A surface modification method of an aluminum alloy

Abstract

This invention belongs to the field of additive manufacturing technology, specifically relating to a method for surface modification of aluminum alloys. The invention uses a cobalt-chromium-tungsten based alloy as the cladding material, performing laser cladding on the surface of a preheated aluminum alloy to obtain a surface-modified aluminum alloy. The laser cladding conditions include: laser output power of 1.0~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feed rate of 3.7~4.5g / min; the preheated aluminum alloy temperature is 130~150℃. This invention employs low-power laser cladding, reducing thermal stress between the laser cladding layer and the aluminum alloy, avoiding the formation of hard and brittle intermetallic compounds at the interface between the cladding layer and the substrate, and preventing aluminum alloy collapse, over-melting, and burn-through caused by excessive heating temperature; it also ensures a good metallurgical bond between the cladding layer and the aluminum alloy, thereby improving the surface properties of the aluminum alloy.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and specifically relates to a method for surface modification of aluminum alloys. Background Technology

[0002] Aluminum alloys are widely used in aerospace, automotive, machinery, shipbuilding, and chemical industries due to their advantages such as light weight, high strength, good plasticity, and strong corrosion resistance. However, aluminum alloys also have drawbacks, including low hardness, poor wear resistance, high thermal conductivity, poor thermal stability, and chemical reactivity, making them prone to oxidation and blackening in humid environments. These defects make them susceptible to thermal deformation during manufacturing. Furthermore, the moisture and oxide crystal water adsorbed in the aluminum alloy oxide film can easily decompose during manufacturing, forming pores and reducing the density of the formed parts. Therefore, improving the surface properties of aluminum alloy parts is urgently needed in industrial applications.

[0003] Currently, surface modification methods mainly include electroplating, vapor deposition, thermal spraying, and laser cladding. Among aluminum alloy surface modification technologies, laser cladding technology in additive manufacturing is the most commonly used technique for improving the surface properties of aluminum alloys. Laser cladding is a surface modification technology that deposits cladding material onto the surface of a substrate material using a pre-positioning method or a simultaneous powder feeding method to improve its hardness, wear resistance, corrosion resistance, oxidation resistance, and heat resistance. Laser cladding technology has advantages such as good metallurgical properties, low dilution rate, small deformation, fast cooling rate, high temperature control, high energy density, narrow heat-affected zone, and fine microstructure.

[0004] However, in the existing technology, the power of laser cladding is relatively high (3~5kW). Under high laser power, the aluminum alloy substrate is prone to over-melting and cracking defects. Furthermore, hard and brittle intermetallic compounds are easily formed at the interface between the cladding layer and the aluminum alloy substrate, which reduces the performance of the aluminum alloy. Summary of the Invention

[0005] The purpose of this invention is to provide a surface modification method for aluminum alloys. The surface modification method provided by this invention can prevent excessive melting and crack defects in aluminum alloys during laser cladding, and can also avoid the formation of intermetallic compounds at the interface between the cladding layer and the aluminum alloy.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for surface modification of aluminum alloys, comprising the following steps:

[0008] Using a cobalt-chromium-tungsten based alloy as the cladding material, laser cladding is performed on the surface of a preheated aluminum alloy to obtain a surface-modified aluminum alloy;

[0009] The conditions for laser cladding include: laser output power of 1.0~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feeding rate of 3.7~4.5g / min;

[0010] The temperature of the preheated aluminum alloy is 130~150℃;

[0011] The laser cladding is performed in an inert atmosphere.

[0012] Preferably, the cobalt-chromium-tungsten based alloy includes one or more of Stellite1 alloy, Stellite6 alloy, Stellite20 alloy, Stellite31 alloy, and Stellite156 alloy.

[0013] Preferably, the aluminum alloy is pretreated before laser cladding.

[0014] The pretreatment includes grinding, immersing in alkaline solution, cleaning and drying the aluminum alloy in sequence.

[0015] Preferably, the polishing is performed by sequentially polishing the aluminum alloy with 220#, 400#, and 800# metallographic sandpaper.

[0016] Preferably, the alkaline solution used for the alkaline soaking is a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is 5-10%.

[0017] The soaking time in the alkaline solution is 3-5 minutes.

[0018] Preferably, before performing the laser cladding, the cobalt-chromium-tungsten based alloy is further subjected to a drying treatment;

[0019] The drying process is carried out at a temperature of 150-180℃ for 1-2 hours.

[0020] Preferably, the thickness of the cladding layer obtained by laser cladding is 0.6~1.0 mm.

[0021] This invention provides a method for surface modification of aluminum alloys, comprising the following steps: using a cobalt-chromium-tungsten based alloy as the cladding material, laser cladding is performed on the surface of a preheated aluminum alloy to obtain a surface-modified aluminum alloy; the laser cladding conditions include: laser output power of 1.0~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feed rate of 3.7~4.5g / min; the temperature of the preheated aluminum alloy is 130~150℃; and the laser cladding is performed in an inert atmosphere. This invention preheats the aluminum alloy to effectively prevent cracking during laser cladding. Using low-power laser cladding reduces thermal stress between the cladding layer and the aluminum alloy substrate, avoids the formation of hard and brittle intermetallic compounds at the interface between the cladding layer and the substrate, and prevents the aluminum alloy substrate from collapsing, over-melting, and burning through due to excessive heating temperature. The laser cladding layer obtained under low-power laser cladding exhibits a dendritic structure with refined grains. The bonding area between the laser cladding layer and the aluminum alloy substrate consists of directional dendrites with associative crystallization characteristics, resulting in a good metallurgical bond between the cladding layer and the aluminum alloy substrate, thereby improving the surface properties of the aluminum alloy. Attached Figure Description

[0022] Figure 1 A schematic diagram of the laser cladding apparatus provided by the present invention;

[0023] Figure 2 This is a schematic diagram of a partial location of the laser cladding head provided by the present invention;

[0024] Figure 3 The image shows the metallographic structure of the surface-modified aluminum alloy obtained in Comparative Example 1.

[0025] Figure 4 The image shows the metallographic structure of the surface-modified aluminum alloy obtained in Example 1.

[0026] Figure 5 The hardness test curves of the aluminum alloy and the surface-modified aluminum alloy in Example 1 are shown.

[0027] Figure 6 The graph shows the potentiodynamic polarization curves of the aluminum alloy and the surface-modified aluminum alloy in Example 1.

[0028] Among them, 1-worktable, 2-aluminum alloy, 3-cladding layer, 4-laser assembly, 5-robotic arm, 6-laser beam emitter, and 7-coaxial powder feeding nozzle. Detailed Implementation

[0029] This invention provides a method for surface modification of aluminum alloys, comprising the following steps:

[0030] Using a cobalt-chromium-tungsten based alloy as the cladding material, laser cladding is performed on the surface of a preheated aluminum alloy to obtain a surface-modified aluminum alloy;

[0031] The conditions for laser cladding include: laser output power of 1.0~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feeding rate of 3.7~4.5g / min;

[0032] The temperature of the preheated aluminum alloy is 130~150℃;

[0033] The laser cladding is performed in an inert atmosphere.

[0034] In this invention, the cobalt-chromium-tungsten based alloy preferably includes one or more of Stellite 1 alloy, Stellite 6 alloy, Stellite 20 alloy, Stellite 31 alloy, and Stellite 156 alloy. In a specific embodiment of this invention, the cobalt-chromium-tungsten based alloy is Stellite 6 alloy; by mass fraction, the Stellite 6 alloy includes 28.18% Cr, 5% W, 1.0% C, 1.02% Si, 0.75% Mn, 0.005% P, 2.83% Ni, 0.20% Mo, 0.003% S, 2.25% Te, and the balance Co.

[0035] Before performing the laser cladding, the present invention preferably includes drying the cobalt-chromium-tungsten based alloy; the drying temperature is preferably 150~180℃, and the drying time is preferably 1~2h.

[0036] The present invention does not have any particular limitation on the type of aluminum alloy, and any alloy well known to those skilled in the art can be used.

[0037] In this invention, the preheating temperature is 130~150℃, preferably 135~140℃. Preheating the aluminum alloy before laser cladding effectively prevents cracking during the laser cladding process.

[0038] Before performing the laser cladding, the present invention preferably includes pretreatment of the aluminum alloy; the pretreatment preferably includes grinding, immersion in alkaline solution, cleaning and drying of the aluminum alloy in sequence.

[0039] In this invention, the polishing is preferably performed by sequentially using 220#, 400#, and 800# metallographic sandpaper.

[0040] In this invention, the alkaline solution used for immersion is preferably a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is preferably 5-10%; and the immersion time is preferably 3-5 minutes. In this invention, the cleaning is preferably performed using anhydrous ethanol; and the drying is preferably achieved by blowing air.

[0041] In this invention, by employing a combination of physical and chemical methods to remove the oxide film and perform surface passivation treatment, the oxide film on the surface of the aluminum alloy substrate is thoroughly removed, eliminating the harmful effects of the oxide film.

[0042] In this invention, the laser cladding conditions include: laser output power of 1.0~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feeding rate of 3.7~4.5g / min. More preferably, the laser output power is 1.2~1.5kW, laser scanning speed is 6~8mm / s, spot diameter is 3~4mm, and powder feeding rate is 3.9~4.2g / min.

[0043] In this invention, the laser cladding is performed in an inert atmosphere, preferably high-purity argon; the flow rate of the high-purity argon is preferably 15-20 L / min. In this invention, by protecting the laser molten pool with high-purity argon and optimizing the laser cladding process parameters, oxidation of the molten metal and the formation of defects such as porosity are prevented, thereby enabling the acquisition of a well-formed, pore-free, and firmly bonded cladding layer on the surface of the aluminum alloy substrate.

[0044] In this invention, the laser used for laser cladding is preferably a BWT-3000W continuous fiber laser; the powder feeding device is preferably a BWT BFL-CW3000-9 continuous fiber laser irradiating a coaxial powder feeding device. A schematic diagram of the laser cladding device in this invention is shown below. Figure 1 As shown, 1 is the worktable, 2 is the aluminum alloy, 3 is the cladding layer, 4 is the laser assembly, and 5 is the robotic arm; a schematic diagram of a partial location of the laser cladding head is shown below. Figure 2 As shown, 1 is the worktable, 2 is the aluminum alloy, 6 is the laser beam emitter, and 7 is the coaxial powder feeding nozzle.

[0045] In this invention, the thickness of the cladding layer obtained by laser cladding is preferably 0.6~1.0 mm, and more preferably 0.8~0.95 mm.

[0046] To further illustrate the present invention, a surface modification method for aluminum alloys provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] The surface of the aluminum alloy was polished with 220#, 400# and 800# metallographic sandpaper in sequence, then immersed in a 5% sodium hydroxide aqueous solution for 5 minutes. After being taken out, it was washed with anhydrous ethanol and dried with a hair dryer to obtain the pretreated aluminum alloy.

[0049] The Stellite 6 alloy was placed in a drying oven and dried at 130°C for 1 hour.

[0050] Using dried Stellite 6 alloy as the cladding material, a BWT-3000W continuous fiber laser was used to perform laser cladding on the pretreated aluminum alloy surface at a preheating temperature of 130℃. A BWT BFL-CW3000-9 continuous fiber laser was used to irradiate the coaxial powder feeding device to deliver powder, allowing the powder to melt and enter the substrate molten pool. The laser cladding conditions were: laser output power of 1.8kW, laser scanning speed of 8mm / s, spot diameter of 4mm, and powder feeding rate of 3.9g / min. During the laser cladding process, high-purity argon gas was used to protect the molten pool to prevent oxidation, and the argon gas flow rate was 15L / min. A 0.6mm thick cladding layer was prepared on the surface of the aluminum alloy by laser cladding, resulting in a surface-modified aluminum alloy.

[0051] Example 2

[0052] The surface of the aluminum alloy was polished with 220#, 400# and 800# metallographic sandpaper in sequence, then immersed in a 10% sodium hydroxide aqueous solution for 3 minutes, and then washed with anhydrous ethanol and dried with a hair dryer to obtain the pretreated aluminum alloy.

[0053] The Stellite 6 alloy was placed in a drying oven and dried at 150°C for 2 hours.

[0054] Using dried Stellite 6 alloy as the cladding material, a BWT-3000W continuous fiber laser was used to perform laser cladding on the pretreated aluminum alloy surface at a preheating temperature of 150℃. A BWT BFL-CW3000-9 continuous fiber laser was used to irradiate the coaxial powder feeding device to deliver powder, allowing the powder to melt and enter the substrate molten pool. The laser cladding conditions were: laser output power of 1.2kW, laser scanning speed of 10mm / s, spot diameter of 4mm, and powder feeding rate of 4.2g / min. During the laser cladding process, high-purity argon gas was used to protect the molten pool to prevent oxidation, and the argon gas flow rate was 15L / min. A cladding layer with a thickness of 0.95mm was prepared on the surface of the aluminum alloy by laser cladding, resulting in a surface-modified aluminum alloy.

[0055] Comparative Example 1

[0056] The surface of the aluminum alloy was polished with 220#, 400# and 800# metallographic sandpaper in sequence, then immersed in a 10% sodium hydroxide aqueous solution for 3 minutes, and then washed with anhydrous ethanol and dried with a hair dryer to obtain the pretreated aluminum alloy.

[0057] The Stellite 6 alloy was placed in a drying oven and dried at 150°C for 2 hours.

[0058] Using dried Stellite 6 alloy as the cladding material, a BWT-6000W continuous fiber laser was used to perform laser cladding on the pretreated aluminum alloy surface at a preheating temperature of 130℃. A BWT BFL-CW6000-9 continuous fiber laser was used to irradiate the coaxial powder feeding device to deliver powder, allowing the powder to melt and enter the substrate molten pool. The laser cladding conditions were: laser output power of 4.0kW, laser scanning speed of 15mm / s, spot diameter of 5mm, and powder feeding rate of 6.2g / min. During the laser cladding process, high-purity argon gas was used to protect the molten pool to prevent oxidation, and the argon gas flow rate was 15~20L / min. A 1.5mm thick cladding layer was prepared on the surface of the aluminum alloy by laser cladding, resulting in a modified aluminum alloy surface layer with obvious cracks.

[0059] Performance testing

[0060] Test Example 1

[0061] The metallographic structures of the surface-modified aluminum alloys obtained in Example 1 and Comparative Example 1 are shown below. Figure 3 and Figure 4 As shown, where Figure 3 Comparative Example 1 (a is a SEM image with a scale bar of 100 μm, b is a SEM image with a scale bar of 50 μm). Figure 4 Example 1 (a is a SEM image with a scale bar of 50 μm, b is a SEM image with a scale bar of 10 μm).

[0062] from Figure 3 It can be seen that the aluminum alloy substrate under high-power laser cladding exhibited excessive melting and severe crack defects; from Figure 4 As can be seen, the present invention uses low-power laser cladding, and the resulting laser cladding layer exhibits a dendritic structure with refined grains. The bonding area between the laser cladding layer and the aluminum alloy substrate is composed of directionally grown dendrites, and exhibits associative crystallization characteristics with the aluminum alloy substrate, thus forming a good metallurgical bond between the cladding layer and the aluminum alloy substrate.

[0063] Test Example 2

[0064] Performance tests were conducted on the aluminum alloy substrate and the surface-modified aluminum alloy in Example 1.

[0065] Figure 5 For the hardness test curve, from Figure 5 It can be seen that the surface-modified aluminum alloy obtained by this invention has a hardness of 870~890 HV. 0.2 The hardness of the aluminum alloy substrate is between 90 and 110 HV. 0.2 Between the two, the former is about 8 times that of the latter, which fully demonstrates the strengthening effect of the surface modification method provided by the present invention on improving the surface hardness of aluminum alloys.

[0066] Figure 6 The graph shows the potentiodynamic polarization curves, from... Figure 6 It can be seen that the corrosion current of the surface-modified aluminum alloy obtained by the present invention is about -1.18V, and the corrosion current of the aluminum alloy substrate is about 1.55V, which fully demonstrates the enhanced effect of the surface modification method provided by the present invention on improving the corrosion resistance of aluminum alloy surfaces.

[0067] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A surface modification method of an aluminum alloy, characterized by, Includes the following steps: Using a cobalt-chromium-tungsten based alloy as the cladding material, laser cladding is performed on the surface of a preheated aluminum alloy to obtain a surface-modified aluminum alloy; The conditions for laser cladding include: laser output power of 1.2~1.8kW, laser scanning speed of 5~10mm / s, spot diameter of 2~5mm, and powder feeding rate of 3.7~4.5g / min; the laser used for laser cladding is a BWT-3000W continuous fiber laser; the powder feeding device used is a BWT BFL-CW3000-9 continuous fiber laser irradiation coaxial powder feeding device. The temperature of the preheated aluminum alloy is 130~150℃; The laser cladding is performed in an inert atmosphere, which is high-purity argon gas, and the flow rate of the high-purity argon gas is 15~20L / min.

2. The surface modification method according to claim 1, wherein, The cobalt-chromium-tungsten based alloy includes one or more of the following: Stellite1 alloy, Stellite6 alloy, Stellite20 alloy, Stellite31 alloy, and Stellite156 alloy.

3. The surface modification method according to claim 1, wherein Before performing the laser cladding, the aluminum alloy is also pretreated. The pretreatment includes grinding, immersing in alkaline solution, cleaning and drying the aluminum alloy in sequence.

4. The surface modification method according to claim 3, wherein The polishing process involves sequentially polishing the aluminum alloy with 220#, 400#, and 800# metallographic sandpaper.

5. The surface modification method according to claim 3, wherein The alkaline solution used for the immersion is a sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is 5-10%. The soaking time in the alkaline solution is 3-5 minutes.

6. The surface modification method of claim 1, wherein, Before performing the laser cladding, the cobalt-chromium-tungsten based alloy is also dried. The drying process is carried out at a temperature of 150-180℃ for 1-2 hours.

7. The surface modification method of claim 1, wherein The thickness of the cladding layer obtained by laser cladding is 0.6~1.0 mm.

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