Dissimilar Welding of Al and Mg Alloys by FSW

TLDR

Laser welding of Al/Mg alloys produces brittle joints because of Mg17Al12 intermetallics, whereas friction stir welding, a solid‑state process, is expected to yield stronger dissimilar joints. The study aimed to fabricate butt joints of Al alloy and AZ31 magnesium alloy by friction stir welding at various tool rotational and welding speeds. Friction stir welding was performed with different tool speeds and welding speeds, and the resulting microstructures and mechanical properties were compared to those of laser‑welded Al/Mg joints. The stir zones exhibited higher hardness than the parent AZ31 alloy due to Mg‑Al intermetallics, but lower hardness than the laser‑welded fusion zone, with hardness varying with welding parameters and optimal conditions identified.

Abstract

Microstructures and mechanical properties of dissimilar welding joint between Al alloy and Mg alloy by Friction Stir Welding (FSW) were investigated in comparison with laser welding of the same combination. Dissimilar joint of Al and Mg alloy by laser welding was very brittle because of building up Mg17Al12 inter metallic compounds in fusion zone. On the other hand, FSW is anticipated to welding dissimilar alloys with enough joint strength because it is a solid-state process without melting. In this paper, FSW was carried out to make dissimilar butt joints of Al alloy and AZ31 magnesium alloy with various tool rotational speed and welding speed. These joints showed higher hardness in their stir zones than that of parent AZ31 alloy because of Mg-Al inter metallic compound formation. However, the hardness of stir zone was lower than that of fusion zone of laser welding, and was changed with the welding parameters of tool rotational speed and welding speed (i.e. heat input ratio of FSW). The optimum welding conditions of Mg and Al dissimilar FSW joint and the influence of inter metallic compound distribution with mixing of materials in stir zone were discussed.