The influence of hot deformation on the exfoliation corrosion behaviour of aluminium alloy 2025

The influence of hot deformation and alloy composition on the tensile properties and exfoliation corrosion susceptibility of the aluminium alloy 2025 has been investigated. Five casts of 2025 were used to make extrusion billets. These were designated, low manganese, high manganese (with low copper), high chromium, high titanium and, outside the permitted range but reflecting more modern alloy design, high zirconium. Billets were then hot extruded and hot forged at a range of temperatures expected to produce unrecrystallised, partially recrystallised and fully recrystallised microstructures. The main objective of the compositional variation was to alter the wrought grain refining intermetallic phase. After the application of a standard heat-treatment, tensile properties were determined, and exfoliation tests were performed in accordance with ASTM-G34. The exfoliation susceptibility and mechanical properties of AA2025 showed a marked dependence on microstructure developed during hot forming and heat-treatment. Higher forming temperatures resulted in coarser recrystallised microstructures, which tended to reduce the susceptibility to exfoliation corrosion, but adversely affected tensile properties.