Intermetallic Compounds in the Banded Structure and Their Effect on Mechanical Properties of Al/Mg Dissimilar Friction Stir Welding Joints

Dissimilar friction stir welding (FSW) between aluminum and magnesium alloy was performed, using various tool rotational speed (TRS) at a fixed travel speed, with tool offset to aluminum to investigate the formation of intermetallic compounds (IMCs) in the banded structure (BS) zone and their effect on mechanical properties. Large quantities of IMCs, in the form of alternating bands of particles or lamellae, were found in the BS zone, where drastic material intermixing occurred during FSW. The BS microstructural characters in terms of the morphology of the bands and the quantity and distribution of IMC particles varied with TRS. All welds exhibited brittle fracture mode with their fracture paths propagating mainly in/along the IMCs in the BS. It is shown that these BS microstructural characters have significant effect on the mechanical properties of the joints. Suggestions on tailoring the BS microstructure were proposed for improving the strength of the BS zone and the final mechanical properties of the Al/Mg FSW joints.