镁合金循环变形过程中的孪生机制及其作用研究

The wrought magnesium alloys typically represented by AZ31B which is widely used in practice will be prepared for the investigation of the twinning mechanism and its role in the cyclic deformation. Based on considering Schmid factor and CRSS of the two kinds of prymary twinning modes, the research is stressed on the establishment of a comprehensive criterion for the prediction of the twinning mode selection. Based on identifying the twin variants, analyzing the regularity of the Schmid factor ranks and analyzing the ralationship between the twinning displament （strain）tensors and the stain accomodation on the suroounding grains,the mechanism of twin variant selection is planed to be studied, meanwhile the relationship between twinning mode and twin variant selection and the crysallographic orientation distribution is expected to be revealed. In addition, the characteristic of the Bauschinger effect and its role in the cyclic deformation are also planed to be investigated. The effect of the orientation distribution on twinning-detwinning and the relationship between the strain amplitude and the residual twin amount will be researched. The influence of the twinning mechanism on the behavior of the cyclic deformation will be investigated. Finally, the effect process of the cyclic frequency, strain path, strain amplitude,texture and grain size on the cyclic deformation mechanism and behavior will be investigated, consequently, the effect pattern of the texture and grain size on the LCF behavior under various loading spectrums is desired to be obtained, which would provide a theoritical basis for the anti- fatigue design of magnesium alloys and their components.

针对镁合金循环变形中的孪生机制及其对变形行为的作用问题，选取以应用最为广泛的AZ31B为代表的变形镁合金为研究对象，通过综合考量两种基本孪生的Schmid因子和CRSS，建立孪生模式选择的综合判断依据，通过孪晶变体的识别，分析Schmid因子序列规律，分析位移张量和应变张量与周围晶粒应变的协调作用关系以及应变协调过程，研究孪晶变体选择机制，揭示晶粒取向分布对孪生及其孪晶变体选择的影响规律；研究孪生-祛孪生和Bauschinger 效应的特征与机制，探索晶体取向分布对孪生-祛孪生的影响规律以及孪生-祛孪生和残留孪晶与塑性应变幅的关系规律，分析孪生机制对循环变形行为的作用；研究循环应变频率、应变路径、应变幅、合金织构及晶粒尺寸对循环变形机制及循环变形行为的影响及机理。在此基础上，得出织构特征、晶粒尺寸对不同载荷谱下的镁合金LCF性能的影响规律，为镁合金及其构件的抗低周疲劳设计提供理论依据。

针对镁合金循环变形中的孪生机制及其对变形行为的作用问题，选取了以应用最为广泛的AZ31B为代表的变形镁合金为研究对象，通过综合考量两种基本孪生的Schmid因子和CRSS，研究了孪生模式选择的综合判断依据，通过孪晶变体的识别，分析了Schmid因子序列规律，位移张量和应变张量与周围晶粒应变的协调作用关系以及应变协调过程，表明了孪晶变体选择机制，晶粒取向分布对孪生及其孪晶变体选择的影响规律；揭示了孪生-祛孪生和Bauschinger 效应的特征与机制，晶体取向分布对孪生-祛孪生的影响规律以及孪生-祛孪生和残留孪晶与塑性应变幅的关系规律，分析了孪生机制对循环变形行为的作用；研究了循环应变频率、应变路径、应变幅、合金织构及晶粒尺寸对循环变形机制及循环变形行为的影响及机理，得出织构特征、晶粒尺寸对不同载荷谱下的镁合金LCF性能的影响规律。除此之外，研究了复杂应力状态下取向因子的建立、计算与表征，为进一步研究复杂应力状态下镁合金变形行为与变形机制奠定了技术基础。