等温热处理对AZ61稀土镁合金半固态组织的影响

Effect of Isothermal Heat-treated on the Microstructure of ZA61 Rare Earth Magnesium Alloy

研究了等温热处理对AZ61稀土镁合金半固态组织的影响,结果表明:随着等温热处理温度的升高,铸态合金中的初始枝晶组织演变成了半固态非枝晶组织,经过了粗化、组织分离和球化三个过程。在等温热处理过程中,稀土La的加入阻碍了原子向固相粒子的聚集和固相粒子的合并,抑制了固相粒子的进一步长大,使半固态非枝晶组织更加细小。经过不同保温时间后,不规则的大块状组织开始球化,形成大量的近球形颗粒。但是,随着保温时间的进一步延长,球化的颗粒开始粗化长大且在颗粒内形成了大量的液岛。枝晶组织的球化过程,包括二次枝晶壁消失和Ostwald熟化。

The effect of the isothermal heat-treatment on semi-solid microstructure of AZ61 rare earth alloy were investigated. The results show that with increasing of the isothermal heat-treated temperature, the serious dendritic in the microstructure of initial cast alloy turned into semi-solid non-dendritic tissue after the isothermal heat-treatment. This microstructure evolution includes coarsening, microstruc- ture separation and spheroidizing. In the process of isothermal heat-treatment , the element La is very important to refine alloy＇s organization.It hinder aggregating and associating of the particles of solid phase , inhibit further growing of the particles of solid phase and make the microstructure of non-dendritic tissue more smaller. After the isothermal heat-treatment for different time, the irregular large block tissue begin spheroidizing and form many nearly spherical particles. But when the time of isothermal heat-treatment exceed a certain range, the spherical particles began to coarsen and many liquid islands formed in the particles. The spheroidizing of dendritic microstructure includes the disappearance of secondary dendrite wall and Ostwald ripening process.