Synergic effects of Gd and Y contents on the age-hardening response and elevated-temperature mechanical properties of extruded Mg-Gd (-Y)-Zn-Mn alloys

This paper investigated the effects of Gd and Y solutes on aging behaviour and corresponding mechanical properties of the extruded Mg-Gd(-Y)-Zn-Mn alloys at room and elevated temperatures. The results show that aging treatment provided significant improvement of similar to 100 MPa in strength by forming ellipsoidal beta' nanophases in the as-extruded alloys. Partially substituting Y for Gd in the as-extruded Mg-Gd-Zn-Mn alloys can delay age-hardening response, but improve the strength increment after aging treatment. As the Y/Gd atomic ratio changed from 0 to 1, the Mg-1.75Gd-0.75Y-0.5Zn-Mn(at.%) alloy with a Y/Gd atomic ratio of 0.4 obtained the higher peak-hardness and mechanical properties. Enhanced age-hardening response and better mechanical properties were detected after separate additions of Y and Gd. The extruded-T5 Mg-2.5Gd-0.75Y-0.5Zn-0.3Mn alloy exhibited superior ultimate tensile strengths of 520 MPa at room temperature, 344 MPa at 250 degrees C, and 225 MPa at 300 degrees C. Fracture behaviours reveal that a change in predominant deformation mechanism from one based on dislocations to one mediated by grain boundary (GB) processes was found as the tensile temperatures arise from 250 degrees C to 300 degrees C. The activation of GB sliding of the fine grains partially resulted in the decrease of tensile strength at 300 degrees C.

Automated summary

The effects of Gd and Y solutes on the mechanical properties of extruded Mg-Gd(-Y)-Zn-Mn alloys were investigated in this study, showing significant improvements in strength and age-hardening response. Partial substitution of Y for Gd delayed age-hardening response but improved strength increment. The addition of Y and Gd separately enhanced age-hardening response and mechanical properties, while grain boundary (GB) sliding affected tensile strength at elevated temperatures.