Effect of Pressure on Microstructure and Cooling Curves of A356 Aluminum Alloy During Solidification

During solidification process of metals and alloys in die casting, the cooling rate of molten material and also freezing time are affected by the heat transfer coefficient of metal/mold interface which is not constant at whole casting time. Therefore, determination of the cooling curves and the heat transfer coefficient is a crucial step in optimization of casting process by simulation because the resultant microstructure of cast components is affected by cooling rate. In the present study, the effect of applied pressure on cooling curves and microstructures of A356 aluminum alloy was investigated using a specially designed apparatus. Results showed that the cooling curves obtained from the central axis of cylindrical sample clearly represent the solidus and liquidus temperatures which can be used for determination of freezing time. It was observed that the solidification time decreases with increasing applied pressure. Also, the side thermocouples showed a temperature drop at the moment of applying pressure in which its magnitude increases with the increase in applied pressure. Moreover, the metallographic examinations showed that the microstructure of as-cast samples is refined with the increase in pressure. Also, the heat transfer coefficient obtained from experiments was used in the simulation of casting process and the simulated cooling curves were matched carefully with the experimental curves.