Correlation between microstructural evolution and corrosion resistance of hypoeutectic Al–Si–Mg alloy: Influence of corrosion product layer

Recycled hypoeutectic Al–Si–Mg alloy, an essential lightweight material, is positioned as a significant alternative to reduce energy usage and CO2 emissions in the automotive sector. Despite the use of recycled aluminum, environmental pollution during aluminum production has continued to increase. This study aims to optimize the Mg and Si composition in recycling-oriented Al–Si–Mg alloy to maximize the use of alloying elements present in the scrap to further reduce CO2 emissions. Hypoeutectic Al–Si–Mg alloys with different Mg/Si ratios and Mg + Si contents were prepared to investigate their influence on the microstructure, corrosion initiation, and corrosion product layer (CPL) behavior of the alloys. Increasing the Mg/Si ratio promoted Mg2Si and π-AlFeSiMg, improving sacrificial protection and delaying Al dissolution. An increase in the Mg + Si content at a constant Mg/Si ratio resulted in a homogeneous distribution and refinement of Mg2Si. The increase in refinement and homogeneity of Mg2Si could offer more sacrificial active sites that delay the dissolution of Al. As corrosion progressed, additional Mg-based corrosion products were formed, crosslinked with Al- and Si-based corrosion products, exhibiting a stable CPL by forming Al–O–Mg and Si–O–Mg bonds. The increase in Mg + Si at a constant Mg/Si ratio yields miniaturization and uniformity of Mg2Si. This promotes a homogeneous dissolution of Mg ions, further ameliorates the crosslinking of the Al–O–Mg and Si–O–Mg bonds, and stabilizes the CPL, improving the corrosion resistance of Al–Si–Mg alloy.