The ranking of W-temper and warm forming of solution-treated AA7075 sheet reverses with strain path

Abstract This study ranks W-temper and warm forming of solution-treated AA7075 sheet over seven strain paths rather than by one formability number. Nakajima blanks 16–100 mm wide were formed at 28°C after quenching and at 100–180°C after cooling from solution treatment. A finite element model and a plane-strain localisation analysis used the measured hardening laws and forming limit curves. The ranking of the routes reversed with strain path. On average, blanks 16–52 mm wide fractured 10.6–30.3% lower after warm forming than in the W temper, whereas blanks 86–100 mm wide fractured 5.7–30.1% higher. The width at which the routes swapped rank fell from 79.4 mm at 100°C to 52.7 mm at 160°C, with a tie over 50–74 mm at 180°C. The model reproduced all 42 heights within 7.35% and the reversal. At 100–140°C the plane-strain limit fell 41–58% below the limit that strain hardening allows, so deformation localised early. After paint bake, W-temper deformation gave up to 195.8 HV, against 172.6 HV for warm deformation. The strain path of the critical feature, rather than a single formability number, should therefore decide between W-temper and warm forming of solution-treated AA7075 sheet.