Experimental Study On Pulsed Laser Cleaning Of 2024 Aluminum Alloy Oxide Film And Its Mechanism

The low density and high strength of 2024 aluminum are widely used as parts of aircraft.The anodic oxide film on the surface of the aluminum alloy needs to be removed when the aircraft is overhauled or secondary painted.The laser cleaning finite element simulation and process test were conducted to analyze the cleaning effect and removal mechanism of the laser cleaning oxide film with the results of the process experiment,and the performance test of the cleaned 2024 aluminum alloy was conducted.Through finite element simulation and analysis,the effect law of different energy densities and different cleaning speeds on the maximum temperature of the aluminum alloy surface,the degree of temperature rise and the rate of temperature rise was obtained.It is found that the higher the energy density,the higher the temperature of the rectangular moving heat source.When the laser energy density q=30.89J/cm~2,the temperature of the center part of the rectangular heat source can reach 970℃.With the increase of cleaning speed,the temperature of the aluminum alloy surface oxide film gradually becomes smaller.The oxide film deformation under the action of more uniform energy is irregular,and the degree of oxide film strain in the local area reaches 0.0103 mm per unit time,which provides a reference basis for the subsequent process test.By constructing the response surface prediction equation of roughness value and using indicators such as significance and complex correlation coefficient,the reliability ANOVA was performed on the prediction equation to obtain the law of response surface interaction of different process parameters on roughness value.The study shows that: at higher energy density,higher pulse frequency and lower cleaning speed,the lower roughness value Ra=0.355μm of the aluminum alloy surface can be obtained.Through laser cleaning process experiments,the effect of cleaning effect on 2024 aluminum alloy surface including macroscopic morphology,microscopic morphology,surface oxygen content and roughness were investigated.It is found that when the laser power is 400 W,the pulse frequency is5.5k Hz,the cleaning speed is 4mm/s,a more ideal cleaning effect can be obtained.When the appropriate laser power(P≤400W)removes the 2024 aluminum alloy oxide film,the explosion fragmentation disintegration mechanism mainly occurs,and when the laser power exceeds 400 W,coexistence of ablation melting and explosive fracture disintegration mechanisms.By exploring the influence of laser process parameters on surface microhardness,tensile strength,elongation at break and wear resistance,it is found that the elongation at break of aluminum alloy surface is reduced to 3.54% when the surface is cleaned with appropriate process parameters(laser power is 400 W,pulse frequency is 5.5k Hz,cleaning speed is4mm/s).The hardness is slightly increased to 134.2HV,and the surface has better wear resistance.