半固态等温热处理对Mg-7Zn-1Cu-0.3V镁合金非枝晶组织的影响

Effect of Semi-Solid Isothermal Heat Treatment on Non-dendritic Structure of Mg-7Zn-1Cu-0.3V Magnesium Alloy

本工作采用半固态等温热处理法研究了保温温度和保温时间对Mg-7Zn-1Cu-0.3V镁合金半固态非枝晶组织演变的影响。结果表明:半固态等温热处理能将Mg-7Zn-1Cu-0.3V合金的原始树枝晶组织转变为半固态非枝晶组织,最终得到细小、圆整且分布均匀的球状颗粒。延长等温时间或升高保温温度有利于非枝晶组织的分离球化;但当保温温度过高或保温时间过长时,半固态颗粒会出现合并及长大现象,其主要演变符合Ostwald熟化机制。在整个等温热处理过程中,半固态组织演变主要经历了初始粗化、组织分离及球化、颗粒合并及熟化三个阶段。Mg-7Zn-1Cu-0.3V合金的最佳等温热处理工艺为:保温温度580℃,保温时间35 min。在该条件下得到的非枝晶颗粒平均尺寸、固相率及形状因子分别为33.25μm、45%及1.33。

In this paper,the effects of holding temperature and holding time on the semi-solid non-dendritic microstructure evolution of Mg-7Zn-1Cu-0.3V magnesium alloy were studied by semi-solid isothermal heat treatment.The results show that the semi-solid isothermal heat treatment can transform the original dendritic structure of the Mg-7Zn-1Cu-0.3V alloy into semi-solid non-dendritic structure,and finally obtain small,round and evenly distributed spherical particles.Prolonging the isothermal time or increasing the holding temperature is beneficial to the separation and spheroidization of non-dendritic structures.However,when the holding temperature is too high or the time is too long,the semi-solid particles will merge and grow,and the main evolution mechanism is in accordance with the Ostwald ripening mechanism.During the whole isothermal heat treatment process,the semi-solid microstructure evolution mainly experienced three stages:initial coarsening,tissue separation and spheroidization,particle combination and ripening.The best isothermal heat treatment process of Mg-7Zn-1Cu-0.3V alloy is held for 35 min at the holding temperature of 580℃.The average size,solid phase rate and shape factor of non-dendritic particles are 33.25μm,45%and 1.33,respectively.