Bimodal grained Mg–0.5Gd–xMn alloys with high strength and low-cost fabricated by low-temperature extrusion

Abstract

Obtaining high strength in Mg alloys generally requires a high alloying content, especially rare earth elements. However, as a lightweight alloy, the heavy rare-earth content has a negative impact on the density of Mg alloys and the related cost, which increases the exploration need of low rare-earth and low-cost Mg alloy. In this work, a new low-cost and high mechanical strength Mg–0.5Gd–xMn (x = 0, 0.5, 1.0, 1.5, 2.0 wt.%) alloys system was developed by the low-temperature extrusion at 250 °C. A typical bimodal grain structure was formed in as-extruded Mg-0.5Gd-xMn alloys. The results presented a gradually increased yield strength and ultimate tensile strength with the increment of the Mn content from 0 to 1.5 wt.%. The tensile yield strength and ultimate tensile strength reached 357 MPa and 364 MPa in Mg–0.5Gd–1.5Mn alloy, which was 62 MPa and 63 MPa higher than that of the Mg–0.5Gd alloy. The high performance was mainly due to the bimodal grain structure, which produced a good Hall-Petch strengthening and the back stress strengthening. The Mg–0.5Gd–xMn alloys possessed a feature of comparable high mechanical strength with heavy rare-earth content traditional Mg alloys but a much lower cost, which promotes the future application.