Effect of Yb and Zr Addition on Microstructure and Mechanical Properties of Al7Si0.3Mg Alloy

The effects of adding Yb and Zr elements on the microstructure and mechanical properties of Al7Si0.3Mg alloy and the mechanism of refinement and modification were investigated. The results show that the addition of Yb and Zr elements can significantly refine the alpha-Al matrix, transforming it from coarse dendritic crystals to fine petal-like crystals with a significant reduction in grain size, and the eutectic silicon metamorphoses from coarse needle-like to short rod-like. The modification mechanism of eutectic silicon is that the adsorption of Yb and Zr at the twin grooves (TPRE) changes the eutectic silicon growth mode and finally changes the eutectic silicon morphology. After heat treatment (T6), a large number of Al-3(Yb, Zr) particles are precipitated to strengthen and refine the grain, and the addition of Yb and Zr can significantly improve the mechanical properties of the alloy. The tensile strength and elongation of the alloy (T6) are 296.3 MPa and 9.2% when the Yb content is 0.3wt% and the Zr content is 0.25wt%, which are 17% and 1.1 times higher than those of the unrefined and unmodified alloy, respectively.