Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy,Al-25Si-5Fe-3Cu(wt%,signed as 3C),fabricated by traditional cast(TC) and spray forming(SF) processes,were investigated by differential scanning calorimetry(DSC) and scanning electron microscopy(SEM) combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques.The results show that Al7Cu2Fe phase can be formed and transformed in TC-and SF-3C alloys between 802-813 K and 800-815 K,respectively.The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC-and SF-3C alloys,respectively.The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments.Also,the mechanisms of the microstructural evolution and phase transformation are discussed.