Basic Research on Multi-Directional Forging of AZ80Mg Alloy for Fabrication of Bulky Mechanical Components

Abstract

In this study, a commercial hot-extruded AZ80Mg alloy was multi-directionally forged (MDFed) at room temperature by employing pass strains of Δε = 0.1. The effects of the combined processes of MDFing and ageing on the microstructural evolution and strengthening were precisely examined in advance. The coarse initial grains were gradually subdivided into ultrafine grains by multiple mechanical twinning and kinking. As observed, the multiple twinning effectively suppressed the evolution of the sharp basal texture and enabled MDFing at room temperature to high cumulative strains. Although the combined processes of MDFing and ageing tended to increase the hardness and yield stress compared to those fabricated using simple MDFing at lower cumulative strain regions, the mechanical properties were almost comparable and independent of the processes at regions of higher cumulative strain beyond ΣΔε = 2.0. Yield strength over 505 MPa, ultimate tensile strength of over 612 MPa and ductility of over 7% were constantly achieved in all the processes. Although certain selected processes were applied to bulk samples for fabricating the mechanical components, frequent cracking hindered the MDFing to high cumulative strain regions. This finding signified that adequate MDFing process is dependent on sample size. However, MDFing with smaller pass strains than Δε = 0.1 enabled MDFing to regions of high cumulative strain. Thus, bulk AZ80Mg alloy with well-balanced mechanical properties—yield strength of 420 MPa, ultimate tensile strength of 540 MPa, and ductility of 10%—could be successfully fabricated.

Fig. 11 Influence of tensile behavior on strain rate of AZ80Mg samples prepared by a process of MDFing to ΣΔε = 1.0, followed by ageing at 423 K for 3.6 ks and further MDFing to ΣΔε = 1.4, i.e., MDFing to ΣΔε = 2.4 in total.