Welding characteristics of ultrasonic-assisted laser-MIG hybrid welding for AA6082-T6 aluminum alloy plate with different vibration modes

Ultrasonic-assisted laser-MIG hybrid welding (LMHW), the ultrasonic vibration applying respectively on the filler wire (LMHW-UF) and workpiece (LMHW-UW), was carried out on the 6 mm thick 6082-T6 aluminum alloy plates. The influences of the ultrasonic vibration modes on the weld formation, porosity defects, microstructure, microhardness, and tensile properties were investigated, and compared with those of the traditional laser-Mig hybrid-welded joints. The results indicated that the arc zone depths increased as the ultrasonic amplitudes increased, and which of the LMHW-UF and LMHW-UW joints were deeper than that of the LMHW joint. The porosity defect contents of the LMHW-UF and LMHW-UW weld seams were both smaller than that of the LMHW weld seams, especially of the LMHW-UF weld seams. The cellular dendrite size in the LMHW weld center was smaller than that in the LMHW-UF and LMHW-UW welds, and the parallel dendrite zone width of the LMHW weld was wider than that of the LMHW-UF and LMHW-UW welds, especially of the LMHW-UF weld. The lowest microhardness existed in the partially melted zone of the LMHW and LMHW-UW joints; however, the lowest microhardness existed in a certain distance from the fusion line of the LMHW-UF joints. The average tensile strengths of the LMHW, LMHW-UF, and LMHW-UW joints were 212.6 MPa, 237.5 MPa, and 228.2 MPa, the fractures occurred in the weld seam, near the fusion line and at the heat-affected zone, respectively. The LMHW and LMHW-UW joints both showed typical mixed ductile and brittle fracture feature, and the LMHW-UF joints showed representative ductile fracture feature.