Cyclic Deformation And Fracture Behavior Of Hot-extruded Al-Mg-Si-Er Alloys

Due to such excellent comprehensive properties as good electric conductivity and high specific strength, aluminum alloys have been widely applied in industrial fields such as bridge architecture, electric engineering and electronic engineering. The Al-Mg-Si series aluminum alloys exhibit good thermoplasticity and excellent corrosion resistance, and have received much attention in recent years. In order to improve their comprehensive properties, the rare earth elements with appropriate content are often added into the Al-Mg-Si series aluminum alloys. In this investigation, the low-cycle fatigue behavior of the extruded Al-0.8%Mg-0.6%Si and Al-0.8%Mg-0.6%Si-0.5%Er alloys at room temperature was studied, and the influence of rare earth element Er and solid solution plus aging (T6) treatment on the low-cycle fatigue behavior of the Al-0.8%Mg-0.6%Si series aluminum alloys was determined.The results show that the addition of rare earth element Er can refine the grains of the Al-0.8%Mg-0.6%Si alloys with both as-extruded and solid solution plus aging states. The extruded Al-0.8%Mg-0.6%Si shows the cyclic strain hardening, softening and stability. However, the extruded Al-0.8%Mg-0.6%Si-0.5%Er exhibits the cyclic strain hardening and stability. The addition of rare earth element Er can enhance the cyclic deformation resistance of as-extruded Al-0.8%Mg-0.6%Si alloy obviously. The solid solution plus aging treatment can increase the cyclic deformation resistance of the extruded Al-0.8%Mg- 0.6%Si and Al-0.8%Mg-0.6%Si-0.5%Er alloys. For the extruded Al-0.8%Mg-0.6%Si and Al-0.8%Mg-0.6%Si-0.5%Er alloys with both as-extruded and solid solution plus aging states, the relationship between reversals to failure with plastic strain amplitude can be well described by the Coffin-Manson equation, while the relationship between reversals to failure with elastic strain amplitude obeys the Basquin equation. The addition of rare earth element Er will decrease the low-cycle fatigue lives of as-extruded Al-0.8%Mg-0.6%Si alloy, but can prolong the low-cycle fatigue lives of the solid solution plus aging treated Al-0.8%Mg-0.6%Si alloy at higher imposed total strain amplitudes. The solid solution plus aging treatment is beneficial for improving the low-cycle fatigue lives of the extruded Al-0.8%Mg-0.6%Si alloy at lower imposed total strain amplitudes, and can also enhance the low-cycle fatigue lives of the extruded Al-0.8%Mg-0.6%Si-0.5%Er alloy at each imposed total strain amplitude. The relationship between the cyclic stress amplitude and plastic strain amplitude can be described by a power law. For the Al-0.8%Mg-0.6%Si and Al-0.8%Mg-0.6%Si-0.5%Er alloys with both as-extruded and solid solution plus aging states, the fatigue cracks initiate on the surfaces of fatigue specimens, and propagate transgranularly.