Vibration Characteristics And Fatigue Properties Of 2024-T351 Aluminum Alloy Treated By Cryogenic Assisted Laser Peening

Cryogenic assisted laser peening(CALP)technology is a new type of surface deformation strengthening technology based on the coupling effect between cryogenic temperature and ultra-high strain rate.The microstructure/stress enhancement effect superior to the conventional laser peening can be achieved by optimizing the microstructure and increasing the plastic deformation.Focus on the problem of vibration fatigue failure of aerospace aluminum alloys,the typical 2024-T351 aerospace aluminum alloy was selected as the research object in this paper.Surface mechanical properties,vibration modes,and vibration fatigue performance of aluminum alloy specimens treated by CALP were studied through a combination of theoretical analysis,experimental research and numerical simulation;Finally,the mechanism of vibration fatigue life extension of CALP-ed aluminum alloy materials was explored by combining with the observation and analysis of fatigue fracture morphology.The specific research contents are as following:(1)The microstructure and residual stress of aluminum alloys treated by cryogenic assisted laser peening were studied by using optical microscope(OM),transmission electron microscope(TEM)and residual stress analyzer,respectively.The effect of cryogenic assisted laser peening on the microstructure and residual stress of 2024-T351 aluminum alloy were investigated.Theoretically,the mechanism of cryogenic assisted laser peening was analyzed.And the effect of microstructure evolution of cryogenic assisted laser peening was described based on condensed matter physics theory.(2)The nano-indentation instrument was used to test and analyze the nanohardness and elastic modulus of the material,and the mechanism of laser hardening on the material hardening was explored;Taking the cantilever structure as the research object,vibration characteristics(natural frequency and damping ratio)of the samples treated by CALP and LP at different laser power densities were acquired,using a selfconstructed vibration modal test system,and the influence of the laser shot peening density on the natural frequency and damping ratio of the specimen was obtained.In addition,a mathematical model of aluminum alloy cantilever structures was established and numerical modal analysis was conducted,and the vibration mode and natural frequency of the modes of the sample were obtained.Based on the theory of vibration mechanics and K-G-L damping theory,the gain mechanism of cryogenic assisted laser peening on the natural frequency and damping ratio of the material was analyzed.(3)The vibration fatigue test system was used to test the fatigue performance of the vibration sample treated by cryogenic assisted laser peening,and the vibration fatigue life and natural frequency of the sample were obtained.The scanning electron microscope(SEM)was used to examine the fatigue fracture of the vibration sample.The characteristics of typical vibration fatigue fracture were analyzed based on fatigue and fracture theory,and the influence of CALP on the morphology of fatigue crack initiation region,fatigue crack growth region,and final rupture region of fatigue fractures was respectively studied;Finally,the mechanism of strengthening the vibration fatigue performance of 2024-T351 aluminum alloy treated by cryogenic assisted laser peening was explored.The research results show that the cryogenic assisted laser peening technology has prominent advantages in microstructure and stress strengthening,which can effectively improve the vibration characteristics and fatigue performance.