The role of microstructure and microchemistry on intergranular corrosion of aluminium alloy AA7085-T7452

The intergranular corrosion (IGC) of an AA7085-T7452 aluminium alloy forging was determined via ASTM G110 exposure, and rationalised with electron backscattered diffraction and transmission electron microscopy. The alloy microstructure, microchemistry and IGC propensity varied depending on the location within the forging, and thus quarter (t/4) and mid (t/2) thicknesses of the forging were explored herein. The number of IGC fissures and mass loss of specimens was lower in the t/2 position, as a result of higher Cu content in grain boundary precipitates, η-phase, Mg(Cu_{x =0.08–0.32}Zn_{1- x})_{y =1.4–2.8} and (Zn, Cu)-rich η-phase, Mg(Cu_{x= 0.2–0.54}Zn_{1- x})_{y =4.4–8.5} in the t/2 position, whilst the t/4 position contained η-phase, Mg(Cu_{x =0.09–0.31}Zn_{1- x})_{y =1.7–2.3} and Zn-rich η-phase, Mg(Cu_{x =0.05–0.12}Zn_{1- x})_{y =4.4–4.5}.