关键词: 半固态, SiC颗粒, 镁基复合材料, 数值模拟, 机械搅拌, 多相流

Abstract: Particle reinforced magnesium matrix composites have various advantages, such as high specific strength, stable size and low production cost. In particular, magnesium matrix composites reinforced by silicon carbide (SiC) has higher wear resistance and temperature resistance. Stirring method is one of the major methods to prepare SiC particle reinforced magnesium matrix composites, but excessive porosity and uneven particle distribution and other problems often occur in practical operation, so it is necessary to accurately control the stirring process. In this paper, the stirring process of SiC particle reinforced magnesium matrix composites was dynamically simulated by commercial computational fluid dynamics (CFD) software Fluent. The effects of different stirring speed, stirring time and temperature on the microstructure of SiCp/AZ91 (SiC particle reinforced magnesium alloy AZ91) were studied. The results show that the stirring time and speed have an obvious impact on the quality of the finished SiCp/AZ91 material. The increase of the stirring speed is helpful for the SiC particles to disperse better, but excessive speed causes the liquid level to fluctuate and then a large amount of gas to enter into the magnesium liquid, thereby leading to more pores in the finished products. In terms of stirring time, when the stirring time is short, SiC particles can not be fully mixed with the alloy liquid, so a large number of SiC particles agglomerate. With the prolonging of the stirring time, the agglomerated particles gradually disperse into the magnesium alloy liquid, it is observed that when the stirring time is 15 min, the mixed phase composed of SiC solid particles and liquid magnesium is the most uniform, and the macroscopic uniformity of the solid particles does not change further when the stirring time is prolonged. According to the simulation and experimental results, the optimal stirring time is 15 min and the stirring speed is 300 r/min.

Key words: semi-solid, SiC particle, magnesium matrix composite, numerical simulation, mechanical mixing, multiphase flow