Gd含量及热处理对Mg-Gd-Zr合金显微组织和力学性能的影响

Microstructure and Mechanical Properties of Mg-Gd-Zr Alloys with Gd Additive and Heat Treatment

采用金相光学显微镜(OM),扫描电镜(SEM),能谱仪(EDS)以及X射线衍射(XRD)等手段,研究了不同Gd含量(1%,2%,3%,原子分数)与不同热处理状态(铸态,固溶态,时效态)对Mg-Gd-Zr合金显微组织和力学性能的影响。结果表明:铸态组织中,Gd元素富集在晶界,随Gd含量增加,共晶组织增多,并逐渐呈网状分布,合金的晶粒逐渐变小。经过535℃,24 h固溶处理,共晶组织分解,残留相主要为富Gd的方块相,数量随Gd含量升高增加,晶粒尺寸比铸态组织长大。再经过220℃,24 h时效处理,合金中析出第二相,晶粒尺寸与固溶态差别不大。合金的抗拉强度,屈服强度和硬度(R_m,R_(p0.2),HB)随Gd含量增加呈上升趋势,断后伸长率随Gd含量升高呈降低趋势。经过535℃,24 h固溶处理,消除了铸造应力,且使合金晶粒长大,降低了合金强度。时效处理后,合金中析出第二相,合金强度升高,且Gd含量越高析出第二相越多,强化效果越明显。拉伸断裂后,铸态合金呈解理断裂,固溶态合金呈穿晶断裂,时效态合金呈沿晶断裂。

The effeets of different Gd contents （1% , 2% , 3% ; atom fraction） and different heat treatments （as-cast, solid solution, aging） on the mierostrueture and mechanical properties of Mg-Gd-Zr alloys were investigated by optical metallographic microscope （OM） , scanning electron microscope（SEM） , energy dispersive spectrum analysis（EDS） , X-ray diffraction （XRD） and other means. The results showed that Gd element enriched at the grain boundaries with the increase of Gd content in the microstructure of as-cast alloys, at the same time, the grains became smaller, and the euteetie structure increased and gradually showed as net distribution. The eutectic structure decomposed and the grain size grew up after 535 ℃, 24 h solid solution treatment. There were a number of residual block phases mainly enriched in Gd element in the alloys and the number of the phase increased with the increase of Gd content in the solid solution alloys. There were a number of second phases separated out after 220 ℃ , 24 h aging treatment, and the grain size had little difference with the solid solution treatment alloys. The tensile strength, yield strength and Brinel] hardness （ R,,, Rr, o 2, HB） were rising with Gd content of the alloys increasing, and the elongation was decreasing with Gd content of the alloys increasing. The strength of the alloy reduced after 535 ℃, 24 h solid solution treatment because the casting stress was eliminated and the grain grew. The alloy strength increased after aging treatment because a number of second phases were separated out, and the higher Gd content was, the more precipitation of second phase was, and the strengthening effect was more obvious. The casting alloys exhibited cleavage fracture, the solid solution alloys exhibited transgranular fracture, and the aged alloys exhibited intergranular fracture after tensile fracture.