As many components of research nuclear reactors are composed of aluminium alloys, the study of the corrosion of aluminium alloys is important for their safe and efficient operation. In particular, at 70°C, pH can be optimized. In order to study the impact of initial pH of aqueous solutions on corrosion of an Al-Mg-Si alloy at 70°C, three corrosion experiments at different pH are performed on AA-6061-T6 alloy, in autoclaves for 33 days. Corrosion solutions with initial pH of 5, 6 and 7 are obtained by dilution of nitric acid in pure water. Various characterization techniques are used to study hydroxide phase, composition and structure. X-ray diffraction on corrosion product indicates bayerite (α-Al(OH3)) is the main crystalline phase formed during the corrosion experiments. Generalized corrosion thickness measured with Scanning Electron Microscopy are the same for all three pH. However, mass gain is most important for samples corroded at pH 6. This difference in mass gain is attributed to pitting corrosion caused by intermetallic Fe-Si-Al in the aluminum matrix. Detailed study of these precipitates by EDS has been performed in order to further understand corrosion mechanisms. From this study, suggestions on optimal pH for corrosion resistance can be proposed.