Influence of the number of FSP passes on the strength-ductility synergy of cold-rolled spark plasma sintered pure aluminum

Abstract

The present investigation aims to understand the effect of the number of friction stir processing (FSP) passes (1–3 passes) on the microstructural evolution and strength-ductility synergy of the cold-rolled spark plasma sintered (SPSed) pure aluminum billet. The increase in FSP passes improved the uniform elongation from ~18% in the 1-pass FSP to ~22% in the 3-pass FSPed specimen. Contrastingly, the yield strength (YS) decreased from ~103 MPa in the 1-pass FSP to ~97 MPa in the 3-pass FSP. Thus, an optimum combination of YS (~99 MPa) and uniform elongation (~20%) is achieved for the 2-pass FSPed specimens. The enhanced strength-ductility combination of the 2-pass FSPed samples is attributed to the fine equiaxed grains (average grain size of ~1 μm) with more than ~77% sharp high angle grain boundaries (HAGBs), large grain aspect ratio (~0.5), and a higher fraction of recrystallized grains (~85%) that is obtained by the discontinuous dynamic recrystallization during the FSP. The theoretical calculations indicate grain boundary or the Hall-Petch strengthening as the dominant mechanism in the FSPed specimens. The high strength-ductility combination of the pure Al billets with the proposed approach set up a benchmark for the efficacy of various expensive reinforcements during the composite fabrication through SPS.