一、绪言共晶和过共晶的Al-Si合金热膨胀系数小、比重轻、耐磨、耐蚀性、流动性、抗热裂性好等一系列优点,早就引起了人们研究的兴趣。西欧在战前若干年就已采用过共晶Al-Si合金制造活塞零件。但是,由于未经变质的共晶合金组织中存在大量粗片状共晶Si和少量多角形初晶Si;过共晶合金组织中存在大量板片状初晶Si及粗针状共晶Si,严重地割裂了铝的金属基体,受力时,往往在Si相尖端和棱角处引起应力集中,故合金容易沿晶粒边界或板状Si本体开裂。此外粗大的板片状初晶Si影响其切削加工性能和铸件 I. Introduction Eutectic and hypereutectic Al-Si alloy has a series of advantages, such as small thermal expansion coefficient, light weight, wear resistance, corrosion resistance, fluidity and good thermal cracking resistance, which have long aroused people’s interest in research. Western Europe used eutectic Al-Si alloys to make piston parts for several years before the war. However, a large amount of coarse eutectic Si and a small amount of polygonal primary Si exist in the unaltered eutectic alloy; a large amount of platelet-shaped primary Si and coarse needle-shaped eutectic Si exist in the hypereutectic alloy structure, Severe fracture of the aluminum metal matrix, stress, often in the Si-phase tip and edges cause stress concentration, so the alloy easily along the grain boundary or plate-like Si body cracking. In addition, coarse platelet-shaped primary Si affects its machinability and castings