Aluminum Alloy's Welding By Laser With Filling Wire And Laser-Arc Hybrid Technology

Aluminum alloy is an ideal material for aerocraft structure, because of its light weight, superior strength-to-weight ratio, and excellent corrosion resistance. Laser welding with higher energy density can offer remarkable advantage over conventional fusion welding processes, such as minimal component distortion and high productivity. Laser welding with filling wire and laser-arc hybrid welding are new technologies, which can reduce assembled precision of butt-joint, improve metallurgic characteristic of weld bead, and enhance joints'mechanical property. In this paper, the experiments of 5A06 aluminum alloy with 1.2mm thickness and 5A90 aluminum-lithium alloy with 3mm thickness by laser welding with filling wire, and the 5A90 alloy by laser-arc hybrid welding have been investigated, which could offer data reference for joint technology of aluminum alloy in aerospace.While laser welding with filling wire, the back width to surface width ratio and the weld shaping quality are controlled by optimizing welding parameters, such as the wire feed speed, laser power, welding speed and geometry position of filling wire. With other optimized welding parameters fixed, the distance (D) between laser and wire must be controled in the range of +0.2～+1.5mm. While laser-arc hybrid welding, D is allowed to from 0mm to 6mm because of the"synergistic effect"with combining laser and arc. The optimized hybrid welding parameters can increase weld width and weld penetration. However, the advantage of hybrid welding will be sufficiently represented when the welding current exceeds some threshold value with constant other parameters. For the welding parameters of the two welding methods, the selecting wire feed speed is relative to the input power. Besides, the thinner aluminum alloy sheet demands higher wire feed speed and boarder wire feed speed range.The gap tolerance for laser welding is improved distinctively by laser welding with filling wire and laser-arc hybrid welding, and the maximal accommodable gap is enlarged above 0.9mm, which is 4～6 times wider than laser welding. The primary defects of welding aluminum alloy are defective weld appearance and porocity. The thicker aluminum sheet would cause more and larger pores in weld bead. However, the weld bead with good appearance and inside quality could be obtained by strict surface treatment and complete-penetration welding. While laser welding with filling wire, the droplet transition modes were inspected by high-velocity-camera. It was found that the surface tension transition of D=+1mm was more stable than the grain transition of D=+0.3mm. The shooting-droplet transition for hybrid welding, which was presented one droplet per pulse, was also comparatively stable. For the laser welding with filling wire and hybrid welding, the interaction between heat reservoir and material expressed periodic changing.The laser welding with filling wire could increase material's absorptivity, weld width, and joint's tensile property. For example, the tensile strength of joint with filling wire is increased nearly 10% than the joint by laser welding. Besides, the microhardness of Al-Li alloy weld bead is tended toward uniform by the laser welding with filling wire and laser-arc hybrid welding.