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The 4xxx series of aluminum fillers are extensively used in aluminum welding owing to their excellent weldability, high cracking resistance, and low melting point. However, joints welded with commercial AA4043 fillers experience low mechanical strength. Therefore, we investigated the performance and mechanical strength of joints welded using newly developed Al-Si-Mg filler metals with different Mg contents (0.6-1.4 wt.%). AA6061-T6 plates were welded as the base metal using a gas metal arc welding process. The microstructures of the welded samples were characterized using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were characterized by microhardness and tensile testing. The results revealed that the new filler metals exhibited weldability similar to that of the ER4043 reference filler. The Mg concentration in the fusion zone of the new fillers was much higher than that of the reference filler. In the as-welded condition, all the fractures occurred outside the fusion zone. Therefore, all the welded samples exhibited similar mechanical strength, much lower than the base metal. After applying the post-weld heat treatment, the mechanical strength of all joints, regardless of the Mg content, reached the same level as the base metal and achieved 100% welding efficiency. Furthermore, the fusion zones were much stronger than the base metal and fusion zone of the reference filler using the new fillers with high Mg content, thus indicating their significant potential for welding high-strength aluminum structures.

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