Enhancing strength and ductility in back extruded WE71 magnesium alloy cylindrical parts by introduction of multi-direction forging process

Abstract

Magnesium cylindrical parts have relatively poor mechanical properties and distinct anisotropy of microstructure, which hinder their application as structural components. To improve the performance of WE71 cylindrical parts, multi-direction forging (MDF) was introduced before back extrusion, and the microstructure and mechanical properties were investigated. Results of microstructure show that the grain size in the outer of the cylindrical bottom is refined from 30.1 to 27.7 μm, the microstructure is more uniform and the dislocation density is higher. The bimodal grain structure is formed in the outer of the cylindrical wall, which is ascribed to the formation of Mg5RE phases along grain boundaries. These phases result in the Zener pinning effect on grain boundaries and the reduction of DRX volume fraction. The texture type of the cylindrical bottom is <0001>∥ED and the cylindrical wall is <101¯0>∥ED, and the maximum pole intensity is 1.986 and 1.664, respectively. Results of the tensile test at room temperature show that combined improved strength and ductility of the cylindrical part is attained after introducing the MDF process. The ultimate tensile strength (UTS), yield strength (YS) and elongation are 279 MPa, 185 MPa and 12% at the bottom and 299 MPa, 212 MPa and 20% at the wall.