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

• 作者: Bibo Li Kui Zhang Guoliang Shi Kaikun Wang Yongjun Li Xinggang Li Minglong Ma Jiawei Yuan
• 来源期刊: 稀土学报（英文版）
• 年，卷（期）: 2021,（5）
• 所属期刊栏目: METALLOGRAPHY AND PYROMETALLURGY
• 页码范围: 600-608
• 页数: 9页
• 语种: 英文

摘要

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 42μm, and the eutectic compounds were determined to be Mg5(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 12μm and the formation of streamlines consisting of Mg12MM particles along the extrusion direction (ED). After T5 treatment (225 ℃for 7 h), a large number ofβ'(Mg7Gd) phases are precipitated on the {11-20}α habit plane and are interconnected, forming an interlaced network structure. The ul-timate tensile strength (Rm = 405 MPa) and yield strength (RP0.2 = 288 MPa) of the T5 sample are significantly higher than those of the as-extruded sample (Rm = 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 °C under 100 MPa, the steady-state creep rates of the as-cast, as-extruded, and T5 samples are 1.59 × 10-8, 1.08 × 10-8, and 1.40 × 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, theβ' 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.