Microstructure and mechanical properties during dissimilar welding of AA2060-T8 and AA6061-T6 by circular laser beam oscillations

Abstract

Circular laser beam oscillations have been applied at 0.5 mm and 1 mm amplitude with four different frequencies of 30, 60, 100 and 200 Hz during dissimilar laser beam welding of 2-mm-thick heat-treated AA2060-T8 with AA6061-T6. The results have been compared with a rectilinear welding case. The width of solidified weld beads produced by laser beam oscillations is wider than that of rectilinear welding due to an increase in the area of the processed zone. Welding defects inside the fusion zone were evaluated by subjecting the joints to 100% of X-ray examination, and it was found that there was absolutely no crack and negligible level of porosity in the fusion zone. Laser beam oscillations have been applied the first time to investigate the evolution of the dendritic equiaxed zone in the central region as well as the nondendritic equiaxed zone besides the fusion line in case of 2060-T8. Optical microscopy was employed to observe the microstructure. It was found that laser beam oscillations have a significant positive impact on the microstructure both in the central region and in the vicinity of the fusion line. The inhibited ability of the formation of equiaxed dendrites due to lesser solute content has been compensated by altering the thermal conditions inside the fusion zone, and a wider equiaxed dendritic region has been achieved. In addition, the nondendritic equiaxed zone, which is undesirable during welding of aluminum–lithium alloys, has been significantly reduced in width by employing laser beam oscillations. In case of rectilinear welding, the average width of the nondendritic equiaxed zone was found to be 43 [Formula: see text]m, while the oscillatory welding reported an average width of the nondendritic equiaxed zone as low as 6 [Formula: see text]m. Enhanced fluid flow inside the melt pool and repeated interaction of the beam with the molten pool are the most probable causes of the observed results. This investigation suggests that laser beam oscillations can be successfully used to alter the microstructure and produce high-quality welds using AA 2060-T8/6061-T6 and can be replaced with conventional rectilinear laser welding for industrial applications.