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What is A-TIG welding technology for titanium alloy

What is A-TIG welding technology for titanium alloy?

A-TIG welding technology and characteristics of titanium alloy

A-TIG welding technology is a process of coating a layer of active flux on the surface of the workpiece to be welded before welding, and then TIG welding along the flux layer. Compared with the conventional TIG welding process, the penetration ability of A-TIG welding arc is significantly enhanced, and the heat input, welding deformation and stress are reduced. When welding product components of the same specifications, under the same welding current conditions, the single pass welding without groove can be realized or the number of surfacing layers can be significantly reduced, so as to improve the welding productivity and product quality, and double the cost.
In addition, active flux can greatly reduce the weld porosity defects in the process of argon arc welding, so as to directly improve the fatigue performance of welded joints and welded structures. The results show that the fatigue limit of TC4 titanium alloy A-TIG welding butt joint is 16% higher than that of conventional TIG welding, and can reach 90% of the base metal. At present, the active flux argon arc welding technology of titanium alloy has developed into a new advanced connection manufacturing technology to ensure the quality of weapons and equipment, improve the processing efficiency and reduce the cost.

Basic principle of A-TIG welding technology for titanium alloy

  1. The existence of the thin film limits the conduction cross section of the arc and makes the arc shrink; 
  2. Because the surface of titanium alloy is covered with active flux layer before welding, in the process of arc conduction, only when the active flux and titanium metal are melted by arc heat and the flux film is successfully squeezed away by liquid titanium can the successful conduction and stable combustion of arc be realized. Because of the good wettability between the molten active flux and liquid titanium, the flux film is not easy to be squeezed away. The less it is squeezed out, the narrower the weld, the more concentrated the heat flux of the arc, and the deeper the penetration depth; 
  3. During A-TIG welding, the active flux molecular vapor enters into the arc atmosphere, which increases the thermal conductivity of the plasma in the arc column and makes the arc shrink; 
  4. The arc heat makes the active flux decompose and ionize and enter into the outer space of the arc, and the flux ions capture the electrons around the arc to form negative ions, which reduces the voltage of the outer space of the arc column and makes the arc shrink. It is because of the synergism of the above aspects that the welding arc shrinks obviously, the current density of arc column increases, and the welding penetration increases.

Development status of foreign technology

The active flux was first developed by Ukraine Barton Welding Research Institute in 1960s. The original purpose of its development is to improve the porosity problem in TIG welding of titanium alloy by adding halide in the weld zone. The results show that the addition of halide not only restrains the porosity of titanium alloy weld, but also affects the weld formation: under the same conditions, the weld penetration (H) increases, the weld width (b) decreases and the weld shape coefficient increases( ψ= B/h) also decreased. In addition, the heat input (Q/V) is also reduced. In view of a series of positive effects brought by halide addition, Barton Institute developed the first multi-component active flux product, AHT-9A, in 1964 for titanium alloy welding. At present, its A-TIG welding process has passed the test confirmation, and is used in Russian aviation, aerospace, chemical industry, pressure vessels, power equipment, nuclear power facilities and other fields. The research of active flux for argon arc welding in the United States is relatively backward than that in Ukraine. However, the active flux for TIG welding of stainless steel and carbon steel developed by the United States has been used in the construction of catamaran hull, oil tanker, nuclear reaction vessel and pressure vessel; The flux is being used by the navy to weld the piping system and some parts of ships and submarines.
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