How to weld titanium?

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//Titanium alloys have a low density, high specific strength, good corrosion resistance, low thermal conductivity, are non-toxic and non-magnetic, and can be welded； It is widely used in industries such as aviation, aerospace, chemical engineering, petroleum, power, medical care, construction, and sports equipment. Common welding methods for titanium and titanium alloys include TIG welding, submerged arc welding, vacuum electron beam welding, etc. Preparation before welding: The surface quality of the workpieces and titanium welding wire has a significant impact on the mechanical properties of the welded joint; therefore, strict cleaning is necessary. 1) For weldments for which high welding quality is not required or for which pickling is difficult, they can be wiped with fine sandpaper or a stainless steel wire brush; however, it is best to use a yellow carbide scraper to remove the oxide layer from titanium plates. 2) Chemical cleaning: Before welding, the test piece and welding wire can be pickled. The pickling solution can be an aqueous solution of HF (5%) + HNO3 (35%). After pickling, rinse with clean water; weld immediately after drying. Alternatively, use propanone, ethanol, carbon tetrachloride, methanol, etc. to wipe the groove of the titanium plate and the areas on either side thereof (within 50 mm of each side), the surface of the welding wire, and the parts of the fixtures that come into contact with the titanium plate. 3) Selection of welding equipment: For TIG welding of titanium and titanium alloy tungsten plates, a DC TIG welding power source with external characteristics and high-frequency arc starting should be used, with a gas delivery delay of at least 15 seconds to prevent the weldment from being oxidized or contaminated. 4) Selection of welding materials: The purity of argon should be no less than 99.99%, with a dew point below -40°C, and the total mass fraction of impurities should be 0.001%. When the pressure in the argon cylinder drops to 0.981 MPa, its use should be stopped to prevent impacts on the quality of the weld joint. 5) Gas protection and welding temperature: The temperature during welding of titanium pipe joints is relatively low. To prevent the welded joints from being contaminated by harmful gases and elements at high temperatures, it is necessary to provide appropriate welding protection and temperature control for the welding area and weld seam; this temperature should be kept below 250°C. Operating guidelines: 1. When performing manual TIG welding, the angle between the welding wire and the workpiece should be kept as small as possible (10–15°). The welding wire should be fed into the molten pool smoothly and evenly along its front edge, and the end of the wire must not be taken out of the argon protection zone. 2. During welding, the welding torch should basically not be moved sideways; if movement is necessary, it should be done at a low frequency and with a limited amplitude, in order to avoid disrupting the protective effect of argon gas. 3. During arc interruption and the final stages of welding, argon shielding must be maintained until the metal in the weld zone and the heat-affected area has cooled to below 350°C before the welding torch can be removed. Surface color of welds and heat-affected zones: 1. The weld zone is silver-white or light yellow (allowed for grades 1, 2, and 3 welds) ； Dark yellow (permissible for second- and third-class welds) ； Gold-purple (allowed for grade 3 welds) ； Dark blue (not allowed for welds of grades 1, 2, or 3). 2. The heat-affected zone is silver-white or light yellow (allowed for welds of grades 1, 2, and 3) ； Dark yellow, golden-purple (permitted for second- and third-grade welds) ； Dark blue (allowed for grade 3 welds).