ZA74镁合金非枝晶组织的演变过程及机理Non-dendritic microstructure evolution process and mechanism of ZA74 magnesium alloy

采用等温热处理法对ZA74镁合金在部分重熔过程中非枝晶组织的演变过程和机理进行研究。结果表明：在重熔过程中，ZA74合金原始组织中沿着晶界分布的Mg₃₂(Al,Zn)₄₉共晶相逐渐向α-Mg基体扩散溶解，当温度达到共晶熔化后,剩余部分开始熔化。非枝晶组织的演变是在体系自由能降低的驱动下完成的，主要机制是共晶组织的固溶，溶质原子扩散，枝晶组织的粗化、分离、球化以及晶粒的合并和长大。其中，ZA74合金固相颗粒的分离是由溶质扩散、能量起伏、成分起伏等因素造成液相沿亚晶界浸渗和根部重熔两种机制起主导作用。

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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