原始组织对半固态AZ91D镁合金重熔行为的影响

Effects of different primary microstructure on semi-solid melting behavior of AZ91D magnesium alloy

采用水淬法研究了具有5种不同凝固组织的AZ91D镁合金半固态熔化过程的行为。结果表明:增加冷却速率、预变形处理和晶粒细化有利于初始凝固组织中存在的非平衡组织的分散细化。原始组织中的非平衡共晶组织在加热过程中大部分扩散溶解而溶入基体中,剩余部分在加热过程中首先熔化;冷却速率越大或预变形处理以后的试样在熔化过程中更容易发生二次枝晶臂之间的合并。提出半固态熔化过程可分为成分均匀化、共晶熔化及部分初生相的熔化和球化完成3个阶段,不同熔化阶段的控制性因素不同。熔化后的半固态组织中固态颗粒的尺寸和形貌主要与初始组织的形貌、加热过程中非平衡组织的溶解速度及加热速度有关。

The semi-solid melting behavior of AZ91D magnesium alloy with different original microstructures was investigated by quenching method. The results show that, increasing cooling rate, pre-deformation and grain refinement are useful for spreading of the non-equilibrium microstructure around the primary grains. Most of non-equilibrium microstructures in the original microstructure dissolve into the α-Mg matrix due to the diffusion of the solute and then the remainder is melted firstly. The more the increasing of cooling rate or pre-deformation, the more the secondary dendrite arms are easy to coarsen. The partial melting process during increasing temperature includes uniformization of the compositions, divorced eutectic melting, and the partial melting and glomeration of primary α-Mg. A predominant factor is different during different stages. The size and shape of solid phase in semi-solid microstructure are related with the original microstructure, diffusion rate of non-equilibrium microstructure and heating-up rate.