Significant improvement in yield stress of Mg-Gd-Mn alloy by forming bimodal grain structure

Abstract Fabricating bimodal grain structure is an effective way to improve the mechanical properties of Mg alloys. In present work, the various Mn contents (0, 0.5, 1.0, 1.5 wt.%) are added in Mg-1.0Gd alloy to fabricate bimodal grain structure and improve the mechanical properties. After extrusion at 300 oC, bimodal grain structure is obtained in the Mg-1.0Gd-1.0Mn and Mg-1.0Gd-1.5Mn alloys. With the increment of Mn content, the average grain sizes of dynamic recrystallization (DRX) grains are refined from 8.6 to 1.2 μm. The mechanical properties are significantly improved. The Mg-1.0Gd-1.5Mn alloy exhibits the best tensile yield stress (TYS) and ultimate tensile stress (UTS), which is 280 MPa and 293 MPa. Comparing with the Mg-1.0Gd alloy, the improvement of TYS and UTS are 165 MPa (143%) and 98 MPa (51%). The enhancement of the strength is mainly attributed to the bimodal grain structure. The formation of the bimodal grain structure and the strengthening mechanisms are also discussed.