Cyanide-free zinc precipitating agent, preparation method thereof and zinc precipitation method

Abstract

The present application relates to the technical field of electroplating, in particular to a cyanide-free zinc deposition agent, a preparation method thereof and a zinc deposition method. The cyanide-free zinc deposition agent comprises the following components in terms of mass concentration: sodium hydroxide 70-130 g / L, zinc element 3-9 g / L, iron element 0.5-3 g / L, manganese element 1-7 g / L, molybdenum element 0.1-1 g / L, disodium ethylenediaminetetraacetate 50-90 g / L and triethanolamine 10-40 g / L. The cyanide-free zinc deposition agent can improve the adhesion of the zinc immersion layer, reduce the contact resistance of the zinc immersion layer, and is green and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more specifically, to a cyanide-free zinc precipitating agent and its preparation method and zinc precipitating method. Background Technology

[0002] Aluminum and aluminum alloys are widely used materials in high-voltage electrical products. Electroplating aluminum or aluminum alloys is an effective way to improve their electrical conductivity, thermal conductivity, weldability, and enhance their surface wear resistance, corrosion resistance, protection, decoration, and optical properties. However, aluminum is relatively reactive and easily forms a natural oxide film. Its electrode potential is also too negative, allowing it to undergo displacement reactions with various metal ions when immersed in the electroplating solution, resulting in weak adhesion between the plating layer and the substrate, making it prone to peeling. Forming a dense and robust zinc layer on the substrate surface, serving as a good transition layer between electroplating and chemical plating, can effectively solve these problems.

[0003] The purpose of zinc immersion before aluminum alloy electroplating (also known as aluminum top zinc immersion) is to remove the oxide film on the surface of aluminum or aluminum alloy, while uniformly and slowly replacing the zinc layer, making the potential of the part surface positive and improving the adhesion between the substrate and the coating. Existing conventional aluminum top zinc immersion agents (zinc immersion baths) often contain cyanide, but cyanide and HCN generated in the residual solution are toxic. Therefore, cyanide-free zinc immersion has become the current trend.

[0004] The principle of alkaline zinc immersion is to reduce the surface activity of aluminum by immersing it in zinc, preventing oxidation of aluminum during operation or in the electroplating solution, and simultaneously preventing displacement reactions between the aluminum parts and the metal ions being plated in the electroplating solution. The main components of the basic zincate solution are NaOH and zinc ions. To achieve high adhesion of the coating on the aluminum parts, the thickness of the zinc immersion layer should be as thin as possible while ensuring good electrodeposition. The two most important factors determining the amount of zinc displaced are the alloy properties and the zinc immersion process used.

[0005] However, existing cyanide-free zinc plating agents are simple alkaline zincate solutions. These solutions suffer from poor adhesion and blistering issues when plating complex parts and blind-hole parts.

[0006] Furthermore, high-voltage electrical products utilize a large number of aluminum alloy components of various grades. In particular, silicon elements on the surface of high-silicon aluminum castings are not removed during acid and alkali etching, which reduces the adhesion between the substrate and the coating. The casting process itself also has defects; although the surface condition is good, its internal structure is loose, with coarse grains, and contains pores, inclusions, and sand holes. During electroplating, these pores, inclusions, and sand holes in the cast aluminum parts often trap solution and hydrogen, thus affecting the adhesion between the coating and the substrate. This places very high demands on the zinc immersion process in electroplating. General cyanide-free zinc immersion solutions produce zinc layers with poor adhesion and high contact resistance, making it difficult to meet the requirements of high-voltage electrical products. Therefore, existing cyanide-free zinc immersion cannot completely replace cyanide-based zinc immersion.

[0007] In view of this, the present invention is hereby proposed. Summary of the Invention

[0008] The primary objective of this invention is to provide a cyanide-free zinc precipitation agent that can completely replace existing cyanide zinc precipitation agents. This cyanide-free zinc precipitation agent is green and environmentally friendly, beneficial to health, and improves the adhesion of the zinc plating layer while reducing its contact resistance.

[0009] The second objective of this invention is to provide a method for preparing a cyanide-free zinc precipitation agent, which has the advantages of simple operation, mild conditions, and suitability for mass production.

[0010] A third objective of this invention is to provide a zinc plating method, wherein the zinc plating layer obtained after zinc plating treatment has good adhesion and low contact resistance.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0012] This invention provides a cyanide-free zinc precipitation agent, comprising the following components by mass concentration: sodium hydroxide 70-130 g / L, zinc 3-9 g / L, iron 0.5-3 g / L, manganese 1-7 g / L, molybdenum 0.1-1 g / L, disodium ethylenediaminetetraacetate 50-90 g / L, and triethanolamine 10-40 g / L.

[0013] Preferably, the cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 75-125 g / L, zinc 4-8 g / L, iron 0.8-2.5 g / L, manganese 2-6 g / L, molybdenum 0.2-0.8 g / L, disodium ethylenediaminetetraacetate 55-85 g / L, and triethanolamine 15-35 g / L.

[0014] Preferably, the cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 80-120 g / L, zinc 5-7 g / L, iron 1-2 g / L, manganese 3-5 g / L, molybdenum 0.3-0.5 g / L, disodium ethylenediaminetetraacetate 60-80 g / L, and triethanolamine 20-30 g / L.

[0015] Preferably, the zinc element is mainly provided by zinc sulfate and / or zinc oxide;

[0016] Preferably, the iron element is mainly provided by ferric chloride.

[0017] Preferably, the manganese element is mainly provided by manganese sulfate monohydrate;

[0018] Preferably, the molybdenum element is mainly provided by ammonium molybdate.

[0019] The present invention also provides a method for preparing the cyanide-free zinc precipitation agent as described above, comprising the following steps:

[0020] The cyanide-free zinc precipitation agent is obtained by uniformly mixing sodium hydroxide, zinc source, iron source, manganese source, molybdenum source, disodium ethylenediaminetetraacetate, triethanolamine, and solvent.

[0021] The solvent includes water.

[0022] Preferably, the zinc source includes zinc sulfate and / or zinc oxide;

[0023] Preferably, the iron source includes ferric chloride;

[0024] Preferably, the manganese element includes manganese sulfate monohydrate;

[0025] Preferably, the molybdenum element includes ammonium molybdate.

[0026] Preferably, the preparation method of the cyanide-free zinc precipitation agent specifically includes the following steps: adding sodium hydroxide and zinc source to water and mixing evenly to obtain a first solution; adding iron source, manganese source, molybdenum source, disodium ethylenediaminetetraacetate, and triethanolamine to water and mixing evenly to obtain a second solution; when the temperature of the first solution drops to 50-60°C, adding the second solution to the first solution, stirring for 10-15 minutes, and letting stand for 10-12 hours to obtain the cyanide-free zinc precipitation agent.

[0027] The present invention also provides a zinc immersion method, which uses the cyanide-free zinc immersion agent described above to perform zinc immersion treatment on metallic aluminum and / or aluminum alloys.

[0028] Preferably, the aluminum alloy comprises a high-silicon aluminum alloy.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The cyanide-free zinc plating agent provided by this invention improves the adhesion of the zinc plating layer by adding specific amounts of manganese and molybdenum elements to change the electrode potential. This solves the problems of poor adhesion and easy blistering in the electroplating of complex parts and blind holes in the existing zincate chemical zinc plating process.

[0031] (2) The cyanide-free zinc precipitator provided by the present invention slows down the displacement reaction by adding a specific amount of disodium ethylenediaminetetraacetate and triethanolamine, resulting in a thinner and denser zinc immersion layer, which improves the adhesion of subsequent coatings and reduces the contact resistance of the zinc immersion layer, thus meeting the electrical performance requirements of high-voltage electrical products.

[0032] (3) The cyanide-free zinc precipitation agent provided by the present invention does not contain cyanide or other toxic chemical components, and is green and environmentally friendly. Attached Figure Description

[0033] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 SEM image of the zinc-impregnated layer in Example 1 of this invention;

[0035] Figure 2 SEM image of the zinc-plated layer in Comparative Example 6 provided by the present invention;

[0036] Figure 3 SEM image of the zinc-plated layer in Comparative Example 7 provided by the present invention;

[0037] Figure 4 SEM image of the cross-section of the junction between the zinc plating layer and the aluminum substrate provided by the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0039] In a first aspect, the present invention provides a cyanide-free zinc precipitation agent comprising the following components by mass concentration: sodium hydroxide 70-130 g / L, zinc 3-9 g / L, iron 0.5-3 g / L, manganese 1-7 g / L, molybdenum 0.1-1 g / L, disodium ethylenediaminetetraacetate 50-90 g / L, and triethanolamine 10-40 g / L.

[0040] The cyanide-free zinc precipitator further includes a solvent, which includes water. Preferably, the water includes pure water. Water-soluble components in the cyanide-free zinc precipitator, such as sodium hydroxide, exist in ionic form.

[0041] That is, the cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 70-130 g / L, zinc 3-9 g / L, iron 0.5-3 g / L, manganese 1-7 g / L, molybdenum 0.1-1 g / L, disodium ethylenediaminetetraacetate 50-90 g / L, triethanolamine 10-40 g / L, and water.

[0042] The mass concentration of a component refers to the mass of that component per unit volume of the mixture.

[0043] That is, each 1L of the cyanide-free zinc precipitation agent contains 70-130g of sodium hydroxide, 3-9g of zinc, 0.5-3g of iron, 1-7g of manganese, 0.1-1g of molybdenum, 50-90g of disodium ethylenediaminetetraacetate, and 10-40g of triethanolamine, with the remainder being water.

[0044] The cyanide-free zinc plating agent provided by this invention changes the electrode potential by adding specific amounts of manganese and molybdenum, thereby improving the adhesion of the zinc plating layer and solving the problems of poor adhesion and easy blistering in the electroplating of complex parts and blind holes in the existing zincate chemical zinc plating process.

[0045] Furthermore, by adding specific amounts of disodium ethylenediaminetetraacetate and triethanolamine as complexing agents, this invention slows down the rate of the displacement reaction, resulting in a thinner and denser zinc plating layer. This improves the adhesion of subsequent coatings, reduces the contact resistance of the zinc plating layer, and meets the electrical performance requirements of high-voltage electrical products.

[0046] Furthermore, the cyanide-free zinc precipitator provided by this invention does not contain cyanide or other toxic chemical components, can be used for harmless electroplating processes, is green and environmentally friendly, and will not harm human health.

[0047] In some specific embodiments of the present invention, the mass concentration of sodium hydroxide includes, but is not limited to, any one of 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, and 125 g / L, or a range between any two; the mass concentration of zinc includes, but is not limited to, any one of 4 g / L, 5 g / L, 6 g / L, 7 g / L, and 8 g / L, or a range between any two; the mass concentration of iron includes, but is not limited to, any one of 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, 1 g / L, 1.5 g / L, 2 g / L, and 2.5 g / L, or a range between any two; and the mass concentration of manganese includes, but is not limited to, 2 g / L. The concentrations of molybdenum are, but are not limited to, any one of the following: 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L; the concentrations of disodium ethylenediaminetetraacetate (EDTA-2Na) are, but are not limited to, any one of the following: 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L; and the concentrations of triethanolamine are, but are not limited to, any one of the following: 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L.

[0048] To further consider the adhesion and contact resistance of the zinc plating layer, the dosage of each component was optimized. Preferably, the cyanide-free zinc plating agent comprises the following components by mass concentration: sodium hydroxide 75-125 g / L, zinc 4-8 g / L, iron 0.8-2.5 g / L, manganese 2-6 g / L, molybdenum 0.2-0.8 g / L, disodium ethylenediaminetetraacetate 55-85 g / L, and triethanolamine 15-35 g / L.

[0049] Preferably, the cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 80-120 g / L, zinc 5-7 g / L, iron 1-2 g / L, manganese 3-5 g / L, molybdenum 0.3-0.5 g / L, disodium ethylenediaminetetraacetate 60-80 g / L, and triethanolamine 20-30 g / L.

[0050] Preferably, the zinc element is provided primarily by zinc sulfate and / or zinc oxide.

[0051] Preferably, the iron element is mainly provided by ferric chloride.

[0052] Preferably, the manganese element is mainly provided by manganese sulfate monohydrate.

[0053] Preferably, the molybdenum element is mainly provided by ammonium molybdate.

[0054] Secondly, the present invention provides a method for preparing the cyanide-free zinc precipitation agent as described above, comprising the following steps:

[0055] The cyanide-free zinc precipitation agent is obtained by uniformly mixing sodium hydroxide, zinc source, iron source, manganese source, molybdenum source, disodium ethylenediaminetetraacetate, triethanolamine, and solvent.

[0056] The solvent includes water.

[0057] The cyanide-free zinc precipitator prepared by this method produces a zinc-immersed layer with good adhesion and low contact resistance after zinc precipitation.

[0058] In addition, the preparation method is simple, easy to implement, and has a short operation process, making it suitable for mass production. Moreover, no cyanide is generated during the preparation process, making it green, environmentally friendly, and safer.

[0059] Preferably, the zinc source includes zinc sulfate and / or zinc oxide.

[0060] Preferably, the iron source includes ferric chloride.

[0061] Preferably, the manganese element includes manganese sulfate monohydrate.

[0062] Preferably, the molybdenum element includes ammonium molybdate.

[0063] Preferably, the preparation method of the cyanide-free zinc precipitation agent specifically includes the following steps: Sodium hydroxide and a zinc source are added to water and mixed evenly to obtain a first solution (mixing continues until the first solution becomes clear). An iron source, a manganese source, a molybdenum source, disodium ethylenediaminetetraacetate, and triethanolamine are added to water and mixed evenly to obtain a second solution (mixing continues until the second solution becomes clear). When the temperature of the first solution drops to 50–60°C, the second solution is added to the first solution, stirred for 10–15 minutes, and then allowed to stand for 10–12 hours to obtain the cyanide-free zinc precipitation agent. Note that since sodium hydroxide releases a large amount of heat during dissolution, reaching temperatures of 80–90°C, the temperature of the first solution needs to be lowered to 50–60°C before adding the second solution for mixing.

[0064] Thirdly, the present invention provides a zinc immersion method, which uses a cyanide-free zinc immersion agent as described above to perform zinc immersion treatment on metallic aluminum and / or aluminum alloys.

[0065] The zinc-immersion layer obtained by this zinc immersion method has good adhesion and low contact resistance.

[0066] In some specific embodiments of the present invention, the zinc immersion treatment method specifically includes: a first cyanide-free zinc immersion—water washing—zinc removal—water washing—a second cyanide-free zinc immersion—water washing, wherein the temperature of the first and second cyanide-free zinc immersions is 10-30°C; and the time of the first and second cyanide-free zinc immersions is 60-90 seconds.

[0067] In some specific embodiments of the present invention, the cyanide-free zinc precipitation agent provided by the present invention can be used for any conventional type of aluminum alloy, such as high-silicon aluminum alloy.

[0068] Preferably, the aluminum alloy comprises a high-silicon aluminum alloy.

[0069] In existing technologies, during the zinc immersion process of high-silicon aluminum alloy castings, pores, inclusions, and sand holes often trap solution and hydrogen, resulting in a loose and non-dense zinc coating that affects the adhesion between the coating and the substrate. This application, however, uses a cyanide-free zinc immersion agent with a specific chemical composition, particularly by adding specific amounts of disodium ethylenediaminetetraacetate and triethanolamine, to create a denser zinc coating and improve the adhesion between the coating and the substrate.

[0070] The contact resistance of the zinc-plated layer obtained after the zinc-plating treatment meets the technical requirements of high-voltage electrical products.

[0071] Preferably, the contact resistance of the zinc-plated layer obtained after the zinc immersion treatment is ≤19μΩ, including but not limited to the point value of any one of 19μΩ, 18μΩ, 17μΩ, 16μΩ, and 15μΩ, or the range between any two.

[0072] In some specific embodiments of the present invention, the thickness of the zinc-immersed layer obtained after the zinc immersion treatment is 0.03 to 0.05 μm.

[0073] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0074] Example 1

[0075] The cyanide-free zinc precipitant provided in this embodiment comprises the following components by mass concentration: 100 g / L sodium hydroxide, 6 g / L zinc, 1.5 g / L iron, 4 g / L manganese, 0.4 g / L molybdenum, 70 g / L disodium ethylenediaminetetraacetate, 25 g / L triethanolamine, and water. The zinc is provided by zinc chloride. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium molybdate.

[0076] The preparation method of the cyanide-free zinc precipitation agent provided in this embodiment includes the following steps: Sodium hydroxide and a zinc source are added to water and stirred until clear to obtain a first solution. An iron source, a manganese source, a molybdenum source, disodium ethylenediaminetetraacetate, and triethanolamine are added to water and stirred until clear to obtain a second solution. When the temperature of the first solution drops to 55°C, the second solution is added to the first solution, stirred for 15 minutes, and then allowed to stand for 11 hours to obtain the cyanide-free zinc precipitation agent.

[0077] Example 2

[0078] The cyanide-free zinc precipitant provided in this embodiment comprises the following components by mass concentration: 80 g / L sodium hydroxide, 5 g / L zinc, 1 g / L iron, 3 g / L manganese, 0.5 g / L molybdenum, 60 g / L disodium ethylenediaminetetraacetate, 20 g / L triethanolamine, and water. The zinc is provided by zinc oxide. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium thiomolybdate.

[0079] The preparation method of the cyanide-free zinc precipitation agent provided in this embodiment is the same as that in Example 1.

[0080] Example 3

[0081] The cyanide-free zinc precipitant provided in this embodiment comprises the following components by mass concentration: 120 g / L sodium hydroxide, 7 g / L zinc, 2 g / L iron, 5 g / L manganese, 0.3 g / L molybdenum, 80 g / L disodium ethylenediaminetetraacetate, 30 g / L triethanolamine, and water. The zinc is provided by zinc chloride. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium molybdate.

[0082] The preparation method of the cyanide-free zinc precipitation agent provided in this embodiment is the same as that in Example 1.

[0083] Example 4

[0084] The cyanide-free zinc precipitation agent provided in this embodiment comprises the following components by mass concentration: 70 g / L sodium hydroxide, 9 g / L zinc, 3 g / L iron, 1 g / L manganese, 1 g / L molybdenum, 50 g / L disodium ethylenediaminetetraacetate, 10 g / L triethanolamine, and water. The zinc is provided by zinc oxide. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium molybdate.

[0085] The preparation method of the cyanide-free zinc precipitation agent provided in this embodiment is the same as that in Example 1.

[0086] Example 5

[0087] The cyanide-free zinc precipitant provided in this embodiment comprises the following components by mass concentration: 130 g / L sodium hydroxide, 3 g / L zinc, 0.5 g / L iron, 7 g / L manganese, 0.1 g / L molybdenum, 90 g / L disodium ethylenediaminetetraacetate, 40 g / L triethanolamine, and water. The zinc is provided by zinc chloride. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium molybdate.

[0088] The preparation method of the cyanide-free zinc precipitation agent provided in this embodiment is the same as that in Example 1.

[0089] Comparative Example 1

[0090] The composition and preparation method of the cyanide-free zinc precipitation agent provided in this comparative example are basically the same as those in Example 1, except that manganese sulfate monohydrate is not added, that is, the cyanide-free zinc precipitation agent provided in this comparative example does not contain manganese.

[0091] Comparative Example 2

[0092] The composition and preparation method of the cyanide-free zinc precipitation agent provided in this comparative example are basically the same as those in Example 1, except that ammonium molybdate is not added, that is, the cyanide-free zinc precipitation agent provided in this comparative example does not contain molybdenum.

[0093] Comparative Example 3

[0094] The composition and preparation method of the cyanide-free zinc precipitation agent provided in this comparative example are basically the same as those in Example 1, except that disodium ethylenediaminetetraacetate is not added, that is, the cyanide-free zinc precipitation agent provided in this comparative example does not contain disodium ethylenediaminetetraacetate.

[0095] Comparative Example 4

[0096] The composition and preparation method of the cyanide-free zinc precipitation agent provided in this comparative example are basically the same as those in Example 1, except that triethanolamine is not added, that is, the cyanide-free zinc precipitation agent provided in this comparative example does not contain triethanolamine.

[0097] Comparative Example 5

[0098] The cyanide-free zinc precipitant provided in this comparative example comprises the following components by mass concentration: 100 g / L sodium hydroxide, 6 g / L zinc, 1.5 g / L iron, 8 g / L manganese, 2 g / L molybdenum, 70 g / L disodium ethylenediaminetetraacetate, 50 g / L triethanolamine, and water. The zinc is provided by zinc chloride. The iron is provided by ferric chloride. The manganese is provided by manganese sulfate monohydrate. The molybdenum is provided by ammonium molybdate.

[0099] The preparation method of the cyanide-free zinc precipitation agent provided in this comparative example is the same as that in Example 1.

[0100] Comparative Example 6

[0101] Commercially available cyanide-free zinc immersion agent is manufactured by Lesi Chemical.

[0102] Comparative Example 7

[0103] Commercially available cyanide multi-alloy zinc immersion agent is manufactured by Anmet.

[0104] Experimental Example 1

[0105] High-silicon aluminum alloy castings were subjected to zinc immersion treatment using the cyanide-free zinc immersion agent prepared in Example 1, the commercially available cyanide-free zinc immersion agent in Comparative Example 6, and the commercially available cyanide-containing multi-element alloying zinc immersion agent in Comparative Example 7, respectively, to obtain zinc immersion layers. SEM analysis was then performed on each zinc immersion layer, and the results are shown below. Figure 1 , Figure 2 and Figure 3 As shown.

[0106] The zinc immersion treatment specifically includes the following steps: first cyanide-free zinc immersion – water washing – zinc removal – water washing – second cyanide-free zinc immersion – water washing. The temperature for both the first and second cyanide-free zinc immersions is 20℃; the time for each cyanide-free zinc immersion is 70 seconds.

[0107] By comparison Figure 1 , Figure 2 and Figure 3 It can be seen that the zinc plating layer prepared by the cyanide-free zinc plating agent of Example 1 has a complete and dense coverage, which is significantly denser than the zinc plating layer prepared by the commercially available cyanide-free zinc plating agent of Comparative Example 6, and is close to the cyanide zinc plating layer of Comparative Example 7.

[0108] Meanwhile, the microstructure of the cross-section of the interface between the zinc layer prepared by the cyanide-free zinc immersion agent in Example 1 and the aluminum substrate (high-silicon aluminum alloy casting) is as follows: Figure 4 As shown. From Figure 4 It can be seen that the zinc plating layer obtained by using the cyanide-free zinc plating agent of Example 1 is firmly bonded to the aluminum substrate.

[0109] Experiment Example 2

[0110] Following the zinc immersion method in Experimental Example 1, the zinc immersion agents of the above embodiments and comparative examples were used to immerse the high-silicon aluminum alloy castings in zinc to obtain each group of zinc immersion layers. Then, the circuit resistance value of each zinc immersion layer was tested. Each group was tested 3 times, and the results are shown in Table 1.

[0111] Table 1. Test results of loop resistance for each group.

[0112]

[0113] As can be seen from Table 1, the circuit resistance of the zinc-immersed layer prepared by the cyanide-free zinc immersion agent in Example 1 is significantly lower than that in Comparative Example 6, and comparable to that in Comparative Example 7. This demonstrates that the cyanide-free zinc immersion agent prepared according to the present invention can reduce the contact resistance of the zinc-immersed layer.

[0114] Experimental Example 3

[0115] Following the zinc immersion method described in Experimental Example 1, the zinc immersion agents used in the above examples and comparative examples were applied to the high-silicon aluminum alloy castings—finger seats—to obtain zinc immersion layers. 100 pieces were treated in each group. Then, nickel, copper, and silver plating were sequentially applied to the surface of each zinc immersion layer, forming nickel, copper, and silver layers sequentially on the surface. Adhesion tests (including thermal shock and grinding tests) were then conducted, and the results are shown in Table 2.

[0116] The thermal shock test conditions are as follows: after being kept at 120℃ for 60 minutes, the sample is removed and allowed to cool naturally at room temperature, and the bubbling is observed.

[0117] The finger seats that pass the thermal shock test will continue to undergo a grinding test. The grinding test method is as follows: use a wire wheel to grind the edge of the electroplated layer (the junction between the silver-plated surface and the non-silver-plated surface). The grinding direction is from the base metal to the cover layer. If the adhesion strength is poor, the cover layer will peel off from the substrate.

[0118] Table 2. Test results of adhesion of zinc-impregnated layers in each group.

[0119]

[0120]

[0121] As can be seen from Table 2, the adhesion of the zinc immersion layer prepared by the cyanide-free zinc immersion agent provided by the present invention is far superior to that of the commercially available cyanide-free zinc immersion agent of Comparative Example 6, and close to that of the commercially available cyanide multi-alloy zinc immersion agent of Comparative Example 7.

[0122] In summary, the cyanide-free zinc precipitator with a specific composition provided by the present invention can improve the adhesion of the zinc immersion layer, reduce the contact resistance of the zinc immersion layer, and the cyanide-free zinc precipitator is green and environmentally friendly, and can completely replace the existing cyanide zinc precipitator.

[0123] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A cyanide-free zinc precipitation agent, characterized in that, It includes the following components by mass concentration: sodium hydroxide 70~130g / L, zinc 3~9g / L, iron 0.5~3g / L, manganese 1~7g / L, molybdenum 0.1~1g / L, disodium ethylenediaminetetraacetate 50~90g / L and triethanolamine 10~40g / L.

2. The cyanide-free zinc precipitation agent according to claim 1, characterized in that, The cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 75~125g / L, zinc 4~8g / L, iron 0.8~2.5g / L, manganese 2~6g / L, molybdenum 0.2~0.8g / L, disodium ethylenediaminetetraacetate 55~85g / L, and triethanolamine 15~35g / L.

3. The cyanide-free zinc precipitation agent according to claim 1, characterized in that, The cyanide-free zinc precipitation agent comprises the following components by mass concentration: sodium hydroxide 80~120g / L, zinc 5~7g / L, iron 1~2g / L, manganese 3~5g / L, molybdenum 0.3~0.5g / L, disodium ethylenediaminetetraacetate 60~80g / L, and triethanolamine 20~30g / L.

4. The cyanide-free zinc precipitation agent according to any one of claims 1 to 3, characterized in that, The zinc element is provided by zinc sulfate and / or zinc oxide; the iron element is provided by ferric chloride.

5. The cyanide-free zinc precipitation agent according to any one of claims 1 to 3, characterized in that, The manganese element is provided by manganese sulfate monohydrate; the molybdenum element is provided by ammonium molybdate.

6. The method for preparing the cyanide-free zinc precipitation agent according to any one of claims 1 to 5, characterized in that, Includes the following steps: Sodium hydroxide, zinc source, iron source, manganese source, molybdenum source, disodium ethylenediaminetetraacetate, triethanolamine and solvent are mixed evenly to obtain the cyanide-free zinc precipitation agent. The solvent includes water.

7. The method for preparing the cyanide-free zinc precipitation agent according to claim 6, characterized in that, The zinc source includes zinc sulfate and / or zinc oxide; The iron source includes ferric chloride; The manganese source includes manganese sulfate monohydrate; The molybdenum source includes ammonium molybdate.

8. The method for preparing the cyanide-free zinc precipitation agent according to claim 6, characterized in that, The preparation method of the cyanide-free zinc precipitation agent specifically includes the following steps: adding sodium hydroxide and zinc source to water, mixing evenly to obtain a first solution; adding iron source, manganese source, molybdenum source, disodium ethylenediaminetetraacetate, and triethanolamine to water, mixing evenly to obtain a second solution; When the temperature of the first solution drops to 50-60°C, the second solution is added to the first solution, stirred for 10-15 minutes, and then allowed to stand for 10-12 hours to obtain the cyanide-free zinc precipitation agent.

9. A zinc precipitation method, characterized in that, The zinc immersion treatment of metallic aluminum and / or aluminum alloys is carried out using the cyanide-free zinc immersion agent as described in any one of claims 1 to 5.

10. The zinc deposition method according to claim 9, characterized in that, The aluminum alloy includes a high-silicon aluminum alloy.

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