Extruded microstructure of Zn–5 wt-Al eutectic alloy processed by twin screw extrusion

Abstract

Semisolid extrusion with twin screw extruder has been successfully developed for eutectic alloy. In this process, the eutectic melt is sheared and cooled down inside the twin screw extruder to a semisolid state and simultaneously extruded through an open die at a temperature close to solidus. The accurate control of heat balance in the extruder results in the formation of two solid phases and one liquid phase in the Zn–5 wt-Al eutectic alloy. A little plastic deformation in the extruded alloy can be introduced by twin screw extrusion. In semisolid extrusion, the particle size in Zn–5 wt-Al eutectic alloy is close to 40 μm for Zn rich particles and 25 μm for Al rich particles. Two solid particles are at the similar size in longitudinal and transverse directions and distribute uniformly and independently on the whole cross-section of the extruded bar. The remnant liquid can act as lubricant for reducing extrusion force during extrusion and solidify in lamellar morphology between Al rich and Zn rich particles.