Effect Of Laser Cleaning Of Corrosion Layer On 6061-T6 Aluminum Alloy On Corrosion Resistance And Welding Quality

The C80 type coal transportation train is a special train designed and manufactured in China for the coal transportation of the Datong-Qinhuangdao Line.Due to the extensive application of aluminum alloys on the train body,its own weight is significantly reduced and its carrying capacity is significantly improved.However,due to the particularity of the service environment,it is necessary to spray a large amount of antifreeze containing chloride ions when transporting cleaned coal in winter to ensure normal transportation.The use of this kind of antifreeze will cause corrosion of the aluminum alloy of the train body and reduce the life of the train.The corrosion layer on the surface of the train body not only affects the appearance,but also affects the welding quality of it,but it has a certain resistance to the corrosive antifreeze.In the maintenance and factory repair stages,in order to ensure the quality of the train body welding and repairing,mechanical cleaning methods are usually used to remove the corrosion layer on the aluminum alloy surface of the train body.Although mechanical cleaning can effectively remove the corrosion layer on the surface,it will cause certain damage to the aluminum alloy of the train body,which will reduce the resistance to antifreeze.Therefore,it is very important to obtain a cleaning method that can remove the corrosion layer on the surface to ensure the quality of welding repairs,and at the same time,the corrosion resistance of the surface to antifreeze is not reduced.In this paper,laser cleaning is used to remove the corrosion layer on the surface of 6061-T6 aluminum alloy for C80 coaltrain.The following are the main research contents:By simulating the service environment of the C80 coal train,the 6061-T6 aluminum alloy used in the car body was prepared by alternating dry and wet experiments in 33wt.%Ca Cl₂ solution to prepare the corrosion layer.The composition and morphology of the corrosion layer were characterized and analyzed by field emission Scanning Electron Microscope（SEM）and Energy Dispersive Spectrometer（EDS）.It was found that the corrosion layer formed on the surface of the aluminum alloy was mainly composed of cracked oxides and flocculent particles.The optimal process parameter window for laser cleaning 6061-T6 aluminum alloy surface corrosion oxide layer was obtained by orthogonal experiment,and the effects of various process parameters（laser power,scanning speed,scanning spacing,pulse frequency）on the oxygen content and roughness of the laser-cleaned aluminum alloy surface were analyzed by single-factor experiments.The results show that when the laser pulse width is60ns,under a specific process parameter window,the oxygen content on the surface of the aluminum alloy decreases with increasing laser power,decrease with increasing scanning speed,decreases with increasing scanning spacing,and shows an upward trend with the increase of pulse frequency;The surface roughness decreases with increasing laser power,increases with increasing scanning speed,shows a trend of decreasing first and then increasing with the increase of scanning spacing,and shows an upward trend with the increase of pulse frequency.Combining the surface oxygen content and surface roughness,it is obtained that when the pulse width is 60ns,the optimal laser cleaning process parameters for the corrosion oxide layer on the surface of 6061-T6 aluminum alloy are:laser power 90W,scanning speed 6000mm/s,scanning spacing 0.03mm,pulse frequency 2000k Hz.Combined with the morphology and composition of the corrosion layer,two mechanisms of pulse laser cleaning of the corrosion layer were expounded.Through the observation of the pulsed laser cleaning process by high-speed camera and the analysis of the composition and morphology of the aerosol particles generated in the pulsed laser cleaning process,combined with the theory,it is concluded that the pulse laser cleaning mechanism of the corrosion layer on the surface of 6061-T6 aluminum alloy is a mixed mechanism of“ablation gasification and thermal vibration”.Through X-ray Photoelectron Spectroscopy（XPS）technology,the surface composition of the original specimen,laser cleaning specimen and mechanical grinding specimen was analyzed.Results show that mechanical grinding and laser cleaning can well remove the corrosion layer composed of Al（OH）₃+Al₂O₃+Mg O on the original surface,and the surface corrosion resistance of the aluminum alloy surface after mechanical grinding is reduced due to the exposure of part of the aluminum matrix,and the surface of the aluminum alloy after laser cleaning is reduced due to the formation of a new and more dense and uniform Al₂O₃+Mg O oxide film increases surface corrosion resistance.The absorptivity of the original sample,the mechanically polished sample and the surface of the laser-cleaned sample to the laser with a wavelength of 1064 nm was compared.After laser cleaning,the aluminum alloy surface has the highest absorption rate of laser light,followed by the original surface,and the mechanically polished surface is the lowest.Through the laser-MIG hybrid welding experiment,it is found that the aluminum alloy weld seam formed by laser cleaning before welding is the best.Because the laser cleaning removes the surface corrosion layer,the absorption and utilization rate of the surface to the laser is improved,so that the weld penetration is the largest,and the welding seam porosity is the lowest.