Preparation and mechanical properties of highly densified nanocrystalline Al

The preparation of highly densified nanocrystalline (NC) Al was conducted in three steps. First, the NC Al powder was synthesized by an active H-2 plasma evaporation method. Then, the NC Al powder was compacted at room temperature into disk-shaped samples with a 25-mm diameter and 2-mm thickness and was sintered at 620 degrees C or 635 degrees C (sintered NC Al), The sintering does not result in grain growth. Finally the sintered NC Al was rolled at room temperature into sheet samples with a 1-mm thickness and 99 pet relative density (cold-deformed NC Al). The microhardnesses and tensile properties of the sintered NC Al and cold-deformed NC Al were tested at room temperature. The results show that their strengths are basically the same, and the yield strengths (sigma(0.2)) and tensile strengths (sigma(b)) are 12 to 16 and 5 to 6 times those of annealed coarse-grained Al, respectively, but the elongation to failure of the cold-deformed NC Al is up to 8 pct, which is 2 times that of the sintered NC Al and higher than that of cold-deformed, coarse-grained Al by 30 pct. The failure features of the sintered NC Al and cold-deformed NC Al belong to typical plastic fracture with ductile dimples, and the mechanism of failure is transgranular shear fracture.