AZ91D Magnesium Alloy By Solid Thermal Expansion Zinc Impregnation And Research Of Corrosion Resistance

Poor corrosion resistance has been one of the important factors for hinder the widerapplications of magnesium alloy in the field of biomedical materials. Surface modification ofmagnesium alloy is the main way to improve the corrosion resistance of magnesium alloy.This research adopts the method of solid powder diffusion process to form a diffusion coatingon the surface ofAZ91D magnesium alloy, the purpose is to improve its corrosion resistance.Zinc power was used as diffusion material, the AZ91D magnesium alloy specimens wereburied in the zinc powder and were heat-treat at different temperature for different time. Afterthat, the analysis was made on the morphology, thickness, composition, phase compositionand the corrosion resistant in the Hank’s simulated body fluids of the diffusion coating formedat different expansion parameter. Combined with the permeability theory of thermalexpansion and the formation mechanism of diffusion layer, and analysis of the influence ofdiffusion coating for magnesium alloy corrosion resistant performance, optimize the processparameters for the magnesium alloy surface thermal expansion. The main conclusions arethe followings:(1) Under the different expansion temperature of360℃~400℃, the infiltration time in4~12hours, diffusion coating with different thickness and different structure of organizationcould be formed on the surface of AZ91D magnesium alloy after zinc thermal expansioninfiltration processing.(2) Diffusion coating layer is mainly composed of expanding Mg0.97Zn0.03, MgZn2andMg, at the same time contains a small amount of Mg7Zn3and Zn.(3) Thermal expansion of permeability of AZ91D magnesium alloy surface with zincpowder, the suitable temperature is380℃, infiltration time is4~12hours. And under thecondition of380℃,8hours to get the expansion of diffusion coating has the best corrosionresistance.(4) The expansion of diffusion layer to form a continuous film on the surface of AZ91Dmagnesium alloy, the layer can significantly reduce corrosion rate, at the same time improvethe corrosion potential of magnesium alloy in3.5%NaCl solution, reduce the corrosion current of magnesium alloys, improve the corrosion resistance of magnesium alloys.