Surface treatment process and application of copper-clad aluminum composite material

Abstract

The invention relates to a copper-clad aluminum composite material surface treatment process and application, and relates to the field of metal surface treatment.The surface treatment process comprises the steps that a copper-clad aluminum workpiece subjected to oil removal pretreatment is subjected to acid activation and secondary activation after water washing; the workpiece subjected to secondary activation is immersed in a zinc immersion solution, so that a zinc transition layer is obtained on the surface of the workpiece; and the workpiece with the obtained zinc transition layer is washed with water and then soaked in a plating solution so that a layer of phosphorus chemical nickel can be plated on the surface of the zinc layer, then the workpiece is soaked in a chromium solution to be passivated, and the nickel-plated copper-clad aluminum composite material is obtained after washing and drying. The surface treatment process provided by the invention is free of current limitation, uniform in plating layer and controllable in thickness; the binding force is strong, the hardness is high and the wear resistance is good; the corrosion resistance is good, the porosity is low, and the method is suitable for complex structures and high-requirement scenes.

Description

Technical Field

[0001] The present invention belongs to the field of metal surface treatment, particularly relates to nickel-plated copper-clad aluminum materials, and specifically relates to a surface treatment process and application of copper-clad aluminum composite materials. Background Art

[0002] Copper-Clad Aluminum (CCA) is a composite material with an aluminum core and a copper layer coated on the outer layer, combining the excellent electrical conductivity of copper (conductivity ≥ 95% IACS) and the lightweight advantage of aluminum (density is only 30% of copper), and is widely used in industries such as high-frequency cables, electronic connectors, and automotive wire harnesses. However, due to the large potential difference between copper and aluminum (ΔE > 1.2V), in complex environments such as humidity or salt spray, copper-clad aluminum is extremely prone to galvanic corrosion, resulting in oxidation of the copper-aluminum interface and peeling of the coating, severely shortening the service life of the product. This problem has become a key bottleneck restricting the further popularization and application of copper-clad aluminum materials.

[0003] Currently, the surface treatment technologies for copper-clad aluminum in the industry mainly include electroplating nickel, pure nickel electroplating, and electroless nickel plating on steel substrates, etc. Although the electroplating nickel process has a simple process, it has problems such as poor adhesion and high porosity, and the plating solution contains a large amount of heavy metal components, which not only harms the environment but also makes it difficult to ensure the stability of the copper-aluminum interface; pure nickel electroplating requires multiple plating operations, with defects such as uneven coating thickness, high cost, and poor corrosion resistance; the electroless nickel plating process on steel substrates does not fully consider the characteristics of copper-aluminum materials, and the plating solution is extremely sensitive to copper ions, easily causing pollution and unable to effectively solve the corrosion problem of copper-clad aluminum.

[0004] Therefore, developing a surface treatment technology for copper-clad aluminum with high corrosion resistance and high adhesion has become an urgent need in the industry. Summary of the Invention

[0005] The purpose of the present invention is to provide a surface treatment process and application of copper-clad aluminum composite materials, which solves problems such as corrosion at the copper-aluminum interface and poor coating uniformity by optimizing the substrate pretreatment and post-treatment processes.

[0006] The present invention achieves the above purpose through the following technical solutions:

[0007] A surface treatment process for copper-clad aluminum composite materials, comprising the following steps:

[0008] (1) Acid-activate the copper-clad aluminum workpiece after degreasing pretreatment, wash it with water, and then perform secondary activation;

[0009] (2) Immerse the workpiece after secondary activation in a zinc immersion solution to obtain a zinc transition layer on the surface of the workpiece;

[0010] (3) After the workpiece with the zinc transition layer is washed with water, it is immersed in the plating solution to deposit a layer of medium-phosphorus electroless nickel on the surface of the zinc layer, and then the workpiece is immersed in the chromium solution for passivation. After washing with water and drying, the nickel-plated copper-clad aluminum composite material is obtained.

[0011] As a further optimized solution of the above invention, the degreasing pretreatment is to immerse the workpiece in the degreasing agent and perform ultrasonic treatment, wherein the degreasing agent includes at least one of silicate, hydroxide, and phosphate. The ultrasonic power is 25 - 30 KHz, the current ≥ 6 A, and pH = 9 - 12.

[0012] As a further optimized solution of the above invention, the acid activation is to immerse the workpiece in a 10 - 15% HCl solution by mass concentration for 45 - 60 s.

[0013] As a further optimized solution of the above invention, the secondary activation is to immerse the workpiece in a mixed acid composed of 5 - 10% HNO3 by mass concentration and 0.5 - 1 g / L thiourea for 30 - 60 s.

[0014] As a further optimized solution of the above invention, the zinc immersion solution includes 5 - 10 g / L ZnO, 50 - 100 g / L NaOH, 5 - 15 g / L sodium potassium tartrate, 2 - 5 g / L ferric chloride, 1 - 5 g / L sodium nitrate, the temperature is 16 - 27 °C, pH = 12 - 14, and the immersion time is 45 - 60 s.

[0015] As a further optimized solution of the above invention, the plating solution immersion time is 60 - 120 min. The composition of the plating solution includes nickel salt, reducing agent, complexing agent, and stabilizer. The nickel salt is one of nickel sulfate or nickel chloride, and the pH of the plating solution is 4 - 5.

[0016] As a further optimized solution of the above invention, the reducing agent is sodium hypophosphite, the complexing agent is a mixture of sodium citrate and sodium acetate, and the stabilizer is a thiourea derivative.

[0017] As a further optimized solution of the above invention, the chromium solution is trivalent chromium solution. The trivalent chromium solution includes 1 - 1.5 g / L chromium nitrate, 0.8 - 1.2 g / L oxalic acid, 3 - 5 g / L sodium nitrate, the immersion time is 60 - 120 s, and pH = 1.8 - 2.2.

[0018] As a further optimized solution of the above invention, the water washing is 2 - 3 passes of water washing.

[0019] A nickel-plated copper-clad aluminum composite material is obtained by the above surface treatment process.

[0020] The beneficial effects of the present invention are as follows:

[0021] In terms of coating quality, the nickel plating process of the present invention completely breaks through the limitation of current distribution by virtue of the autocatalytic reaction mechanism, and can form a coating with uniform thickness on the surfaces of complex structures such as blind holes, deep grooves, threads, etc., thoroughly solving the problems of excessive thickness at the corners and missing plating in the inner cavity caused by uneven distribution of power lines in electroplated nickel. At the same time, the coating thickness can be precisely controlled by accurately controlling the reaction time (usually 10 - 25μm / h), without additional machining, greatly improving the production efficiency and product accuracy.

[0022] In terms of bonding strength and mechanical properties, the electroless nickel plating layer prepared by the present invention forms a diffusion bond with the substrate, and the bonding strength is as high as over 400MPa, far higher than 200MPa of electroplated nickel. For the aluminum substrate treated by zinc immersion, the bonding strength is increased by more than 30%. In addition, the hardness of the electroless nickel plating layer reaches 400 - 600HV, with excellent wear resistance, and the amorphous Ni - P alloy structure has no grain boundary defects. The salt spray test in 5% NaCl solution can reach 72 hours, and the corrosion resistance far exceeds 24 hours of electroplated nickel. The seawater corrosion resistance is comparable to that of titanium alloy, and the dense and pore - free coating can effectively isolate the penetration of corrosive media.

[0023] In terms of process adaptability and environmental protection and economy, the nickel plating process of the present invention can be applied to non - conductive and complex metal surfaces for plating. The equipment is simple, without a power supply and an anode, suitable for small - batch and multi - variety production; the plating solution does not contain cyanide or hexavalent chromium, the wastewater treatment cost is low, and the one - time qualification rate of electroless nickel plating on aluminum alloy reaches over 95%, and the comprehensive cost is reduced by 20% - 30%, achieving a double improvement in environmental protection and economic benefits. Description of the Drawings

[0024] Figure 1 Front - view metallographic detection and analysis diagrams of the coating uniformity and thickness for Example 1 and Comparative Examples 1 - 3; A - Example 1, B - Comparative Example 1, C - Comparative Example 2, D - Comparative Example 3;

[0025] Figure 2 Side - view metallographic detection and analysis diagrams of the coating uniformity and thickness for Example 1 and Comparative Examples 1 - 3; A - Example 1, B - Comparative Example 1, C - Comparative Example 2, D - Comparative Example 3;

[0026] Figure 3 Comparison diagrams before and after the salt spray test for Example 1 and Comparative Examples 1 - 3. Detailed Embodiments

[0027] The following further describes the present application in detail with reference to the drawings. It is necessary to point out here that the following detailed embodiments are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non - essential improvements and adjustments to the present application based on the above application content.

[0028] 1. Description

[0029] In the present invention, the copper-clad aluminum workpiece has an aluminum core with a copper layer coated on the outside. There are holes on the copper-clad aluminum workpiece, and the aluminum at both ends and the drilled parts are exposed. The total volume of the copper layer accounts for about 25% of all materials.

[0030] In at least one embodiment of the present invention, a surface treatment process for copper-clad aluminum composite materials is disclosed, including the following steps:

[0031] Step 1: Immerse the copper-clad aluminum workpiece in a degreasing agent for 5 - 15 minutes. The degreasing agent used includes silicate, hydroxide, and phosphate; in the following tests, the degreasing agent is a mixture of sodium silicate pentahydrate, sodium hydroxide, and trisodium phosphate.

[0032] Step 2: Perform ultrasonic degreasing with an ultrasonic power of 25 - 30 KHz and a current ≥ 6 A. Immerse the copper-clad aluminum workpiece soaked in the degreasing agent in Step 1 for ultrasonic degreasing. The pH is 9 - 12, and the time is 5 - 10 minutes to further promote the degreasing treatment of the surface of the workpiece by the degreasing agent.

[0033] Step 4: Immerse the copper-clad aluminum workpiece in a 10 - 15% mass concentration HCl solution to remove the oxide film on the surface of the copper layer for about 45 - 60 seconds.

[0034] Step 5: Immerse the copper-clad aluminum workpiece in a mixed acid of 5 - 10% mass concentration HNO3 and 0.5 - 1 g / L thiourea to remove the oxide layer on the surface of the exposed aluminum layer, reduce the surface roughness of the copper layer (Ra < 0.5 μm), and reduce plating defects. The immersion time is 30 - 60 seconds.

[0035] Step 6: Immerse the copper-clad aluminum workpiece in a zinc immersion solution to form a zinc immersion transition layer on the surface of the exposed aluminum layer (ZnO 5 - 10 g / L, NaOH 50 - 100 g / L, sodium potassium tartrate 5 - 15 g / L, ferric chloride 2 - 5 g / L, sodium nitrate 1 - 5 g / L, temperature 16 - 27 °C, pH 12 - 14), relieve the potential difference between copper and aluminum, and enhance the adhesion of the subsequent plating layer. The immersion time is 45 - 60 seconds.

[0036] Step 7: Immerse the copper-clad aluminum workpiece washed in Step 6 in a plating solution. The plating solution includes one of nickel sulfate and nickel chloride. Main salt: nickel sulfate (20 - 30 g / L), reducing agent: sodium hypophosphite (25 - 35 g / L), complexing agent: sodium citrate + sodium acetate (20 - 30 + 10 - 15 g / L), and stabilizer: thiourea derivative (0.01 - 0.05 g / L) to inhibit the self-decomposition of the plating solution. The temperature environment of the plating solution is 85 - 90 °C, the pH environment is 4.0 - 5.0, and the nickel plating time is about 60 - 120 minutes to further improve the brightness and performance of the workpiece surface, and improve hardness, wear resistance, and corrosion resistance.

[0037] Step 8) After electroless nickel plating, soak it in trivalent chromium passivation solution, including chromium nitrate 1 - 1.5 g / L, oxalic acid 0.8 - 1.2 g / L, sodium nitrate 3 - 5 g / L, soak for 60 - 120 s, pH = 1.8 - 2.2, to form a dense Cr(OH)3 - Cu(OH)2 film, and complete the preparation of nickel-plated copper-clad aluminum composite material.

[0038] The methods used in the present invention are all conventional methods known to those skilled in the art without special instructions. The reagents and other materials used are all commercially available products without special instructions. The instruments used are all conventional instruments known to those skilled in the art without special instructions.

[0039] 2. Test preparation

[0040] Example 1

[0041] The surface treatment process of the copper-clad aluminum composite material in this example includes the following steps:

[0042] 1) Degreasing: Immerse the copper-clad aluminum workpiece in a degreasing agent with pH = 13, which is a mixture of sodium metasilicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1. Degrease at 60 °C for 5 min, and then perform 2 - 3 rinses with water; then immerse the workpiece in the degreasing agent again for ultrasonic degreasing, with an ultrasonic power of about 25 KHz, for 10 min, and the ultrasonic temperature is 60 °C. Rinse the workpiece with water 2 - 3 times again;

[0043] 2) Acidification: Immerse the above workpiece in a 10% HCl solution to remove the oxide film on the aluminum layer surface for 45 s;

[0044] 3) Secondary acidification activation: Then immerse the above workpiece in a mixed acid solution of 5% mass concentration of HNO3 and 0.5 g / L of thiourea for 30 s;

[0045] 4) Zinc immersion: Immerse the activated workpiece above in a mixed solution of ZnO 6 g / L, NaOH 60 g / L, sodium potassium tartrate 80 g / L, ferric chloride 2 g / L, and sodium nitrate 1 g / L, at a temperature of 27 °C, pH = 12, for 45 s;

[0046] 5) Electroless nickel plating: After washing the workpiece with the zinc transition layer, soak it in the plating solution, and deposit a layer of medium-phosphorus electroless nickel nickel sulfate on the zinc layer surface. The composition of the plating solution: nickel sulfate 30 g / L, sodium hypophosphite 35 g / L, sodium citrate 20 g / L, sodium acetate 15 g / L, thiourea derivative 0.05 g / L. The plating solution environment is 88 °C, the pH environment is 4.0, and the immersion plating time is 120 min; after nickel plating is completed, rinse the workpiece 2 - 3 times with water;

[0047] 6) Passivation: Immerse the workpiece after water washing into a chromium nitrate mixed solution with a chromium nitrate concentration of 1.5 g / L, oxalic acid of 0.8 g / L, and sodium nitrate of 5 g / L for 60 s at a pH of 2.0, then dry it after water washing to obtain the finished product.

[0048] Comparative Example 1

[0049] A copper-clad aluminum surface treatment process includes the following steps:

[0050] 1) Degreasing: Immerse the copper-clad aluminum workpiece in a degreasing agent with a pH of 13, which is a mixture of sodium silicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1, degrease at 60 °C for 5 min, then perform 2 - 3 water washes; then immerse the workpiece in the degreasing agent again for ultrasonic degreasing with an ultrasonic power of about 25 KHz for 10 min at an ultrasonic temperature of 60 °C, and then perform 2 - 3 water washes;

[0051] 2) Acidification: Immerse the degreased copper-clad aluminum workpiece in a mixed solution of 10% HNO3 + 1% HF to remove the oxide films on the surfaces of aluminum and copper;

[0052] 3) Copper electroplating: Electroplate copper (cuprous cyanide 35 g / L, sodium cyanide 54 g / L, sodium hydroxide 5 g / L, temperature 50 °C, current density 2 A / dm 3 ) for about 120 s, and then perform 2 - 3 water washes after plating;

[0053] 4) Nickel electroplating: After water washing the workpiece with a copper plating layer, immerse it in the plating solution to electroplate a layer of medium-phosphorus electroless nickel nickel sulfate on the surface of the copper plating layer. The plating solution composition: nickel sulfate 150 g / L, nickel chloride 40 g / L, boric acid 40 g / L, sodium sulfate 15 g / L, temperature 45 °C, current density 2 A / dm 2 , electroplate nickel for 20 min at a pH of 4.0; after nickel electroplating is completed, perform 2 - 3 water washes on the workpiece;

[0054] 5) Passivation: Immerse the workpiece after water washing into a chromium nitrate mixed solution with a chromium sulfate concentration of 1.2 g / L, citric acid of 1 g / L, and potassium nitrate of 0.5 g / L for 60 s at a pH of 2.0, and then obtain the finished product after water washing.

[0055] Comparative Example 2

[0056] A copper-clad aluminum surface treatment process includes the following steps:

[0057] 1) Degreasing: Immerse the copper-clad aluminum workpieces in a degreasing agent with a pH of 13, which is a mixture of sodium metasilicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1. Degrease at 60 °C for 5 minutes, then perform 2 - 3 water rinses; Immerse the workpieces in the degreasing agent again for ultrasonic degreasing. The ultrasonic power is about 25 KHz, lasting for 10 minutes, and the ultrasonic temperature is 60 °C. Then perform 2 - 3 water rinses;

[0058] 2) Acid activation: Immerse the degreased copper-clad aluminum workpieces in sulfuric acid with a mass concentration of 5% to remove the oxide films on the surfaces of aluminum and copper;

[0059] 3) Nickel electroplating: After washing the above copper-clad aluminum workpieces with water, immerse them in the plating solution to deposit a layer of medium-phosphorus electroless nickel sulfate nickel on the surface. The composition of the plating solution is: nickel sulfate 150 g / L, nickel chloride 40 g / L, boric acid 40 g / L, sodium sulfate 15 g / L, temperature 45 °C, current density 2 A / dm 2 , nickel plating time 30 minutes, pH environment is 4.0; After nickel plating is completed, perform 2 - 3 water rinses on the workpieces; pH environment is 4.0; After nickel plating is completed, perform 2 - 3 water rinses on the workpieces;

[0060] 4) Passivation: Immerse the workpieces after water rinsing in a chromium nitrate mixed solution with a chromium sulfate concentration of 1.2 g / L, citric acid 1 g / L, potassium nitrate 0.5 g / L, soak for 60 seconds, pH environment is 2.0, and obtain the finished product after water rinsing.

[0061] Comparative Example 3

[0062] A copper-clad aluminum surface treatment process includes the following steps:

[0063] 1) Degreasing: Immerse the copper-clad aluminum workpieces in a degreasing agent with a pH of 13, which is a mixture of sodium metasilicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1. Degrease at 60 °C for 5 minutes, then perform water rinsing; Immerse the workpieces in the degreasing agent again for ultrasonic degreasing. The ultrasonic power is about 25 KHz, lasting for 10 minutes, and the ultrasonic temperature is 60 °C. Then perform 2 - 3 water rinses;

[0064] 2) Acidification: Immerse the degreased copper-clad aluminum workpieces in sulfuric acid with a mass concentration of 5% to remove the oxide films on the surfaces of aluminum and copper;

[0065] 3) Nickel electroplating: After washing the above copper-clad aluminum workpieces with water, immerse them in the nickel plating solution to deposit a layer of nickel on the surface. The composition of the plating solution is: nickel sulfate 150 g / L, nickel chloride 40 g / L, boric acid 40 g / L, sodium sulfate 15 g / L, temperature 45 °C, current density 2 A / dm 2 , nickel plating time 10 minutes, pH environment is 4.0; After nickel plating is completed, perform 2 - 3 water rinses on the workpieces;

[0066] 4) Tin electroplating: Immerse the nickel-plated copper-clad aluminum workpiece into an acidic tin plating solution, whose main components include stannous sulfate (SnSO4 40 g / L), sulfuric acid (H2SO4 100 g / L), phenolsulfonic acid 40 g / L, gelatin 1 g / L, etc. The tin plating time is 30 min, the temperature is 30 °C, and the current density is 1 A / dm 2 , and obtain the finished product after cleaning and drying.

[0067] Comparative Example 4

[0068] A surface treatment process for copper-plated aluminum substrates, where the aluminum substrate is solid aluminum and copper is plated on the surface of the aluminum substrate, including the following steps:

[0069] 1) Degreasing: Immerse the copper-plated aluminum substrate in a degreasing agent with pH = 13, which is a mixture of sodium silicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1. Degrease at 60 °C for 5 min, and then perform water washing; Immerse the workpiece in the degreasing agent again for ultrasonic degreasing, with an ultrasonic power of about 25 kHz, lasting for 10 min, and an ultrasonic temperature of 60 °C, and then perform 2 - 3 water washes;

[0070] 2) Acid activation: Immerse the degreased copper-plated aluminum substrate in sulfuric acid with a mass concentration of 5% to remove the surface oxide layer, and perform 2 - 3 water washes;

[0071] 3) Zinc immersion: Immerse the copper-plated aluminum substrate into a mixed solution of ZnO 6 g / L, NaOH 60 g / L, sodium potassium tartrate 80 g / L, ferric chloride 2 g / L, and sodium nitrate 1 g / L, with pH = 12, and the immersion time is 60 s. After zinc immersion, perform 2 - 3 water washes;

[0072] 4) Nickel electroplating: Immerse the above copper-plated aluminum substrate in the plating solution to deposit a layer of medium-phosphorus electroless nickel nickel sulfate on the surface. The composition of the plating solution is: nickel sulfate 150 g / L, nickel chloride 40 g / L, boric acid 40 g / L, sodium sulfate 15 g / L, the temperature is 45 °C, and the current density is 2 A / dm 2 , the nickel plating time is 60 min, and the pH environment is 4.0; After nickel plating, perform 2 water washes on the workpiece.

[0073] 5) Passivation: Immerse the water-washed workpiece into a mixed solution of chromium nitrate, with a chromium sulfate concentration of 12 g / L, citric acid 10 g / L, potassium nitrate 5 g / L, the immersion time is 40 s, the pH environment is 2.0, and obtain the finished product after water washing and drying.

[0074] Among them, the preparation of the copper-plated aluminum substrate is: Immerse the aluminum substrate in a copper plating solution (cuprous cyanide 40 g / L, sodium cyanide 54 g / L, sodium hydroxide 5 g / L, sodium potassium tartrate 60 g / L, sodium carbonate 30 g / L), the plating solution temperature is 50 °C, the electroplating time is 60 min, and the current density is 2 A / dm 2, after plating, perform 2 - 3 water rinses to obtain a copper - plated aluminum substrate with a copper plating layer about 1 mm thick.

[0075] Comparative Example 5

[0076] A surface treatment process for an aluminum substrate, where the aluminum substrate is solid aluminum, comprising the following steps:

[0077] 1) Degreasing: Immerse the aluminum substrate in a degreasing agent with pH = 13, which is a mixture of sodium silicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1, degrease at 60°C for 5 min, and then perform a water rinse; then immerse the workpiece in the degreasing agent for ultrasonic degreasing, with an ultrasonic power of about 25 KHz, for 10 min, at an ultrasonic temperature of 60°C, and then perform 2 - 3 water rinses;

[0078] 2) Acid activation: Immerse the degreased aluminum substrate in sulfuric acid with a mass concentration of 5% to remove the surface oxide layer, and perform 2 - 3 water rinses;

[0079] 3) Zinc immersion: Immerse the aluminum substrate in a mixed solution of 6 g / L ZnO, 60 g / L NaOH, 80 g / L sodium potassium tartrate, 2 g / L ferric chloride, and 1 g / L sodium nitrate, with pH = 12, for 60 s, and perform 2 - 3 water rinses after zinc immersion;

[0080] 4) Copper electroplating: Perform copper electroplating on the surface of the aluminum substrate after zinc immersion. The copper plating solution: cuprous cyanide 40 g / L, sodium cyanide 54 g / L, sodium hydroxide 5 g / L, electroplating temperature 50°C, current density 2 A / dm 2 , for a time of about 120 s. After copper plating, recover the copper plating solution and clean the residual liquid on the workpiece surface;

[0081] 5) Electroless nickel plating: Immerse the above - mentioned copper - plated aluminum substrate in the plating solution to deposit a medium - phosphorus electroless nickel on the surface. The plating solution composition: nickel sulfate 30 g / L, sodium hypophosphite 35 g / L, sodium citrate 20 g / L, sodium acetate 15 g / L, thiourea derivative 0.05 g / L, the plating solution environment is 88°C, the immersion time is 120 min, and the pH environment is 4.0; after nickel plating, rinse the plating solution on the workpiece surface clean.

[0082] Comparative Example 6

[0083] A surface treatment process for a steel material, where the steel material is matrix steel, comprising the following steps:

[0084] 1) Degreasing: Immerse the steel material workpiece in the degreasing agent, which is a mixture of sodium silicate pentahydrate: sodium hydroxide: trisodium phosphate in a mass ratio of 4:1:1. Degrease at 60°C for 5 minutes, then perform two water rinses; Immerse the workpiece in the degreasing agent again for ultrasonic degreasing. The ultrasonic power is about 25 KHz, lasting for 10 minutes, and the ultrasonic temperature is 60°C. Then perform 2 - 3 water rinses on the workpiece again;

[0085] 2) Acid activation: Immerse the above workpiece in a 10% HCl solution to remove the surface oxide film for 45 seconds;

[0086] 3) Zinc immersion: Immerse the activated workpiece above in a mixed solution of 6 g / L ZnO, 60 g / L NaOH, 80 g / L sodium potassium tartrate, 2 g / L ferric chloride, and 1 g / L sodium nitrate, with pH = 12 for 60 seconds, and perform 2 - 3 water rinses;

[0087] 4) Electroless nickel plating: After washing the workpiece with the zinc transition layer, immerse it in the plating solution to deposit a medium - phosphorus electroless nickel layer on the zinc layer surface. The composition of the plating solution: 30 g / L nickel sulfate, 35 g / L sodium hypophosphite, 20 g / L sodium citrate, 15 g / L sodium acetate, 0.05 g / L thiourea derivative. The plating solution environment is 88°C, the nickel plating time is 60 minutes, and the pH environment is 4.0; After nickel plating is completed, blow - wash the plating solution on the workpiece surface clean;

[0088] 3. Performance

[0089] (1) Coating thickness and uniformity

[0090] Perform metallographic analysis on the finished products prepared by the processes of Example 1 and Comparative Examples 1 - 6. The results are shown in Tables 1 - 3:

[0091] Table 1. Front - side coating thickness of each finished product

[0092]

[0093] ① is Example 1; ② is Comparative Example 1; ③ is Comparative Example 2; ④ is Comparative Example 3; ⑤ is Comparative Example 4; ⑥ is Comparative Example 5; ⑦ is Comparative Example 6;

[0094] Table 2. Side - side coating thickness of Example 1 and Comparative Examples 1 - 3

[0095]

[0096] Table 3. Coating interface and structure of each finished product

[0097]

[0098] Combined with Tables 1 - 3 and Figure 1-2, it can be clearly seen that the coating obtained by the process of the present invention has excellent uniformity, and there is a significant improvement in thickness compared to Comparative Examples 1-6, and the uniformity far exceeds that of the comparative examples.

[0099] (2) Coating hardness

[0100] The hardness of the finished products of Example 1 and Comparative Examples 1-6 was tested, and the results are shown in Table 4:

[0101] Table 4. Coating hardness of each finished product

[0102]

[0103] It can be seen from the data that the average hardness of the coating in Example 1 is 559 HV, which is much higher than that of each comparative example, and its wear resistance is better. Among the comparative examples, the average hardness of Comparative Example 3 with the lowest hardness is only 80 HV, and the average hardness of Comparative Example 1 with the highest hardness is only 175 HV. This shows that the coating in Example 1 is outstanding in terms of hardness, has obvious advantages compared to each comparative example, and in application scenarios where high-hardness coatings are required, the solution of Example 1 may have more application value and performance advantages.

[0104] (3) Salt spray test

[0105] Example 1 and Comparative Examples 1-6 were put into a salt spray chamber for salt spray test, and the results are shown in Table 5.

[0106] Test standard: GB / T 10125-2021 (neutral salt spray)

[0107] Test time: ≥48 h

[0108] Salt solution concentration: 5% NaCl, pH = 7.0

[0109] Table 5. Salt spray time results of each finished product

[0110]

[0111] Among them, the pictures of the finished workpieces before and after the salt spray test in Example 1 and Comparative Examples 1-3 are as Figure 3 shown.

[0112] From the data and Figure 3 it can be seen that Example 1 passed the 48-hour salt spray test, without white rust or red rust, and there was no rust at the punched holes. However, rust occurred in each comparative example. There was pitting corrosion at some points on the aluminum substrate in Comparative Examples 1-3, and pitting corrosion occurred at the punched positions. There was white rust on the surface of Comparative Example 4, and red rust on Comparative Examples 5 and 6. It shows that the protective performance of Example 1 is significantly better than that of each comparative example, and the salt spray corrosion resistance is stronger.

[0113] (4) Coating thickness and porosity

[0114] Coating thickness reference (1); Porosity: Tested according to GB / T 17720-1999. The results are shown in Table 6.

[0115] Table 6. Coating thickness and porosity results of each finished product

[0116]

[0117] Judging from the tabular data, the front coating thickness of Example 1 is 20.81 μm, the side is 20.1 μm, and the porosity is 7%. There are significant differences in the coating thickness and porosity in the comparative examples. Generally speaking, the coating thickness of Example 1 is relatively moderate, the porosity is low, and it performs well in terms of coating thickness uniformity and denseness, which may be more conducive to improving the comprehensive performance.

[0118] (5) Coating adhesion

[0119] Tested according to GB / T 5270-2005, and the results are shown in Table 7.

[0120] Table 7. Coating thickness and porosity results of each finished product

[0121]

[0122] 4. Conclusions

[0123] To sum up, for the nickel-plated copper-clad aluminum material prepared by the present invention, in terms of coating quality, the nickel-plating process of the present invention completely breaks through the limitation of current distribution by virtue of the autocatalytic reaction mechanism, and can form a coating with uniform thickness on the surfaces of complex structures such as blind holes, deep grooves, and threads, completely solving the problems of over-thick corners and unplated inner cavities caused by uneven distribution of power lines in electroplated nickel.

[0124] In terms of adhesion and mechanical properties, the electroless nickel plating layer prepared by the present invention forms a diffusion bond with the substrate, and the bonding strength is as high as over 400 MPa, far higher than 200 MPa of electroplated nickel. For the aluminum substrate treated by zinc immersion, the adhesion is increased by more than 30%. In addition, the hardness of the electroless nickel plating layer reaches 400-600 HV, with excellent wear resistance, and the amorphous Ni-P alloy structure has no grain boundary defects. The salt spray test in 5% NaCl solution can reach 72 hours, and the corrosion resistance is far beyond 24 hours of electroplated nickel. The seawater corrosion resistance is comparable to that of titanium alloys. The dense and pore-free coating can effectively isolate the penetration of corrosive media.

[0125] In terms of process adaptability and environmental protection and economy, the nickel-plating process of the present invention can be plated on non-conductive and complex metal surfaces. The equipment is simple and does not require a power supply and an anode, which is suitable for small-batch and multi-variety production; the plating solution does not contain cyanide or hexavalent chromium, the wastewater treatment cost is low, and the one-time qualification rate of electroless nickel plating on aluminum alloy reaches over 95%, and the comprehensive cost is reduced by 20%-30%, achieving a double improvement in environmental protection and economic benefits.

[0126] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A surface treatment process for copper-clad aluminum composite materials, characterized in that It includes the following steps: (1) Acid-activate the copper-clad aluminum workpiece that has undergone degreasing pretreatment, and then perform secondary activation after water washing; (2) Immerse the workpiece after secondary activation in a zinc immersion solution to obtain a zinc transition layer on the surface of the workpiece; (3) After water washing the workpiece with the zinc transition layer, immerse it in a plating solution to deposit a layer of medium-phosphorus electroless nickel on the surface of the zinc layer, and then immerse the workpiece in a chromium solution for passivation. After water washing and drying, a finished product is obtained.

2. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that, The degreasing pretreatment is to immerse the workpiece in a degreasing agent and perform ultrasonic treatment. The degreasing agent includes at least one of silicate, hydroxide, and phosphate. The ultrasonic power is 25 - 30 KHz, the current ≥ 6 A, and the pH = 9 - 12.

3. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that, The acid activation is to immerse the workpiece in a 10 - 15% HCl solution by mass concentration for 45 - 60 s.

4. The surface treatment process of a copper-clad aluminum composite material according to claim 3, characterized in that, The secondary activation is to immerse the workpiece in a mixed acid composed of 5 - 10% HNO3 by mass concentration and 0.5 - 1 g / L thiourea for 30 - 60 s.

5. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that The zinc immersion solution includes 5 - 10 g / L ZnO, 50 - 100 g / L NaOH, 5 - 15 g / L sodium potassium tartrate, 2 - 5 g / L ferric chloride, 1 - 5 g / L sodium nitrate, the temperature is 16 - 27 °C, the pH = 12 - 14, and the immersion time is 45 - 60 s.

6. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that, The plating solution immersion time is 60 - 120 min. The composition of the plating solution includes a nickel salt, a reducing agent, a complexing agent, and a stabilizer. The nickel salt is one of nickel sulfate or nickel chloride, and the pH of the plating solution is 4 - 5.

7. The surface treatment process of a copper-clad aluminum composite material according to claim 6, characterized in that, The reducing agent is sodium hypophosphite, the complexing agent is a mixture of sodium citrate and sodium acetate, and the stabilizer is a thiourea derivative.

8. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that, The chromium solution is a trivalent chromium solution. The trivalent chromium solution includes 1 - 1.5 g / L chromium nitrate, 0.8 - 1.2 g / L oxalic acid, 3 - 5 g / L sodium nitrate, the immersion time is 60 - 120 s, and the pH = 3.7 - 4.

8.

9. The surface treatment process of a copper-clad aluminum composite material according to claim 1, characterized in that, The water washing is 2 - 3 passes of water washing.

10. A nickel-plated copper-clad aluminum composite material, characterized in that, Prepared by the surface treatment process according to any one of claims 1 - 9.

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