Evolution of microstructure, texture and mechanical properties of AZ80 Mg alloy tubular produced by rotating backward extrusion with modified open punch

Abstract

Deformation behavior, microstructures and mechanical properties of AZ80 alloy with modified open punches (groove numbers of 0, 1, 4, 6 and 8) during rotating backward extrusion (RBE) were investigated. The results showed that increasing groove numbers effectively improved the accumulative strain and resulted in lower deformation load. When the groove number increased to 8, the bottom metal could be accelerated to flow towards the wall. Meanwhile, the grain refinement and DRX proportion could also be promoted by the increase of groove numbers. And the most homogeneous microstructure and severe deformation was obtained in six-groove tubular (G6). The accelerated metal flow in the eight-groove tubular (G8) preserved a relatively fine microstructure along the tubular wall, resulting in an excellent axial homogeneity. Moreover, increasing groove numbers could disrupted the tendency for developing an intense basal texture during extrusion, and the minimum texture intensity was formed in G6. It demonstrated that with the groove increasing, the comprehensive effects, random grain orientation distribution resulted from new nucleation and grown dynamic recrystallization (DRX) grains and the c-axis rotation of grains triggered by increased activity of pyramidal slip, contributed to the texture weakening. The mechanical property was significantly improved with the groove increasing, and the microhardness of open punch was considerably improved in comparison with the non-open counterpart. Favored by the grain refinement and dislocation strengthening, the G6 and the four-groove sample (G4) achieved maximum hardness values of 98.8 HV and 98.5 HV at the tubular bottom and wall, respectively.

Keywords

• Rotating backward extrusion
• AZ80 magnesium alloy
• Deformation behavior
• Microstructure
• Mechanical properties