Microstructure inhomogeneity of the constituent particles of 7075-T6 aluminum alloy after alkaline cleaning and desmutting

The microstructural evolution of AA7075-T6 aluminum alloy during alkaline cleaning in NaOH solution and desmutting in HNO3 solution was studied. AA7075-T6 contained micro-sized Mg-Si and Al-Fe-Cu constituent particles. After desmutting, Mg-Si particles transformed to Si-O particles, leaving gaps with the aluminum matrix. The aluminum matrix nearby Al-Fe-Cu particles suffered slight trenching corrosion; meanwhile, the corrosion of Al-Fe-Cu particles varied from slight corrosion, dealloying, and nano-scale galvanic corrosion induced by re-deposited Cu particulates. After alkaline cleaning and desmutting, the microstructure of constituent particles was inhomogeneous although a uniform, 5 similar to 15-nm-thick Al oxide/hydroxide film covered the aluminum matrix.