Abstract:The microstructures and tensile properties of semi-solid metal high pressure die cast (SSM-HPDC) F357 alloys with low and high levels of Fe, Ni and Cr were compared in different temper conditions. ThermoCalc software was used to predict the different intermetallics that can be expected in the alloys, and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to investigate the actual intermetallics that formed. The influence of these intermetallics on tensile properties was quantified. The results show that lower strength is obtained in the alloy with high Fe, Ni and Cr levels. This is attributed mainly to the formation of more p-Al₈FeMg₃Si₆ phase, which removes strengthening Mg atoms from solid solution. Also, the ductility of the high Fe, Ni and Cr levels alloy is decreased significantly due to microcracking of the higher volume fraction p-Al₈FeMg₃Si₆ and Al₉FeNi phases. The combination of lower strength and ductility results in a decrease of the quality index of this alloy compared with the alloy with low levels of Fe, Ni and Cr.

Key words: semi-solid metal (SSM) forming; alloy F357; heat treatment; intermetallics; p-Al₈FeMg₃Si₆; Al₉FeNi; b-Al₅FeSi