Research On High Power CO₂ Laser Welding Of 6061 Alumunim Sheet With Filler Wire

The main application backgrounds of this paper are the fuselage weld panels used in large civil aircrafts, and its research subjects are high power CO₂ laser welding of 6061 aluminum sheet with filler wire. Combined with the advanced manufacturing methods of weld panels abroad, the wire ER4043 and ER5356 were selected in order to achieve the laser welding of 6061 aluminum, the influence of laser welding parameters were studied, and the microstructure and properties of the joints were also analyzed.The laser penetration welding threshold experiments of the 6061-T6 aluminum indicates that the scope of welding parameters is small when the welding speed is slow. Compared with the plate welding, the critical laser power reduces greatly in butt welding. The scope of matching parameters between laser power and welding speed is small, and the scope becomes bigger when increase welding speed or laser power, and in order to ensure welding stability and good weld surface, the welding speed should be controlled quicker than 4 m/min.In order to achieve the laser welding and get a good weld surface, the plug-in wire feeding should be selected, and the distance between the wire and the laser spot should be controlled within±1.5 mm. When wire feeding rate is 5 m/min, the permissible maximum gap between the two plates was 0.1 mm. For a given laser power with the two wires, with the increase of welding speed, the scope of matching wire feeding rate becomes smaller.The wire improved the porosity sensitivity of laser welding aluminum, the porosity rate of the joints obtained with ER5356 is higher. The wire also improves the hot cracking sensitivity significantly, the hot cracking sensibility of weld obtained with wire ER4043 is lower, and the hot cracking rate can reach zero with the available parameters, but the hot cracking sensibility of weld obtained with wire ER5356 is relative higher, indicating wire ER5356 is not suitable for high-speed laser welding of 6061-T6 aluminum alloy.Under appropriate parameters, the weld joints have moderate reinforcement, and without undercut defects. For the joints obtained with wire ER4043, there are typical columnar crystals near the fusion line and the dendritic Al-Si eutectic lie in the weld center with a lot of equiaxed crystals, that is hypoeutectic. For the joints obtained with wire ER5356, there are typical columnar crystals near the fusion line, and equiaxed and columnar grains lie in the weld center, that is the (Al) +β(Mg₂Al₃). The microhardness of the weld center in joints of 6061-T6 aluminum obtained with wire ER4043 or ER5356 is HV60⁷0. Under optimized parameters, the tensile strength of the joints obtained without wire, with wire ER4043 and ER5356 are 197 MPa, 262 MPa, 232 MPa respectively, the fracture of joints are near the fusion line, as 45°fracture. There is obvious dimple fracture in the joints obtained with wire ER4043, while the fracture lies near the fusion line when using wire ER5356, which belongs to brittle fracture.The joints obtained with wire ER4043 have good bending properties, there are no cracks when bending angle reaches 120°, and the bending strength from the front and back side are 645.9 MPa and 592.8 MPa respectively. But the bending strength of the joints obtained with wire ER5356 is relative lower, bending strength from the front and back side are just 556.3 MPa and 500.5 MPa respectively.The laser weld joints of 6061-O aluminum with wire ER4043 were treated by T6 solid solution and aging treatment, after heat treatment, the microhardness of the weld increases significantly, reaching HV90¹10, the soften zone disappeared almost. And the tensile strength of the joints after heat treatment also significantly increase, reaching 301 MPa, the strength coefficient reaches 94%, and the extensibility increases from 2.2% to 7.4%, the tensile fracture appear in the base metal.