Friction stir welding welded joints have non-porous, small grain, good fatigue, tensile and bending properties, no fumes, no splash when welding, energy saving, no welding wire and shielding gas, residual stress and deformation after welding, etc. It is a kind of welding method with good applicability. Copper-chromium alloy is a preferred material for preparing resistance welding electrodes, metal molds, large-scale high-speed turbine generator bars, power tool steering devices, etc. due to its high strength, hardness, good electrical conductivity, thermal conductivity, and corrosion resistance. Copper-chromium alloys need to be welded during the manufacture of generator bars and power tool steering gears. Currently, fusion welding, pressure welding and brazing are used. Because of the physical and chemical properties of copper and the influence of impurity elements, the joints are prone to problems such as porosity, strength, corrosion resistance, and large welding distortion. Currently, there are not many reports on the microstructure and properties of copper-chromium alloy friction stir welding welded joints. For this reason, the authors carried out the microstructure, hardness and electrical conductivity of friction stir welding joints of solid-solution and aging copper-chromium alloys. A comparative study provides experimental evidence for the use of friction stir welding in chrome alloys.
The grains of the solid solution copper-chromium alloy welded joint matrix are coarse, and the weld nugget is a fine equiaxed grain. The grain size of the heat affected zone is slightly larger than the weld nugget zone and has a certain flow direction. The grain size of the heat affected zone is The difference between the matrix is ​​not great; the hardness of the weld zone is up to 78HB, and the hardness is farther away from the center of the weld until it reaches the hardness of the substrate.
The microstructure of the aged copper-chromium alloy joint is an equiaxed grain with uneven size. The grain size in the weld nugget is refined and the distribution is not uniform. The crystal grain in the heat affected zone is elongated and has a certain flow direction; the grain size in the heat affected zone is relatively low. The substrate grew slightly; the weld zone had the highest hardness of 113 HB. The farther away the center of the weld was, the lower the hardness was. The HAZ had the lowest hardness, 91 HB, and then rebounded to the base hardness.
The conductivity of the solid solution state of the copper-chromium alloy joint is the highest, which is 73.3%IACS. The farther away from the center of the weld is the smaller the electrical conductivity. The conductivity of the welded joint of the aging alloy gradually decreases from the matrix to the weld zone. The lowest is 78.1% IACS.
The grains of the solid solution copper-chromium alloy welded joint matrix are coarse, and the weld nugget is a fine equiaxed grain. The grain size of the heat affected zone is slightly larger than the weld nugget zone and has a certain flow direction. The grain size of the heat affected zone is The difference between the matrix is ​​not great; the hardness of the weld zone is up to 78HB, and the hardness is farther away from the center of the weld until it reaches the hardness of the substrate.
The microstructure of the aged copper-chromium alloy joint is an equiaxed grain with uneven size. The grain size in the weld nugget is refined and the distribution is not uniform. The crystal grain in the heat affected zone is elongated and has a certain flow direction; the grain size in the heat affected zone is relatively low. The substrate grew slightly; the weld zone had the highest hardness of 113 HB. The farther away the center of the weld was, the lower the hardness was. The HAZ had the lowest hardness, 91 HB, and then rebounded to the base hardness.
The conductivity of the solid solution state of the copper-chromium alloy joint is the highest, which is 73.3%IACS. The farther away from the center of the weld is the smaller the electrical conductivity. The conductivity of the welded joint of the aging alloy gradually decreases from the matrix to the weld zone. The lowest is 78.1% IACS.
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