AZ80镁合金环形通道转角挤压组织与性能研究

Microstructure and mechanical properties of AZ80 magnesium alloy fabricated by annular channel angular extrusion

用环形通道转角挤压工艺在300、350、380℃制备AZ80镁合金壳体构件,通过光学显微镜、扫描电子显微镜、电子背散射衍射及拉伸试验研究变形温度对构件显微组织、织构、力学性能的影响,对变形工艺进行初步探索。结果表明:经过环形通道转角连续两次剪切变形,AZ80合金晶粒细化;当变形温度高于300℃,材料基本实现完全动态再结晶;当变形前均匀化坯料的预热温度低于350℃时,连续β-Mg_(17)Al_(12)相静态析出,一定程度阻碍变形中动态再结晶进行。同时,大量颗粒状β-Mg_(17)Al_(12)相动态析出,部分对晶粒长大产生钉扎效应;最终,在350℃变形时挤压件壁部的晶粒尺寸被细化至约25.1μm。织构分析表明,通道剪切变形的引入促进了晶粒激活滑移面向剪切面分布,利于镁合金典型基面织构弱化。环形通道挤压变形后材料性能大幅提升。在低温变形时,挤压件性能受高密度连续析出相影响,加工硬化能力强但断裂韧性极差。随变形温度升高,挤压件性能与晶粒细化幅度正相关,在350℃时强度和塑性较好平衡。断裂和强韧化分析表明,综合性能显著提升主要得益于晶粒细化和织构弱化的协同作用。

AZ80 magnesium alloy shell parts were successfully fabricated by annular channel angular extrusion at 300,350 and380℃.The effects of deformation temperature on microstructures,texture,mechanical properties and fracture behavior of the extruded parts were studied by optical microscopy,scanning electron microscopy,electron backscattering diffraction and tensile tests,and the deformation process was preliminarily explored.The results show that the grain of AZ80 magnesium alloy can be effectively refined by two successive shear deformations during the annular channel angular extrution.When the deformation temperature is higher than 300℃,the full dynamic recrystallization structure is basically achieved.When the preheating temperature of homogenized billet before deformation is lower than 350℃,the continuousβ-Mg_(17)Al_(12) phases statically precipitate from the matrix,which hinder the subsequent dynamic recrystallization nucleation to a certain extent.At the same time,numerous of granularβ-Mg_(17)Al_(12) phase particles dynamically precipitate from the matrix,and some of them inhibit the grain growth via pinning effect.Finally,the grain size of the extrusion wall is effectively refined to about 25.1μm at the deformation temperature of 350℃.Texture analysis result shows that the introduction of shear deformation effectively promotes the redistribution of grains activated slip system toward the shear plane,which is conducive to the weakening of typical basal texture in Mg alloy.Compared with the initial state,the properties of the material are greatly improved after the annular channel angular extrusion.During lower deformation temperature,the properties of extruded part are affected by high density continuous precipitated phases,where the work hardening ability is strong but the fracture toughness is extremely poor.With the increase of deformation temperature,the properties of the extruded parts are positively correlated with the grain refinement,and a good balance between strength and plasticity is obtained at 350℃.Fracture and toughening analysis show that the significant improvement of comprehensive properties is mainly due to the synergistic effect of grain refinement and texture weakening.