Achieving high strain rate superplasticity in cast 7075Al alloy via friction stir processing

Abstract

Cast 7075Al alloys under as-cast and homogenized conditions were subjected to single-pass friction stir processing (FSP). FSP converted the coarse as-cast structure to the fine-grained structure with a grain size of 2.5–3.2 μm. A pre-homogenization prior to FSP was beneficial to the generation of a more uniform microstructure in the FSP sample with smaller particles and grains. Both FSP samples exhibited high strain rate superplasticity at 1 × 10−2 s−1 and 450 °C. Cavitation developed at the particles and the grain triple junctions. The superplasticity of the FSP sample was significantly improved by the pre-homogenization prior to FSP, with a maximum superplasticity of 890% being observed, due to reduced particle size. The analyses of the superplastic data and scanning electronic microscopic (SEM) examinations indicated that grain boundary sliding is the main deformation mechanism for the FSP 7075Al.