加热工艺对AZ91D镁合金部分重熔组织的影响

Effect of Heating Process on Microstructure of AZ91D Magnesium Alloy During Partial Remelting

提出半固态金属坯料先在液相线以上温度适当加热再降低温度至两相区温度继续等温保温的二次加热工艺。采用该工艺对晶粒细化AZ91D镁合金坯料进行部分重熔,研究了其组织演变规律,并与等温二次加热工艺进行比较。结果表明,与等温二次加热工艺相比,坯料先在液相线以上温度适当加热再降低温度至两相区温度继续保温,坯料重熔速度明显加快,相同加热时间时,晶粒更加细小和圆整。组织演变机理分析表明,加快液相形成速度可适当抑制晶粒的合并,降低晶粒长大速度,并促进晶粒球化。

A reheating process was proposed. In this process, the semi-solid metal billet was firstly heated over liquidus temperature and then isothermally held at solid-liquid zone temperature. Such reheating process was applied to perform partial remelting experiment on grain-refined AZ91D magnesium alloy billet. The microstructure evolution was studied and compared with that during isothermal reheating process. The results show that the billets remelting rate during this reheating process is faster than that during isothermal reheating process. Under the same reheating time, the grains of billet reheated by this reheating process are finer and rounder than those by isothermal reheating process. The present experimental results indicate that accelerating the formation rate of liquid phase during reheating can restrain the coalescence of grains to a certain extent, and thus reduce the grain growth rate and promote the grain spheroidization.