摘要
以Mg-Gd-Y-Zn-Zr挤压态合金为材料,采用同步轧制(SR)和异步轧制(DSR)工艺,通过光学显微镜(OM)、电子背散射衍射(EBSD)、X射线衍射(XRD)宏观织构检测以及室温拉伸等手段研究了两种轧制方式下板材微观组织的演变、织构组态及力学性能。结果表明:经SR和DSR轧制后,大尺寸的变形组织由于剪切破碎作用被细小的再结晶组织取代,两种轧板表层组织都比中心层组织更加细小均匀;与SR轧板相比,DSR轧板残留的变形区组织很少,动态再结晶程度更高,组织更加均匀;由EBSD分析结果可知,SR和DSR板材的再结晶机制均为连续动态再结晶;SR板材内部存在大量的低角度晶界(67.8%),仍然存在15μm以上的大晶粒,动态再结晶程度不高;DSR板材低角度晶界比例大大降低(25.8%),晶粒尺寸分布均匀,动态再结晶程度较高;SR板材呈现基底织构的特征,织构强度达到13.9;DSR板材基极向横向(TD)和轧向(RD)呈现均匀发散状态,织构强度降低到4.8;相同轧制条件下,DSR板材的抗拉强度和屈服强度分别比SR板材高30.1 MPa和38.2 MPa,DSR板材的延伸率(8.7%)比SR板材(5.6%)高出约55%;均匀分布的细晶组织和弱化的织构强度使DSR板材性能优于SR板材。
With the development of lightweight,it had become a trend to replace steel and aluminum materials in aerospace,transportation and other fields with lightweight magnesium alloys with excellent specific strength and specific stiffness.However,the room temperature forming ability of magnesium alloys was not good because the crystal structure of their hexagonal close-packed(hcp)structure limited the activation of sufficient slip systems.In addition,strong crystal texture and mechanical anisotropy would be generated during traditional extrusion and rolling deformation of magnesium alloy materials,which was also very unfavorable to the application of wrought magnesium alloy.In recent years,many scholars at home and abroad had studied various methods to improve the formability of magnesium alloys.In general,the texture could be effectively modified by adding rare earth elements to magnesium alloys.In addition,some advanced processing methods such as equal-channel angular extrusion(ECAP),friction stir and asymmetric rolling(ASR)had also been used to improve the texture of magnesium alloys by introducing shear deformation.As a kind of asymmetric rolling,different speed rolling(DSR)was the simplest to operate and the easiest to achieve on an industrial scale,so it deserved special attention.In order to further explore the effect of shear deformation on the microstructure,texture and mechanical properties of magnesium alloy sheet during rolling,the microstructure evolution and texture configuration of Mg-Gd-Y-Zn-Zr extruded alloy sheet under symmetric rolling(SR)and different speed rolling(DSR)were studied,and the reasons for the improvement of properties of magnesium alloy sheet under asynchronous rolling were analyzed.A number of sheets of 60 mm×50 mm×6 mm was cut from the bar along the extrusion direction.SR and DSR tests were carried out on an asymmetric mill with the same upper and lower roll diameters(100 mm)and adjustable roll speeds,and the speed ratios were 1.0 and 1.5,respectively.After rolling 6 mm thick sheet for 6 passes,3 mm thick sheet was obtained(the deformation of each pass was about 10%),and the total deformation was 50%.Optical microstructure(OM)of the upper surface,the center layer and the lower surface of the rolled plate were observed,and the microstructure of center layer was sampled for electron back-scattered diffraction(EBSD)detection.The macro-texture in the center layer of the sheets was detected by X-ray diffraction(XRD).The mechanical properties of the rolled sheets along the rolling direction were tested by three repeated tests at room temperature with a standard distance of 25 mm.The initial strain rate was 1×10^(-3)s^(-1).The results showed that:after SR and DSR rolling,the large deformation microstructure was replaced by small recrystallized microstructure due to shearing and crushing,and the surface layer microstructure of both kinds of rolling sheets was finer and more uniform than that of the center layer.Compared with SR rolled sheet,the residual deformation zone microstructure of DSR rolling plate was less,the dynamic recrystallization degree is higher,and the microstructure was more uniform.From the EBSD analysis results,there were a large number of low angle grain boundaries(67.8%)in SR sheet,and the sub-structure was formed,especially in the large-scale deformed grains.Continuous dynamic recrystallization occurred in the rolling process of SR sheet,and fine recrystallized grains were formed around the large grains,accompanied by the change of grain boundaries from a low angle grain boundary to the high angle grain boundaries.For DSR sheet,the proportion of low angle grain boundaries in DSR sheet was greatly reduced(25.8%),with uniform grain size distribution and high degree of dynamic recrystallization.From the XRD analysis results,SR sheet showed the characteristics of basal texture,and the maximum texture density reached 13.9;DSR sheet showed uniform inclination or scattering into the transverse direction(TD)and rolling direction(RD),and the maximum texture density decreased to 4.8.Under the same rolling conditions,the tensile strength and yield strength of DSR sheet were 381.3 MPa and 316.4 MPa,which were 30.1 MPa and 38.2 MPa higher than 351.2 MPa and 278.2 MPa of SR sheet,respectively.Meanwhile,the elongation increases by 5%in DSR sheet(8.7%)than that of SR sheet(5.6%).The better mechanical properties of DSR sheet were attributed to the finer and more uniform grain structure and weak texture configuration.
作者
王旭
黄元春
王强
胡嘉伟
李湘粤
Wang Xu;Huang Yuanchun;Wang Qiang;Hu Jiawei;Li Xiangyue(Light Alloy Research Institute,Central South University,Changsha 410083,China;School of Materials Sci⁃ence and Engineering,Central South University,Changsha 410083,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2023年第7期934-941,共8页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(U1837207)资助
关键词
镁合金
异步轧制(DSR)
组织演变
织构
力学性能
magnesium alloy
different speed rolling(DSR)
microstructure evolution
texture
mechanical properties
