The effect of heat treatment on tensile properties of the cold-compacted nanocrystalline Al

The present work studied the effect of heat treatment on tensile properties of bulk nanocrystalline Al (nano-Al) cold-compacted from nano-Al powder. The nano-Al powder synthesized by the active H plasma evaporation was compacted under 1.42 GPa pressure at room temperature into disks with 25 mm diameter and 2 mm thickness. The cold-compacted disks were heat-treated at temperature range from 540°C to 635°C, then machined into the tensile specimens with 25 mm total length. The results indicated that the grain size of the cold-compacted nano-Al heat-treated at 635°C is basically consistent with the primary powder. The tensile specimens heat-treated at temperatures lower than 600°C are broken prematurely in the elastic deformation region during the tensile test process with a brittle intergranular fracture. The specimens heat-treated at temperatures higher than 600°C give the complete stress-strain curves, the yield strengths σ_0.2 and tensile strengths σ_b are 12–16 times and 5–6 times those of annealed coarse-grained Al respectively, the elongations-to-failure are all 4%, and the mechanism of failure is transgranular shear fracture with a ductile dimples fracture.