Effect of sintering temperature on microstructures and mechanical properties of spark plasma sintered nanocrystalline aluminum

Organic-coated aluminum nano-powders were consolidated by spark plasma sintering technique with low initial pressure of 1 MPa and high holding pressure of 300 MPa at different sintering temperature. The effect of sintering temperature on microstructures and mechanical properties of the compact bulks was investigated. The results indicate that both the density and the strain of the nanocrystalline aluminum increase with an increase in sintering temperature. However, the micro-hardness, compressive strength and tensile stress of the compact bulks increase initially and then decrease with increasing sintering temperature. The nanocrystalline aluminum sintered at 773 K has the highest micro-hardness of 3.06 GPa, the best compressive strength of 665 MPa and the supreme tensile stress of 282 MPa. A rapid grain growth of nanocrystalline aluminum sintered at 823 K leads to a decrease in micro-hardness, compressive strength and tensile stress. After annealing, a remarkable increase in strain and a slight rise in strength were obtained due to the relief of the residual stress in nanocrystalline Al and the formation of composite structure.