汽车发动机用AZ91D合金的表面喷涂与性能

采用热喷涂工艺在压铸态AZ91D合金表面制备了Al涂层,研究了热处理温度和保温时间对AZ91/Al涂层界面组织形貌的影响,并对比分析了扩散层的耐腐蚀性能和耐磨性能。结果表明,热处理前Al涂层与基材为机械结合,热处理后Al涂层与AZ91合金基材的界面处可形成冶金结合扩散层,且随着保温时间延长,扩散层厚度不断增加;热处理温度在375 ℃以下时扩散层主要由β-Mg₁₇Al₁₂相构成,375 ℃×8 h热处理后为α-Mg+β-Mg₁₇Al₁₂相,425 ℃×1 h热处理后为γ-Mg₂Al₃和β-Mg₁₇Al₁₂相。AZ91合金基材和扩散层腐蚀电位从高至低顺序为γ>β>α+β>AZ91合金基材,扩散层的腐蚀电流密度均低于AZ91合金基材,阻抗谱图中容抗弧半径从大至小顺序为γ>β>α+β>AZ91合金基材,扩散层的耐腐蚀性能均优于AZ91合金基材;γ、β和α+β扩散层的摩擦稳定性系数都高于AZ91合金基材,而磨损速率和磨痕宽度都要小于AZ91合金基材,其中β扩散层的磨损速率和磨痕宽度最小,具有最佳的抵抗磨损的能力。

Surface spraying and properties of AZ91 alloy for automotive engine

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.