Enhanced strength-ductility combination in the cold-rolled spark plasma sintered pure aluminium by FSP

Abstract

In the present study, the microstructural characterization and tensile deformation behaviour of pure aluminium (Al) billet manufactured through the combination of spark plasma sintering (SPS), cold rolling, and friction stir processing (FSP) are reported. The grain size is reduced from ~17 μm in the SPSed specimen (S) to ~7 μm after cold rolling, further refined to ~1 μm by FSP. The modified microstructure includes fine equiaxed grains with more than ~77% sharp high angle grain boundaries (HAGBs), a large grain aspect ratio (~ 0.5), and a higher fraction of recrystallized grains (~ 85%). The superior grain boundary characteristics are attributed to the discontinuous dynamic recrystallization during the FSP of the rolled SPSed billet. The ultimate tensile strength (UTS) of pure Al billet is increased from ~124 MPa in the as-SPSed condition to ~131 MPa (~ 6% increment) after the combination of SPS, cold rolling, and FSP. On the other hand, percentage elongation increases from ~32.3% in the cold-rolled SPSed condition to ~43.2% after FSP indicating an overall increment of ~34% in the ductility. The HAGB and dislocation strengthening with the contribution of ~45% and ~ 17% in the strengthening are primarily responsible for the improved tensile properties of the FSPed specimen, respectively. 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. • Microstructural modification of cold rolled SPSed pure Al by FSP is reported. • Extremely fine grains (~1 μm) with 77% HAGBs are obtained after FSP. • Enhanced strength-ductility combination is achieved.