Microstructure evolution, mechanical properties and creep mechanisms of Mg-12Gd-1MM-0.6Zr (wt%) magnesium alloy

In this research, the microstructure evolution, mechanical properties, and creep mechanisms of Mg-12Gd-1MM-0.6Zr (wt%) alloy under different conditions were systematically studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile creep tests. Regarding the microstructure of the as-cast sample, the average grain size is about 42 mu m, and the eutectic compounds were determined to be Mg-5(Gd0.8MM0.2). During homogenization, these eutectic compounds gradually dissolve, and Mg12MM particles are precipitated. During hot extrusion, complete dynamic recrystallization (DRX) occurs, resulting in equiaxial grains with an average grain size of about 12 mu m and the formation of streamlines consisting of Mg12MM particles along the extrusion direction (ED). After T5 treatment (225 degrees C for 7 h), a large number of beta'(Mg7Gd) phases are precipitated on the {11-20}(alpha) habit plane and are interconnected, forming an interlaced network structure. The ultimate tensile strength (R-m = 405 MPa) and yield strength (RP0.2 = 288 MPa) of the T5 sample are significantly higher than those of the as-extruded sample (R-m = 289 MPa, RP0.2 = 185 MPa), but the elongation (A = 4%) was remarkably lower than that of the as-extruded sample (A = 18%). When crept at 225 degrees C under 100 MPa, the steady-state creep rates of the as-cast, as-extruded, and T5 samples are 1.59 x 10(-8), 1.08 x 10(-8), and 1.40 x 10(-8) s(-1), respectively, and their total strains within 100 h are respectively breaking, 0.81%, and 0.92%, indicating that the as-extruded alloy exhibits the best creep resistance. TEM analysis reveals that, during the creep process of the T5 sample, the beta' particles coarsen and the precipitate-free zones (PFZs) widen, which increase the steady-state creep rate and the total strain within 100 h as compared with the as-extruded sample. (C) 2021 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.