Influence of Mold Temperature on Microstructure and Shrinkage Porosity of the A357 Alloys in Gravity Die Casting

摘要

In gravity die casting, mold temperature is a significant parameter during filling and solidification. The selection of mold temperature is commonly based on individual experience in production. No clear specification of mold temperature is pointed out in the international standard. Therefore, in this study the experimental and simulated methods were used to compare the effect of the mold temperature on microstructure and shrinkage porosity during solidification of the A357 alloys. The GB/T1173-2013 standard mold was used at different temperature (150,250,350°C). The microstructure of sample was compared in each condition. It was found that increasing the mold temperature, which influenced the cooling rate in solidification, increased the second dendritic arm space of α-Al phase and the size of Si particles in microstructure. Moreover, increasing the mold temperature also decreased the temperature gradient of sample during solidification and impaired the filling of the liquid in dendrites. When the mold temperature was 150°C, no shrinkage porosity was observed in the microstructure. When the mold temperature increased to 350°C, severe shrinkage defects were observed on the fracture of the samples. The simulated method was also applied to determine the tendency of shrinkage porosity and the results calculated by ProCAST agreed well with the experimental results.