Investigations on the long-term stability of 6013-T6 sheet

Sheet material of the Al–Mg–Si–Cu alloy 6013-T6 was additionally aged at 191 °C for up to 100 h and thermally exposed at temperatures ranging from 85 to 150 °C for time periods up to 3000 h. Microstructure, tensile properties and corrosion behaviour were investigated in the different heat treatment conditions using differential scanning calorimetry and transmission electron microscopy as well as performing tensile tests and various corrosion tests. Hardening precipitates present in the peak-aged microstructure were the metastable β″ and Q′ phases. Alloy 6013-T6 exhibited sensitivity to pitting and intergranular corrosion when immersed in chloride solutions, but was immune to intergranular stress corrosion cracking. Increasing aging at 191 °C resulted in progress in the precipitation sequence and coarsening of the precipitates. However, the degradation of tensile properties due to overaging was slight, and no change in corrosion behaviour was observed. Prolonged thermal exposure at temperatures between 85 and 120 °C did not cause significant alterations in microstructure, tensile properties, and corrosion performance of peak-aged 6013 sheet, indicating thermal stability of this alloy when used in fuselage applications.