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 beta-Al5FeSi to delta-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 delta-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 delta-Al4FeSi2 ->beta-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.