Change in dominant deformation mechanism of Mg alloy via grain boundary control

Abstract

The impact of grain boundary structures on mechanical properties and its deformation behavior was investigated on a wrought processed Mg-0.3 at%Mn binary alloy. The Mg-Mn alloy, which had an average grain size of 1.2 µm and a high density of low-angle grain boundaries, was fabricated via caliber rolling. This alloy exhibited yield strength of more than 300 MPa and had low strain rate dependence in both tension and compression tests at room temperature. The major deformation mechanism was dislocation slip for tension and deformation twinning for compression, respectively, as is well established for conventional wrought processed magnesium alloys. However, an extruded Mg-Mn alloy having an average grain size of 1.8 µm is reported to exhibit a good elongation-to-failure and large strain rate dependence. While the same cast billet was used, the result obtained from caliber rolled alloy is inconsistent with that from the extruded alloy. This is due to the difference in grain boundary structures, i.e., the existence of low-angle grain boundaries in the caliber rolled alloy. Low-angle grain boundaries, which do not have free volume, are difficult for segregation of alloying elements. The mechanical properties and deformation mechanism can be clearly controlled by grain boundary structures through wrought process.