Method for surface modification of aluminum alloy bar for friction stir deposition

Abstract

The invention discloses a method for surface modification of an aluminum alloy bar for friction stir deposition. The method comprises the following steps: (1) preparing composite powder of metal powder and hexagonal boron nitride powder; (2) mixing the composite powder, a solvent, a binder and a dispersant to prepare a suspension; (3) the surface of the aluminum alloy bar is subjected to oil removal, acid pickling and sand blasting roughening pretreatment; and (4) spraying the suspension prepared in the step (2) on the surface of the aluminum alloy bar pretreated in the step (3) by adopting a spraying process. And the metal powder-hexagonal boron nitride composite coating is lubricated, so that the formation of a brittle phase Al4C3 can be avoided, and the possibility of interlayer fracture can be reduced. The metal powder-hexagonal boron nitride coating is not prone to oxidation failure, and a good lubricating effect can be kept within the working temperature range of friction stir deposition.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of friction stir additive technology, and particularly relates to a method for surface modification of an aluminum alloy rod for friction stir deposition. BACKGROUND

[0002] Aluminum alloy is a lightweight material with excellent performance, and its core advantages are light weight, high strength, strong corrosion resistance and excellent processing performance. Compared with traditional steel, the density of aluminum alloy is only about 1 / 3 of that of steel, but through alloy ratio and heat treatment process, the strength close to that of steel can be achieved. This high specific strength characteristic makes it widely used in key components such as aircraft fuselage and rocket fuel tank in the aerospace field.

[0003] Currently, graphite is mostly used as a lubricant to lubricate aluminum alloy in the application of friction stir deposition additive (AFSD). However, the application of graphite lubricant has significant defects. Due to the continuous contact of graphite and aluminum alloy at the high-temperature friction interface, Al4C3 phase is easily generated with aluminum. The intermetallic compound is distributed in the grain boundary area in the form of needles or lamellar, which significantly reduces the toughness and plasticity of the material, resulting in defects such as micro-cracks in the deposited layer. Especially under dynamic load conditions, the difference in thermal expansion coefficient between Al4C3 phase and the matrix will exacerbate the interface peeling, which seriously affects the fatigue life and service reliability of the additive component. SUMMARY

[0004] In view of the deficiencies in the prior art, the application provides a method for surface modification of an aluminum alloy raw material rod for friction stir deposition.

[0005] The technical scheme of the application is as follows:

[0006] A method for surface modification of an aluminum alloy rod for friction stir deposition, comprising the following steps:

[0007] (1) preparing a composite powder of metal powder and hexagonal boron nitride powder;

[0008] (2) mixing the composite powder, solvent, binder and dispersant to prepare a suspension;

[0009] (3) performing oil removal, pickling and sandblasting roughening pretreatment on the surface of the aluminum alloy rod;

[0010] (4) spraying the suspension prepared in step (2) on the surface of the aluminum alloy rod pretreated in step (3) by using a spraying process, and the thickness of the coating is 20-30 microns, and the surface modification of the aluminum alloy rod for friction stir deposition is obtained after air drying.

[0011] The method, the metal powder in step (1) is spherical copper powder, the hexagonal boron nitride powder is flaky, the mass ratio of copper powder and hexagonal boron nitride powder is 4:1-5:1; copper powder and hexagonal boron nitride powder are mixed at a speed of 250 rpm for 4 hours to obtain a composite powder, and the composite powder is placed in an argon environment for 2 days.

[0012] The method, the mass ratio of the composite powder, the solvent, the binder in step (2) is 2-3:1:1, and the amount of the dispersing agent is 3-5% of the total mass of the composite powder, the solvent and the binder.

[0013] The method, the solvent in step (2) can be N-methyl pyrrolidone or anhydrous ethanol, the binder can be polyimide or ethyl silicate, and the dispersing agent can be polyethylene glycol or polyvinyl pyrrolidone.

[0014] The method, the aluminum alloy rod in step (3) is a cuboid, and the grade can be selected from 6061 or 7075.

[0015] The method, the oil removal treatment in step (3) can use acetone or alcohol treatment, and the treatment time is 10-15 minutes.

[0016] The method, the pickling in step (3) can use 5-10% nitric acid solution, and the treatment time is 20-30s.

[0017] The method, the sand blasting roughening treatment in step (3) uses 100-200 mesh alumina sand, the sand blasting pressure is 0.3-0.5 MPa, the sand blasting time is 10-15s, and the surface roughening is 3 μm≤Ra≤5 μm.

[0018] The method, the spraying in step (4) can use a spray gun liquid tank or an aerosol tank, the spray gun pressure of the spray gun liquid tank is 0.4-0.6 MPa, the spraying distance is 15-20 cm, and the spraying is placed in air to dry for 2-5 minutes after spraying.

[0019] Compared with the prior art, the present application has the following beneficial technical effects:

[0020] 1. Compared with the traditional use of graphite lubricated aluminum alloy for additive manufacturing, the metal powder-hexagonal boron nitride composite coating lubrication can avoid the formation of brittle phase Al4C3 and reduce the possibility of interlayer fracture.

[0021] 2. The metal powder-hexagonal boron nitride coating is not easy to oxidize and fail, and can maintain good lubrication effect in the working temperature range of friction stir deposition.

[0022] 3. The use of metal powder-hexagonal boron nitride lubricates aluminum alloy can obtain better lubrication effect, and the chemical inertness of hexagonal boron nitride can avoid reaction with aluminum alloy, and the metal powder in the coating can form a reinforcing phase with the aluminum alloy substrate, which can enhance the interlayer bonding force and interface bonding degree. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a cross-sectional morphology of the surface modified aluminum alloy rod prepared in Example 1; DETAILED DESCRIPTION

[0024] The present application will be described in detail below in conjunction with specific examples.

[0025] The present embodiment provides a method for surface modification of aluminum alloy rod for friction stir deposition, comprising the following steps:

[0026] (1) Put 45g of spherical copper powder with a particle size of 40μm and 11g of flaky hexagonal boron nitride powder with a particle size of 20μm into a mechanical mixer for powder mixing, mix at a speed of 250rpm for 4 hours to obtain a composite powder, and place the composite powder in an argon environment for 2 days;

[0027] (2) Put the composite powder prepared in step 1, 22.4g of binder ethyl silicate, 22.4g of solvent anhydrous ethanol and 3.4g of dispersant polyvinylpyrrolidone into a high-speed shearing disperser to prepare a suspension and fill it into an aerosol can, stirring at 3000rpm for 30 minutes;

[0028] (3) Select a 6061 aluminum alloy rod with a size of 10mm*10mm*300mm and pretreat it;

[0029] (3.1) Use alcohol to remove oil from the surface of the aluminum alloy rod, and the treatment time is 10 minutes;

[0030] (3.2) Use 5% nitric acid to pickle the aluminum alloy rod after oil removal, and the pickling time is 30s;

[0031] (3.3) Sandblast the aluminum alloy rod after oil removal and pickling for roughening pretreatment, use 200 mesh alumina sand, sandblast pressure is 0.4MPa, sandblast time is 10s, surface roughening to Ra=4μm;

[0032] (4) Use the aerosol can to directly spray on the rod surface prepared in step (3) to obtain a surface modified 6061 aluminum alloy rod, the spraying distance is 20cm, after spraying, place it in the air to dry for 5 minutes, and the thickness of the coating obtained by the last spraying is 20μm;

[0033] (5) The copper-hBN modified aluminum alloy rod prepared in step (4) is used as the feedstock of the friction stir deposition additive equipment, loaded into the clamp of the friction stir deposition additive equipment, and programmed in combination with simulation analysis of the shape of the target component;

[0034] (6) The copper-hBN modified aluminum alloy is deposited by multi-pass deposition of the tool head of the friction stir deposition tool on the substrate, wherein the rotation speed of the tool head is 400 r / min, the feed speed is 1 mm / s, the travel speed of the tool head is 200 mm / min, and the single-layer deposition thickness is 1.5 mm.

[0035] Effect verification:

[0036] The component obtained by multi-pass deposition is machined and polished to obtain the required shaped component. The micro-morphology diagram of the surface modified aluminum alloy deposition component obtained in this embodiment is as shown in Figure 1 It can be seen that the deposition layer contains uniformly distributed Al2Cu intermetallic compounds and a small amount of hBN particles.

[0037] According to the GB / T 12444-2006 standard, the dynamic friction coefficient test was carried out on the friction and wear testing machine (MM-200). The dynamic friction coefficient of the aluminum rod using graphite lubrication was 0.20, and the dynamic friction coefficient of the aluminum rod obtained in Example 1 was 0.18.

[0038] According to the GB / T 228.1-2021 standard, the sample was prepared, and the room temperature tensile test was carried out on the electronic universal testing machine (MTS E45.105). The tensile strength of the original aluminum rod deposition component was 170 MPa, and the tensile strength of the composite component obtained in Example 1 was 178 MPa.

[0039] It can be seen that the surface modified aluminum alloy rod prepared by the method can not only ensure the lubrication effect of the surface, but also improve the mechanical properties of the deposition component to a certain extent

[0040] It should be understood that those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the appended claims of the present application.

Claims

1. A method for surface-modified aluminum alloy rods used in friction stir deposition, characterized in that, Includes the following steps: (1) Preparation of composite powder of metal powder and hexagonal boron nitride powder; (2) A suspension is prepared by mixing composite powder, solvent, binder and dispersant; (3) The surface of the aluminum alloy rod is pretreated by degreasing, pickling, and sandblasting. (4) The suspension prepared in step (2) is sprayed onto the surface of the aluminum alloy rod pretreated in step (3) using a spraying process. The thickness of the coating is 20-30 μm. After drying, the aluminum alloy rod for surface modification by stirring and friction deposition is obtained.

2. The method according to claim 1, characterized in that, The metal powder mentioned in step (1) is spherical copper powder, and the hexagonal boron nitride powder is flake-shaped. The mass ratio of copper powder to hexagonal boron nitride powder is 4:1-5:

1. The copper powder and hexagonal boron nitride powder are mixed at 250 rpm for 4 hours to obtain composite powder.

3. The method according to claim 1, characterized in that, The mass ratio of the composite powder, solvent, and binder in step (2) is 2-3:1:1, and the amount of dispersant is 3-5% of the total mass of the composite powder, solvent, and binder.

4. The method according to claim 1, characterized in that, In step (2), the solvent can be N-methylpyrrolidone or anhydrous ethanol, the binder can be polyimide or ethyl silicate, and the dispersant can be polyethylene glycol or polyvinylpyrrolidone.

5. The method according to claim 1, characterized in that, The aluminum alloy rod mentioned in step (3) is in the shape of a cuboid, and the grade can be 6061 or 7075.

6. The method according to claim 1, characterized in that, The degreasing treatment described in step (3) can be performed using acetone or alcohol for 10-15 minutes.

7. The method according to claim 1, characterized in that, The pickling in step (3) can be performed using a 5-10% nitric acid solution for 20-30 seconds.

8. The method according to claim 1, characterized in that, The sandblasting roughening treatment in step (3) uses 100-200 mesh alumina sand, sandblasting pressure 0.3-0.5MPa, sandblasting time 10-15s, and surface roughening to 3μm≤Ra≤5μm.

9. The method according to claim 1, characterized in that, The spraying described in step (4) can be done using a spray gun reservoir or an aerosol can. The spray gun air pressure in the spray gun reservoir is 0.4-0.6MPa, the spraying distance is 15-20cm, and after spraying, it is placed in the air to dry for 2-5 minutes.

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