ZA74鎂合金非枝晶組織的演變過程及機理Non-dendritic microstructure evolution process and mechanism of ZA74 magnesium alloy

采用等溫熱處理法對ZA74鎂合金在部分重熔過程中非枝晶組織的演變過程和機理進行研究。結果表明：在重熔過程中，ZA74合金原始組織中沿著晶界分布的Mg₃₂(Al,Zn)₄₉共晶相逐漸向α-Mg基體擴散溶解，當溫度達到共晶熔化后,剩余部分開始熔化。非枝晶組織的演變是在體系自由能降低的驅動下完成的，主要機制是共晶組織的固溶，溶質原子擴散，枝晶組織的粗化、分離、球化以及晶粒的合并和長大。其中，ZA74合金固相顆粒的分離是由溶質擴散、能量起伏、成分起伏等因素造成液相沿亞晶界浸滲和根部重熔兩種機制起主導作用。

The non-dendritic microstructure evolution process and mechanism analysis of ZA74 magnesium alloy during partial remelting were investigated by isothermal heat-treatment. The results indicate that the Mg₃₂(Al,Zn)₄₉eutectic phases distribute on grain boundary of ZA74 alloy initial microstructure, which gradually dissolves into α-Mg matrix due to the diffusion of the solute and the remainder is melted when the temperature reaches up to eutectic melted. The evolution of non-dendritic microstructure is driven by the free energy reduction. The main mechanisms are the eutectic microstructure solution, solute diffusion, coarsening, dendrite separation, spheroidization and final coarsening during partial remelting. Furthermore, the appearance of subboundary and root remelting results from the solute diffusion, energy fluctuation and constituent fluctuation which are the separation mechanisms of ZA74 particle during partial remelting.

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