一、前言 过共晶铝硅合金具有热膨胀系数小,比重小以及耐磨性、流动性和抗热裂性好等优点。它必须经过变质处理,否则,显微组织中会生成板片状初生Si和粗针状共晶Si,使基体严重割裂,不仅降低合金的机械性能,也使合金的切削加工性能恶化。 First, the preface hypereutectic Al-Si alloy has a small coefficient of thermal expansion, a small proportion and wear resistance, good flow and thermal cracking resistance and so on. It must be metamorphic, otherwise, the microstructure will generate sheet-like primary Si and coarse needle-like eutectic Si, so that the matrix severed, not only reduce the mechanical properties of the alloy, but also deteriorate the machinability of the alloy.