Manual Welding Technology Of Titanium Alloy Conduits
Aug 13, 2025
Titanium alloy has the characteristics of low density, high strength and corrosion resistance. As a new type of material, titanium alloy pipes are widely used in the aerospace field. The proportion of titanium alloy conduits in aerospace engine pipelines is increasing. In addition, titanium alloy is a very active metal. It has a great affinity for gases such as oxygen, hydrogen and nitrogen at high temperatures and has a strong ability to absorb and dissolve gases. Especially in the welding process, this ability is particularly strong as the welding temperature increases. During welding, it is necessary to control the absorption and dissolution of gases such as oxygen, hydrogen and nitrogen to avoid product scrapping. This brings great difficulties to the welding of titanium alloy pipes.
2 Manual argon arc welding of titanium alloy conduits
2.1 Weldability of titanium alloy conduits
(1) Brittleness of welded joints
At room temperature, titanium reacts with oxygen to form a dense oxide film, which makes it have good chemical stability and corrosion resistance. At high temperatures, especially during welding, titanium alloys react very quickly with oxygen, hydrogen, and nitrogen. When harmful gases such as oxygen, hydrogen, and nitrogen invade the molten pool, the plasticity, toughness, and surface color of the welded joint change significantly. Especially at temperatures above 882°C, the grain growth of the joint tends to be serious, and martensite structure is formed during cooling, resulting in a decrease in the strength, hardness, plasticity, and toughness of the joint. The overheating tendency is serious, and the joint becomes severely brittle. Therefore, when welding titanium alloys, the molten pool, droplets, and high-temperature areas, whether on the front or back, should be fully and reliably protected by gas.
(2) Porosity
Porosity is the most common defect in the welding of titanium and titanium alloys, and mainly occurs near the fusion line. Hydrogen is the main cause of pore formation. During welding, titanium has a strong ability to absorb hydrogen (even stronger at high temperatures), but its solubility decreases significantly as the temperature drops. Therefore, hydrogen dissolved in the liquid metal often does not have time to escape and accumulates near the fusion line to form pores.
(3) Delayed cracks in the near-seam area
Titanium alloys are prone to cracks (delayed cracks) in the near-seam area within a period of time after welding. The reason for this is that hydrogen diffuses from the high-temperature molten pool to the low-temperature heat-affected zone. As the hydrogen content increases, the amount of TiH2 precipitated increases, making the heat-affected zone more brittle. In addition, the structural stress generated by the volume expansion of the precipitated hydride eventually leads to cracks.
2.2 Welding requirements and precautions for titanium alloy conduits
(1) Try to set up a dedicated welding workshop. Smoking is strictly prohibited indoors. The environment should be kept clean and dry, and air convection should be strictly controlled.
(2) Welders should wear clean work clothes and degreased gloves when welding. It is strictly forbidden to touch parts with bare hands.
(3) The welding area and the surface of the welding wire should be degreased with acetone.
(4) Use high-purity protective argon gas with a purity of not less than 99.99%. The gas flow rate during welding should be in accordance with the value specified in the process regulations to protect the front and back of the weld.
(5) During the welding process, the argon flow rate in the pipe and the argon flow rate in the welding tool nozzle should be kept constant to prevent the weld pool in the pipe from forming convex and concave phenomena.
(6) Short arc welding should be used as much as possible, and the welding line energy should be small.
(7) When spot welding the butt pipe, the gap should be less than 30% of the wall thickness. Each weld should be completed in one pass as much as possible.
(8) During welding, the welding tool should not be swung left and right, and the molten end of the welding wire should not be moved out of the gas protection zone. When striking the arc, the gas should be supplied 10-15 seconds in advance. When the arc is extinguished, the welding gun should not be lifted immediately. The gas supply should be delayed for 15-30 seconds until the temperature drops below 250℃.
2.3 Welding process
2.3.1 Cleaning before welding.
The occurrence of welding defects is closely related to the surface cleanliness of the weldment and welding wire. Before welding, the oil, water, oxide film and other dirt within 15 to 20 mm of the pipe joint edge and the surface of the welding wire should be cleaned. The cleaning method can be chemical methods (pickling) or mechanical means (stainless steel brushing) to remove the surface oxide scale. Acetone or alcohol should also be used for cleaning before welding. The weldment after cleaning must be welded within 24 hours, otherwise it needs to be cleaned again. It is best to vacuum dehydrogenate the welding wire after pickling and degrease it with acetone before welding.
2.3.2 Gas protection.
When welding titanium pipe joints, in order to prevent the weld joint from being contaminated by harmful gases and elements at high temperatures, the weld must be protected by necessary argon gas with a purity of not less than 99.99%.
2.3.3 Selection of welding process parameters.
(1) Selection of welding wire. The brand of filler wire should be selected according to the base material. Generally, the same material as the base material should be used. Sometimes, in order to improve the plasticity of the joint, a wire with a slightly lower alloying degree than the base material can be selected. The diameter of the welding wire should be selected according to the thickness of the base material.
(2) Selection of power supply and polarity. Titanium and titanium alloy welding generally uses a DC manual tungsten arc power supply, and its polarity connection method uses DC positive connection.
(3) Selection of tungsten electrode. The diameter of the tungsten electrode is selected according to the wall thickness of the titanium alloy tube, generally between 1.0-3.0mm, and the end of the tungsten electrode should be ground into a 25° to 45° cone.
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