Study on corrosion resistance of artificially aged 7075 aluminium alloy by using Cs-corrected STEM

Abstract

This research studied the mechanism of the corrosion resistance enhancement of artificially aged 7075 aluminium alloy using advanced Cs-corrected scanning transmission electron microscopy (STEM). The corrosion behaviors of artificially aged 7075 aluminium alloys in a 3.5 wt.% NaCl solution were investigated by impedance spectra, equivalent circuit analyses, polarization measurements and immersion tests. The results show that a longer aging treatment leads to better corrosion resistance, which can be attributed to the following microstructural features, as revealed by STEM. The Cu segregation at grain boundaries under over-aged conditions helps retard intergranular corrosion. The Mg(Zn, Cu)2 precipitates formed on the surfaces of Al18Mg3(Cr,Mn)2 dispersoids effectively insulate the dispersoids as cathodes in corrosion, from the Al matrix. This study demonstrates a potential strategy to design corrosion-resistant alloys achieved by proper alloying and subsequent aging.