Effect of interlayer on interface microstructure and properties of Al/Mg friction stir welded joints

In this paper, Ag foil and Zn foil were used as interlayers for butt welding of 2 mm thick 5052 aluminum alloy and AZ31 magnesium alloy, and the influence of different interlayers on the thickness, distribution and type of IMCs at the joint interface was studied. The results show that the interfacial IMCs without the interlayer are 3.52 µm thick, and the main types are Al₃Mg₂ and Al₁₂Mg₁₇, which are continuously distributed along the plate thickness direction. The fracture of the joint occurred in the band area, and the tensile strength and elongation were 175 MPa and 2.75%, respectively, showing the characteristics of brittle fracture. Compared with the pure Al/Mg joint, the thickness, distribution and type of IMCs at the interface with Ag interlayer are changed, and the thickness of IMCs decreases to 2.38 µm, Al₃Mg₂ and Al₁₂Mg₁₇ on the interface are discontinuous, and Ag₂Al and Mg₃Ag are generated at the same time. The tensile strength and elongation of the joint are the highest, 190 MPa and 5.13%, respectively, showing the characteristics of ductile fracture. The interface IMCs thickness of the joint with Zn interlayer is 3.09 µm, and no Zn-containing IMCs are generated at the interface. The tensile strength and elongation of the joint with Zn interlayer are the lowest, only 161 MPa and 1.45%, which is lower than those of the joints without interlayer and with Ag interlayer.