High elongation heterostructure rare earth magnesium alloy based on rotating backward extrusion process

Abstract

In this paper, Mg-9.5Gd-4Y–2Zn-0.5Zr cylindrical parts were prepared by the conventional backward extrusion (CBE) process and rotating backward extrusion (RBE) process. The effects of the two processes on the microstructure and mechanical properties of different orientation regions of rare earth magnesium alloy were analyzed and compared. The RBE process introduces a torsional shear quantity based on the CBE process. By changing the direction of plastic flow, has a positive effect on the elongation (EL) of the alloy. It was found that dynamic recrystallization (DRX) occurred in both CBE and RBE processes. With the transition of deformation, the strain continues to accumulate, and the DRX mechanism changes from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX). Compared with the CBE process, the grain refinement of the RBE process is more significant. After deformation, a more significant heterostructure is obtained in the RBE-45° region, and the average grain size reaches 24.7 μm. The ultimate tensile strength (UTS), yield strength (YS), and EL of the alloy in this region are 292.5 ± 7.7 MPa, 226.6 ± 7.4 MPa, and 21.5 ± 1.3 %, respectively. Although the strength is slightly lower than that of CBE alloy, better plasticity is obtained. The excellent strength-toughness synergy is attributed to the synergistic effect between heterogeneous regions of non-uniform microstructure. This study provides some theoretical guidance for the industrial production of large-size magnesium alloy cylindrical parts and subsequent applications.

Keywords

• Mg-9.5Gd-4Y–2Zn-0.5Zr
• Cylindrical parts
• Rotating backward extrusion
• High elongation
• Heterostructure