Abstract
In this research, Ultrasonic spot welding (USW) was used as a solid-state joining method to strengthen the joints. Magnesium-alloy (AZ61A) and aluminum-alloy (AA5052) welded structures are commonly found in lightweight vehicles. Under this process, plastic deformation was observed in the weld joint at an energy level of 1550 J, with increasing welding energies beyond 1550 J, and a reaction layer of intermetallic compounds (IMCs) forms, with a thickness of about 17 µm. The γ-Mg17Al12 + β-Mg2-Al3 phase comprises the majority of the IMCs; the β-Mg2-Al3 phase exhibits a hardness of 6.7 GPa and a classic pop-in phenomenon, while the γ-Mg17Al12 cubic structure phase has an average hardness of 3.5 GPa. For welding energies exceeding 1550 J, the rapid formation of these phases can negatively impact the joint's performance. The observed fractures feature multiple secondary cracks, which could indicate a cleavage fracture, although further analysis would be necessary to confirm this.
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