Reasonable utilization of {10-12} twin for optimizing microstructure and improving mechanical property in a Mg-Gd-Y alloy

Abstract

During the deformation of Mg alloys, {10-12} extension twin, as one of the most active deformation mechanisms, contributed much to the formation of basal texture, yet little to dynamic recrystallization (DRX) grains, i.e., effective grain refinement. In this work, {10-12} extension twin had been creatively utilized to achieve grain refinement and property improvement in a Mg-Gd-Y alloy by multi-directional impact forging (MDIF). Firstly, flourishing {10-12} extension twins divided the parent grain into many fine independent regions (~10 μm). Meanwhile, a large number of twin boundaries were pinning mainly by interaction with neighboring dislocations in twin or matrix. Secondly, those pinned twin boundaries can effectively accumulate dislocation slips and promote the formation of extensive low angle grain boundaries (LAGBs). These high densities of LAGBs can further subdivide the independent regions provided by extension twins into micro-regions (~5 μm). Thirdly, those fine micro-regions developed to be DRX after a dynamic recovery. Finally, we obtained a yield isotropy high-strength Mg alloy with an ultimate tensile strength of 354 MPa after MDIF of 110 passes. This work proposed a brand new insight to prepare wrought Mg alloy with fine grain, yet without strong texture, which is beneficial to better formability and mechanical property isotropy.