Effect Of Laser Cleaning Process On Surface Microstructure And Properties Of High Strength Aluminum Alloy

As a new type of cleaning method,laser cleaning has the many advantages including high efficiency,good accessibility,environment-friendliness,easy to automation control.Laser cleaning has been widely used in cultural relics decontamination,tyre mould cleaning,paint cleaning,rust removal and so on.In order to promote the application of laser cleaning on pre-welding cleaning of high strength aluminum alloy in high-speed train industry,the influence of laser cleaning on the surface microstructure and performance of high-strength aluminum alloy A7N01 was studied through the four process parameters of laser cleaning including laser power,defocusing amount,laser pulse frequency and laser spot scanning speed.In this paper,the surface of the aluminum alloy A7N01 was observed and analyzed after laser cleaning treated by different laser power,defocusing amount,pulse frequency and spot scanning speed,composition analysis and roughness test were also carried out before and after cleaning.It was found that the surface of the material was tidewater-shape with nano-particles after laser cleaning.Laser cleaning breaks down the MgAl₂O₄ layer on the surface of A7N01aluminum alloy,and then generate a new MgO and Al₂O₃ mixed oxide layer.With different power of laser cleaning,the mass fraction of oxygen element on the material surface increases with the increase of power,and it is the lowest 2.52%when the power is 6 W;The oxygen mass fraction on the surface is symmetrical with the focal point when the laser cleaning with different defocusing amount,and the surface oxygen element mass fraction get the lowest 3.72%when the defocusing is-1 mm;When the laser pulse frequency is 900 kHz,the mass fraction of oxygen on the surface is the lowest 2.72%;With the spots scanning speed of laser cleaning increases,the oxygen mass fraction on the surface first decreases and then increases,it gets the lowest 3.58%when the scanning speed is 7000 mm/s.The surface roughness of the aluminum alloy after laser cleaning?x direction and y direction?is basically smaller than that in the corresponding direction of the original material and mechanical polishing.When the power is 24 W,the defocusing is 2 mm?-2 mm,+2 mm?,the pulse frequency is 700 kHz,and the scanning speed is 1000 mm/s,the roughness in the x direction get the maximum.The roughness in y direction get the maximum when the power is 12 W,defocusing+2 mm,pulse frequency is 700 kHz,and scanning speed is 9000 mm/s.Laser cleaning has no effect on the tensile performance,impact performance and surface hardness of A7N01 aluminum alloy,for there is no thickness loss found on the surface after laser cleaning,and the depth of laser cleaning influenting on A7N01 aluminum alloy is only4.78?m,which is about 0.956‰of the material thickness.Before and after the laser cleaning,the tensile strength was 325 MPa,the yield strength was 312 MPa,the elongation was 11.5%,the impact toughness was 19.5 J/cm²,and the hardness was 111.7 HV.The surface exfoliation corrosion performance of A7N01 aluminum alloy is closely related to the oxygen mass fraction on the surface and surface morphology.The electrochemical corrosion performance is closely related to the surface oxygen mass fraction.The higher the surface oxygen mass fraction,the faster the electrochemical corrosion rate and the more obvious the electrochemical corrosion tendency.When the power is 6 W,the defocusing is-1mm,the pulse frequency is 900 kHz,and the scanning speed of the spot is 7000 mm/s,the corrosion resistance is the worst,the maximum corrosion pit on the surface is the deepest,the electrochemical corrosion rate is the fastest,and the corrosion tendency is the most obvious.Laser cleaning has an effect on the surface structure and corrosion resistance of A7N01aluminum alloy with a thickness of 5 mm,but has no effect on the mechanical properties.It can replace the traditional cleaning method under certain conditions.