Deformation Responses of Extruded Zinc Alloy

Abstract

Severe plastic deformation (SPD) is a technique used to obtain ultrafine grains (UFGs). However, this technology is expensive and time consuming. In this study, conventional deformation technique is used to study the deformation responses of extruded zinc alloy for fine grain development with varying die entry angles. Zinc alloy samples were cast into cylindrical billets in sand mould, the samples were machined and tapered at the edges to allow for easy entry into the die for the extrusion process. The die and tools materials were made from mild steel with the die entry angles of 15o, 30o, 45o, 60o, 75o and 90o respectively. Prior to extrusion, the samples were annealed at 400°C because of its hexagonal close packed (HCP) structure for ease of deformation. After annealing, the plastic deformation of alloy samples occurred at 350°C as the deformation was not feasible at ambient temperature (32°C). The extrusion was done with the aid of a hydraulic press machine that applies pressure on a cylindrical punch and forces the billet through the extrusion die. Extruded zinc recorded the highest extrusion stress of 192MPa at 45° die entry angle with fine grains neatly distributed in the matrix and at 60° die entry angle, the tensile strength and hardness are 177MPa and 95HV respectively with improved ductility. The microstructure of Zn alloy showed equally distributed dendrite-like second phase intermetallic in the matrix.