Effect of forming conditions on microstructure and room-temperature mechanical characterization of Zn–22Al superplastic microtubes fabricated by direct extrusion

Abstract

The Zn–22Al alloy was processed under different microextrusion conditions to fabricate long and smooth microtubes with good strength and ductility. After direct microextrusion, the outer diameter variation and microstructure evolution of micro-extruded Zn–22Al microtubes under different extrusion conditions were investigated, followed by tensile tests at ambient temperature. With an increase in extrusion temperature and a decrease in extrusion speed, the microhardness, elongation, and tensile strength of the Zn–22Al microtubes decreased. The optimal extrusion conditions including temperature and speed for the microtubes were 250 °C and 1 mm/min, respectively, which were selected for preparing billet microtubes in the following process for fabricating microneedles. The mechanical behavior can be controlled by the microstructure of the extruded microtubes. The extruded microtubes at 340 °C and 1 mm/min had the highest tensile strength and hardness owing to the thinner lamellar structure, whose composition was analyzed by EDS.