Effect of Mg content on the aging behaviour and tensile properties of squeeze-cast Al-7Si-xMg alloys (x = 0–0.8 wt. %)

The present study investigates the effect of Mg addition on the aging and tensile behaviour of squeeze cast Al-7Si-(x)Mg alloys (x = 0–0.8 wt. %). The results show that increasing Mg content leads to a significant enhancement in the peak hardness of the alloys, with the maximum hardness of 149 HV observed for the Al-7Si-0.8Mg alloy after aging for 10 h. Additionally, the study reveals that Mg addition delays the aging kinetics, likely due to the interplay between the optimized number density and size of the precipitates, which require longer aging times to reach their optimal size for maximum strengthening. The tensile strength of the alloys increases with higher Mg content, with the peak-aged Al-7Si-0.8Mg alloy achieving a tensile strength of 337 MPa. The increase in hardness and strength with increasing Mg addition is attributed to the higher number of Mg₂Si precipitates formed during aging which hinder dislocation movement. The yield strength of all alloys was predicted using the standard strengthening formula, showing that precipitation strengthening contributes the maximum to the overall yield strength for all the alloys, followed by solid solution strengthening. The present study also reveals the presence of both the βʺ and the β precipitates in the peak-aged samples, suggesting a combined strengthening effect from both precipitates.