Research On Laser Removal Process And Performance Of Q345 Surface Pollutants

The surface of the material will produce pollutants during long-term service.In order to improve its service life,it is necessary to clean up the polluntants on the surface of the material in time,such as rust,paint layer and mixed pollutant composed of rust and paint layer.Thus,the research on laser cleaning of the rust layer,the paint layer and the mixed pollutant of Q345 steel was carried out.By changing laser power,frequency,speed and other process parameters,the characterization of the surface morphology,the element distribution and the roughness would be evaluated quantitatively using stereo microscope,scanning electron microscope,energy spectrum analyzer and confocal laser.In addition,the corrosion resistance and hardness of the cleaned materials would be tested using electrochemical workstation and vickers hardness tester.The results are as follows:In the preliminary exploration of the rust removal and paint removal process,the paint and rust removal effect could be improved by higher laser power,and the laser rust and paint removal effect was better at laser power of 200 W.The scanning speed had a greater influence on the cleaning effect.The effect of the laser could be enhanced under a lower scanning speed.The distribution and content of chemical elements could be used to further judge the cleaning quality.The results of laser cleaning the rust layer shows that when the scanning speed was less than 1000 mm/s,the substrate would be damaged by laser greatly;when the scanning speed reached 5000 mm/s,some rust remained on the surface of the material;when the scanning speed was 3000 mm/s,the substrate would not be damaged.As the scanning speed increased from1000 mm/s to 6000 mm/s,the Fe content on the surface of Q345 steel after cleaning had a trend of firstly increasing and then decreasing,while the O content was firstly decreasing and then increasing.When the scanning speed was 3000 mm/s,the Fe content after cleaning the surface of Q345 steel reached the peak value of about 90 %,the O element content reached the valley value of about 7%,the compound of Fe and O was less,and the surface roughness of the material was Ra ? 6.9 ?m.At the same time,the electrochemical corrosion performance of the Q345 steel surface was improved after laser cleaning.The result of laser cleaning the paint layer shows that the cleaning quality could be affected by the scanning speed and the cleaning speed.When the scanning speed was 1500 mm/s and the cleaning speed was 7 mm/s,the surface of the material after cleaning was relatively flat and the residual paint layer was less.In addition,the content of Fe and C elements on the surface of the material reached 89 % and 9 %,respectively.Observed by the three-dimensional topography,the roughness was at least 0.5 ?m.After laser cleaning at two scanning speeds of 500 mm/s and1000 mm/s,a layer of fine grains appeared on the surface of the material.The maximum hardness of the fine-grained layer was greater than 400 HV,which was about twice that of the base metal.The result of laser cleaning mixed pollutant shows that when other parameters were constant,with increasing the laser power,the content of Fe element increased,and the content of C and O elements decreased,and the melting effect on the surface of the material was more obvious.When the laser power was 200 W,the residual contaminants were less,but the roughness was higher at 23.4 ?m.Increasing the pulse frequency could improve the effect of the light spot.When the pulse frequency was 100 k Hz,the Fe content on the surface of the cleaned material reached 92 %,and the roughness was only 2.4 ?m.Therefore,the cleaning quality could be improved through enhancing peeling of mixed pollutant as a result of increasing pulse frequency.