Microstructures, mechanical properties and creep behavior of a Mg-3Yb-0.6Zn-0.4Zr casting alloy

Microstructures, mechanical properties and creep behavior of a gravity casting Mg - 3Yb - 0.6Zn - 0.4Zr (wt%) alloy were investigated. The results indicate that the studied alloy has smaller grains compared with the conventional Mg-RE based casting alloys, and the dominant intermetallic phase is Mg2Yb although minor Mg41Yb5 was also found in grain interior. In addition, the studied alloy exhibits medium tensile strength but excellent ductility at room temperature. Simultaneously, a complicated serrated flow phenomenon was observed in its flow curves at 150-250 degrees C. Finally, we found that the studied alloy exhibits poor creep resistance compared with the conventional Mg-RE based alloys. This could be mainly attributed to both poor thermal stability Mg2Yb phase and discontinuous intermetallic phase skeleton. Also, based on the analyses of the stress exponent and activation energy as well as microstructural observation, dislocation climb was proposed as the dominated creep mechanisms of the studied alloy at 180-220 degrees C and 40-80 MPa.