Thermo-mechanical processing characteristics and strain-rate-sensitive degradation properties of Mg-Er-Ni alloys

Hot deformation behavior, the corresponding microstructure evolution, and degradation properties of a weak-textured Mg-Er-Ni alloy containing a high-volume fraction of Ni-LPSO phases, have been investigated. Hot deformation behavior has been carried out in the temperatures range of 370 ∼ 460 °C and strain rates range of 0.001 ∼ 1 s−1. Flow stress-strain curves of high strain rate cases show a continuous increase trend without a steady or a peak stage, while that of low strain rate cases show an obvious dynamic softening after peak stress. Based on flow stress-strain curves, materials constants calculated by an Arrhenius-type constitutive equation, show a high n and Q compared to those of high-volume fraction α-Mg matrix Mg alloys. Optimal processing windows, based on the dynamic material model, is determined as high temperature domains. As for microstructure evolution, a complete recrystallization and dispersive Ni-LPSO fragments for high temperature & low strain rates while a restricted recrystallization and a streamline distribution LPSO phase for high temperature & high strain rates are observed. Varying degrees of continuous dynamic recrystallization, particle induced nucleation mechanism, as well as coordinated deformation of LPSO through kinking and bending account for the strain-rate-dependence hot deformation mechanism. As a result, dispersive Ni-LPSO fragments at low strain rates provide more degradation channels for the α-Mg matrix and thus possess better a degradation rate than the streamlined LPSO at high strain rates. •High strain rate cases show a continuous increase trend while low strain rate cases show an obvious dynamic softening.•A restricted DRX and a streamline distribution Ni-LPSO phases for high temperature & high strain rates are observed.•A complete DRX and dispersive Ni-LPSO fragments for high temperature & low strain rates are observed.•Dispersive LPSO fragments provide more degradation channels for the α-Mg and thus a faster degradation rate.