Effect of cooling rate on microstructural formation of A356 alloy under sequential solidification condition

摘要

Effect of cooling rate on as-cast microstructure of commercial A356 alloy has been studied by means of end-chilled plate casting technique. The changes of temperature at four different positions of casting mould are simultaneously recorded by thermocouples. Thermal behaviors upon solidification of the alloys are examined by using Differential Scanning Calorimetry (DSC), etc. It is found that thermal behaviors upon solidifications recorded by thermocouples and DSC show similar characteristics. Evolution of the as-solidified microstructures with respect to different cooling rates is investigated by using optical microscopy. It is shown that the applied cooling rate (V) plays an important role in microstructural formation. With increasing V from 0.1°C/s to 0.4°C/s, the grain size and the microstructure change slightly, while the volume fraction of eutectic phase decreases remarkably from 80% to 15%. It is also interesting to find that during the post-solidification period Al-Si eutectic is subjected to a quasi-heat treatment and is spheroidized which normally happens during T6 heat treatment.