| As the light metallic materials with high specific strength and high specific rigidity, magnesium alloys have been widely used in automobile, aeronautical, computer and communication fields. 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 behavior of magnesium alloys is of both academic and practical significance. In this investigation, the strain-controlled fatigue deformation and fracture behaviors of extruded Mg-Mn-Si-RE 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 fatigue tests reveal that at all total strain amplitudes used in this investigation, the alloys with different treatment states exhibit the cyclic strain softening, cyclic strain hardening or stable cyclic stress response, which mainly depends on the imposed total strain amplitude and heat treatment state. At the total strain amplitudes above 0.45%, the heat treatment leads to a reduction in the cyclic stress amplitude during whole fatigue deformation of the extruded Mg-Mn-Si-RE alloy, where the decreasing degree in the cyclic stress amplitude is the maximum for the extruded Mg-Mn-Si-RE alloy subjected to solid solution treatment. It is noted that solid solution plus aging treatment can increase the fatigue life of the Mg-Mn-Si-RE alloy at the higher total strain amplitudes, while either solid solution or aging treatment usually decreases the fatigue life of the alloy. For the extruded Mg-Mn-Si-RE alloys with different treatment states, the relations between elastic strain amplitude, plastic strain amplitude and reversals to failure can be described by Basquin and Coffin-Manson equations, respectively. A linear relationship between calculated tensile hysteresis energy and strain fatigue life has been noted, and can be used for predicting the strain fatigue lives of the extruded Mg-Mn-Si-RE alloys with different treatment states. In addition, the relations between cyclic stress amplitude and plastic strain amplitude present bilinear behavior for the extruded Mg-Mn-Si-RE alloys subjected to different treatments. The observations on fracture surface of fatigued specimens reveal that for extruded Mg-Mn-Si-RE alloys with different processing states, the fatigue cracks initiate in a transgranular mode at the surface of fatigue specimens, and propagate transgranularly. In addition, so-called cleavage feature can be found in the fatigue crack growth region.
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