CN110760906B - Nano zinc-cobalt alloy coating based on double-pulse electrodeposition and preparation method thereof - Google Patents
Nano zinc-cobalt alloy coating based on double-pulse electrodeposition and preparation method thereof Download PDFInfo
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- CN110760906B CN110760906B CN201911036209.2A CN201911036209A CN110760906B CN 110760906 B CN110760906 B CN 110760906B CN 201911036209 A CN201911036209 A CN 201911036209A CN 110760906 B CN110760906 B CN 110760906B
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- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
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- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/18—Electroplating using modulated, pulsed or reversing current
Abstract
The invention discloses a nano zinc-cobalt alloy coating based on double-pulse electrodeposition and a preparation method thereof. Based on dipulseThe preparation method of the electro-deposition nano zinc-cobalt alloy coating comprises the steps of taking a zinc plate as an anode and a low-carbon steel sheet as a cathode, and electroplating the nano zinc-cobalt alloy coating in a plating solution by adopting a double-pulse electro-deposition process, wherein the pH of the plating solution is 4-5, the concentration of zinc ions is 0.64-0.70mol/L, the concentration of cobalt ions is 0.1-0.16mol/L, the electro-deposition time is 20min, and the forward current density is 1.5-3.0A/dm2The forward duty ratio is 30-70%, the forward period is 30-70ms, and the reverse current density is 0.2-0.4A/dm2The reverse duty cycle is 30-70%, the forward working time is 100ms, the reverse working time is 12ms, and the reverse cycle is 1 ms. The nano zinc-cobalt alloy coating prepared by the preparation method of the nano zinc-cobalt alloy coating based on double-pulse electrodeposition has the advantages of bright and smooth surface, uniform and compact crystallization, good bonding force with a base material and excellent corrosion resistance.
Description
Technical Field
The invention relates to the technical field of electroplating alloys, in particular to a nano zinc-cobalt alloy coating based on double-pulse electrodeposition and a preparation method thereof.
Background
Metal corrosion is a spontaneous, ubiquitous phenomenon in nature. The corrosion of metal materials is widely existed in various fields, the loss caused by the corrosion is very large, particularly in the damp and hot marine environment, steel is easy to be corroded by salt fog, tide and the like, and serious electrochemical corrosion occurs, so that huge economic loss can be caused, and safety accidents are more easily caused. Due to the vigorous development of modern scientific and industrial technologies such as aviation, energy, navigation and the like, the rigorous requirements on the use of materials in special environments are continuously improved. The zinc coating is widely applied to the protection of steel base materials because of simple production process and better corrosion resistance, but the pure zinc coating cannot meet the requirement of high corrosion resistance due to the development of technology and the change of environment. The alloy plating layer composed of different metals has excellent performance, the Zn-Co alloy plating layer has good corrosion resistance, and the corrosion resistance of the Zn-Co alloy plating layer with the cobalt content of only about 1.0 percent can be 3 to 5 times higher than that of a pure zinc plating layer.
The electrodeposition methods include three types, i.e., direct current electrodeposition, single-pulse electrodeposition and double-pulse electrodeposition. Due to the existence of double-pulse reverse current, the coating can dissolve burrs on the surface of the coating to enable the coating to be more flat and compact, and meanwhile, the hydrogen embrittlement can be eliminated, the internal stress is reduced, the binding force of the coating and a substrate is increased, and the coating has great advantages compared with direct current and single-pulse electrodeposition. At present, the research on the double-pulse electrodeposition of the zinc-cobalt alloy is few, and the specific research is not carried out on the influence of double-pulse parameters on the zinc-cobalt alloy coating.
Disclosure of Invention
The invention aims to provide a preparation method of a nano zinc-cobalt alloy coating based on double-pulse electrodeposition, aiming at the defects in the prior art.
The purpose of the invention can be realized by the following technical scheme:
a preparation method of a nano zinc-cobalt alloy coating based on double-pulse electrodeposition takes a zinc plate as an anode and a low-carbon steel plate as a cathode, and the nano zinc-cobalt alloy coating is electroplated in a plating solution by adopting a double-pulse electrodeposition process, wherein the pH value of the plating solution is 4-5, the concentration of zinc ions is 0.64-0.70mol/L, and the concentration of cobalt ions is 0.1-0.16 mol/L.
Preferably, the sum of the concentrations of the zinc ions and the cobalt ions is 0.8 mol/L.
Preferably, the electroplating parameters of the double pulse electrodeposition process are as follows: the electrodeposition time is 20min, and the forward current density is 1.5-3.0A/dm2The forward duty ratio is 30-70%, the forward period is 30-70ms, and the reverse current density is 0.2-0.4A/dm2The reverse duty cycle is 30-70%, the forward working time is 100ms, the reverse working time is 12ms, and the reverse cycle is 1 ms.
Preferably, the plating solution further comprises the following components: 30-45g/L of boric acid, 25-30g/L of sodium sulfate and 30-50g/L of sodium citrate.
Preferably, the plating solution comprises the following components in percentage by weight: 183-197g/L of zinc sulfate heptahydrate, 28-45g/L of cobalt sulfate heptahydrate, 30-45g/L of boric acid, 25-30g/L of sodium sulfate and 30-50g/L of sodium citrate.
Preferably, the electrodeposition temperature is 25 to 30 ℃.
Preferably, the purity of the zinc plate for the anode is more than 99.99%, the distance between the anode and the cathode is 6cm, and the specifications are 60mm multiplied by 90mm multiplied by 1 mm.
Preferably, the surface of the zinc plate is sequentially subjected to polishing, oil removal and cleaning treatment.
Preferably, the surface of the low-carbon steel plate is sequentially subjected to grinding, polishing, degreasing and weak etching treatment.
The invention provides a preparation method of a nanometer zinc-cobalt alloy coating based on double-pulse electrodeposition, which is characterized in that forward pulses and reverse pulses are alternately carried out, and due to the existence of double-pulse reverse currents, the coating can dissolve burrs on the surface of the coating to enable the coating to be smoother and more compact, the concentration of metal ions on the surface of a cathode can be raised, concentration polarization is reduced, hydrogen embrittlement can be eliminated, and internal stress is reduced, so that the alloy coating with a bright, smooth, uniform and compact surface is obtained, and the coating has good bonding force with a substrate and excellent corrosion resistance.
Drawings
FIG. 1a is a picture of the pure zinc coating after salt spray erosion for 120 h;
FIG. 1b is a photograph of the pure zinc coating after salt spray etching for 288 h;
FIG. 1c is a photograph showing the appearance of a pure zinc coating after salt spray etching for 576 hours;
FIG. 1d is a picture of the morphology of the nano-zinc-cobalt alloy coating after salt spray erosion for 120 h;
FIG. 1e is a photograph of the nano zinc-cobalt alloy coating after salt spray etching for 288 h;
FIG. 1f is a picture of the appearance of the nano zinc-cobalt alloy coating after salt spray erosion for 576 hours;
FIG. 2 is an X-ray spectrum of a pure zinc plating layer and a nano zinc-cobalt alloy plating layer with different cobalt contents in example 4 of the present invention;
FIG. 3 is a graph of the corrosion rate of pure Zn coating and nano Zn-Co alloy coatings with different Co contents in example 4 of the present invention as a function of time;
FIG. 4 is a graph showing the relationship between the cobalt content of the plating layer and the time at which red rust begins to appear in the plating layer in the salt spray test of the pure zinc plating layer and the nano zinc-cobalt alloy plating layer with different cobalt contents in example 4 of the present invention;
FIG. 5 shows the cathode polarization curves of pure Zn plating and nano Zn-Co alloy plating with different Co contents in example 4 of the present invention;
FIG. 6 is a cyclic voltammogram of pure zinc coatings and nano-zinc-cobalt alloy coatings of different cobalt contents in example 4 of the present invention;
FIG. 7 Tafel polarization curves of pure Zn coatings and nano Zn-Co alloy coatings with different Co contents in example 4 of the present invention;
fig. 8 is a graph of the relationship between the self-etching potential and the self-etching current density and the cobalt content in the plating layer, which is obtained from the Tafel polarization curve by using a linear extrapolation method, for the pure zinc plating layer and the nano zinc-cobalt alloy plating layer with different cobalt contents in example 4 of the present invention.
Detailed Description
The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.
Example 1
1) The zinc plate with the purity of more than 99.99 percent is used as an anode plate after being treated as follows: firstly, sanding with sand paper to remove surface oxide layers, stains and the like, then washing with distilled water, then removing oil, washing with distilled water, and blow-drying with electric air blow for later use.
2) The low-carbon steel plate is used as a cathode plate after being treated as follows, the low-carbon steel plate is sequentially polished and polished by abrasive paper, then is chemically degreased and cleaned, and then is subjected to weak erosion, wherein the weak erosion has the function of removing an oxide film on the surface of the cathode plate so as to completely expose the substrate of the cathode plate, so that the substrate of the cathode plate and an electroplated layer can be better combined, and a better electroplating effect is achieved, and the process conditions of chemical degreasing and weak erosion are as follows:
1. chemical degreasing
| Basic composition | Concentration or process conditions |
| Sodium carbonate | 20g/L |
| Trisodium phosphate decahydrate | 20g/L |
| OP-10 detergent | 10mL/L |
| Temperature of | 65-75℃ |
| Time of day | 15-25min |
2. Weak erosion
| Basic composition | Concentration or process conditions |
| Sulfuric acid (1.84g/L) | 40mL/L |
| Temperature of | At normal temperature |
| Time of day | 10-20s |
3) Preparing a plating solution, wherein the pH of the plating solution is 5, and the plating solution in this example comprises the following components in percentage by weight: 190g/L of zinc sulfate heptahydrate, 37g/L of cobalt sulfate heptahydrate, 30g/L of boric acid, 30g/L of sodium sulfate and 30g/L of sodium citrate.
4) Injecting the prepared plating solution into an electrodeposition tank with the specification of 10cm multiplied by 8cm, respectively taking a zinc plate and a low-carbon steel plate which are subjected to surface treatment as an anode and a cathode, wherein the electrode distance between the anode and the cathode is 6cm, the specifications are both 60mm multiplied by 90mm multiplied by 1mm, the electrodeposition time is 20min, the electrodeposition temperature is 25 ℃, and a nano zinc-cobalt alloy plating layer is synthesized by adopting a double-pulse electrodeposition process, wherein the double-pulse electrodeposition process parameters are as follows: the forward current density is 2.5A/dm2The forward duty cycle is 70%, the forward cycle is 50ms, and the reverse current density is 0.4A/dm2The reverse duty cycle is 40%, the forward working time is 100ms, the reverse working time is 12ms, and the reverse cycle is 1 ms.
The following performance detection and result comparison are carried out on the nano zinc-cobalt alloy coating sample and the pure zinc coating sample, wherein the plating solution in the process for preparing the pure zinc coating sample comprises the following components: 197g/L of zinc sulfate heptahydrate, 30g/L of boric acid, 30g/L of sodium sulfate and 30g/L of sodium citrate, and the rest steps are the same as the double-pulse electrodeposition nano zinc-cobalt alloy plating process:
EDAX Spectroscopy testing
Performing EDAX energy spectrum test on the nano zinc-cobalt alloy coating sample and the pure zinc coating sample to obtain a nano zinc-cobalt alloy coating with the Co content of 2.11% and a pure zinc coating sample with the Co content of 0% through analysis and test.
X-ray diffraction detection
The grain sizes of the nano zinc-cobalt alloy coating sample and the pure zinc coating sample are measured by an X-ray diffractometer (XRD). The average grain size of the nano zinc-cobalt alloy coating calculated by using the Scherrer formula is 23.8nm, and the average grain size of a pure zinc coating sample is 112.7 nm. Experiments show that compared with a pure zinc coating, the average grain size of the nano zinc-cobalt alloy coating is greatly reduced.
3. Static immersion test
And (3) carrying out corrosion resistance test on the nano zinc-cobalt alloy coating sample and the pure zinc coating sample in a NaCl solution with the mass percentage concentration of 5% by using a soaking method. Experiments show that the corrosion rate of the nano zinc-cobalt alloy coating sample is lower than that of a pure zinc coating sample.
4. Salt spray experiment
And (3) performing a neutral salt spray experiment on the nano zinc-cobalt alloy coating sample and the pure zinc coating sample according to the GB/T10125 standard by adopting an FQY010A type salt spray test box. After 120h, 288h and 576h of salt spray corrosion, respectively analyzing the surface macro-morphology of the nano zinc-cobalt alloy plating layer sample and the pure zinc plating layer sample, wherein the deep color part in the drawings is rust, and a small amount of red spots appear on the surface of the pure zinc plating layer after 120h of salt spray corrosion, which indicates that a low-carbon steel base material is corroded to generate an oxide Fe2O3 red rust; after the salt spray corrosion is carried out for 288h, the red corrosion points of the pure zinc plating layer are increased and have wider range, while the nano zinc-cobalt alloy plating layer is still a great amount of white corrosion products, and the formation of red rust spots is not observed. After the salt spray corrosion reaches 576h, large-area rust of the pure zinc coating can be observed and almost spreads over the whole coating area, which indicates that the substrate is severely corroded and the zinc coating can be seen to fall off at the position of the rust by light touch; and at the moment, a small amount of red rust distributed in a point shape begins to appear on the surface of the nano zinc-cobalt alloy coating, which shows that the corrosion rate of the nano zinc-cobalt alloy coating is less than that of the zinc coating in the same time, and the corrosion resistance of the nano zinc-cobalt alloy coating is superior to that of the zinc coating.
5. Electrochemical testing
And (3) performing Tafel polarization curve test on the nano zinc-cobalt alloy coating sample and the pure zinc coating sample by using a CHI660C type electrochemical workstation. Obtaining self-corrosion potential and self-corrosion current density from Tafel polarization curve by linear extrapolation, wherein the self-corrosion potential of the nano zinc-cobalt alloy coating is-1.064V, and the self-corrosion current density is 0.46 multiplied by 10-6A·cm-2(ii) a The self-corrosion potential of the pure zinc coating is-1.185V, and the self-corrosion potential isThe flow density was 6.31X 10-5A·cm-2The experiment shows that: the self-corrosion potential of the nano zinc-cobalt alloy coating is greater than that of the pure zinc coating, and the self-corrosion current density of the nano zinc-cobalt alloy coating is less than that of the pure zinc coating, so that the corrosion resistance of the nano zinc-cobalt alloy coating is better than that of the pure zinc coating.
The invention provides a preparation method of a nanometer zinc-cobalt alloy coating based on double-pulse electrodeposition, which is characterized in that forward pulses and reverse pulses are alternately carried out, and due to the existence of double-pulse reverse currents, the coating can dissolve burrs on the surface of the coating to enable the coating to be smoother and more compact, the concentration of metal ions on the surface of a cathode can be raised, concentration polarization is reduced, hydrogen embrittlement can be eliminated, and internal stress is reduced, so that an alloy coating with a bright and smooth surface, uniform and compact crystallization is obtained, the grain size of the coating is small, and the coating has good bonding force with a substrate and excellent corrosion resistance.
Example 2
The difference between this example and example 1 is that the plating solution electrodeposition temperature is 30 ℃, the plating solution pH is 5.0, and the double pulse electrodeposition process parameters are: the forward current density is 1.5A/dm2The forward duty cycle is 30%, the forward cycle is 30ms, and the reverse current density is 0.2A/dm2The reverse duty cycle is 30%.
The nano zinc-cobalt alloy plating layer is subjected to appearance inspection, X-ray test, static immersion test, salt spray test and electrochemical test, the average grain size of a sample of the nano zinc-cobalt alloy plating layer is 37.6nm, the self-corrosion potential is-1.106V, and the self-corrosion current density is 0.79 multiplied by 10-6A·cm-2The surface of the plating layer is bright and smooth, the crystallization is uniform and compact, the grain size of the plating layer is small, and the plating layer has good binding force with a base material and excellent corrosion resistance.
Example 3
The difference between the present example and example 1 is that the pH of the plating solution is 4.5, the concentration of boric acid contained in the plating solution is 45g/L, the concentration of sodium sulfate is 25g/L, the concentration of sodium citrate is 50g/L, and the parameters of the double pulse electrodeposition process are as follows: a forward current density of3.0A/dm2The forward duty cycle is 30%, the forward cycle is 70ms, and the reverse current density is 0.4A/dm2The reverse duty cycle is 70%.
The nano zinc-cobalt alloy plating layer is subjected to appearance inspection, X-ray test, static immersion test, salt spray test and electrochemical test, the average grain size of a sample of the nano zinc-cobalt alloy plating layer is 43.1nm, the self-corrosion potential is-1.114V, and the self-corrosion current density is 0.67 multiplied by 10-6A·cm-2The surface of the plating layer is bright and smooth, the crystallization is uniform and compact, the grain size of the plating layer is small, and the plating layer has good binding force with a base material and excellent corrosion resistance.
Example 4
The difference between this example and example 1 is that, with the other conditions unchanged, the ratio of the mass concentrations of the zinc ions and the cobalt ions in the plating solution was changed, and the sum of the concentrations of the zinc ions and the cobalt ions in the plating solution was 0.8mol/L, and five plating solutions with different zinc-cobalt ion concentration ratios were respectively configured, and the mass concentration ratios of the zinc ions and the cobalt ions in the plating solution were respectively: infinity, 7:1, 6:1, 5:1 and 4: 1. The five plating solutions with different zinc-cobalt ion concentration ratios are adopted to respectively prepare a pure zinc plating layer and a nano zinc-cobalt alloy plating layer with different cobalt contents, and the following analysis is carried out on the pure zinc plating layer and the nano zinc-cobalt alloy plating layer:
EDAX Spectroscopy testing and X-ray diffraction detection
Table 1 is a comparison of grain sizes of pure zinc coatings and nano zinc cobalt alloy coatings of different cobalt contents. Experiments show that after cobalt ions are added into the plating solution, the grain size of the obtained nano zinc-cobalt alloy plating layer is greatly reduced compared with that of a pure zinc plating layer, and the average grain size is gradually reduced along with the increase of the cobalt content in the plating layer, so that the plating layer is more uniformly deposited, and the plating layer is more flat and compact.
TABLE 1
| Coating layer | Ratio of zinc to cobalt ions | Cobalt content (wt.%) in the coating | Average grain size (nm) |
| Zn | ∞ | 0 | 112.7 |
| Zn-Co | 7:1 | 1.47 | 43.4 |
| Zn-Co | 6:1 | 1.75 | 42.5 |
| Zn-Co | 5:1 | 2.11 | 38.5 |
| Zn-Co | 4:1 | 2.52 | 34.0 |
Fig. 2 is X-ray spectra of a pure zinc plating layer and a nano zinc-cobalt alloy plating layer with different cobalt contents, which are X-ray spectra of the pure zinc plating layer respectively, and the plating solution zinc-cobalt ion ratio is 7:1, the X-ray atlas of the nano zinc-cobalt alloy coating has a plating solution zinc-cobalt ion ratio of 6:1, the X-ray atlas of the nano zinc-cobalt alloy coating, the zinc-cobalt ion ratio of the plating solution is 5:1, the X-ray atlas of the nano zinc-cobalt alloy coating, the zinc-cobalt ion ratio of the plating solution is 4: 1X-ray spectrum of the nano zinc-cobalt alloy coating. From FIG. 2, it can be seen that: the pure zinc plating layer is in a single Zn-eta phase, the addition of cobalt changes the preferred orientation of crystal planes of the nano zinc-cobalt alloy plating layer, the preferred orientation of main crystal planes is changed into a (101) plane and a formed new phase CoZn13 crystal plane, the nano zinc-cobalt alloy plating layer mainly takes a Zn-eta phase and a CoZn 13-gamma alloy phase as main materials, the CoZn13 crystal plane is increased and then reduced along with the increase of cobalt content in the plating layer, the CoZn13 crystal plane in the plating layer is the largest when the concentration ratio of zinc-cobalt ions is 5:1, namely the cobalt content in the nano zinc-cobalt alloy plating layer is 2.11%, and the CoZn13 has a complex crystal structure and is beneficial to improving the corrosion resistance of the alloy plating layer.
2. Static immersion test
And (3) carrying out corrosion resistance tests on the nano zinc-cobalt alloy coating samples and the pure zinc coating samples with different cobalt contents in NaCl solution with the mass percentage concentration of 5% by using a soaking method. In fig. 3, a is a pure zinc plating layer, b is a plating solution with a zinc-cobalt ion ratio of 7:1, c is a plating solution with a zinc-cobalt ion ratio of 6:1, d is a plating solution with a zinc-cobalt ion ratio of 5:1, e is a plating solution with a zinc-cobalt ion ratio of 4:1 of nano zinc-cobalt alloy coating. From FIG. 3, it can be seen that: the corrosion rate of the nano zinc-cobalt alloy coating samples with different cobalt contents is smaller than that of the pure zinc coating samples, and when the concentration ratio of zinc ions to cobalt ions is 5:1, namely the cobalt content of the coating is 2.11%, the corrosion rate of the nano zinc-cobalt alloy coating samples is the smallest, which shows that the corrosion resistance of the nano zinc-cobalt alloy coating prepared with the concentration ratio of zinc ions to cobalt ions of 5:1 is the best.
3. Salt spray experiment
Adopting an FQY010A type salt spray test box to carry out neutral salt spray tests on a pure zinc plating layer and nano zinc-cobalt alloy plating layers with different cobalt contents according to the GB/T10125 standard. From FIG. 4, it can be seen that: the shortest time for the pure zinc plating layer sample to start to generate red rust is 120h, and the longest time for the nano zinc-cobalt alloy plating layer sample prepared by the plating solution with the concentration ratio of zinc ions to cobalt ions of 5:1 to start to generate red rust is 576 h. This shows that the nano zinc-cobalt alloy coating prepared by the plating solution with the concentration ratio of zinc-cobalt ions of 5:1 has the best corrosion resistance.
4. Electrochemical testing
The analysis of cathode polarization curve (figure 5), cyclic voltammetry curve (figure 6) and Tafel polarization curve (figure 7) was carried out using CHI660C model electrochemical workstation pure zinc coating and nano zinc cobalt alloy coating with different cobalt content.
In fig. 5, a is a pure zinc plating layer, b is a plating solution with a zinc-cobalt ion ratio of 7:1, c is a plating solution with a zinc-cobalt ion ratio of 6:1, d is a plating solution with a zinc-cobalt ion ratio of 5:1, a nano zinc-cobalt alloy coating; e is the plating solution zinc-cobalt ion ratio of 4:1, a nano zinc-cobalt alloy coating; from FIG. 5, it can be seen that: the higher the molar concentration ratio of the zinc and cobalt ions in the electrolyte, namely the higher the concentration of the zinc ions, the closer the polarization curve of the alloy and the polarization curve of pure zinc are, and the lower the cobalt content in the prepared coating is. Along with the reduction of the molar concentration ratio of zinc ions in the electrolyte, the polarization current is reduced, the polarization curve of the Zn-Co ion common discharge moves towards the negative potential direction, the cathode polarization degree is increased, and the compactness, the brightness and the leveling property of the coating are improved.
In fig. 6, a is a pure zinc plating layer, b is a plating solution with a zinc-cobalt ion ratio of 7:1, c is a plating solution with a zinc-cobalt ion ratio of 6:1, d is a plating solution with a zinc-cobalt ion ratio of 5:1, e is a plating solution with a zinc-cobalt ion ratio of 4:1 of nano zinc-cobalt alloy coating. From FIG. 6, it can be seen that: under the condition that the total concentration of the zinc and cobalt ions is kept unchanged, the molar concentration ratio of the zinc and cobalt ions is changed, and the shapes of cyclic voltammetry curves of the electrolyte are basically similar. The cathode peak current of the nano zinc-cobalt alloy coating with different cobalt contents is obviously lower than that of the pure zinc coating. This is because Zn (OH) is formed on the surface of the cathode as the concentration of zinc ions in the solution decreases, i.e., as cobalt ions are added2The colloidal film is thinned, so that the precipitation of cobalt ions at a cathode can not be effectively hindered, and the precipitation of zinc is not influenced, thereby increasing the cobalt content in the plating layer. The pure zinc coating has the most negative peak potential (minus 0.45V) and the maximum peak current (4.5A/dm)2) Positive peak potential of nano zinc-cobalt alloy coating with different cobalt contentsThe dissolution peak is reduced, the peak current is reduced, and the prepared nano zinc-cobalt alloy plating with different cobalt contents has improved corrosion resistance compared with a pure zinc plating.
In fig. 7, a is a pure zinc plating layer, b is a plating solution with a zinc-cobalt ion ratio of 7:1, c is a plating solution with a zinc-cobalt ion ratio of 6:1, d is a plating solution with a zinc-cobalt ion ratio of 5:1, a nano zinc-cobalt alloy coating; e is the plating solution zinc-cobalt ion ratio of 4:1 of nano zinc-cobalt alloy coating. Fig. 8 is a graph of the relationship between the self-corrosion potential, the self-corrosion current density and the cobalt content in the plating layer obtained from the Tafel polarization curve by a straight-line extrapolation method for the pure zinc plating layer and the nano zinc-cobalt alloy plating layer with different cobalt contents, wherein a is a graph of the relationship between the self-corrosion potential and the cobalt content in the plating layer, and b is a graph of the relationship between the self-corrosion current density and the cobalt content in the plating layer. From fig. 7 and 8, it can be seen that: with the increase of the cobalt content in the plating layer, namely the reduction of the concentration ratio of zinc and cobalt ions, the self-corrosion potential of the nano zinc-cobalt alloy plating layer is increased firstly and then reduced, and when the concentration ratio of the zinc and cobalt ions is 5:1, namely the cobalt content of the plating layer is 2.11%, the self-corrosion potential of the nano zinc-cobalt alloy plating layer is the largest, and the corrosion resistance of the plating layer is the best; the self-corrosion current of the pure zinc coating is the maximum (6.31 multiplied by 10)-5A·cm-2) Along with the increase of the cobalt content in the plating layer, the self-corrosion current of the plating layer is greatly reduced and tends to be gentle, at the moment, the corrosion speed of the plating layer is reduced, and the corrosion resistance of the plating layer is improved.
From the above, it can be obtained: the corrosion resistance of the nano zinc-cobalt alloy plating layer is superior to that of a pure zinc plating layer, and the nano zinc-cobalt alloy plating layer prepared by the plating solution with the concentration ratio of zinc ions to cobalt ions being 5:1 has the best corrosion resistance.
Example 5
The difference between this example and example 3 is that different double-pulse electrodeposition process parameters are designed to prepare 16 sets of samples of the nano-zinc-cobalt alloy plating layer, so as to analyze the influence degree of single-parameter double-pulse electrodeposition process parameters on the corrosion resistance of the nano-zinc-cobalt alloy plating layer.
Designing an orthogonal test of double pulse parameters, and selecting a forward current density J+Positive duty cycle theta+Positive direction period T+Reverse current density J-And reverse duty cycle theta-The design orthogonal experiment of five factors, each factor takes four horizontal values, is shown in table 2, the forward working time is 100ms, the reverse working time is 12ms, and the reverse period is 1 ms.
TABLE 2
Table 3 shows the values of the self-corrosion potential E of the prepared 16 groups of nano-zinc-cobalt alloy coating samplescorrAnd the self-corrosion potential is changed between-1.102V and-1.119V, which shows that the prepared nano zinc-cobalt alloy plating layer has better integral corrosion resistance.
TABLE 3
Table 4 shows the calculated corrosion potential range R corresponding to the five parameters of the forward current density, the forward duty cycle, the forward period, the reverse current density and the reverse duty cycle, respectively, with the self-corrosion potential of the nano-zinc-cobalt alloy plating layer as the reference standard, and the influence sequence of the five dipulse parameters on the corrosion resistance of the plating layer according to the range value sequence is as follows: forward duty cycle > reverse duty cycle > forward cycle > reverse average current density > forward current density.
TABLE 4
The above is not relevant and is applicable to the prior art.
The features of the embodiments and embodiments described herein above may be combined with each other without conflict.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A preparation method of a nano zinc-cobalt alloy coating based on double-pulse electrodeposition is characterized in that a zinc plate is used as an anode, a low-carbon steel plate is used as a cathode, and the nano zinc-cobalt alloy coating is electroplated in a plating solution by adopting a double-pulse electrodeposition process, wherein the pH value of the plating solution is 4-5, the concentration of zinc ions is 0.64-0.70mol/L, and the concentration of cobalt ions is 0.1-0.16 mol/L; the electroplating parameters of the double-pulse electrodeposition process are as follows: the electrodeposition time is 20min, and the forward current density is 1.5-3.0A/dm2The forward duty ratio is 30-70%, the forward period is 30-70ms, and the reverse current density is 0.2-0.4A/dm2The reverse duty cycle is 30-70%, the forward working time is 100ms, the reverse working time is 12ms, and the reverse cycle is 1 ms.
2. The method for preparing the nano zinc-cobalt alloy coating based on the double pulse electrodeposition according to claim 1, wherein the sum of the concentrations of the zinc ions and the cobalt ions is 0.8 mol/L.
3. The preparation method of the nano zinc-cobalt alloy coating based on the double pulse electrodeposition as claimed in claim 1 or 2, wherein the plating solution further comprises the following components: 30-45g/L of boric acid, 25-30g/L of sodium sulfate and 30-50g/L of sodium citrate.
4. The preparation method of the nano zinc-cobalt alloy coating based on the double-pulse electrodeposition as claimed in claim 3, wherein the plating solution comprises the following components in percentage by weight: 183-197g/L of zinc sulfate heptahydrate, 28-45g/L of cobalt sulfate heptahydrate, 30-45g/L of boric acid, 25-30g/L of sodium sulfate and 30-50g/L of sodium citrate.
5. The method for preparing a nano zinc-cobalt alloy coating based on double pulse electrodeposition according to claim 1 or 2, wherein the electrodeposition temperature is 25-30 ℃.
6. The method for preparing a nano zinc-cobalt alloy coating based on double pulse electrodeposition according to claim 1 or 2, wherein the purity of the zinc plate for the anode is more than 99.99%, the distance between the anode and the cathode is 6cm, and the specifications are 60mm x 90mm x 1 mm.
7. The preparation method of the nano zinc-cobalt alloy coating based on the double pulse electrodeposition as claimed in claim 1 or 2, wherein the surface of the zinc plate is sequentially subjected to grinding, degreasing and cleaning treatments.
8. The method for preparing the nano zinc-cobalt alloy coating based on the double-pulse electrodeposition as claimed in claim 1 or 2, wherein the surface of the low carbon steel plate is sequentially subjected to grinding, polishing, degreasing and weak etching treatment.
9. A nanometer zinc-cobalt alloy coating based on double-pulse electrodeposition is characterized in that: prepared by the preparation method of any one of claims 1 to 8.
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