Research On Low-Cycle Fatigue Behavior Of Hot-Extruded AZ31 Magnesium Alloy

As the light metallic materials with high specific strength and high specific rigidity, magnesium alloys have been widely used in automobile industry. Thus, how to utilize safely magnesium alloys has been paid much more attention. Fatigue is a main failure form of various structural components during operation. For the magnesium alloy components, the same case is also true. Therefore, the investigation concerning fatigue and fracture behavior of magnesium alloys is of both academic and practical significance. In this investigation, the strain-controlled fatigue deformation and fracture behaviors of extruded AZ31 alloys with different treatment states has been studied in order to provide a reliable theoretical foundation for both fatigue resistant design and reasonable usage of this magnesium alloy.The results of low-cycle fatigue tests reveal that the hot-extruded AZ31 alloys withdifferent treatment states at various strain amplitudes exhibit the cyclic strain hardening. The heat treatment can enhance the cyclic stress amplitude at the lower total strain amplitudes of the hot-extruded AZ31 magnesium alloy. The solution plus aging treatment leads to a reduction in the cyclic stress amplitude at the higher total strain amplitudes. It is noted that the heat treatment can enhance the fatigue lives of the alloy at higher total strain amplitudes, while leads to a reduction in the fatigue lives of the hot-extruded AZ31 alloy at lower total strain amplitudes. For the hot-extruded AZ31 alloys with different treatment states, the relations between elastic strain amplitude, plastic strain amplitude and reversals to failure are linear and can be described by Basquin and Coffin- Manson equations, respectively. In addition, a linear relationship between cyclic stress amplitude and plastic strain amplitude is also noted for the hot extruded AZ31 alloys with different treatment states. It has also been observed that when the hot-extruded AZ31 alloys with different treatment states is subjected to fatigue deformation at the total strain amplitudes is bigger than or equal to 0.6%, the width of theσ-εhysteresis loop in the tensile direction is greater than that in compressive direction, and the maximum tensile stress is significantly higher than the maximum compressive stress. The alloys exhibit the pronounced anisotropic deformation behavior in the direction of tension and compression.The observations on fracture surface of fatigued specimens reveal that for hot-extruded AZ31 alloys with different treatment states, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly. In addition, the cleavage fracture feature can be found in the fatigue crack growth region.