Study On The Technology And Filler Wire Melting Dynamics During The Laser Welding With Filler Wire

Laser welding with filler wire is a novel welding technology with great developing potential, which has overcome some disadvantages of laser autogenous welding (such as the difficulties in the welding metallurgy and tight joint fit-up requirement) while maintaining its many advantages, e.g. high welding quality, low heat-input, high welding speed, low distortion and so on. So far, the industrial applications for the novel technology have been hardly found, although it recently received growing attention in domestic and abroad. This can be mainly attributable to two reasons. First, the filler wire has increased the process complexity. Second, the basis of test data about the novel welding technology is not enough to support its industrial applications.In order to solve the practical problems in application, this paper has carried out a systematic process test of laser welding with filler wire on the self-built test platform for the 5A06 aluminum alloy. Combined with high-speed video camera and theoretical analysis, the wire melting dynamics and the effects of filler wire on the efficiency of laser welding have been study. Then, under the condition of narrow gap groove, the low carbon steel with 17mm in thickness had been bridging by use of multi-layer laser welding with filler wire.The results showed that the characteristics of wire melting and transition have a closely related to the filler wire point position. The different characteristics of wire melting and transition cause of the different stability of the welding process. The melting and transition behaviors of filler wire can be divided into three categories, named as "Explosion", "Big-Droplet" and "Molten Metal Bridge". The first two types of transition can strongly disturb the weld pool flow and cause of the fluctuations of welding process. The welding process can be carrying out with high stability only when the filler wire is transition into the welding pool through a molten metal bridge. It is an ideal stable welding process, and the weld shape is smooth and uniform.One of the main advantages of laser welding with filler wire is the good gap bridging capability. After optimized the feeding parameters of filler wire, the tolerance of gap bridging can be greatly improved during laser welding aluminum alloy with filler wire. The largest bridge gap can be up to 1.0mm when the welded plate is 2.0mm in thickness. Under optimum conditions, a weld joint with excellent mechanical properties can be obtained; the minimum tensile strength of joints can reach more than 90% of the base metal.Pore, especially the technology pore (with irregular shape and large size) is a major problem during the laser welding of aluminum alloy with filler wire. The mechanical properties of joints should be deterioration sharply when a certain number of technology pores was formation in the weld. Based on the high-speed video, a systematic study on the formation mechanism of technology pore during laser welding of aluminum alloy with filler wire had been carried out. The result showed that the formation mechanism of technology pore is closely related to the stability of laser holes, weld pool flow and melting dynamics of filler wire. The metal vapor deposition film layer has been found in the internal wall of technology pore through the Scanning Electron Microscope (SEM). This further confirmed the differences of formation mechanism between the technology pore and hydrogen pore. Based on the above theory, a 0.4mm butt gap have been prefabricated during the laser welding aluminum alloy (4.0mm in thickness) with filler wire to enhance the penetration and the stability of the laser holes. After take some prevention and suppression measures, the good weld joints without technology pores have been got.Based on the previous research achievements, after groove design and optimization of side-blown protective gas, the low carbon steel with 17mm in thickness have been bridging by combination of single laser autogenous welding and three-layer laser welding with filler wire. A welding joint whithout significant welding defect is formed, and its appearance is smooth and uniform.