Titanium alloy materials are widely used in aviation, aerospace, petroleum, chemical industry and ship industry for their excellent mechanical properties, corrosion resistance and low density.Argon tungsten arc welding (tig) is one of the most commonly used welding methods for titanium alloy welding structures which are widely used in the above industries.This method has the characteristics of large process margin, strong process adaptability and good weld quality, but it also has the disadvantages of low arc energy density, poor penetration ability, large heat input during welding, large heat damage to materials, large welding stress deformation, etc.Especially in titanium alloy welding, porosity and other defects are easy to occur, which directly affect the performance of welding components.
At present, the development of new aircraft for the titanium alloy welding structure of the requirements of higher and higher, urgent need to develop new, high quality, efficient welding methods, to meet the advanced aircraft engine, aircraft high efficiency, high performance and high reliability of structural design for advanced manufacturing technology long life, low cost requirements.Active flux argon tungsten arc welding (a-tig) technology is developed to meet this requirement.This technology can not only solve the above shortcomings of conventional TIG welding, but also improve the welding quality and service life of components [1-3] under the same technological conditions, and open up a new application prospect for argon tungsten arc welding technology.
Welding technology and characteristics of titanium alloy a-tig
A-tig welding technology is the process of applying A layer of active flux on the upper 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 titanium alloy a-tig welding arc is significantly enhanced, and the heat input, welding deformation and stress are reduced.When welding product components of the same specification, under the same welding current condition, single welding without groove opening or surfacing layer number can be significantly reduced, so as to improve the welding productivity and product quality, and reduce the cost exponentially.
In addition, active flux can greatly reduce weld blowhole defects in the process of argon arc welding, so as to directly improve the fatigue properties 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 90% of base metal.At present, argon arc welding technology of active flux of titanium alloy has developed into a new advanced joint manufacturing technology to improve the quality, improve the processing efficiency and reduce the cost of weapons and equipment.
Basic principle of titanium alloy a-tig welding technology
The existence of thin film limits the conduction cross section of arc and makes arc contract.Secondly, because the surface of titanium alloy material is covered with active flux layer before welding, in the arc conduction process, only arc heat can melt the active flux and titanium metal, and realize liquid titanium to successfully squeeze out the flux film, in order to achieve successful arc conduction and stable combustion.Due to the good infiltration between the molten active flux and the liquid titanium, the flux film is not easy to squeeze out.The less it is squeezed out, the narrower the weld, the more concentrated the heat flow of the arc, and the deeper the penetration.Third, during a-tig welding, the active flux molecular vapor enters the arc atmosphere, which increases the thermal conductivity of plasma in the arc column, thus making the arc contract.Fourth, arc heat disintegrates and ionizes the active flux and enters the outer space of the arc. The flux ions capture the electrons in the outer space of the arc and form anions, which reduces the voltage in the outer space of the arc column and thus causes the arc to contract.Due to the synergism of the above mentioned aspects, the welding arc in a-tig welding process is obviously contracted, the current density of arc column is increased, and the welding fusion depth is increased.
Status quo of foreign technology development
Active flux was first developed by patton welding research institute in Ukraine in the 1960s.Its original purpose was to improve the porosity in TIG welding of titanium alloy by adding halide in the weld area.Test results show that the adding of halide in the inhibition of titanium alloy weld porosity at the same time, also affect the weld forming: in the case of other conditions are equal, the weld penetration increases (h), (b) welding pool width decreases, and the weld shape factor (bits = b/h) also decreased accordingly.In addition, the heat input (q/V) during welding is also reduced.In view of the positive effects of the addition of halides, barton developed the first multi-active flux product, aht-9a, for titanium alloy welding in 1964.At present, the a-tig welding process has been tested and confirmed, and used in Russian aviation, aerospace, chemical industry, pressure vessels, power equipment, nuclear power facilities and other fields.The United States lags behind Ukraine in the study of active flux for argon arc welding.But at present, the active flux for argon arc welding of stainless steel and carbon steel has been used in the construction of catamaran hull, oil tanker, nuclear reaction vessel and pressure vessel.The navy is using the flux to weld piping systems and parts for ships and submarines.