Research On Solid Diffusion Treatment On The Surface Of AZ91 Magnesium Alloy

Bad corrosion resistance has been a serious factor limiting wider applications of magnesium and its alloys, surface treatment is an effective method to improve the corrosion resistance. In this research, solid diffusion process was used to form a diffusion coating on the surface of AZ91 magnesium alloy to improve its corrosion resistance.Pure aluminum powder, mixed powder with different mass ratio of zinc and aluminum (1:3, 1:1, 3:1) was used as diffusion powder, the AZ91 specimens were buried in the mixed powder and were heat-treated at different temperature for different time. After examining the morphology, thickness, composition, phase constitutes and corrosion resistance of coatings formed at different processing parameter, combining analyze of diffusion coating forming mechanism and the effect of diffusion coating on corrosion resistance, optimized processing parameter. It could be got the conclusions as follows:(1) diffusion coatings could be formed on the surfaces of AZ91 specimens after Al diffusion treatment at 420℃-450℃ for 8-12 hours and Al-25wt%Zn, Al-50wt%Zn diffusion treatment at 410℃-430℃ for 4-8 hours, the coatings were metallurgical bonded with the substrates, the Al-75wt%Zn mixed powder is not fit for used as diffusion powder for AZ91 magnesium alloy.(2)The Al diffusion coatings were thin, ranged from 5μm to 20μm, and mainly consisted of Mg₁₇Al₁₂ and Mg; the thickness of Al-Zn diffusion coatings were approximately 50-500μm related to the processing parameters, and the main phases were Al₆Mg₁₀Zn, Al₅Mg₁₁Zn₄, Mg₁₇Al₁₂ and a small amount of Mg_0.97Zn_0.03(3)The suitable processing parameters of Al diffusion treatment for AZ91 magnesium alloy is heat-treated at 430±5℃ for 8-12 hours, and 415±5℃ for 6 hours when using Al-25wt%Zn and Al-50wt%Zn mixed powder, Al-Zn diffusion coating could be formed on the surface of AZ91 magnesium alloy by burying the sample in Al-25wt%Zn or Al-50wt%Zn powder during the process of solution treatment.(4)The microstructure of the AZ91 specimens was not changed after diffusion...