Corrosion-resistant and temperature-shock-resistant composite layer, corrosion-resistant and temperature-shock-resistant treatment method for aluminum substrate, and corrosion-resistant and temperature-shock-resistant aluminum terminal

Abstract

Provided in the present disclosure are a corrosion-resistant and temperature-shock-resistant composite layer, a corrosion-resistant and temperature-shock-resistant treatment method for an aluminum substrate, and a corrosion-resistant and temperature-shock-resistant aluminum terminal. The corrosion-resistant and temperature-shock-resistant composite layer comprises: an alkaline copper layer, a pyrophosphate copper layer, a nickel aminosulfonate layer and a silver layer, wherein the thickness of the alkaline copper layer is 1-10 μm, the thickness of the pyrophosphate copper layer is 2-18 μm, the thickness of the nickel aminosulfonate layer is 0.5-28 μm, and the thickness of the silver layer is 0.2-25 μm. The corrosion-resistant treatment method for an aluminum substrate comprises the step of providing the corrosion-resistant and temperature-shock-resistant composite layer on the surface of an aluminum substrate. The surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with the corrosion-resistant and temperature-shock-resistant composite layer. The corrosion-resistant and temperature-shock-resistant composite layer provided by the present disclosure has good salt spray corrosion resistance, the duration of the salt spray corrosion resistance can still reach 120 hours after a temperature shock, and the corrosion-resistant and temperature-shock-resistant composite layer still has a long mechanical life in a severe environment which features rapid temperature changes and high corrosivity.

Description

Corrosion-resistant and temperature-shock-resistant composite layer, corrosion-resistant and temperature-shock-resistant treatment method for aluminum substrate, and corrosion-resistant and temperature-shock-resistant aluminum terminal

[0001] Related applications

[0002] This application claims priority to the Chinese invention patent application with application number 202310935034.9 filed on July 27, 2023, and cites the entire disclosure of the above patent application as part of this application. Technical Field

[0003] The present disclosure relates to a corrosion-resistant and temperature-shock-resistant composite layer, a corrosion-resistant and temperature-shock-resistant treatment method for an aluminum substrate, and a corrosion-resistant and temperature-shock-resistant aluminum terminal, belonging to the technical field of corrosion resistance. Background Art

[0004] Current electroplating, chemical plating, spraying, laser surface treatment and other processes can protect the substrate by coating a film layer on the surface of aluminum and its alloys. However, the results of salt spray resistance tests are not ideal. Common aluminum workpieces can only withstand salt spray for 48 hours before corrosion occurs, which greatly limits the service life of aluminum workpieces in the assembly. At the same time, the expansion coefficient of metal aluminum is very large, which is 23.21×10 -6 / K, the temperature shock will inevitably cause stress on the surface film layer, tearing the film layer. In the subsequent salt spray test, the protective effect of the damaged film layer is greatly reduced, so that the aluminum workpiece after the temperature shock cannot even reach 12 hours of salt spray.

[0005] Current electroplating manufacturers have done little research and development on aluminum electroplating processes. They only perform secondary zinc deposition followed by nickel plating to proceed to the next electroplating step. The choice of plating solutions varies and the effects are average. It is difficult to meet the electroplating requirements of aluminum workpieces that still have high corrosion resistance after temperature shock. This is especially true for aluminum workpieces used in military, aerospace, automotive and other fields, which are used in harsh environments with rapid temperature changes and cannot meet the requirements.

[0006] Currently, all terminals or workpieces used in connectors, car bodies, controllers, battery packs and other assemblies on the market are subjected to temperature shock tests. They are kept at -40°C for 30 minutes, transferred to 140°C within 30 seconds and kept at 30 minutes. After 100 cycles of testing, there are no problems such as excessive contact resistance, poor appearance, and excessive withstand voltage. The terminals that have passed this test appear to be good on the surface, but cracks appear at the microscopic level, and the aluminum terminals are more serious.

[0007] However, the existing technology has not paid attention to the corrosion resistance after temperature shock cycles. At this time, the coating has been damaged and the corrosion resistance of the coating has been lost, which has a great impact on the performance of the terminals or workpieces. If the corrosion resistance of the terminals or workpieces after undergoing temperature shock cycles cannot meet the actual use requirements, serious consequences will occur.

[0008] Summary of the Invention

[0009] In order to solve the above technical problems, the purpose of the present disclosure is to provide a corrosion-resistant and temperature-shock-resistant composite layer, which has excellent salt spray corrosion resistance, especially corrosion resistance after temperature shock, and can be used for corrosion-resistant and temperature-shock-resistant treatment of aluminum substrates.

[0010] To achieve the above objectives, the present disclosure first provides a corrosion-resistant and temperature-shock-resistant composite layer, which includes: an alkali copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer.

[0011] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, an alkali copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer are provided in sequence.

[0012] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, the thickness of the alkali copper layer is exemplarily 1-10 μm, further exemplarily 1-6 μm, and further exemplarily 2-4 μm.

[0013] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, the thickness of the char copper layer is exemplarily 2-18 μm, further exemplarily 5-15 μm, and further exemplarily 8-10 μm.

[0014] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, the thickness of the nickel sulfamate layer is 0.5-28 μm, more preferably 0.5-18 μm, and more preferably 6-9 μm. In some cases, the thickness of the nickel sulfamate layer can be controlled to be 3-28 μm, and more preferably 4-15 μm.

[0015] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the silver layer is 0.2-25μm. Depending on the different corrosion resistance requirements of the applicable location, the silver layer can have different thicknesses. For example, in the contact area or welding area of ​​the male and female aluminum terminals, these areas have a small contact area with the environment and are semi-exposed areas. The requirements for corrosion resistance are low, and a thinner silver layer can be set. Exemplarily, the thickness of the silver layer (thin silver layer) is 0.2-3μm, and further exemplarily 0.5-2μm; in the fully exposed area where the aluminum terminal has a large contact area with the environment, the requirements for corrosion resistance are high, and a thicker silver layer needs to be set. Exemplarily, the thickness of the silver layer (thick silver layer) is 8-15μm, and further exemplarily 10-15μm. In some cases, the thickness of the silver layer can be further controlled to 10-13μm.

[0016] In the aforementioned corrosion-resistant and temperature-shock-resistant composite layer, the composite layer illustratively further includes a transition layer disposed on the side of the alkaline copper layer that is not in contact with the charred copper layer. The transition layer is disposed between the alkaline copper layer and the substrate requiring corrosion resistance treatment to serve as a transition, and can be achieved using appropriate surface treatment methods.

[0017] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the transition layer includes a zinc layer, or a combination of a zinc layer and a secondary zinc deposition layer; the zinc layer (or zinc layer, secondary zinc deposition layer), alkali copper layer, char copper layer, and silver layer are arranged in sequence. The zinc layer and the secondary zinc deposition layer serve as transition layers for subsequent electroplating layers, which can ensure their adhesion. According to the specific embodiment of the present disclosure, the combination of the zinc layer and the secondary zinc deposition layer includes a method in which the zinc layer and the secondary zinc deposition layer are superimposed (superimposed up and down, the secondary zinc deposition layer covers the zinc layer); and a method in which the zinc layer and the secondary zinc deposition layer are located in different areas of the same layer, and in this method, a part of the two can be superimposed on each other. The transition layer disclosed in the present disclosure is not limited to the zinc layer and the secondary zinc deposition layer, and other metal or alloy materials can also be used, as long as it can be beneficial to improve the adhesion of the corrosion-resistant and temperature-shock-resistant composite layer. For example, other metal transition layers or alloy transition layers can be formed on the surface of the aluminum terminal through surface treatment processes such as spraying and vacuum plating.

[0018] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the zinc layer is 0.1-10.0 μm, and further illustratively is 0.5-1 μm.

[0019] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the secondary zinc deposition layer is 0.1-10 μm, and further illustratively is 1.5-2.5 μm.

[0020] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the zinc layer, the secondary zinc deposition layer, the alkaline copper layer, the char copper layer, the sulfamate nickel layer, and the silver layer are electroplated layers respectively.

[0021] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer further includes a chemical copper layer (or chemically plated copper layer).

[0022] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the chemical copper layer is arranged on the surface of the alkali copper layer or the surface of the charred copper layer, that is, the chemical copper layer can be arranged in the following ways: (1) arranged on the side surface of the alkali copper layer that is not in contact with the charred copper layer; (2) arranged between the alkali copper layer and the charred copper layer; (3) arranged on the side surface of the charred copper layer that is not in contact with the alkali copper layer.

[0023] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the chemical copper layer is 3-25 μm, and further illustratively is 5-15 μm.

[0024] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer further includes an acid copper layer.

[0025] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the acid copper layer is arranged on the surface of the alkali copper layer or the surface of the charred copper layer, that is, the chemical copper layer or the acid copper layer can be arranged in the following ways: (1) arranged on the side surface of the alkali copper layer that is not in contact with the charred copper layer; (2) arranged between the alkali copper layer and the charred copper layer; (3) arranged on the side surface of the charred copper layer that is not in contact with the alkali copper layer.

[0026] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the acid copper layer is 1-20 μm, and further illustratively is 3-10 μm.

[0027] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer further includes a Watt nickel layer.

[0028] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the Watt nickel layer is arranged on the surface of the sulfamate nickel layer, that is, the Watt nickel layer can be arranged in the following ways: (1) between the sulfamate nickel layer and the char copper layer; (2) between the sulfamate nickel layer and the silver layer.

[0029] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the thickness of the Watt nickel layer is 1-20 μm, and further illustratively is 3-9 μm.

[0030] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, for example, the corrosion-resistant and temperature-shock-resistant composite layer can simultaneously include a chemical copper layer and an acid copper layer, and the specific positions of the two can be set at any one or two of the three positions: the surface of the side of the alkali copper layer not in contact with the charred copper layer, between the alkali copper layer and the charred copper layer, and the surface of the side of the charred copper layer not in contact with the alkali copper layer. When two of them are in the same position, their order can be arbitrary. For example, when the chemical copper layer and the acid copper layer are both located between the alkali copper layer and the charred copper layer, the order can be either alkali copper layer, chemical copper layer, acid copper layer, charred copper layer, or alkali copper layer, acid copper layer, chemical copper layer, charred copper layer. On this basis, a Watt nickel layer can also be provided at the same time.

[0031] Due to the difference in expansion coefficient between the aluminum substrate (such as aluminum terminals, workpieces) and the electroplated film layer, and the difference in expansion coefficient between the electroplated film layers, the expansion coefficient of the aluminum substrate is generally 23.21×10 -6 / K, the expansion coefficient of nickel is 13×10 -6 / K, the thermal expansion volume of the aluminum substrate is much greater than that of the nickel layer. This volume difference creates significant tensile stress between the workpiece and the electroplated film. This stress can tear or even damage the electroplated film. During salt spray testing, workpieces with torn surface films are easily penetrated by chloride ions in the salt spray solution, coming into contact with the aluminum substrate and causing electrochemical corrosion.

[0032] The expansion coefficient of the alkali copper layer, the char copper layer and the silver layer of the corrosion-resistant and temperature-shock-resistant composite layer provided by the present invention is similar to that of aluminum (copper 17×10 -6 / K, Silver 19.5×10 -6 / K), which greatly reduces the tensile stress caused by volume expansion during temperature shock. At the same time, the use of a highly ductile and tough nickel sulfamate layer can withstand tensile stress without being torn and still maintain its original density. It can effectively protect the workpiece from corrosion in salt spray tests.

[0033] The present disclosure also provides a method for preparing the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, which includes the following steps: forming an alkali copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer on the surface of a substrate in sequence by electroplating to obtain a corrosion-resistant and temperature-shock-resistant composite layer.

[0034] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the alkaline copper layer illustratively contains, based on the total volume of the electroplating solution, 40-50 g / L of cuprous cyanide, 40-60 g / L of total sodium cyanide, 8-14 g / L of free sodium cyanide, 30-45 g / L of potassium sodium tartrate, 1-3 g / L of sodium hydroxide, and 3-5 mL / L of an additive (one or a mixture of two or more selected from the group consisting of polyethylene glycol, fatty amine polyoxyethylene ether (AEO), and OP series octylphenol polyoxyethylene ether). The remainder of the electroplating solution is water.

[0035] In the preparation method of the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the temperature of the electroplated alkali copper layer is 40-50°C, the anode and cathode area ratio is 1:1-2 (illustratively 1:1.5), and the current density is 0.7-1.2A / dm 2 , the electroplating time is 5-15min.

[0036] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the charcoal copper layer illustratively contains, based on the total volume of the electroplating solution, 50-70 g / L of copper pyrophosphate, 300-450 g / L of potassium pyrophosphate, 15-30 g / L of ammonium citrate, and 2-5 mL / L of aqueous ammonia. The remainder of the electroplating solution is water.

[0037] In the method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, for example, the temperature of the electroplated copper layer is 40-50°C, and the current density is 0.7-1.2A / dm 2 The area ratio of the anode and cathode is 1:1-2 (exemplarily 1:1.5), and the electroplating time is 50-90 min (exemplarily 70 min).

[0038] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the nickel sulfamate layer illustratively contains, based on the total volume of the electroplating solution, 300-500 g / L of nickel sulfamate, 10-25 g / L of nickel chloride, 30-40 g / L of boric acid, 100-150 g / L of sulfamate, and 5-10 ml / L of an additive (one or a mixture of two or more of a pyridine derivative, a propargyl alcohol derivative, saccharin, etc.). The remainder of the electroplating solution is water.

[0039] In the method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, for example, the temperature of the nickel sulfamate electroplating layer is 50-60° C., and the current density is 0.8-1.2 A / dm 2 The area ratio of the anode and cathode is 1:1-2 (exemplarily 1:1.5), and the electroplating time is 1-80 min (exemplarily 40-60 min, further exemplarily 50 min).

[0040] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the silver layer illustratively contains, based on the total volume of the electroplating solution, 30-50 g / L of silver cyanide, 130-150 g / L of potassium cyanide, 45-60 g / L of free potassium cyanide, 15-25 g / L of potassium carbonate, 4-10 g / L of potassium hydroxide, and 20-30 g / L of additives. The remaining component of the electroplating solution is water. Exemplary additives include one or a mixture of two or more of thiocarbamates, sodium lauryl sulfonate, and OP series octylphenol polyoxyethylene ethers.

[0041] In the preparation method of the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the temperature of the electroplated silver layer is 20-25°C, the anode and cathode area ratio is 1:1-2 (illustratively 1:1.5), and the current density is 0.2-0.5A / dm 2 , the electroplating time is 1-90 min (exemplarily 30-60 min, further exemplary 40 min).

[0042] In the above-mentioned preparation method of the corrosion-resistant and temperature-shock-resistant composite layer, for example, the electroplated alkali copper layer, the electroplated coke copper layer, the electroplated silver layer, etc. can adopt a pulse electroplating process, which can further improve their original density, thereby making the electroplated layer denser, with fewer pores and stronger salt spray resistance.

[0043] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, illustratively, when a chemical copper layer, an acid copper layer, and a Watt nickel layer are contained, these layers can be obtained by corresponding methods at an appropriate time.

[0044] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the zinc layer and the secondary zinc deposition layer can be prepared by a conventional electroplating method.

[0045] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, in order to ensure its electroplating bonding strength, other steps can be added to the electroplating process, such as adding acid activation treatment before each step, adding pure water washing and cleaning before each step, etc.

[0046] The present disclosure also provides a method for treating an aluminum substrate to resist corrosion and temperature shock, which includes the step of providing a corrosion-resistant and temperature shock-resistant composite layer provided by the present disclosure on the surface of the aluminum substrate. The aluminum substrate disclosed in the present disclosure includes a pure aluminum substrate and an aluminum alloy substrate.

[0047] In the above-mentioned method for treating the aluminum substrate for corrosion resistance and temperature shock resistance, illustratively, corrosion resistance refers to resistance to salt spray corrosion.

[0048] In the above-mentioned corrosion-resistant and temperature-shock-resistant treatment method for an aluminum substrate, illustratively, temperature-shock resistance refers to resistance to temperature cycle shock, that is, resistance to alternating hot and cold cycle shock.

[0049] In the above-mentioned corrosion-resistant and temperature-shock-resistant treatment method for an aluminum substrate, illustratively, the surface roughness of the aluminum substrate is less than Ra 3.6, and further illustratively less than Ra 0.8.

[0050] The present disclosure also provides a corrosion-resistant and temperature-shock-resistant aluminum terminal, wherein a partial area or the entire area of ​​the surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with the corrosion-resistant and temperature-shock-resistant composite layer provided by the present disclosure.

[0051] In the above-mentioned corrosion-resistant and temperature-shock-resistant aluminum terminal, the corrosion-resistant and temperature-shock-resistant composite layer may cover the entire surface of the aluminum terminal, or may only cover the surface area that requires corrosion-resistant and temperature-shock-resistant treatment.

[0052] The present disclosure also provides a method for preparing the above-mentioned corrosion-resistant and temperature-shock-resistant aluminum terminal, which comprises the following steps:

[0053] The front surface of the aluminum terminal is rolled and polished;

[0054] Stamping the sides of the aluminum terminals;

[0055] A zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, and a silver layer are sequentially formed on the front and side surfaces of the treated aluminum terminal by electroplating to obtain a corrosion-resistant and temperature-shock-resistant aluminum terminal.

[0056] In the above-mentioned preparation method, rolling, polishing, and stamping processes can be performed only on the areas requiring corrosion and temperature shock resistance, and are not limited to the entire surface of the aluminum terminal. This localized treatment facilitates welding and can be combined with various joining processes, such as friction welding, friction stir welding, ultrasonic welding, molecular diffusion welding, and resistance welding, to produce highly reliable corrosion-resistant terminals that can be used in a variety of connection processes.

[0057] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal, illustratively, by rolling the terminal material, the density of the terminal surface can be enhanced, thereby enhancing the corrosion resistance and temperature-shock resistance of the subsequent electroplating treatment.

[0058] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal, for example, by polishing the terminal material, the smoothness of the terminal surface can be enhanced, thereby enhancing the corrosion resistance and temperature-shock resistance of the subsequent electroplating process. The polishing process can be performed by chemical polishing, mechanical polishing, etc.

[0059] In the method for preparing the corrosion-resistant aluminum terminal, the roughness of the front surface of the aluminum terminal after the rolling and polishing processes is exemplarily less than Ra 3.6, and further exemplarily less than Ra 0.8.

[0060] In the method for preparing the corrosion-resistant aluminum terminal, the side roughness of the rolled aluminum terminal is exemplarily less than Ra 3.6 (further exemplarily less than Ra 0.8), and the bright band is greater than 50% (further exemplarily greater than 98%).

[0061] In the above-mentioned method for preparing the corrosion-resistant aluminum terminal, illustratively, when a transition layer is provided, the transition layer is first formed on the front and side surfaces of the treated aluminum terminal before the alkaline copper layer is formed by electroplating.

[0062] The technical solution disclosed in the present invention is based on the perspective of practical application (in practical applications, terminals are more susceptible to corrosion after rapid temperature changes, and corrosion is always present). The anti-corrosion performance of aluminum terminals after temperature shock cycles is optimized, and it can achieve 100 cycles of maintaining the temperature at -40°C for 30 minutes to 140°C for 30 minutes while still having good corrosion resistance. The fully exposed area of ​​the aluminum terminal provided with the corrosion-resistant and temperature shock-resistant composite layer can withstand salt spray for up to 120 hours, and the semi-exposed area of ​​the aluminum terminal provided with the corrosion-resistant and temperature shock-resistant composite layer can withstand salt spray for 28 hours, and still has a long mechanical life in harsh environments with rapid temperature changes and high corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG1 is a schematic diagram of the overall structure of an embodiment of an aluminum terminal provided by the present disclosure.

[0064] FIG2 is a schematic diagram of an exemplary electroplating process of the aluminum terminal provided in the present disclosure.

[0065] Figure 3 is the SEM images of conventional aluminum plates and rolled aluminum plates.

[0066] Figure 4 shows the morphology of the side of the aluminum terminal obtained by ordinary stamping and precision stamping.

[0067] FIG5 is a picture of corrosion spots appearing on the side of Comparative Example 9.

[0068] Figure 6 shows the morphology of the samples before and after the temperature shock test.

[0069] Figure 7 shows a sample with poor adhesion when direct electroplating of the copper and silver layers was performed.

[0070] FIG8 is a surface SEM image and a side cross-sectional metallographic image of a conventional coating (nickel plating) before and after temperature shock.

[0071] FIG9 is a side cross-sectional metallographic image of a conventional coating (nickel coating) and a coating according to Example 1 of the present disclosure after temperature shock. DETAILED DESCRIPTION

[0072] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present disclosure, the technical solution of the present disclosure is now described in detail below, but it should not be understood as limiting the scope of implementation of the present disclosure.

[0073] The aluminum terminal provided by the present disclosure is an aluminum terminal with an electroplated film layer, including an aluminum terminal material and an electroplated film layer, wherein the material refers to a substrate that has not been subsequently processed. In the embodiment of the present disclosure, the aluminum terminal material is an unprocessed aluminum substrate in the shape of a terminal without an electroplated film layer. Among them, the aluminum terminal material has a terminal surface and a terminal side; the electroplated film layer (corrosion-resistant and temperature-shock-resistant composite layer) includes: a zinc layer, a secondary zinc deposition layer, an alkali copper layer, a charred copper layer, an aminosulfonate nickel layer, and a silver layer. An exemplary overall structure of an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer is shown in Figure 1, wherein a zinc layer 2, an alkali copper layer 3, a charred copper layer 4, an aminosulfonate nickel layer 5, and a silver layer 6 are sequentially provided on the surface of the aluminum substrate 1; if necessary, a secondary zinc deposition layer can be further provided between the zinc layer 2 and the alkali copper layer 3.

[0074] An exemplary electroplating process for aluminum terminals is shown in Figure 2. The process includes the following steps: ultrasonic degreasing, alkaline cleaning, pickling, chemical zinc deposition, chemical stripping, secondary zinc deposition, activation, alkaline copper electroplating, coke copper electroplating, nickel sulfamate electroplating, pre-silver plating, silver electroplating, post-treatment, pure water washing, and drying. The secondary zinc deposition step can be selected as needed. In other words, the secondary zinc deposition step can be included or excluded as needed.

[0075] The technical solution disclosed in the present invention starts with a design that prevents chloride ions from contacting the substrate. The front side of the material terminal is subjected to roller pressing and polishing treatments, and the roughness after treatment is less than Ra 3.6, and exemplarily less than Ra 0.8; the side of the material terminal is processed using a precision stamping process, and the bright band after treatment is greater than 50%, exemplarily greater than 98%, and the roughness is less than Ra 3.6, and exemplarily less than Ra 0.8.

[0076] Roll-pressing increases the surface density of the aluminum material by mechanically applying pressure, thereby reducing the porosity of the aluminum terminal material surface and improving its density, preparing it for the next electroplating layer. The less porous the material, the less porous the electroplating layer, and the higher the protective effect. SEM images of conventional and roll-pressed aluminum sheets are shown in Figure 3. In Figure 3, Figure a shows a conventional aluminum sheet, and Figure b shows a roll-pressed aluminum sheet. As can be seen from Figure 3, the roll-pressing treatment reduces the surface roughness of the aluminum sheet and significantly improves its flatness.

[0077] The polishing process is carried out by magnetic polishing. Specifically, a magnetic field is generated by powering on. The magnetic field drives the stainless steel needle to move. During the movement, the stainless steel needle rubs the surface of the terminal material, thereby achieving the effect of mechanical polishing and improving the smoothness and flatness of the terminal material surface.

[0078] Polishing and precision stamping processes are all used to improve the smoothness and flatness of the terminal material surface and sides.

[0079] By improving the flatness and smoothness of the terminal material, it can be greatly beneficial to the electroplating film layer. Because of the influence of the current, the electroplating process will accumulate more electroplating film layers at the electron-rich positions of the workpiece, which will cause the thickness of the electroplating film layer on the terminal surface to be uneven, and even a large number of pits to appear, causing the chloride ions in the salt mist to gather and penetrate. When the flatness of the terminal material is insufficient, due to the principle of tip discharge, the more curved the conductor surface is, the more charges will be accumulated in places with smaller relative surface areas. The uneven protrusions on the surface of the material will gather a large number of electrons, making the protruding positions on the surface of the workpiece after electroplating more convex and the concave positions more concave, thus forming small holes that easily gather salt mist solution, causing the penetration of chloride ions, and then causing corrosion. After being processed by the process disclosed in the present invention, the terminal material can effectively cover the electroplating film layer, effectively improving its corrosion resistance.

[0080] Alkali copper electroplating: Alkali copper electroplating is cyanide copper plating. Cyanide has a strong complexing ability in water, which can greatly increase the cathode polarization of electroplating, so that copper ions accumulate in large quantities at the cathode and deposit together, increasing the density of the electroplated film layer. The coating electroplated by the cyanide system is dense and reacts quickly and efficiently, and can cover the zinc layer with a dense and flat copper layer. In addition, copper is chemically inactive and has low internal stress during electroplating, making it an excellent intermediate coating and easy to electroplate subsequent metal coatings.

[0081] Electroplating parameters are as follows: cuprous cyanide: 40-50 g / L, total sodium cyanide: 40-60 g / L, free sodium cyanide: 8-14 g / L, potassium sodium tartrate: 30-45 g / L, sodium hydroxide: 1-3 g / L, additives: 3-5 mL / L; temperature: 40-50 ° C, cathode and anode area ratio: 1:1.5, current density: 0.7-1.2 A / dm 2 , electroplating time: 5-15min, coating thickness: exemplary 1-6μm.

[0082] In order to enhance the density of the coating, the present invention has carried out process optimization: Generally, in order to meet the requirements of electroplating efficiency and faster production, the current density of electroplating alkaline copper in electroplating plants is 4-10A / dm 2, far higher than that of the present disclosure. Current density directly affects the compactness of the coating. High current density weakens cathodic polarization and makes it easier to reach the overpotential for hydrogen ion evolution in the solution, causing the hydrogen evolution side reaction during electroplating. The evolved hydrogen gas leaves pores in the coating, reducing the compactness of the coating. The alkaline copper electroplating process used in the present disclosure reduces the current density while increasing the concentration of the main salt, cuprous cyanide, and free sodium cyanide, thereby producing an alkaline copper coating with excellent electroplating efficiency and compactness.

[0083] Electroplated copper: The electroplated copper layer is copper pyrophosphate. The complexing ability of pyrophosphate in water is stronger than that of cyanide. The cathodic polarization effect in the pyrophosphate system is also stronger. Because [Cu(P2O7)2] 6- The more negative charges it carries, the greater the impact on the cathode process. At the same time, [Cu(P2O7)2] 6- Difficult to discharge, needs to be hydrolyzed into [CuP2O7] 2- To discharge and deposit the copper layer, [CuP2O7] 2- The hydrolysis of copper is slow, thus increasing the cathodic polarization again. The copper plating film is denser and has fewer pores, which can effectively prevent the penetration of chloride ions in salt spray tests and enhance the corrosion resistance and temperature shock resistance of the workpiece.

[0084] Electroplating parameters are as follows: copper pyrophosphate: 50-70 g / L, potassium pyrophosphate: 300-450 g / L, ammonium citrate: 15-30 g / L, ammonia: 2-5 mL / L; current density 0.7-1.2 A / dm 2 , temperature 40-50°C, cathode and anode area ratio: 1:1.5, electroplating time 50-90 min, electroplating thickness: exemplary 5-15 μm. Similarly, to improve the density of the coating, the process used in the present disclosure is optimized to reduce the current density.

[0085] Electroplating nickel sulfamate: nickel sulfamate is used as the main salt and nickel chloride is used as the anode depolarizer. The nickel layer electroplated in this solution system has good ductility. Compared with other electroplated nickel layers, the film layer electroplated with nickel sulfamate is more resilient and has lower internal stress. It can withstand tensile stress generated by temperature shock without being torn, and still maintains its original density. It can effectively protect the workpiece and avoid corrosion in the salt spray test.

[0086] Electroplating parameters are as follows: nickel sulfamate: 300-500g / L, nickel chloride: 10-25g / L, boric acid: 30-40g / L, sulfamate: 100-150g / L, additives: 5-10ml / L; current density: 0.8-1.2A / dm 2Temperature: 50-60°C, cathode and anode area ratio: 1:1.5, electroplating time: 1-80 minutes; the coating thickness can be controlled by adjusting the parameters of the electroless copper plating as needed. Similarly, to improve the density of the coating, the process used in this disclosure has been optimized to reduce the current density.

[0087] The chemical copper layer is formed by autocatalytic chemical reaction plating, which deposits copper ions in an orderly manner on the substrate. Adding the chemical copper layer between each layer can achieve good bonding strength. The chemical copper layer is an excellent intermediate coating, which can enhance the bonding strength of the entire coating. Furthermore, because the preparation process of the chemical copper layer is a simple chemical reaction, the coating thickness and porosity are not affected by the current distribution. As a result, the chemical copper layer has a more uniform thickness, lower porosity, and good corrosion resistance. In the present disclosure, adding this layer can enhance the corrosion resistance of the entire coating.

[0088] The chemical copper plating parameters are as follows: composition of the chemical plating solution: copper sulfate: 5-20g / L, sodium hypophosphite: 20-50g / L, sodium citrate: 5-30g / L, nickel sulfate: 0.1-5g / L, potassium ferrocyanide: 0.5-7mg / L, boric acid: 15-50g / L; temperature 60-90°C, pH 7.8-10.2, electroplating time 40-100min, general plating speed 1μm / 6min, i.e.: 6min-1μm, i.e. 24min-4μm, 48min-8μm; the coating thickness can be controlled as needed by controlling the chemical copper plating parameters.

[0089] The acid copper layer (i.e., acid copper plating) is copper sulfate electroplated, has good bonding strength with other plating layers, and can serve as an excellent intermediate plating layer. In addition, the copper sulfate plating solution used in preparing the acid copper layer is stable and low in cost. Adding acid copper between or on both sides of the alkali copper layer and the coke copper can enhance the brightness and corrosion resistance of the overall plating layer itself.

[0090] The parameters for electroplating acid copper are as follows: composition of the electroplating solution: copper sulfate pentahydrate: 160-250 g / L, sulfuric acid: 25-50 mL / L, chloride ion: 40-120 ppm, additives (one or a mixture of two or more of polydisulfide propane sulfonate, 2-mercaptobenzimidazole, 1,2-ethylene thiourea, and polyamine compounds): 4-15 mL / L, current density 0.8-2.0 A / dm 2 , temperature 20-30℃, anode and cathode area ratio of 1:1.5, electroplating time 20-80min, and coating thickness can be controlled by controlling electroplating parameters as needed.

[0091] Watt nickel layer (i.e. Watt nickel plating, bright nickel plating) is a nickel sulfate electroplating layer, which has good bonding strength with other plating layers and can be used as an excellent intermediate plating layer. When Watt nickel is added between or on both sides of the alkaline copper layer and the coke copper layer, a potential difference will be generated in a corrosive environment. It can act as an anode and be corroded first, thus protecting other plating layers and enhancing the brightness and corrosion resistance of the overall plating layer itself.

[0092] The parameters of the electroplating Watt nickel layer are as follows: the composition of the electroplating solution: nickel sulfate hexahydrate: 250-350g / L, nickel chloride hexahydrate: 60-95g / L, boric acid: 40-60g / L, additives (one or more mixtures of sodium lauryl sulfate, saccharin, butynediol ethoxylate): 6-12mL / L, pH 3-5, current density 0.8-2.0A / dm 2 , temperature 50-60℃, anode and cathode area ratio of 1:1.5, electroplating time 30-70min, and coating thickness can be controlled by controlling electroplating parameters as needed.

[0093] The function of pre-silver plating is to pre-plating a layer of silver at a high current density and dilute solution concentration to enhance the bonding strength between the electroplated film layers and prepare for the next step.

[0094] The electroplating parameters are as follows:

[0095] Silver cyanide: 30-120g / L, potassium cyanide: 80-200g / L, free potassium cyanide: 30-80g / L, potassium carbonate: 5-30g / L, potassium hydroxide: 2-20g / L, temperature: 20-25℃, cathode and anode area ratio: 1:1.5, current density: 0.5-2A / dm 2 , electroplating time: about 1min.

[0096] Electroplating silver: Electroplating silver is cyanide silver plating, which also has strong cathodic polarization, making the coating denser. Cyanide silver plating can effectively prevent the penetration of chloride ions in salt spray tests, enhancing the workpiece's corrosion and temperature shock resistance. Silver has a standard electrode potential of +0.799V. Silver is extremely chemically inert, reacting only with sulfur in air and almost no other substances. It has strong corrosion and temperature shock resistance. Electroplating silver on the surface of the workpiece can effectively improve corrosion and temperature shock resistance.

[0097] The electroplating parameters are as follows:

[0098] Silver cyanide: 30-50g / L, potassium cyanide: 130-150g / L, free potassium cyanide: 45-60g / L, potassium carbonate: 15-25g / L, potassium hydroxide: 4-10g / L, additive: 20-30g / L, temperature: 20-25℃, cathode and anode area ratio: 1:1.5, current density: 0.2-0.5A / dm 2, electroplating time: 1-90min, the thickness of the coating is controlled by controlling the electroplating parameters as needed. Similarly, in order to improve the density of the coating, the process used in the present disclosure is optimized to reduce the current density.

[0099] The aluminum terminal provided by the present invention can still achieve a salt spray resistance of 120 hours after impact testing. The expansion coefficients of the alkali copper layer, charred copper layer, and silver layer used in the present invention are close to those of aluminum. During the temperature shock cycle, the expansion volume of these coatings is similar to that of the aluminum material, and the tensile stress they are subjected to is smaller, and the impact of volume change on the coating is smaller. At the same time, the ductility of the alkali copper, charred copper, and silver layers is also excellent. They can effectively withstand tensile stress during the temperature shock cycle (on the one hand, they can reduce tensile stress, and on the other hand, they can withstand the applied tensile stress) without damage.

[0100] The nickel sulfamate layer used in the present disclosure has good ductility and toughness, and can easily withstand the stress caused by volume change without causing microscopic damage to the coating. It can continue to maintain its good density and still have a good protective effect.

[0101] The present disclosure can achieve the following technical effects by cooperating with each other through the alkaline copper layer, the char copper layer, the nickel sulfamate layer, the silver layer, etc.:

[0102] 1. During temperature cycling, rising temperatures can release stress within the electroplating layer, leading to a loss of inter-plating adhesion. The alkaline copper layer, as the bottom layer, has excellent adhesion, ensuring the terminal's adhesion during temperature shocks without causing blistering or peeling. Furthermore, nickel sulfamate, also a low-stress nickel plating solution (i.e., a low-stress nickel plating solution), inherently has low internal stress. This, in conjunction with the alkaline copper layer, effectively enhances the terminal's plating adhesion.

[0103] 2. Enhanced salt spray effect: Since the surface state of the substrate has a great influence on the electroplating layer, it is impossible to directly electroplate a very dense coating on the porous surface of the aluminum material. The present disclosure exemplarily adopts a scheme of gradually increasing density. The density of the zinc layer is lower than that of the alkaline copper, and the density of the alkaline copper is slightly lower than that of the coke copper. The density of these three layers is gradually improved, so that the density of the final coke copper layer is optimized. Therefore, the present disclosure exemplarily adopts a combination of 1-6μm alkaline copper + 5-15μm coke copper, which can effectively improve the corrosion resistance of the workpiece.

[0104] When the electroplated alkaline copper layer is thicker, the coating is prone to roughness. Therefore, the present disclosure chooses to electroplate 1-10μm (exemplary 1-6μm). At this coating thickness, both the bonding strength and density can meet the requirements. The exemplary selection of the char copper layer is between 5-15μm. The thicker the coating, the more it can cover its own pores, but considering the influence of the electroplating time, 5-15μm is selected as an example. The thickness range of nickel sulfamate is 4-15μm, and the exemplary thickness is 4-15μm. Too thick a coating will still lead to an increase in its internal stress and a decrease in ductility, so after comprehensive consideration, 4-15μm is selected as an example.

[0105] In the corrosion-resistant composite layer provided by the present invention, the electroplated film layers such as the alkali copper layer, the char copper layer, the nickel sulfamate layer, and the silver layer all have a high density and can effectively prevent the penetration of chloride ions in the salt spray test. Moreover, the metal / alloy layers interact and overlap with each other, so that the pores originally existing in the single plating layer are covered by other electroplated film layers. Even if chloride ions penetrate one electroplated film layer in the salt spray test, there are still other dense plating layers that can effectively prevent further penetration of chloride ions, thereby greatly improving the corrosion resistance of the aluminum substrate. The corrosion resistance can be further improved by adding a zinc layer, a secondary zinc deposition layer, a chemical copper layer, an acid copper layer, a watt nickel layer, etc.

[0106] The aluminum terminals of the embodiments and comparative examples of the present disclosure can be prepared by referring to the above method.

[0107] Example 1

[0108] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0109] The front of the aluminum terminal material was rolled and polished to a roughness of less than Ra 0.8. The side was precision stamped to a gloss band greater than 98% and a roughness less than Ra 0.8. Figure 4 (left) shows the side view of the standard stamped aluminum terminal, while the second (right) shows the side view of the precision stamped aluminum terminal. As shown in Figure 4, the standard stamped aluminum terminal exhibits a high percentage of rough bands on its side, while the precision stamped aluminum terminal exhibits a gloss band of greater than 98%. The gloss bands were determined using a projector and their percentage was determined by calculating their length or area. The roughness of the aluminum terminal material before and after polishing was 0.315μm and 0.282μm on its side, respectively. This indicates that polishing significantly reduces surface roughness and improves finish. The filter used in the roughness test had a sampling cutoff wavelength of λc = 0.8mm × 5, where 0.8mm is the sampling length and 5 is the magnification factor.

[0110] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a silver layer provided on the fully exposed area of ​​the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 2μm, 8μm, 8μm, and 10μm, respectively.

[0111] Example 2

[0112] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0113] The front of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8, and the side has been processed by precision stamping, with a bright band greater than 98% and a roughness of less than Ra 0.8;

[0114] The composite corrosion-resistant and temperature-shock-resistant layer consists of a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer, applied to the fully exposed surface of the aluminum terminal material. The thicknesses are approximately 0.5μm, approximately 2.0μm, approximately 2.0μm, approximately 10μm, approximately 10μm, and approximately 15μm, respectively. After the composite corrosion-resistant layer is formed, the surface roughness of the aluminum terminal is also improved, reduced to 0.203μm.

[0115] Example 3

[0116] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0117] The front of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8, and the side has been processed by precision stamping, with a bright band greater than 98% and a roughness of less than Ra 0.8;

[0118] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a silver layer provided in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 2μm, 2μm, 1μm, and 0.5μm, respectively.

[0119] Example 4

[0120] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0121] The front of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8, and the side has been processed by precision stamping, with a bright band greater than 98% and a roughness of less than Ra 0.8;

[0122] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer provided on the fully exposed area of ​​the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 5μm, and 5μm, respectively.

[0123] Example 5

[0124] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0125] The front of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8, and the side has been processed by precision stamping, with a bright band greater than 98% and a roughness of less than Ra 0.8;

[0126] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a silver layer provided on the fully exposed area of ​​the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 5μm, and 20μm, respectively.

[0127] Example 6

[0128] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0129] The front of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8, and the side has been processed by precision stamping, with a bright band greater than 98% and a roughness of less than Ra 0.8;

[0130] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a char copper layer, a nickel sulfamate layer, and a silver layer provided on the fully exposed area of ​​the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 18μm, and 5μm, respectively.

[0131] Comparative Example 1

[0132] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and an alkaline copper layer with thicknesses of 0.5 μm, 2 μm, and 28 μm.

[0133] The thickness of each comparative example is kept constant with that of Example 1, and the total thickness of each layer remains unchanged.

[0134] Comparative Example 2

[0135] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and a charred copper layer with thicknesses of 0.5 μm, 2 μm, and 28 μm.

[0136] Comparative Example 3

[0137] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and an aminosulfonate nickel layer with thicknesses of 0.5 μm, 2 μm, and 28 μm.

[0138] Comparative Example 4

[0139] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer. This differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer consists solely of a zinc layer, a secondary zinc deposition layer, and a silver layer, with thicknesses of 0.5 μm, 2 μm, and 28 μm, respectively. The aluminum terminal obtained in this comparative example 4 exhibited extensive peeling, indicating a lack of adhesion between the composite layer (electroplated layer) and the aluminum terminal surface, as shown in Figure 7.

[0140] Comparative Example 5

[0141] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the alkaline copper layer and only has a zinc layer, a secondary zinc deposition layer, a charred copper layer, an aminosulfonic acid nickel layer, and a silver layer, with thicknesses of 0.5 μm, 2 μm, 10 μm, 8 μm, and 10 μm.

[0142] Comparative Example 6

[0143] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the charred copper layer and only has a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, an aminosulfonic acid nickel layer, and a silver layer, with thicknesses of 0.5 μm, 2 μm, 10 μm, 8 μm, and 10 μm.

[0144] Comparative Example 7

[0145] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the nickel sulfamate layer and only has a zinc layer, a secondary zinc deposition layer, an alkali copper layer, a charred copper layer, and a silver layer, with thicknesses of 0.5 μm, 2 μm, 2 μm, 8 μm, and 18 μm.

[0146] Comparative Example 8

[0147] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the silver layer and only has a zinc layer, a secondary zinc deposition layer, an alkali copper layer, a charred copper layer, and an aminosulfonate nickel layer with thicknesses of 0.5 μm, 2 μm, 2 μm, 8 μm, and 18 μm.

[0148] Comparative Example 9

[0149] This comparative example provides a wire-cut aluminum material: the coating is the same as that in Example 1, and no precision stamping and polishing are performed.

[0150] Comparative Example 10

[0151] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the coating is the same as that in Example 1 and has not been subjected to roller pressing.

[0152] Comparative Examples 11-14

[0153] These comparative examples respectively provide an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 3 in that the coating thickness is different from that of Example 3, as shown in Table 1.

[0154] Comparative Example 15

[0155] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the thickness of the coating is different from that of Example 1, as shown in Table 1.

[0156] Comparative Example 16

[0157] This comparative example provides an aluminum terminal, the surface of which is provided with a transition layer and a conventional chemical nickel layer.

[0158] Table 1 shows a comparison of the salt spray corrosion resistance test results of the aluminum terminals of the embodiment and the comparative example and the wire-cut aluminum material of comparative example 9 after the temperature shock cycle test.

[0159] The temperature shock test was conducted as follows: the sample was first held at -40°C for 30 minutes, then transferred to 140°C within 30 seconds and held for 30 minutes. After 100 cycles of "-40°C for 30 minutes" and "140°C for 30 minutes," the sample was then subjected to a salt spray corrosion test in accordance with the national standard GB / T 2423.17-2008. Acceptance criteria: The coating showed no corrosion, no surface pitting, peeling, blistering, or other signs of spotting or color change.

[0160] Table 1

[0161] Test results:

[0162] Through experiments, it was found that the aluminum terminal disclosed herein does not have problems such as excessive contact resistance, poor appearance, and excessive withstand voltage.

[0163] The four coatings of alkaline copper, char copper, ammonia nickel (i.e. nickel sulfamate) and silver are superimposed on each other, and the anti-corrosion effect is better than that of a single coating.

[0164] Compared with the conventional electroplating method (Comparative Example 16, a 3 μm thick chemical nickel layer is plated on the transition layer by chemical plating), the corrosion-resistant layer obtained by the conventional electroplating method is corroded after 12 hours of salt spray resistance test after temperature cycling (as shown in Table 1), and the solution provided by the present invention has better corrosion resistance.

[0165] Comparative Example 9 is based on wire-cut substrate processing. In the corrosion resistance test, corrosion spots first appeared on the side of the sample at 48 hours. The corrosion spot situation is shown in FIG5 .

[0166] The following performance comparisons were made with conventional electroplated terminals: 1. SEM images after temperature cycling (to examine plating damage); 2. Salt spray images after temperature cycling (to examine corrosion resistance). The test results are shown in Figure 6 , where Figure 6 (a) shows the conventional plating layer (1μm copper plating + 4μm silver plating) after 100 temperature shocks, Figure 6 (b) shows the corrosion-resistant layer of Example 1 of the present disclosure after 100 temperature shocks, Figure 6 (c) shows the conventional plating layer without temperature shocks, and Figure 6 (d) shows the plating layer of Example 1 of the present disclosure without temperature shocks.

[0167] As can be seen from Figure 6, the corrosion resistance of the aluminum terminal after the temperature shock is greatly reduced, and the number of corrosion points is significantly more than that of the sample without temperature shock. The conventional plating (only 1μm copper plating + 4μm silver plating) has worse corrosion resistance than the corrosion-resistant layer disclosed in this invention, regardless of whether the temperature shock test is performed or not, and more serious corrosion occurs.

[0168] FIG8 is a surface SEM image and a side cross-sectional metallographic image of a conventional coating (nickel plating) before and after temperature shock.

[0169] In Figure 8, (a) and (b) show the surface SEM image and side cross-sectional metallographic image of the conventional nickel coating before the temperature shock, respectively. (c) and (d) show the surface SEM image and side cross-sectional metallographic image of the conventional nickel coating after the temperature shock, respectively. Figure 8 shows that after the temperature shock, the conventional nickel coating exhibits visible cracks under SEM. Cross-sectional metallographic testing also reveals significant side cracks, indicating that the temperature shock significantly impacted the coating, leading to coating failure and, consequently, loss of terminal protection.

[0170] Figure 9 is a side cross-sectional metallographic image of a conventional coating (nickel plating) and the corrosion-resistant layer of Example 1 of the present disclosure after temperature shock, wherein the left image is the conventional coating and the right image is the corrosion-resistant layer of Example 1 of the present disclosure.

[0171] As can be seen from FIG9 , the corrosion-resistant layer of Example 1 of the present disclosure can effectively withstand temperature shock without generating cracks, and can have good ductility in an environment with rapid temperature changes, maintaining the integrity of the coating.

[0172] The salt spray corrosion resistance of the aluminum terminal with a corrosion-resistant composite layer in the semi-exposed area provided by Example 3 of the present disclosure can reach 28H. Although it is not as good as Example 1 in terms of corrosion resistance time, the test is carried out in a completely exposed salt spray environment. In the actual use of the aluminum terminal, this area is not completely exposed to the environment. Therefore, the corrosion resistance time obtained by the test of Example 3 is lower than that of Example 1 and does not affect the service life of the aluminum terminal. This part of the corrosion-resistant composite layer will still exert a good corrosion resistance effect. That is, if the semi-exposed area of ​​the aluminum terminal of Example 1 is set with the corrosion-resistant composite layer in Example 3, the service life of the corrosion-resistant composite layer in the semi-exposed area will not be lower than the service life of the corrosion-resistant composite layer in the exposed area, and the overall corrosion resistance of the aluminum terminal is also guaranteed.

[0173] Based on this, the present disclosure can set different corrosion-resistant composite layers at different positions of the aluminum terminal according to regional characteristics (whether exposed to the environment, the level of corrosion resistance requirements) and usage requirements, thereby reducing costs while ensuring corrosion resistance and service life.

[0174] Other properties of the coating obtained in Example 1 of the present disclosure:

[0175] 1. Roughness Ra<0.4;

[0176] 2. Keep it at 500℃ for half an hour and then put it into water for sudden cooling. No bubbling will occur (national standard is 220℃), which means that the coating has good adhesion and the electroplating layers are closely connected.

[0177] Experiment on the influence of surface roughness and bright band on corrosion resistance:

[0178] In Example 7, Comparative Example 9, and Comparative Examples 17-19, the same corrosion-resistant layer (i.e., the corrosion-resistant layer in Example 1) was formed on the surfaces of terminals (including wire-cut materials) with different surface roughness (surface roughness before forming the corrosion-resistant layer) and different bright band ratios. Salt spray resistance tests (performed in accordance with the national standard GB / T 2423.17-2008) were then performed to evaluate the effects of surface roughness and bright band ratio on salt spray corrosion resistance. Acceptance criteria included: no corrosion, no surface pitting, peeling, blistering, etc., and no spots or color changes in the coating. The experimental results are shown in Table 2.

[0179] Table 2

[0180] According to the experimental data of Example 7, Comparative Example 17, and Comparative Example 18 given in Table 2, it can be seen that, under the same conditions, the smaller the surface roughness of the substrate surface, the longer the salt spray resistance of the aluminum terminal with the corrosion-resistant composite layer on the surface, and the better the salt spray corrosion resistance;

[0181] According to the experimental data of Example 7, Comparative Example 19, and Comparative Example 9 given in Table 2, it can be seen that: when other conditions are the same and the surface roughness is similar, the higher the proportion of the bright band on the substrate surface, the longer the salt spray resistance of the aluminum terminal with a corrosion-resistant composite layer on the surface, and the better the salt spray corrosion resistance.

[0182] The technical solution disclosed in this disclosure has the following advantages:

[0183] 1. Low cost and simple process; 2. The composite layer has excellent performance. When a thicker silver layer is used, it can meet the 120H salt spray corrosion resistance requirement, and when a thinner silver layer is used, it can meet the 28H salt spray corrosion resistance requirement. It can be applied to different situations and meet different corrosion resistance requirements; 3. The adhesion of each layer is excellent; 4. Although the surface of the aluminum terminal is provided with a corrosion-resistant and temperature shock-resistant composite layer, the conductivity is still very good.

Claims

1. A corrosion-resistant and temperature-shock-resistant composite layer, comprising: Alkali copper layer, char copper layer, nickel sulfamate layer, silver layer; Wherein: the thickness of the alkali copper layer is 1-10 μm, the thickness of the char copper layer is 2-18 μm, the thickness of the nickel sulfamate layer is 0.5-28 μm, and the thickness of the silver layer is 0.2-25 μm; Preferably, the alkali copper layer, the char copper layer, the aminosulfonate nickel layer and the silver layer are arranged in sequence.

2. The corrosion-resistant and temperature-shock-resistant composite layer according to claim 1, wherein: The thickness of the alkali copper layer is 1-6 μm.

3. The corrosion-resistant and temperature-shock-resistant composite layer according to claim 1, wherein: The thickness of the charred copper layer is 5-15 μm.

4. The corrosion-resistant and temperature-shock-resistant composite layer according to claim 1, wherein: The thickness of the nickel sulfamate layer is 0.5-18 μm.

5. The corrosion-resistant and temperature-shock-resistant composite layer according to claim 1, wherein: The thickness of the silver layer is 0.2-3 μm or 8-15 μm.

6. The corrosion-resistant and temperature-shock-resistant composite layer according to claim 1, wherein: The corrosion-resistant and temperature-shock-resistant composite layer further comprises a transition layer, which is arranged on a side of the alkali copper layer that is not in contact with the coke copper layer; Preferably, the transition layer comprises a zinc layer, or a combination of a zinc layer and a secondary zinc deposition layer; Preferably, the thickness of the zinc layer is 0.1-10.0 μm, more preferably 0.5-1 μm; Preferably, the thickness of the secondary zinc deposition layer is 0.1-10 μm, more preferably 1.5-2.5 μm.

7. The corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 6, wherein: The alkaline copper layer, the char copper layer, the aminosulfonate nickel layer and the silver layer are electroplated layers respectively.

8. The corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 7, wherein: The corrosion-resistant and temperature-shock-resistant composite layer further comprises a chemical copper layer, which is disposed on the surface of the alkali copper layer or the surface of the coke copper layer; Preferably, the thickness of the chemical copper layer is 3-25 μm, more preferably 5-15 μm.

9. The corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 8, wherein: The corrosion-resistant and temperature-shock-resistant composite layer further comprises an acid copper layer, which is disposed on the surface of the alkali copper layer or the surface of the coke copper layer; Preferably, the acid copper layer has a thickness of 1-20 μm, more preferably 3-10 μm.

10. The corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 9, wherein: The corrosion-resistant and temperature-shock-resistant composite layer further comprises a Watt nickel layer, and the Watt nickel layer is arranged on the surface of the aminosulfonate nickel layer; Preferably, the thickness of the Watt nickel layer is 1-20 μm, more preferably 3-9 μm.

11. The method for preparing the corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 10, comprising the following steps: An alkali copper layer, a char copper layer, an aminosulfonic acid nickel layer, and a silver layer are sequentially formed on the surface of the substrate by electroplating; Preferably, based on the total volume of the electroplating solution, the electroplating solution used for the alkali copper layer contains cuprous cyanide: 40-50 g / L, total sodium cyanide: 40-60 g / L, free sodium cyanide: 8-14 g / L, potassium sodium tartrate: 30-45 g / L, sodium hydroxide: 1-3 g / L, and additives: 3-5 mL / L; the temperature for electroplating the alkali copper layer is 40-50°C, the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the current density is 0.7-1.2 A / dm 2 , the electroplating time is 5-15min; Preferably, the electroplating solution used for the charred copper layer contains copper pyrophosphate: 50-70 g / L, potassium pyrophosphate: 300-450 g / L, ammonium citrate: 15-30 g / L, and ammonia water: 2-5 mL / L, based on the total volume of the electroplating solution; the temperature for electroplating the charred copper layer is 40-50° C., and the current density is 0.7-1.2 A / dm 2 , the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the electroplating time is 50-90min, preferably 70min; Preferably, the electroplating solution used for the sulfamate nickel layer contains 300-500 g / L of sulfamate nickel, 10-25 g / L of nickel chloride, 30-40 g / L of boric acid, 100-150 g / L of sulfamate acid, and 5-10 ml / L of additives, based on the total volume of the electroplating solution; the temperature for electroplating the sulfamate nickel layer is 50-60° C., and the current density is 0.8-1.2 A / dm 2 , the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the electroplating time is 1-80min, preferably 40-60min, and more preferably 50min; Preferably, based on the total volume of the electroplating solution, the electroplating solution used for the silver layer contains silver cyanide: 30-50 g / L, potassium cyanide: 130-150 g / L, free potassium cyanide: 45-60 g / L, potassium carbonate: 15-25 g / L, potassium hydroxide: 4-10 g / L, and additives: 20-30 g / L; the temperature of the electroplated silver layer is 20-25°C, the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the current density is 0.2-0.5 A / dm 2 The electroplating time is 1-90 min, preferably 30-60 min, and more preferably 40 min.

12. A method for treating an aluminum substrate with corrosion resistance and temperature shock resistance, comprising the step of providing the corrosion resistance and temperature shock resistance composite layer according to any one of claims 1 to 10 on the surface of the aluminum substrate.

13. The method according to claim 12, wherein: The corrosion resistance refers to salt spray corrosion resistance, and the temperature shock resistance refers to temperature cycle shock resistance.

14. The method according to claim 12, wherein: The surface roughness of the aluminum substrate is less than Ra 3.6, more preferably less than Ra 0.

8.

15. A corrosion-resistant and temperature-shock-resistant aluminum terminal, wherein: A partial area or the entire area of ​​the surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with the corrosion-resistant and temperature-shock-resistant composite layer according to any one of claims 1 to 10.

16. The method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal according to claim 15, comprising the following steps: The front surface of the aluminum terminal is subjected to rolling and polishing treatment. Preferably, the front surface roughness of the aluminum terminal subjected to rolling and polishing treatment is less than Ra 3.6, more preferably less than Ra 0.8; The side of the aluminum terminal is subjected to stamping treatment. Preferably, the side roughness of the aluminum terminal after roll pressing is less than Ra 3.6, more preferably less than Ra 0.8, and the bright band is greater than 50%, more preferably greater than 98%; An alkali copper layer, a char copper layer, an aminosulfonic acid nickel layer, and a silver layer are sequentially formed by electroplating on the front and side surfaces of the treated aluminum terminal to achieve the corrosion-resistant and temperature-shock-resistant aluminum terminal; Preferably, before forming the alkaline copper layer by electroplating, a transition layer is first formed on the front and side surfaces of the processed aluminum terminal.

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