Enhanced formability in two-step forming for AA7075 sheet in -T6 and -W tempers

Abstract. In response to stringent environmental regulations, the automotive industry is increasingly prioritizing lightweighting, prompting a shift towards high-strength aluminum alloys while the low formability of these alloys remain a limiting factor. This study explores a solution through a two-step forming process applied to AA7075 sheets utilizing -T6 and -W tempers. Firstly, two-step uniaxial tension experiments are performed at two prestraining levels in the -T6 temper followed by subsequent tensions in the -W. Both cases exhibit significant plastic deformation before fracture, overcoming the thinning accumulated in the first step. Additionally, a two-step hole expansion experiment is conducted under the same tempering conditions. Results are compared with single operations in each temper, evaluating force-displacement curves and thickness strain distribution around the hole. The study highlights the substantial contribution to formability enhancement, demonstrating 80% higher cup height and twice greater thinning to fracture compared to conventional single-step operations.