloys with less than 2.5% magnesium, such as 5005, 5050 and 5052, can be welded with ER4043 wire.

A basic common knowledge of common aluminum welding wire is that ER4043 is an aluminum filler metal based on the addition of 5% silicon and ER5356 is an aluminum filler metal based on the addition of 5% magnesium.

(1) ER4043 is not recommended for welding any magnesium-based alloys (5000 series ) with more than 2.5% magnesium content, such as 5086 or 5083, etc. This is mainly due to the fact that a large amount of silicon in the ER4043 welding wire will combine with the magnesium in the base material and reduce the mechanical properties.

(2) ER4043 is capable of operating at temperatures in excess of 150°F (66°C). In contrast, ER5356 welding wire is not suitable for prolonged high temperature environments due to its 5% magnesium content. If used in such environments, it may result in the formation of a continuous grain boundary network of precipitates that are highly anodic to the aluminum-magnesium matrix. This in turn can lead to premature failure of the welded structure.

(3) ER4043 welding wire is less ductile in the weld state than ER5356 welding wire. If molding is required after welding, be sure to take this characteristic into account. In addition, if ER4043 wire is used, due to this difference in ductility, special bending pass criteria need to be set when conducting guided bending tests for welding process evaluation and welder skill qualification.

(4) ER4043 wire is softer than ER5356. Typically, when gas metal arc welding (GMAW) is performed, the feedability of the wire is worse in comparison. Feedability is an issue with any aluminum wire compared to steel, especially with smaller diameter wires. Lower hardness filler metals, such as the 1000 and 4000 series, can compound this problem.

(5) ER4043 welding wire generally provides higher weldability ratings and lower crack susceptibility than ER5356. ER4043 produces welds that generally have a better appearance, smoother surfaces, less spatter, and fewer weld stains. Therefore, ER4043 filler metal is more attractive to welders.

(6) ER4043 welding wire is not recommended if post-welding anodizing is required because it usually turns a dark gray color after the anodizing process. ER5356 will provide a closer color match after anodizing, especially in Series 6 aluminum alloys.

(7) When the transverse tensile strength of a full penetration weld is required to meet the base metal requirements (usually for welding process evaluation), ER5356 welding wire will usually only meet the minimum weld strength requirements for 5005, 5050, 5052, and 5086, and may not be able to meet the minimum weld strength requirements for, e.g., 5083 and 5456.

(8) ER4043 wire has a lower tensile strength than ER5356. The lower strength also relates to shear strength, which is important when calculating the dimensions of fillet welds. the nominal weld state tensile strength of ER4043 is approximately 24 ksi, while the nominal weld state tensile strength of ER5356 is approximately 35 ksi. the difference is significant and, if not adequately understood and taken into account, is likely to affect the performance of the welded structure.