Titanium alloys are characterized by low density, high strength, and corrosion resistance. As a new material, titanium alloy pipes are widely used in the aerospace field, and their proportion in Aeroengine pipes is increasing. In addition, titanium alloy is a very active metal. It has a great affinity to oxygen, hydrogen, nitrogen, and other gases at high temperatures, with a strong ability to absorb and dissolve gases, especially during welding, whose ability is particularly strong with increasing welding temperatures. during welding, it is necessary to control the absorption and dissolution of oxygen, hydrogen, nitrogen, and other gases to avoid the scrap of products, which brings great difficulties to the welding of titanium alloy tubes.
Manual argon arc welding of titanium alloy pipes
Weldability of titanium alloy tubes
|
|
(1) Embrittlement of welded joints
At room temperature, titanium reacts with oxygen to form a dense oxide film, which makes it have better chemical stability and corrosion resistance. At high temperatures, especially during welding, the reaction speed of titanium alloy with oxygen, hydrogen, and nitrogen is extremely fast. when harmful gases such as oxygen, hydrogen, and nitrogen are intruded into the molten pool, the plasticity, toughness, and surface color of the welded joint have obvious changes. Especially when the temperature is above 882 C, the grain growth tendency of the joint is serious, and martensite structure is formed when cooling, resulting in the decrease of strength, hardness, plasticity, and toughness of the joint and the tendency of overheating is serious. The joint is severely brittle. Therefore, when titanium alloy welding, the melting pool, droplets, and high-temperature zone, both front, and back, should be fully and reliably protected by gas.
(2) Gas holes
A pore is the most common defect in titanium and titanium alloy pipes welding, mainly near the fusion line. Hydrogen is the main cause of pore formation. During welding, titanium has a strong ability to absorb hydrogen (stronger at high temperatures), but its solubility decreases significantly with decreasing temperature, so hydrogen dissolved in liquid metals tends to accumulate near the fusion line and form pores before it escapes.
(3) Delayed cracks in the near seam area
Titanium alloy is prone to crack (delay crack) in the near seam area for a period of time after welding. The reason is that hydrogen diffuses from the high-temperature molten pool to a low-temperature heat-affected zone. With the increase of hydrogen content, the amount of TiH2 precipitated increases, the brittleness of the heat-affected zone increases, and the structure stress produced when the volume of precipitated hydride expands, which finally leads to crack formation.
