Abstract: Thermal sprayed Al coating was prepared on the surface of die casting AZ91 alloy to investigate the effects of heating temperature and holding time on the microstructure of AZ91/Al coating interface. The corrosion resistance and wear resistance of the diffusion layers were compared and analyzed. The results show that the Al coating is mechanically bonded to the substrate before heat treatment, and the metallurgical bonded diffusion layer can be formed at the interface between Al coating and AZ91 alloy substrate after heat treatment, and the thickness of the diffusion layer increases with the prolongation of holding time. When the heating temperature is below 375 ℃, the diffusion layer is mainly consists of β-Mg ₁₇ Al ₁₂ phase, but when heating at 375 ℃ for 8 h, it is α-Mg+β-Mg ₁₇ Al ₁₂ phase, and when heating at 425 ℃ for 1 h, it is γ-Mg ₂ Al ₃ and β-Mg ₁₇ Al ₁₂ phase. The corrosion potential of AZ91 alloy substrate and diffusion layers is in the order of γ>β>α+β> AZ91 alloy substrate from high to low, the corrosion current density of diffusion layers is all lower than that of AZ91 alloy substrate, the order of capacitive arc radius in impedance spectroscopy is γ>β>α+β>AZ91 alloy substrate, which shows the corrosion resistance of diffusion layers is all better than that of AZ91 alloy base material. The friction stability coefficients of γ, β and α+β diffusion layer are all higher than that of AZ91 alloy substrate, and the wear rate and the wear scar width are all less than those of AZ91 alloy substrates, in which the wear rate and the wear scar width of β diffusion layer are the smallest and has the best wear resistance.

Key words: die casting AZ91 alloy, surface spraying, heat treatment, corrosion resistance, wear resistance