1, preparation before welding: welding parts and titanium welding wire surface quality has a great impact on the mechanical properties of welding joints, so it must be strictly cleaned. Iron plate and
titanium wire can use mechanical cleaning and chemical cleaning two methods.
1.1 Mechanical cleaning of welding quality is not high or difficult to pickle welding parts, can use fine sandpaper or stainless steel wire brush to wipe, but it is best to use hard alloy yellow scraping
titanium plate, remove the oxide film.
1.2 Chemical cleaning. Before welding, the test piece and the welding wire can be pickled, and the pickling solution can be HF5%+HNO335% water melt. After pickling, wash with clean water and apply welding immediately after drying. Or with acetone, ethanol, carbon tetrachloride, methanol, etc. wipe the groove and both sides of the titanium plate (within 50mm each), the surface of the welding wire, the part of the fixture and the titanium plate in contact.
2. Selection of welding equipment: the argon arc welding of
titanium and titanium alloy gold
tungsten plate should choose the DC argon arc welding power supply with descending external characteristics and high frequency arc initiation, and the delay gas transfer time should not be less than 15 seconds to avoid oxidation and pollution of welding.
3. Selection of welding materials: Argon gas purity should not be less than 99.99%, dew point below -40℃, and total mass fraction of impurities < 0.001%. When the pressure in the argon cylinder drops to 0.981MPa, it should be stopped to prevent the quality of the welded joint from being affected. In principle, the titanium wire with the same composition as the base metal should be selected. Sometimes, in order to improve the plasticity of the weld metal, the welding wire with a slightly lower strength than the base metal can be selected.
4. Gas protection and welding temperature: the
titanium pipe joint is welded to the ground. In order to prevent the welding joint from being polluted by harmful gases and elements at high temperature, the necessary welding protection and temperature control must be carried out on the welding area and the weld, and the temperature should be below 250℃. The main methods of protection and temperature control are as follows: one is to add protective gas drag cover to the surface weld; The second is to fill the welded pipe with protective gas. Protective gas is argon, whose purity should be ≥ 99.99%. The flow of protective gas should meet the welding technical requirements.
5. Selection of welding parameters
5.1 Titanium alloy welding wire. The grade of the filler wire should be selected according to the base metal. Generally, the principle of homogeneity with the base metal is adopted. Sometimes, in order to improve the plasticity of the joint, the welding wire with slightly lower alloying degree than the base metal can be selected. The diameter of welding wire should be selected according to the thickness of base metal.
5.2 tungsten electrode. The best choice of cerium tungsten electrode, its diameter according to the thickness of
titanium alloy tube selection, generally in 1.0 ~ 3.0mm, tungsten extreme part should be ground into 30 ~ 45 degrees of cone.
6, the choice of groove form: the principle of minimizing the number of welding layers and welding metal. With the increase of the number of welding layers, the accumulative suction of the welding seam increases, which may affect the performance of the welding joint. Moreover, because of the large size of the welding pool during the welding of titanium and titanium alloy, the single V-shaped groove of the test piece is 70~80°.
7, the specimen group and positioning welding: in order to reduce the welding deformation, positioning welding is carried out before welding, generally positioning welding spacing of 100~150mm, length of 10~ 15mm. The welding wire used for position welding, welding process parameters and gas protection conditions should be the same as the welding joint. The clearance is 0~2mm and the blunt edge is 0~1.0mm.
