采用传统铸造工艺和喷射成形技术制备了无Cr和含Cr的含Fe过共晶Al-Si合金,并利用SEM(EDS)、XRD及DSC对其显微组织、相组成及相变过程进行了研究.结果表明:2%Cr的加入不光使铸态粗大针片状的δ-Al_4FeSi_2相变为"骨骼状"α-Al(Fe,Cr)Si相,而且使沉积态Al-25Si-5Fe-3Cu合金中短棒状的富铁相(～10 μm左右)被尺寸小于3～5 μm的颗粒状α-Al(Fe,Cr)Si相所替代,从而细化的组织更有利于合金性能的提高.等温处理实验结果显示沉积态含Cr合金具有较好的组织热稳定性,其主要归因于颗粒状α-Al(Fe,Cr)Si相自身的高温稳定性,而沉积态AL-25Si-5Fe-3Cu合金热稳定差主要由于β-Al_5FeSi相的长大和A_7Cu_2Fe相的形成.另外,结合显微组织和喷射成形工艺特点对沉积态组织形成机制分析发现α-Al(Fe,Cr)Si相有可能通过直接从液相析出和经δ-Al(Fe,Cr)si相转变而来.
The Fe-contained hypereutectic Al-Si alloys with or without Cr were prepared via traditional casting process and spray forming technique. The Micrstructures, phase components and phase transformation of present alloys were studied using scanning elec-tron microscopy ( SEM ) with energy diffraction spectrum ( EDS ), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results showed that adding 2% ( mass fraction) Cr the Fe-contained hypereutectic Al-Si alloys could not only transform the coarse plate-like δ-Al_4FeSi_2 phase into skeletal α-Al( Fe, Cr)Si phase in the east alloys but also promote the substitution of short-rod Fe-bearing phases ( ～ 10μm) in spray-formed Al-25Si-5Fe-3Cu alloy with granular α-Al ( Fe, Cr)Si phase smaller than 3 ～5 μm so as to improve the mechanical properties. The results of isothermal treatments showed that the as-depesited AI-25Si-5Fe-3Cu-2Cr alloy had excellent thermal stability which was mainly due to the existence of high thermostable α-Al( Fe, Cr)Si phase, while the growth of β-Al_5 FeSi phase and formation of Al_7 Cu_2 Fe phase led to the poor thermal stabihty of the as-depesited Al-25Si-5Fe-3Cu alloy. Two mech-anisms could be related to the formation of α-Al( Fe, Cr)Si phase with direct precipitation from the liquids or transformation of metasta-hie δ-Al( Fe, Cr) Si.
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