Outstanding dynamic tensile response of pure Mg and diluted MgMn alloy under very high strain rates

Abstract

Hetero deformation induced (HDI) and bi-modal grain structure induced (BI) hardening are effective ways to increase the performance of magnesium (Mg) alloys. However, loading rate, texture, and microstructure features play a decisive role in achieving the full advantage of these mechanisms. In particular, we reported that the heterogeneous grain structured MgMn alloy and bimodal grain structured pure Mg, having low strength and low elongation to fracture (EF) under quasi-static (QS) loading, can show exceptionally high strength and high EF under high strain rate (HSR) loading. To prove it, we have conducted QS ($\dot{\epsilon }=0.001s^{-1}$) and HSR ($\dot{\epsilon }=2400-4200s^{-1}$) tensile properties of a bi-modal grain structure extruded Mg and a heterogeneous grain structure extruded MgMn alloy having different textures. Subsequently, the ultimate tensile strength (UTS) ∼ 334 MPa is achieved for Mg under HSR loading, which is 110 % higher than the UTS (∼ 159 MPa) under QS loading. Likewise, the MgMn alloy also displayed an exceptional UTS of ∼382 MPa, which is ∼105 % higher than the UTS (∼ 185 MPa) of the MgMn alloy under QS loading. Most specifically, EF is 2-fold and ∼ 3–4 fold in Mg and MgMn alloy under HSR compared to the QS loading. The results also revealed that Mg displayed structure instability, and MgMn alloy displayed structure stability. Therefore, MgMn alloy displayed a higher UTS ∼ 81 MPa than that of Mg under the same HSR (4100 and 4182 s⁻¹). Thus, the maximum advantage of the HDI and BI mechanisms is attained at HSR loading, and the Mg and MgMn alloy that were not high strength and ductile under QS loading are high strength and ductile under HSR tensile loading.