Tungsten plate argon arc welding is the most used in the production of titanium and titanium alloy welding, and the vacuum argon filling welding method is also widely used. The arc of argon arc welding is maintained and cooled by the argon flow, the arc heat is more concentrated, the current density is high, the heat affected zone is small, and the welding quality is high.

When welding titanium and titanium alloys, when the temperature is higher than 500 ° C ~ 700 ° C, it is easy to absorb gas, hydrogen and nitrogen in the air, which seriously affects the welding quality. Therefore, when welding titanium and titanium alloys, it is necessary to strictly maintain the weld area of ​​the overall molten pool and the high temperature (400 ° C ~ 650 ° C above). Therefore, special maintenance must be taken when welding titanium and titanium alloys. The measure is to use a welding torch with a larger spray size to expand the area of ​​the gas protection area. When the nozzle is not enough to protect the weld and the high temperature metal in the near seam area, an argon maintenance drag cover is required. Weld seam and near seam color are indicators of maintenance. Snow white indicates the best maintenance, yellow is a slight oxidation, which is generally allowed.

When argon arc welding of titanium and titanium alloys, attention should also be paid to the maintenance of the north face of the weld bead. Considering the welding deformation, we choose the method of slotting and fixing the copper backing plate for argon filling maintenance. A porous copper tube is added to the slag, so that the argon gas enters the maintenance area evenly through the copper tube holes, and the maintenance effect is excellent, and the reverse side of the weld bead is snow-white. Let's learn about the choice of titanium and titanium alloy welding process!

Selection of welding process and parameters for manual tungsten plate argon arc welding:

1. Preparation 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 organize. There are two methods of mechanical finishing and chemical finishing for iron plate and titanium welding wire.

1) Mechanical finishing For welding parts with low quality requirements or difficulty in pickling, use fine sandpaper or stainless steel wire brush to scrub, but it is best to scrape the titanium plate with hard alloy yellow to remove the oxide film.

2) Chemical finishing Before welding, the test piece and welding wire can be pickled, and the pickling solution can be HF5% HNO335% water melt. Rinse with water after pickling, and apply welding immediately after drying. Or use acetone, ethanol, carbon tetrachloride, methanol, etc. to scrub the groove of the titanium plate and its two sides (within 50mm each), the surface of the welding wire, and the part that touches the tool and the titanium plate.

2. Selection of welding equipment

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 oxidation and pollution of the welding.

3. Selection of welding materials

氩气纯度应不低于99.99%，露点在-40℃以下，杂质总的质量分数<0.001%。当氩气瓶中的压力降至0.981MPa时，应停止使用，以避免影响焊接接头质量。原则上应挑选与根本金属成分相同的钛丝，有时为了握高焊缝金属塑性，也可选用强度比根本金属稍低的焊丝。

4. The choice of groove method

The principle is to reduce the number of welding layers and welding metal as much as possible. With the increase of the number of welding layers, the cumulative suction position of the weld increases, which even affects the performance of the welded joint, and because the size of the welding pool is large when welding titanium and titanium alloys, the specimen is billed with a V-shaped groove of 70~80°.

5. Specimen alignment and tack welding

In order to reduce welding deformation, tack welding is performed before welding. Generally, the tack welding distance is 100~150mm and the length is 10~15mm. The welding wire, welding process parameters and gas maintenance conditions used for tack welding should be the same as those used for welding joints. Gap 0~2mm, blunt edge 0~1.0mm.

6. Selection of welding parameters

After comparing the functions of welding joints under different processes, we have found a more suitable welding process specification.

Process (1), the welding current is 150A, 170A, 180A, welding according to this parameter, the appearance of the welded joint shows dark blue and gold color, indicating that the joint is oxidized seriously and does not meet the technical requirements, this process is not advisable.

In process (2), the welding current is relatively reduced to 120A, 150A, and 160A. When welding is performed according to these parameters, the surface of the weld appears golden purple and dark yellow, and the X-ray inspection is flawless, but the mechanical function bending test is unqualified, which clarifies the welded joint. The plasticity is significantly reduced and the skill requirements cannot be met. This process is also not desirable.

Process (3), the welding current is 95A, 115A, 120A, and welding is performed according to these parameters, the appearance of the weld is white and light yellow, and the X-ray flaw detection has no defects, but the mechanical function bending test is qualified, and the tensile strength also meets the requirements. The joint function meets the technical requirements, and this process is more suitable. When titanium and titanium alloys are welded, the grains tend to be coarse, which directly affects the mechanical function of the welded joints. Therefore, the selection of welding process parameters should not only consider the oxidation of the weld metal and the formation of pores, but also consider the factors of grain coarsening, so the smaller welding heat input should be selected as much as possible. Process (1), (2), because the welding specification Larger factors, the formation of joint oxidation is more severe than process (3). And the microscopic metallographic test results show that the degree of grain coarsening of the joint is also more severe than that of the process (3). Therefore, the mechanical function of the welded joint is poor.

7. Operational essentials of tungsten argon arc welding of titanium and titanium alloys

1) During manual argon arc welding, the minimum angle (10~15°) should be kept as far as possible between the welding wire and the weldment. The welding wire should be smoothly and evenly fed into the molten pool along the front of the molten pool, and the end of the welding wire should not be moved out of the argon gas maintenance area.

2) During welding, the welding torch does not swing laterally at all. When swinging is required, the frequency should be low, and the swinging fluctuation should not be too large to avoid affecting the maintenance of argon gas.

3) When the arc is broken and the welding seam ends, continue to maintain the argon gas until the welding seam and the metal in the heat-affected zone cool down to below 350 ℃ before removing the welding torch.

8. Quality inspection

1) Appearance inspection conforms to GB/T13149-91.

2) The ray deep injury conforms to JB4730-94.

3) The mechanical function test conforms to GB/T13149-91.