Alkaline zinc-nickel electroplating process preparation method

Abstract

The invention relates to the field of electroplating, and provides a technological preparation method for alkaline electroplating of zinc and nickel, which comprises the following steps: S1, pretreating a workpiece; s2, preparing a tank solution; s3, preparing a first reagent, a second reagent and a third reagent; s4, extracting a proper amount of bath solution, analyzing the content of zinc in the extraction bath solution by using a first reagent, analyzing the content of sodium hydroxide in the extraction bath solution by using a second reagent, and analyzing the content of nickel in the extraction bath solution by using a third reagent; s5, judging whether the contents of zinc, sodium hydroxide and nickel in the bath solution are within a specified process range or not according to electroplating process requirements, and if not, returning to the step S2; s6, the workpiece is put into a plating tank, tank liquid is added, electroplating parameters are controlled, and electroplating is completed; the content of substances in the bath solution can be detected, and the preparation stability of the bath solution is improved.

Description

Technical Field

[0001] The invention relates to the field of electroplating, and in particular to a process preparation method for alkaline zinc-nickel electroplating. Background Art

[0002] In the production of automotive parts, many parts need to be electroplated with zinc and nickel. The alkaline zinc-nickel alloy electroplating process generally includes the steps of pre-cleaning of the workpiece, preparation of the electroplating solution and electroplating. Electroplating requires placing the workpiece in a plating tank, adding the electroplating solution, and outputting appropriate electroplating control parameters to complete the preparation. In order to ensure the stability of the coating and the good corrosion resistance of the workpiece, the content of nickel, zinc, etc. in the coating must be controlled. This requires us to improve the existing technology and better control the content ratio of the substances in the bath liquid, that is, the electroplating solution. Summary of the invention

[0003] The problem solved by the invention is how to provide a process preparation method for alkaline zinc-nickel electroplating which can detect the content of substances in a bath solution and improve the stability of the bath solution configuration.

[0004] In order to solve the above problems, the present invention provides a process preparation method for alkaline electroplating zinc-nickel, comprising: step S1: pre-treating a workpiece;

[0005] Step S2: preparing tank liquid;

[0006] Step S3: preparing a first reagent, a second reagent and a third reagent;

[0007] Step S4: extracting an appropriate amount of tank solution, using a first reagent to analyze the zinc content in the extracted tank solution, using a second reagent to analyze the sodium hydroxide content in the extracted tank solution, and using a third reagent to analyze the nickel content in the extracted tank solution;

[0008] Step S5: according to the electroplating process requirements, determine whether the contents of zinc, sodium hydroxide and nickel in the bath are within the specified process range; if not, return to step S2;

[0009] Step S6: Place the workpiece into the plating tank, add the tank liquid, control the electroplating parameters, and complete the electroplating.

[0010] Furthermore, the first reagent includes: xylenol orange indicator; 0.1M EDTA reagent; pH=5.5 buffer solution; 12.5% ​​HCl reagent.

[0011] Further, the use of the first reagent to analyze the zinc content in the extraction tank solution includes:

[0012] Step S11: Take 2 ml of the tank solution sample into a clean conical flask with a capacity of 250 ml, and add 50 ml of pure water as the first detection solution;

[0013] Step S12: adding 5 ml of 12.5% ​​HCl reagent to the first detection solution;

[0014] Step S13: adding 20 ml of pH=5.5 buffer solution to the first detection solution;

[0015] Step S14: adding xylenol orange indicator to the first detection solution until the color of the first detection solution turns red;

[0016] Step S15: titrating the first detection solution in the conical flask with 0.1M EDTA standard solution until the first detection solution changes from red to yellow;

[0017] Step S16: Calculate the zinc content, the expression is:

[0018] Zn(g / l)=NEDTA×VEDTA×32.7.

[0019] Furthermore, the second reagent includes: phenolphthalein indicator; 0.5N hydrochloric acid standard solution; 25% BaCl2 reagent.

[0020] Further, the use of the second reagent to analyze the sodium hydroxide content in the extraction tank liquid includes:

[0021] Step S21: Take 5 ml of the tank solution sample into a clean conical flask and add 50 ml of pure water as the second detection solution;

[0022] Step S22: Add 20 ml of BaCl2 reagent to the second detection solution, shake well, and then add 5 drops of phenolphthalein indicator;

[0023] Step S23: titrating the second detection solution with 0.5N hydrochloric acid standard solution until the second detection solution changes from red to colorless;

[0024] Step S24: Record the volume of the consumed hydrochloric acid standard solution as VHCl;

[0025] Step S25: Calculate the sodium hydroxide content, the expression is:

[0026] Sodium hydroxide (g / l) = NHCl × VHCl × 8.

[0027] Furthermore, the third reagent includes: 12.5% ​​HCl solution; pH=5.5 buffer solution; 20% ammonium citrate reagent; 0.5% 1,2-cyclohexanedione dioxime solution; 5% gum arabic solution.

[0028] Further, the use of a third reagent to analyze the nickel content in the extraction tank solution includes:

[0029] Step S31: Pipette 10 ml of the tank solution into a 100 ml first volumetric flask, and add water to the full scale line as the third detection solution;

[0030] Step S32: pipetting 2 ml of the third detection solution into a 100 ml second volumetric flask, and adding 2 ml of 20% ammonium citrate solution into the second volumetric flask;

[0031] Step S33: Add 5 ml of 12.5% ​​HCl solution and 20 ml of pH=5.5 buffer solution into the second volumetric flask to ensure that the pH is between 4 and 6;

[0032] Step S34: Add 2 ml of gum arabic solution and 2 ml of 0.5% 1,2-cyclohexanedione dioxime solution to the second volumetric flask, and then add water to the full mark to serve as the fourth detection solution;

[0033] Step S35: leaving the fourth testing solution to stand for 15 minutes;

[0034] Step S36: using a spectrophotometer to perform colorimetry on the fourth detection solution, with an absorbance of 520 nm;

[0035] Step S37: Determine the nickel concentration using a standard nickel curve.

[0036] Furthermore, after the bath solution is prepared, the method further includes adding additives to the bath solution.

[0037] Furthermore, after placing the workpiece into a plating tank, adding tank liquid, and controlling electroplating parameters, the electroplating process also includes cleaning and drying the electroplated workpiece.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] By detecting and controlling the content of zinc, sodium hydroxide and nickel in the electroplating solution, the bath solution is very stable, the deposition rate is fast and the electroplating efficiency is high, so that the content of each substance in the workpiece coating can be accurately and stably controlled, and the coating thickness is evenly distributed. The workpieces after zinc-nickel electroplating have good corrosion resistance and can fully meet the stringent requirements of the automotive industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the overall principle structure of an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of parameter control in an embodiment of the present invention;

[0042] Figure 3 The figures are for the additive dosage of the examples of the present invention. DETAILED DESCRIPTION

[0043] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0044] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] In the description of this specification, the description with reference to the terms "embodiment", "one embodiment" and "one implementation" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or implementation are included in at least one embodiment or implementation of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or implementation. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or implementations in a suitable manner.

[0046] like Figure 1 As shown, the present invention provides a process preparation method for alkaline electroplating zinc-nickel, comprising: step S1: pretreating a workpiece;

[0047] Step S2: preparing tank liquid;

[0048] Step S3: preparing a first reagent, a second reagent and a third reagent;

[0049] Step S4: extracting an appropriate amount of tank solution, using a first reagent to analyze the zinc content in the extracted tank solution, using a second reagent to analyze the sodium hydroxide content in the extracted tank solution, and using a third reagent to analyze the nickel content in the extracted tank solution;

[0050] Step S5: according to the electroplating process requirements, determine whether the contents of zinc, sodium hydroxide and nickel in the bath are within the specified process range; if not, return to step S2;

[0051] Step S6: Place the workpiece into the plating tank, add the tank liquid, control the electroplating parameters, and complete the electroplating.

[0052] It should be noted that, usually, pretreatment of workpieces includes mechanical cleaning, chemical degreasing and pickling activation; mechanical cleaning is to remove impurities such as oil, rust, scale and so on on the surface of workpieces, so that the surface of workpieces is flat and smooth, providing a good matrix for subsequent electroplating; chemical degreasing is to remove grease on the surface of workpieces. Grease will hinder the deposition of zinc-nickel alloy, resulting in problems such as poor bonding strength of the coating. The commonly used chemical degreasing solution is a mixed solution of sodium hydroxide (NaOH), sodium carbonate (Na2CO3) and trisodium phosphate (Na3PO4); pickling activation is to remove the oxide film on the surface of the workpiece, activate the metal surface, and make the surface of the workpiece in a state that is easy for electroplating deposition. For steel workpieces, HCl solution can be used for pickling.

[0053] The electroplating solution is the bath solution, which generally needs to be configured by adding zinc, nickel and a conductive agent. Zinc sulfate (ZnSO4) is usually used as the zinc source, and nickel sulfate (NiSO4) is often used as the nickel source. For example, nickel sulfate is directly dissolved in distilled water and added to the electroplating solution. Sodium hydroxide (NaOH) is used as a conductive agent in the electroplating solution to improve the conductivity of the electroplating solution, reduce the bath voltage, and reduce power consumption. It also helps to disperse the current and make the coating more uniform. Therefore, it is particularly important to ensure the accuracy of the content of zinc, sodium hydroxide and nickel in the electroplating solution.

[0054] After the electroplating solution is prepared, in order to improve the appearance of the coating, make the coating bright and smooth, and also refine the grains and improve the corrosion resistance of the coating, it is necessary to add brighteners and additives to the electroplating solution. The amount of brighteners and additives added varies depending on the conditions such as the carry-out amount, so it needs to be set according to the situation of the production line. For general situations, you can refer to Figure 3 Add the amounts in the table.

[0055] When electroplating, it is necessary to control the electroplating parameters, including current density, temperature, stirring method, etc. For details, please refer to Figure 2 The chart shown.

[0056] Figure 2In the document, the range of zinc, sodium hydroxide and nickel content required by the electroplating solution under different processes is given. For example, in the rack plating process, the zinc content should be 6-8g / l, the nickel content should be 0.8-1.5g / l, and the sodium hydroxide content should be 120-140g / l. In electroplating, if the current density is too small, the coating deposition speed is slow and the production efficiency is low. If the current density is too large, the coating will be burnt, rough, and even have defects such as dendritic crystals. In the rack plating process, the current density is generally controlled at 1.0-3.0A / dm2; in the roll plating process, the current density is generally controlled at 0.5-1.0A / dm2. The temperature of the electroplating solution is usually controlled at 20-30℃. If the temperature is too high, the decomposition of additives and the evaporation of the electroplating solution will be accelerated, and the coating crystallization may be coarse. If the temperature is too low, the conductivity of the electroplating solution will decrease, the current efficiency will decrease, and the coating deposition speed will slow down. Stirring the plating solution can make the metal ions in the plating solution more evenly distributed, reduce concentration polarization, and improve the uniformity of the coating. In the figure, the stirring starts from the cathode.

[0057] After the electroplating is completed, the workpiece will be cleaned and dried: After the electroplating is completed, the workpiece surface will have residual electroplating liquid, which needs to be cleaned with clean water to remove the residual liquid and prevent the residual liquid from corroding the coating and other adverse effects. Generally, a multi-stage countercurrent cleaning method is adopted, that is, first rinse with flowing clean water, and then rinse with deionized water, and the rinsing time is 3-5 minutes; the cleaned workpiece is dried to remove moisture so that the coating maintains a good appearance and performance. The drying temperature is generally controlled at 60-100℃, and the drying time depends on the size and shape of the workpiece, generally 10-30 minutes.

[0058] In one embodiment of the invention, the analytical method for the content of zinc, sodium hydroxide and nickel is as follows:

[0059] 1. Analysis of Zn.

[0060] Reagents used: xylenol orange indicator; 0.1M EDTA; pH=5.5 buffer solution; 12.5% ​​HCl solution; 25% BaCl2 solution; 0.1M EDTA, i.e., EDTA standard solution with a concentration of 0.1 mol / L.

[0061] Specific analysis method:

[0062] 1. Take 2 ml of tank liquid sample into a 250 ml clean conical flask and add 50 ml of pure water;

[0063] 2. Add 5 ml of 12.5% ​​HCl 3. Add 20 ml of pH = 5.5 buffer solution;

[0064] 4. Add a little xylenol orange indicator and the solution will turn red;

[0065] 5. Titrate with 0.1M EDTA standard solution until the solution changes from red to yellow, which is the end point;

[0066] 6. Calculation: Zn (g / l) = NEDTA × VEDTA × 32.7. In the EDTA titration method, EDTA can form a stable complex with zinc ions. By accurately titrating a known volume of zinc ion solution, the mass concentration of zinc ions in the solution can be calculated based on the concentration and volume of the consumed EDTA standard solution and the above conversion factor. Among them, NEDTA represents the molar concentration of the EDTA standard solution, usually in mol / L, VEDTA: is the volume of the EDTA standard solution consumed during the titration, in liters, and 32.7 is the value obtained by converting the product of the molar mass of zinc and the ratio of the stoichiometric number of the reaction between EDTA and zinc.

[0067] 2. Analysis of NaOH content.

[0068] Reagents used: phenolphthalein indicator; 0.5N hydrochloric acid standard solution; 25% BaCl2 reagent.

[0069] Specific analysis method:

[0070] 1. Take 5 ml of tank liquid sample into a clean conical flask and add 50 ml of water;

[0071] 2. Add 20 ml of BaCl2, shake well, and then add 5-10 drops of phenolphthalein indicator;

[0072] 3. Titrate with 0.5N hydrochloric acid standard solution until the color changes from red to colorless;

[0073] 4. Record the volume of hydrochloric acid standard solution consumed as V;

[0074] 5. Calculation: Sodium hydroxide (g / l) = NHCl × VHCl × 8; wherein NHCl is the concentration of the consumed hydrochloric acid standard solution. Generally, the concentration of 0.5N hydrochloric acid standard solution is 12 mol / L, and VHCl is the volume of the consumed hydrochloric acid standard solution.

[0075] 3. Ni content analysis can be determined by spectrophotometer.

[0076] The reagents used are: 12.5% ​​HCl solution; pH=5.5 buffer solution; 20% ammonium citrate reagent; 0.5% 1,2-cyclohexanedione dioxime solution; 5% gum arabic solution.

[0077] Specific analysis method:

[0078] 1. Accurately pipette 10 ml of tank solution into a 100 ml volumetric flask and add water to the scale line;

[0079] 2. Pipette 2 ml of this solution into a 100 ml volumetric flask and add 2 mls of 20% ammonium citrate solution;

[0080] 3. Add 5 ml of 12.5% ​​HCl and 20 ml of pH 5.5 buffer solution to ensure that the pH is between 4 and 6.

[0081] 4. Add 2 ml of gum arabic solution, then add 2 ml of 0.5% 1,2-cyclohexanedione dioxime solution, and add water to the mark;

[0082] 5. Let stand for 15 minutes;

[0083] 6. Use a spectrophotometer to compare the color, and the absorbance is 520nm.

[0084] 7. Calculation: Use the standard nickel curve to determine the nickel concentration.

[0085] Among them, the basic principle of spectrophotometry is the Lambert-Beer law. When a beam of parallel monochromatic light passes through a solution containing an absorbing substance, the absorbance of the solution is proportional to the product of the concentration of the absorbing substance and the thickness of the liquid layer. In colorimetric analysis, the optical path length is fixed, and for a specific substance (such as nickel ions) at a specific wavelength, the molar absorption coefficient is a constant. Therefore, the absorbance is only related to the concentration of nickel ions in the solution; the relationship between absorbance and concentration requires experiments to determine the exact linear range. The purpose of drawing a standard curve is to establish this quantitative relationship between absorbance and concentration. By measuring the absorbance of a standard solution of known concentration to obtain a standard curve, the corresponding concentration can be found on the curve based on the absorbance of the unknown solution.

[0086] For example, the standard curve is drawn by preparing a series of nickel standard solutions of known concentrations, such as C1, C2, and CN, and then measuring their absorbance at 520nm on a spectrophotometer to obtain the corresponding absorbance values ​​A1, A2, and AN; the standard curve is drawn with nickel concentration as the horizontal coordinate and absorbance as the vertical coordinate, which generally conforms to the Lambert-Beer law A=εbC (where A is the absorbance, ε is the molar absorption coefficient, b is the optical path length, and C is the solution concentration). Within a certain concentration range, the standard curve is a straight line, and its linear regression equation can be expressed as y=kx+b (in the standard curve, y represents absorbance, x represents concentration, k is the slope, and b is the intercept); after measuring the absorbance of the unknown nickel solution, substitute it into the linear regression equation A 未知 =kC 未知 + b, we can calculate the concentration C of the unknown nickel solution 未知 .

[0087] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A process for preparing alkaline electroplating zinc nickel, characterized in that: include: Step S1: pre-processing the workpiece; Step S2: preparing tank liquid; Step S3: preparing a first reagent, a second reagent and a third reagent; Step S4: extracting an appropriate amount of tank solution, using a first reagent to analyze the zinc content in the extracted tank solution, using a second reagent to analyze the sodium hydroxide content in the extracted tank solution, and using a third reagent to analyze the nickel content in the extracted tank solution; Step S5: according to the electroplating process requirements, determine whether the contents of zinc, sodium hydroxide and nickel in the bath are within the specified process range; if not, return to step S2; Step S6: placing the workpiece into the plating tank, adding the tank liquid, controlling the electroplating parameters, and completing the electroplating.

2. The process for preparing alkaline electroplating zinc nickel according to claim 1, characterized in that: The first reagent includes: xylenol orange indicator; 0.1M EDTA reagent; pH=5.5 buffer solution; 12.5% ​​HCl reagent.

3. The process for preparing alkaline electroplating zinc nickel according to claim 2, characterized in that: The use of the first reagent to analyze the zinc content in the extraction tank solution comprises: Step S11: Take 2 ml of the tank solution sample into a clean conical flask with a capacity of 250 ml, and add 50 ml of pure water as the first detection solution; Step S12: adding 5 ml of 12.5% ​​HCl reagent to the first detection solution; Step S13: adding 20 ml of pH=5.5 buffer solution to the first detection solution; Step S14: adding xylenol orange indicator to the first detection solution until the color of the first detection solution turns red; Step S15: titrating the first detection solution in the conical flask with 0.1M EDTA standard solution until the first detection solution changes from red to yellow; Step S16: Calculate the zinc content, the expression is: Zn(g / l)=NEDTA×VEDTA×32.

7.

4. The process for preparing alkaline electroplating zinc-nickel according to claim 3, characterized in that: The second reagent includes: phenolphthalein indicator; 0.5N hydrochloric acid standard solution; 25% BaCl2 reagent.

5. The process for preparing alkaline electroplating zinc-nickel according to claim 4, characterized in that: The use of the second reagent to analyze the sodium hydroxide content in the extraction tank solution comprises: Step S21: Take 5 ml of the tank solution sample into a clean conical flask and add 50 ml of pure water as the second detection solution; Step S22: Add 20 ml of BaCl2 reagent to the second detection solution, shake well, and then add 5 drops of phenolphthalein indicator; Step S23: titrating the second detection solution with 0.5N hydrochloric acid standard solution until the second detection solution changes from red to colorless; Step S24: Record the volume of the consumed hydrochloric acid standard solution as VHCl; Step S25: Calculate the sodium hydroxide content, the expression is: Sodium hydroxide (g / l) = NHCl × VHCl × 8.

6. The process for preparing alkaline electroplating zinc-nickel according to claim 5, characterized in that: The third reagent includes: 12.5% ​​HCl solution; pH=5.5 buffer solution; 20% ammonium citrate reagent; 0.5% 1,2-cyclohexanedione dioxime solution; 5% gum arabic solution.

7. The process for preparing alkaline electroplating zinc-nickel according to claim 6, characterized in that: The use of the third reagent to analyze the nickel content in the extraction tank solution comprises: Step S31: Pipette 10 ml of the tank solution into a 100 ml first volumetric flask, and add water to the full scale line as the third detection solution; Step S32: pipetting 2 ml of the third detection solution into a 100 ml second volumetric flask, and adding 2 ml of 20% ammonium citrate solution into the second volumetric flask; Step S33: Add 5 ml of 12.5% ​​HCl solution and 20 ml of pH=5.5 buffer solution into the second volumetric flask to ensure that the pH is between 4 and 6; Step S34: Add 2 ml of gum arabic solution and 2 ml of 0.5% 1,2-cyclohexanedione dioxime solution to the second volumetric flask, and then add water to the full mark to serve as the fourth detection solution; Step S35: leaving the fourth testing solution to stand for 15 minutes; Step S36: using a spectrophotometer to perform colorimetry on the fourth detection solution, with an absorbance of 520 nm; Step S37: Determine the nickel concentration using a standard nickel curve.

8. The process for preparing alkaline electroplating zinc-nickel according to claim 7, characterized in that: After the bath solution is prepared, the process further includes adding additives to the bath solution.

9. The process for preparing alkaline electroplating zinc-nickel according to claim 8, characterized in that: The process of placing the workpiece into a plating tank, adding a bath solution, and controlling the electroplating parameters includes cleaning and drying the electroplated workpiece after the electroplating is completed.

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