半固态搅拌制SiC颗粒增强镁基复合材料过程的数值模拟

采用商用的计算流体动力学(CFD)计算软件Fluent对SiC颗粒增强镁基复合材料搅拌过程进行动态模拟,研究了不同搅拌速度、搅拌时间及温度对于SiCp/AZ91(SiC颗粒增强镁合金AZ91)组织的影响。研究结果表明,搅拌时间和搅拌速度对于SiCp/AZ91材料成品质量有显著的影响,搅拌速度的增加有助于SiC颗粒的分散,但速度过快导致液面起伏较大,大量气体进入镁液中,最终使成品中气孔较多。而在搅拌时间方面,当时间较短时,SiC颗粒未充分与合金液混合,因此出现大片SiC颗粒团聚现象。随着搅拌时间的延长,团聚的颗粒逐渐向镁合金液中均匀分散,当搅拌时间为15 min时,SiC固相颗粒与镁合金液所组成的混合相最为均匀,此时继续延长搅拌时间,其固相颗粒的宏观均匀性并未发生进一步变化。根据模拟和试验的结果得出最佳的搅拌时间为15 min,搅拌速度为300 r/min。

Composites by Semi-Solid Stirring During Preparation Process

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.