Effects of yttrium and heat treatment on the microstructure and tensile properties of Al–7.5Si–0.5Mg alloy

The effects of yttrium (Y) additions (0, 0.1, and 0.3 wt.%) and T6 heat treatment on the microstructure and tensile properties of Al–7.5Si–0.5Mg alloy have been investigated in the present work. The microstructures and fracture surfaces of as-cast and heat treated samples were examined by scanning electron microscopy (SEM). It was found that Y modified the eutectic silicon from a coarse plate-like and acicular structure to a fine branched and some fibrous one with a better uniform distribution. In addition, T6 heat treatment played a crucial role in the fragmentation and spheroidization of eutectic silicon, especially in the well modified alloys. The tensile properties were improved by the addition of Y followed by the T6 heat treatment, and a good combination of ultimate tensile strength (353 MPa), yield strength (287 MPa) and elongation (12.1%) was obtained when the Y addition was 0.3 wt.%. Furthermore, fractographic examinations revealed that dimple-like mechanism was responsible for ductile fracture.