Effect of chromium content on microstructure and properties of casting Al‐7Si‐0.35Mg‐0.02Sr alloy

Abstract

The effect of the addition of chromium between 0.1 % and 0.3 % on the structure and properties of Al-7Si-0.35Mg-0.02Sr alloy was studied. The results show that as the chromium content increases, the alloy grains are refined, and the grains appear fine equiaxed after 0.2 % chromium addition. At the same time, chromium combines with iron to form AlCrFeSi phase, which significantly improves the iron phase morphology, making it change from needle shape to fish bone shape. In the aging stage, the Al 13 Cr 4 Si 4 phase is dispersed in the alloy, and its phase relationship with the matrix is semi-coherent and non-coherent. When the chromium content continues to increase, the degree of dispersion of the Al 13 Cr 4 Si 4 phase is higher, but the performance of the alloy decreases, because the chromium containing precipitate phase consumes magnesium and silicon solute atoms from the nearby melt, making the amount of magnesium silicide decrease. The Al-7Si-0.35Mg-0.02Sr alloy with 0.2 % chromium showed the best mechanical properties (ultimate tensile strength, yield strength, elongation and hardness).