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液态压铸是镁合金最主要的成形方式,但液态压铸件存在气孔等缺陷,限制了镁合金的进一步推广使用。介绍了采用双螺旋流变制浆技术,对镁合金AZ91D进行了流变压铸研究。首先,将镁合金AZ91D熔体浇入到双螺旋流变制浆机中,然后根据不同工艺参数制备流变镁合金浆料,待制浆结束后,将半固态浆料转移到压铸机内,制得半固态压铸件。采用Micro-Image Analysis&Process(MIAP)软件分析了双螺旋流变制浆工艺参数(搅拌温度、搅拌时间和转速)对镁合金AZ91D的初生相晶粒大小的影响,并研究了镁合金压铸成形性。结果表明:随着搅拌温度的降低,晶粒尺寸变化不是很大;随着搅拌时间延长,镁合金晶粒尺寸逐渐增大;随着搅拌速度的增加,镁合金平均晶粒尺寸减少。镁合金流变压铸件中的初生α相由搅拌中形成的球状晶及压铸过程中二次凝固形成的更为细小的球状晶组成。对比了普通压铸件与流变压铸件热处理后的力学性能,流变压铸件的力学性能得到大幅提高,其原因归结为铸态组织的细小和均匀化。
Liquid die-casting is the most important forming method of magnesium alloy, but the existence of porosity and other defects in the liquid die-casting, limiting the further promotion of the use of magnesium alloys. The rheological die-casting of magnesium alloy AZ91D was introduced by using double helical rheological pulping technology. First, magnesium alloy AZ91D melt poured into the twin-screw rheological pulping machine, and then prepared according to different process parameters rheological magnesium alloy slurry until after the pulping, the semi-solid slurry transferred to the die-casting machine, Preparation of semi-solid die-casting. The effects of technological parameters (stirring temperature, stirring time and rotation speed) of twin-screw rheological pulping process on the grain size of primary phase of magnesium alloy AZ91D were analyzed by using Micro-Image Analysis & Process (MIAP) software and the die-formability of magnesium alloy was studied. The results show that with the decrease of stirring temperature, the grain size does not change much. With the increase of stirring time, the grain size of magnesium alloy increases gradually. With the increase of stirring speed, the average grain size of magnesium alloy decreases. The primary α-phase in magnesium alloy rheo-diecasting consists of spherulites formed during stirring and the finer spherulites formed by secondary solidification in the die-casting process. Comparing the mechanical properties of ordinary die-castings and rheo-diecastings after heat treatment, the mechanical properties of rheo-diecastings have been greatly improved, which is attributed to the fine and uniform as-cast microstructure.