Microstructures and hot tensile properties of pressure-diecast and gravity-cast commercial zinc-based alloys

Abstract

The tensile properties of zinc-aluminium based commercial alloys: No.3, ZA-8 and ZA-27 in pressure-diecast and gravity-cast forms have been investigated over a temperature range from 20 degrees C to 260 degrees C. At low temperatures, the maximum stress, proof stress and the modulus of elasticity of the pressure-diecast alloys were superior to those of the gravity-cast alloys, but as the temperature increased they decreased sharply and castings in both forms had virtually the same maximum and proof stresses at about 200 degrees C and the same elasticity of modulus at about 90 degrees C. The elongation results were also temperature dependent, but the rates of increase with temperature were higher for the pressure-diecast alloys. Scanning electron microscopy showed that the proportions of the phases in these castings, and their sizes, differed according to the method of casting used. These differences were considered to be the principal reason for the differences in mechanical property variations with temperature.