According to many years’experience in titanium welding, simply summarized the prevention methods for the formation of pores and crack in titanium welding as following:
(1) do the preparation before welding, Weldments and wire surface quality have a significant effect on the mechanical properties of welded joints, therefore it must be carefully cleaned before welding. Iron sheet and titanium wire can be clearned by two methods, one is mechanical cleaning, the other one is chemical cleaning.
(2) the correct choice of welding materials. Argon purity should not be less than 99.99%, dew point below -40 ℃, impurity total mass fraction <0.001%. the back of Important components should be protected by argon, when the pressure in the argon cylinder dropped to 0.981MPa, it should stopped to be used, in order to prevent the impact of welding joint quality. In principle, the titanium wire should be same with the base metal component of welding part, the wire is supplied in a vacuum annealed state. Sometimes in order to improve the weld metal plastic, can also choose a slightly lower strength than the base metal wire.
(3) grasp the welding groove. In principle, the number of welds and weld metal should be minimized. With the increase in the number of welding layers, the cumulative increase in the number of welds, and even affect the performance of welded joints, but also because of titanium and titanium alloy welding bath when the larger size, so the specimen open V-70 ° ~ 80 ° slope Mouth, and not swing. The end of the wire shall not be removed from the gas protection range, and the nozzle diameter may be suitably increased to expand the protection area.
(4) the correct choice of welding process parameters. Increased deep pool residence time to prevent the use of bubbles to escape, can effectively reduce the pores. At the same time, the use of small current, high welding speed welding specifications, the less the number of layers.
(5) Note that the choice of protective gas flow. The choice of gas flow to achieve a good protective effect prevail, too large flow is not easy to form a stable laminar flow, and increase the cooling rate of the weld, the weld surface layer appears more α phase, and even cause micro-cracks. When the flow of argon in the hood is insufficient, the weld exhibits different oxidation color, and when the flow rate is too large, it will interfere with the airflow of the main nozzle. The flow of argon on the back of the weld can not be too large, otherwise it will affect the front of the first layer of weld gas protection effect. In short, to control the gas flow and flow rate, to prevent turbulence phenomenon, affecting the protective effect.
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