Phase evolution in AlSi20/8009 aluminum alloy during high temperature heating near melting point and cooling processes

The AlSi20/8009 aluminum alloy was heated to high temperatures near the melting point and cooled to investigate the effect of external Si addition on the phase evolution of Al12(Fe,V)3Si dispersion. Differential scanning calorimeter, scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer were employed. The results showed that Al12(Fe,V)3Si and Si phases evolved into a needle-like Al4.5FeSi phase and a nano-sized V-rich phase during holding the alloy at 580−600 °C. With increasing holding temperature to 620−640 °C, Al4.5FeSi and nano-sized V-rich phases evolved reversibly into Al12(Fe,V)3Si and Si phases, of which Al12(Fe,V)3Si occupied a coarse and hexagonal morphology. During the alloy (after holding at 640 °C) furnace cooling to 570 °C or lower, Si and Al12(Fe,V)3Si phases evolved into strip-like Al4.5FeSi and the V-rich phases, which is a novel formation route for Al4.5FeSi phase different from Al−Fe−Si ternary system.