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采用真空感应熔炼与阶梯型铜模喷铸方式,制备出含SiC异质颗粒的AZ91镁合金非平衡凝固试样,研究了异质颗粒与铜模冷速协同作用下亚快速凝固合金的组织演化规律。结果表明,在铜模相同内径条件下,SiC颗粒的加入可以有效细化镁合金的凝固组织。400℃/2 h固溶处理后,晶界处β-Mg_(17)Al_(12)相消失,初生α-Mg晶粒由细小粒状分布向多边形组织发生转变。由于SiC颗粒对晶粒长大的钉扎效应,固溶处理后原始细晶组织得以保存,晶粒尺寸分布趋于均匀。随铜模内径减小,冷却速度增大,晶粒细化效果更加明显。当SiC含量为2%,铜模内径为2 mm时,非平衡凝固镁合金的HV显微硬度值最高,可达1.42 GPa,相比铸态提高了87%。
The heterogeneous solidified samples of AZ91 magnesium alloy with heterogeneous particles of SiC were prepared by vacuum induction melting and stepwise copper die casting. The microstructure evolution of the sub-rapid solidified alloy law. The results show that under the same inner diameter of copper mold, the addition of SiC particles can effectively refine the solidified microstructure of magnesium alloy. After the solid solution treatment at 400 ℃ for 2 h, the β-Mg 17 Al 12 phase in the grain boundary disappeared and the primary α-Mg grains changed from fine granular distribution to polygonal structure. Due to the pinning effect of SiC particles on grain growth, the original fine grain structure is preserved after solution treatment, and the grain size distribution tends to be uniform. With the copper mold diameter decreases, the cooling rate increases, the grain refinement effect is more obvious. When the content of SiC is 2% and the inner diameter of copper mold is 2 mm, the HV microhardness of non-equilibrium solidified magnesium alloy is the highest (1.42 GPa), which is 87% higher than that of as-cast.