Mechanical properties and failure of ECAE processed Mg₉₇Y₂Zn₁ at different strain rates

As-cast Mg₉₇Y₂Zn₁ billets with a two-phase microstructure were processed with four passes of equal channel angular extrusion (ECAE) using different routes (A, B_C, and C) at 350 °C to refine the microstructure. The duplex microstructure of this material consists of a Mg-rich alloy matrix with a long-periodic-stacking-order (LPSO) reinforcement phase. Mechanical properties were evaluated under both quasi-static and dynamic loading conditions. It was found that routes A and B_C were more effective in producing a Mg alloy with nearly isotropic properties. For route C, the specimens more easily fractured due to pre-existing localized shear planes induced by ECAE. Microstructural observations revealed that the post-processed average matrix grain size could be as fine as ∼1 μm. Uniaxial compressive loading and micro-hardness measurements verified the enhancement of strength, and it was noticed that the increase of strength comes primarily from grain refinement of the Mg matrix. In the composite, we also focused on elucidating the deformation mechanism of the LPSO phase. It is believed that localized deformation is responsible for the final failure of the ECAE processed Mg₉₇Y₂Zn₁ alloy under both quasi-static and high strain rate loading. The grain morphology and distribution after deformation indicated that the shear localization resulted from the rotation and rearrangement of grains. Moreover, cracks were found to propagate along the grain boundaries leading to final failure.