Low Temperature Fatigue Deformation And Fracture Behavior Of Al-7.5Zn-2Mg-2Cu-0.2Sc-0.1Er Alloy

The research on the fatigue properties of aluminum alloy materials is very deep and extensive,the research on the fatigue deformation behavior of aluminum alloy within low temperature environment is very few,and the microstructure evolution and deformation mechanism during fatigue deformation of the aluminum alloy under low temperature conditions are still unclear.Al-Zn-Mg-Cu serial aluminum alloys as experimental material,this paper studied the tensile strength,yield strength and fracture elongation of Al-7.5Zn-2Mg-2Cu-0.2Sc-0.1Er alloy and its fatigue deformation behavior after single aging,double aging and regressive reaging at room temperature,-15? and-30?,respectively.The influence of low-temperature environment on low cycle fatigue behavior of Al-Zn-Mg-Cu series aluminum alloy was analyzed;the fatigue deformation mechanism of the alloy within low temperature environment was studied specifically.This paper also analyzed the microstructure evolution within the alloy during fatigue deformation at low temperatures and its influence on the fatigue deformation behavior.Tensile results show that the tensile strength and yield strength of Al-7.5Zn-2Mg-2Cu-0.2Sc-0.1Er alloy were considerably improved after single aging,double aging and regressive reaging state.For all three kinds of aging treatment processes,the internal precipitate size of the Al-7.5Zn-2Mg-2Cu-0.2Sc-0.1Er alloy after regressive reaging is the smallest and the strengthening effect is the best;the tensile strength,yield strength and elongation of the alloy at peak aging state are 682.2MPa,650.9MPa and 12.3%,respectively.Fatigue experiment results at room and low temperatures show that under the condition of low cycle fatigue with the same applied total strain amplitude,the Al-7.5Zn-2Mg-2Cu-0.2 Sc-0.1Er alloy after regressive reaging shows cyclic stress response behavior with cyclic stability at room temperature,-15? and 30?.At room temperature,-15?and 30?,the fatigue life of Al-7.5Zn-2Mg-2Cu-0.2Sc-0.1Er alloy decreased greatly with decreasing temperature.Under the condition of low cycle fatigue loading with the same external total strain amplitude,the plastic strain amplitude,elastic strain amplitude and loading inversion number for the Al-7.5Zn-2 Mg-2Cu-0.2Sc-0.1Er alloy after regression treatment are consistent with Coffin-Manson and Basquin,respectively.The fatigue crack at room temperature,-15? and-30? initiated on the fatigue specimen surface by means of trans-granular mode and expanded trans-granularly.In the process of low cycle fatigue deformation with the same external total strain amplitude,the amounts of dislocation net configuration and sub-grain boundaries formed within Al-7.5 Zn-2 Mg-2 Cu-0.2 Sc-0.1 Er alloy at-30? temperature increased much more.