Laser-arc Hybrid Welding Of Pure Copper

Copper has been widely applied in industries because of its excellent properties, such as high electrical and thermal conductivities, excellent mechanical properties. However, copper is very difficult to be welded. In laser-arc hybrid welding, the high reflectivity of copper can be improved by laser-arc interaction. It is of great value for using high energy density laser to obtain high quality weld. This dissertation had a research on laser-MIG?Metal-Inert Gas Welding? hybrid welding of T2 pure copper. The main results are as follows:The laser-arc interaction largely improves weld formability. Continuous and regular welds were achieved in hybrid welding when the laser power was 4kW, while it was hard to be obtained in laser welding even the laser power reached 6kW. The process stability enhancement mechanism is in two aspects. First, arc preheating improves the laser absorbtivity of copper, which increases the energy density in the keyhole and reduces its closing tendency. Second, the keyhole opening diameter is enlarged by the arc pressure and arc plasma force, which reduces the recoil pressure on the keyhole rear wall. Therefore, the keyhole rear wall maintains smooth instead of depression, and the keyhole stability is elevated.The microstructure of hybrid welds are apparently coarsening compared to that of base metal. The fusion zone is composed of massive column dendrites perpendicular to the fusion line and equiaxed dendrites in the center. And the heat affected zone is composed of massive annealing twins. The tensile properties of hybrid welds are lower than that of base metal. The maximum of the ultimate tensile strength?UTS? and the elongation?YS? of the hybrid welds are 208.6 MPa and 26.9% that are 83.9% and 81.8% of base metal, respectively. It is found that the big pores in the weld are the main reason for joint properties reduction when the heat input is low. And as the heat input increasing the porosity reduces, the coarsen microstructure begins to become the main factor for joint properties decline.The effects of pure copper wire, CuSi₃ wire and CuSn₆ wire on the joint mechanical properties, electrical conductivity and corrosion resistance were studied. The results showed that the alloy elements improves the joint mechanical properties and corrosion resistance, but reduces electrical conductivity. By comparison, the CuSn₆ wire joint has the best mechanical property and the CuSi₃ wire joint has the best corrosion resistance.