Granulation of Si Phase Precipitates in 500℃ Solution Treatment of Al-8%Si Alloy Thin Castings

Abstract

  Hypo-eutectic Al-Si alloy die casting is gradually being applied to manufacture automobile bodies and frames. However, since the cast product is thin, it is difficult to deal with distortion during heat treatment. Short-time heat treatment is a potential method for avoiding this. In order to develop a short-time heat treatment technique to granulate the eutectic Si phase without coarse precipitate phase, we investigated the number of coarse precipitate phases and behavior of morphological change in this study. As a result, it was clarified that the number coarse precipitate phases decreases with time while the plate shape is gradually changed to granular shape, after the number of coarse precipitate phases sharply increased at the beginning of heat treatment. As the preferred heat treatment condition, we proposed retention of 60 minutes at about 500℃.