Studies on Aging and Corrosion Properties of Cryorolled Al–Zn–Mg–Cu (AA7075) Alloy

Ultrafine grained AA7075 aluminum alloy (Al–6Zn–2Mg–1Cu), was produced by cryorolling the solutionized samples followed by annealing and peak aging treatments. In the cryorolled and peak aged (CRPA) alloy, the presence of large amount of dislocations acted as nucleation sites for precipitation, resulting in finer and densely distributed precipitates, when compared to its coarse grain peak aged (CGPA) alloy. Potentiodynamic polarization studies revealed increased Epit by about 300 mV for CRPA alloy compared to CGPA alloy, indicating improved corrosion resistance to pitting. Intergranular corrosion tests were performed according to ASTM G-110 and the results revealed no grain boundary attack and improved resistance of CRPA when compared to severe grain boundary attack in CGPA alloy. The improved corrosion resistance in CRPA was mainly attributed to the reduced galvanic couples formation within the alloy due to absence of anodic coarse precipitates along the grain boundaries and the associated precipitate free zones.