Titanium alloy has low density, high specific strength, good corrosion resistance, low thermal conductivity, non-toxic and non-magnetic, and can be welded; it is widely used in aviation, aerospace, chemical industry, petroleum, electric power, medical treatment, construction, sporting goods, and other fields.
Commonly used welding methods for titanium and titanium alloys are argon arc welding, submerged arc welding, vacuum electron beam welding, etc.
Preparation before welding
The surface quality of weldment and titanium welding wire has a great influence on the mechanical properties of welded joints, so it must be cleaned strictly.
1) Mechanical cleaning of weldments that do not require high welding quality or are difficult to pickle can be wiped with fine sandpaper or stainless steel wire brush, but it is best to scrape the titanium plate with cemented carbide yellow to remove the oxide film.
2) Chemical cleaning: before welding, the test piece and welding wire can be pickled, and the pickling solution can be HF (5%) + HNO3 (35%) aqueous solution. Rinse with clean water after pickling, and weld immediately after drying. Or use acetone, ethanol, carbon tetrachloride, methanol, etc. to wipe the groove of the titanium plate and its two sides (within 50mm each), the surface of the welding wire, the part where the tool and fixture are in contact with the titanium plate.
3) Selection of welding equipment: Titanium and titanium alloy tungsten plate argon arc welding should use a DC argon arc welding power supply with external characteristics and high-frequency arc ignition, and the delayed gas delivery time should not be less than 15 seconds to avoid the weldment being oxidized and pollution.
4) Selection of welding materials: the purity of argon gas should not be lower than 99.99%, the dew point should be below -40°C and the total mass fraction of impurities should be 0.001%. When the pressure in the argon cylinder drops to 0.981MPa, stop using it to prevent affecting the quality of the welded joint.
5) Gas protection and welding temperature: When welding titanium pipe joints, in order to prevent the welded joints from being polluted by harmful gases and elements at high temperatures, necessary welding protection, and temperature control must be carried out on the welding area and weld seam, and special welding equipment should be used. The protective drag cover provides all-around protection, and its temperature should be below 250°C.
Operation essentials
1. During manual argon arc welding, the angle between the welding wire and the weldment should be kept as small as possible (10~15°). The welding wire is fed into the molten pool smoothly and evenly along the front end of the molten pool, and the end of the welding wire must not be moved out of the argon protection zone.
2. During welding, the welding torch basically does not swing laterally. When it is necessary to swing, the frequency should be low, and the swing range should not be too large, so as not to affect the protection of argon gas.
3. When the arc is broken and the welding seam is finished, the argon gas protection should be continued until the welding seam and the metal in the heat-affected zone cool down to below 350°C before removing the welding torch.
Weld seam and heat-affected zone surface color
1. Weld area
Silvery white, light yellow (allowed for first, second, and third-grade welds); dark yellow (allowed for second and third-grade welds); golden purple (allowed for third-grade welds); dark blue (permitted for first, second and third-grade welds) are not allowed).
2. Heat-affected zone
Silvery white, light yellow (allowed for first, second and third-grade welds); dark yellow, golden purple (allowed for second and third-grade welds); dark blue (allowed for third-grade welds).
Contact
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EMAIL: zhangjixia@bjygti.com
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No. 195, Gaoxin Avenue, High-tech Development Zone, Baoji City, Shaanxi, China
