Brazing method for TC4 titanium alloy and dissimilar metal material

Abstract

The invention discloses a brazing method for TC4 titanium alloy and dissimilar metal materials, and belongs to the field of brazing. The problems that in the existing TC4 and dissimilar metal material brazing process, brittle phases are likely to be generated, microcrack defects are generated, the joint strength is low, and brazing filler metal with the excessively-high flowability of a thin-wall component brazing interface is likely to flow all around are solved. The method comprises the following steps: 1, treating solder powder by plasmas; 2, preparing soldering paste; thirdly, a to-be-welded component is prepared; and 4, brazing. The method is used for brazing of TC4 titanium alloy and dissimilar metal materials.

Description

Technical Field

[0001] This invention belongs to the field of brazing. Background Technology

[0002] Ti-6Al-4V (TC4) is a typical α+β dual-phase titanium alloy with advantages such as high specific strength and low density. Compared with traditional structural materials, such as stainless steel, using TC4 titanium alloy as a substitute can improve structural strength while reducing structural weight, with a total weight reduction of about 40% to 50%. It is suitable for various types of spacecraft and is a common aerospace structural material.

[0003] Welding TC4 titanium alloy with other dissimilar metals presents two major challenges: First, TC4 contains a large amount of reactive Ti, which readily reacts with other metals to form brittle intermetallic compounds. Second, the significant difference in thermal expansion coefficients between dissimilar materials leads to high residual stress after welding, making them prone to cracking. Common welding methods for dissimilar metals include fusion welding, diffusion welding, and brazing. Fusion welding, including electron beam welding and laser beam welding, while reducing the heat-affected zone by lowering heat input, still inevitably causes Ti to react with other elements to form brittle intermetallic compounds, resulting in microcracks after welding. Diffusion welding, by adding a metal foil interlayer, can suppress or reduce the formation of brittle intermetallic compounds in the weld to some extent; however, diffusion welding has significant limitations on the connection method of the base material and the size of the specimen, making it difficult to meet the engineering requirements of thin-walled components in the aerospace field. Brazing the connection between TC4 and dissimilar alloys is simple to operate, highly adaptable, and has no special requirements on the shape of the base material, making it suitable for connecting TC4 with dissimilar thin-walled materials.

[0004] Current research on brazing TC4 titanium alloys with dissimilar metals often employs the method of adding a metal interlayer to suppress interfacial reactions. Examples include adding Cu, Ni, or Ag foils, or Nb / Cu composite interlayers. However, due to the inherent high reactivity of Ti, this method has limited effectiveness in restricting the formation of brittle phases, leading to reduced interfacial bonding strength. Furthermore, in practical engineering applications, thin-walled components face challenges in controlling wetting and spreading at the brazing interface due to their geometric characteristics. Excessively fluid brazing filler metal tends to spread, causing unbonded defects in localized areas. Therefore, a suitable brazing method for TC4 with dissimilar metals is urgently needed. Summary of the Invention

[0005] This invention aims to solve the problems of brittle phase formation, microcrack defects, low joint strength, and excessive fluidity of brazing filler metal that easily spreads during the brazing process of TC4 with dissimilar metal materials. In this way, it provides a method for graphene-assisted brazing with plasma surface treatment.

[0006] A brazing method for TC4 titanium alloy to dissimilar metal materials, comprising the following steps:

[0007] I. Plasma treatment of solder powder:

[0008] The solder powder is placed in a tube furnace and a vacuum is drawn. Then, a mixed gas is introduced until the pressure is 30Pa~100Pa. The temperature is then raised to 400℃~550℃. During the heat preservation stage, the PECVD radio frequency system is turned on. Plasma treatment is performed at a temperature of 400℃~550℃ and a plasma radio frequency power of 200W~300W. Finally, the PECVD radio frequency system and heating program are turned off. After the tube furnace cools down to room temperature, the plasma-treated solder powder is obtained.

[0009] II. Preparation of solder paste:

[0010] The plasma-treated solder powder, cellulose, and ethanol are mixed evenly to obtain solder paste;

[0011] III. Preparation of components to be welded:

[0012] The In foil is assembled on one side of the TC4 titanium alloy, the brazing foil is assembled on the other side of the dissimilar alloy base material, the solder paste is then evenly applied to the surface of the brazing foil, and finally assembled in the order of TC4 titanium alloy / In foil / solder paste / brazing foil / dissimilar alloy base material to obtain the component to be welded.

[0013] IV. Brazing:

[0014] The components to be welded are placed in a vacuum brazing furnace and evacuated. The temperature is gradually increased to 700℃~900℃. Then, the brazing is carried out for 5 to 10 minutes at a brazing temperature of 700℃~900℃. Finally, the temperature is lowered to complete the brazing method of TC4 titanium alloy with dissimilar metal materials.

[0015] The beneficial effects of this invention are:

[0016] 1. This invention utilizes the synergistic effect of plasma treatment of solder powder and pre-placed In foil to reduce the formation of TC4 and dissimilar metal interface compounds. After plasma treatment, the surface of the solder powder is coated with a layer of non-metallic element N, which reduces the possibility of reaction between the active Ti element in the TC4 base material and the solder or dissimilar base material, thereby reducing the formation of intermetallic compounds and improving the mechanical properties of the joint.

[0017] 2. This invention helps reduce the scattering of brazing filler metal during the welding of thin-walled materials. The fluidity of the brazing filler metal powder decreases after plasma treatment, and non-directional scattering is controlled to a certain extent.

[0018] 3. The heating program designed in this invention helps reduce interfacial reactions and release residual stress as much as possible, thereby improving mechanical properties. During the heating stage, multiple heat-preheating platforms are set before the liquidus of the brazing filler metal; reducing the heat-preheating time during the heat-preservation stage, and employing rapid cooling above the solidus of the brazing filler metal during the cooling stage, all help reduce the flow of the brazing filler metal and interfacial reactions with the base metal; rapid cooling below the solidus can reduce thermal stress in front of the base metal, ultimately resulting in a brazed joint between TC4 titanium alloy and a dissimilar metal with good welding quality and high mechanical strength. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of plasma treatment of solder powder in step one of Example 1;

[0020] Figure 2 This is a temperature curve of the brazing process in step four of Example 1;

[0021] Figure 3 This is a scanning electron microscope image of the solder powder after plasma treatment in step one of Example 1;

[0022] Figure 4 Digital photographs of TC4 / 4J40 brazed parts prepared in Comparative Experiment and Example 1 before and after plasma treatment;

[0023] Figure 5 For comparison, the interface morphology of the TC4 / 4J40 brazed joint prepared in Example 1 is shown in the following figures: (a) Comparative experiment, (b) Example 1.

[0024] Figure 6 The figure shows the tensile strength test results of the TC4 / 4J40 brazed part prepared in Example 1. Detailed Implementation

[0025] Specific Implementation Method 1: This implementation method is a brazing method for TC4 titanium alloy and dissimilar metal materials, which is carried out according to the following steps:

[0026] I. Plasma treatment of solder powder:

[0027] The solder powder is placed in a tube furnace and a vacuum is drawn. Then, a mixed gas is introduced until the pressure is 30Pa~100Pa. The temperature is then raised to 400℃~550℃. During the heat preservation stage, the PECVD radio frequency system is turned on. Plasma treatment is performed at a temperature of 400℃~550℃ and a plasma radio frequency power of 200W~300W. Finally, the PECVD radio frequency system and heating program are turned off. After the tube furnace cools down to room temperature, the plasma-treated solder powder is obtained.

[0028] II. Preparation of solder paste:

[0029] The plasma-treated solder powder, cellulose, and ethanol are mixed evenly to obtain solder paste;

[0030] III. Preparation of components to be welded:

[0031] The In foil is assembled on one side of the TC4 titanium alloy, the brazing foil is assembled on the other side of the dissimilar alloy base material, the solder paste is then evenly applied to the surface of the brazing foil, and finally assembled in the order of TC4 titanium alloy / In foil / solder paste / brazing foil / dissimilar alloy base material to obtain the component to be welded.

[0032] IV. Brazing:

[0033] The components to be welded are placed in a vacuum brazing furnace and evacuated. The temperature is gradually increased to 700℃~900℃. Then, the brazing is carried out for 5 to 10 minutes at a brazing temperature of 700℃~900℃. Finally, the temperature is lowered to complete the brazing method of TC4 titanium alloy with dissimilar metal materials.

[0034] The beneficial effects of this embodiment are:

[0035] 1. This embodiment utilizes the synergistic effect of plasma treatment of the solder powder and pre-placed In foil to reduce the formation of TC4 and dissimilar metal interface compounds. After plasma treatment, the surface of the solder powder is coated with a layer of non-metallic element N, which reduces the possibility of reaction between the active Ti element in the TC4 base material and the solder or dissimilar base material, thereby reducing the formation of intermetallic compounds and improving the mechanical properties of the joint.

[0036] 2. This embodiment helps reduce the spread of solder throughout the welding process of thin-walled materials. The fluidity of the solder powder decreases after plasma treatment, and non-directional spread is controlled to a certain extent.

[0037] 3. The heating program designed in this embodiment helps reduce interfacial reactions and release residual stress as much as possible, thereby improving mechanical properties. During the heating stage, multiple heat-preheating platforms are set before the liquidus of the brazing filler metal; reducing the heat-preheating time during the heat-preservation stage, and employing rapid cooling above the solidus of the brazing filler metal during the cooling stage, all help reduce the flow of the brazing filler metal and interfacial reactions with the base metal; rapid cooling below the solidus can reduce thermal stress in front of the base metal, ultimately resulting in a brazed joint between TC4 titanium alloy and a dissimilar metal with good weld quality and high mechanical strength.

[0038] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the particle size of the brazing filler powder mentioned in step one is 200 mesh to 400 mesh; the brazing filler powder mentioned in step one is AgCuTi powder, AgCu powder, or AgCuZnSn powder; the mixed gas mentioned in step one is a mixture of argon and nitrogen, and the gas flow ratio of argon to nitrogen is 1:(5~10). Everything else is the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, the vacuum level is ≤5×10⁻⁶. -3 Pa; In step one, plasma treatment is carried out for 10 to 20 minutes at a temperature of 400℃ to 550℃ and a plasma radio frequency power of 200W to 300W. Other procedures are the same as in specific implementation method one or two.

[0040] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the surface of the solder powder after plasma treatment in step one is covered with a layer of non-metallic element N. Everything else is the same as in Specific Implementation Methods One to Three.

[0041] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the cellulose mentioned in step two is methylcellulose, ethylcellulose, or carboxymethylcellulose; the plasma-treated solder powder in the solder paste mentioned in step two has a mass percentage of 75% to 85%, the ethylcellulose has a mass percentage of 5% to 10%, and the remainder is ethanol. Everything else is the same as in Specific Implementation Methods One to Four.

[0042] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the dissimilar alloy base material mentioned in step three is a Ni-based high-temperature alloy, an Nb-based high-temperature alloy, or a 4J series low-expansion alloy; the solder foil mentioned in step three is an AgCu foil, an AgCuTi foil, or an AgCuInTi foil. Everything else is the same as in Specific Implementation Methods One to Five.

[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the thickness of the dissimilar alloy base material in step three is 2mm to 10mm; the thickness of the In foil in step three is 50μm to 200μm; the thickness of the solder foil in step three is 20μm to 200μm; and in step three, the solder paste is evenly applied to the surface of the solder foil with a coating thickness of 100μm to 200μm. Everything else is the same as in Specific Implementation Methods One to Six.

[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the TC4 titanium alloy, dissimilar alloy base material, brazing foil, and In foil mentioned in step three are all pretreated according to the following steps: the surface oxide layer is removed by sanding with sandpaper, and then the surface is cleaned with ethanol and deionized water for 5 to 30 minutes respectively. Everything else is the same as in Specific Implementation Methods One to Seven.

[0045] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One through Eight in that: in step four, the vacuum level is ≤5×10⁻⁶. -3 Pa. The rest is the same as in specific embodiments one through eight.

[0046] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: the gradient heating to 700℃~900℃ in step four is specifically carried out as follows: first, the temperature is increased to 200℃~400℃ at a heating rate of 10℃ / min~15℃ / min, and held at 200℃~400℃ for 5min~30min; then, the temperature is increased at a heating rate of 5℃ / min~10℃ / min, and held for 10min~20min for every 50℃~150℃ increase, until the brazing temperature of 700℃~900℃ is reached; the cooling in step four is specifically carried out as follows: first, the temperature is reduced to 600℃~700℃ at a cooling rate of 10℃ / min~15℃ / min, then reduced to 200℃~400℃ at a cooling rate of 3℃ / min~5℃ / min, and finally cooled to room temperature with the furnace. Everything else is the same as in Specific Implementation Methods One to Nine.

[0047] The beneficial effects of the present invention are verified using the following embodiments:

[0048] Example 1, combined with Figure 1 and Figure 2 Detailed explanation:

[0049] A brazing method for TC4 titanium alloy to dissimilar metal materials, comprising the following steps:

[0050] I. Plasma treatment of solder powder:

[0051] The brazing filler metal powder was placed in a tube furnace and evacuated to a vacuum level of 5×10⁻⁶. -3 Pa, then the mixed gas is introduced until the pressure is 60 Pa, then the temperature is raised to 400℃, the PECVD RF system is turned on during the heat preservation stage, and the plasma treatment is carried out for 15 minutes at a temperature of 400℃ and a plasma RF power of 200W. Finally, the PECVD RF system and heating program are turned off, and after the tube furnace cools down to room temperature, the plasma-treated solder powder is obtained.

[0052] The brazing filler powder has a particle size of 200 mesh to 400 mesh; the brazing filler powder is AgCu powder, and the mass ratio of Ag to Cu in the AgCu powder is 72:28; the mixed gas is a mixture of argon and nitrogen, and the gas flow ratio of argon to nitrogen is 1:5.

[0053] The surface of the plasma-treated solder powder is coated with a layer of non-metallic element N;

[0054] II. Preparation of solder paste:

[0055] The plasma-treated solder powder, cellulose, and ethanol are mixed evenly to obtain solder paste;

[0056] The cellulose is ethyl cellulose; the solder paste contains 85% by mass of plasma-treated solder powder, 5% by mass of ethyl cellulose, and the remainder is ethanol;

[0057] III. Preparation of components to be welded:

[0058] Using a spot welding machine, In foil is assembled onto one side of TC4 titanium alloy, and brazing foil is assembled onto one side of dissimilar alloy base material. Then, with a coating thickness of 100μm, solder paste is evenly applied to the surface of the brazing foil. Finally, the components are assembled in the order of TC4 titanium alloy / In foil / solder paste / brazing foil / dissimilar alloy base material to obtain the component to be welded.

[0059] The dissimilar alloy base material is 4J40 alloy; the brazing foil is AgCu foil, and the mass ratio of Ag to Cu in the AgCu foil is 72:28;

[0060] The thickness of the TC4 titanium alloy is 5 mm; the thickness of the dissimilar alloy base material is 5 mm; the thickness of the In foil is 100 μm; the thickness of the solder foil is 100 μm.

[0061] The TC4 titanium alloy, dissimilar alloy base material, brazing foil, and In foil are all pretreated according to the following steps: the surface oxide layer is removed by sanding with sandpaper, and then the surface is cleaned with ethanol and deionized water for 20 minutes respectively.

[0062] IV. Brazing:

[0063] The components to be welded are placed in a vacuum brazing furnace and evacuated to a vacuum level of 5×10. -3Pa, first, the temperature is increased to 400℃ at a rate of 15℃ / min, and held at 400℃ for 30min. Then, the temperature is increased at a rate of 10℃ / min, and held for 10min for every 100℃ increase, until the brazing temperature of 800℃ is reached. Then, brazing is performed at 800℃ for 5min. First, the temperature is decreased to 600℃ at a rate of 15℃ / min, and then decreased to 400℃ at a rate of 3℃ / min. Finally, the temperature is cooled to room temperature with the furnace to obtain the TC4 / 4J40 brazed part.

[0064] Comparative Experiment: This comparative experiment differs from Example 1 in that step one is omitted, and in step two, untreated AgCu powder, cellulose, and ethanol are mixed evenly to obtain solder paste. Everything else is the same as in Example 1.

[0065] Figure 3 The image shown is a scanning electron microscope image of the solder powder after plasma treatment in step one of Example 1. It can be seen that after plasma treatment, the surface of the solder powder is covered with a layer of non-metallic element N, which can reduce the possibility of the active Ti element in the TC4 base material reacting with the solder or other base materials.

[0066] Figure 4 The images show digital photographs of the TC4 / 4J40 brazed parts prepared in the comparative experiment and Example 1 before and after plasma treatment; it can be seen that the brazing filler metal flow was well controlled after plasma treatment.

[0067] Figure 5 For comparison, the interface morphology of the TC4 / 4J40 brazed joint prepared in Example 1 is shown in the following figures: (a) Comparative experiment, (b) Example 1. It can be seen that when AgCu powder is used to directly braze 4J40 and TC4, there are multiple cracks at the brazing interface, and dark intermetallic compounds are also present around the cracks. However, the interface of the brazing filler powder treated with plasma has no obvious cracks, and the interface structure is Ag-based solid solution and Cu-based solid solution. No dark intermetallic compounds are generated, and the inhibition effect is very good.

[0068] Tensile strength tests were conducted on TC4 / 4J40 brazed parts according to GB / T 11363-2008 standard, and parallel experiments were performed on 5 groups of samples. Figure 6 The figure shows the tensile strength test results of the TC4 / 4J40 brazed parts prepared in Example 1. It can be seen that the average tensile strength of the 5 groups of samples is about 318 MPa, which shows that the brazing method of this example can obtain high-quality TC4 and dissimilar alloy brazed joints.

Claims

1. A brazing method for TC4 titanium alloy and dissimilar metal materials, characterized in that... It is done in the following steps: I. Plasma treatment of solder powder: The solder powder is placed in a tube furnace and a vacuum is drawn. Then, a mixed gas is introduced until the pressure is 30Pa~100Pa. The temperature is then raised to 400℃~550℃. During the heat preservation stage, the PECVD radio frequency system is turned on. Plasma treatment is performed at a temperature of 400℃~550℃ and a plasma radio frequency power of 200W~300W. Finally, the PECVD radio frequency system and heating program are turned off. After the tube furnace cools down to room temperature, the plasma-treated solder powder is obtained. II. Preparation of solder paste: The plasma-treated solder powder, cellulose, and ethanol are mixed evenly to obtain solder paste; III. Preparation of components to be welded: The In foil is assembled on one side of the TC4 titanium alloy, the brazing foil is assembled on the other side of the dissimilar alloy base material, the solder paste is then evenly applied to the surface of the brazing foil, and finally assembled in the order of TC4 titanium alloy / In foil / solder paste / brazing foil / dissimilar alloy base material to obtain the component to be welded. IV. Brazing: The components to be welded are placed in a vacuum brazing furnace and evacuated. The temperature is gradually increased to 700℃~900℃. Then, the brazing is carried out for 5 to 10 minutes at a brazing temperature of 700℃~900℃. Finally, the temperature is lowered to complete the brazing method of TC4 titanium alloy with dissimilar metal materials.

2. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The particle size of the brazing filler powder mentioned in step one is 200 mesh to 400 mesh; the brazing filler powder mentioned in step one is AgCuTi powder, AgCu powder or AgCuZnSn powder; the mixed gas mentioned in step one is a mixture of argon and nitrogen, and the gas flow ratio of argon to nitrogen is 1:(5~10).

3. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... In step one, the vacuum level is ≤5×10. -3 Pa; In step one, plasma treatment is carried out for 10 to 20 minutes at a temperature of 400℃ to 550℃ and a plasma radio frequency power of 200W to 300W.

4. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The surface of the solder powder after plasma treatment described in step one is covered with a layer of non-metallic element N.

5. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The cellulose mentioned in step two is methylcellulose, ethylcellulose, or carboxymethylcellulose; the solder paste mentioned in step two contains 75% to 85% by mass of plasma-treated solder powder, 5% to 10% by mass of ethylcellulose, and the remainder is ethanol.

6. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The dissimilar alloy base material mentioned in step three is a Ni-based high-temperature alloy, an Nb-based high-temperature alloy, or a 4J series low-expansion alloy; the brazing foil mentioned in step three is an AgCu foil, an AgCuTi foil, or an AgCuInTi foil.

7. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The thickness of the dissimilar alloy base material mentioned in step three is 2mm~10mm; the thickness of the In foil mentioned in step three is 50μm~200μm; the thickness of the brazing foil mentioned in step three is 20μm~200μm; in step three, the solder paste is evenly applied to the surface of the brazing foil with a coating thickness of 100μm~200μm.

8. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... The TC4 titanium alloy, dissimilar alloy base material, brazing foil, and In foil mentioned in step three are all pretreated according to the following steps: the surface oxide layer is removed by sanding with sandpaper, and then the surface is cleaned with ethanol and deionized water for 5 min to 30 min respectively.

9. The brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... In step four, the vacuum level is ≤5×10. -3 Pa.

10. A brazing method for TC4 titanium alloy and dissimilar metal materials according to claim 1, characterized in that... Step four involves gradient heating to 700℃~900℃, specifically performed as follows: First, heat to 200℃~400℃ at a rate of 10℃ / min~15℃ / min, and hold at 200℃~400℃ for 5min~30min. Then, heat to 5℃ / min~10℃ / min, holding for 10min~20min for every 50℃~150℃ increase, until the brazing temperature reaches 700℃~900℃. Step four also involves cooling to 600℃~700℃ at a rate of 10℃ / min~15℃ / min, then cooling to 200℃~400℃ at a rate of 3℃ / min~5℃ / min, and finally cooling to room temperature with the furnace.

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