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

摘要:

本文通过光学显微镜（OM）、电子背散射（EBSD）及单轴拉-压研究了Y元素含量（1，5 wt.%）、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±1.9μm~16.5±1.6μm；室温拉伸屈服强度（TYS）由173±3MPa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±1MPa（~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±9MPa（~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。

Abstract:

Optical microscope(OM), electron back scattering diffraction(EBSD) and uniaxial tension and compression tests were carried out to investigate the effect of Y content (1，5 wt.%), extrusion temperature(ET) and extrusion ratio(ER) on the microstructure and tension-compression deformation behavior of extruded Mg-Y alloy bars. Results show that the grain 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 two alloy bars are close and approximately 14.1±1.9μm~16.5±1.6μm. 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±3MPa to 125±6MPa while fracture strain remarkably raises 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 increasing extrusion ratio from 9 to 32 (ET=300℃),the TYS of Mg-1Y alloy bars drastically increases to 242±1MPa (~40%), which may be closely related to fully dynamic recrystallization, finer grain size (~10.1±1.4μm) 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-1Y alloy bars (ER=32) while compression yield strength (CYS) raises to 236±9MPa (~15%), the value of CYS/TYS changes from 0.85 to 1.02 which means alloy exhibit tension-compression symmetry. Y content has an obvious influence on the deformation behavior of extruded Mg-Y alloy bars. All of the extruded Mg-1Y alloy bars show sigmoid compression stress-strain curve while no similar phenomenon in Mg-5Y alloy bar is observed. Observation of microstructure after compression suggests that this phenomenon is closely related to twining dominant deformation mechanism.