摘要
The microstructural evolution and kinetic characteristics were studied during solution treatment of AM60B Mg alloy prepared by thixoforming. The results indicate that the microstructural evolution includes two stages： the first stage involves rapid dissolution of eutectic β （Mg 17 Al 12 ） phase, homogenization and coarsening, and the second stage is regarded as normal grain growth consisting of primary α-Mg particles （primary particles） and secondary α-Mg grains （secondary grains）. In the first stage, the dissolution completes in a quite short time because the fine β phase can quickly dissolve into the small-sized secondary grains. The homogenization of Al element needs relatively long time. Simultaneously, the microstructure morphology and average grain size obviously change. The first stage sustains approximately 1 h when it is solutionized at 395 ℃ Comparatively, the second stage needs very long time and the microstructure evolves quite slowly as a result of low Al content gradient and thus low diffusivity of Al element after the homogenization of the first stage. The growth model of primary particles obeys power function while that of the secondary grains follows the traditional growth equation in the first stage. In the second stage, both of the primary particles and secondary grains behave a same model controlled by diffusion along grain boundaries and through crystal lattice.
研究触变成形AM60B镁合金在固溶处理过程中的组织演变及其热处理动力学。结果表明:触变成形AM60B镁合金在固溶处理过程中其组织演变可分为两个阶段,第一阶段为共晶β (Mg17Al12) 相的迅速溶解、溶质快速均匀化及晶粒粗化,第二阶段为初生颗粒及二次晶粒的正常长大阶段。在第一阶段,由于细小的β相快速溶入小的二次晶粒,造成该溶解过程较短,而溶质Al元素的均匀化则需要相对较长的时间,同时,组织形貌及颗粒尺寸有很大变化。在395 °C固溶时,第一阶段持续约1 h。与第一阶段相比第二阶段需要较长的时间,在本次实验条件下约60 h。第一阶段的快速均匀化使Al的浓度梯度在第二阶段大幅度减小,因此在该阶段组织变化并不明显。在第一阶段,初生相颗粒的长大模式满足幂函数关系,而二次晶粒则遵从传统的长大方程;然而,在第二阶段两者的长大方式相同。
基金
Project(G2007CB613706)supported by the National Basic Research Program of China
Project supported by the Development Program for Outstanding Young Teachers in Lanzhou University of Technology, China
Project(SKL03004)supported by the Opening Foundation of State Key Laboratory of Advanced Nonferrous Materials, China
