Schmid因子的理论计算及其在镁合金高速变形过程中的应用

Theoretical Calculation of Schmid Factor and Its Application Under High Strain Rate Deformation in Magnesium Alloys

为了便于分析镁合金在高速变形过程中的变形机制,计算了4种滑移方式(基面滑移、柱面滑移、锥面<a>滑移和锥面<c+a>滑移)和2种孪晶方式({1012}拉伸孪晶和{1011}压缩孪晶)的Schmid因子。结合电子背散射衍射(EBSD)技术,获得了轧制态AZ31镁合金原始样品的Schmid因子实验值,并将理论计算值与实验值进行了比较。采用Hopkinson压杆对AZ31镁合金轧制板材在1600 s-1的应变速率下进行了高速冲击实验,对所获得的样品进行了金相组织观察。结合Schmid因子计算结果,讨论了不同方向样品在不同加载方向下的主要变形机制。结果表明,Schmid因子的理论计算值与实验值可以很好吻合。Schmid因子计算简单、表达方便,可以有效分析镁合金中主要的变形方式和解释应力-应变曲线特征。镁合金中不同变形方式的Schmid因子值及其变化规律均不相同,其计算结果可为镁合金中织构所引起的各向异性现象的分析提供理论依据。

As an important parameter, the Schmid factor has been widely applied to analyze the deformation modes in metals. In order to analyze the deformation mechanisms of magnesium alloys under high strain rate, the Schmid factors of four slip modes（basal, prismatic, pyramidal a and pyramidal c＋a slips） and two twinning systems（{101ˉ2} tension and {101ˉ1} contraction twinnings） were systematically calculated in this work. The experimental values of Schmid factor of as-received AZ31 rolling magnesium alloy sheets were obtained by electron backscatter diffraction（EBSD） technique, and then the theoretical calculated values were compared with those values. The high strain rate compression test of AZ31 rolling magnesium sheets was conducted by using split Hopkinson pressure bar at the strain rate of 1600 s-1, and the microstructures after compression were observed by optical microscopy.The Schmid factors and microstructures are combined to discuss the predominant deformation mechanisms for different orientation samples under different loading directions. The results showed that the theoretical calculated values of Schmid factors are in good agreement with their experimental values. Therefore, the Schmid factor, owing to its simplicity and convenience, could be used to analyze the predominant deformation mechanism and interpret the unique characteristics of ＂true stress-true strain＂ curves inmagnesium alloys. Furthermore, since the Schmid factor and its variation trend associated with deformation behavior in magnesium alloys are related, the calculation result of Schmid factor can provide a theoretical analytic approach to understand anisotropic phenomena caused by strong texture in magnesium alloys.