Microstructure and Mechanical Properties of 6061 Aluminum Alloy Joint by Laser Welding with Filler Wire

6061 aluminum alloy with thickness of 6 mm was welded by laser welding with filler wire. The microstructure and mechanical properties of the welded joint were studied by micro-hardness and tensile testers, scanning electron microscope and X-ray diffractometer. The results show that the microstructure of weld center was equiaxial grains composed of α-Al solid solution and no β(Mg₂Si) strengthening phase was found. The microstructure of the weld near fusion zone was columnar grains. The hardness of the weld in the welded joint was the lowest of 73 HV and that of base metal was the highest of 110 HV. With the increase of the distance from the weld center, the hardness in heat affected zone increased first in a wave mode, then decreased at the position located at 2.2-3.8 mm from the weld center, namely the softening zone in heat affected zone, and finally increased rapidly at the position located at 3.8-4.4 mm from the weld center. The tensile strength of the welded joint was 234 MPa, 71% of that of the base metal and higher than that of metal inert-gas welding joint. The welded joint both fractured at the weld and both the joint and base metal fractured in ductile mode.