1. Preparation before welding
The surface quality of the weldment and titanium wire has a great influence on the mechanical properties of the welded joint, so it must be cleaned up strictly. Iron plate and titanium welding wire can be cleaned by two methods: mechanical cleaning and chemical cleaning.
1.1 Mechanical cleaning Welding parts with low quality requirements or difficult pickling can be wiped with fine sandpaper or stainless steel wire brush, but it is best to scrape the titanium plate with carbide yellow to remove the oxide film.
1.2 Chemical cleaning. Before welding, the test piece and the welding wire can be pickled. The pickling solution can be HF5% + HNO335% water melt. After pickling, rinse with clean water and apply solder immediately after drying. Or use acetone, ethanol, carbon tetrachloride, methanol, etc. to wipe the groove of the titanium plate and its both sides (within 50mm each), the surface of the welding wire, and the part of the jig that contacts the titanium plate.
2. Selection of welding equipment Titanium and titanium alloy gold tungsten plate argon arc welding should use a DC argon arc welding power source with reduced external characteristics and high frequency arc starting, and the delay of gas delivery time is not less than 15 seconds to avoid welding from oxidation ,Pollution.
3. Selection of welding materials The purity of argon gas should not be less than 99.99%, the dew point should be below -40 ℃, and the total mass fraction of impurities should be 0.001%. When the pressure in the argon gas cylinder drops to 0.981MPa, it should be stopped to prevent affecting the quality of the welded joint. In principle, the titanium wire with the same composition as the basic metal should be selected. Sometimes, in order to hold the high weld metal plasticity, a welding wire with a slightly lower strength than the basic metal can also be selected.
4. Gas protection and welding temperature Titanium pipe joints are welded in place. In order to prevent the welded joints from being contaminated by harmful gases and elements at high temperatures, the welding area and welding seam must be welded and temperature controlled. The temperature should be 250 Below ℃. The main methods of protection and temperature control: one is to add a protective gas drag cover to the surface weld; the second is to fill the welded head tube with protective gas. The protective gas is argon, and its purity should be ≥99.99%. The flow of shielding gas should meet the welding technical requirements
5. Selection of welding parameters
5.1 Titanium alloy welding wire. The grade of 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, a welding wire slightly lower in alloying degree than the base metal may be selected. The diameter of the welding wire should be selected according to the thickness of the base material
5.2 Tungsten electrode. The best choice is cerium tungsten electrode, the diameter is selected according to the thickness of the titanium alloy tube, generally 1.0 ~ 3.0mm, the tungsten tip should be ground into a 30 ~ 45 degree cone.
6. The choice of groove form The principle is to minimize the number of welding layers and welding metal. With the increase of the number of welding layers, the cumulative suction position of the weld seam increases, which affects the performance of the welded joint. Due to the larger size of the welding pool when welding titanium and titanium alloys, the V-shaped 70-80 ° groove is opened .
7. Specimen pairing and tack welding In order to reduce welding deformation, tack welding is performed before welding. Generally, the tack welding interval is 100 ~ 150mm and the length is 10 ~ 15 mm. The welding wire, welding process parameters and gas protection conditions used for tack welding should be the same as those for welding joints. The gap is 0 ~ 2mm, and the blunt edge is 0 ~ 1.0mm.
1. Preparation before welding