Effect of Sc on microstructure and properties of A357 alloy under different casting conditions

Abstract

The effect of Sc on microstructure and mechanical properties of A357 alloy was investigated using sand molds and metal molds. The results showed that the eutectic Si in A357-0.5Sc alloy showed finer fibrous structure and smaller secondary dendrite spacing than that of A357 alloy in metal mold casting; a significant degeneration of secondary and tertiary dendrites has happened during solidification in A357-0.5Sc alloy using sand molds. UTS and YS of A357-0.5Sc alloy were higher than those of A357 Alloy in both metal molds and sand molds. In metal mold casting, the elongation of A357-0.5Sc alloy was higher than that of A357 alloy. In sand casting, the elongation of A357 and A357-0.5Sc alloys is almost equal. The YS of A357-0.5Sc alloy in sand mold is 7.5% higher than that of A357 alloy in metal mold, and the UTS and EI are almost equal. Taken together, the mechanical properties of A357-0.5Sc using in sand molds shows better than that of A357 using metal molds, which can improve mechanical properties in sand molds to meet the requirements of casting of complex parts in sand molds.The secondary dendrite of A357 and A357-0.5Sc alloys was obvious in metal mold casting. The main factor affecting the mechanical properties of the metal mold alloy was the secondary dendrite spacing. The addition of Sc would degrade the secondary and tertiary dendrites of A357 alloy in sand-casting. Moreover, the main factor affecting the mechanical properties of the sand-casting alloy was grain size.