Deformation responses of extruded zinc alloy

Abstract

Severe plastic deformation (SPD) is a technique used to obtain ultra-fine grains (UFGs). However, this technology is expensive and time-consuming. In this study, the conventional deformation technique is used to examine the deformation responses of extruded zinc alloy to achieve fine grain structure by varying die entry angles. Zinc alloy samples were cast into cylindrical billets in sand mould, the samples were machined and tapered at the edge to ease entry into the die for the extrusion process. The die and tools materials were made of mild steel with die entry angles of 15o, 30o, 45o, 60o, 75o, and 90o. Prior to extrusion, the samples were annealed at 400°C because of their hexagonal close-packed (HCP) structure to ease deformation. After annealing, the plastic deformation of alloy samples occurred at 350°C. The extrusion was performed with the aid of a hydraulic press machine that applied pressure on a cylindrical punch and forced the billet through the extrusion die. The results show that the extruded zinc alloy has the highest extrusion stress of 192MPa at 45° die entry angle with fine grains neatly distributed in the matrix and at a 60° die entry angle, the tensile strength and hardness are 177MPa and 95HV respectively with improved ductility. The microstructure of zinc alloy shows equally distributed dendrite-like second-phase intermetallic in the matrix.