挤压参数和Y含量对Mg-Y合金棒材显微组织及拉-压变形行为的影响

Effect of Extrusion Parameters and Y Content on the Microstructure and Tension-Compression Deformation Behavior of Extruded Mg-Y Alloy Bars

通过光学显微镜(OM)、电子背散射(EBSD)及单轴拉-压研究了Y元素含量(1%,5%,质量分数)、挤压温度(ET)、挤压比(ER)对Mg-Y合金挤压棒材显微组织、织构及拉-压变形行为的影响规律。结果表明:当Y含量由1%增加到5%(ET=300℃,ER=9):由"双峰"组织变为细小均匀的完全动态再结晶组织;两种棒材横截面(ED面)和纵剖面(TD面)的平均晶粒尺寸相近,约为(14.1±1.9)～(16.5±1.6)μm;室温拉伸屈服强度(TYS)由173±3 MPa降低到125±6MPa,但断裂延伸率则由(11.0±2.1)%大幅增加到了(31.0±1.2)%,这主要是由于基面丝织构的显著弱化和织构强度的明显降低(～53%)导致;CYS/TYS由0.87变为1.10,材料由通常的正拉压不对称性变为反拉压不对称性。当ER由9增加到32(ET=300℃):Mg-1Y的TYS大幅增加到(242±1) MPa(～40%),同时断裂延伸率增加到(12.9±1.5)%(～17%),这主要与大挤压比使得动态再结晶趋于完全、晶粒更加细小均匀(10.1±1.4μm)以及基面丝织构的显著弱化(～75%)密切相关。增加挤压温度(300～400℃)对Mg-1Y棒材(ER=32)的晶粒尺寸和拉伸力学性能的影响较小,但可提高压缩屈服强度(CYS)至(236±9) MPa(～15%),CYS/TYS由0.85增加到1.02,材料拉压屈服对称。Y含量显著影响材料的变形行为,不同挤压参数的Mg-1Y合金棒材均表现出"S"型压缩曲线,而Mg-5Y则无此现象,变形后组织观察表明"S"型曲线与孪晶主导变形密切相关。

Optical microscope（OM）,electron back scattering diffraction（EBSD） and uniaxial tension and compression tests were carried out to investigate the effect of Y content（1 wt%,5 wt%）,extrusion temperature（ET） and extrusion ratio（ER） on the microstructure,texture and tension-compression deformation behavior of extruded Mg-Y alloy bars.Results show that the grains change from typical bimodal structure to small,homogeneous and fully dynamic recrystallized grains with increasing Y content from 1% to 5%（ET=300 ℃,ER=9）.The average grain size of cross section（ED plane） and longitudinal section（TD plane） of the two alloy bars are close and approximately（14.1±1.9） μm～（16.5±1.6） μm.As a result of dramatically weakened basal plane fiber texture and decreasing texture intensity（～53%）,the room temperature tensile yield strength（TYS） decreases from（173±3） MPa to（125±6） MPa while elongation remarkably rises from（11.0±2.1）% to（31.0±1.2）%.Furthermore,the tension-compression asymmetry changes from common（CYS/TYS=0.8） to inverse（CYS/TYS=1.10） with increasing of Y content.With the extrusion ratio increasing from 9 to 32（ET=300 ℃）,the TYS of Mg-1 Y alloy bars drastically increases to（242±1） MPa（～40%）,and the elongation increases to（12.9±1.5） MPa（～17%）,which may be closely related to fully dynamic recrystallization,finer grain size（～10.1±1.4 μm） and obviously weakened basal plane fiber texture（～75%）.The increasing extrusion temperature（300～400 ℃） has little effect on grain size and tension mechanical properties of Mg-1 Y alloy bars（ER=32） while compression yield strength（CYS） rises to（236±9） MPa（～15%）,the value of CYS/TYS changes from 0.85 to 1.02 which means the alloy exhibits tension-compression symmetry.Y content has an obvious influence on the deformation behavior of extruded Mg-Y alloy bars.All of the extruded Mg-1 Y alloy bars show sigmoid compression stress-strain curve while no similar phenomenon in Mg-5 Y alloy bar is observed.Observation of microstructure after compression suggests that this phenomenon is closely related to twining dominant deformation mechanism.