ZL201合金半固态二次加热时的组织演变

利用理论计算与实际观测等手段,研究了采用近液相线方法铸造的ZL201合金坯料在进行二次加热时,α晶粒形貌演变和长大的规律.结果表明,半固态二次加热时,α晶粒形态的整个演变过程可以分为三个阶段:第一阶段为共晶组织的熔化阶段;第二阶段为α晶粒的球化阶段;第三阶段为理论液固成分的平衡阶段.在第一、二阶段α晶粒以合并方式长大;第三阶段α晶粒按Ostwald模型长大.二次加热温度影响组织演化进程,而保温时间决定α晶粒球化效果.在较高的温度下进行二次加热,能够在较短的保温时间内得到适合于触变成形的均匀细小的近球形组织.

Microstructural Evolution of Semi-Solid ZL201 Alloy During Reheating

The semi-solid ZL201 alloys cast with near-liquidus casting technology were reheated, and its microstructural evolution and α-grain growth mechanism were studied by means of theoretical calculation and actual observation. The results indicated that the microstructural evolution of the α-grain formation consists of three stages, i.e., eutectic structure melting, grain spheroidizing and theoretical liquid-solid equilibrium. The α-grains grow in form of coalescence in the first two stages in accordance to Ostwald model in the third stage. In addition, the microstructure evolves faster with increasing reheating temperature,and the spheroidization of α-grain depends on the isothermal holding time. It implies that the homogeneous, fine and near-spherical microstructure can be obtained via thixoforming at relatively higher reheating temperature within shorter holding time.