Study On Fiber Laser Scanning Welding Of 5052 Aluminum Alloy

With the development of science and technology and the progress of mankind,aluminum alloys have played a more and more important role in the production and life of human beings by virtue of its excellent characteristics,particularly in the fields of transportation and aerospace.It has become the preferred metal material for energy saving and emission reduction.The application of aluminum alloy promotes the welding of aluminum alloys.As a highly efficient and precise welding method,laser welding has been widely used in industrial production.However,due to the special physical properties of aluminum alloys,it is difficult to obtain excellent weld appearances for laser welding of aluminum alloys,and welding defects such as pores,cracks,and joint softening are easily generated,which greatly hinders the application of aluminum alloy laser welding.In order to solve the problems of poor welding quality and joint strength in laser welding of aluminum alloy,a laser scanning welding test platform for aluminum alloy was set up.The 5052 aluminum alloy with 5mm and 3mm thickness wa s taken as the research object.The characteristics of weld formation,flow rule of molten pool and mechanical properties of aluminum alloy under laser scanning welding were studied in detail.(1)The mechanism and technical characteristics of laser welding were introduced.The material characteristics of aluminum alloy and the technical difficulties of laser welding of aluminum alloy were summarized.The working principle of laser scanning welding head,the advantages,research status and development prospect of laser scanning welding were introduced.A laser scanning welding test platform for aluminum alloy with high speed camera system was built.(2)Single factor variable method was used to study the influence of the scanning amplitude and frequency on weld surface morphology and cross-section morphology under different scanning trajectories.The results show that the increase of the scanning frequency and scanning amplitude will reduce the energy of laser line and change the welding mode from deep penetration welding to heat conduction weld ing.The weld width will increase first and then decrease with the increase of scanning amplitude and frequency,and the weld penetration will continue to decrease with the increase of scanning amplitude and frequency.Compared with conventional laser welding,laser scanning welding can obtain better weld surface quality,and the fish scale pattern on the weld surface is more compact and uniform.(3)The aluminum alloy molten pool with different scanning trajectories was observed by high speed camera system,and the porosity of weld seam was measured under different scanning amplitude and frequency.The results show that compared with conventional laser welding,the length of weld pool is longer,the width of weld pool is increased to a certain extent,the cooling time of weld pool is also prolonged,and the porosity of weld is decreased significantly.Laser scanning welding accelerates pool flow and enhances pool stability.The "?" laser scanning welding has the best stability of the weld pool and the least amount of spatter,while the "8" laser scanning welding has the longest length of the weld pool and the longest cooling time.When the scanning amplitude is between 0.7~1.9mm and scanning frequency in 80~180Hz,the porosity of weld is lower than 2%.Laser scanning welding has a significant effect on the inhibition of porosity in the weld.(4)The tensile strength of laser scanning welded specimens was analyzed by orthogonal test of five factors and five levels.The influence of laser power,welding speed,defocus,scanning amplitude and scanning frequency on the ex perimental results was studied.The results show that in the "0" laser scanning welding,the scanning amplitude has the greatest effect on the tensile strength of the welded specimens,and the welding speed has the greatest influence on the tensile strength of the "8" laser scanning welding specimens,and in the "?" laser scanning welding,Laser power,welding speed and defocus almost have the same effect on tensile strength of welded specimens.