The influence of impurity elements on the mechanical properties of Al-Mg alloy die castings has been investigated in various studies to date. In this study, box-shaped die-castings were fabricated to investigate the influence of Si, Cu, and Cr contents on the mechanical properties (0.2% proof stress and elongation) of Al-Mg alloys. The results showed that the 0.2% proof stress increased and elongation decreased with the addition of Si, Cu, and Cr. Microstructural analysis confirmed that the Mg2Si phase increased with increasing in Si contents. Furthermore, the distance between the intermetallic compounds of Al6 (Fe, Mn) and Mg2Si phases decreased. These findings suggest that the dislocation glide distance was restricted, contributing to the increase in 0.2% proof stress and decrease in elongation. The addition of Cu and Cr each increased the Al6 (Fe, Mn) phases and reduced the distance between intermetallic compounds, suggesting that the dislocation glide distance was relatively restricted, similarly to the case of Si addition. The reduction in elongation should be attributed to the increase in needle-like Al6 (Fe, Mn) phases which acts as stress concentrators and initiates fracture. Calculated 0.2% proof stress values by thermophysical and mechanical property simulation software (JMatPro) were approximately 1.5 times higher than experimental values. This is thought to be due to the overestimation of the solid-solution strengthening and/or eutectic-phase strengthening terms. Furthermore, unlike the experimental results, no effect of increasing Si contents on the 0.2% proof stress was observed, suggesting that the JMatPro calculations do not take into account the restriction of dislocation glide caused by the increase in the eutectic structure composed of the α-Al and Mg2Si phases. When using the estimation formula proposed by Uesugi et al., which represents the strengthening mechanisms of solid-solution and grain refinement strengthening, the error between the experimental and calculated values was within approximately 10%.
