铸态和沉积态Al-25Si-5Fe-3Cu合金的显微组织与相形成

采用常规铸造和喷射成形工艺制备了含硅达25%(质量分数)的过共晶Al-Si合金,利用SEM(EDS)、XRD和DSC等分析方法对合金的显微组织和相熔解析出进行了分析研究.结果表明,铸态合金含有粗大块状初晶Si相和粗大针片状含铁相,而喷射成形工艺能够使二者的尺寸、形貌发生改变而有利于合金性能的提高.同时,铸态和沉积态合金中均含有基体Al、初晶Si和Al₂Cu相,不同的是铸态合金中含铁相主要为δ-Al₄FeSi₂相,而沉积态合金中以β-Al₅FeSi相为主.分析其原因主要是糊状层的存在引起沉积坯冷却速度降低而导致沉积坯中发生δ-Al₄FeSi₂相的转变及共晶组织增加,致使沉积态合金中β-Al₅FeSi相为主要含铁相.采用DSC实验对沉积态合金在熔化和凝固过程中发生的反应进行了讨论.

Microstructures and phase formation of cast and spray-formed Al-25Si-5Fe-3Cu alloys

A hypereutectic Al-Si alloy with 25% (mass fraction) Si was prepared by traditional cast and spray forming processes, and its microstructures, melting and precipitation processes were studied using SEM(EDS), XRD and DSC methods. The results show that the cast alloy contains coarse plate primary silicon phase and coarse needle-like Fe-bearing phase, but the sizes and morphologies of coarse primary silicon phase and coarse needle-like Fe-bearing phase can be improved by spray forming process so as to improve the properties of the hypereutectic Al-Si alloy. Al matrix, primary silicon phase and Al₂Cu phase are present in both the cast and spray-formed alloys, but the difference is that the main Fe-bearing phase in the cast alloy is Al₄FeSi₂ as well as β-AI₅FeSi phase does in the spray-formed alloy. The main reason is that the cooling rate of the as-deposited preform decreases due to the existence of mushy layer on the preform surface so that the phase transformation about Al₄FeSi₂ phase can be occurred and the eutectic microstructure increases, and β-Al₅FeSi phase can dominate Fe-bearing phase in the spray-formed alloy. The melting and solidification process of phases in the spray-formed alloy was discussed via DSC experiment.