Special protective measures must be taken when welding titanium and titanium alloys!

Release time：2024-06-24 17:27:03 丨 Number of visits：

When welding titanium alloys, when the temperature is above 500-700 ℃, it is easy to absorb oxygen, hydrogen, and nitrogen from the air, which seriously affects the welding quality. Therefore, when welding titanium alloys, strict protection must be applied to the weld seam area in the entire molten pool and high-temperature areas (above 400-650 ℃). Therefore, special protective measures must be taken when welding titanium and titanium alloys. Therefore, the method of argon arc welding is adopted for treatment, and a larger welding torque is sprayed to expand the area of the gas protection zone. When the nozzle is insufficient to protect the weld seam and high-temperature metal near the seam, an argon protection drag cover needs to be added. Special protective measures must be taken when welding titanium and titanium alloys!

Preparation before welding and groove selection

(1) The surface quality of welded parts and welding wires has a significant impact on the mechanical properties of welded joints. Before welding, the test piece and welding wire can be pickled first. Rinse with clean water, dry and immediately apply welding. Use acetone, ethanol, carbon tetrachloride, methanol, etc. to wipe the titanium plate groove and the parts on both sides (within 50mm), the welding wire surface, and the tool clamp in contact with the titanium plate.

(2) Selection of welding equipment. Titanium and titanium alloy argon arc welding should use a DC argon arc welding power source with descending external characteristics and high-frequency arc ignition, and the delayed gas delivery time should not be less than 15 seconds to avoid oxidation and pollution during welding. So WSM-315 IGBT inverter DC pulse argon arc welding machine is adopted.

(3) Selection of welding materials. The purity of argon gas should not be lower than 99.99%, the dew point should be below -40 ℃, and the relative humidity should be less than 5%. When the pressure in the argon cylinder drops to 0.981 MPa, it should be stopped from use. The filling wire is generally made of homogeneous materials. To improve the plasticity of the joint, TC3 welding wire can be used, which has a slightly lower alloy degree than the base material. TC3 welding wire is used for this welding.

(4) The selection of groove form. In principle, try to reduce the number of welding layers and welding metal as much as possible. As the number of welding layers increases, the cumulative suction amount of the weld seam increases, which affects the performance of the welded joint. Due to the large size of the welding pool during titanium and titanium alloy welding, a V-shaped 70-80 ° groove is required for the welded part.

Correctly select welding process parameters to thoroughly remove organic substances such as oxide skin and oil stains on the surface of the welded parts and welding wires. Control the flow rate and velocity of argon gas to prevent turbulence and affect the inflation protection effect. The method of using manual tungsten inert gas arc welding to treat cracks in titanium alloy welding is feasible and can achieve satisfactory results.

Main defects and repair methods during titanium alloy welding

(1) When welding titanium and titanium alloys, the possibility of thermal cracking in the welded joints is very low. This is because the impurities such as S, P, and C in titanium and titanium alloys are very low, and the low melting point eutectic formed by S and P is not easy to appear at the grain boundaries. In addition, the effective crystallization temperature range is narrow, and the shrinkage of titanium and titanium alloys during solidification is small, so the weld metal will not produce thermal cracks. However, during the welding of titanium and titanium alloys, cold cracks may appear in the heat affected zone, characterized by cracks occurring several hours or even longer after welding, known as delayed cracks. During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower temperature heat affected zone. The increase in hydrogen content leads to an increase in the amount of TiH2 precipitated in this zone, increasing the brittleness of the heat affected zone. In addition, due to the volume expansion of hydride precipitation, significant structural stress is caused, and hydrogen atoms diffuse and aggregate towards the high stress areas of this zone, resulting in the formation of cracks.

(2) Pores are a common problem encountered during welding of titanium and titanium alloys. The fundamental reason for the formation of pores is due to the influence of hydrogen. The formation of pores in the weld metal mainly affects the fatigue strength of the joint. Hydrogen is the main cause of cold cracking and pore formation. Because hydrogen has a low solubility in the alpha phase at temperatures below 300 ℃, its ultimate solubility at room temperature is only 0.002%. When the weld seam or heat affected zone is cooled below 300 ℃ after welding, supersaturated hydrogen precipitates in the form of titanium hydride (gamma phase). The increase in volume generates intergranular stress, which can lead to intergranular microcracks. Intergranular microcracks will propagate into cracks under external stress.