稀土元素Ce对挤压态Mg-0.3Al-0.2Ca-0.5Mn合金板材体织构及力学各向异性的影响

Effect of Rare Earth Element Ce on the Bulk Texture and Mechanical Anisotropy of As-Extruded Mg-0.3Al-0.2Ca-0.5Mn Alloy Sheets

针对Mg-0.3Al-0.2Ca-0.5Mn合金在热挤压过程中容易形成对称性差的强基面织构从而导致力学性能各向异性的问题,本工作通过稀土元素Ce合金化的方法优化其基面织构进而改善材料的力学性能。利用中子衍射技术,结合SEM和EBSD等微观测试手段,研究稀土元素Ce对Mg-0.3Al-0.2Ca-0.5Mn挤压态镁合金板材的微观组织、体织构和力学各向异性的影响。结果表明,随着Ce含量的增加,挤压态镁合金板材中的第二相颗粒逐渐从A_(l8)Mn_(5)转变为A_(l8)Mn_(4)Ce和Al_(11)Ce_(3),且第二相颗粒数量明显增多。0.05%Ce(质量分数)的添加并未明显改变合金板材的基面织构,而添加0.5%Ce后合金板材沿着挤压方向(ED)的双峰基面织构向双峰非基面织构转变,同时沿横向(TD)分布的丝织构组分明显减少,从而使得沿着ED和TD的拉伸屈服强度比值接近于1,合金板材各向异性显著降低。

Because deformed magnesium alloys with low density and desirable mechanical properties can save energy and reduce emissions,they are in considerable demand in industrial applications.However,due to their hcp crystal structure,magnesium alloys have a limited number of slip systems that can be activated at room temperature.At present,many deformed magnesium alloys still face the problems of insufficient formability and poor mechanical anisotropy at room temperature,which limit the development of secondary forming processes.Meanwhile,many reports have proven that regulating the texture of deformed magnesium alloys is an effective strategy to improve their formability.Therefore,this study primarily employs the neutron diffraction technology,combined with microscopic characterization methods such as SEM and EBSD,to systematically study the effects of the minor rare earth element Ce on the microstructure,bulk texture,and mechanical anisotropy of extruded Mg-0.3Al-0.2Ca-0.5Mn magnesium alloy sheet.The results show that as the Ce content increases,second-phase particles in the extruded magnesium alloy sheet gradually transform from A_(l8)Mn_(5) to Ce-containing A_(l8)Mn_(4)Ce and Al_(11)Ce_(3) particles and the number density of second-phase particles increases remarkably.The addition of 0.05%Ce(mass fraction)did not considerably improve the basal texture of the sheet.However,after the addition of 0.5%Ce,fiber texture components distributed along the transverse direction(TD)are substantially reduced while the texture of(0002)pole figure of the alloy changed from a bimodal basal texture to a bimodal nonbasal texture along the extrusion direction(ED).This nonbasal texture formation is mainly caused by larger Ce-containing second-phase particles(>1μm)promoting the particle-stimulated nucleation effect and preferential growth of nonbasal-oriented recrystallized grains.Therefore,when 0.5%Ce is added,the basal texture of the alloy is remarkably optimized,so that the ratio of the tensile yield strength along TD to that along ED is close to 1,implying that the anisotropy of the extruded Mg-0.3Al-0.2Ca-0.5Mn alloy has been substantially reduced by the minor addition of Ce element.