Experimental And Mechanism Study On Pulse Laser Cleaning 7075 Aluminum Alloy Anodic Oxide Film

7075 aluminum alloy is often used in the manufacturing stress structural components such as aircraft frames and wing beams due to its lightweight and outstanding mechanical properties.When serving in a marine salt spray atmospheric environment,friction between structural components and the effects of a salt spray atmosphere will inevitably wear,crack and spall.The damaged oxide film can not effectively protect the surface of aluminum alloy,so that aluminum alloy substrate and air direct contact.Direct contact between the aluminum alloy substrate and the air may even cause corrosion of the aluminum alloy substrate,affecting navigation safety.As a result,the aircraft will be inspected and serviced regularly.In order to remove the damaged anodic oxide film on the surface of the aluminum alloy substrate without damaging it,and to improve the corrosion resistance of the aluminum alloy substrate,laser cleaning technology is used to remove the original anodic oxide layer on the surface of the aluminum alloy in this research.The impact of laser process parameters on the surface temperature field,stress field,surface properties and corrosion resistance has been investigated through simulation analysis and experimental studies.The main research contents are as follows:(1)The finite element simulation model of nanosecond pulsed laser cleaning of 7075 aluminum alloy substrate surface anodic oxide film was established to simulate the temperature field,stress field and removal process during laser cleaning.The effects of laser process parameters(average power,pulse frequency,and scanning speed)on the surface temperature and stress fields of the sample were investigated,and the removal process of anodic oxide film and the generation process of substrate surface morphology were also studied.The surface temperature field nephogram,temperature variation curve,and thermal stress variation curve of the anodic oxide film under different laser process parameters were obtained.Furthermore,the impact laws of the laser process parameters on the surface temperature field,stress field and sample removal morphology were summarized.These provides theoretical guidance for laser cleaning process test and mechanism analysis.(2)Pulse fiber laser was used to clean 7075 aluminum alloy anodic oxide film.The effect of the average power,pulse frequency,and scan speed on the surface morphology and composition after cleaning were investigated,the effect of the laser cleaning process parameters on the surface cleaning rate and surface roughness was also obtained.When the average power is 250 W,the pulse frequency is 2.5k Hz,and the scanning speed is 2500mm/s,the oxide film is almost cleaned,the highest cleaning rate is 98.7%,and the surface roughness Sa is 0.45μm.Coupled effects of ablation gasification,phase explosion,and elastic vibrational stripping mechanisms have been found in laser-cleaned stress field simulations and process experiments on anodized oxide films on the surface of aluminum alloys.As the ablation temperature increases,the ablation gasification effect increases.(3)The microhardness and hydrophobicity of the samples after laser cleaning were measured,and the corrosion resistance of the samples surface was studied.The effects of laser parameters(average power,pulse frequency and scanning speed)on the microhardness,hydrophobicity and corrosion resistance of the cleaned sample surface were obtained.The results show that the corrosion resistance of the sample surface can be improved under suitable laser cleaning parameters(average power is 250 W,pulse frequency is 2.5k Hz,scanning speed is 2500mm/s).