A laser welding method for TiAl alloy and TC4 dissimilar materials

Abstract

This invention relates to a laser welding method for TiAl alloy and TC4 dissimilar materials. The aim of this invention is to address the technical problems of current laser welding methods for TiAl alloys, such as the occurrence of macro / micro cracks, poor weld quality, and a high content of brittle phases at the weld joint. This invention avoids welding defects caused by heat input mismatch between the two metals due to excessively rapid cooling during laser welding by controlling the laser welding parameters. Furthermore, by controlling the laser heat input and performing laser preheating before welding, the cooling rate of the molten pool is slowed down, thereby reducing thermal stress between the weld and the base material, releasing residual stress as much as possible, reducing the crack sensitivity of the brittle TiAl alloy, and suppressing the formation of a large number of brittle phases at the weld joint. This results in a TiAl / TC4 weld joint with good forming quality and no macro-cracks, achieving a good connection between TiAl / TC4 dissimilar material plates.

Description

Technical Field

[0001] This invention relates to a laser welding method for dissimilar alloy materials. Background Technology

[0002] Laser welding technology, characterized by high welding speed, high welding precision, and high processing efficiency, is attracting increasing attention from scholars both domestically and internationally. However, as a fusion welding method, laser welding requires melting two base metals to achieve a connection. This is particularly problematic for brittle materials like TiAl alloys, which are prone to macro / micro cracks, poor weld quality, and a high content of brittle phases at the weld joint. Therefore, certain technical challenges exist in the welding of dissimilar materials like TiAl / TC4. The heat input mismatch between the two materials leads to welding defects such as cracks and porosity at the weld joint and on the TiAl alloy side, reducing the quality of the TiAl / TC4 weld joint. Furthermore, compared to brazing and arc welding, laser welding has lower heat input, higher energy density, and faster cooling rates. Optimizing and improving the laser welding process parameters for TiAl / TC4 dissimilar materials to obtain high-quality TiAl / TC4 weld joints remains a key technical challenge. TiAl alloys are inherently brittle, with room temperature plasticity generally not exceeding 2%. During welding, the process window is narrow, resulting in poor weld controllability. During the welding process, due to the input of heat, a large number of metallurgical reactions occur at the weld joint. The rapid diffusion of Ti and Al elements can easily lead to the formation of a large number of brittle phases such as α2-Ti3Al in the TiAl / TC4 weld joint, making the weld joint highly susceptible to cracking and reducing the quality of the weld. Summary of the Invention

[0003] The present invention aims to solve the technical problems of easy occurrence of macro / micro cracks, poor weld quality, and high content of brittle phases at the weld joint in the current laser welding of TiAl alloy, and provides a laser welding method for TiAl alloy and TC4 dissimilar materials.

[0004] The laser welding method for TiAl alloy and TC4 dissimilar material of the present invention is carried out according to the following steps:

[0005] 1. TiAl alloy and TC4 alloy are cut into plates using wire EDM.

[0006] 2. Pre-welding heat treatment: The TiAl and TC4 plates after wire cutting are subjected to stress-relief annealing to reduce the residual stress in the original materials, thereby reducing the accumulation of stress during welding and the generation of surface welding microcracks.

[0007] 3. Cleaning: Polish and grind the surfaces of TiAl alloy and TC4 plates, as well as the welded joint surfaces, to remove the oxide scale. Then clean with acetone and dry.

[0008] IV. Clamping and fixing: Use clamps to clamp the TiAl and TC4 alloy plates onto the welding platform, ensuring that the two welding surfaces are aligned, flush, and clamped together.

[0009] V. Install protective gas devices: Install a bypass protective gas above the two plates and a back protective gas below the two plates;

[0010] VI. Laser Multi-Laser Scanning Preheating: Under the protection of the paraxial protective gas and the back protective gas, the TiAl and TC4 dissimilar metals are preheated in situ by efficiently heating the TiAl and TC4 plates by controlling the laser power, scanning speed, number of scans and defocusing amount. During preheating, the laser spot is biased to one side of the TiAl plate; the laser path is a straight line during preheating.

[0011] VII. Single-pass laser welding: Under the protection of off-axis shielding gas and back shielding gas, the heat input of TiAl and TC4 plates is matched by adjusting the laser power, welding speed and defocusing amount, effectively controlling the metallurgical reaction inside the weld, thereby inhibiting the formation of porosity, cracks and brittle phase defects at the weld, realizing the effective welding of dissimilar materials TiAl alloy and TC4 alloy, and obtaining a good weld joint; during laser welding, the laser spot is biased to one side of the TiAl plate; the laser welding path is a straight line.

[0012] The advantages of this invention are as follows:

[0013] I. This invention avoids welding defects caused by heat input mismatch between the two metals due to excessively rapid cooling during laser welding by adjusting laser welding parameters such as laser power, scanning speed, shielding gas flow rate, and laser welding offset. Ultimately, it obtains TiAl / TC4 bimetallic plates with beautiful weld formation and good quality.

[0014] Second, by controlling the laser heat input and performing laser preheating before welding, this invention slows down the cooling rate of the molten pool, thereby reducing the thermal stress between the weld and the base material, releasing residual stress as much as possible, reducing the crack sensitivity of the brittle TiAl alloy material, improving the weldability of TiAl / TC4, suppressing the formation of a large number of brittle phases at the weld, obtaining a TiAl / TC4 welded joint with good forming quality and no macroscopic cracks, and realizing a good connection of TiAl / TC4 dissimilar material plates. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of laser welding of TiAl / TC4 dissimilar materials according to the present invention;

[0016] Figure 2 TiAl / TC4 bimetallic sheet prepared according to the laser welding process parameters of Experiment 1;

[0017] Figure 3 Microstructure of TiAl / TC4 bimetallic welded joint obtained without preheating during the comparative experiment;

[0018] Figure 4 The image shows the microstructure of the TiAl / TC4 bimetallic welded joint obtained in Experiment 1.

[0019] Figure 5 for Figure 3 Element content distribution diagram of the intermediate weld area;

[0020] Figure 6 for Figure 4 Element content distribution diagram of the weld seam region. Detailed Implementation

[0021] Specific Implementation Method 1: This implementation method is a laser welding method for TiAl alloy and TC4 dissimilar material, specifically carried out according to the following steps:

[0022] 1. TiAl alloy and TC4 alloy are cut into plates using wire EDM.

[0023] II. Pre-welding heat treatment: The TiAl and TC4 plates after wire cutting are subjected to stress-relief annealing to reduce the accumulation of stress during welding and the generation of surface welding microcracks.

[0024] 3. Cleaning: Polish and grind the surfaces of TiAl alloy and TC4 plates, as well as the welded joint surfaces, to remove the oxide scale. Then clean with acetone and dry.

[0025] IV. Clamping and fixing: Use clamps to clamp the TiAl and TC4 alloy plates onto the welding platform, ensuring that the two welding surfaces are aligned, flush, and clamped together.

[0026] V. Install protective gas devices: Install a bypass protective gas above the two plates and a back protective gas below the two plates;

[0027] VI. Laser Multi-Laser Scanning Preheating: Under the protection of the paraxial protective gas and the back protective gas, the TiAl and TC4 dissimilar metals are preheated in situ by efficiently heating the TiAl and TC4 plates by controlling the laser power, scanning speed, number of scans and defocusing amount. During preheating, the laser spot is biased to one side of the TiAl plate; the laser path is a straight line during preheating.

[0028] VII. Single-pass laser welding: Under the protection of off-axis shielding gas and back shielding gas, the heat input of TiAl and TC4 plates is matched by adjusting the laser power, welding speed and defocusing amount, effectively controlling the metallurgical reaction inside the weld, thereby inhibiting the formation of porosity, cracks and brittle phase defects at the weld, realizing the effective welding of dissimilar materials TiAl alloy and TC4 alloy, and obtaining a good weld joint; during laser welding, the laser spot is biased to one side of the TiAl plate; the laser welding path is a straight line.

[0029] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the stress-relief annealing temperature of the TiAl alloy in step two is 850℃, and the holding time is 10 hours. Everything else is the same as in Specific Implementation Method One.

[0030] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the stress-relief annealing temperature of TC4 in step two is 650℃, and the holding time is 4 hours. Everything else is the same as in Specific Implementation Method One or Two.

[0031] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step three, 60 to 1000 grit sandpaper is used for sanding until the surface of the board is smooth and free of obvious scratches. Everything else is the same as in Specific Implementation Methods One to Three.

[0032] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the bypass protection gas flow rate in step five is 0.8 L / min. Everything else is the same as in Specific Implementation Method Four.

[0033] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the flow rate of the back protective gas in step five is 0.3 L / min. Everything else is the same as in Specific Implementation Method Five.

[0034] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that both the off-axis protective gas and the back protective gas in step five are argon. Everything else is the same as in Specific Implementation Method Six.

[0035] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that: in step six, the laser power is 0.5kW, the laser scanning speed is 80mm / s, the number of scans is 3, and the defocusing amount is 15mm. Everything else is the same as in Specific Implementation Method Seven.

[0036] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the laser power in step seven is 1kW, the welding speed is 10mm / s, and the defocusing amount is 15mm. Everything else is the same as in Specific Implementation Method Eight.

[0037] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the laser bias amount in steps six and seven is 0.5mm. Everything else is the same as in Specific Implementation Method Nine.

[0038] The invention was verified using the following experiments:

[0039] Experiment 1: This experiment demonstrates a laser welding method for TiAl alloy and TC4 dissimilar materials, specifically carried out according to the following steps:

[0040] 1. TiAl alloy and TC4 alloy were cut into plates using wire cutting method. The dimensions of both plates were 48mm×30mm×2mm.

[0041] II. Pre-welding heat treatment: The wire-cut TiAl and TC4 plates were subjected to stress-relief annealing to reduce stress accumulation during welding and the generation of surface welding microcracks. The annealing temperature of TiAl alloy was 850℃ and the holding time was 10h. The annealing temperature of TC4 was 650℃ and the holding time was 4h.

[0042] 3. Cleaning: Polish and grind the surfaces of the two alloy plates and the welded surfaces, then use 60 to 1000 grit sandpaper to grind and clean the surface oxide scale until the plate surface is smooth and free of obvious scratches; then clean with acetone and dry.

[0043] IV. Clamping and fixing: Use clamps to clamp the TiAl and TC4 alloy plates onto the welding platform, ensuring that the two welding surfaces are aligned, flush, and clamped together.

[0044] V. Installation of protective gas devices: A bypass protective gas is installed above the two plates, and a back protective gas is installed below the two plates; both protective gases are argon; the flow rate of the bypass protective gas is 0.8 L / min, and the flow rate of the back protective gas is 0.3 L / min;

[0045] VI. Laser Multi-Laser Scanning Preheating: Under the protection of the parietal protective gas and the back protective gas, the laser power is set to 0.5kW, the laser scanning speed is 80mm / s, the number of scans is 3, and the defocusing amount is 15mm. This efficiently heats the TiAl and TC4 plates to achieve in-situ preheating of the TiAl / TC4 dissimilar metals. During preheating, the laser spot is biased to one side of the TiAl plate, and the laser bias is 0.5mm. The laser path is a straight line during preheating.

[0046] VII. Single-pass laser welding: Under the protection of the off-axis shielding gas and the back shielding gas, the laser power is 1kW, the defocusing amount is 15mm, and the welding speed is 10mm / s, realizing the effective welding of dissimilar materials TiAl alloy and TC4 alloy, and obtaining a good weld joint; during laser welding, the laser spot is biased to one side of the TiAl plate with an offset of 0.5mm; the laser welding path is a straight line.

[0047] Figure 2 The TiAl / TC4 bimetallic sheet prepared using the laser welding process parameters of Experiment 1 is shown on the right. The right side is TiAl and the left side is TC4. It can be seen that the forming quality is good and there are no macroscopic cracks.

[0048] Comparative test: This test is a comparative test. Preheating before welding was not used. Compared with test one, step six is ​​not used. The rest of the process flow and parameters are the same as those in test one.

[0049] Figure 3 To compare the microstructure of the TiAl / TC4 bimetallic welded joint obtained without preheating before welding in the experiment, it can be seen from the figure that the weld width is relatively wide and there are porosity defects in the weld area.

[0050] Figure 4 The microstructure of the TiAl / TC4 bimetallic welded joint obtained in Experiment 1 shows that the width of the weld area and the heat-affected zone is significantly reduced after preheating, and no obvious porosity defects are observed, indicating good welding quality.

[0051] Figure 5 for Figure 3 Element content distribution diagram of the weld seam region. Figure 6 for Figure 4 The elemental distribution diagram of the weld area shows that the weld area at the weld joint is reduced after using the preheating method of Experiment 1, and the area containing the α2-Ti3Al brittle phase is reduced.

[0052] Table 1 shows... Figure 5 The average content of each element in the three regions of TiAl, weld zone and TC4.

[0053] Table 1

[0054]

[0055] Table 2 is... Figure 6 The average content of each element in the three regions of TiAl, weld zone and TC4.

[0056] Table 2

[0057]

[0058] Tables 1 and 2 mainly focus on the atomic ratio at the weld. It can be inferred that the main constituent phase at the weld is the α2-Ti3Al brittle phase. The atomic ratio on both sides is approximately the same as that of the two base metals, which can be considered as the base metal region. Tables 1 and 2 reflect the same conclusion. Although preheating cannot completely suppress the appearance of brittle phase at the weld, the weld width decreases significantly after preheating, and the brittle phase decreases.

Claims

1. A method for laser welding of TiAl alloy and TC4 dissimilar materials, characterized in that The laser welding method of TiAl alloy and TC4 dissimilar materials is carried out according to the following steps: I. The TiAl alloy and TC4 alloy are cut into plates by using wire cutting method; II. Pre-welding heat treatment: the TiAl plates and TC4 plates cut by wire cutting are respectively subjected to stress relief annealing to reduce the residual stress of the original materials, so as to reduce the accumulation of stress and the generation of surface welding micro-cracks during welding; In step II, the stress relief annealing temperature of the TiAl alloy is 850 DEG C, and the holding time is 10h; In step II, the stress relief annealing temperature of TC4 is 650 DEG C, and the holding time is 4h; III. Cleaning: the surfaces of the TiAl alloy and TC4 plates and the welding joint surface are polished, ground and cleaned to remove the oxide skin, and then washed with acetone and dried; IV. Clamping and fixing: the TiAl and TC4 alloy plates are clamped on the welding platform by using a clamp, so that the two welding surfaces are aligned, leveled and clamped; V. Installing a protective gas device: setting a side-shaft protective gas above the two plates and a back protective gas below the two plates; in step V, the flow rate of the side-shaft protective gas is 0.8L / min; in step V, the flow rate of the back protective gas is 0.3L / min; VI. Laser multi-layer scanning preheating: under the protection of the side-shaft protective gas and the back protective gas, the TiAl plate and the TC4 plate are efficiently heated by controlling the laser power, scanning speed, scanning times and defocusing amount to realize in-situ preheating of the TiAl / TC4 dissimilar metal, and the laser spot is deviated to one side of the TiAl plate during preheating; the laser path is a straight line during preheating; In step VI, the laser power is 0.5kW, the laser scanning speed is 80mm / s, the scanning times are 3, and the defocusing amount is 15mm; in step VI, the laser offset amount is 0.5mm; VII. Laser single-pass welding: under the protection of the side-shaft protective gas and the back protective gas, the matching of the heat input of the TiAl plate and the TC4 plate is adjusted by adjusting the laser power, welding speed and defocusing amount, so as to effectively control the metallurgical reaction in the weld, thereby inhibiting the formation of pores, cracks and brittle phase defects at the weld, realizing the effective welding of the TiAl alloy and the TC4 alloy dissimilar materials, and obtaining a good welding joint; the laser spot is deviated to one side of the TiAl plate during laser welding; the laser welding path is a straight line; in step VII, the laser power is 1kW, the welding speed is 10mm / s, and the defocusing amount is 15mm; in step VII, the laser offset amount is 0.5mm.

2. The laser welding method of TiAl alloy and TC4 dissimilar materials according to claim 1, characterized in that In step III, 60 to 1000 mesh sandpaper is used for grinding until the plate surface is smooth and no obvious scratches are left.

3. The laser welding method of TiAl alloy and TC4 dissimilar materials according to claim 1, characterized in that In step V, the side-shaft protective gas and the back protective gas are both argon.

Images