CN105506693A - Surface nickel coating grain size regulating method capable of improving corrosion resistance - Google Patents

Abstract

The invention provides a method for controlling the grain size of a nickel coating on a surface to improve corrosion resistance. The corrosion resistance is improved by electrodepositing Ni coatings with different grain sizes, and belongs to the field of metal surface engineering. The invention adopts the nickel sulfamate plating solution system, and controls the electrodeposition parameters to regulate the grain size of the Ni coating under the condition of not adding any grain refiner. The invention adopts two methods of direct current electrodeposition and pulse electrodeposition to obtain Ni coatings with different grain sizes ranging from nanometer to micrometer. On the premise of not adding grain refiners, adjusting the electrodeposition parameters to achieve nickel coating grain refinement can effectively improve its corrosion resistance and avoid the segregation of impurity elements caused by additives. The invention has the advantages of simple operation process, low cost, high efficiency and the like.

Description

A method for controlling grain size of surface nickel coating to improve corrosion resistance

technical field

The invention relates to surface treatment technology, in particular to a method for controlling the grain size of nickel coatings on the surface of alloys to improve their corrosion resistance, more specifically to obtain Ni coatings with micron to nanometer sizes on the surface of alloys by regulating different electrodeposition parameters. layer method.

Background technique

At present, metal alloys are widely used, common ones include copper alloys, magnesium alloys, titanium alloys, aluminum alloys, etc., which are mainly used in automobile manufacturing, building materials, aerospace, offshore platforms and other industries. However, due to the defects of the alloy itself, such as composition segregation, loose structure, etc., it suffers severe corrosion in humid air, marine atmosphere and other corrosive environments, including electrochemical corrosion and chemical corrosion, which greatly reduces the service life of component materials and limits its scope of application.

In response to the above phenomena, surface treatment processes including friction stir processing, thermal spraying, surface laser cladding and electroplating can reasonably control the surface microstructure of the modified metal without changing the matrix structure, and have outstanding advantages in effectively improving the corrosion resistance. Among them, electroplating coating technology is widely used in the field of surface protection of materials due to its simple preparation equipment, compact structure of the obtained coating, and excellent corrosion resistance.

Electroplated nickel coating is widely used because of its high corrosion resistance, and the smaller the grain size, the better the corrosion resistance. At present, the traditional electroplating nickel coating process often achieves nano-sized nickel coatings by adding grain refiners such as saccharin. , It is easy to cause segregation of impurity elements, such as the addition of saccharin will lead to grain boundary segregation of sulfur element, sulfidation embrittlement, which will lead to deterioration of alloy properties. The patent number is CN104562111A, and the electroplated Ni-Cr coating introduced in "A Method of Improving the Corrosion Resistance of Nickel-Aluminum Bronze" has unsustainable increase in thickness, uncontrollable Cr content, and there are many additives in the electroplating solution Thus affecting the coating quality and other defects. Based on the above reasons, it is beneficial to electrodeposit nickel coating on the surface of the alloy to improve its corrosion resistance.

For the above reasons, it would be advantageous to develop an electroplating method for electrodepositing a coating with fine grain size on the surface of the alloy.

Based on the above reasons, it is necessary to develop an electrodeposition method of nickel coating with nano-grain size only by controlling the electrodeposition parameters without adding a grain refiner.

Based on the above reasons, it is necessary to develop a Ni coating electrodeposition method with adjustable thickness and good repeatability, which is suitable for the surface of various metal materials requiring anticorrosion.

Contents of the invention

In view of the defects in the prior art, the object of the present invention is to provide a method for controlling the grain size of the surface nickel coating to improve corrosion resistance, without adding a grain refiner, and only by adjusting different electrodeposition parameters on the surface of the alloy to obtain Ni coating with micron to nanometer size variation for improved corrosion resistance.

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

The invention provides a method for controlling the grain size of a nickel coating on the surface of an alloy to improve the corrosion resistance, characterized in that the method comprises the following steps:

A. Mechanical grinding, degreasing and pickling activation of the alloy surface that needs to be improved in corrosion resistance;

B, the alloy processed in step A is used as the cathode and the insoluble nickel plate as the anode is placed in the electroplating solution together, and is connected with the power supply for electroplating;

C. Take out the alloy after electroplating, rinse it with deionized water, dry it with cold wind, and prepare a Ni coating on its surface to improve the corrosion resistance.

Preferably, the alloy is specifically a nickel-aluminum-bronze alloy.

Preferably, in step _A , the mechanical grinding uses 180#, 400#, 800#, 1200# water sandpaper in sequence _; 50g/LNa ₃ PO ₄ oil removal solution, the oil removal condition is: 70-80°C constant temperature for 1-2 minutes; the activation solution used in the pickling activation is 100-150mL/LH ₂ SO ₄ solution or 100-150mL/LHCl solution to remove surface oxides. In the degreasing solution, NaOH has a strong saponification ability, the degreasing speed is slow if the concentration is too low, and the soap produced by the concentration is too high is difficult to dissolve; Na ₂ CO ₃ mainly acts as a buffer; Na ₃ PO ₄ acts as an emulsifier, reducing The surface tension between the oil stain and the degreasing liquid prevents the oil droplets from reuniting. If the content is too low, the oil droplets are reunited and adsorbed on the surface and are not easy to fall off.

Preferably, in step B, the main salt composition of the electroplating solution is 300-400 g/LNi(SO ₃ NH ₂ ) ₂ ·4H ₂ O, 15-60 g/LNiCl ₂ ·6H ₂ O. The main salt component of the electroplating solution can provide a higher content of Ni and has better dispersion and covering capabilities, thereby improving the electroplating speed and efficiency. The sulfamic acid nickel plating solution system can obtain semi-bright, smooth, low-stress nickel plating.

Preferably, in step B, the electroplating solution also contains 30-50 g/LH ₃ BO ₃ pH buffer and 0.1-0.15 g/LC ₁₂ H ₂₅ SO ₄ Na surfactant. The pH buffering agent exceeds a certain concentration range to reduce the current efficiency or produce other side effects.

Preferably, in step B, the electroplating solution composition is:

Preferably, in step B, the electroplating solution does not contain any grain refiner. Such as saccharin, sodium hypophosphite, hydroxylamine hydrochloride, sodium borohydride, formaldehyde, aminoborane and water and hydrazine.

Preferably, in step B, the temperature of the electroplating solution during the electroplating process is 49-51° C., the pH value of the electroplating solution is 3.8-4.2, and the electroplating time is 60 minutes. Electroplating efficiency can be maximized at this electroplating temperature, but exceeding this temperature will lead to increased thermal stress of the coating; choosing this pH value of the electroplating solution can maximize the anode solubility and current efficiency, and if the pH value exceeds this range, basic nickel salt will be formed Precipitation will cause hydrogen bubbles to stay on the surface of the cathode to form pinholes.

Preferably, the pH value of the electroplating solution is adjusted by using NH ₃ ·H ₂ O solution, and the pH value of the electroplating solution needs to be slowly added while stirring during the adjustment process.

Preferably, in step B, the electroplating adopts direct current electroplating and/or pulse square wave electroplating; the direct current electroplating current density is 1-5A/dm ² , and the greater the direct current density, the larger the grain size of the obtained nickel coating ; The forward current density of the pulse plating is 1-30A/dm ² , the reverse current density is 0-5A/dm ² , the pulse frequency is 100-500Hz, and the duty cycle is 20-50%. Nickel coatings with different grain sizes are obtained.

The principle of the present invention is: pulse electroplating mainly uses the pulse relaxation of current or voltage to increase the activation polarization of the cathode and reduce the concentration polarization of the cathode. When the current is turned on, the cathode metal ions are deposited; The ions return to their initial concentration. The higher the current density, the formation rate of crystal nuclei is much higher than the growth rate of the original crystal; the shorter the plating time, the higher the frequency, which makes the deposition time of nickel coating shorter and the growth rate of crystal grains is very slow. Different grain sizes can be obtained by changing the current density, off time T _off , on time T _on , pulse frequency f (pulse period T=1/f), duty cycle T _on /(T _on +T _off ) nickel plating.

The Ni coating obtained by the present invention is a layer of dense, smooth, and crack-free coating, with a thickness of 20-50 μm. The thickness of the coating is related to the current density and the electroplating time. The greater the current density, the longer the electroplating time, and the greater the thickness of the coating. The surface of the obtained nickel coating is uniform and dense, and has good adhesion to the substrate. By controlling different electroplating parameters, the grain size of the nickel coating can be changed from micron (2-3um) to nano-scale (10-20nm); and The obtained nickel coating has no additives such as saccharin in the electroplating solution, so that the nickel coating does not have serious sulfur segregation during subsequent heat treatment to remove internal stress, improve bonding force, and uniformly refine the surface, so the surface has no cracks.

Compared with the prior art, the present invention has the following beneficial effects:

1. No grain refiner is added to the plating solution, so that the coating does not contain sulfur elements, so that the internal stress is removed during the subsequent heat treatment and the surface is uniformly refined without vulcanization and embrittlement of the coating, which improves the quality of the coating.

2. The fine-grained coating obtained by controlling the electroplating parameters has the advantages of dense coating and uniform structure.

3. The coating has excellent corrosion resistance and high hardness, and can serve under harsh working conditions, thereby protecting the substrate from corrosion.

4. Nickel coatings of different thicknesses can be obtained by controlling the electroplating time, and the selection of process parameters has good repeatability.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is the transmission electron microscope figure of the micron size nickel coating of embodiment 1;

Fig. 2 is the current density schematic diagram of the pulse electroplating submicron Ni coating of embodiment 2;

Fig. 3 is the transmission electron microscope figure of the submicron size nickel coating of embodiment 2;

Fig. 4 is the current density schematic diagram of the pulse electroplating nanoscale Ni coating of embodiment 3;

Fig. 5 is the transmission electron microscope figure of the nano-sized nickel coating of embodiment 3;

Fig. 6 is a comparison diagram of the potentiodynamic polarization curves of nickel coatings with different grain sizes obtained in the present invention in 3.5% NaCl solution.

detailed description

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

This example relates to a kind of electroplating method that obtains micron nickel coating with DC electroplating, and described method comprises the steps:

Step 1: Mechanically polish the surface of the nickel-aluminum-bronze alloy with 180#—400#—800#—1200# water sandpaper in sequence, and then remove oil in the prepared degreasing solution (containing 30g/LNaOH, 35g/LNa ₂ CO ₃ , 40g/LNa ₃ PO ₄ ) at 70°C for 1 min, remove residual grease, rinse with water and set aside;

Step 2: Pickling and activating the treated nickel-aluminum bronze in 100mL/LH ₂ SO ₄ , rinse with water and blow dry with cold air, then place it in the following plating solution immediately:

Heat the temperature of the electrolyte to 50±1°C; adjust its pH value to 4.0±0.2 with ammonia water; the DC current density is 5A/dm ² ; the electroplating time is 60min;

Step 3: Take out the electroplated nickel-aluminum-bronze alloy, rinse it with deionized water, and dry it with cold air.

Embodiment 1 provides surface observation and test data after electroplating treatment. Figure 1 shows the grain size of the coating under the transmission electron microscope, and it can be seen that the grain size is between 2-3um.

Example 2

This example relates to a kind of electroplating method that obtains submicron nickel coating with pulse electroplating, and described method comprises the steps:

Step 1: Mechanically polish the surface of the nickel-aluminum-bronze alloy with 180#—400#—800#—1200# water sandpaper in sequence, and then remove oil in the prepared degreasing solution (containing 30g/LNaOH, 35g/LNa ₂ CO ₃ , 40g/LNa ₃ PO ₄ ) at 70°C for 1 min, remove residual grease, rinse with water and set aside;

Step 2: pickling and activating the treated nickel-aluminum-bronze alloy with 100mL/LH ₂ SO ₄ , rinse with water and blow dry with cold air, then immediately place it in the plating solution in Example 1, and heat the temperature of the electrolyte to 50±1°C; Adjust the pH value to 4.0±0.2 with ammonia water; the applied bidirectional pulse current waveform is shown in Figure 2, the forward pulse current density Ic is 2A/dm ² , the reverse pulse current density Ia is 0.5A/dm ² , The pulse frequency is 100Hz, the forward energization time t is 5ms, and the reverse energization time t is 5ms, that is, the duty cycle is 50%; the electroplating time is 60min;

Step 3: Take out the electroplated nickel-aluminum-bronze alloy, rinse it with deionized water, and dry it with cold wind.

Embodiment 2 provides surface observation and test data after electroplating treatment. Figure 3 shows the grain size of the coating under the transmission electron microscope. It can be seen that the grain size distribution is uniform, and the grain size can be seen to be between 100-150nm.

Example 3

This example relates to a kind of electroplating method that obtains nanoscale nickel coating with pulse electroplating, and described method comprises the steps:

Step 1: Mechanically polish the surface of the nickel-aluminum-bronze alloy with 180#—400#—800#—1200# water sandpaper in sequence, and then put it in the prepared degreasing solution (containing 30g/LNaOH, 35g/LNa2CO3, 40g/LNa3PO4) for 70 Keep the temperature at ℃ for 1 minute, remove the residual oil, rinse with water and set aside;

Step 2: pickling the treated nickel-aluminum bronze with 100mL/LH2SO4 for acid pickling activation, rinsing with water and blowing dry with cold wind, immediately placing it in the plating solution in Example 1, heating the temperature of the electrolyte to 50±1°C; adjusting it with ammonia water pH value to 4.0±0.2; the applied pulse current waveform is shown in Figure 4, the current density Ip is 30A/dm ² , the pulse frequency is 500Hz, the power-on time t-on is 0.4ms, and the power-off time t-off is 1.6ms , that is, the duty cycle is 20%; the electroplating time is 60min;

Step 3: Take out the electroplated nickel-aluminum-bronze alloy, rinse it with deionized water, and dry it with cold air.

Embodiment 3 provides surface observation and test data after electroplating treatment. Figure 5 shows the grain size of the coating under the transmission electron microscope. It can be seen that the grain size distribution is uniform, and the grain size can be seen to be between 10-15nm.

Using CHI660D electrochemical workstation, the standard three-electrode system was used to test the electrochemical corrosion performance of the electroplated Ni coating obtained by different electroplating parameters in 3.5% NaCl solution, and the results are shown in Figure 6. It can be seen from Figure 6 that the self-corrosion potential of as-cast nickel-aluminum bronze is -0.32V, and the corrosion current density is 9.678e-6A/cm ² ; the self-corrosion potential of the micron nickel coating is -0.178V, and the corrosion current density is 66.7e-6A /cm ² ; the self-corrosion potential of the submicron nickel coating is -0.135V, and the corrosion current density is 12.32e-6A/cm ² ; the self-corrosion potential of the nano-scale nickel coating is -0.088V, and the corrosion current density is 1.676e- 6A/cm ² . That is, the smaller the grain size of the nickel coating, the positive movement of the self-corrosion potential, and the gradual decrease of the corrosion current density, indicating that the smaller the grain size, the better the corrosion resistance of the Ni coating.

In summary, fine-grained nickel coatings can be obtained by controlling the electroplating parameters, and the corrosion resistance of nano-sized Ni coatings is about 60 times better than that of micron-sized Ni coatings.

In the Ni coating obtained in Examples 1-3, during the subsequent heat treatment to improve the bonding force between the substrate and the coating, since no grain refiner is added, no sulfidation embrittlement occurs, the coating surface is smooth and does not fall off, and no cracks appear.

Comparative example 1

This comparative example relates to a kind of electroplating method that obtains the nanoscale nickel coating by pulse electroplating, and the difference between the described method and the method of embodiment 2 is only: the electroplating solution composition that this comparative example adopts is: Ni(SO ₃ NH ₂ )2·4H ₂ O (550g/L), NiCl ₂ ·6H ₂ O (10g/L) and H ₃ BO ₃ (35g/L). The nickel coating thus obtained causes cathodic polarization to decrease due to an excessively high main salt concentration, and the dispersion ability and deposition efficiency of the plating solution decrease, making the coating crystallization coarser, and the grain size of the obtained nickel coating is 46.0nm, And there are many pores on the surface.

Comparative example 2

This comparative example relates to a kind of method that pulse electroplating obtains nickel coating, and the difference of described method and the method of embodiment case 3 is only: added grain refining agent saccharin 10g/L in electroplating liquid, the obtained nickel The grain size of the coating is 10nm, but during the subsequent heat treatment to improve the bonding force between the substrate and the coating, due to the addition of saccharin, the S element contained in the coating will be sulfided and embrittled, the surface of the coating will fall off, and cracks will appear, thereby destroying the nickel coating.

Comparative example 3

This comparative example relates to an electroplating method for obtaining a nickel coating by pulse electroplating. The method differs from the method in Example 2 in that the forward current density used in the present invention is 10A/dm ² , and the reverse current density is 1A. /dm ² . The forward energization time t is 6ms, and the reverse energization time t is 4ms, that is, the duty cycle is 60%. Due to the lower current density, the growth rate of the crystal nucleus is higher, thereby forming a larger grain size. The Ni coating grain size obtained in this comparative example is 37.7nm, but the surface of the nano-Ni coating obtained by this method is not Flat and dense, corrosion activation points increase, and its corrosion resistance decreases.

Comparative example 4

This comparative example relates to a method for improving the corrosion resistance of nickel-aluminum bronze. For specific steps, refer to Example 1 in the specific implementation mode of the description in the patent CN104562111A. The surface internal stress of the Ni-Cr coating obtained by this method is relatively large, and cracks occur, and its performance decreases under load conditions; and the Cr content is not easy to control, and the repeatability of process parameters is poor.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (8)

1. improve a surface nickel coated grains degree regulate and control method for erosion resistance, it is characterized in that, said method comprising the steps of:

A, by alloy surface mechanical grinding, oil removing, acid-wash activation;

B, alloy processing of step A crossed are placed in electroplate liquid in the lump as negative electrode with as the insoluble nickel plate of anode, be connected electroplate with power supply;

C, by plating after alloy take out, deionized water rinsing, cold wind dries up, and prepares Ni coating on its surface.

2. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 1, it is characterized in that, in steps A, described mechanical grinding is to 1200# waterproof abrasive paper; Described oil removing adopts and comprises 20 ~ 30g/LNaOH, 30 ~ 40g/LNa ₂cO ₃, 20 ~ 50g/LNa ₃pO ₄degreasing fluid, oil removing condition is: 70 ~ 80 DEG C of constant temperature 1 ~ 2min; The activation solution that described acid-wash activation adopts is 100 ~ 150mL/LH ₂sO ₄solution or 100 ~ 150mL/LHCl solution.

3. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 1, it is characterized in that, in step B, the main salt component of described electroplate liquid is 300 ~ 400g/LNi (SO ₃nH ₂) ₂4H ₂o, 15 ~ 60g/LNiCl ₂6H ₂o.

4. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 3, is characterized in that, in step B, also containing 30 ~ 50g/LH in described electroplating bath components ₃bO ₃, 0.1 ~ 0.15g/LC ₁₂h ₂₅sO ₄one or both in Na.

5. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 1, is characterized in that, in step B, described electroplate liquid is not containing grain-refining agent.

6. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 1, it is characterized in that, in step B, in electroplating process, temperature of electroplating solution is 49 ~ 51 DEG C, and bath pH values is 3.8 ~ 4.2.

7. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 6, is characterized in that, described bath pH values uses NH ₃h ₂o solution regulates, and needs limit slowly to drip limit and stir in regulate process.

8. the surface nickel coated grains degree regulate and control method improving erosion resistance as claimed in claim 1, is characterized in that, in step B, described plating adopts direct current electrode position/pulse square wave plating; Described direct current electrode position current density is 1 ~ 5A/dm ²; Described pulse plating forward current density is 1 ~ 30A/dm ², reverse current density is 0 ~ 5A/dm ², pulse-repetition is 100 ~ 500Hz, and dutycycle is 20 ~ 50%.