A composition and a method for electroless plating of high-silicon die cast aluminum alloys

Abstract

The application relates to the technical field of metal surface treatment, and discloses a composition for electroless plating of high-silicon die-casting aluminum alloy and an electroless plating method, the composition for electroless plating of high-silicon die-casting aluminum alloy comprising an acidic solution and an electroless nickel plating solution; the acidic solution comprises the following components: an oxidizing agent, a polyhydric alcohol, lanthanum nitrate, cerium nitrate, a fluoride, an acrylic acid-2-acrylamide-2-methylpropane sulfonic acid copolymer, diethylene triamine pentaformyl phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid and a dispersing agent; the electroless nickel plating solution comprises the following components: an organic acid, a reducing agent, a nickel salt, a buffer, thiourea, 1,4-butynediol, sodium saccharin and 2,2'-bipyridine. The composition is used for electroless plating of high-silicon die-casting aluminum alloy, and a plating layer with high gloss and good weather resistance can be obtained on the surface of the high-silicon die-casting aluminum alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface treatment, in particular to a composition and a chemical plating method for high-silicon die-casting aluminum alloy. BACKGROUND

[0002] In the aspect of aluminum alloy, high-silicon die-casting aluminum alloy (ADC12) is applied more and more widely in automobile accessories, industrial materials and the like. However, due to high silicon content (the silicon content is more than 10%), the ADC12 has poor electrical conductivity, and when treated by a traditional anodic oxidation treatment process, the oxidation film is formed very slowly, and the anodic oxidation film obtained is very uneven, the surface is dark and gray, and the gloss is low, so it is difficult to meet the decorative and other functional requirements of users. When treated by a chemical oxidation treatment process such as trivalent chromium or chromium-free passivation, the surface gloss is low, the surface is uneven, the passivation layer after treatment has poor weather resistance, and cannot meet the high weather resistance requirements of automobile accessories or other industrial materials.

[0003] Chemical plating is a widely used surface treatment process in recent years. The process is a process of depositing metal or metal alloy on the surface of a substrate through oxidation-reduction reaction by using a reducing agent in the solution. The chemical plating process does not require external power supply, is easy to operate, can be applied to workpieces with complex shapes, and has low production cost, so it is widely favored. Currently, the process for chemical plating of ADC12 usually adopts an acid pickling system of hydrofluoric acid + nitric acid. Because of the existence of active nitric acid component, the service life is short, a large amount of heat is generated during pickling, and yellow smoke which seriously affects the environment is formed. During the continuous pickling process, the working liquid is heated quickly, and if not properly controlled, it is easy to cause unstable quality and blackening phenomenon.

[0004] Therefore, it is necessary to further improve the gloss and weather resistance of the plating layer of high-silicon die-casting aluminum alloy. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a composition and a chemical plating method for high-silicon die-casting aluminum alloy. The high-silicon die-casting aluminum alloy is chemically plated by using the composition of the present application, and a plating layer with high gloss and good weather resistance can be obtained on the surface of the high-silicon die-casting aluminum alloy.

[0006] The first aspect of the present application provides a composition for chemical plating of high-silicon die-casting aluminum alloy, comprising an acid solution and a chemical nickel plating solution.

[0007] The acid pickling solution comprises the following components: an oxidizing agent, a polyol, lanthanum nitrate, cerium nitrate, a fluoride, an acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer, diethylene triamine pentaformyl phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, and a dispersing agent.

[0008] The chemical nickel plating solution comprises components: organic acid, reducing agent, nickel salt, buffer, thiourea, 1,4-butynediol, sodium saccharin, 2,2'-bipyridine.

[0009] According to some embodiments of the present application, in the pickling solution, the oxidizing agent comprises at least one of sodium persulfate, ammonium persulfate, hydrogen peroxide, sodium chlorate, potassium ferrate; the polyol comprises at least one of polyethylene glycol, pentaerythritol, glycerol; the fluoride comprises at least one of ammonium bifluoride, ammonium fluoride, sodium fluorosilicate, hydrofluoric acid; the dispersant comprises polyethylene glycol and / or glycerol.

[0010] The main function of the acid pickling and ash removal in the chemical plating pretreatment process is to remove the black ash on the surface of the high-silicon die-casting aluminum alloy after alkaline washing, so that the metal substrate is fully exposed, and the surface of the substrate is slightly etched to have a certain roughness, thereby enhancing the adhesion of the subsequent plating layer. Therefore, the acid pickling and ash removal process is particularly important in the pretreatment of high-silicon die-casting aluminum alloy. In order to play the ash removal effect on the high-silicon die-casting aluminum alloy, the oxidizing agent, fluoride and acidic environment are indispensable. In the acid pickling and ash removal reaction, the above-mentioned pickling solution of the present application reacts and dissolves the black ash (silicides and metal compounds, etc.) generated on the surface of the high-silicon die-casting aluminum alloy by the alkaline washing reaction through the combination of strong oxidizing agents (such as ammonium persulfate, sodium chlorate, lanthanum nitrate, cerium nitrate) and fluorides (such as ammonium bifluoride), and is washed clean; at the same time, the use of organic acid copolymer (such as acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer) and organic phosphorus (such as diethylenetriamine pentamethylene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid) metal complexing agent can enhance the ability to remove ash, that is, the special metal compound ash that cannot be removed by the reaction of strong oxidizing agents and fluorides can be completely removed after complexing reaction; and in the acid pickling and ash removal reaction process, there is a certain etching reaction, in order to ensure the uniformity of the etching reaction on the surface of the substrate, it is necessary to introduce a non-foaming dispersant, the use of dispersant (such as polyethylene glycol, glycerol) can make the surface of the high-silicon die-casting aluminum alloy after acid pickling and ash removal by the above-mentioned pickling solution uniform and consistent, without producing defects such as mottling.

[0011] According to some embodiments of the present application, the acidic solution comprises components: ammonium persulfate 80±20g / L, sodium chlorate 20±10g / L, lanthanum nitrate 2±1g / L, cerium nitrate 2±1g / L, ammonium bifluoride 200±50g / L, acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer 20±5g / L, diethylenetriamine pentamethylene phosphonic acid 10±2g / L, 2-phosphonobutane-1,2,4-tricarboxylic acid 10±2g / L, polyethylene glycol 1.5±0.5g / L, glycerol 1.5±0.5g / L.

[0012] The main functions of the components in the above-mentioned pickling solution are as follows:

[0013] Ammonium persulfate as a strong oxidizing agent, in the high silicon die casting aluminum alloy washing process can play a role in the ash whitening effect, can ensure that the high silicon die casting aluminum alloy after surface treatment is relatively neat, not black, high silicon die casting aluminum alloy with ordinary acid pickling or alkaline process without strong oxidizing agent, the surface is easy to black, completely not ideal surface cleaning effect; when the concentration of ammonium persulfate is less than 60g / L, the surface of high silicon die casting aluminum alloy is easy to black, when the concentration of ammonium persulfate is greater than 100g / L, the high silicon die casting aluminum alloy after surface treatment has white stripes, the surface is uneven.

[0014] Sodium chlorate as an auxiliary strong oxidizing agent, mainly to the high silicon die casting aluminum alloy pickling process produced black ash play inhibition and completely remove effect; when its concentration is less than 10g / L, the surface of high silicon die casting aluminum alloy after pickling still has black ash, need to be manually wiped off, the operation is more troublesome, when its concentration is greater than 30g / L, the surface after pickling will also produce uneven spots or lines, seriously affect the surface treatment quality.

[0015] Cerium nitrate and lanthanum nitrate as brightener, oxidizing agent component, when the concentration of cerium nitrate or lanthanum nitrate is less than 1g / L, the surface after treatment is white but relatively matte, no brightness; concentration greater than 3g / L, although the surface is relatively white, but due to the cerium and lanthanum element exceeds the standard and easy to produce uneven distribution of small needle point, seriously affect the subsequent chemical plating surface quality.

[0016] The main role of ammonium bifluoride is to react with the surface of high silicon die casting aluminum alloy and remove the dirt such as release agent adhered to the surface, when the concentration of ammonium bifluoride is less than 150g / L, the surface of high silicon die casting aluminum alloy is weak, can not completely clean the release agent and other dirt adhered to the surface of high silicon die casting aluminum alloy, can not achieve the ideal cleaning effect, when the concentration is greater than 250g / L, the reaction is too intense and unstable, the reaction foam is more, the surface after cleaning is relatively rough, also can not achieve the ideal cleaning effect.

[0017] Acrylic acid-2-acrylamide-2-methyl propyl sulfonic acid copolymer can be used as a complexing agent, when the pickling tank liquid is used for a long time, the concentration of metal ions in it is high, which can complex with metal ions and will not produce sediment or crystallization phenomenon. When the concentration of acrylic acid-2-acrylamide-2-methyl propyl sulfonic acid copolymer is less than 15g / L, the pickling tank liquid will produce more sediment after a period of use, which seriously affects the subsequent cleaning effect and the stability of the tank liquid; but the concentration is greater than 25g / L, the surface of high silicon die casting aluminum alloy after pickling will appear pitting.

[0018] Diethylene triamine penta (methylene phosphonic acid) and 2-phosphonobutane-1,2,4-tricarboxylic acid as organic phosphorus chelating agent, have chelation effect on the surface of high silicon die-casting aluminum alloy metal ions, so that the color of the surface after treatment is more uniform. When the concentration of diethylene triamine penta (methylene phosphonic acid) or 2-phosphonobutane-1,2,4-tricarboxylic acid is less than 8g / L, the color of the surface after pickling treatment is uneven, and part of the surface area is bright, and part of the surface area is dark; when the concentration is greater than 12g / L, the surface after pickling has a bright band phenomenon, which also seriously affects the quality of the subsequent chemical plating layer.

[0019] Polyethylene glycol and glycerol as non-foaming wetting agent components can change the surface tension of the surface of high silicon die-casting aluminum alloy during cleaning, not only can help clean the surface oil stains, but also can play a good dispersion role, so that the surface after pickling is more uniform. When the concentration of polyethylene glycol or glycerol is less than 1g / L, the oil removal capacity of cleaning is not enough, and the surface after treatment may not be uniform enough; when the concentration is greater than 2g / L, the surface of high silicon die-casting aluminum alloy after pickling produces white spots due to too high concentration, which affects the quality of the subsequent chemical plating layer.

[0020] According to some embodiments of the present application, in the chemical nickel plating solution, the organic acid includes at least one of citric acid, aminoacetic acid, potassium sodium tartrate, tartaric acid, sulfosalicylic acid, and DL-malic acid; the reducing agent includes at least one of sodium hypophosphite, sodium borohydride, hydrazine sulfate, and alkyl amine borane; the nickel salt includes at least one of nickel sulfate, nickel chloride, nickel sulfamate, and nickel acetate; and the buffer includes at least one of sodium acetate, borax, and sodium pyrophosphate.

[0021] The reaction process of bright chemical nickel plating of high-silicon die-casting aluminum is a self-catalytic redox process. The above-mentioned chemical nickel plating solution reduces divalent nickel ions of nickel main salt (nickel sulfate, nickel chloride, nickel sulfamate, nickel acetate, etc.) to metallic nickel by a reducing agent (sodium hypophosphite, sodium borohydride, hydrazine sulfate, alkyl amine borane, etc.) to uniformly deposit on the surface of aluminum alloy to form a bright nickel plating layer. In the process of depositing nickel plating, a complexing agent (such as sodium potassium tartrate, citric acid, tartaric acid) with good collocation can control the concentration of free nickel ions available for reaction, inhibit the precipitation of nickel hypophosphite, improve the stability of the plating solution, prolong the service life of the plating solution, and at the same time, can improve the deposition rate of the plating solution, and play the role of an accelerator. Due to the generation of hydrogen ions as a byproduct in the chemical nickel plating reaction, the pH value of the plating solution will decrease, so a buffer (such as sodium acetate, borax, sodium pyrophosphate) is added to stabilize the pH value of the plating solution, so that the pH value of the plating solution is maintained within a normal range. At the same time, the addition of a chemical plating accelerator (such as thiourea, aminoacetic acid) can activate the hypophosphite ion, thereby improving the deposition rate of the chemical nickel plating and accelerating the film formation speed of the chemical nickel plating. The collocation and addition of brighteners (such as 1,4-butynediol, sodium saccharin, 2,2'-dipyridyl) in the chemical nickel plating solution can obtain a fully bright, flat and ductile plating layer.

[0022] According to some embodiments of the present application, the chemical nickel plating solution comprises the following components: sodium hypophosphite 35±5g / L, nickel sulfate 25±5g / L, potassium sodium tartrate 15±5g / L, citric acid 15±5g / L, thiourea 3±1mg / L, aminoacetic acid 3±1g / L, DL-malic acid 3±1g / L, sodium acetate 2±1g / L, 1,4-butynediol 1±0.2g / L, sodium saccharin 0.2±0.1mg / L, 2,2'-dipyridyl 0.2±0.1mg / L.

[0023] The main functions of each component in the above-mentioned chemical nickel plating solution are as follows:

[0024] Sodium hypophosphite, as a reducing agent, reduces nickel in the chemical nickel plating bath to the surface of high-silicon die-casting aluminum alloy. When the concentration is less than 30g / L, the reduction is not thorough enough, and the speed of chemical nickel plating on the surface of high-silicon die-casting aluminum alloy is too slow. If the concentration is greater than 40g / L, the concentration of the reducing agent is excessive, the speed of chemical nickel plating is too fast, and the plating layer is not uniform in thickness and not firm.

[0025] Nickel sulfate is the main salt of chemical nickel plating. When the concentration is less than 20g / L, the thickness of the chemical plating layer is not enough. When the concentration is greater than 30g / L, the thickness of the plating layer is not uniform, and the surface smoothness is not good.

[0026] The sodium potassium tartrate and citric acid mainly play a role of complexing nickel ions, so that the chemical nickel plating layer is good in flatness, and the plating layer is relatively dense and uniform.

[0027] The thiourea as a catalyst can accelerate the film forming speed of the chemical nickel plating layer in a proper small amount, and when the concentration is less than 2 mg / L, the effect of catalyzing and accelerating the film forming speed cannot be achieved, and when the concentration is greater than 4 mg / L, the catalyst is excessive, so that pinholes, pitting and other defects are generated on the surface of the chemical nickel plating layer, and the surface effect is seriously affected.

[0028] The aminoacetic acid and DL-malic acid as metal ion chelating agents play an effect of promoting uniform precipitation of metal nickel on the surface of the high-silicon die-casting aluminum alloy during the chemical nickel plating; when the concentration is less than 2 g / L, the promoting effect cannot be achieved, and when the concentration is greater than 4 g / L, the nickel precipitation is non-uniform, so that the surface of the chemical nickel plating is rough and uneven.

[0029] The 1,4-butynediol can improve the surface morphology and microstructure of the nickel plating layer, improve the battery reaction efficiency and dispersion capacity of the plating solution, reduce the tensile stress of the plating layer, and make the surface more smooth; when the concentration is less than 0.8 g / L, the surface of the chemical nickel plating layer is not delicate and smooth, and when the concentration is greater than 1.2 g / L, the surface of the chemical nickel plating layer is prone to being gray and peeled, and the surface effect of the nickel plating layer is affected.

[0030] The sodium saccharin and 2,2'-dipyridyl as brighteners of the chemical nickel plating layer play a role of reducing the influence of metal impurities, and can also synergistically increase the brightness, and the amount is very small; when the concentration is less than 0.1 mg / L, the glossiness of the chemical nickel plating layer is not enough, and when the concentration is greater than 0.3 mg / L, the surface leveling property of the chemical nickel plating layer is affected, and the surface smoothness is poor.

[0031] According to some embodiments of the present application, the chemical nickel plating solution further comprises components: a surfactant and a rare earth compound.

[0032] According to some embodiments of the present application, the surfactant comprises at least one of sodium dodecyl sulfate, sodium n-octyl sulfate and sodium dodecyl benzene sulfonate; and the rare earth compound comprises lanthanum sulfate and / or cerium sulfate.

[0033] In the process of electroless nickel plating, sometimes continuous hydrogen bubbles generated on the surface of the plated part can cause the underlying layer to produce stripes or pockmarks. The addition of surfactants such as sodium dodecyl sulfate, sodium n-octyl sulfate, and sodium dodecyl benzene sulfonate can help the escape of gas on the surface of the workpiece, reducing the porosity of the coating. Rare earth elements can improve the throwing power and dispersing power of the plating solution in electroless plating. A small amount of rare earth compounds such as lanthanum sulfate and cerium sulfate can significantly improve the plating layer of the plating solution and improve the wear resistance and corrosion resistance of the coating.

[0034] According to some embodiments of the present application, the electroless nickel plating solution further comprises the following components: 0.2±0.1g / L of sodium dodecyl sulfate and 0.1±0.05g / L of lanthanum sulfate.

[0035] The second aspect of the present application provides a method for electroless nickel plating of high-silicon die-casting aluminum alloy, which comprises the steps of pickling and electroless nickel plating after the pickling. The pickling solution used in the pickling is the acidic solution according to the present application. The plating solution used in the electroless nickel plating is the electroless nickel plating solution according to the present application.

[0036] According to some embodiments of the present application, the operating conditions of the pickling include a temperature of 20-30℃ and a time of 1-5 minutes.

[0037] According to some embodiments of the present application, the operating conditions of the electroless nickel plating include a pH of 4.6-5.2, a temperature of 80-85℃, a plating rate of 13-14μm / h, and a time of 40-60 minutes.

[0038] According to some embodiments of the present application, before the pickling, the method further comprises the step of removing oil and water washing the high-silicon die-casting aluminum alloy.

[0039] According to some embodiments of the present application, the specific process of oil removal is to immerse the high-silicon die-casting aluminum alloy in an alkaline solution for alkaline cleaning, with a cleaning temperature of 40-50℃ and a time of 2-5 minutes.

[0040] According to some embodiments of the present application, before the electroless nickel plating, the method further comprises the step of water washing, surface activation, and again water washing the high-silicon die-casting aluminum alloy after the pickling.

[0041] According to some embodiments of the present application, the specific process of surface activation is to immerse the high-silicon die-casting aluminum alloy in a nitric acid solution with a mass concentration of 40-45% at room temperature for 30-60 seconds. Room temperature in the present application refers to 20-30℃.

[0042] According to some embodiments of the present application, after the electroless nickel plating, the method further comprises the step of water washing, sealing treatment, again water washing, and drying the high-silicon die-casting aluminum alloy after the electroless nickel plating.

[0043] According to some embodiments of the present application, the specific process of the sealing treatment is that the high-silicon die-casting aluminum alloy is immersed in a polyacrylic resin liquid and soaked at room temperature for 2-5 minutes.

[0044] According to some embodiments of the present application, the operation conditions of the drying include that the drying temperature is 60-70℃ and the drying time is 15-30 minutes.

[0045] The third aspect of the present application provides a high-silicon die-casting aluminum alloy composite material prepared by the electroless plating method of the high-silicon die-casting aluminum alloy, which comprises a high-silicon die-casting aluminum alloy substrate and a nickel plating layer attached to the surface of the high-silicon die-casting aluminum alloy substrate, and the surface gloss of the high-silicon die-casting aluminum alloy composite material is ≥600GU.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] The composition of the present application comprises an acidic liquid and an electroless nickel plating liquid, wherein the acidic liquid can completely replace the traditional hydrofluoric acid + nitric acid pickling system, no dangerous or polluting gas is released during the pickling process, and the ash removal and whitening ability is good. The surface flatness and color of the high-silicon die-casting aluminum alloy after pickling are significantly better than the treatment effect of the traditional hydrofluoric acid + nitric acid system, even if the high-silicon die-casting aluminum alloy adheres to a large amount of irregularly shaped release agent and other dirt, after the treatment of the acidic liquid of the present application, the surface is bright and clean, the color is uniform, thereby ensuring the subsequent effective electroless nickel plating process; at the same time, the nickel plating layer obtained by the treatment of the electroless nickel plating liquid of the present application has high gloss, good corrosion resistance, good wear resistance, high hardness, smooth and flat surface, good self-cleaning property, good adhesion between the film layer and the substrate, which is very suitable for the requirements of high-functionality and high-decorative film layer, and the electroless nickel plating liquid system has good stability, long service life, fast plating speed and mirror-like brightness, and the comprehensive performance is better than that of the traditional electroplating process, the operation process is simpler, and the comprehensive treatment cost is lower. DETAILED DESCRIPTION

[0048] In order to make the skilled in the art more clearly understand the technical solutions of the present application, the following examples are used for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0049] The raw materials, reagents or devices used in the following examples are commercially available or can be obtained by existing technical methods unless otherwise specified. Unless otherwise specified, the test or test method is a conventional method in the art.

[0050] Example 1

[0051] The embodiment provides a composition for electroless plating of high-silicon die-casting aluminum alloy.

[0052] The composition comprises an acidic solution and an electroless nickel plating solution; wherein the acidic solution is composed of the following components:

[0053] 80 g / L of ammonium persulfate, 20 g / L of sodium chlorate, 2 g / L of lanthanum nitrate, 2 g / L of cerium nitrate, 200 g / L of ammonium hydrogen fluoride, 20 g / L of acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer, 10 g / L of diethylene triamine pentaformyl phosphonic acid, 10 g / L of 2-phosphonobutane-1,2,4-tricarboxylic acid, 1.5 g / L of polyethylene glycol, 1.5 g / L of glycerol, and the balance being water;

[0054] The electroless nickel plating solution is composed of the following components:

[0055] 35 g / L of sodium hypophosphite, 25 g / L of nickel sulfate, 15 g / L of potassium sodium tartrate, 15 g / L of citric acid, 3 mg / L of thiourea, 3 g / L of aminoacetic acid, 3 g / L of DL-malic acid, 2 g / L of sodium acetate, 1 g / L of 1,4-butynediol, 0.2 mg / L of sodium saccharin, 0.2 mg / L of 2,2'-bipyridine, 0.2 g / L of sodium dodecyl sulfate, 0.1 g / L of lanthanum sulfate, and the balance being water.

[0056] Embodiment 2

[0057] The embodiment provides a composition for electroless plating of high-silicon die-casting aluminum alloy.

[0058] The composition comprises an acidic solution and an electroless nickel plating solution; wherein the acidic solution is composed of the following components:

[0059] 60 g / L of ammonium persulfate, 10 g / L of sodium chlorate, 1 g / L of lanthanum nitrate, 1 g / L of cerium nitrate, 150 g / L of ammonium hydrogen fluoride, 15 g / L of acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer, 8 g / L of diethylene triamine pentaformyl phosphonic acid, 8 g / L of 2-phosphonobutane-1,2,4-tricarboxylic acid, 1 g / L of polyethylene glycol, 1 g / L of glycerol, and the balance being water;

[0060] The electroless nickel plating solution is composed of the following components:

[0061] 30 g / L of sodium hypophosphite, 20 g / L of nickel sulfate, 10 g / L of potassium sodium tartrate, 10 g / L of citric acid, 2 mg / L of thiourea, 2 g / L of aminoacetic acid, 2 g / L of DL-malic acid, 1 g / L of sodium acetate, 0.8 g / L of 1,4-butynediol, 0.1 mg / L of sodium saccharin, 0.1 mg / L of 2,2'-bipyridine, 0.1 g / L of sodium dodecyl sulfate, 0.05 g / L of lanthanum sulfate, and the balance being water.

[0062] Example 3

[0063] The present embodiment provides a composition for electroless plating of high-silicon die-casting aluminum alloy.

[0064] The composition comprises an acidic solution and an electroless nickel plating solution; wherein the acidic solution is composed of the following components:

[0065] 100 g / L of ammonium persulfate, 30 g / L of sodium chlorate, 3 g / L of lanthanum nitrate, 3 g / L of cerium nitrate, 250 g / L of ammonium hydrogen fluoride, 25 g / L of acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer, 12 g / L of diethylenetriamine pentamethylene phosphonic acid, 12 g / L of 2-phosphonobutane-1,2,4-tricarboxylic acid, 2 g / L of polyethylene glycol, 2 g / L of glycerol, and the balance being water;

[0066] The electroless nickel plating solution is composed of the following components:

[0067] 40 g / L of sodium hypophosphite, 30 g / L of nickel sulfate, 20 g / L of potassium sodium tartrate, 20 g / L of citric acid, 4 mg / L of thiourea, 4 g / L of aminoacetic acid, 4 g / L of DL-malic acid, 3 g / L of sodium acetate, 1.2 g / L of 1,4-butynediol, 0.3 mg / L of sodium saccharin, 0.3 mg / L of 2,2'-bipyridine, 0.3 g / L of sodium dodecyl sulfate, 0.15 g / L of lanthanum sulfate, and the balance being water.

[0068] Comparative Example 1

[0069] The present comparative example 1 provides a composition for electroless plating of high-silicon die-casting aluminum alloy, which is different from example 1 in that the acidic solution in comparative example 1 does not contain lanthanum nitrate and cerium nitrate, and the remaining components of the acidic solution and the electroless nickel plating solution are the same as in example 1.

[0070] Comparative Example 2

[0071] The present comparative example 2 provides a composition for electroless plating of high-silicon die-casting aluminum alloy, which is different from example 1 in that the acidic solution in comparative example 2 does not contain diethylenetriamine pentamethylene phosphonic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid, and the remaining components of the acidic solution and the electroless nickel plating solution are the same as in example 1.

[0072] Comparative Example 3

[0073] Comparative Example 3 provides a composition for electroless plating of high-silicon die-casting aluminum alloy, which is different from Example 1 in that the electroless nickel plating solution in Comparative Example 3 does not contain thiourea, and the remaining components of the electroless nickel plating solution and the acidic solution are the same as in Example 1.

[0074] Comparative Example 4

[0075] Comparative Example 4 provides a composition for electroless plating of high-silicon die-casting aluminum alloy, which is different from Example 1 in that the electroless nickel plating solution in Comparative Example 4 does not contain sodium saccharin and 2,2'-bipyridine, and the remaining components of the electroless nickel plating solution and the acidic solution are the same as in Example 1.

[0076] Application Example 1

[0077] Application Example 1 provides a high-silicon die-casting aluminum alloy composite material.

[0078] The high-silicon die-casting aluminum alloy composite material includes a high-silicon die-casting aluminum alloy substrate and a nickel plating layer attached to the surface of the high-silicon die-casting aluminum alloy substrate; the nickel plating layer is prepared by electroless plating using the composition of Example 1, and the specific preparation process of electroless plating is as follows:

[0079] 1) Soak the high-silicon die-casting aluminum alloy in an alkaline solution at 40°C for 2 minutes to remove oil, and then wash with water; the composition of the alkaline solution is: sodium carbonate 2wt%, sodium tetraborate 1wt%, layered sodium disilicate 1wt%, trisodium citrate 0.5wt%, sodium gluconate 0.5wt%, AEO-9 surfactant 0.1wt%, German WinChem G-16 surfactant 0.1wt%, and water in balance;

[0080] 2) Soak the high-silicon die-casting aluminum alloy treated in step 1) in the acidic solution provided in Example 1 at 25°C for 1 minute, and then wash with water;

[0081] 3) Soak the high-silicon die-casting aluminum alloy treated in step 2) in a 40% mass concentration nitric acid solution at 25°C for 30 seconds, and then wash with water;

[0082] 4) Soak the high-silicon die-casting aluminum alloy treated in step 3) in the electroless nickel plating solution (pH 5.0) provided in Example 1 at 80°C for 60 minutes, and then wash with water;

[0083] 5) Soak the high-silicon die-casting aluminum alloy treated in step 4) in a polyacrylic resin liquid at 25°C for 2 minutes, and then wash with water, followed by drying at 60°C for 15 minutes to obtain a high-silicon die-casting aluminum alloy composite material.

[0084] The high-silicon die-casting aluminum alloy after step 2) has a bright and uniform surface, no blackening, and no residual dirt such as release agent on the surface, and has good surface flatness.

[0085] The high-silicon die-casting aluminum alloy composite material of the application example has a nickel plating layer on the surface with a thickness of 13 μm (measured by a film thickness meter), a fast plating speed on the plating layer (13 μm / h), a mirror-like bright plating layer (measured by a visual method), a glossiness of 700 GU, a plating layer hardness of more than HB (measured by a pencil hardness method), a good plating layer adhesion (measured by a grid method, no plating layer falling off between two grid lines), and good surface flatness of the plating layer with a porosity of 2-5 pieces / cm (measured by a filter paper method). 2 The plating layer has good corrosion resistance, and no discoloration, no blistering, and no falling off of the plating layer after neutral salt spray for 48 h (NSS neutral salt spray test).

[0086] Application Example 2

[0087] The application example 2 provides a high-silicon die-casting aluminum alloy composite material.

[0088] The high-silicon die-casting aluminum alloy composite material comprises a high-silicon die-casting aluminum alloy substrate and a nickel plating layer attached to the surface of the high-silicon die-casting aluminum alloy substrate, and the nickel plating layer is prepared by chemical plating using the composition of the application example 2.

[0089] 1) The high-silicon die-casting aluminum alloy is immersed in an alkali solution, soaked for 5 minutes at 45°C for oil removal, and then taken out for water washing; the alkali solution has the same composition as the alkali solution used in the application example 1.

[0090] 2) The high-silicon die-casting aluminum alloy after step 1) is immersed in the acidic solution provided in the application example 2, soaked for 5 minutes at 25°C, and then taken out for water washing.

[0091] 3) The high-silicon die-casting aluminum alloy after step 2) is immersed in a 40% nitric acid solution, soaked for 60 seconds at 25°C, and then taken out for water washing.

[0092] 4) The high-silicon die-casting aluminum alloy after step 3) is immersed in the chemical nickel plating solution (pH 4.6) provided in the application example 2, soaked for 40 minutes at 85°C, and then taken out for water washing.

[0093] 5) The high-silicon die-casting aluminum alloy after step 4) is immersed in a polyacrylic resin liquid, soaked for 5 minutes at 25°C, taken out for water washing, and then baked at 70°C for 20 minutes to obtain the high-silicon die-casting aluminum alloy composite material.

[0094] The performance of the nickel plating layer on the surface of the high-silicon die-casting aluminum alloy composite material of the application example has no obvious difference from that of the application example 1.

[0095] Application Example 3

[0096] The application example 3 provides a high-silicon die-casting aluminum alloy composite material.

[0097] The high-silicon die-casting aluminum alloy composite material comprises a high-silicon die-casting aluminum alloy base and a nickel plating layer attached to the surface of the high-silicon die-casting aluminum alloy base; the nickel plating layer is prepared by electroless plating using the composition of the embodiment 3, and the specific preparation process of the electroless plating is as follows:

[0098] 1) The high-silicon die-casting aluminum alloy is immersed in an alkali solution, soaked for 3 minutes at 50°C, and then taken out for water washing to remove oil; the composition of the alkali solution is the same as that of the alkali solution used in the application example 1;

[0099] 2) The high-silicon die-casting aluminum alloy treated in the step 1) is immersed in the acidic solution provided in the embodiment 3, soaked for 3 minutes at 25°C, and then taken out for water washing;

[0100] 3) The high-silicon die-casting aluminum alloy treated in the step 2) is immersed in a 40% nitric acid solution, soaked for 40 seconds at 25°C, and then taken out for water washing;

[0101] 4) The high-silicon die-casting aluminum alloy treated in the step 3) is immersed in the electroless nickel plating solution (pH is 5.2) provided in the embodiment 3, soaked for 60 minutes at 80°C, and then taken out for water washing;

[0102] 5) The high-silicon die-casting aluminum alloy treated in the step 4) is immersed in a polyacrylic resin liquid, soaked for 3 minutes at 25°C, taken out for water washing, and then baked at 65°C for 30 minutes to obtain the high-silicon die-casting aluminum alloy composite material.

[0103] The performance of the nickel plating layer on the surface of the high-silicon die-casting aluminum alloy composite material of the application example is not obviously different from that of the application example 1.

[0104] Comparative application example 1

[0105] The comparative application example 1 provides a high-silicon die-casting aluminum alloy composite material, which is different from the application example 1 in that the nickel plating layer of the comparative application example 1 is prepared by electroless plating using the composition of the comparative example 1, and the preparation process of the electroless plating is the same as that of the application example 1.

[0106] The high-silicon die-casting aluminum alloy in the comparative application example 1 is immersed in the acidic solution of the comparative example 1, and then taken out for water washing, and the surface of the high-silicon die-casting aluminum alloy is whitish and not bright, without any luster, and does not turn black, and the luster of the nickel plating layer is affected after the treatment in the electroless plating process, and the luster is relatively low, lower than 400GU.

[0107] Comparative application example 2

[0108] The comparative application example 2 provides a high-silicon die-casting aluminum alloy composite material, which is different from the application example 1 in that the nickel plating layer of the comparative application example 2 is prepared by electroless plating using the composition of the comparative example 2, and the preparation process of the electroless plating is the same as that of the application example 1.

[0109] The high-silicon die-casting aluminum alloy in the comparative application example 2 is soaked in the acidic liquid of the comparative example 2, and after water washing, the surface is black and not white, and mottling occurs on the surface, and after entering the next electroless plating process, the surface is also black and not white, and mottling occurs, which seriously affects the visual effect and quality of the electroless plating layer.

[0110] The comparative application example 3

[0111] The comparative application example 3 provides a high-silicon die-casting aluminum alloy composite material, which is different from the application example 1 in that the nickel plating layer of the comparative application example 3 is prepared by electroless plating using the composition of the comparative example 3, and the preparation process of the electroless plating is the same as that of the application example 1.

[0112] The thickness of the nickel plating layer obtained in the comparative application example 3 is 8 μm, the thickness is relatively thin, the plating layer has a slow film forming speed, the hardness of the plating layer is not enough, reaches only 2B (pencil hardness method), the bonding force of the plating layer is good (crosshatch method, the plating layer between two lines has no any part falling off), and the corrosion resistance of the plating layer is poor, the plating layer has discoloration phenomenon after neutral salt spray (NSS neutral salt spray test) for 48 h.

[0113] The comparative application example 4

[0114] The comparative application example 4 provides a high-silicon die-casting aluminum alloy composite material, which is different from the application example 1 in that the nickel plating layer of the comparative application example 4 is prepared by electroless plating using the composition of the comparative example 4, and the preparation process of the electroless plating is the same as that of the application example 1.

[0115] The glossiness of the nickel plating layer obtained in the comparative application example 4 is poor, and the glossiness is 400 GU.

[0116] The preferred embodiments of the application are specifically described above, but the application is not limited to the described embodiments, and those skilled in the art can make various equivalent modifications or replacements without departing from the spirit of the application, and these equivalent modifications or replacements are all included in the scope defined by the claims of the application.

Claims

1. A method for electroless plating of a high-silicon die cast aluminum alloy, characterized by, The acid pickling solution comprises the following components: ammonium persulfate 80±20 g / L, sodium chlorate 20±10 g / L, lanthanum nitrate 2±1 g / L, cerium nitrate 2±1 g / L, ammonium hydrogen fluoride 200±50 g / L, acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer 20±5 g / L, diethylene triamine pentaformyl phosphonic acid 10±2 g / L, 2-phosphonobutane-1,2,4-tricarboxylic acid 10±2 g / L, polyethylene glycol 1.5±0.5 g / L, glycerol 1.5±0.5 g / L; the plating solution for electroless nickel plating comprises the following components: sodium hypophosphite 35±5 g / L, nickel sulfate 25±5 g / L, potassium sodium tartrate 15±5 g / L, citric acid 15±5 g / L, thiourea 3±1 mg / L, aminoacetic acid 3±1 g / L, DL-malic acid 3±1 g / L, sodium acetate 2±1 g / L, 1,4-butynediol 1±0.2 g / L, sodium saccharin 0.2±0.1 mg / L, 2,2'-dipyridyl 0.2±0.1 mg / L.

2. The electroless plating method of high-silicon die-cast aluminum alloy according to claim 1, characterized by, The operation conditions of the acid pickling include that the temperature of the acid pickling is 20-30℃, and the time of the acid pickling is 1-5 minutes.

3. The electroless plating method of high-silicon die-cast aluminum alloy according to claim 1, characterized by, The operation conditions of the electroless nickel plating include that the pH of the plating solution is 4.6-5.2, the temperature of the plating solution is 80-85℃, the plating speed is 13-14 μm / h, and the time of the electroless nickel plating is 40-60 minutes.

4. The electroless plating method of high-silicon die-cast aluminum alloy according to claim 1, characterized by, Before the electroless nickel plating, the acid-pickled high-silicon die-casting aluminum alloy is subjected to water washing, surface activation, and re-water washing.

5. A high-silicon die cast aluminum alloy composite material, characterized by, The high-silicon die-casting aluminum alloy composite material comprises a high-silicon die-casting aluminum alloy substrate and a nickel plating layer attached to the surface of the high-silicon die-casting aluminum alloy substrate, and the surface glossiness of the high-silicon die-casting aluminum alloy composite material is ≥600 GU.