The effects of Cu and Er on the microstructure and mechanical properties of in situ hypoeutectic Mg

2

Si/Al composites prepared by conventional metal mold casting were investigated. The results indicate that the grain size of eutectic Mg

2

Si is significantly refined and the morphology is transformed from coarse strip and Chinese character to fine strip

point and fiber after adding Cu and Er. Meanwhile

the needle-like β-Al

5

FeSi is converted into fine and irregular Er

Cu-rich particles. After T6 heat treatment

the eutectic Mg

2

Si phase containing 0.45% Er and 3.5%Cu reaches complete spheroidization

and most of the particulate phase containing Er and Cu disappear. The tensile strength

yield strength and elongation are improved with the simultaneous addition of Er and Cu

reaching up to 351 MPa

187 MPa and 2.8%

which are increased by 57.4%

37.5% and 86.7%

respectively

compared with the specimens without Er and Cu addition. After T6 treatment

the tensile strength are greatly increased to 408 MPa.