Influence of Zn/Mg ratio on mechanical strength and corrosion resistance of Al-Zn-Mg alloys

Abstract

This study demonstrates the superior balance between the mechanical strength and corrosion resistance of Al-Zn-Mg alloys by optimizing the Zn/Mg ratio. Alloys with Zn/Mg atomic ratios of 0.53–2.51 are systematically analyzed, with emphasis on their mechanical strength, exfoliation corrosion susceptibility, and microstructural characteristics. As the Zn/Mg ratio increases, the mechanical strength initially improves and peaked at a ratio of 1.30, with a yield strength of 536.93 MPa. Meanwhile, the corrosion resistance decreases with a ratio of 1.94 showing the poorest resistance. The optimal Zn/Mg ratio is determined to be 0.89, which offers an outstanding balance between mechanical strength and corrosion resistance. Microstructural analysis reveals that the coexistence of η' and T′ phases with high number density contributes to the high strength observed in the alloy with an intermediate Zn/Mg ratio, as validated by the strength model. The discontinuous distribution of grain boundary precipitates (GBPs) in the alloys with low Zn/Mg ratios effectively reduces their susceptibility to exfoliation corrosion. Furthermore, the compositions of the GBPs vary with the Zn/Mg ratio, and the increased Zn concentration in the AlZnMg phases associated with higher Zn/Mg ratios deteriorates the corrosion resistance of the alloys.