Influence of severe plastic deformation on dynamic strain aging of ultrafine grained Al-Mg alloys

This investigation addressed the influence of severe plastic deformation (SPD) on dynamic strain aging (DSA) of ultrafine grained (UFG) Al-Mg alloys with different Mg content. Confined channel die pressing (CCDP) carried out at room temperature was used for SPD. Microcharacterization by TEM revealed a remarkable grain refinement and retarded dynamic recovery with increasing Mg content and plastic strain during SPD. Mechanical tests with jumping and constant strain rates demonstrated a complicated deformation behaviors of the UFG Al-Mg alloys: (i) the critical strain ε_c for initiation of serrated flow increased considerably with increasing strain and Mg content contrary to the behavior of the coarse grained and non-deformed counterparts; (ii) the instantaneous stress response (Δσ_i) and the instantaneous strain rate sensitivity (m_i) during rate jumps were always positive and increased monotonically with CCDP pass and Mg content, however, they exhibited a distinctive asymmetry with respect to the strain rate jump direction, i.e. the values for strain rate towards down were about one order of magnitude larger than those for rate towards up and increased with progressing CCDP as well as with increasing Mg content; (iii) the steady state strain rate sensitivity m_s was negative and decreased firstly with progressing CCDP up to a certain strain and then increased again. This mechanical behavior of UFG Al-Mg alloys is discussed on the basis of recently developed DSA models by relating the microstructure evolution of Al-Mg alloys during SPD to the influence of SPD on DSA.