| Aluminum alloy has the advantages of small density,high strength,corrosion resistance and thermal conductivity,and its welding structure is used more and more widely in power machinery,shipbuilding,aerospace and other fields.However,the natural oxidation of aluminum alloy is easy to occur in the atmosphere,and a porous oxide film is formed on the surface of the aluminum alloy.The oxide film is easy to absorb water and dirt,which increases the source of hydrogen in the weld ing of aluminum alloy,thus resulting in the increase of hydrogen gas hole in the weld seam and the poor welding quality.Traditional film removal methods of mechanical grinding or chemical corrosion have many disadvantages,such as large labor intensity,polluted environment,damaged substrate material,low film removal efficiency,and laser cleaning of the surface oxide film of aluminum alloy has the advantages of small substrate damage,no pollution,simple process,wide adaptation and high efficiency.In view of this,the laser cleaning test platform and the laser-MIG arc composite welding test platform of aluminum alloy were built in this thesis.The laser cleaning test was carried out on the surface oxide film of 5A06 aluminum alloy,and the welding test was carried out on this basis,which proves the feasibility and superiority of the laser cleaning pretreatment to improve the welding quality of aluminum alloy.The specific research contents and conclusions are as follows:(1)The laser cleaning experiment of aluminum alloy was carried out by picosecond laser and fiber laser respectively.The effect of the laser average power,the laser spot overlap ratio,the laser scanning path overlap ratio and the auxiliary gas(air and argon)on the cleaning effect were studied by the full factor test method.The results show that,whether it is picosecond laser cleaning or fiber laser cleaning,the cleaning depth is positively related to laser power,but with the increase of laser power,the growth trend of cleaning depth gradually slows down.Reducing laser power will reduce the quality of cleaning,and after increasing the overlap ratio,the cleaning quality will be good again.When cleaning in air,the second oxidation of aluminum alloy surface will happen,the greater the average power,the more serious the second oxidation will be.Laser cleaning in argon can effectively avoid the second oxidation of aluminum alloy during cleaning.For picosecond laser cleaning,too large or too small overlap ratio will cause the roughness of the cleaning surface to increase and the surface morphology to become worse.When the average laser power is 100 W,the laser spot overlap ratio and the laser scanning path overlap ratio are both 40%,the auxiliary gas is argon,the cleaning effect is the best.For fiber laser cleaning,the roughness of the cleaning surface can be divided into three stages with the increase of the overlap ratio: maintaining high,rapidly decreasing and stabilizing.When the average laser power is 100 W,the laser spot overlap ratio and the laser scanning path overlap ratio are both 60%,and the auxiliary gas is argon,the cleaning effect is the best.(2)According to the results of laser cleaning experiment,the difference of the laser cleaning effect between fiber laser and picosecond laser was compared and analyzed from two aspects of cleaning quality and cleaning efficiency.The results show that fiber laser cleaning will cause serious melting of aluminum alloy surface,while picosecond laser cleaning does not exist.The surface roughness of fiber laser cleaning is large,and the surface roughness of picosecond laser cleaning is small.Under the best cleaning parameters,the cleaning depth of fiber laser i s larger,but the area cleaning efficiency and volume cleaning efficiency are not as good as picosecond laser.(3)On the basis of laser cleaning experiment,the experiment of aluminum alloy laser-MIG arc composite welding was carried out.The effect of pi cosecond laser cleaning pretreatment on the surface forming and the porosity of aluminum alloy weld seams was studied.The results show that the laser cleaning pretreatment can effectively improve the surface forming quality of aluminum alloy weld seams,and compared with the grinding method of the angle grinder,the collapse defects of weld seams surface caused by uneven grinding depth can be avoided.The surface oxide film has an important effect on the porosity of aluminum alloy weld seams.The porosity of aluminum alloy weld seams can be greatly reduced by laser cleaning pretreatment or grinding before welding in air,and the weld seam porosity of the aluminum alloy by laser cleaning in argon is the lowest. |
