Grain Refinement Of AZ91D Magnesium Alloy And Microstructural Evolution During Partial Remelting

As a new engineering material,the potenial development and advantages of maqnesium alloy is undoubted.However,due to the self-limitation and shortage of traditional forming technology,it is hard to spread its appliation.Now this problem is solved by the semi-solid forming technology.Therefore,it is very significance for the study of maqnesium alloy's Semi-solid forming.Semi-solid forming is a forming method.It makes use of the metal's speciality when the mental changes from liquid state to solid state or from solid state to liquid state. Preparation of casting ingot is the base of this technology.This thesis explores the refined grains and the technology of making AM60B partially casting ingot in the partially remelted method.This technology encompasses two parts:SiC inoculation refined AM60B alloy and semi-solid remelting.Through studing the influence of some factors to the refined grains and microcosimic structure,it established a group of technics parameter of SiC transformed refined AM60B alloy.The factors include:append content,transformed temperature,helding time of the fused mass,iron mold temperature,casting temperature,dimension of ingot metal and so on. SiC affiliated quantity is 0.2%wt;transformed temperature is 790℃;helding time is 0 min; casting temperature is 720℃.The temperture of iron mold is room temperature.The study of refined mechanism reveals that the reaction of SiC with alloy produces a wealth of dispersed Al₄C₃ while Al₄C₃ can be used as heterogeneous nucleation ofα-Mg atom rime and speeds rime and the form and core.The process can be demonstrated as follows:3SiC+4Al→Al₄C₃ +3Si;2Mg+Si→Mg₂Si.The microstructural evolution was researched in the subsequent experience of the partially remelt.The microstructural evolution could be divided three stages,the petty dendritic grain were coarsing and disappear,structure separation and spheroidization due to partial melting of primary particles and the final coarsening stage of the remnant primary particles.The further phase transition analysis believed,the microstructural evolution could be divided four stages,β→L stage,α+β→L stage,α→L stage andα=L stage.At the same time,the influence of the heating-up temperature,the primary grain size,the ingot metal size to the semi-solid microstructural was be researched in the subsequent experience.Come to a final conclusion,SiC is an excellent grain refiner for AM60B magnesium alloy,the technology of grain refinement and partially remelted methed to pepare AM60B magnesium alloy' casting ingot can be used in the practice.