Effect Of Calium And Yttrium On Microstructure And Properties Of Injection-molded AZ91D Magnesium Alloy

Magnesium alloy as the lightest commercial metal material in the 21st century,with high specific strength,specific stiffness,excellent damping properties and electromagnetic shielding properties,etc.,in the automotive,aerospace,communications and electronic products and other fields have important application value and broad application prospects.However,for the cast magnesium alloy,the traditional cast magnesium alloy due to low solidification rate,the organization of the alloy matrix and precipitation of the phase is relatively coarse and uneven distribution,resulting in its strength,plasticity,thermal stability and corrosion resistance is not ideal,it is difficult to meet the requirements of the use of high-performance structural materials,seriously limiting the application of magnesium alloy materials.In order to solve this problem,two methods are used in this paper,one is to add alloying elements to the existing composition of magnesium alloy to enhance the properties of magnesium alloy,and the other is to use injection molding process,this new process has higher solidification cooling rate,which can significantly refine the grain and second phase,increase the homogeneity of organization and composition,and at the same time increase the solid solution of alloying elements and form a new substable phase,thus significantly enhance the The mechanical properties and corrosion resistance of magnesium alloys were significantly improved.In this paper,AZ91D magnesium alloy was taken as the object,and the master alloy specimen was prepared by high frequency vacuum induction melting furnace,and then the injection molding alloy specimen was prepared by high vacuum extrusion casting system to study the effect of solidification cooling rate and Ca and Y addition alone and compound addition on the organization,mechanical properties and corrosion resistance of the alloy,and analyze the mechanism.The experimental results show that both alloying and injection molding processes can significantly improve the alloy properties.For alloying elements,the addition of Ca and Y alone can refine the microstructure of magnesium alloy and evenly distribute the second phase.The mechanical properties of the alloy are improved better by adding Ca than by adding Y,while the corrosion resistance of the alloy is improved better by adding Y,and the mechanical properties and corrosion resistance of the alloy are improved obviously by adding Ca.For the injection molding process,the faster solidification speed makes the alloy produce Al₂Ca phase and Al₂Y phase,the microstructure is fine granular,the alloy grain is further refined,so that the mechanical properties and corrosion resistance of the alloy are further improved.With the increase of Ca and Y content,the mechanical properties and corrosion resistance of the alloy showed a rising and then decreasing trend,and the optimal additions of Ca and Y were 1.6wt%and 1.2wt%,respectively.When the Ca addition is 1.6wt%,the injection molded alloy has 27.2%and 30.6%higher compressive strength and yield strength,respectively,and 96.3%lower electrochemical corrosion current density and 90.6%lower immersion corrosion rate than the parent alloy.When Y is added at 1.2 wt%,the injection molded alloy has 32.6%and 35%higher compressive strength and yield strength,respectively,and 87.5%lower corrosion current density and 62%lower immersion corrosion rate than the parent alloy.With the composite addition,the compressive strength and yield strength of AZ91D-1.6Ca-1.2Y injection molding alloy increased by 24.9%and 28.4%,respectively,and the electrochemical corrosion current density decreased by 81.9%and the immersion corrosion rate decreased by 88.6%compared with that of AZ91D parent alloy.