Effect of the precipitation state on high temperature tensile and creep behaviors of Mg-15Gd alloy

Due to the effective precipitation strengthening effect of the ss ' phase, Mg-Gd alloys exhibit excellent room temperature mechanical behaviors. However, when served at high temperatures, the metastable ss ' phase will transform to other phases, resulting in severe performance degradation. In this study, we investigated the effect of precipitation state achieved by different heat treatments on high temperature tensile and creep behaviors of the Mg-15Gd alloy by comparing the properties of the as-cast, solid-solutioned (T4) and peak-aged (T6) alloys. The results showed that the tensile mechanical properties of the T6 alloy were always highest from room temperature to 300 degrees C, in spite of an abnormal strength increase with temperature existed in the T4 alloy. For tensile creep properties, the T6 alloy exhibited the lowest steady creep rate below 235 degrees C while the T4 alloy possessed the best properties above 260 degrees C. Microstructure characterization revealed that the transition was caused by the stress-promoted precipitation of ss ' phase in the T4 alloy and rapid phase transformation in the T6 alloy at high temperatures. At 260 degrees C, the calculated stress exponent n was 3.1 and 2.8 for the T4 and T6 alloys, respectively, suggesting the creep deformation mechanism was dislocation slip, which was further confirmed by the microstructure after creeping. Our findings can provide new insights into the heat treatment process of Mg-Gd alloys served at high temperatures. (c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University

Automated summary

This study investigates the effect of different heat treatments on the mechanical behaviors of Mg-Gd alloys at high temperatures. The results show that the T6 alloy exhibits the highest tensile properties from room temperature to 300 degrees C, while the T4 alloy possesses the best creep properties above 260 degrees C.