挤压铸造SiC_p/AZ91D镁基复合材料的试验研究

Study on Technologies of Squeeze Casting of SiC_p/AZ91D Magnesium Composites

以AZ91D镁合金和平均颗粒尺寸为0.5μm的SiC颗粒分别作为基体和增强相,通过全液态搅拌铸造法和挤压铸造法结合制备出SiC颗粒增强镁基复合材料。力学性能测试结果显示:当模具温度为200℃、保压时间为15 s时,SiCp/AZ91D镁基复合材料抗拉强度最高为157 MPa;金相显微组织显示,碳化硅颗粒可作为镁合金凝固时异质形核的中心,也可能会随着凝固时固液界面的推移,使SiC颗粒处于晶界处;存在SiC颗粒团聚现象,这是其抗拉强度降低的原因;SiCp/AZ91D镁基复合材料在室温下拉伸时的断口形貌呈现脆性断裂特征;热处理工艺为固溶处理温度420℃,保温20 h空冷,时效处理温度200℃,保温8 h空冷,经过热处理后,镁基复合材料的抗拉强度均有所提高,最高可提高48.95%。

The SiCp/AZ91D magnesium matrix composites, i. e. AZ91 magnesium alloy reinforced by SiC particulates with average sizes of 0.5 μm, were fabricated by the method of combining the whole liquid stirring casting and squeeze casting. The results show that the highest tensile strength of the composites fabricated with the die temperature 200 ℃ and the holding time 15 s by squeeze casing is 157 MPa. Metallographic structure show that SiC particles could be heterogeneous nucleation center also could be push into the grain boundary during the liquid-solid boundary moving with the solidification. The phenomenon of SiC particles agglomeration may be the reason to reduce the tensile strength. The SiCr/AZ91D magnesium composites are one kind of brittle materials in normal temperature. The heat treatment process of the SiC/AZ91D magnesium composites is： solution treatment at 420 ℃ for 20 h, aging treatment at 200 ℃ for 8 h. After heat treatment, the tensile strengths of the SiCp/AZ91 composite get enhanced, the highest increase by 48.95%.