Achievement of high strength and good ductility in the large-size AZ80 Mg alloy using a designed multi-directional forging process and aging treatment

Abstract

Most high-performance Mg alloy samples obtained by severe plastic deformation processes are difficult to implement in industrial utilization due to their small size. The strength of large samples developed using the multi-directional forging (MDF) process is significantly lower than that of small samples. This work developed a large commercial AZ80 alloy sample with dimensions of 100 × 100 × 140 mm3 using a two-step MDF process and artificial aging. The designed process is different from the reported MDF and aging processes. The T5 treated sample exhibits uniform mechanical properties with the ultimate tensile strength of 430 MPa (Engineering stress) and elongation to failure of 11.4%, reaching the level of wrought Mg-RE alloys. MDF at elevated temperatures improves the plasticity of the sample resulting in a good forgeability at 180 °C. The high density defects introduced by the MDF process include grain boundaries, dislocations and stacking faults (SFs) that accelerate the subsequent aging response. The good strength-ductility synergy is attributed to the simultaneous effect of an overall bimodal microstructure composed of fine grains and coarse grains, nanoscale β-Mg17Al12 precipitates, and a high density of dislocations and SFs. The designed process can benefit the general community of Mg alloys since the excellent mechanical properties do not rely on the strengthening mechanism due to the addition of specific elements. This work provides an effective way to develop large-size Mg alloy billets applied to load-bearing components.