Aluminum coating and preparation method thereof

Abstract

The invention relates to the technical field of electroplating, in particular to an aluminum coating and a preparation method thereof. The invention discloses a preparation method of an aluminum coating, which comprises the following steps: modulating the output of an original power supply into electroplating current, and electroplating a substrate by using ionic liquid as electroplating liquid to obtain the aluminum coating, wherein the ripple coefficient of the original power supply is less than or equal to 0.5%. According to the aluminum coating and the preparation method thereof, an original power source with the ripple coefficient smaller than or equal to 0.5% is adopted, the adverse effect of ripples on ionic liquid electroplating aluminum is eliminated from the source, the flatness and compactness of the aluminum coating are remarkably improved, and the technical problems that in the prior art, due to the power source ripples, the number of coating defects is large, and the quality is unstable are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electroplating, in particular to an aluminum plating layer and a preparation method thereof. BACKGROUND

[0002] Aluminum has low density, good ductility, excellent corrosion resistance and metallic luster, and its plating layer can further form a high-hardness and wear-resistant colored surface layer through anodic oxidation, which is an extremely valuable surface protection and decoration material in the industrial field. At present, the methods for preparing aluminum plating layer include hot dipping, physical vapor deposition, chemical vapor deposition and electroplating, etc. Among them, ionic liquid electroplating of aluminum has the advantages of mild reaction, high purity of plating layer, adaptation to complex-shaped workpieces, no combustion and explosion risk, low requirement for equipment, green environmental protection, etc., and becomes the preferred technology for large-scale preparation of aluminum plating layer.

[0003] However, in the existing ionic liquid electroplating of aluminum technology, there are core defects in the selection and application of electroplating power supply, which directly restricts the quality improvement of aluminum plating layer. Specifically, the existing technology generally uses a high-frequency rectifier to convert commercial power (220V / 380V alternating current) into a "direct current power supply" for electroplating, but such power supply is essentially a "pseudo direct current" with a certain ripple factor. The ripple factor is a key process parameter affecting the quality of the plating layer, which reflects the proportion of alternating current components in the direct current power supply. A too high ripple factor will lead to uneven reduction rate of aluminum ions in the electroplating process, and thus cause defects such as rough plating layer crystallization, pinholes, loose dendrites and burning, and even damage to the stability of the plating solution. At present, ordinary protective electroplating (such as zinc plating) allows a ripple factor of ≤5%, and precise decorative electroplating (such as nickel plating and chromium plating) allows a ripple factor of ≤3%, but even so, the ripple interference of the existing power supply still cannot meet the stringent requirements of ionic liquid electroplating of aluminum on the density and flatness of the plating layer.

[0004] In order to improve the quality of the plating layer, some studies attempt to optimize the crystallization process by adding organic additives such as nicotinamide and o-phenanthroline, but organic additives generally have poor stability, are volatile, flammable and explosive, are harmful to the environment and human body, and will cause the plating layer to be mixed with reaction products, thereby reducing the purity and adhesion of the plating layer, and have significant application limitations. SUMMARY

[0005] The present application provides an aluminum plating layer and a preparation method thereof, which eliminates the adverse effects of ripple on ionic liquid electroplating of aluminum from the source by using an original power supply with a ripple factor of ≤0.5%, significantly improves the flatness and density of the aluminum plating layer, and solves the technical problems of existing technology such as multiple defects in the plating layer and unstable quality caused by power supply ripple.

[0006] Therefore, the first object of the present application is to provide a preparation method of an aluminum plating layer.

[0007] The second object of the present application is to provide an aluminum coating.

[0008] To achieve the first object of the present application, the technical solution of the present application provides a preparation method of an aluminum coating, comprising: modulating an original power output into an electroplating current, using an ionic liquid as an electroplating solution, and performing electroplating treatment on a substrate to obtain an aluminum coating; wherein the ripple coefficient of the original power is ≤0.5%.

[0009] Compared with the prior art, the technical effects achieved by adopting the technical solution are as follows: the ripple coefficient of the original power is ≤0.5%, which is much lower than the ripple coefficient of the "pseudo direct current" of the ordinary high-frequency rectifier in the prior art, the interference of the alternating component on the aluminum ion reduction crystallization can be eliminated from the source, the problem of uneven deposition rate of aluminum ions caused by ripple can be avoided, the defects such as roughness, pinholes, loose dendrites and burning of the coating can be reduced, and the flatness and compactness of the aluminum coating can be significantly improved; the low-ripple power output is stable, and the electrochemical characteristics of the ionic liquid electroplating solution form a synergistic adaptation, so that the decomposition of the ionic liquid or the decrease in the stability of the plating solution caused by power fluctuations can be avoided, the electroplating process can be continuously and stably carried out, the loss of the plating solution and the production cost can be reduced, and the problems of easy volatilization, flammability, explosion, environmental hazards and impurities in the coating caused by organic additives can be avoided, so that the purity and adhesion of the coating can be improved, and green and environmentally friendly electroplating can be realized.

[0010] In one technical solution of the present application, the original power is selected from at least one of a direct current generator, a chemical battery, a photovoltaic cell, a linear voltage stabilizer or a reference voltage power supply; and the output type of the electroplating current includes at least one of a continuous square wave, a single-pulse square wave, a double-pulse square wave and a sawtooth wave.

[0011] Compared with the prior art, the technical effects achieved by adopting the technical solution are as follows: the selection of multiple power types adapts to different application scenarios, the direct current generator and the linear voltage stabilizer adapt to the stable power supply demand of industrialized large-scale production, the chemical battery adapts to temporary plating operations in field scenarios without commercial power, and the photovoltaic cell conforms to the trend of green and low-carbon production, thereby widening the application range of the technical solution and solving the limitation of single power adaptability in the prior art; the multiple output types of the electroplating current can be matched with different substrates and different plating quality requirements, the continuous square wave adapts to scenarios with high requirements for the uniformity of the plating layer thickness, the single-pulse square wave can optimize the grain refinement effect, the double-pulse square wave can repair small defects on the surface of the plating layer, and the sawtooth wave can regulate the growth rate gradient of the plating layer. The selected power types do not require complex ripple filtering equipment, have simple structures and low maintenance costs, and can adapt to the plating requirements of different workpieces through flexible switching of diversified output types without the need to replace the core power supply equipment, thereby reducing the equipment investment and debugging costs of industrialized production and improving the production efficiency.

[0012] In one technical solution of the present application, the electroplating treatment specifically comprises: S100, an initial nucleation stage, the electroplating current is a single pulse square wave, the frequency is 500Hz-800Hz, the duty cycle is 20%-30%, the current density is 5mA / cm2-10mA / cm2, and the reaction time is 5min-10min; S300, a middle growth stage, the electroplating current is continuous pure direct current, the current density is 15mA / cm2-25mA / cm2, and the reaction time is 30min-40min; S300, a late densification stage, the electroplating current is a double pulse square wave, the forward pulse frequency is 300Hz-500Hz, the duty cycle is 40%-50%, the reverse pulse frequency is 100Hz-200Hz, the duty cycle is 10%-15%, the current density is 8mA / cm2-12mA / cm2, and the reaction time is 5-10min.

[0013] Compared with the prior art, the technical effects achieved by adopting the technical solution are: the parameters of the initial nucleation stage are accurately matched with the crystal nucleus growth law, the single pulse square wave with a frequency of 500Hz-800Hz can produce moderate cathode polarization, the low duty cycle of 20%-30% cooperates with the low current density of 5mA / cm2-10mA / cm2, which can inhibit the excessive growth of crystal nucleus and promote the formation of a large number of fine crystal nuclei with uniform size; the continuous pure direct current is adopted in the middle growth stage, the current density of 15mA / cm2-25mA / cm2 is adapted to the migration and reduction rate of aluminum ions in the ionic liquid, which can ensure the rapid thickening of the plating layer while avoiding the layering defects of the plating layer that may be caused by the pulse current; the double pulse square wave design in the late densification stage forms a “deposition-repair” synergistic effect: the forward pulse maintains the growth of the plating layer, and the reverse pulse can selectively dissolve the small defects on the surface of the plating layer, the forward frequency of 300Hz-500Hz and the reverse frequency of 100Hz-200Hz, and the reverse low duty cycle of 10%-15% can repair pinholes, porosity and other problems without damaging the main body of the plating layer.

[0014] In one technical solution of the present application, the voltage range of the electroplating current is 1.5V-3.0V.

[0015] Compared with the prior art, the technical effects achieved by adopting the technical solution are: the voltage range matches the reduction potential of aluminum ions in the ionic liquid, forms a synergy with the low ripple power supply, avoids the current density drift caused by voltage fluctuation, adapts to the electrochemical characteristics of the ionic liquid system, reduces the occurrence of disproportionation reaction, and improves the purity of the plating layer.

[0016] In one technical solution of the present application, the peak current fluctuation amplitude of the single pulse square wave in the initial nucleation stage is ≤±0.2mA / cm2.

[0017] Compared with the prior art, the technical effects achieved by adopting the technical scheme are: the accurate definition of the fluctuation range of the peak current plays a core role in ensuring the uniformity of the crystal nucleus growth, avoiding the difference in the local crystal nucleus growth rate caused by the current fluctuation, and then forming uneven grains or agglomeration defects, the fluctuation range threshold is adapted to the low current density in the initial nucleation stage, and the relative fluctuation ratio is less than or equal to 4%, which can meet the requirement of crystal nucleus refinement, and will not cause the cost of power supply equipment to increase sharply due to excessive limitation of fluctuation, and the stable current environment can avoid the burning or insufficient deposition of the plating layer caused by local overcurrent, prolong the service life of the ionic liquid plating solution, reduce the replacement frequency of the plating solution, reduce the production cost, and at the same time, avoid the imbalance of the plating solution composition caused by the current fluctuation, and ensure the continuous and stable plating process.

[0018] In one technical scheme of the present application, the reverse pulse current density in the late dense stage is 1 / 3 to 1 / 2 of the forward pulse current density.

[0019] Compared with the prior art, the technical effects achieved by adopting the technical scheme are: the current density ratio of 1 / 3 to 1 / 2 can selectively dissolve the small defects such as pinholes and dendrite tips on the surface of the plating layer, while avoiding damage to the main body of the plating layer caused by excessive reverse current; the low-ripple power supply is formed to optimize the stability of the forward pulse deposition, and the crystalline structure is further refined; the uniform improvement of the conductivity makes the reduction and deposition of aluminum ions on the surface of the substrate more uniform, and reduces the problem of insufficient adhesion between the plating layer and the substrate caused by the difference in local ion concentration.

[0020] In one technical scheme of the present application, the electroplating solution further comprises: anhydrous lithium chloride, with a mass fraction of 0.01% to 0.03%.

[0021] Compared with the prior art, the technical effects achieved by adopting the technical scheme are: the anhydrous lithium chloride can enhance the charge transfer capability of the ionic liquid system to improve the conductivity of the electrolyte; the mass fraction of 0.01% to 0.03% is adapted to the parameters of each stage of the segmented pulse current, and will not cause the competition between lithium ions and aluminum ions for deposition and the introduction of impurities due to excessive concentration, and will not fail to achieve the effect of improving the conductivity due to insufficient concentration.

[0022] In one technical scheme of the present application, the preparation method further comprises: post-treating the substrate, sequentially performing ultrasonic cleaning on the substrate with anhydrous ethanol, rinsing the substrate with deionized water, and vacuum drying the substrate at a temperature of 40 DEG C to 60 DEG C for 20 min to 30 min, with a vacuum degree of less than or equal to-0.09 MPa.

[0023] Compared with the prior art, the technical effects achieved by the technical scheme are as follows: the anhydrous ethanol can quickly dissolve the residual ionic liquid on the surface of the substrate, the ultrasonic vibration can strip the attached tiny plating solution particles, the subsequent deionized water flushing can remove the residual ethanol and trace salt, the temperature range of 40 DEG C to 60 DEG C can quickly remove the moisture on the surface of the substrate, and the aluminum coating will not be oxidized or the crystal grains will not grow due to the high temperature, the time length of 20 min to 30 min and the vacuum degree of less than or equal to-0.09 MPa can effectively discharge the residual water vapor and air in the coating and the interface, the oxygen is isolated in the vacuum environment, and the aluminum coating is prevented from being oxidized and discolored in the drying process. The surface of the cleaned and dried coating is free of impurity residues, and a clean substrate is provided for the subsequent optional passivation treatment, so that the passivation film is tightly combined with the aluminum coating.

[0024] In one technical scheme of the present application, the vacuum drying is further followed by a passivation treatment: the substrate is placed in a chromate solution with a concentration of 0.3 mol / L to 0.5 mol / L, and is immersed at 25 DEG C to 30 DEG C for 2 min to 3 min, and a passivation protective film is formed after air drying.

[0025] Compared with the prior art, the technical effects achieved by the technical scheme are as follows: the chromate solution reacts with the surface of the aluminum coating to form a uniform and dense aluminum chromate passivation film, which fills the tiny pores on the surface of the coating and blocks the contact channels of oxygen and moisture with the aluminum coating; the concentration of 0.3 mol / L to 0.5 mol / L, the temperature of 25 DEG C to 30 DEG C and the immersion time of 2 min to 3 min can ensure the rapid formation of the passivation film and avoid the corrosion and discoloration of the coating caused by the high concentration or high temperature.

[0026] To achieve the second object of the present application, the technical scheme of the present application provides an aluminum coating prepared by the preparation method of the aluminum coating of any of the above technical schemes, wherein the thickness of the aluminum coating is 15 mu m to 30 mu m, the surface roughness Ra of the aluminum coating is less than or equal to 0.2 mu m, and the porosity of the aluminum coating is less than or equal to 0.5%.

[0027] Compared with the prior art, the technical effects achieved by the technical scheme are as follows: the aluminum coating of the present technical scheme is prepared by the preparation method of the aluminum coating of any of the technical schemes of the present application, and thus has all the beneficial effects of the preparation method of the aluminum coating of any of the technical schemes of the present application, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical schemes in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be described below. Obviously, the technical schemes described in the description in combination with the drawings are only some embodiments of the present application, and other embodiments and drawings thereof can be obtained by those skilled in the art without creative labor on the basis of the embodiments shown in the drawings.

[0029] Figure 1 is a metallograph of the aluminum coating in Example 1 of the present application under a 500-fold magnifying lens; Figure 2 is a metallograph of the aluminum coating in Comparative Example 1 of the present application under a 500-fold magnifying lens. DETAILED DESCRIPTION

[0030] The technical solutions of the embodiments of the present application will be described clearly and completely in combination with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments described in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0031]

Example 1

[0032]

Example 2

[0033] Example 3 The preparation method of this example refers to Example 1, the difference is that no anhydrous lithium chloride is added in the plating solution; the obtained aluminum coating has a thickness of 19 μm, Ra = 0.19 μm, porosity of 0.45%, and neutral salt spray test of 480 h.

[0034] Example 4 The preparation method of this example refers to Example 1, the difference is that the reverse pulse current density in the later densification stage is 1 / 3 (3.3 mA / cm²) of the forward one; the obtained aluminum coating has a thickness of 20 μm, Ra = 0.16 μm, porosity of 0.32%, and neutral salt spray test of 510 h.

[0035] Comparative Example 1 The preparation method of this example refers to Example 1, the difference is that the original power source is a common high-frequency rectifier with a ripple coefficient of 3%; the obtained aluminum coating has a thickness of 21 μm, Ra = 0.52 μm, porosity of 1.8%, and neutral salt spray test of 120 h.

[0036] Comparative Example 2 The preparation method of this example refers to Example 2, the difference is that the original power source is a common high-frequency rectifier with a ripple coefficient of 3%; the obtained aluminum coating has a thickness of 23 μm, Ra = 0.65 μm, porosity of 2.3%, and neutral salt spray test of 90 h.

[0037] According to the test results of the above examples and comparative examples, the aluminum coating provided by Examples 1-4 has a thickness of 19 μm-21 μm, surface roughness Ra of only 0.15 μm-0.19 μm, porosity of 0.3%-0.45%, and neutral salt spray test life of 480 h-520 h, with stable and excellent comprehensive performance, which is greatly improved compared with Comparative Examples 1-2 (aluminum coating thickness of 21 μm-23 μm, Ra of 0.52 μm-0.65 μm, porosity of 1.8%-2.3%, and salt spray test of only 90 h-120 h). The flatness, density and corrosion resistance of the coating of the present application are significantly better, and the defect rate is greatly reduced.

[0038] As can be seen from Examples 1 and 2, the type of original power source (linear voltage regulator, direct current generator) has little effect on the performance of the coating, with a difference of less than 10% in Ra, porosity and salt spray test results, indicating that the low-ripple power source type defined in the present application has strong universality and can stably achieve the core technical effect.

[0039] As can be seen from Examples 1 and 3, adding 0.02% anhydrous lithium chloride to the plating solution can reduce the porosity of the coating from 0.45% to 0.3% and increase the salt spray test life from 480h to 520h. This indicates that anhydrous lithium chloride can help improve the density and corrosion resistance of the coating. However, even without its addition, the coating performance is still far superior to that of the comparative example.

[0040] As can be seen from Examples 1 and 4, when the reverse pulse current density in the later densification stage is 1 / 3 to 2 / 5 of that in the forward direction, the coating Ra is only 0.15μm to 0.16μm and the porosity is 0.3% to 0.32%, with minimal performance differences. This indicates that this ratio range can effectively repair coating defects, has a high process tolerance, and is suitable for industrial production needs.

[0041] Reference Figure 1 and Figure 2 As shown, the aluminum coating of Example 1 exhibits a uniform and dense layered structure, with a clear and tightly bonded interface between the coating and the substrate, and no obvious defects such as pores or cracks. In contrast, the aluminum coating of Comparative Example 1 shows a rough and uneven structure with numerous dispersed pores inside. A comparison between Examples 1-4 and Comparative Examples 1-2 reveals that the original power supply ripple coefficient is crucial to coating quality; a low-ripple power supply can prevent uneven crystal growth and pinhole defects in the coating from the outset.

[0042] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims, not by the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an aluminum coating, characterized in that, The preparation method includes: modulating the original power supply output into an electroplating current, using an ionic liquid as an electroplating solution, and electroplating the substrate to obtain an aluminum coating. The ripple factor of the original power supply is ≤0.5%.

2. The method for preparing the aluminum coating according to claim 1, characterized in that, The original power source is selected from at least one of a DC generator, a chemical cell, a photovoltaic cell, a linear regulated power supply, or a reference voltage power supply; The output type of the electroplating current includes at least one of continuous square wave, single pulse square wave, double pulse square wave and sawtooth wave.

3. The method for preparing the aluminum coating according to claim 1, characterized in that, The electroplating process specifically includes: S100, Initial nucleation stage, the electroplating current is a single-pulse square wave with a frequency of 500Hz~800Hz, a duty cycle of 20%~30%, a current density of 5mA / cm²~10mA / cm², and a reaction time of 5min~10min; S300, the intermediate growth stage, the electroplating current is a continuous pure DC current with a current density of 15mA / cm²~25mA / cm² and a reaction time of 30min~40min; S300, the later densification stage, the electroplating current is a double-pulse square wave, the forward pulse frequency is 300Hz~500Hz, the duty cycle is 40%~50%, the reverse pulse frequency is 100Hz~200Hz, the duty cycle is 10%~15%, the current density is 8mA / cm²~12mA / cm², and the reaction time is 5min~10min.

4. The method for preparing the aluminum coating according to claim 1, characterized in that, The voltage range of the electroplating current is 1.5V~3.0V.

5. The method for preparing the aluminum coating according to claim 3, characterized in that, The peak current fluctuation amplitude of the single-pulse square wave during the initial nucleation stage is ≤ ±0.2mA / cm².

6. The method for preparing the aluminum coating according to claim 3, characterized in that, The reverse pulse current density in the later denser stage is 1 / 3 to 1 / 2 of the forward pulse current density.

7. The method for preparing the aluminum coating according to claim 3, characterized in that, The electroplating solution also includes anhydrous lithium chloride, with a mass fraction of 0.01% to 0.03%.

8. The method for preparing an aluminum coating according to claim 1, characterized in that, The preparation method further includes: post-processing the substrate by sequentially ultrasonically cleaning the substrate with anhydrous ethanol, rinsing it with deionized water, and vacuum drying it at a temperature of 40℃~60℃ for 20min~30min, with a vacuum degree ≤-0.09MPa.

9. The method for preparing an aluminum coating according to claim 8, characterized in that, After vacuum drying, a passivation treatment is also included: the substrate is placed in a 0.3 mol / L to 0.5 mol / L chromate solution and immersed at 25℃ to 30℃ for 2 min to 3 min, and then dried to form a passivation protective film.

10. An aluminum coating, prepared by the method for preparing the aluminum coating according to any one of claims 1-9, characterized in that, The thickness of the aluminum coating is 15μm~30μm; The surface roughness Ra of the aluminum coating is ≤0.2μm; The porosity of the aluminum coating is ≤0.5%.

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