Reserch On The Work-hardening Behavior And Numerical Simulation Of Heat Generation Of AZ31B Magnesium Alloy Under Cyclic Loading

Magnesium alloy has been widely used in aerospace, automobile manufacturing and other fields for its light weight, high strength and stiffness, good electrical and thermal conductivity, and can be all recovered without pollution, and its subject to fatigue loading has become the weakness to limit its widespread use. Fatigue fracture often leads to serious accidents for its suddenness, so the research on fatigue property of magnesium alloy can provide scientific basis for its application under the cyclic loading. Infrared thermography is a non-contact and real-time method, which is widely used in the study of fatigue properties of metallic materials, and deeply explores the fatigue failure based on the energy dissipation in the process of fatigue. Therefore, it is of practical value and significance to study the fatigue of magnesium alloy by using infrared thermography. The fracture process of metallic materials under cyclic loading mainly includes: the work-hardening / softening behavior under cyclic loading, crack initiation, crack propagation and final fracture. Therefore, it is significant to study the work-hardening behavior of magnesium alloy under cyclic loading. In this paper, the work-hardening behavior of AZ31 B magnesium alloy under cyclic loading is studied, and the following conclusions are obtained:The temperature evolution of AZ31 B magnesium alloy in the fatigue process has been studied using infrared thermography. The results show that there are five different stages during the temperature evolution. The workhardening leads to the initial rapid temperature rise and the sharp temperature drop. The microstructures of AZ31 B magnesium alloy under different cycles were observed by transmission electron microscope. It shows that there are proliferation and annihilation of dislocations in the fatigue process. The proliferation and annihilation and the cyclic hardening/softening and the change of temperature have a good corresponding relationship. The variation of hysteresis loop in fatigue process was studied. The results show that the area of hysteresis loop has a good relationship with the change of temperature and the proliferation of dislocation.Tensile test(with post-fatigue) was conducted to quantify the workhardening/softening behavior. It shows that the tensile strength increase first, then decrease and increase again with the fatigue cycles. When the cyclic loading is below 130 MPa, the tensile strength increases with the increase of post-fatigue loading. When the cyclic loading is 130 MPa, the fatigue damage leads to the decrease of tensile strength. The variation of tensile strength has a good agreement with cyclic-hardening/softening behavior during fatigue process. The temperature change of the tensile process was studied by using infrared thermal imaging system. The results show that the maximum temperature rise in the tensile process can reflect the phenomenon of the work-hardening and softening of the material during the fatigue process. The microstructures were studied after tensile tests by optical microscope. It shows that there is a large number of twinning after tensile tests in the post-fatigue specimens due to the dislocation. The scanning electron microscopy was used to investigate the fracture morphology, and the results show that the micro fracture mechanism is quasi cleavage fracture.The temperature evolution of magnesium alloy during the fatigue process was simulated using the finite element software ABAQUS. It shows that the simulations with the kinematic hardening model are in good accordance with the temperature evolution curves of the fatigue test, which proves the heat producing mechanism of the magnesium alloy and the work-hardening behavior under the cyclic loading.