The effect of Sr additions on Al–Cu–Si ternary eutectic alloys for a high-ductility bimodal microstructure

Abstract

Al–Cu–Si ternary eutectic alloys with a bimodal eutectic structure exhibit a good combination of strength and plasticity owing to the multiscale hierarchical microstructure. Previous studies have reported that bimodal eutectic structures can be successfully prepared by rapid solidification at a cooling rate of greater than 102 °C/s. In the present study, a bimodal eutectic structure was successfully prepared at a cooling rate of less than 10 °C/s by adding a small amount of Sr to Al–Cu–Si ternary eutectic alloys. Additions of Sr led to a notable modification of the microstructure from a mixed eutectic structure to a bimodal eutectic structure. Samples with the bimodal eutectic structure showed greater hardness, strength, and elongation than samples with mixed eutectic structure. In particular, the elongation increased significantly from 6% to 28%. The additions of Sr changed the microstructure of the Al–Si phase from needles to globular shapes, which are finely dispersed all through the microstructure. These results indicate that the improved mechanical properties with the addition of Sr can mainly be attributed to the development of a multiscale hierarchical microstructure with fine eutectic cells.