Dislocation cells tailored precipitation enhancing mechanical properties of a high Gd content Mg alloy

Abstract

High Gd content Mg alloys are expected to overcome the poor heat resistance of magnesium (Mg) alloys. However, the low ductility limits their applications. Nano-precipitates is a viable method to enhance the strength without seriously plummeting ductility. In this study, ultrafine and densely arranged dislocation cells, with an average size of 27 nm, were obtained in Mg-11.5Gd-2Y-0.5Zr-0.5Ag-0.5Nd alloy after hot rolling. During the aging process, the dislocation cells facilitated the precipitation of fine and high-density β'. In the peak-aged (225 °C, 15 h) alloy, the volume fraction of β′ could reach 20.3 %, and the average length and thickness of β′ are 10 and 5.9 nm, respectively. The alloy with such a microstructure exhibited a yield strength (YS) of 403 MPa, and an EL of 8.3 % at room temperature. YS of the alloy was still 357 MPa, 310 MPa, and 206 MPa at 200 °C, 250 °C, and 300 °C, respectively. The high YS is attributed to grain boundary, dislocation, solid solution, and precipitation strengthening, among which precipitation strengthening is dominant. Moreover, the nano-β′ could be sheared, thereby coordinating the plastic deformation. Therefore, the present alloy achieved high YS while maintaining good ductility.