Improvement of Superplasticity of Zn-22Al Pre-alloy Powder by the Use of Rapid Solidification Technique and Heat-treatment Method

Zn-22Al pre-alloy powders were fabricated by air-atomized, argon-atomized and rapidly solidified methods. The rapidly solidified powder was fabricated by centrifugal atomization method. To improve the superplasticity of the air-atomized and argon-atomized powders, a simple heat-treatment of the powders, i.e. rapid cooling after heating at 380°C for half an hour, was attempted. Microstructures of the rapidly solidified and the heat-treated Zn-22Al pre-alloy powders were observed by optical microscope, SEM and TEM. It was found that the microstructures of the heat-treated powders were refined and granulated, and that also the grains became equiaxed in shape. Compactibility of the rapidly solidified powder was inferior to those made from the air-atomized and argon-atomized powders, because the shape of the rapidly solidified powder was nearly spherical. However, the refinement and homogenization of the rapidly solidified powder was almost same to those of the heat-treated powders and elongation of the compact reached about 1000%.