| Laser welding of aluminum alloys has disadvantages such as poor stability,poor morphology,and severe porosity defects,which restricts the application of laser welding in aluminum alloy joints.Laser oscillating welding was proven effective in reducing porosity and improving weld morphology.Currently,most of the studies were performed by using the mechanical laser beam oscillation head that could not achieve a complex laser beam oscillation path and high-frequency oscillation.In this paper,a new laser welding head with two wedge-shaped lenses to shift the beam was used to study the effects of high frequency and large-scale circular oscillating on the morphology of 5083 aluminum alloy welds and the suppression of porosity defects.The influence of laser oscillation on the microstructure and mechanical properties of the weld was explored.Firstly,the influence of oscillating amplitude,oscillating frequency,and defocus amount on the morphology of 5083 aluminum alloy weldding was studied through a single factor experiment.A process window was established and the mechanism of laser oscillation on weld morphology was revealed.With the oscillating diameter being changed from 0mm to3.0 mm,the weld penetration depth decreased significantly and the aspect ratio of the weld was increased.By using laser oscillation welding,the weld defects such as spatters,beads and undercuts were suppressed and the morphology was improved.When the amount of defocusing distance was above 0mm,the weld morphology was sound.The test results showed that the process range of the aluminum alloy laser oscillation welding was as follows:defocusing distance 0mm?+4mm,oscillating diameter 2mm?2.5mm,oscillating frequency 200Hz?300Hz.By analyzing the motion trajectory of the circular oscillating laser spot,the energy of the laser oscillating welding line was calculated.Combined with the laser energy distribution of oscillating welding,the influence of oscillating characteristic parameters on the penetration depth and welding width of the weld was revealed.Further,the influence of oscillating amplitude and frequency on the porosity of welds was studied,and the relevant laws were obtained.By observing the welding process,the mechanism of porosity inhibition was revealed.Laser oscillaion welding could effectively suppress porosity defects in aluminum alloy welds.The porosity decreased as the oscillating frequency changing from 100 to 300 Hz and the diameter changing from 1 to 3 mm.When the defocusing distance was+2mm,the oscillating diameter was 2mm,and the oscillating frequency was 200Hz,sound welds could be obtained.There were two main reasons for the porosity suppression mechanism of laser oscillation welding.First,high-speed camera observations showed that as the oscillating diameter increased,the welding process became stable,and bubbles in the molten pool decreased.Second,with the same penetration depth of4mm,the area of the laser oscillation welding pool was larger.The thermal imaging results showed that the solidification time of the oscillation welding pool was longer,which was conducive to the escape of bubbles.Finally,the effect of laser oscillating welding on the microstructure and mechanical properties of the joint was studied.It was found that laser oscillation could increase the area of the equiaxed crystal zone of the weld,refine the grains,and improve the mechanical properties such as tensile and fatigue.Laser oscillation improved joint tensile and fatigue performance by optimizing joint formation and reducing defects such as porosity,undercuts,and pits.When the oscillating amplitude was 2mm and the frequency was 200Hz,the tensile strength of the weld was 293 MPa(approximately 94%of the base metal)and the elongation was 6.06%.The fatigue test results showed that when the fatigue test is performed at 1×10~6cycles,the fatigue strength of the laser oscillation welding joints was 91.4Mpa,which was77.1%higher than that of the joints obtained without oscillation. |
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