Effects of oscillating frequency on keyhole stability and porosity inhibition in high-power laser-arc hybrid welding of 10-mm-thick 6082 aluminum alloy

Abstract

Keyhole instability and high porosity are prone to occur in laser-arc hybrid welding (LAHW) with an increase in aluminum alloy thickness. In this study, a high-power laser up to 8.0 kW at different oscillating frequencies (f) was used to achieve acceptable hybrid welding of a 10-mm-thick 6082 aluminum alloy. According to the observations of the laser keyhole from a high-speed camera, increasing f from 0 to 100 Hz increased the opening diameter from 1.3 to 1.6 mm and decreased the collapse frequency from 642 to 353 Hz. With the improved keyhole stability, the weld porosity decreased from 4.5% to 1.8%. In addition, beam oscillation refined the weld microstructure by 15% and transferred the tensile fracture from the weld center to the heat-affected zone (HAZ). Although the change in the ultimate tensile strength (UTS) was not obvious, the elongation increased by 25%. Beam oscillation promoted the formation of turbulent flow inside the molten pool, homogenized the melt flow, and reduced the necking tendency of the keyhole caused by the melt flow, thus greatly improving the keyhole stability.