The effect of beam oscillation on laser welding of AA2219-T87 under subatmospheric pressure

Abstract

Aluminum alloy AA2219 is widely used in the aerospace industry due to its high specific strength, and corrosion resistance, especially for the production of propellant tanks of space rockets. With the rapid development of laser sources, the welding of metal materials changes gradually from arc welding to laser welding, but pore defect drags the application of laser welding of aluminum alloy. To solve this bottleneck problem, this paper investigates the effect of laser beam oscillation on welding of AA2219 under subatmospheric pressure (LOWSP). The experimental results showed that LOWSP has significantly improved the surface morphology, penetration depth, microstructure,and mechanical properties of the weld seam. The EBSD testing analysis shows that the low-angle grain boundaries (LAGBs) take up the largest proportion in the microstructure with the increased proportion of equiaxed grains, and the grain size is further refined in LOWSP. When welded at the optimal laser beam oscillation frequency of 80 Hz under the pressure of 102 Pa, the pore was almost inhibited and the tensile strength of the weld seam reached 388.62 MPa, up to 83.16% of the base metal (the current level of the industry is generally between 300 ∼ 360 MPa). It is believed that the reduced boiling point of the aluminum alloy under subatmospheric pressure accelerated the molten metal flow rate, the stirring effect of laser beam oscillation on weld microstructure within molten pool significantly eliminate porosity, therefore the LOWSP process generated the refined grain size and the improved mechanical properties of the weld seam.