Microstructure evolution and property analysis of Mg1/Al1060 vacuum diffusion welded joints

The reaction of industrial pure magnesium Mg1 and industrial pure aluminum Al1060 was realized by using vacuum diffusion welding technology. Scanning electron microscope, energy spectrometer, universal mechanical testing machine, microhardness tester and electrochemical workstation were used to study the microstructure, physical composition and properties of diffusion bonding layer. The results show that Mg/Al vacuum diffusion welding generated a diffusion reaction layer composed of magnesium-aluminum intermetallic compounds at the joint, and with the prolongation of the holding time, the thickness of the reaction layer gradually increases, and the microstructure morphology undergoes obvious changes. At the initial stage of diffusion, the reaction layer shows a monolayer structure, and the Mg₂Al₃ phase precipitates preferentially at the joint interface; when the holding time reaches 60 min, the interface generates a new phase layer of Mg₁₇Al₁₂; when the holding time is extended to 90 min, the reaction layer evolves into a three-layer structure consisting of a Mg₂Al₃ layer, a Mg₁₇Al₁₂ layer, and a (Mg₁₇Al₁₂ + Mg-based solid solution) layer. With the prolongation of the holding time, the shear strength of the joint showed a tendency of increasing and then decreasing, and the shear force that could be withstood during the holding time of 60 min reached 1245.7 N, and the fracture occurred at the Mg₂Al₃ reaction layer near the aluminum side. The microhardness of each welded layer was significantly higher than that of the magnesium and aluminum base material, and the Mg₂Al₃ layer exhibited the highest microhardness of 320.6 HV. The corrosion current density of the Mg1 layer was the smallest, 2.199 × 10⁻³ A/cm² , while the corrosion current density of the Al1060 layer, the Mg₂Al₃ layer, the Mg₁₇Al₁₂ layer, and the (Mg₁₇Al₁₂ + Mg based solid solution) layer increased by one order of magnitude. The order of corrosion rate is Mg1 > (Mg₁₇Al₁₂ + Mg based solid solution)> Mg₂Al₃ > Mg₁₇Al₁₂ > Al1060.