There is a tendency of grain growth in TC4
titanium bar welding of
titanium alloy forgings, especially in β-titanium alloy, but the grain growth is difficult to be adjusted by heat treatment. Therefore, the selection of welding parameters of titanium and titanium alloy should not only prevent the tendency of grain coarsening in the welding seam under the action of arc, but also avoid the formation of brittle microstructure in the cooling process after welding. The welding shall be conducted with a small welding line energy so that the temperature is just above the minimum temperature required for weld formation. If the line energy is too large, the weld is easy to be polluted and form defects.
The DC arc welding power source with constant current characteristic is generally used in argon tungsten arc welding, and direct DC connection is adopted to obtain larger weld depth and narrower weld width. In multi-layer welding, the first layer is generally without welding wire, from the second layer to add welding wire. The heated wire should be protected by gas. When multi-layer welding, the temperature between layers should be kept as low as possible, and the next weld should be welded after the previous layer cools to room temperature to prevent overheating.
For pure titanium and
titanium alloy sheet with thickness of 0.1~2.0m, titanium alloy sensitive to welding thermal cycle and thin-walled titanium tube in all position welding, pulsed argon arc welding is used. This method can successfully control the forming of titanium weld, reduce the tendency of overheat and coarse grain, and improve the plasticity of welded joints. In addition, the welding seam is easy to realize single-sided welding and double-sided forming, so that the welded joint with high quality and small deformation can be obtained. Table 8 shows the process parameters of pulsed automatic TIG welding of
titanium plates with thickness of 0.8~2.0m.The pulse current plays a major role in the depth of welding seam, and the function of the base current is to keep the arc burning stably, and there is no need to start the arc again when the next pulse is applied.
When the titanium and titanium alloy plate is very thick, the melting ammonia arc welding (MG) can reduce the number of welding layers, improve the welding speed and productivity, reduce the cost, and also reduce the porosity of the welding seam. But G welding is the use of fine particles, filling metal is likely to be contaminated, so the protection requirements are more stringent than TIG welding. In addition, the spatter of MG welding is large, which affects the weld forming and protection effect. Short circuit transition is usually used in thin plate welding, while jet transition is used in thick plate welding.
MIG welding wire filling more, which requires welding groove Angle is large, the thickness of 15~25m plate, can choose 90° single-sided V-shaped groove. The towing cover of argon tungsten arc welding can be used for melting electrode welding. However, due to the high welding speed and long high temperature zone of MG welding, the towing cover should be lengthened and cooled by water flow. The selection of welding materials for MG welding is the same as that for T welding, but the requirements for gas purity and surface cleanliness of the welding wire are higher, and the welding wire must be thoroughly cleaned before welding.
