When titanium alloys are welded, some defects cannot be avoided, so how to avoid these defects? Next, let's take a look at the defects and preventive measures of titanium alloy welding, and hope to help you!

The primary problem when welding titanium and its alloys is that it is easy to produce two kinds of defects, such as pores and cracks, as follows:

(1) Porosity is one of the most common defects in the welding of titanium and its alloys. Porosity not only constitutes stress concentration, but also causes plasticity and fatigue of the entire welded joint, reducing the life span.

(2) Cold cracks are another common defect in the welding of titanium and its alloys. Cold cracks in butt joints are generally located on the cross section of the weld.

At room temperature, titanium and titanium alloys are relatively stable. However, experiments have shown that during the welding process, the liquid droplet and molten pool metal have the effect of strongly absorbing hydrogen, oxygen, and nitrogen, and in the solid state, these gases have already reacted with them. As the temperature increases, the ability of titanium and titanium alloys to absorb hydrogen, oxygen and nitrogen also increases significantly. It begins to absorb hydrogen at about 250 °C, absorbs oxygen from 400 °C, and absorbs nitrogen from 600 °C. After the gas is absorbed, it will directly cause embrittlement of the welded joint, which is an important factor leading to the welding defects of titanium and titanium alloys.

Preventive measures include:

(1) Make preparations before welding

The surface quality of the weldment and welding wire has a great influence on the mechanical function of the welded joint, so it is necessary to strictly arrange it. There are two methods of mechanical finishing and chemical finishing for iron plate and titanium welding wire. Correct selection of welding equipment. According to the welding technical requirements and technical standards, select the corresponding welding equipment in detail. For example, for argon arc welding of titanium and titanium alloy gold-tungsten plates, a DC argon arc welding power source with reduced external characteristics and high-frequency arc ignition should be used, and the gas delivery time should be delayed for not less than 15 seconds to avoid welding from being oxidized, Pollution.

(2) Correct selection of welding materials

The purity of argon should not be less than 99.99%, the dew point should be below -40℃, and the total mass fraction of impurities should be less than 0.001%. The reverse side of important components should be flushed with argon gas for maintenance. When the pressure in the argon gas cylinder drops to 0.981MPa, it should be stopped to avoid affecting the quality of welded joints. In principle, the titanium wire with the same composition as the base metal should be selected, and the welding wire is supplied in a vacuum annealed state. Sometimes in order to improve the plasticity of the weld metal, a wire with a slightly lower strength than the base metal can also be used.

(3) Master the welding groove

In principle, the number of welding layers and welding metal should be minimized. With the increase of the number of welding layers, the cumulative suction position of the weld increases, which affects the function of the welded joint. Because the size of the welding pool is large when welding titanium and titanium alloys, the test piece is billed with a V-shaped groove of 70° to 80°. , and do not swing. The end of the welding wire shall not be moved out of the gas maintenance area, and the diameter of the nozzle can be appropriately increased to expand the maintenance area.

(4) Pay attention to the selection and maintenance of gas flow

The selection of gas flow is based on achieving a good maintenance effect. Excessive flow is not easy to form a stable laminar flow, and increase the cooling rate of the weld, so that more α phase appears on the outer surface of the weld, resulting in micro-cracks. When the flow of argon gas in the drag hood is insufficient, the weld shows different oxidation colors; and when the flow is too large, it will interfere with the airflow of the main nozzle. The argon gas flow on the reverse side of the weld should not be too large, otherwise it will affect the gas maintenance effect of the first layer of weld on the front. All in all, it is necessary to control the flow and flow rate of the gas to avoid turbulence and affect the maintenance effect.

(5) Correct selection of welding process parameters

Increase the dwell time in the deep pool to avoid air bubbles from escaping during use, which can effectively reduce pores. At the same time, the welding standard of low current and high welding speed is selected, and the number of welding layers is less.