Room-temperature Multi-directional Forging of AZ80Mg Alloy to Induce Ultrafine Grained Structure and Specific Mechanical Properties

A commercial hot-extruded AZ80Mg alloy was multi-directionally forged at room temperature. In the multi-directional forging method, the samples were forged with changing forging direction 90 degrees pass-by-pass. Although AZ80Mg alloy was one of brittle materials, severe plastic deformation by multi-directional forging was successively carried out even at room temperature by employing a small pass true strain of Δɛ = 0.1. The coarse initial grains of about 20 μm were gradually subdivided to ultrafine ones by multiple mechanical twinning pass-by-pass of multi-directional forging. Ultrafine grained structure with an average grain size of 0.3 μm was uniformly evolved at the cumulative strain of ∑Δɛ= 2.0. The multi-directionally forged Mg alloy up to ∑Δɛ = 2.0 exhibited marvelous mechanical properties of 530 MPa in yield stress and 650 MPa in ultimate tensile strength with 9% plastic strain to fracture. The relatively large ductility even after large plastic deformation by multi-directional forging could be reasonably understood by grain orientation randomization due to multiple twinning and suppression of sharp basal texture evolution.