A laser cladding coating assisted CNTs reinforced aluminum matrix composite fusion brazing process

Abstract

The application provides a laser cladding coating assisted CNTs reinforced aluminum matrix composite fusion brazing process, which comprises the following steps: A) forming a cladding layer on the surface of a CNTs reinforced aluminum matrix composite to be welded by adopting a laser cladding method; the cladding powder comprises the following components in mass fraction: Zn: 15-25%, Ti: 10-15%, and the balance is Al; B) abutting two cladding layers of CNTs reinforced aluminum matrix composite, and performing laser fusion brazing. Through the Al-Zn-Ti-B composite interlayer technology prepared in situ by laser cladding, the traditional interlayer assembly gap problem is solved, the interface metallurgical bonding is realized by optimizing the powder formula and the cladding parameters, the process conversion is reduced, and the operation efficiency is improved through the design of the laser fusion brazing double-station integration.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite welding technology, and particularly relates to a laser cladding coating-assisted CNTs reinforced aluminum matrix composite fusion brazing process. Background Technology

[0002] With the advancement of lightweight transformation and upgrading of my country's rail transit, traditional aluminum alloy materials can no longer meet the higher requirements of transportation vehicles for efficiency and energy saving. Metal matrix composites have emerged to address this need. These composites introduce nano-reinforcing particles (such as carbon nanotubes (CNTs) and SiC particles) into the aluminum alloy matrix through powder metallurgy and other methods. Utilizing the load transfer effect between the nanoparticles and the matrix, as well as the second-phase strengthening effect, the overall performance of the material is significantly improved. Among these, CNTs, due to their high strength, excellent wear resistance, and corrosion resistance, have become ideal reinforcements. CNT-reinforced aluminum matrix composites prepared through powder metallurgy and other processes are expected to become a new generation of key materials in future transportation, weaponry, and other fields.

[0003] Despite the excellent performance of these composite materials, achieving reliable bonding of CNTs-reinforced aluminum matrix composites faces numerous challenges due to the significant differences in thermophysical properties between CNTs and the Al matrix (such as coefficient of thermal expansion and melting point). Currently, the more mature welding processes mainly include friction stir welding and brazing. These processes effectively avoid thermal damage to the base material by controlling low heat input, but they require high precision in workpiece surface assembly and specific environmental conditions. Patent CN 111230357A provides a Zn-based amorphous brazing foil, whose core innovation lies in the amorphous preparation process and low melting point characteristics of the brazing foil itself, used to improve the brazing performance of traditional aluminum alloys. However, it is still a prefabricated, assembled sandwich or foil, and in the welding of large-size CNTs-reinforced aluminum matrix composite components targeted in this application, instability of the molten pool and porosity defects caused by assembly gaps cannot be avoided. Summary of the Invention

[0004] The purpose of this invention is to provide a laser cladding coating-assisted brazing process for CNTs-reinforced aluminum matrix composites. The brazing process in this invention can eliminate porosity defects caused by assembly gaps, achieve a joint strength of 240~280MPa, reduce heat input by 30%, and is suitable for welding large-sized irregularly shaped components.

[0005] This invention provides a laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials, comprising the following steps:

[0006] A) A laser cladding method is used to form a cladding layer on the surface of the CNTs-reinforced aluminum matrix composite material to be welded using cladding powder;

[0007] The cladding powder comprises the following components by mass fraction:

[0008] Zn: 15~25%, Ti: 10~15%, balance Al;

[0009] B) The cladding layers of the two CNTs-reinforced aluminum matrix composites are joined together and laser brazed.

[0010] Preferably, the content of CNTs reinforcing phase in the CNTs reinforced aluminum matrix composite material is 0.5~3.5%.

[0011] Preferably, the aluminum alloy substrate in the CNTs-reinforced aluminum matrix composite material includes 6N01, 5083 aluminum alloy or 2A14 aluminum alloy.

[0012] Preferably, the surface of the CNTs-reinforced aluminum matrix composite material to be welded is subjected to a first grinding, a first cleaning, a second grinding, and a second cleaning in sequence, and then subjected to laser shock peening treatment.

[0013] Preferably, the first cleaning is performed using an alkaline solution, the polishing is performed using sandpaper, and the second cleaning is performed using acetone or alcohol followed by drying.

[0014] Preferably, the particle size of the cladding powder is 50~80μm.

[0015] Preferably, during the laser cladding process, the laser power is 800~1200W, the scanning speed is 45~60mm / s, the powder feeding rate is 10~15g / min, and the spot diameter is 2~3mm.

[0016] Preferably, after the laser cladding in step A) is completed, the cladding layer is polished to make the cladding layer thickness 0.3~0.45mm and the surface roughness less than 0.1mm.

[0017] Preferably, during the laser brazing process, the laser beam is deflected at an angle of 5 to 10° to the vertical direction, and the laser beam spot is located at the joint between the two test plates.

[0018] Preferably, during the laser brazing process, the laser power is 900~1200W, the welding speed is 1.2~1.5m / min, and the laser defocusing amount is 0.5~0.8mm.

[0019] This invention provides a laser cladding-assisted brazing process for CNTs-reinforced aluminum matrix composites, comprising the following steps: A) forming a cladding layer on the surface of the CNTs-reinforced aluminum matrix composite to be welded using a laser cladding method; the cladding powder comprises the following mass fractions: Zn: 15~25%, Ti: 10~15%, with the balance being Al; B) joining the cladding layers of two CNTs-reinforced aluminum matrix composites together and performing laser brazing. This invention solves the gap problem in traditional sandwich assembly by using in-situ laser cladding to prepare an Al-Zn-Ti-B composite interlayer. By optimizing the powder formulation and cladding parameters, metallurgical bonding at the interface is achieved. The integrated dual-station laser brazing design reduces process changes and improves operational efficiency.

[0020] Specifically, compared with the prior art, the present invention has the following advantages:

[0021] 1. The laser cladding intermediate interlayer process provided by this invention can achieve a reliable connection between the intermediate brazing filler metal and the composite substrate with a lower heat input, avoiding the assembly errors and low efficiency caused by directly clamping the intermediate brazing filler metal. At the same time, by controlling the cladding parameters and movement trajectory, the automated operation of complex components can be achieved, further improving efficiency. The cladding process can also further improve the powder ratio and uniformity, avoiding the problem of poor weld formation caused by severe local Zn evaporation.

[0022] 2. The Al-Zn-Ti cladding powder ratio in this invention has good wettability between Ti and CNTs reinforced aluminum matrix composites. The large addition of Zn can further reduce the heat input of the laser to the base material through evaporation, promote the escape of pores in the molten pool, and reduce the degree of thermal damage to the base material.

[0023] 3. The fusion brazing method proposed in this invention for welding aluminum matrix composites can achieve joints with good performance while ensuring welding efficiency. Compared with existing brazing processes, efficiency is significantly improved. At the same time, the non-contact welding method has better process adaptability than friction stir welding, and is expected to be widely used in CNT-reinforced aluminum matrix composites or other particle-reinforced aluminum matrix composites with poor weldability. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1This is a schematic diagram of the laser brazing process assisted by laser cladding coating in this invention;

[0026] Figure 1 In the diagram, 1 represents the cladding laser beam, 2 represents the cladding layer, 3 represents the cladding powder feeding mechanism, 4 represents the laser welding heat source, 5 represents the CNTs-reinforced aluminum-based composite material, and 6 represents the butt-jointed cladding layer.

[0027] Figure 2 Microscopic image of the joint surface formation and joint morphology obtained by laser brazing assisted by laser cladding coating in Embodiment 1 of the present invention.

[0028] Figure 3 Microscopic images show the joint surface formation and joint morphology obtained by laser brazing with prefabricated sandwich assisted in Comparative Example 1 of the present invention.

[0029] Figure 4 The tensile strength curves of the welded joints obtained in Embodiment 1 and Comparative Example 1 of the present invention;

[0030] Figure 5 The image shows the joint microstructure obtained under an optical microscope for laser brazing assisted by laser cladding coating in Embodiment 1 of the present invention.

[0031] Figure 6 The microstructure of the joint obtained under an optical microscope for the laser brazing assisted by the prefabricated sandwich layer in Comparative Example 1 of this invention;

[0032] Figure 7 The morphology of the joint port obtained under an optical microscope for laser brazing assisted by laser cladding coating in Embodiment 1 of the invention;

[0033] Figure 8 The image shows the joint port morphology obtained under an optical microscope for the laser brazing assisted by the prefabricated sandwich layer in Comparative Example 1 of this invention. Detailed Implementation

[0034] This invention provides a laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials, comprising the following steps:

[0035] A) A laser cladding method is used to form a cladding layer on the surface of the CNTs-reinforced aluminum matrix composite material to be welded using cladding powder;

[0036] The cladding powder comprises the following components by mass fraction:

[0037] Zn: 15~25%, Ti: 10~15%, balance Al;

[0038] B) The cladding layers of the two CNTs-reinforced aluminum matrix composites are joined together and laser brazed.

[0039] The present invention preferably pre-treats the surface of the CNTs-reinforced aluminum matrix composite material, especially the surface to be welded, by cleaning, and then performs laser cladding treatment on the surface of the CNTs-reinforced aluminum matrix composite material to be welded.

[0040] In this invention, the CNTs-reinforced aluminum matrix composite material is a CNTs-reinforced aluminum alloy composite material, wherein the aluminum alloy matrix is ​​preferably 6N01 aluminum alloy, 5083 aluminum alloy, or 2A14 aluminum alloy; the mass fraction of the CNTs reinforcing phase in the CNTs-reinforced aluminum matrix composite material is preferably 0.5-3.5%, more preferably 1-3%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, preferably within the range of any of the above values ​​as the upper or lower limit.

[0041] In this invention, the cleaning pretreatment preferably includes a first grinding, a first cleaning, a second grinding, and a second cleaning. Specifically, in this invention, the surface of the CNTs reinforced aluminum matrix composite material is first ground, and the surface to be welded is first cleaned with an alkaline solution to remove surface oil. Then, the surface is second-ground with sandpaper to remove the oxide film on the material surface. Finally, the material surface is second-cleaned with acetone or alcohol and then dried.

[0042] In this invention, the alkaline solution is preferably a NaOH solution, and the concentration of the alkaline solution is preferably 1.5 wt%; the sandpaper used for polishing is preferably 400 mesh, 800 mesh, 1200 mesh, and 1600 mesh in sequence, and polishing is performed using a cashmere polishing cloth in conjunction with a diamond suspension with a particle size of 2.5 μm.

[0043] After surface cleaning, the present invention uses ball milling to prepare cladding powder, and after the prepared cladding powder is mixed evenly, it is placed in the powder feeding device of the cladding equipment. Then, the CNTs reinforced aluminum matrix composite material test plate is fixed on the clamp of the laser cladding equipment, and a cladding layer is formed on the surface to be welded by laser cladding.

[0044] In this invention, the cladding powder comprises the following components by mass fraction:

[0045] Zn: 15~25%, Ti: 10~15%, balance Al;

[0046] In this invention, the mass fraction of Zn in the cladding powder is preferably 15-25%, more preferably 18-22%, such as 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, preferably within the range of any of the above values ​​as the upper or lower limit; the mass fraction of Ti in the cladding powder is preferably 10-15%, more preferably 11-14%, such as 10%, 11%, 12%, 13%, 14%, 15%, preferably within the range of any of the above values ​​as the upper or lower limit. In this invention, the Al-Zn-Ti composite powder, within the above specific composition range, can ensure that it achieves the dual functional mechanism of "Zn evaporation actively reducing heat input" and "Ti suppressing brittle phases" during the welding process.

[0047] In this invention, the particle size of the cladding powder is preferably 50~80μm, more preferably 55~60μm.

[0048] In this invention, the use of laser cladding technology to prepare a uniform and dense intermediate layer in situ on the surface of CNTs-reinforced aluminum composite to be welded is the basis for achieving gapless connection and subsequent low heat input welding. During the laser cladding process, the laser power is preferably 800~1200W, more preferably 850~1150W, such as 800 W, 850 W, 900 W, 950 W, 1000 W, 1050 W, 1100 W, 1150 W, 1200 W, preferably within the range of any of the above values ​​as the upper or lower limit; the scanning speed is preferably 45~60 mm / s, more preferably 50~55 mm / s, such as 45 mm / s, 48 ​​mm / s, 50 mm / s, 52 mm / s, 55 mm / s, 58 mm / s, 60 mm / s, preferably within the range of any of the above values ​​as the upper or lower limit; the powder feeding rate is preferably 10~15 g / min, more preferably 11~14 g / min, such as 10 g / min, 11 g / min, 12 g / min, 13 g / min, 14 g / min, 15 ... g / min, preferably a range of values ​​with the above values ​​as the upper or lower limit; the spot diameter is preferably 2~3 mm, more preferably 2.5 mm.

[0049] After the laser cladding is completed, the present invention takes out the cladding test piece, uses a grinding machine to grind the cladding layer on the surface to be welded to be smooth, and wipes the ground test piece with 75% alcohol and blows it dry.

[0050] In this invention, the thickness of the cladding layer after polishing is preferably 0.35 mm, and the surface roughness is preferably less than 0.1 mm.

[0051] In this invention, the cladding layers of two CNTs-reinforced aluminum matrix composite material test blocks that have undergone the above-mentioned laser cladding treatment are joined together. A fixture is used to ensure that the cladding sides of the test plates are in close contact and that the upper surface of the test plates to be welded is parallel. The attitude and position of the laser are adjusted so that the laser beam spot is located in the central area of ​​the test plates, and laser brazing is used for welding.

[0052] In this invention, the laser beam's angle of deviation from the vertical direction is preferably 5~10°, such as 5°, 6°, 7°, 8°, 9°, 10°, preferably within the range of any of the above values ​​as the upper or lower limit. The laser power is preferably 900~1200W, more preferably 1000~1100 W, such as 900 W, 950 W, 1000 W, 1050 W, 1100 W, 1150 W, 1200 W, preferably within the range of any of the above values ​​as the upper or lower limit. The welding speed is preferably 1.2~1.5 m / min, such as 1.2 m / min, 1.3 m / min, 1.4 m / min, 1.5 m / min, preferably within the range of any of the above values ​​as the upper or lower limit. The laser defocusing amount is preferably 0.5~0.8 mm, such as 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, preferably within the range of any of the above values ​​as the upper or lower limit.

[0053] This invention provides a laser cladding-assisted brazing process for CNTs-reinforced aluminum matrix composites, comprising the following steps: A) forming a cladding layer on the surface of the CNTs-reinforced aluminum matrix composite to be welded using a laser cladding method; the cladding powder comprises the following mass fractions: Zn: 15~25%, Ti: 10~15%, with the balance being Al; B) joining the cladding layers of two CNTs-reinforced aluminum matrix composites together and performing laser brazing. This invention solves the gap problem in traditional sandwich assembly by using in-situ laser cladding to prepare an Al-Zn-Ti-B composite interlayer. By optimizing the powder formulation and cladding parameters, metallurgical bonding at the interface is achieved. The integrated dual-station laser brazing design reduces process changes and improves operational efficiency.

[0054] Specifically, compared with the prior art, the present invention has the following advantages:

[0055] 1. The laser cladding intermediate interlayer process provided by this invention can achieve a reliable connection between the intermediate brazing filler metal and the composite substrate with a lower heat input, avoiding the assembly errors and low efficiency caused by directly clamping the intermediate brazing filler metal. At the same time, by controlling the cladding parameters and movement trajectory, the automated operation of complex components can be achieved, further improving efficiency. The cladding process can also further improve the powder ratio and uniformity, avoiding the problem of poor weld formation caused by severe local Zn evaporation.

[0056] 2. The Al-Zn-Ti cladding powder ratio in this invention has good wettability between Ti and CNTs reinforced aluminum matrix composites. The large addition of Zn can further reduce the heat input of the laser to the base material through evaporation, promote the escape of pores in the molten pool, and reduce the degree of thermal damage to the base material.

[0057] 3. The fusion brazing method proposed in this invention for welding aluminum matrix composites can achieve joints with good performance while ensuring welding efficiency. Compared with existing brazing processes, efficiency is significantly improved. At the same time, the non-contact welding method has better process adaptability than friction stir welding, and is expected to be widely used in CNT-reinforced aluminum matrix composites or other particle-reinforced aluminum matrix composites with poor weldability.

[0058] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a laser cladding-assisted brazing process for CNTs-reinforced aluminum matrix composites provided by the present invention, but it should not be construed as a limitation on the scope of protection of the present invention.

[0059] Example 1

[0060] The material used in this embodiment is CNTs-reinforced 6N01 aluminum alloy, wherein the CNTs reinforcing phase content is 2.5%wt, and the specific size is 50mm×50mm×3mm.

[0061] 1) Grind the surface of the material and clean the surface to be welded with an alkaline solution to remove surface oil. Then, grind the surface with sandpaper to remove the oxide film on the material surface. After that, clean the material surface with acetone or alcohol and blow it dry.

[0062] 2) The cladding powder was prepared using a ball mill. The chemical composition of the prepared laser cladding powder, by mass percentage, was: Zn: 19.8%, Ti: 14.4%, with the balance being Al. The powder was mixed evenly and placed in the powder feeding module of the cladding equipment.

[0063] 3) Fix the plate to be welded on the clamp of the laser cladding equipment, use a coaxial powder feeding laser cladding equipment and the following parameters to clad the middle layer on the side of the composite material: laser power 1000W, scanning speed 50mm / s, powder feeding rate 10g / min, spot diameter 2.5mm.

[0064] 4) Take out the cladding test piece and use a grinding machine to grind the cladding layer on the surface to be welded to make the thickness of the coating layer control to about 0.4 mm and the surface roughness control to below 0.1 mm. Wipe the ground test piece with 75% alcohol solution and blow it dry.

[0065] 5) Butt the two treated test plates together on their cladding sides, and use a clamp to make the cladding sides of the test plates in close contact and ensure that the upper surface of the test plates to be welded is parallel.

[0066] 6) Adjust the attitude and position of the laser so that the laser beam spot is located in the center area of ​​the test plate, and the laser beam is deflected at an angle of 5 degrees to the vertical direction. Use the following parameters for welding: laser power 1500W, welding speed 1.5m / min, laser defocusing amount -5mm.

[0067] After welding is completed, the macroscopic morphology of the obtained welded joint will be as follows: Figure 2 As shown, by Figure 2 It can be seen that the weld formation in Example 1 is good, the porosity of the weld in the specimen after laser cladding of the intermediate layer is fully suppressed, and the influence of heat input on the composite matrix is ​​small. The joint exhibits typical brazing characteristics of the filler metal melting while the base metal does not melt.

[0068] The microstructure of the welded joint obtained in Example 1 is as follows: Figure 5 As shown, the port morphology of the welded joint is as follows: Figure 7 As shown.

[0069] The welded specimens were subjected to tensile strength testing according to GB / T2652-2008. The test results are as follows: Figure 4 As shown, the tensile strength of the laser brazed joint assisted by the laser cladding intermediate layer is 272.14 MPa, which is more than 65% of the strength of the base material.

[0070] Comparative Example 1

[0071] Welding of CNTs-reinforced 6N01 aluminum alloy test plates was performed according to the method in Example 1. The difference was that steps 2), 3), and 4) in Example 1 were omitted. A 0.04mm Zn foil + 0.33mm aluminum foil + 0.03mm Ti foil was used as an interlayer to fill the gap between the two materials to be welded. The mass ratio of Zn:Al:Ti was 19.8:65.8:14.4. The fixing screws of the fixture were adjusted to ensure that the interlayer was clamped by the materials to be welded to prevent it from falling off.

[0072] The joint forming was analyzed using an optical microscope, and the results are as follows: Figure 3 As shown, by Figure 3 It can be seen that the joint in Comparative Example 1 without laser cladding coating has serious porosity defects, which is mainly related to the small gap of the pre-set interlayer assembly error. However, the assembly gap of the specimen with laser cladding to add an intermediate layer is basically non-existent, and the stability of the molten pool during the welding process is enhanced, which is more conducive to obtaining a CNTs-reinforced aluminum composite brazing joint with better quality.

[0073] In addition, tensile strength tests were conducted on the brazed joints in Comparative Example 1 that did not employ laser cladding of the intermediate layer and the pre-placed interlayer. The results are as follows: Figure 4 As shown, the strength of the brazed joint assisted by laser cladding reached 272.17 MPa, while the strength of the brazed joint assisted by pre-placed interlayer was 215.48 MPa. The joint obtained by using the cladding interlayer showed a certain improvement in both the plasticity and toughness of the joint.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials, comprising the following steps: A) A laser cladding method is used to form a cladding layer on the surface of the CNTs-reinforced aluminum matrix composite material to be welded using cladding powder; The cladding powder comprises the following components by mass fraction: Zn: 15~25%, Ti: 10~15%, balance Al; B) The cladding layers of the two CNTs-reinforced aluminum matrix composites are joined together and laser brazed.

2. The laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials according to claim 1, characterized in that, The content of CNTs reinforcing phase in the CNTs-reinforced aluminum matrix composite material is 0.5-3.5%.

3. The laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials according to claim 1, characterized in that, The aluminum alloy substrate in the CNTs-reinforced aluminum matrix composite material includes 6N01, 5083 aluminum alloy or 2A14 aluminum alloy.

4. The laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials according to claim 1, characterized in that, The surface of the CNTs-reinforced aluminum matrix composite material to be welded is subjected to a first grinding, a first cleaning, a second grinding, and a second cleaning in sequence, and then laser shock peening treatment is performed.

5. The laser cladding coating-assisted brazing process for CNTs-reinforced aluminum matrix composites according to claim 4, characterized in that, The first cleaning is performed using an alkaline solution, and the polishing is done with sandpaper. The second cleaning is performed using acetone or alcohol and then the surfaces are dried.

6. The laser cladding-assisted brazing process for CNTs-reinforced aluminum matrix composites according to claim 1, characterized in that, The particle size of the cladding powder is 50~80μm.

7. The laser cladding coating-assisted brazing process for CNTs-reinforced aluminum matrix composites according to claim 1, characterized in that, During the laser cladding process, the laser power is 800~1200W, the scanning speed is 45~60mm / s, the powder feeding rate is 10~15g / min, and the spot diameter is 2~3mm.

8. The laser cladding-assisted brazing process for CNTs-reinforced aluminum-based composite materials according to claim 1, characterized in that, After the laser cladding in step A) is completed, the cladding layer is polished to make the thickness of the cladding layer 0.3~0.45mm and the surface roughness less than 0.1mm.

9. The laser cladding-assisted brazing process for CNTs-reinforced aluminum matrix composites according to claim 1, characterized in that, During the laser brazing process, the laser beam is deflected at an angle of 5 to 10° from the vertical direction, and the laser beam spot is located at the joint between the two test plates.

10. The laser cladding coating-assisted brazing process for CNTs-reinforced aluminum matrix composites according to claim 1, characterized in that, During the laser brazing process, the laser power is 900~1200W, the welding speed is 1.2~1.5m / min, and the laser defocusing amount is 0.5~0.8mm.

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