Composite welding method for titanium alloy thick plate

Abstract

The invention relates to a composite welding method for a titanium alloy thick plate. The welding method comprises the following steps: pre-welding pretreatment: forming a welding groove in the back surface of a workpiece needing tungsten electrode inert gas shielded welding, pre-treating the surface, and additionally installing a fixing piece; a fixing piece on the front face of the workpiece is removed, local vacuum electron beam welding is conducted on a welding seam on the front face of the workpiece, and sealing cover welding on the front face of the welding seam is formed; stress is eliminated after welding, and a welding seam is detected. Two different welding modes are adopted, the welding pass number during single welding is reduced, the welding efficiency is improved, the welding period is shortened, meanwhile, the process that a backing plate is additionally arranged on the back face of an original workpiece is omitted, backing plate cutting and post-welding shape correction are not needed after welding, the welding seam quality of the obtained titanium alloy thick plate workpiece is good, and the process quality is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a composite welding method for titanium alloy thick plates, and more particularly to a composite welding method for welding titanium alloy thick plates by TIG welding bottom sealing and vacuum electron beam welding surface covering. BACKGROUND

[0002] In the prior art, titanium alloy occupies an important position in shipbuilding and marine equipment manufacturing due to its high strength and superior corrosion resistance. Titanium alloy thick plate generally refers to a workpiece with a thickness of 40-50 mm. Currently, in the field of shipbuilding, titanium alloy is mainly welded by manual multi-layer multi-pass tungsten inert gas welding (TIG welding). This welding method often requires filling a large number of welding passes, and the TIG welding speed is slow. In addition, it needs to wait for post-weld cooling and control the interlayer temperature, resulting in a long welding cycle and affecting the overall workpiece construction efficiency. At the same time, due to the characteristics of low energy density and wide heat-affected zone of TIG welding, the post-weld thermal deformation is high.

[0003] Vacuum electron beam welding is a welding method with high energy density, which can quickly heat and cool the weld metal. Compared with TIG welding, it has the characteristics of high penetration and small post-weld workpiece deformation. When welding thick plate titanium alloy, it usually takes days to fill the butt weld of thick plate using TIG welding, while it usually takes hours to fill the same butt weld using vacuum electron beam welding. Therefore, vacuum electron beam welding has a shorter welding cycle and higher welding efficiency. At the same time, since it is welded in a high vacuum environment, it can effectively isolate oxygen and hydrogen in the air, avoid the reaction of titanium alloy with them during welding, and reduce the occurrence of welding defects such as oxidation and hydrogen-induced cracking. In the use of vacuum electron beam welding for welding test plates, due to the characteristics of large penetration, in order to ensure that the weld is penetrated and the back is formed, the vacuum electron beam welding does not penetrate the back workpiece, a certain thickness of backing plate needs to be installed on the back of the workpiece. However, in actual production, due to the complex structure of the workpiece to be welded, the backing plate is combined with the workpiece after welding, and it is difficult to cut the backing plate.

[0004] Therefore, it is necessary to develop a new vacuum electron beam welding process to overcome the bottlenecks encountered in the application of the prior art and achieve efficient welding of titanium alloy thick plates. SUMMARY

[0005] The purpose of the present application is to provide an improved composite welding method for titanium alloy thick plates. By improving the method, two welding methods are adopted to improve the welding efficiency and obtain good vacuum electron beam welds of titanium alloy thick plates.

[0006] In order to achieve the above object, the technical scheme of the present application is: a composite welding method for titanium alloy thick plates, characterized in that the composite welding method comprises the following steps: a, welding pretreatment: opening a welding groove on the back of a workpiece to be welded by tungsten inert gas welding, surface pretreatment and installation of a fixing part; b, tungsten inert gas welding at the welding groove to form a back sealing welding of the workpiece; c, removing the fixing part on the front of the workpiece, and performing local vacuum electron beam welding on the weld on the front of the workpiece to form a front sealing welding of the weld; and d, stress relief after welding and detection of the weld.

[0007] Preferably, in the step a, a V-shaped groove is opened on the back of the two titanium alloy thick plates to be welded, the depth of the groove is 6-12 mm, the width is 4-8 mm, a polishing machine is used to polish the weld and the area 50 mm on both sides to remove the chlorination layer, and acetone is used to wipe off the oil stains.

[0008] Further, in the step a, the positions of the two workpieces are adjusted, and the two workpieces are assembled by gapless spot welding, and a clamp plate is installed and fixed in an intermittent welding manner on the front of the workpiece in the middle and on both sides.

[0009] Further, in the step b, 99.999% Ar gas is used as the protective gas, and the flow rate of the protective gas is set to 20-25 L / min.

[0010] Further, a TC4 welding wire with a diameter of 1.2 mm is selected, and the manual tungsten inert gas welding parameter is set to 125-135 A.

[0011] Further, in the step c, a cutting sheet is used to remove the clamp plate in the middle of the front of the workpiece, the gap between the front welds is protected during cutting to prevent metal spatter generated by cutting from entering the inside of the weld, and then the front welds and the surrounding area are cleaned.

[0012] Further, the area 50 mm on both sides of the front weld area is mechanically polished and cleaned, acetone is used to wipe off the oil stains, and then the front weld of the workpiece is locally vacuum electron beam welded, the workpiece is placed in a local vacuum electron beam welding tool, the tool seals the weld area, the sealed weld area is pumped to a low vacuum state, the vacuum degree of the vacuum chamber is set to 6.5x10 -1 Pa, and the vacuum degree of the vacuum gun is set to 2x10 -2Pa, the beam current size is set to 110mA-106mA, the focusing current size is set to 755mA, the slit beam size is set to 1mA, the acceleration voltage is set to 80kv, the welding speed is set to 3.56mm / s, the scanning mode adopts circular swing, and the swing frequency is set to 80Hz. When the local vacuum electron beam is welded, the beam current size is sequentially weakened in time periods to prevent the molten pool from collapsing.

[0013] Further, in the d step, after stress relief treatment after welding, X-ray nondestructive testing, metallographic observation, room temperature impact and tensile test are carried out.

[0014] Compared with the prior art, the technical scheme of the present application not only improves the overall technical scheme, but also improves many details. Specifically, it has the following beneficial effects: 1. The improved scheme of the present application uses tungsten inert gas welding at the welding groove to form the back sealing welding of the workpiece, and then uses local vacuum electron beam welding on the front weld of the workpiece to form the front sealing welding of the weld, which reduces the number of welding passes in single welding, improves the welding efficiency, and shortens the welding cycle. 2. In the technical scheme of the present application, tungsten inert gas welding is used to form the back sealing welding of the workpiece, which reduces the process of adding a backing plate to the back of the workpiece, and eliminates the need for cutting the backing plate after welding and post-weld straightening, thereby shortening the process flow and reducing costs. 3. In the technical scheme of the present application, two welding methods are used in cooperation to obtain a titanium alloy thick plate workpiece with good weld quality, improving the process quality. 4. The method of the present application is simple and easy to implement, improves the welding efficiency, reduces the cost, and is easy to promote and utilize. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The figure is a schematic diagram of the metallographic structure of the workpiece after welding of the present application.

[0016] Figure 2 The figure is a schematic diagram of the back structure of the workpiece after tungsten inert gas welding of the present application.

[0017] Figure 3 The figure is a schematic diagram of the front structure of the workpiece after vacuum electron beam welding of the present application. DETAILED DESCRIPTION

[0018] The technical scheme of the present application will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0019] The application provides a composite welding method for a titanium alloy thick plate, and particularly refers to Figure 1 The composite welding method comprises the following steps: a, welding pretreatment: welding grooves are formed on the back surface of a workpiece to be welded by tungsten inert gas welding, the surface is pretreated, and a fixing member is installed; b, tungsten inert gas welding is performed at the welding grooves to form bottom sealing welding on the back surface of the workpiece; c, the fixing member on the front surface of the workpiece is removed, and local vacuum electron beam welding is performed on the weld on the front surface of the workpiece to form cover sealing welding on the front surface of the weld; and d, stress is eliminated after welding, and the weld is detected.

[0020] In the implementation, two different welding methods are adopted, that is, tungsten inert gas welding is first performed on the back surface of the workpiece to form bottom sealing welding on the back surface of the workpiece, and then local vacuum electron beam welding is performed on the weld on the front surface of the workpiece to form cover sealing welding on the front surface of the weld, so that the number of welding passes during single welding is reduced, the welding efficiency is improved, the welding cycle is shortened, the process of adding a backing plate to the back surface of the workpiece is reduced, and after welding, the backing plate does not need to be cut and the workpiece does not need to be straightened, so that the weld quality of the titanium alloy thick plate workpiece is good, and the process quality is improved.

[0021] Embodiment 1 In the embodiment, the composite welding method comprises the following steps: a, welding pretreatment: welding grooves are formed on the back surface of a workpiece to be welded by tungsten inert gas welding, the surface is pretreated, and a fixing member is installed; b, tungsten inert gas welding is performed at the welding grooves to form bottom sealing welding on the back surface of the workpiece; c, the fixing member on the front surface of the workpiece is removed, and local vacuum electron beam welding is performed on the weld on the front surface of the workpiece to form cover sealing welding on the front surface of the weld; and d, stress is eliminated after welding, and the weld is detected.

[0022] Specifically, two Ti-6Al-4V titanium alloy thick plates with a thickness of 45 mm are used as the workpiece for welding, in the step a, V-shaped grooves are formed on the back surface of the two titanium alloy thick plates to be welded, the depth of the grooves is 6-12 mm, the width is 4-8 mm, a polishing machine is used to polish the weld and the area of 50 mm on both sides to remove the chlorination layer, and acetone is used to wipe off the oil stains. The positions of the two workpieces are adjusted, and the two workpieces are assembled by gapless spot welding, and the Mabian plates are installed and fixed in the form of intermittent welding on the front surface of the workpiece in the middle and on both sides.

[0023] Further, in the step b, 99.999% Ar gas is used as the protective gas, and the flow rate of the protective gas is set to 20-25 L / min. A TC4 welding wire with a diameter of 1.2 mm is selected, and the parameters of the manual tungsten inert gas welding are set to 125-135 A.

[0024] Further, in the c step, the middle plate in the front surface of the workpiece is removed by cutting, and the gap between the welds in the front surface is protected during cutting to prevent metal spatter generated by cutting from entering the welds. Then, the welds in the front surface and the surrounding area are cleaned. The area to be welded in the front surface and the area within 50 mm on both sides thereof are mechanically polished and cleaned, and then the welds in the front surface are locally vacuum electron beam welded. The workpiece is placed in a local vacuum electron beam welding tool, the tool seals the area to be welded, and the sealed area to be welded is pumped to a low vacuum state. The tool drives the electron beam gun to move and weld while maintaining the vacuum degree in the tool. The vacuum degree in the vacuum chamber is set to 6.5 x 10 -1 Pa, the vacuum degree of the vacuum gun is set to 2 x 10 -2 Pa, the beam current is set to 110 mA-106 mA, the focusing current is set to 755 mA, the slit beam current is set to 1 mA, the acceleration voltage is set to 80 kv, the welding speed is set to 3.56 mm / s, and the scanning mode is circular oscillation with an oscillation frequency of 80 Hz.

[0025] To prevent the molten pool from collapsing during local vacuum electron beam welding, the beam current is gradually reduced in time periods. In the welding time of 0-51 s, the beam current of the local vacuum electron beam welding is set to 110 mA, in the welding time of 51-71 s, the beam current of the local vacuum electron beam welding is set to 109 mA, in the welding time of 71-91 s, the beam current of the local vacuum electron beam welding is set to 108 mA, in the welding time of 91-101 s, the beam current of the local vacuum electron beam welding is set to 107 mA, in the welding time of 101-128 s, the beam current of the local vacuum electron beam welding is set to 106 mA, and the other parameters remain unchanged. By gradually reducing the heat input of the vacuum electron beam welding, the overall heat of the workpiece is controlled to ensure the quality of the weld formation.

[0026] Specifically, in the welding time of (0-T) s, the beam current of the local vacuum electron beam welding is V mA, in the welding time of (T-T+20) s, the beam current of the local vacuum electron beam welding is (V-1) mA, in the welding time of (T+20-T+40) s, the beam current of the local vacuum electron beam welding is (V-2) mA, and the beam current decreases by 1 mA for every 20 seconds of welding time. The initial welding time T is 51 s, the beam current V of the local vacuum electron beam welding is 110 mA, and the beam current of the local vacuum electron beam welding in the welding time of 101-128 s is set to 106 mA.

[0027] In the d step, after stress relief treatment, X-ray non-destructive testing, metallographic observation, room temperature impact and tensile testing are carried out.

[0028] Example 2 In this embodiment, the composite welding method comprises the following steps: a, pre-welding treatment: opening a welding groove on the back of the workpiece to be subjected to tungsten inert gas welding, surface pretreatment and installation of a fixing part; b, performing tungsten inert gas welding at the welding groove to form a back sealing weld of the workpiece; c, removing the fixing part on the front of the workpiece and performing local vacuum electron beam welding on the weld on the front of the workpiece to form a front sealing weld of the weld; d, eliminating stress after welding and detecting the weld.

[0029] Specifically, two TC4 titanium alloy butt welding test plates (each TC4 test plate has a length of 500 mm, a width of 200 mm and a thickness of 48 mm) are welded, including the following steps: First, pre-welding treatment and assembly: V-shaped grooves are opened on the back of the two TC4 workpieces (TIG welding back sealing surface), with a single-side groove depth of 8 mm and a width of 6 mm; mechanical polishing is used to polish the weld and the area 50 mm away from the weld on both sides to remove the oxide layer, and acetone is used to wipe the surface to remove oil stains. The workpieces are adjusted so that the maximum value of the assembly gap and the misalignment amount are both <0.1 mm, and the workpieces are fixed by spot welding with small heat input parameters by using manual TIG welding. A plurality of short welds are used to fix the test plates on the middle position of the front of the workpieces and on both sides of the test plates to prevent deformation of the workpieces caused by TIG welding on the back of the workpieces.

[0030] Then, tungsten inert gas welding (TIG welding): since the manual TIG welding on the back of the workpiece needs to fill multiple layers and multiple passes, in order to reduce the welding deformation of the workpiece caused by TIG welding, the welding sequence of the filling passes is performed by the method of segmented back welding. A TC4 welding wire with a diameter of 1.2 mm is selected, and 99.999% argon is used as the shielding gas to ensure the welding quality, with a shielding gas flow rate of 20-25 L / min and a welding current of 125 A-135 A.

[0031] Then, vacuum electron beam welding is performed: the test plate is placed in a vacuum welding chamber for vacuumizing treatment, the vacuum degree inside the welding chamber is maintained at 6.5×10 -1 Pa, and the vacuum degree of the electron beam welding gun is maintained at 2×10 -2 Pa. The welding parameters are shown in the following table: In order to prevent the local vacuum electron beam welding from increasing the penetration depth due to excessive accumulation of welding heat, and thus welding through the TIG welding bottom layer, the beam current of the local vacuum electron beam welding is attenuated with the increase of welding time. In the welding time of 0-51s, the beam current of the local vacuum electron beam welding is set to 110mA, in the welding time of 51-71s, the beam current of the local vacuum electron beam welding is set to 109mA, in the welding time of 71-91s, the beam current of the local vacuum electron beam welding is set to 108mA, in the welding time of 91-101s, the beam current of the local vacuum electron beam welding is set to 107mA, in the welding time of 101-128s, the beam current of the local vacuum electron beam welding is set to 106mA, and the rest of the parameters remain unchanged. By adopting the method of slow reduction of the heat input of the vacuum electron beam welding, the heat of the whole workpiece is controlled, and the quality of the weld forming is ensured.

[0032] Finally, post-weld detection is carried out: residual stress elimination work is carried out on the post-weld test plate, X-ray non-destructive testing is carried out on the weld, no obvious defects are found, full-thickness room temperature tensile test is carried out on the mechanical properties of the weld, room temperature impact test is carried out on the vacuum electron beam welding area (upper layer and lower layer area), TIG bottom sealing welding area, and vacuum electron beam welding and TIG bottom sealing welding remelted area respectively, and the test results are as follows: In summary, the welding process provided by the present application is simple, and the post-weld straightening process is reduced. In addition, by using the vacuum electron beam welding cover, the total number of test plate welding is reduced, and the production efficiency is improved.

[0033] The above is a further detailed description of the present application in combination with specific preferred embodiments, and cannot be regarded as limiting the specific implementation of the present application to the above description. For ordinary skilled persons in the technical field to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the present application.

Claims

1. A composite welding method for thick titanium alloy plates, characterized in that: The composite welding method includes the following steps: a) Pre-welding treatment: a welding bevel is made on the back of the workpiece to be welded by tungsten inert gas (TIG) welding, the surface is pre-treated and a fixing component is installed; b) Tungsten inert gas welding is performed at the welding bevel to form a bottom sealing weld on the back of the workpiece; c) The fixing component on the front of the workpiece is removed, and the weld on the front of the workpiece is locally vacuum electron beam welded to form a top sealing weld on the front of the weld; d) Stress is relieved after welding, and the weld is inspected.

2. The composite welding method for thick titanium alloy plates according to claim 1, characterized in that: In step a, for the two titanium alloy thick plates that need to be welded, a V-shaped bevel is opened on the back of the workpiece. The depth of the bevel is 6-12mm and the width is 4-8mm. A polishing machine is used to grind the weld and the 50mm area on both sides to remove the chlorination layer, and acetone is used to wipe away the oil stains.

3. The composite welding method for thick titanium alloy plates according to claim 1, characterized in that: In step a, the positions of the two workpieces are adjusted, and the two workpieces are assembled by seamless spot welding. On the front center and both sides of the workpieces, the mounting plates are added and fixed by intermittent welding.

4. The composite welding method for thick titanium alloy plates according to claim 1, characterized in that: In step b, 99.999% Ar gas is used as the protective gas, and the protective gas flow rate is set to 20-25 L / min.

5. A composite welding method for thick titanium alloy plates according to claim 4, characterized in that: The welding wire used is 1.2mm TC4 welding wire, and the parameters for manual tungsten inert gas welding are set to 125-135A.

6. The composite welding method for thick titanium alloy plates according to claim 1, characterized in that: In step c, the plate in the middle of the front of the workpiece is removed using a cutting blade. During the cutting, the gap of the front weld is protected to prevent metal splatter from entering the weld. Then the front weld and its surrounding area are cleaned.

7. A composite welding method for thick titanium alloy plates according to claim 6, characterized in that: The area to be welded on the front side and the area within 50mm on both sides are mechanically ground and cleaned. Acetone is used to wipe away oil stains. Then, local vacuum electron beam welding is performed on the weld seam on the front side of the workpiece. The workpiece is placed in a local vacuum electron beam welding fixture, which seals the area to be welded. The sealed area is evacuated to a low vacuum state. The fixture moves the electron beam gun while welding, maintaining the vacuum level within the fixture. The vacuum level of the vacuum chamber is set to 6.5 × 10⁻⁶. -1 Pa, the vacuum level of the vacuum gun is set to 2×10 Pa. - 2 Pa, beam current is set to 110mA-106mA, focusing current is set to 755mA, seam beam current is set to 1mA, accelerating voltage is set to 80kV, welding speed is set to 3.56mm / s, scanning mode is circular oscillation, and oscillation frequency is set to 80Hz.

8. A composite welding method for thick titanium alloy plates according to claim 6, characterized in that: During vacuum electron beam welding, the beam current decreases sequentially over time.

9. A composite welding method for thick titanium alloy plates according to claim 1, characterized in that: In step d, the workpiece is subjected to stress relief treatment after welding, followed by X-ray non-destructive testing, metallographic observation, room temperature impact and tensile testing.

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