Abstract: In order to solve the problem of joint performance degradation caused by poor weld formation and uneven structure in laser welding of aluminum alloy, ultrasonic vibration assisted laser wire filling welding was carried out for 3 mm thick 5A06 aluminum alloy. The ultrasonic horn is in direct contact with the welding specimen, and then the ultrasonic wave is introduced into the molten pool. The stability and fluidity of the molten pool are enhanced after the ultrasonic wave is introduced into the molten pool, which can effectively improve the weld formation and increase the weld penetration. The experiments of different welding speeds show that the high temperature retention time of the molten pool is long and the composition uniformity is good at low welding speed. The introduction of ultrasonic only enhances this effect. The cavitation effect, sonic flow effect and mechanical stirring effect caused by ultrasonic wave propagation in the molten pool can not only effectively improve the nucleation rate in the molten pool, but also promote the transformation of grain growth mode from columnar crystal to equiaxed crystal, which has the effect of refining grains. The fine grain strengthening improves the fracture mode of the joint, improves the plastic toughness and stability resistance of the joint. When the pressure of ultrasonic horn is 125.7 N, the grain size of the weld is obviously refined. The tensile strength of the joint increased from 258.3 MPa to about 293.1 MPa, and the elongation increased from 11.2% to about 13.1%.

Key words: 5A06 aluminum alloy, laser filler wire welding, ultrasonic vibration, melt flow, grain refining