Preparation of semisolid A356 alloy feedstock cast through vertical pipe

It is demonstrated that the fine spheroidal and equiaxed non-dendritic microstructures required for semisolid casting can be formed by using a vertical pipe. Various pouring temperatures (615-660 degrees C) and cooling rates of the vertical pipe (no, 200, 400 degrees C preheat) were used to investigate their influence on the semisolid microstructure of an A356 alloy. The results indicate that suitable semisolid billets can be generated at both lower and higher pouring temperatures; thus the vertical pipe technique may be readily exploited in industrial applications. The results also reveal that the microstructure is affected significantly by the cooling effect of the vertical pipe. Furthermore, in the longitudinal section, non-uniform grain sizes were observed, namely the primary alpha-Al at the bottom of the billet was coarser than that at the top, an effect attributed to the differences of solidification time and cooling rate. The relevant mechanisms are discussed.