Study On The Porosity Inhibition Of 6061 Aluminum Alloy With High Power Solid Laser Scanning Welding Process

Aluminum alloy with high specific strength,lightweight,corrosion-resistant,good electrical and thermal conductivity is an important material in the area of manufacturing such as aerospace,transportation and weapons etc.Laser welding with the advantage of high welding speed,small thermal damage,low deformation and more and more receives takes in the welding of aluminum alloy.Welding porosity is the major problem produced by deep penetration laser welding of Aluminum alloy.Welding of aluminum could be attributed into"Metallurgical feature-type" porosity and "process-type" porosity according to the formation reasons,"process-type" porosity are the type of pores that are peculiar to the deep penetration laser welding of aluminum alloy,the traditional ways of inhibiting porosity such as cleaning impurities on the work piece before welding and good protection during welding cannot restrain such porosity which is nearly impossible to avoid especially in the incomplete penetration structure,which has affected the application of laser welding of aluminum alloy.In this paper a high-power solid laser scanning welding technique was developed for the welding of 6061 aluminum alloy.The effect of welding parameters such as scanning trace,scanning amplitude and scanning frequency on the weld appearance and porosity inhibition of aluminum laser scanning welding was studied.Research showed that the scanning of laser beam perpendicular to the weld,parallel to the weld and adopting circular trace had inhibitory effect on the welding porosity and the adopting the circular trace restrained the porosity more effectively.Different scanning amplitude and frequency restrain the porosity differently,Using circular scanning mode,under the condition of 4 kw in laser power,2m/min in welding speed,laser scanning welding was very difficult to suppress the generation of porosity when the scanning amplitude was less than 0.3 mm;When scanning amplitude ranged from 0.4 mm to 0.6 mm,the porosity rate can satisfy the standard of ISO laser welding class B(the most stringent)with the corresponding scanning frequency 150Hz-220Hz;When scanning amplitude greater than 0.7 mm,the laser hole features disappeared,so the "process-type"porosity cannot happen.The porosity inhibition of laser scanning welding was closely related to the welding appearance.Research have showed that no matter using what kind of scanning parameters,when the weld depth width ratio was below 0.85,all the "process-type" porosity can be restrained and controlled below 3%.On the basis of studying the laws of the effect of scanning parameters on porosity inhibition and weld appearance,using high speed camera and methods of mathematical statistics,the fluctuation characteristics of laser-caused plasma and laser keyhole under the conditions of different laser scanning welding were studied and the comparison with conventional laser welding were analyzed.Research have showed that there existed a process that the plasma caused whether by scanning laser or conventional laser were from producing to disappearing,and the size of the plasma produced in the welding process was changing continuously.Compared with conventional laser,scanning laser's fluctuation frequency which was from producing to disappearing was about 1/3 as much as that of conventional laser welding,and the standard deviation of fluctuation of plasma area was about 1/2 to conventional laser welding.The keyhole in conventional laser welding were from producing to disappearing,however,there was no disappearing process of the holes in the scanning laser welding.Statistical analysis showed that the open area of the holes in scanning laser welding was about 2 times as much as that of conventional laser welding.The physical phenomena mentioned above was the main reason that the scanning laser welding can restrain the occurrence of "process-type" porosity.