Research On Pretreatment Mechanism And Experiment Of 6061 Aluminum Alloy By Nanosecond Laser Before Welding

The welding of aluminum alloy technology has a wide range of applications and developments in the industrial production,manufacturing and maintenance field.Due to the fact that the aluminum alloy has good thermal conductivity?about 3 times that of steel materials?,a large coefficient of linear expansion?about 2 times that of steel materials?and high specific strength,it exists questions that porosity,loss of alloying elements and cracking,etc.after laser welding.In order to reduce the occurrence of laser welding defects,it is necessary to conduct the surface pretreatment of the aluminum alloy before welding.Laser pretreatment before welding is a novel method.The laser pretreatment before welding refers to that the laser directly acts to the surface of the aluminum alloy material and the surface oxide absorbs the laser energy.And then the surface oxide rapidly undergoes vaporization,ionization,etc.phenomenon and is removed from the surface of the aluminum alloy,which achieve removal aim.The laser pretreatment before welding has the advantages of green,non-contact,non-destructive,localized fine removal and easily integration of welding equipment.At present,there are literatures reveling that the laser surface pretreatment before welding can solve the problem of welding defects,but the research is in the starting stage.It exists a large research space that the laser-oxide interaction mechanism,the effect of laser parameters on the quality of pretreatment before welding,and the on-line inspection technology of the pretreatment process.In this paper,combining with theoretical and experiment,the surface pretreatment technology of 6061 aluminum alloy by nanosecond pulse laser was researched.the effect of surface condition on quality of the weld was characterized by the laser welding experiment,which solved the problem of porosity defects of aluminum alloy after welding.The heat conduction equation was used to research the mechanism of the interaction between laser and aluminum alloy materials,which was used as the theoretical basis for laser pretreatment of aluminum alloy surface.Laser-induced breakdown spectroscopy?LIBS?technology was applied to on-line test the aluminum alloy surface condition of laser pretreatment and a method for quality evaluation of laser pretreatment before welding was proposed.The laser cleaning threshold and damage threshold were tested.The regularity of surface oxygen content with the variety of laser parameters was significantly researched and the optimum process parameters were obtained.The main research content was as follows:1.The mechanism of laser surface pretreatment was analyzed theoretically.The MATLAB simulation software was adopted to acquire temperature-rising law of material surface with the variety of laser parameters.According to the melting line of6061 aluminum alloy?660??and gratification line of Al₂O₃?2977??,the removal threshold of oxide on the aluminum alloy and the damage threshold of the aluminum alloy matrix was obtained.The laser pretreatment mechanism before welding was established to provide a theoretical basis for the following research.2.The quality of surface pretreatment was on-line tested.Using the echelle grating spectrometer,by comparing the difference of the spectral characteristics before and after laser cleaning,the material composition of the current cleaning material was obtained,which determined the residue situation of surface oxidation.The experiment verified the single measurement certainty of the laser-induced breakdown spectroscopy technology by multiple measurements and statistics of the intrinsic constituents in the air.3.Laser surface pretreatment technology of 6061 aluminum alloy was researched experimentally.The surface characteristic of the interaction between single pulse laser and aluminum alloy was tested,which obtained the laser cleaning threshold and damage threshold.Scanning electron microscope was used to observed the surface morphology and X-ray energy spectrum was used to analyze the surface composition.It was found that by the line-scan and surface-scan,the uniqueness of the oxygen distribution on the aluminum alloy surface pretreated by the laser.By researching the influence of laser parameters factors on the surface quality of the aluminum alloy,the optimal process parameters of the 6061 aluminum alloy surface pretreated by the laser before welding were obtained.4.The effect of laser cleaning on the quality of weld was characterized.The aluminum alloy surface pretreatment by laser before welding was performed using the optimal process parameters.The X-ray inspection machine was used to non-destructive detected the weld quality of laser pretreatment material before welding.The results showed that the surface pretreatment before welding helped to form a good weld morphology.The surface pretreatment technology by laser before welding,compared to the ordinary pretreatment methods?sandpaper polishing?,greatly reduced the generation of pore defects.