Manual Welding Technology For Titanium Alloy Conduits

Titanium alloy has the characteristics of low density, high strength, corrosion resistance, etc. Titanium alloy tubing, as a new type of material, is widely used in the field of aerospace, and the proportion of titanium alloy conduit in the aero-engine piping is increasing. In addition, titanium alloy is a very active metal, at high temperatures to oxygen, hydrogen, nitrogen and other gases have a great affinity for the absorption and dissolution of gases is very strong, especially in the welding process, this ability is accompanied by an increase in the welding temperature, the performance of the particularly strong, the need for oxygen, hydrogen, nitrogen and other gases in the welding of the absorption and dissolution of the control, to avoid product obsolescence, which gives titanium alloy tubing welding has brought about a great deal of difficulty. This brings great difficulties to the welding of titanium alloy tube.
At room temperature, titanium reacts with oxygen to produce a dense oxide film, which gives it good chemical stability and corrosion resistance. At high temperatures, especially in the welding process, titanium alloy and oxygen, hydrogen, nitrogen reaction rate is extremely fast, when the molten pool invasion of oxygen, hydrogen, nitrogen and other harmful gases, welded joints, plasticity, toughness and surface color, etc., there are obvious changes, especially in the 882 ℃ and above, the joints grain growth tends to be serious, the formation of martensitic organization cooling, resulting in joints, strength, hardness, plasticity, toughness decline, tendency to overheating Serious, serious embrittlement of joints. Therefore, when welding titanium alloy, the molten pool, molten droplets and high temperature zone, whether it is the front or back, should be comprehensive, reliable gas protection.

Porosity is the most common defect in the welding of titanium and titanium alloys, which mainly appears near the fusion line. Hydrogen is the main cause of the formation of porosity. In welding, titanium absorption of hydrogen is very strong (stronger at high temperatures), but the solubility is significantly reduced with the drop in temperature, so the hydrogen dissolved in the liquid metal is often too late to escape from the fusion line in the vicinity of the fusion line to form pores.
Titanium alloy in a period of time after welding. In the near seam area is often prone to cracking (delayed cracking). The reason is that hydrogen from the high-temperature melt pool to the low-temperature heat-affected zone diffusion, with an increase in the amount of hydrogen content, the precipitation of TiH2 increased, so that the heat-affected zone brittleness increases, coupled with the precipitation of the volume of the hydride expansion of the organizational stresses generated, ultimately resulting in cracks.
Titanium alloy conduit welding requirements and precautions
(1) Try to set up a dedicated welding workshop, indoor smoking is strictly prohibited, the environment is kept clean and dry, and air convection is strictly controlled.
(2) Welders wear clean overalls and degreasing gloves when welding, and it is strictly prohibited to touch the parts with bare hands.
(3) Welding area and wire surface should be degreased with acetone.
(4) The use of high-purity protective argon gas, purity is not less than 99.99%. Welding gas supply flow should be in accordance with the values specified in the process regulations on the front and back of the weld channel for protection.
(5) In the welding process, the argon gas in the pipe and the argon gas flow of the welding tool nozzle should be maintained at a constant level to prevent convexity and concavity of the weld pool molding in the pipe.
(6) Welding should be used as much as possible short arc welding, using a small welding line energy.
(7) The gap is less than 30% of the wall thickness when positioning spot welds on the receiver. Each weld should be welded as far as possible.
(8) When welding, the welding tool should not swing from side to side, the melted end of the wire shall not move out of the gas protection zone. Arc should be sent ahead of the gas 10-15s, the rest of the arc can not immediately lift the welding torch, should be delayed gas supply 15-30s, until the temperature drops below 250 ℃.