Divorced eutectic growth of hypereutectic Al-Si alloy in sand casting and its influence on mechanical and thermal properties

In order to receive the divorced eutectic growth in Al-Si system like in Fe-G (graphite), the divorced eutectic growth behavior of hypereutectic Al-18Si-5Cu alloy in sand casting was investigated and its influence on mechanical and thermal properties was evaluated in this study. Results show that divorced eutectic growth in Al-18Si-5Cu alloy can be successfully achieved in sand casting. The pouring temperature plays an important role in it. At pouring temperature 680 °C and 650 °C, the eutectic growth is completely-divorced, accompanying with significant refinement of Si particles and considerable improvement in its shape factor. The divorced eutectic growth results in significant improvements both in ultimate tensile strength (UTS) and elongation (EL). In as-cast state, compared with the non-divorced alloy, the UTS and EL of the completely-divorced alloy are increased by 60.0% and 92.3%, and, in T6 state, by 113.9% and 64.7%, respectively. The divorced growth of eutectic has little influence on the thermal diffusivity and conductivity. However, the average coefficient of thermal expansion increases approximately 10% with the improvement in divorced degree of eutectic growth.