Study On Surface Aluminizing Processes,Microstructure And Properties Of AZ31 Wrought Magnesium Alloy

AZ31 magnesium alloy is the lightest metal structural material in practical use,and is widely used in aerospace,automotive,electronic products and other fields.However,the electrode potential of AZ31 magnesium alloy is low,and the corrosion resistance is weak,which greatly limits the use of magnesium alloy.The current research shows that infiltrating alloying elements on the surface of magnesium alloy is a very effective surface protection method,which can improve the surface hardness and corrosion resistance of AZ31 magnesium alloys without damaging its original properties.In this paper,the corrosion resistance of AZ31 magnesium alloy was improved by aluminizing on the surface of AZ31 magnesium alloy.The main work is as follows:(1)Two different aluminizing layers were prepared by powder embedding method in box furnace with two different aluminizing agents.(2)Different heating methods(box furnace heating and induction heating)were used to prepare the diffusion coating on the surface of AZ31 magnesium alloy under the holding time of 1 hour and 3 hours,respectively.(3)After the AZ31 magnesium alloy extrusion rod was twisted,the powder coating was prepared on the surface of AZ31 magnesium alloy extrusion rod by powder embedding method.Through the above research,the following conclusions are obtained:(1)When AlCl₃ powder is used as the diffusion agent,the diffusion coating is thicker than when AlCl₃ and pure aluminum composite powder is used as the diffusion agent,but the flatness of the latter is better.When AlCl₃ powder is used as the diffusion agent,the layer consists of a small amount of ?-Mg₂Al₃,coarse eutectic structure(?-Mg₁₇Al₁₂+?-Mg)and fine ?-Mg₁₇Al₁₂+?-Mg precipitation.When using AlCl₃ and pure aluminum as the diffusion agent,the layer contains only one thin layer of Al2O3 and a small amount of?-Mg₁₇Al₁₂ precipitation.Al2O3 layer hinders the further infiltration of active Al atoms into magnesium matrix,which leads to the thin aluminizing layer.(2)In a short time(1 hour),the diffusion of induction heating is faster than that of box furnace,and the diffusion layer is thicker;but with the increase of time(3 hours),the diffusion of box furnace is more uniform and the thickness increases obviously.The diffusion layer of box furnace and induction heating for 1 hour is composed of single phase layer of ?-Mg2Al3 and layer of ?-Mg₁₇Al₁₂.After 3 hours in the box furnace,the sample consists of a small amount of ?-Mg2Al3 phase,(?-Mg₁₇Al₁₂+?-Mg)eutectic layer and?-Mg₁₇Al₁₂+?-Mg precipitation layer;after 3 hours of induction heating,no precipitation phase appears in the sample.(3)For the torsional samples,with the increase of holding time,the diffusion coatings gradually changed from a certain amount of Al-Mg solid solution and Mg₁₇Al₁₂ precipitate phase to a eutectic structure composed of Mg₁₇Al₁₂+?-Mg,and a large amount of Mg₁₇Al₁₂ precipitated second phase.After twisting,the diffused samples all improve the corrosion resistance of the magnesium matrix.