Study on Inhomogeneity of Microstructure and Intergranular Corrosion Properties on Thickness Section of 7075-T6 Aluminum Alloy

The inhomogeneity of microstructure and intergranular corrosion resistance of longitudinal sections of 7075-T6 aluminum alloy were studied by intergranular corrosion test, optical microscope, scanning electron microscope and transmission electron microscope. The results show that there are obvious differences in microstructure and intergranular corrosion resistance between the surface layer and the central layer. The recrystallization fraction of the surface layer is about 89%, the length/width ratio of recrystallized grains is about 6, and the size of aging precipitates is about 3 nm. The corrosion sensitivity of recrystallized grains is low, and the corrosion characteristics are uniform. The recrystallization fraction of the central layer is about 50%, and there are a large number of subgrains with an average size of about 3 μm. The length/width ratio of the recrystallized grains is about 11, and the size of the aging precipitates is about 6 nm. The recrystallization corrosion sensitivity is high. Because the subgrain boundary is a small-angle grain boundary, the corrosion channel to the subgrain boundary is indirectly cut off, so that the corrosion spreads along the recrystallized grain, showing local corrosion characteristics. Compared with those of the surface layer, the length-width ratio and intragranular aging precipitated phase size of recrystals in the central layer are larger, resulting in higher intergranular corrosion sensitivity.