Stress tensor in various structural states of the Mg-Zn-Zr-Ce alloy formed by severe plastic deformation

The medium-strength, deformable magnesium alloy MA-20 has wide applications in aerospace and potential use in medical implants due to its low density, acceptable strength, and bioresorbability. This study investigates the alloy in coarse-grained (CG), fine-grained (FG), and ultrafine-grained (UFG) states. Severe plastic deformation (SPD) effectively refines grain size and modifies residual stress as well as forms new complex of physical and mechanical properties in the alloy. Results show significant grain refinement with SPD, decreasing average grain size from 27 ±10 μm in the CG state to about 1 μm in the UFG state. SPD led to grain elongation along the (0002) planes in the FG state and formation of uniaxial grains in the UFG state due to the structure rearrangement. Principal stress for the (101−0) planes did not significantly change, while for the (0002) planes, stress decreased in the FG state and increased in the UFG state by 23 %. (112−0) planes also did not show significant changes of residual stress as well as (101−1) planes showed virtually unchanged total stress across all states. Such behavior is accompanied by growth of defects density and microstrains within the alloy as well as by active twinning process. Therefore, SPD is an effective technique that allows improvements of mechanical properties and suitability for biomedical applications of MA-20 alloy.