Microstructures and mechanical properties of cast Al–Mg–Si alloy with combined addition of Sc and Zr

In present work, an Al–Mg–Si-Sc-Zr alloy with high Mg/Si ratio and the combined addition of Sc, Zr elements was designed to fabricate the cast Al alloys with uniform microstructure. The effect of heat treatment on the microstructure evolution and mechanical properties of designed Al–Mg–Si-Sc-Zr alloy was investigated. The scanning electron microscopy and transmission electron microscopy were used to analyze the second phase evolution. The result suggests that the aging temperature mainly affects the size, phase type and number density of matrix precipitates. It confirms that both the strength and ductility are controlled by precipitates, which are strongly dependent on aging temperature. With proper heat treatment, the ductility of materials is notably enhanced from 2.6% to 13.3% by high number density of nano-sized precipitates (β’’ phase) and plate-like GPII zones with {111}Al habit plane. The formation of plate-like GPII zones should be attributed to the high Mg content of Al–Mg–Si alloys and named as GPII-Mg zones. The β’’ precipitates and GPII zone may precipitate at the Al/Al 3 (Sc,Zr) interface to form the interface precipitate. High Mg/Si ratio and combined addition of Sc, Zr may provide new insights on alloy design strategy for high performance cast Al–Mg–Si alloys.