CN111607816A - A kind of method for pulse electrodepositing Ni-SiC composite coating on aluminum alloy surface - Google Patents

Abstract

The invention provides a method for pulse electrodeposition of Ni-SiC composite coating on the surface of aluminum alloy, wherein the electroplating solution comprises: sodium citrate, disodium EDTA, nickel sulfate, nickel chloride, boric acid, silicon carbide particles and Surfactant sodium stearate; wherein the pH of the electroplating solution is 5-6; mechanical stirring is carried out in the electrodeposition process; the current density of the electrodeposition is 15-22A/dm ² . The method of the invention can obtain the Ni-SiC composite coating layer that is refined and dense, the silicon carbide is uniformly dispersed and the content is high, the technical problem of poor wear resistance of aluminum alloy is solved, and the bonding force is good, and the content of silicon carbide hard particles is high and uniformly distributed. , Ni-SiC composite coating with high hardness and good wear resistance can effectively protect the aluminum alloy samples.

Description

A kind of method for pulse electrodepositing Ni-SiC composite coating on aluminum alloy surface

technical field

The invention relates to the technical field of surface modification of metal materials, in particular to a method for pulse electrodeposition of Ni-SiC composite coating on the surface of aluminum alloy.

Background technique

In recent years, with the rapid development of my country's industrial technology, in order to further improve the production efficiency of parts and reduce production costs, the industrial field has put forward higher and more stringent requirements for the performance of materials. For example, high strength, hardness, friction and wear resistance and corrosion resistance, etc., while maximizing the performance of parts, while minimizing the emission of environmentally harmful pollutants. In the industrial and mining fields with harsh conditions, in order to better protect the aluminum alloy equipment, a protective film will be prepared on the surface of the aluminum alloy product to improve its surface hardness, wear resistance and corrosion resistance, and then to protect the aluminum alloy. Alloy products for better protection.

At present, in order to improve the surface hardness, wear resistance, corrosion resistance and other mechanical properties of aluminum alloy products, the surface of aluminum alloy is usually electroplated. The existing electroplating processes include Ni-SiC composite electroplating and chrome plating. Chromium metal coating shows many superior properties, such as high corrosion resistance, wear resistance and hardness, as well as low oxidation rate and good strength retention at high temperature, which solves the wear problem of aluminum alloy during use. Improve its service life. However, the gas and waste liquid generated in the process of chrome plating will cause great harm to human body and the environment, so it is necessary to find a new green and healthy process to replace chrome plating.

Ni-SiC composite plating is a process in which metal Ni and SiC particles are co-deposited by electrodeposition or electroless plating to obtain composite materials. As a relatively new material surface treatment technology, it has become an important method to improve the surface wear resistance, hardness and corrosion resistance of materials. Compared with the chrome plating process, Ni-SiC composite plating conforms to the concept of national clean production. Its process avoids pollutants to the human body and the environment, and reduces the cost of electroplating. Corrosion resistance and other main properties are equivalent to or better than chromium metal coatings.

At present, there are many documents and patents that introduce the preparation method of Ni-SiC composite coating deposited on the surface of aluminum alloy and the electroplating solution used; patent CN109797413 "Ni-P-SiC composite coating electroplating solution and electroplating method of aluminum alloy substrate" used in Sulfamate type plating solution, the pH value of the plating solution is 1.5, and the current of 3.5A/dm ² is provided by the DC power supply for electroplating. Under the sulfonate type bath system, it is difficult to ensure the content of silicon carbide in the coating when the current is less than 2A/dm ² .

Chinese patent CN105506526 "Preparation method of Ni-SiC composite coating on aluminum alloy surface and its electroplating solution" adopts constant DC power supply, and electroplating is carried out by air stirring. The electroplating solution used is relatively acidic, and the pretreatment adopts secondary immersion Zinc to improve the adhesion of the coating to the aluminum alloy substrate.

In the field of electroplating, very low cathodic current densities are rarely used during production and testing. As the cathode current density increases, the polarization of the cathode also increases, and the crystallization of the coating becomes finer and tighter. The upper limit of the current density in the electroplating process reported in the literature is generally maintained at 5-10A/dm ² For the use of different types of plating solutions, the current density on the cathode cannot be too large, and cannot exceed the allowable upper limit, otherwise it will seriously affect the quality of the coating. In the article "Preparation and Properties of High-Frequency Pulse Electrodeposited Ni-SiC Nanocomposite Coatings", the frequency range of power applied in the experiment is 20-140kHz, and the upper limit of the current density used is 5A/dm ² , when the current density is At 5A/dm ² , the coating has begun to foam seriously and cannot be formed.

Therefore, in order to reduce the cost of electroplating and avoid the problems of coarse Ni-SiC composite coating, uneven particle distribution and weak adhesion between the coating and the substrate during the electroplating process, a new type of electrodeposited Ni-SiC composite coating is urgently needed. method.

SUMMARY OF THE INVENTION

In order to solve the shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for the pulse electrodeposition of Ni-SiC composite coating on the surface of aluminum alloy. The method determines the pretreatment process of aluminum alloy, the bath formula and parameters of Ni-SiC composite electroplating and other conditions, uses pulse electrodeposition technology, uses mechanical stirring in the system with weak acidity of the bath, and applies high current density Depositing a layer of Ni-SiC composite coating with high SiC content, uniform distribution and good bonding force with the substrate on the surface of the aluminum alloy is of great significance for accelerating the actual industrial production efficiency and reducing the cost.

The object of the present invention is achieved through the following technical solutions:

A method for pulse electrodeposition of Ni-SiC composite coating on the surface of aluminum alloy, wherein the electroplating solution used comprises:

Wherein the pH of the electroplating solution is 5-6;

Mechanical stirring is performed during the electrodeposition process;

The current density of the electrodeposition was 15-22 A/dm ² .

After the plating solution is prepared, it can be mechanically stirred with a stirrer, preferably for 3-5 hours, and at a stirring rate of 150 r/min, so that the silicon carbide particles are evenly distributed in the plating solution.

Preferably, the frequency of the pulse is 800-1200 Hz, and the duty ratio is 0.6-0.8.

Preferably, the mechanical stirring rate is 120-200 r/min.

Preferably, the pulse electrodeposition temperature is 40-50° C., and the time is 30-60 min.

Preferably, the particle size of the SiC is 60 nm-25 μm.

In the electroplating process, the magnitude of the current density is the decisive factor to determine the electroplating efficiency. In the previous electroplating process, due to the use of different plating solutions, the upper limit of the current density during the electroplating process is generally maintained in the range of 5-10A/dm ² , and the efficiency is low. , the production speed is slow, which indirectly increases the production cost. When the plating solution prepared by the present invention is used for electroplating, when the current density is maintained between 15 and 22 A/dm ² , the plating solution does not decompose due to the high current density. it is good.

Sodium stearate is used as a surfactant in the existing plating solution. There are lone pairs of electrons on the hydroxyl oxygen atom of the stearate ion, while the outer electron arrangement of the Ni atom is 3d84s2, and the d orbital has two vacancies, which are easy to accept electrons, so the lone pair of electrons can enter the vacant d orbital to form a coordination covalent The stearic acid ions are chemically adsorbed on the surface of the Ni-SiC coating, and the long-chain alkane groups outside the film are intertwined into a network structure with physical isolation and water repellency. At the same time, stearate ions can react with Ni in the coating layer or silanol groups in silane molecules at the voids of the silane film, thereby making the silane film denser and more uniform. The ability of the composite film on the surface of the Ni-SiC coating to be hydrophobic and to isolate the corrosive medium is stronger, so it can give the coating better corrosion resistance.

The present invention uses the pulse composite electrodeposition technology to prepare the Ni-SiC composite coating. When other DC electroplating is used, the metal ions are continuously deposited as they approach the cathode, thus inevitably causing hydrogen evolution and concentration polarization, resulting in poor coating. uniform and dense. Since the pulsed composite electrodeposition technology uses the relaxation of current or voltage pulses to increase the activation polarization of the cathode and reduce the concentration polarization of the cathode, so as to improve the purity, density and uniformity of the deposited layer, and reduce the porosity of the coating. Purpose. At the same time, the pulsed composite electrodeposition technology has simple operation, low cost and high electroplating efficiency.

In the present invention, in the electroplating process of preparing the Ni-SiC composite coating layer by the pulse composite electrodeposition technology, compared with other electroplating technologies of DC power supply under the condition of low pH, pretreatment such as secondary dipping zinc is performed before electroplating. In the plating solution under the conditions, the bonding force between the plating layer and the substrate is improved by controlling the content of sodium citrate and disodium EDTA in the plating solution, the frequency of the pulse power supply and the duty cycle parameters.

The present invention appropriately increases the concentration of nickel sulfate and nickel chloride, and simultaneously reduces the concentration of silicon carbide in the plating solution, so that a refined and dense composite plating layer can be obtained at a higher electroplating rate.

In the present invention, the pH value of the plating solution is adjusted by controlling the addition of the amount of boric acid.

In the present invention, mechanical stirring is adopted in the electroplating process, and the stirring rate is preferably 120-200 r/min, so that the silicon carbide nanoparticles are uniformly dispersed in the plating solution, the cluster phenomenon is avoided, and the plating layer is more dense and uniform.

The method for pulse electrodepositing Ni-SiC composite coating on the surface of aluminum alloy provided by the invention can prepare a Ni-SiC composite coating with small porosity, strong binding ability, high content of silicon carbide particles and uniform distribution on the surface of the aluminum alloy. It has high microhardness and good wear resistance and corrosion resistance.

Description of drawings

FIG. 1 is a schematic diagram of an experimental apparatus according to an embodiment of the present invention.

FIG. 2 is a microscopic surface topography diagram of the Ni-SiC nanocomposite coating prepared in the embodiment of the present invention.

3 is a microscopic surface topography diagram of the Ni-SiC micro-composite coating prepared in the embodiment of the present invention.

4 is a microhardness histogram of the Ni-SiC micro-nano composite coating prepared in the embodiment of the present invention.

FIG. 5 is an EIS curve diagram of the Ni-SiC micro-nano composite coating prepared in the embodiment of the present invention.

FIG. 6 is a Tafel curve diagram of the Ni-SiC micro-nano composite coating prepared in the embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

Example 1

The preparation method of Ni-SiC micro-composite coating sample 1 includes the following steps:

(1) Preparation of electroplating solution: The composite plating solution is prepared from deionized water and drug powder in proportion, and the drug powder and deionized water are fully mixed by mechanical stirring; the duration of mechanical stirring is 3.5h, and the rotating speed is 150r/min. The composition of the Ni-SiC micro-composite plating bath is as follows: sodium citrate: 110g/L, disodium EDTA: 27g/L, nickel sulfate: 220g/L, nickel chloride: 28g/L, boric acid : 18g/L, silicon carbide micro-powder with a particle size of 25μm: 50g/L, surfactant sodium stearate: 1.5g/L.

(2) Mechanical leveling and pretreatment of aluminum alloy samples: First, use a wire cutting machine to cut the aluminum alloy blank into a sheet structure with a flat surface and a moderate size, and then use 300#, 600#, 800#, 1000#, 1500# sandpaper for grinding, and then use emery polishing paste for polishing to remove the oxide film produced on the surface of the aluminum alloy sheet during the mechanical leveling process; after that, use 35g/ The mixed solution of L NaOH, 20g/L Na ₃ PO ₄ and 15g/L Na ₂ CO ₃ was cleaned for 7 minutes to remove the oil stains on the aluminum alloy samples, and then ultrasonic cleaning was used to remove oil. Before the surface ultrasonic cleaning, first rinse with deionized water After 2 min, put the sample into a beaker containing ethanol, adjust the ultrasonic cleaning temperature at 45 °C, clean under ultrasonic vibration for 10 min, further remove the grease on the aluminum alloy test piece, and then rinse with deionized water for 2 min. At room temperature, the degreasing aluminum alloy samples were immersed in a mixed solution of 45 ml/L HF and 25 ml/L HNO ₃ for 15 s for pickling activation.

(3) A zinc precipitation layer is arranged on the surface of the aluminum alloy sample; the first zinc immersion treatment is the same as the second zinc immersion treatment, and the zinc precipitation liquid used includes: zinc oxide (ZnO): 12g/L, sodium hydroxide (NaOH): 120 g/L, ferric chloride (FeCl ₃ ·6H ₂ O): 1.5 g/L, potassium sodium tartrate (KNaC ₄ H ₄ O ₆ ·4H ₂ O): 10 g/L. The galvanizing temperature is 30°C, and the treatment time is 50s. The said zinc removal is that after the first zinc immersion treatment, the aluminum alloy sample that has undergone the first zinc immersion treatment is immersed in a KNO ₃ solution with a mass fraction of 34% at 20 to 30 ° C for 30s, and then taken out, and the second immersion treatment is carried out. The aluminum alloy test piece after zinc was rinsed with ionized water for 2 minutes, then dried with a blower with cold air, and stored in a beaker containing ethanol for use in composite electroplating.

(4) Composite electroplating process: put the pretreated substrate into the prepared electroplating solution for electroplating, and use a stirrer for mechanical stirring during the deposition process, which can increase the uniform dispersion of SiC microparticles in the electroplating solution and prevent SiC agglomerates in the plating bath. The rotational speed of the stirrer was 120 r/min, the temperature of the plating solution was 50° C., the current density was 18 A/dm ² , and the pH value of the plating solution was 5. At the same time, connect an external pulse power supply to start pulse composite electroplating. The frequency of the pulse is 1000Hz, the duty cycle is 0.7, and the electroplating time is 40min.

Example 2

The preparation method of Ni-SiC nanocomposite coating sample 2 includes the following steps:

(1) Preparation of electroplating solution: The composite plating solution is prepared from deionized water and drug powder in proportion, and the drug powder and deionized water are fully mixed by mechanical stirring; the duration of mechanical stirring is 3.5h, and the rotating speed is 150r/min. The components of the Ni-SiC nanocomposite plating bath are as follows: sodium citrate: 110g/L, disodium EDTA: 27g/L, nickel sulfate: 220g/L, nickel chloride: 28g/L, boric acid : 18g/L, silicon carbide nanopowder with a particle size of 60nm: 50g/L, surfactant sodium stearate: 1.5g/L.

(2) Mechanically leveling and pre-processing the aluminum alloy sample: Use a wire cutting machine to cut the aluminum alloy blank into a sheet structure with a flat surface and a moderate size. The aluminum alloy samples were polished with 300#, 600#, 800#, 1000#, and 1500# sandpaper respectively, and then polished with emery polishing paste to remove the oxide film produced on the surface of the aluminum alloy test piece during the mechanical leveling process; Under the condition of 50℃, use the mixed solution of 35g/L NaOH, 20g/L Na ₃ PO ₄ , 15g/L Na ₂ CO ₃ to clean the aluminum alloy samples for 7min to remove the oil stains on the aluminum alloy samples, then use ultrasonic cleaning to remove oil, and ultrasonically ultrasonically remove the oil on the surface. Before cleaning, first rinse with deionized water for 2 minutes, then put the sample into a beaker containing ethanol, adjust the ultrasonic cleaning temperature to 45 °C, and clean under ultrasonic vibration for 7 minutes to further remove the grease on the aluminum alloy test piece. After that, rinse with deionized water for 2 min. At room temperature, the degreasing aluminum alloy samples were immersed in a mixed solution of 45 ml/L HF and 25 ml/L HNO ₃ for 15 s for pickling activation.

(3) A zinc precipitation layer is arranged on the surface of the aluminum alloy sample; the first zinc immersion treatment is the same as the second zinc immersion treatment, and the zinc precipitation liquid used includes: zinc oxide (ZnO): 12g/L, sodium hydroxide (NaOH): 120 g/L, ferric chloride (FeCl ₃ ·6H ₂ O): 1.5 g/L, potassium sodium tartrate (KNaC ₄ H ₄ O ₆ ·4H ₂ O): 10 g/L. The galvanizing temperature is 30°C, and the treatment time is 50s. The said zinc removal is that after the first zinc immersion treatment, the aluminum alloy sample that has undergone the first zinc immersion treatment is immersed in a KNO ₃ solution with a mass fraction of 34% at 20 to 30 ° C for 30s, and then taken out, and the second immersion treatment is carried out. The aluminum alloy test piece after zinc was rinsed with ionized water for 2 minutes, then dried with a blower with cold air, and stored in a beaker containing ethanol for use in composite electroplating.

(4) Composite electroplating process: put the pretreated substrate into the prepared electroplating solution for electroplating, and use a stirrer for mechanical stirring during the deposition process, which can increase the uniform dispersion of SiC nanoparticles in the electroplating solution and prevent SiC agglomerates in the plating bath. The rotating speed of the stirrer was 120 r/min, the temperature was 50° C., the current density was 18 A/dm ² , and the pH value was 5. At the same time, connect the external pulse power supply to start pulse composite electroplating, the pulse frequency is 1000Hz, the duty cycle is 0.7, and the electroplating time is 40min.

Experimental example 3

The structure and properties of the prepared coatings were measured by SEM, microhardness test, and corrosion resistance test. The experimental results show that under the condition of mechanical stirring, the Ni-SiC composite coating prepared by pulsed power supply has high density, and SiC Uniform particle distribution, high hardness and excellent wear and abrasion resistance.

(1) Surface morphology of Ni-SiC composite coating:

Phenom XL desktop scanning electron microscope was used to observe the surface morphology of the coating, as shown in Figure 2 and Figure 3: In the Ni-SiC micro-composite coating prepared by the pulsed composite electrodeposition technology in the present invention, the SiC particles are uniformly distributed, and there is no obvious agglomeration. Clustering phenomenon occurs; in the prepared Ni-SiC nanocomposite coating, the grain size of the coating becomes smaller and the morphology becomes more uniform and dense. It is also easy to see that the addition of silicon carbide nanoparticles changes the surface morphology of the coating. Compared with the Ni-SiC microcomposite coating, the nanocomposite coating is denser, the surface roughness is reduced, and the coating is smoother.

(2) Microhardness test:

The microhardness of Ni-SiC composite coating was tested by using HXD-1000TMSC digital microhardness tester. The load of the hardness tester is 200g and the load time is 15s. The measurement results are shown in Figure 4. The surface hardness of the aluminum alloy sample without composite coating is about 93HV, while the hardness of the deposited Ni-SiC nanocomposite coating can reach About 558HV, the hardness of Ni-SiC micro-composite coating can reach about 420HV.

(3) Corrosion resistance test

The corrosion resistance of the prepared Ni-SiC composite coatings was tested by using a CHI660C electrochemical workstation. A three-electrode system is used in the test process: the sample is the working electrode, the platinum sheet is the auxiliary electrode, the saturated calomel electrode (SCE) is used as the reference electrode, the scanning speed is 0.5mV/s, and the corrosive medium is 0.5mol/L. Sodium chloride solution, tested at room temperature. It can be seen from Figure 5 and Figure 6 that compared with the corrosion potential of the substrate, the corrosion voltage of the deposited Ni-SiC composite coating has a larger positive shift. At the same time, the addition of nanoparticles refines the grains and makes the electrodeposition The structure of the layer is more uniform and dense, which greatly reduces the porosity of the electrodeposited layer, thereby enhancing the corrosion resistance.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (5)

1. A method for pulse electrodeposition of a Ni-SiC composite coating on the surface of an aluminum alloy is characterized in that an electroplating solution comprises the following components:

wherein the pH of the electroplating solution is 5-6;

mechanically stirring in the electrodeposition process;

the current density of the electrodeposition is 15-22A/dm²。

2. The method for pulse electrodeposition of the Ni-SiC composite coating on the surface of the aluminum alloy according to claim 1, wherein the pulse frequency is 800 to 1200Hz, and the duty ratio is 0.6 to 0.8.

3. The method for pulse electrodeposition of a Ni-SiC composite coating on an aluminum alloy surface as recited in claim 1, wherein the mechanical stirring rate is 120-200 r/min.

4. The method for pulse electrodeposition of the Ni-SiC composite coating on the surface of the aluminum alloy according to claim 1, wherein the pulse electrodeposition temperature is 40-50 ℃ and the time is 30-60 min.

5. The method for pulse electrodeposition of the Ni-SiC composite coating on the surface of the aluminum alloy according to claim 1, wherein the grain size of SiC is 60nm to 25 μm.

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