Abstract:The joining of AZ31B Mg alloy to 6061 Al alloy was investigated at different joining temperatures by vacuum diffusion bonding method. The microstructures of Mg/Al dissimilar joints were studied by means of optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The results show that the thickness of each layer in the diffusion zone increases with the increase of joining temperature, and the microstructure changes obviously. At joining temperature of 440 °C, the diffusion zone is composed of Mg₂Al₃ layer and Mg₁₇Al₁₂ layer. At joining temperatures of 460 and 480 °C, the diffusion zone is composed of Mg₂Al₃ layer, Mg₁₇Al₁₂ layer, eutectic layer of Mg₁₇Al₁₂ and Mg-based solid solution. The width of high-hardness zone in the joint increases with increasing joining temperature, and the micro-hardnesses at different locations in the diffusion zone are significantly different. The joining temperature of 440 °C offers the highest tensile strength of 37 MPa, and the corresponding joint exhibits brittle fracture at the intermetallic compound layer of Mg₁₇Al₁₂.

Key words: vacuum diffusion bonding; 6061 aluminum alloy; AZ31 magnesium alloy; dissimilar metal joint; microstructure; mechanical property