Corrosion and temperature shock resistant composite layer based on tin layer, method for treating an aluminum substrate against corrosion and temperature shock, and aluminum terminal

Abstract

The application provides a tin layer-based corrosion-resistant and temperature impact-resistant composite layer, an aluminum base material corrosion-resistant and temperature impact-resistant treatment method and an aluminum terminal. The tin layer-based corrosion-resistant and temperature impact-resistant composite layer comprises an alkaline copper layer, a cupric pyrolysis layer, a chemical nickel layer and a tin layer; the thickness of the alkaline copper layer is 1-10 microns, the thickness of the cupric pyrolysis layer is 2-18 microns, the thickness of the chemical nickel layer is 1-30 microns, and the thickness of the tin layer is 3-30 microns. The aluminum base material corrosion-resistant treatment method comprises the step of arranging the tin layer-based corrosion-resistant and temperature impact-resistant composite layer on the surface of the aluminum base material. The surface of the corrosion-resistant aluminum terminal is provided with the tin layer-based corrosion-resistant and temperature impact-resistant composite layer. The composite layer has excellent performance, can still have good corrosion resistance after temperature cycle impact, and can still meet the 240H salt mist corrosion resistance requirement after temperature cycle impact.

Description

Technical Field

[0001] This invention relates to a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, a method for treating aluminum substrates to resist corrosion and temperature shock, and aluminum terminals, belonging to the field of corrosion resistance technology. Background Technology

[0002] Current electroplating, electroless plating, spraying, and laser surface treatment processes can protect the substrate by coating aluminum and its alloys with a film. However, the results in salt spray tests are not ideal; common aluminum workpieces can only withstand salt spray for 48 hours before corrosion occurs, significantly limiting their service life in assemblies. Furthermore, aluminum has a high coefficient of thermal expansion, 23.21 × 10⁻⁶. -6 / K, during temperature shock, stress will inevitably be generated in the surface film layer, causing it to tear. In subsequent salt spray tests, the protective effect of the damaged film layer is greatly reduced, resulting in aluminum workpieces failing to reach 12 hours of salt spray protection after temperature shock.

[0003] Currently, electroplating manufacturers have limited research and development on aluminum electroplating processes. They often rely on secondary zinc immersion followed by nickel plating for further electroplating. The selection of plating solutions varies and the results are generally poor. This makes it difficult to meet the electroplating requirements of aluminum workpieces that still possess high corrosion resistance after temperature shocks. In particular, aluminum workpieces used in harsh environments with rapid temperature changes in fields such as military, aerospace, and automotive cannot meet the usage requirements.

[0004] Currently, terminals or components used in connectors, vehicle bodies, controllers, battery packs, and other assemblies undergo temperature shock testing. They are kept at -40°C for 30 minutes, then transferred to 140°C within 30 seconds and kept at 140°C for 30 minutes. After 100 cycles of this test, there are no problems such as excessive contact resistance, poor appearance, or excessive withstand voltage. The terminals that have passed this test appear to be in good condition on the surface, but cracks have appeared under the microscopic level, which is more serious for aluminum terminals.

[0005] However, existing technologies do not address corrosion resistance after temperature shock cycling. By this time, the coating has been damaged and loses its corrosion resistance, which greatly affects the performance of terminals or workpieces. If the corrosion resistance of terminals or workpieces after temperature shock cycling cannot meet the actual usage requirements, it will cause serious consequences. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention aims 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.

[0007] To achieve the above objectives, the present invention first provides a corrosion-resistant and temperature shock-resistant composite layer based on a tin layer, which includes: an alkaline copper layer, a pyrometallurgical copper layer, a chemical nickel layer, and a tin layer;

[0008] Wherein: the thickness of the alkali copper layer is 1-10μm, the thickness of the pyrometallurgical copper layer is 2-18μm, the thickness of the electroless nickel layer is 1-30μm, and the thickness of the tin layer is 3-30μm.

[0009] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, an alkali copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer are arranged sequentially.

[0010] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the alkali copper layer is 1-6 μm, more preferably 2-4 μm.

[0011] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the pyrocopper layer is 5-15 μm, more preferably 8-10 μm.

[0012] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the electroless nickel layer is 4-15 μm, more preferably 5-10 μm.

[0013] In the aforementioned tin-based corrosion-resistant and temperature shock-resistant composite layer, the tin layer can have different thicknesses depending on the corrosion resistance requirements of the applicable location. 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, so the requirements for corrosion resistance are lower, and a thinner tin layer can be provided. Preferably, the thickness of the tin layer (thin tin layer) is 3-10 μm, more preferably 3-6 μm. In the completely exposed area where the aluminum terminal has a large contact area with the environment, the requirements for corrosion resistance are higher, and a thicker tin layer is required. Preferably, the thickness of the tin layer (thick tin layer) is 10-25 μm, more preferably 14-18 μm.

[0014] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the tin-based corrosion-resistant and temperature-shock-resistant composite layer further includes a transition layer, which is disposed on the side of the alkaline copper layer that does not contact the pyrolytic copper layer. This transition layer is disposed between the alkaline copper layer and the substrate requiring corrosion resistance treatment as a transition, and can be implemented using an appropriate surface treatment method.

[0015] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the transition layer includes a zinc layer, or a combination of a zinc layer and a secondary immersion zinc layer; the zinc layer (or zinc layer and secondary immersion zinc layer), alkali copper layer, pyrometallurgical copper layer, and tin layer are sequentially arranged. The zinc layer and secondary immersion zinc layer serve as a transition for subsequent electroplating layers, ensuring their adhesion. According to a specific embodiment of the present invention, the combination of the zinc layer and the secondary immersion zinc layer includes a configuration where the zinc layer and the secondary immersion zinc layer are stacked (top to bottom, with the secondary immersion zinc layer covering the zinc layer); and a configuration where the zinc layer and the secondary immersion zinc layer are located in different areas of the same layer, and in this configuration, they can be partially superimposed on each other. The transition layer of the present invention is not limited to a zinc layer or a secondary immersion zinc layer; other metals or alloys can also be used, as long as they can improve the adhesion of the multifunctional 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 or vacuum electroplating.

[0016] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the zinc layer is 0.1-10 μm, more preferably 0.5-1 μm.

[0017] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on tin layer, preferably, the thickness of the secondary zinc plating layer is 0.1-10μm, more preferably 1.5-2.5μm.

[0018] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the zinc layer, the secondary zinc plating layer, the alkali copper layer, the pyrolytic copper layer, the electroless nickel layer, and the tin layer are all electroplated layers.

[0019] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the tin-based corrosion-resistant and temperature-shock-resistant composite layer further includes a chemical copper layer (or chemical copper plating layer).

[0020] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on tin layer, preferably, the chemical copper layer is disposed on the surface of the alkali copper layer or the surface of the pyrolytic copper layer, that is, the chemical copper layer can be disposed in the following ways: (1) disposed on the side surface of the alkali copper layer that is not in contact with the pyrolytic copper layer; (2) disposed between the alkali copper layer and the pyrolytic copper layer; (3) disposed on the side surface of the pyrolytic copper layer that is not in contact with the alkali copper layer.

[0021] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the chemical copper layer is 3-25 μm, more preferably 5-15 μm.

[0022] In the above-mentioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes an acid copper layer.

[0023] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on tin layer, preferably, the acid copper layer is disposed on the surface of the alkali copper layer or the surface of the pyrolytic copper layer, that is, the chemical copper layer can be disposed in the following ways: (1) disposed on the side surface of the alkali copper layer that is not in contact with the pyrolytic copper layer; (2) disposed between the alkali copper layer and the pyrolytic copper layer; (3) disposed on the side surface of the pyrolytic copper layer that is not in contact with the alkali copper layer.

[0024] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the acid copper layer is 1-20 μm, more preferably 3-10 μm.

[0025] In the above-mentioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes a Watt nickel layer.

[0026] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on tin layer, preferably, the Watt nickel layer is disposed on the surface of the chemical nickel layer, that is, the Watt nickel layer can be disposed in the following ways: (1) disposed between the chemical nickel layer and the copper plating layer; (2) disposed between the chemical nickel layer and the silver layer.

[0027] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the thickness of the Watt nickel layer is 1-20 μm, more preferably 3-9 μm.

[0028] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, preferably, the tin-based corrosion-resistant and temperature-shock-resistant composite layer can simultaneously include a chemical copper layer and an acid copper layer. Furthermore, the specific positions of these two layers can be selected from one or two of three locations: the surface of the alkali copper layer that is not in contact with the pyrocopper layer, between the alkali copper layer and the pyrocopper layer, and the surface of the pyrocopper layer that is not in contact with the alkali copper layer. When both layers are selected at the same location, their order can be arbitrary. For example, when both the chemical copper layer and the acid copper layer are located between the alkali copper layer and the pyrocopper layer, the order can be either alkali copper layer, chemical copper layer, acid copper layer, pyrocopper layer, or alkali copper layer, acid copper layer, chemical copper layer, pyrocopper layer. In addition, a Watt's nickel layer can also be provided simultaneously.

[0029] Due to the difference in the coefficient of thermal expansion between the aluminum substrate (e.g., aluminum terminals, workpieces) and the electroplated film layer, as well as the difference in the coefficient of thermal expansion between different electroplated film layers, the coefficient of thermal expansion of the aluminum substrate is typically 23.21 × 10⁻⁶ during temperature shock testing. -6In temperature shock tests, the thermal expansion volume of the aluminum substrate is greater than that of the electroplated film layer. This volume difference creates significant tensile stress between the workpiece and the electroplated film layer. This stress can cause the electroplated film layer to tear or even break. When the workpiece with a torn surface film layer undergoes a salt spray test, chloride ions in the salt spray solution can easily penetrate and come into contact with the aluminum substrate, causing electrochemical corrosion of the aluminum substrate.

[0030] The alkali copper layer, pyrocopper layer, and tin layer of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer provided by this invention have a coefficient of thermal expansion similar to that of aluminum (copper 17×10). -6 / K, Tin 26.7×10 -6 / K), which greatly reduces the tensile stress caused by volume expansion during temperature shock, avoids damage to the electroplated film layer by temperature shock test, and effectively protects the workpiece from corrosion.

[0031] The chemical nickel layer of the corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer provided by this invention is a chemical nickel plating layer. Under the action of iron ions as a catalyst, hypophosphatemoids in the solution undergo catalytic dehydrogenation to form active hydrides, which then react with nickel ions in the solution to reduce them, thereby chemically depositing nickel onto the workpiece surface to form a chemical nickel layer. The nickel layer deposited by the chemical reaction has a very uniform thickness, and because there is no additional current, it is not affected by the magnitude of the current or the effect of tip discharge. There is no internal stress generated by electroplating between the chemical nickel layer and the workpiece, truly achieving stress-free operation. In general electroplating layers, during thermal shock, temperature changes cause the release of internal stress between the plating layer and the substrate. At the same time, tensile stress caused by the difference in the coefficient of thermal expansion also appears, i.e., the dual effect of "internal stress + tensile stress," making the electroplated plating layer more prone to tearing and losing its protective function for the workpiece. The chemical nickel layer is a chemical deposition layer. Since there is no internal stress, it only bears tensile stress in the temperature shock test. Compared with other electroplating processes, it is subjected to less force, and the risk of tearing due to force is lower. It can withstand the effects of temperature shock and prevent subsequent corrosion.

[0032] The present invention also provides a method for preparing the above-mentioned corrosion-resistant and temperature shock-resistant composite layer based on a tin layer, which includes the following steps: forming an alkaline copper layer, a pyrometallurgical copper layer, a chemical nickel layer, and a tin layer sequentially on the surface of a substrate by electroplating.

[0033] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, 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 (one or a mixture of two or more of polyethylene glycol, fatty amine polyoxyethylene ether (AEO), and OP series octylphenol polyoxyethylene ether, etc.): 3-5 mL / L. The remaining component in the electroplating solution is water.

[0034] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the electroplating temperature of the alkaline copper layer is 40-50℃, the anode-cathode area ratio is 1:1-2 (preferably 1:1.5), and the current density is 0.7-1.2 A / dm². 2 The electroplating time is 5-15 minutes.

[0035] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, based on the total volume of the electroplating solution, the electroplating solution used for the pyrophosphate 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. The remaining component in the electroplating solution is water.

[0036] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the temperature for electroplating the copper plating layer is 40-50℃, and the current density is 0.7-1.2A / dm³. 2 The ratio of anode to cathode area is 1:1-2 (preferably 1:1.5), and the electroplating time is 50-90 min (preferably 70 min).

[0037] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, based on the total volume of the chemical plating solution, the chemical plating solution used for the chemical nickel layer contains nickel sulfate: 15-25 g / L, sodium hypophosphite: 15-25 g / L, sodium acetate: 20-30 g / L, succinic acid: 5-10 g / L, and lactic acid: 10-20 g / L; the remaining component in the plating solution is water.

[0038] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the electroless nickel plating temperature is 85-95℃, and the electroless plating time is 5-150 min (preferably 20-100 min, more preferably 40 min). The electroless nickel plating reaction rate is stable. According to the method of the present invention, the nickel plating rate is generally 1 μm / 5 min, that is: 5 min-1 μm, 20 min-4 μm, 40 min-8 μm.

[0039] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, based on the total volume of the electroplating solution, the electroplating solution used for the tin layer contains: stannous sulfate: 10-50 g / L, sulfuric acid: 60-190 ml / L, gelatin: 1-10 g / L, formaldehyde: 5-10 ml / L, and benzylidene acetone: 5-30 g / L. The remaining component in the electroplating solution is water.

[0040] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the temperature for electroplating the tin layer is 10-40℃, the anode-cathode area ratio is 1:1-2 (preferably 1:1.5), and the current density is 0.5-2A / dm². 2 (Preferred value: 0.7-1.2 A / dm) 2 The electroplating time is 15-120 min (preferably 60 min).

[0041] The tin layer of the present invention can be either a matte tin layer or a bright tin layer, both of which can achieve good corrosion resistance. The specific electroplating preparation process can be determined as needed.

[0042] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the electroplated alkaline copper layer, electroplated coke copper layer, electroplated tin layer, etc., can be prepared by pulse electroplating process, which can further enhance 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 a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, when it contains a chemical copper layer, an acid copper layer, and a Watt's nickel layer, these layers can be obtained at an appropriate time and in an appropriate manner.

[0044] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, preferably, the zinc layer and the secondary zinc plating layer can be prepared using conventional electroplating methods.

[0045] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, in order to ensure its electroplating adhesion, other processes can be added to the electroplating process, such as adding acid activation treatment before each process or adding pure water washing before each process.

[0046] This invention also provides a method for treating aluminum substrates to resist corrosion and temperature shock, comprising the step of depositing a tin-based corrosion-resistant and temperature-shock-resistant composite layer provided by this invention on the surface of the aluminum substrate. The aluminum substrates of this invention include pure aluminum substrates and aluminum alloy substrates.

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

[0048] In the above-mentioned method for treating aluminum substrates to resist corrosion and temperature shock, preferably, the resistance to temperature shock refers to resistance to temperature cycling shock, that is, resistance to alternating hot and cold cycling shock.

[0049] In the above-mentioned method for treating aluminum substrates to resist corrosion and temperature shock, preferably, the surface roughness of the aluminum substrate is less than Ra 3.6, more preferably less than Ra 0.8.

[0050] The present invention also provides a corrosion-resistant and temperature-shock-resistant aluminum terminal, wherein a portion or all of the surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with a tin-based corrosion-resistant and temperature-shock-resistant composite layer provided by the present invention.

[0051] In the aforementioned corrosion-resistant and temperature-shock-resistant aluminum terminals, the corrosion-resistant and temperature-shock-resistant composite layer can cover the entire surface of the aluminum terminal, or it can only cover the surface area that requires corrosion-resistant and temperature-shock-resistant treatment.

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

[0053] The front side of the aluminum terminals is rolled and polished.

[0054] The sides of the aluminum terminals are stamped.

[0055] The aluminum terminals are electroplated sequentially on the front and sides to form a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, thereby achieving the corrosion-resistant and temperature-shock-resistant aluminum terminals.

[0056] In the above preparation methods, rolling, polishing, and stamping processes can be performed only on the areas requiring corrosion and temperature shock resistance treatment, and are not limited to the entire surface of the aluminum terminal. By employing localized treatment, welding is facilitated, allowing for the application of various joining processes such as friction welding, friction stir welding, ultrasonic welding, molecular diffusion welding, and resistance welding, thereby obtaining corrosion-resistant terminals with high reliability and multiple joining capabilities.

[0057] In the above-mentioned method for preparing corrosion-resistant and temperature-shock-resistant aluminum terminals, preferably, rolling the terminal material can enhance the density of its terminal surface and improve the corrosion resistance and temperature-shock resistance of subsequent electroplating treatment.

[0058] In the above-mentioned method for preparing corrosion-resistant and temperature-shock-resistant aluminum terminals, preferably, polishing the terminal material can enhance the surface smoothness of the terminal and improve the corrosion and temperature-shock resistance of subsequent electroplating processes. Polishing can be performed using methods such as chemical polishing or mechanical polishing.

[0059] In the above-mentioned method for preparing corrosion-resistant aluminum terminals, preferably, the surface roughness of the aluminum terminals after roll forming and polishing is less than Ra 3.6, more preferably less than Ra 0.8.

[0060] In the above-mentioned method for preparing corrosion-resistant aluminum terminals, preferably, the side roughness of the aluminum terminal after roll forming 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%).

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

[0062] The technical solution of this invention is based on practical application (in practical applications, terminals are more susceptible to corrosion after rapid temperature changes, and corrosion is a constant process). It optimizes the corrosion resistance of aluminum terminals after temperature shock cycles, achieving good corrosion resistance even after 100 cycles of maintaining -40℃ for 30 minutes to 140℃ for 30 minutes. The fully exposed area with a thick tin layer can withstand salt spray for up to 240 hours, while the semi-exposed area with a thin tin layer can withstand salt spray for 44 hours. It still has a long mechanical life in harsh environments with rapid temperature changes and high corrosiveness. Attached Figure Description

[0063] Figure 1 This is an exemplary overall structural diagram of the aluminum terminal provided by the present invention.

[0064] Figure 2 This is a schematic diagram of an exemplary electroplating process for the aluminum terminals provided by the present invention.

[0065] Figure 3 These are topographic images of the sides of aluminum terminals obtained by conventional stamping and precision stamping.

[0066] Figure 4 SEM images of conventional aluminum sheets and roll-formed aluminum sheets.

[0067] Figure 5 These are images of the sample morphology before and after the temperature shock test.

[0068] Figure 6 The images show surface SEM images and side cross-sectional metallographic images of a conventional coating (nickel plating) before and after temperature shock.

[0069] Figure 7 The images show the metallographic cross-sections of a conventional plating layer (nickel plating) after temperature shock and the plating layer of Example 1 of this invention. Detailed Implementation

[0070] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0071] The aluminum terminal provided by this invention is an aluminum terminal with an electroplated film layer, comprising an aluminum terminal material and an electroplated film layer. The aluminum terminal material has a terminal surface and terminal sides. The electroplated film layer (corrosion-resistant and temperature-shock-resistant composite layer) includes: a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrometallurgical copper layer, a chemical nickel plating layer, and a tin layer. An exemplary overall structure of the aluminum terminal with the corrosion-resistant and temperature-shock-resistant composite layer is shown below. Figure 1 As shown, a zinc layer 2, an alkaline copper layer 3, a pyrolytic copper layer 4, a chemical nickel layer 5, and a tin layer 6 are sequentially disposed on the surface of the aluminum substrate 1; if necessary, a secondary zinc plating layer can be further disposed between the zinc layer 2 and the alkaline copper layer 3.

[0072] An exemplary electroplating process for aluminum terminals is as follows: Figure 2 As shown: The electroplating process includes the following steps: ultrasonic degreasing, alkaline washing, acid washing, chemical zinc immersion, chemical zinc stripping, secondary zinc immersion, activation, electroplating alkaline copper, electroplating coke copper, chemical nickel plating, electroplating tin, post-treatment, pure water washing, and drying; among them, the secondary zinc immersion step can be selected as needed.

[0073] Terminal corrosion principle: Common corrosion of metallic materials is oxidative corrosion and electrochemical corrosion.

[0074] The principle of oxidative corrosion is the oxidation reaction of metals in air. The more reactive the metal, the easier it is to be oxidized and corroded. Generally, the following two methods are used to avoid corrosion: 1. Surface treatment: A thin film is coated on the metal surface to isolate it from the air and prevent the metal from reacting with the air; 2. Converting oxidative corrosion into electrochemical corrosion: The workpiece is protected by corroding another metal, i.e., the sacrificial anode cathodic protection method: A metal with stronger reducing properties is used as the protective electrode and connected to the metal being protected to form a galvanic cell. The metal with stronger reducing properties will act as the negative electrode and undergo an oxidation reaction and be consumed, while the metal being protected acts as the positive electrode to avoid corrosion.

[0075] The principle of electrochemical corrosion is a galvanic cell reaction of metals in a marine atmosphere. Metal, impurities, water, and ionic salts such as sodium chloride form a galvanic cell. Oxidation occurs at the anode (metal), causing it to dissolve (i.e., the metal is corroded), while reduction occurs at the cathode, transferring electrons and discharging. The corrosion process is extremely long, and salt spray testing is generally used to verify the corrosion resistance of metallic materials. Salt spray testing simulates the environment of metallic materials in a marine atmosphere or humid air, using artificially created salt spray conditions to assess the corrosion resistance of products or metallic materials. Electrochemical corrosion under salt spray is generally prevented by surface treatment and coating to prevent the salt spray solution from contacting the metal material. However, chloride ions have a very strong penetrating power in a salt spray environment and can penetrate into the substrate through the pores of the metal surface coating, causing corrosion. This invention designs the terminal material and electroplated film layer to effectively prevent chloride ion penetration, greatly improving the corrosion resistance of aluminum terminals.

[0076] The corrosion principle after terminal temperature shock testing: Due to the difference in the coefficient of thermal expansion between the workpiece and the electroplated film layer, and the difference in the coefficient of thermal expansion between different electroplated film layers, the coefficient of thermal expansion of the aluminum workpiece is 23.21 × 10⁻⁶ during the temperature shock test. -6 / K, the coefficient of thermal expansion of the nickel electroplated film is 13×10. -6 / K, the thermal expansion volume of the aluminum workpiece is much larger than that of the nickel layer. This volume difference creates a large tensile stress between the workpiece and the electroplated film. This stress can cause the electroplated film to tear or even break. When the workpiece with a torn surface film is subjected to salt spray testing, chloride ions in the salt spray solution can easily penetrate and come into contact with the aluminum workpiece substrate, causing electrochemical corrosion of the workpiece.

[0077] This invention is designed with the selection of electroplated film layers in mind, using a copper electroplated film layer and a tin layer (copper 17×10) with a coefficient of thermal expansion similar to that of aluminum. -6 / K, Tin 26.7×10 -6 / K), which greatly reduces the tensile stress caused by volume expansion during temperature shock. At the same time, the use of a stress-free chemical nickel layer can reduce the tensile stress it bears without tearing, and still maintain its original density. It can effectively protect the workpiece and avoid corrosion in salt spray test.

[0078] The technical solution of this invention also focuses on the design of the terminal material, enabling the electroplated film layer of the terminal to effectively hinder the penetration of chloride ions, thus greatly improving the corrosion resistance of the aluminum terminal. The front side of the material terminal undergoes roll forming and polishing, resulting in a roughness less than Ra 3.6, preferably less than Ra 0.8. The side side of the material terminal is processed using precision stamping, resulting in a bright band greater than 50%, preferably greater than 98%, and a roughness less than Ra 3.6, preferably less than Ra 0.8.

[0079] The roll forming process increases the surface density of aluminum by applying pressure mechanically, thereby reducing the porosity of the aluminum terminal material and improving its compactness. This prepares the material for the subsequent electroplating layer. The fewer the pores in the material, the fewer the pores in the electroplating layer, resulting in higher protective properties. SEM images of conventional aluminum plates and roll-formed aluminum plates are shown below. Figure 4 As shown. In Figure 4 In the diagram, image a shows a conventional aluminum sheet, and image b shows a roll-formed aluminum sheet. (From...) Figure 4 It can be seen that the surface roughness of the aluminum plate is reduced and the flatness is greatly improved through roll forming.

[0080] The polishing process uses magnetic polishing, which involves generating a magnetic field by passing an electric current through the material. The magnetic field drives a stainless steel needle to move, and during the movement, the stainless steel needle rubs against the surface of the terminal material, thereby achieving a mechanical polishing effect and improving the smoothness and flatness of the terminal material surface.

[0081] Polishing and precision stamping processes are all used to improve the smoothness and flatness of the surface and sides of the terminal material.

[0082] Improving the flatness and smoothness of the terminal material greatly benefits the electroplating film layer. Due to the influence of current, the electroplating process accumulates more film in areas where electrons are concentrated on the workpiece. This results in uneven film thickness on the terminal surface, and even numerous pits, allowing chloride ions in the salt spray to accumulate and penetrate. When the flatness of the terminal material is insufficient, due to the principle of point discharge, the more curved the conductor surface and the smaller the relative surface area, the more charge accumulates. Uneven protrusions on the material surface will accumulate a large number of electrons, making the protrusions on the electroplated workpiece surface even more prominent and the depressions even more recessed. This forms pinholes, easily accumulating salt spray solution and causing chloride ion penetration, leading to corrosion. After processing with the process of this invention, the terminal material can be effectively covered with an electroplated film layer, effectively improving its corrosion resistance.

[0083] The purpose of ultrasonic degreasing is to remove oil stains from the workpiece surface through both physical ultrasonic vibration and chemical esterification reaction. The oil stains on the workpiece surface must be thoroughly removed; otherwise, the remaining oil stains will affect the effective coverage of the subsequent electroplating film, causing the electroplating film to peel off or be incompletely plated.

[0084] The purpose of alkaline washing is as follows: Aluminum is an amphoteric metal, reacting with both acids and alkalis. This process uses a strong alkaline solution (NaOH, KOH, etc.) to dissolve the aluminum oxide and some aluminum on the workpiece surface, providing a good surface for the subsequent electroplating film and ensuring its adhesion.

[0085] The purpose of pickling is: 1. To neutralize any remaining alkaline solution adhering to the workpiece surface from the previous alkaline pickling step. 2. To further dissolve the aluminum oxide and some aluminum on the workpiece surface, providing a good surface for the subsequent electroplating film and ensuring its adhesion. 3. To activate the aluminum metal on the workpiece surface, making its aluminum atoms active, lowering the activation energy of subsequent reactions, and facilitating subsequent processes.

[0086] The purpose of chemical zinc deposition is to address the significant potential difference between aluminum and copper electrodes (aluminum -1.662V, copper +0.34V). This makes it impossible to directly electroplate copper onto aluminum; a zinc layer must first be chemically deposited on the aluminum before subsequent metal plating can proceed. The zinc layer deposited in this process has a very rough and uneven surface, which significantly affects subsequent electroplating.

[0087] The purpose of chemical stripping is to use a strong acid solution to dissolve most of the zinc layer on the surface of the workpiece, leaving only a very thin layer of zinc. The surface of the zinc is very smooth after being dissolved by the strong acid, which can then be used for subsequent electroplating.

[0088] The purpose of secondary zinc plating is to chemically deposit another layer of zinc on the surface of the workpiece. This zinc layer is smooth and dense, and the surface of the aluminum workpiece has been modified to zinc, making it easy to electroplate other metals.

[0089] The activation process serves two purposes: 1. Zinc is chemically reactive and easily oxidized by oxygen in the air to form an oxide film. This process requires removing the oxide film formed when the workpiece comes into contact with oxygen during process intervals. 2. Activating the zinc layer surface keeps the zinc atoms in an active state, lowering the activation energy of subsequent reactions and facilitating subsequent processes.

[0090] Alkaline copper electroplating: Alkaline copper electroplating is a cyanide copper plating process. Cyanide has a very strong complexing ability in water, which can greatly increase the cathode polarization of electroplating, causing copper ions to accumulate in large quantities at the cathode and deposit together, increasing the density of the electroplated film. The coating produced by cyanide system electroplating is dense and the reaction is fast and efficient, which can cover the zinc layer with a dense and smooth copper layer. Moreover, copper is chemically inert and has low electroplating internal stress, making it an excellent intermediate coating that is easy to electroplat with subsequent metal coatings.

[0091] The 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℃, anode-cathode area ratio: 1:1.5, current density: 0.7-1.2 A / dm² 2 Electroplating time: 5-15 min, coating thickness: preferably 1-6 μm.

[0092] To enhance the density of the coating, the present invention has optimized the process: generally, to meet the requirements of electroplating efficiency and achieve faster production, the current density for electroplating alkaline copper is 4-10 A / dm³. 2 The current density directly affects the density of the coating. A high current density weakens cathodic polarization and makes it easier to reach the hydrogen ion evolution overpotential in the solution, causing hydrogen evolution side reactions during electroplating. The evolved hydrogen gas leaves pores in the coating, reducing its density. The alkaline copper electroplating process used in this invention increases the concentration of the main salt cuprous cyanide and free sodium cyanide while reducing the current density, thereby obtaining an alkaline copper coating with excellent electroplating efficiency and density.

[0093] Electroplated copper pyrophosphate: The electroplated copper pyrophosphate layer is made of copper pyrophosphate. Pyrophosphate has a stronger complexing ability in water than cyanide, and its cathodic polarization in the pyrophosphate system is also stronger. This is because [Cu(P₂O₇)₂] in the solution... 6- It carries a greater number of negative charges and has a greater impact on the cathode process, while [Cu(P2O7)2] 6- It is difficult to discharge and needs to be hydrolyzed into [CuP2O7]. 2- Only then can a copper layer, [CuP2O7], be deposited via electrical discharge. 2- The hydrolysis is relatively slow, thus further increasing cathodic polarization. The charred copper electroplated film is denser with fewer pores, effectively preventing chloride ion penetration in salt spray tests and enhancing the workpiece's corrosion resistance and temperature shock resistance.

[0094] The 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 / dm³ 2 The temperature is 40-50℃, the anode-cathode area ratio is 1:1.5, the electroplating time is 50-90 min, and the preferred electroplating thickness is 5-15 μm. Similarly, to improve the density of the coating, the process used in this invention has been optimized by reducing the current density.

[0095] The chemical copper layer is formed by the orderly deposition of copper ions on a substrate through a chemical reaction autocatalytic plating method. Adding a chemical copper layer between each layer results in good adhesion. The chemical copper layer is an excellent intermediate plating layer that enhances the overall adhesion of the coating. Furthermore, because the preparation process of the chemical copper layer is a purely chemical reaction, it is not affected by current distribution in terms of coating thickness and porosity. Therefore, the chemical copper layer has a more uniform thickness, lower porosity, and good corrosion resistance. Adding this layer in this invention enhances the overall corrosion resistance of the coating.

[0096] The parameters for electroless copper plating are as follows: Composition of the electroless plating solution: copper sulfate: 5-20 g / L, sodium hypophosphite: 20-50 g / L, sodium citrate: 5-30 g / L, nickel sulfate: 0.1-5 g / L, potassium ferrocyanide: 0.5-7 mg / L, boric acid: 15-50 g / L; temperature: 60-90℃, pH: 7.8-10.2, plating time: 40-100 min, typical plating rate: 1 μm / 6 min, i.e., 6 min-1 μm, 24 min-4 μm, 48 min-8 μm; the plating thickness can be controlled as needed by adjusting the electroless copper plating parameters.

[0097] The acid copper layer (i.e., acid copper plating) is made by electroplating copper sulfate. It has good adhesion to other plating layers and can serve as an excellent intermediate plating layer. Furthermore, the copper sulfate plating solution used in the preparation of the acid copper layer is stable and low in cost. Adding acid copper between or on both sides of the alkaline copper layer and the pyrolytic copper layer can enhance the overall brightness and corrosion resistance of the plating layer itself.

[0098] The parameters for electroplating copper sulfate are as follows: Electroplating solution composition: Copper sulfate pentahydrate: 160-250 g / L, sulfuric acid: 25-50 mL / L, chloride ions: 40-120 ppm, additives (sodium polydithiopropane sulfonate, 2-mercaptobenzimidazole, 1,2-ethylidene thiourea, or a mixture of one or more polyamine compounds): 4-15 mL / L, current density: 0.8-2.0 A / dm³ 2 The temperature is 20-30℃, the anode-cathode area ratio is 1:1.5, the electroplating time is 20-80 minutes, and the coating thickness is controlled by adjusting the electroplating parameters as needed.

[0099] Watt's nickel layer (i.e. Watt's nickel plating, bright nickel plating) is a nickel sulfate electroplating layer. It has good adhesion to other plating layers and can be used as an excellent intermediate plating layer. When Watt's nickel is added between or on both sides of alkali copper layer or pyrocopper layer, a potential difference will be generated in the corrosive environment. It can act as an anode and be corroded first, protecting other plating layers and enhancing the overall brightness and corrosion resistance of the plating layer itself.

[0100] The parameters for electroplating Watt's nickel layer are as follows: Electroplating solution composition: Nickel sulfate hexahydrate: 250-350 g / L, Nickel chloride hexahydrate: 60-95 g / L, Boric acid: 40-60 g / L, Additives (sodium dodecyl sulfate, saccharin, butynediol ethoxylate, or one or more of these): 6-12 mL / L, pH 3-5, Current density 0.8-2.0 A / dm³ 2 The temperature is 50-60℃, the anode-cathode area ratio is 1:1.5, the electroplating time is 30-70 minutes, and the coating thickness is controlled by adjusting the electroplating parameters as needed.

[0101] Electroless nickel plating: Electroless nickel plating involves the chemical deposition of nickel onto the workpiece surface. Under the catalytic action of iron ions, hypophosphatemoids in the solution undergo catalytic dehydrogenation, forming active hydrides. These hydrides then react with nickel ions in the solution, resulting in the chemical deposition of nickel into a layer. The deposited nickel layer is highly uniform in thickness and, due to the absence of an additional current, is unaffected by current magnitude or tip discharge effects. There is no internal stress generated during electroplating between the electroless nickel layer and the workpiece, truly achieving stress-free plating. In contrast, conventional electroplated layers experience stress release due to temperature changes during thermal shock, while tensile stress arises due to differences in thermal expansion coefficients. This combined effect of internal and tensile stress makes the electroplated layer more prone to tearing, thus compromising its protective function. Electroless nickel plating, being a chemical deposition process, experiences less stress during temperature shock tests, only tensile stress. Compared to other electroplating processes, it bears less stress and is less susceptible to tearing. It can withstand the effects of temperature shock and effectively prevents chloride ion penetration and corrosion during salt spray tests.

[0102] Meanwhile, in general electroplating, hydrogen evolution is a side reaction that occurs during the deposition process. The generation and escape of hydrogen leave microscopic pores in the nickel layer, so the amount of hydrogen evolution directly affects the density of the film. Electroless nickel plating, being a purely chemical reaction, does not involve the influence of current density or the overpotential of hydrogen atoms. Therefore, the amount of hydrogen produced by the side reaction is far less than that of electroplated nickel layers. Consequently, electroless nickel layers have lower porosity, better density, and can more effectively hinder chloride ion penetration, greatly improving the corrosion resistance of the workpiece.

[0103] The electroless nickel plating parameters are as follows: Based on the total volume of the electroless plating solution, the electroless nickel layer is formed by using a solution containing nickel sulfate: 15-25 g / L, sodium hypophosphite: 15-25 g / L, sodium acetate: 20-30 g / L, succinic acid: 5-10 g / L, and lactic acid: 10-20 g / L; the remaining component in the plating solution is water. The electroless nickel plating temperature is 85-95℃, and the electroless plating time is 5-150 min (preferably 20-100 min, more preferably 40 min). The electroless nickel plating reaction rate is stable. Following the method of this invention, the typical nickel plating rate is 1 μm / 5 min, i.e., 5 min-1 μm, 20 min-4 μm, and 40 min-8 μm.

[0104] Tin plating: Compared to silver plating, tin plating has better density and a softer film, allowing for tighter bonding with other workpieces and better electrical performance. Furthermore, tin is significantly cheaper than silver, making it the optimal choice for corrosion-resistant aluminum terminals.

[0105] The electroplating parameters are as follows:

[0106] Electroplating solution composition: Stannous sulfate: 10-50 g / L, sulfuric acid: 60-190 ml / L, gelatin: 1-10 g / L, formaldehyde: 5-10 ml / L, benzyl acetone: 5-30 g / L; temperature: 10-40℃, anode-cathode area ratio: 1:1.5, current density: 0.7-1.2 A / dm² 2 Electroplating time: 15-120 min; the coating thickness can be controlled as needed by adjusting the parameters of the electroless copper plating.

[0107] The purpose of post-treatment is: 1. To prevent the tin plating film on the workpiece surface from discoloring at high temperatures, affecting its appearance; 2. To initially fill some of the pores in the tin plating film and enhance its corrosion resistance.

[0108] The purpose of pure water washing is to thoroughly clean the workpiece using flowing deionized water. Tap water contains a large number of metal ions, such as calcium and sodium, which can remain on the surface of the workpiece during cleaning, making it more susceptible to corrosion in a salt spray environment. Therefore, it is essential to use flowing deionized water for cleaning.

[0109] The purpose of drying is to use an oven at 85℃ to dry the moisture on the surface of the workpiece in a timely manner, to prevent water residue from the previous process from adhering to the workpiece, forming watermarks that affect the appearance, and to prevent corrosion and oxidation of the workpiece.

[0110] The aluminum terminals provided by this invention, after impact testing, still achieve a salt spray resistance of 240 hours when using a thick tin layer, meeting the corrosion resistance requirements for the fully exposed areas of the aluminum terminals; when using a thin tin layer, they can achieve a salt spray resistance of 44 hours, meeting the corrosion resistance requirements for the semi-exposed areas of the aluminum terminals. The expansion coefficients of the alkali copper layer and the pyrocopper layer used in this invention are close to those of aluminum. During temperature shock cycling, the expansion volume of these coatings is similar to that of aluminum, resulting in lower tensile stress and less impact of volume change on the coatings. At the same time, the ductility of the alkali copper, pyrocopper, and tin layers is also excellent, effectively withstanding tensile stress during temperature shock cycling (both reducing and withstanding the applied tensile stress) without breakage.

[0111] The electroless nickel layer used in this invention has good ductility and toughness, and can easily withstand the stress caused by volume changes without causing microscopic damage to the coating. It can maintain its good density and still has a good protective effect.

[0112] This invention, through the synergistic interaction of an alkali copper layer, a pyrometallurgical copper layer, a chemical nickel layer, and a tin layer, achieves the following technical effects:

[0113] 1. During temperature cycling, the increase in temperature will cause the release of internal stress in the electroplated layer, resulting in the failure of the bonding force between the plating layers. As the bottom layer, the alkaline copper layer has good bonding force and can ensure the bonding force of the terminal under temperature shock, without problems such as blistering and peeling.

[0114] 2. Enhanced Salt Spray Effect: Since the surface condition of the substrate has a great influence on the electroplating layer, it is impossible to directly electroplat a very dense coating on the porous surface of aluminum. This invention preferably adopts a scheme of gradually increasing density. The density of the zinc layer is lower than that of alkali copper, and the density of alkali copper is slightly lower than that of pyrolytic copper. The density of these three layers is gradually increased, so that the final pyrolytic copper layer has the best density. Therefore, this invention preferably uses a combination of alkali copper and pyrolytic copper, which can effectively improve the corrosion resistance of the workpiece.

[0115] When the electroplated alkaline copper layer is too thick, a rough coating can easily occur. Therefore, this invention selects an electroplating thickness of 1-10 μm (preferably 1-6 μm), at which the adhesion and density meet the requirements. The cobalt plating layer is selected between 2-18 μm; the thicker the plating, the better it can cover its own pores. However, considering the influence of electroplating time, a preferred option is 5-15 μm. The thickness of the electroless nickel plating layer is 3-28 μm. Excessive plating can still lead to an increase in internal stress and a decrease in ductility; a preferred option is 4-15 μm.

[0116] The corrosion-resistant composite layer provided by this invention comprises electroplated layers such as alkali copper, pyrometallurgical copper, electroless nickel, and tin, all exhibiting strong density. This effectively hinders chloride ion penetration during salt spray testing. Furthermore, the interaction and superposition of these metal / alloy layers cover the pores present in a single plating layer. Even if chloride ions penetrate one electroplated layer during salt spray testing, other dense plating layers effectively prevent further penetration, significantly improving the corrosion resistance of the aluminum substrate. Further improvements in corrosion resistance can be achieved by adding zinc layers, secondary zinc plating layers, electroless copper layers, acid copper layers, and Watt's nickel layers.

[0117] Example 1

[0118] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0119] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8. Figure 3 The first image is a side view of conventional stamping, and the second image is a side view of precision stamping. Figure 3 It can be seen that the aluminum terminals obtained by ordinary stamping have a higher proportion of rough bands on their sides, while the aluminum terminals obtained by precision stamping have mostly bright bands on their sides, accounting for more than 98%. The condition of the bright bands was determined by projector detection, and the proportion of bright bands 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, respectively. This shows that polishing can significantly reduce surface roughness and improve surface finish. The sampling cutoff wavelength λc of the filter in the roughness test was 0.8mm × 5.

[0120] The tin-based corrosion-resistant and temperature-shock-resistant composite layer comprises a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, with thicknesses of 0.5 μm, 2 μm, 2 μm, 10 μm, 8 μm, and 15 μm, respectively, applied to the fully exposed area of ​​the aluminum terminal material. After forming the tin-based corrosion-resistant and temperature-shock-resistant composite layer, the surface roughness of the aluminum terminal is also improved, reduced to 0.168 μm.

[0121] Example 2

[0122] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0123] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0124] The corrosion-resistant and temperature shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer on the fully exposed area of ​​the aluminum terminal material surface, with thicknesses of 0.5μm, 2μm, 2μm, 15μm, 10μm, and 20μm, respectively.

[0125] Example 3

[0126] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0127] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0128] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, respectively, located on the semi-exposed area of ​​the aluminum terminal material surface. The thicknesses are 0.5μm, 2μm, 2μm, 2μm, 1μm, and 3μm.

[0129] Example 4

[0130] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0131] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0132] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, respectively, located on the semi-exposed area of ​​the aluminum terminal material surface. The thicknesses are 0.5μm, 2μm, 3μm, 5μm, 5μm, and 7μm.

[0133] Example 5

[0134] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0135] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0136] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, respectively, located in the semi-exposed area on the surface of the aluminum terminal material. The thicknesses are 0.5μm, 2μm, 3μm, 5μm, 25μm, and 7μm.

[0137] Example 6

[0138] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0139] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0140] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer on the fully exposed area of ​​the aluminum terminal material surface, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 5μm, and 29μm, respectively.

[0141] Example 7

[0142] This embodiment provides an aluminum terminal with a tin-based corrosion-resistant and temperature shock-resistant composite layer, wherein:

[0143] The front side of the aluminum terminal material has been rolled and polished, with a roughness of less than Ra 0.8. The side side has been processed by precision stamping, with a bright band of more than 98% and a roughness of less than Ra 0.8.

[0144] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer on the fully exposed area of ​​the aluminum terminal material surface, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 10μm, and 20μm, respectively.

[0145] Comparative Example 1

[0146] This comparative example provides an aluminum terminal with a corrosion-resistant layer, which differs from Example 1 in that the corrosion-resistant composite layer consists only of a zinc layer, a secondary zinc plating layer, and an alkaline copper layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm, respectively.

[0147] The thickness of each comparative example is kept the same as that of Example 1, and the total thickness of each layer remains unchanged.

[0148] Comparative Example 2

[0149] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer consists only of a zinc layer, a secondary zinc plating layer, and a copper plating layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm, respectively.

[0150] Comparative Example 3

[0151] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer consists only of a zinc layer, a secondary zinc plating layer, and a chemical nickel plating layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm, respectively.

[0152] Comparative Example 4

[0153] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer consists only of a zinc layer, a secondary zinc plating layer, and a tin layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm, respectively.

[0154] Comparative Example 5

[0155] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer omits the alkali copper layer and only has a zinc layer, a secondary zinc plating layer, a pyrometallurgical copper layer, a chemical nickel layer, and a tin layer, with thicknesses of 0.5μm, 2μm, 12μm, 8μm, and 15μm.

[0156] Comparative Example 6

[0157] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer omits the pyrometallurgical layer and only has a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a chemical nickel layer, and a tin layer, with thicknesses of 0.5μm, 2μm, 12μm, 8μm, and 15μm.

[0158] Comparative Example 7

[0159] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer omits the electroless nickel layer and only has a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrometallurgical copper layer, and a tin layer, with thicknesses of 0.5μm, 2μm, 2μm, 10μm, and 23μm.

[0160] Comparative Example 8

[0161] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the corrosion-resistant composite layer omits the tin layer and only has a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrometallurgical copper layer, and a chemical nickel plating layer, with thicknesses of 0.5μm, 2μm, 2μm, 10μm, and 23μm.

[0162] Comparative Example 9

[0163] This comparative example provides a wire-cut aluminum material: the coating is the same as in Example 1, but it has not undergone precision stamping and polishing.

[0164] Comparative Example 10

[0165] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the coating is the same as that in Example 1 and has not undergone roll forming.

[0166] Comparative Examples 11-14

[0167] These comparative examples each 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.

[0168] Comparative Example 15

[0169] This comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which differs from Example 1 in that the coating thickness is different from that of Example 1, as shown in Table 1.

[0170] Comparative Example 16

[0171] This comparative example provides an aluminum terminal with a transition layer and a conventional electroless nickel layer on its surface.

[0172] Table 1 shows a comparison of the salt spray corrosion resistance test results of the aluminum terminals and wire-cut aluminum materials of the examples and comparative examples after temperature shock cycling tests.

[0173] Table 1

[0174]

[0175]

[0176] Temperature shock testing was conducted according to national standard GB / T 2423.22-2012. Specifically, the sample was first held at -40℃ for 30 minutes, then transferred to 140℃ within 30 seconds and held for 30 minutes. This cycle of "holding at -40℃ for 30 minutes" and "holding at 140℃ for 30 minutes" was repeated 100 times. Then, salt spray corrosion resistance testing was conducted according to national standard GB / T 2423.17-2008. Acceptance criteria: No corrosion, surface pitting, peeling, blistering, etc., and no spots or color changes on the coating.

[0177] Test results:

[0178] Compared with conventional electroplated terminals, the following performance parameters were compared: 1. SEM image after temperature cycling (to observe plating damage); 2. Salt spray test after temperature cycling (to observe corrosion resistance). Test results are as follows... Figure 5 As shown, where, Figure 5 Figure a shows the conventional coating after 100 temperature shocks, Figure b shows the coating of Example 1 of the present invention after 100 temperature shocks, Figure c shows the conventional coating without temperature shocks, and Figure d shows the coating of Example 1 of the present invention without temperature shocks.

[0179] Depend on Figure 5 It can be seen that the corrosion resistance of aluminum terminals decreased significantly after temperature shock, and the number of corrosion points was significantly greater than that of samples that did not undergo temperature shock. Conventional plating (tin plating only) showed poorer corrosion resistance than the plating of the present invention, regardless of whether temperature shock tests were conducted, and more severe corrosion occurred.

[0180] Comparative Example 16 involved electroless plating a 3 μm thick nickel layer onto the transition layer. After temperature cycling, this sample showed corrosion after 12 hours of salt spray testing.

[0181] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer of this invention underwent a salt spray corrosion test after being subjected to 100 temperature shocks. The test results showed that after the temperature shocks, the corrosion-resistant and temperature-shock-resistant composite layer based on the thick tin layer of Example 1 could still maintain a good condition without corrosion in the 240-hour salt spray test, while the corrosion-resistant and temperature-shock-resistant composite layer based on the thin tin layer of Example 3 could still maintain a good condition without corrosion in the 44-hour salt spray test.

[0182] Figure 6 The images show surface SEM images and side cross-sectional metallographic images of a conventional coating (nickel plating) before and after temperature shock.

[0183] Depend on Figure 6 It can be seen that after temperature shock, the conventional nickel plating layer shows obvious cracks under SEM. After cross-sectional metallographic testing, obvious cracks can be observed on the side, indicating that temperature shock has a great impact on the plating layer, causing the plating layer to fail and thus lose its protection for the terminals.

[0184] Figure 7 The images show side cross-sectional metallographic images of a conventional plating layer (nickel plating) after temperature shock and the plating layer of Example 1 of the present invention. The left image shows the conventional plating layer, and the right image shows the plating layer of Example 1 of the present invention.

[0185] Depend on Figure 7 It can be seen that the coating of Embodiment 1 of the present invention can effectively withstand temperature shock without cracking, and has good ductility in environments with rapid temperature changes, maintaining the integrity of the coating.

[0186] Adhesion test: The aluminum terminal obtained in Example 1 of the present invention was baked at 220°C for 30 minutes and then placed in water for rapid cooling. There was no poor adhesion such as peeling or blistering.

[0187] The aluminum terminal with a tin-based corrosion-resistant and temperature-shock-resistant composite layer in the semi-exposed area provided in Embodiment 3 of the present invention can achieve a salt spray corrosion resistance of 44 hours. Although the corrosion resistance time is not as good as that in Embodiment 1, the test was conducted under complete exposure to salt spray environment. In the actual use of aluminum terminals, this area is not completely exposed to the environment. Therefore, the lower corrosion resistance time obtained by Embodiment 3 compared to Embodiment 1 will not affect the service life of the aluminum terminal. This tin-based corrosion-resistant and temperature-shock-resistant composite layer will still have a good corrosion resistance effect. That is, if the semi-exposed area of ​​the aluminum terminal in Embodiment 1 is provided with the tin-based corrosion-resistant and temperature-shock-resistant composite layer in Embodiment 3, the service life of the tin-based corrosion-resistant and temperature-shock-resistant composite layer in the semi-exposed area will not be lower than the service life of the tin-based corrosion-resistant and temperature-shock-resistant composite layer in the exposed area, and the overall corrosion resistance of the aluminum terminal is also guaranteed.

[0188] Based on this, the present invention can set different tin-based corrosion-resistant and temperature shock-resistant composite layers at different locations of aluminum terminals according to regional characteristics (whether exposed to the environment, the level of corrosion resistance requirements) and usage needs, thereby reducing costs while ensuring corrosion resistance and service life.

[0189] Experiment on the effect of surface roughness and gloss band on corrosion resistance:

[0190] Examples 8, 9, and 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 roughnesses (surface roughness before the preparation of the corrosion-resistant layer) and different proportions of bright bands. Salt spray resistance tests were then conducted (according to national standard GB / T 2423.17-2008) to evaluate the influence of surface roughness and the proportion of bright bands on salt spray corrosion resistance. The acceptance criteria were: 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.

[0191] Table 2

[0192]

[0193] According to the experimental data of Example 8, 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 time of the aluminum terminal with the corrosion resistant composite layer on the surface, and the better the salt spray corrosion resistance.

[0194] According to the experimental data of Example 8, Comparative Example 19 and Comparative Example 9 given in Table 2, it can be seen that under the same conditions and similar surface roughness, the higher the proportion of bright band on the surface of the substrate, the longer the salt spray resistance time of the aluminum terminal with the corrosion resistant composite layer on the surface, and the better the salt spray corrosion resistance.

[0195] The technical solution of the present invention has the following advantages:

[0196] 1. Low cost and simple process; 2. Excellent performance of the composite layer, which can still maintain good corrosion resistance after temperature cycling shock; after temperature cycling shock, the thicker tin layer can still meet the 240H salt spray corrosion resistance requirement, and the thinner tin layer can meet the 44H salt spray corrosion resistance requirement, which can be used for different situations and meet different corrosion resistance requirements; 3. Excellent adhesion of each layer; 4. Although the aluminum terminal surface 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 based on a tin layer, comprising, in sequence: a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel plating layer, and a tin layer; in: The thickness of the alkali copper layer is 1-10 μm, the thickness of the pyrometallurgical copper layer is 2-18 μm, the thickness of the electroless nickel layer is 1-30 μm, and the thickness of the tin layer is 3-10 μm or 10-25 μm.

2. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin 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 based on a tin layer according to claim 1, wherein, The thickness of the copper plating layer is 5-15 μm.

4. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 1, wherein, The thickness of the electroless nickel layer is 4-15 μm.

5. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 1, wherein, The thickness of the zinc layer is 0.5-1 μm.

6. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 1, wherein, The thickness of the secondary zinc plating layer is 1.5-2.5 μm.

7. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to any one of claims 1-6, wherein, The alkali copper layer, pyrometallurgical copper layer, electroless nickel layer, and tin layer are all electroplated layers.

8. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to any one of claims 1-6, wherein, The tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes a chemical copper layer, which is disposed on the surface of the alkali copper layer or the pyrolytic copper layer.

9. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 8, wherein, The thickness of the chemical copper layer is 3-25 μm.

10. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 9, wherein, The thickness of the chemical copper layer is 5-15 μm.

11. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 7, wherein, The tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes a chemical copper layer, which is disposed on the surface of the alkali copper layer or the pyrolytic copper layer.

12. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 11, wherein, The thickness of the chemical copper layer is 3-25 μm.

13. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 12, wherein, The thickness of the chemical copper layer is 5-15 μm.

14. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to any one of claims 1-6, wherein, The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer also includes an acid copper layer, which is disposed on the surface of the alkali copper layer or the surface of the pyrolytic copper layer.

15. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 14, wherein, The thickness of the acid copper layer is 1-20 μm.

16. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 15, wherein, The thickness of the acid copper layer is 3-10 μm.

17. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 7, wherein, The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer also includes an acid copper layer, which is disposed on the surface of the alkali copper layer or the surface of the pyrolytic copper layer.

18. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 17, wherein, The thickness of the acid copper layer is 1-20 μm.

19. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 18, wherein, The thickness of the acid copper layer is 3-10 μm.

20. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to any one of claims 1-6, wherein, The tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes a Watt nickel layer, which is disposed on the surface of the electroless nickel layer.

21. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 20, wherein, The thickness of the Watt nickel layer is 1-20 μm.

22. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 21, wherein, The thickness of the Watt nickel layer is 3-9 μm.

23. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 7, wherein, The tin-based corrosion-resistant and temperature-shock-resistant composite layer also includes a Watt nickel layer, which is disposed on the surface of the electroless nickel layer.

24. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 23, wherein, The thickness of the Watt nickel layer is 1-20 μm.

25. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to claim 24, wherein, The thickness of the Watt nickel layer is 3-9 μm.

26. The method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer as described in claim 1, comprising the following steps: A zinc layer, a secondary zinc layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer are sequentially formed on the surface of a substrate through electroplating.

27. The preparation method according to claim 26, wherein, Based on the total volume of the electroplating solution, the electroplating solution used for the alkaline 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 electroplating temperature for the alkaline copper layer is 40-50℃, the anode-cathode area ratio is 1:1-2, and the current density is 0.7-1.2 A / dm². 2 The electroplating time is 5-15 minutes.

28. The preparation method according to claim 27, wherein, The ratio of the anode to cathode area in the electroplated alkaline copper layer is 1:1.

5.

29. The preparation method according to claim 26, wherein, Based on the total volume of the electroplating solution, 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; the electroplating temperature for the charred copper layer is 40-50℃, and the current density is 0.7-1.2 A / dm³. 2 The ratio of anode to cathode area is 1:1-2, and the electroplating time is 50-90 minutes.

30. The preparation method according to claim 29, wherein, The ratio of the anode to cathode area in the electroplated copper layer is 1:1.

5.

31. The preparation method according to claim 26, wherein, Based on the total volume of the electroless plating solution, the electroless nickel layer is prepared using a solution containing nickel sulfate: 15-25 g / L, sodium hypophosphite: 15-25 g / L, sodium acetate: 20-30 g / L, succinic acid: 5-10 g / L, and lactic acid: 10-20 g / L; the electroless nickel plating temperature is 85-95℃, and the electroless plating time is 5-150 min.

32. The preparation method according to claim 26, wherein, Based on the total volume of the electroplating solution, the electroplating solution used for the tin layer contains stannous sulfate: 10-50 g / L, sulfuric acid: 60-190 ml / L, gelatin: 1-10 g / L, formaldehyde: 5-10 ml / L, and benzylidene acetone: 5-30 g / L; the temperature for electroplating the tin layer is 10-40℃, the anode-cathode area ratio is 1:1-2, and the current density is 0.5-2 A / dm². 2 The electroplating time is 15-120 minutes.

33. The preparation method according to claim 32, wherein, The ratio of the anode to cathode area of ​​the electroplated tin layer is 1:1.

5.

34. The preparation method according to claim 32, wherein, The current density for electroplating tin layers is 0.7-1.2 A / dm³. 2 .

35. A method for treating an aluminum substrate to resist corrosion and temperature shock, comprising the step of applying a tin-based corrosion-resistant and temperature-shock-resistant composite layer as described in claim 1 to a portion or all of the surface of the aluminum substrate.

36. The method according to claim 35, wherein, The corrosion resistance refers to resistance to salt spray corrosion, and the temperature shock resistance refers to resistance to temperature cycling shock.

37. The method of claim 35, wherein, The surface roughness of the aluminum substrate is less than Ra 3.

6.

38. The method according to claim 37, wherein, The surface roughness of the aluminum substrate is less than Ra 0.

8.

39. A corrosion-resistant and temperature-shock-resistant aluminum terminal, wherein, The surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with the tin-based corrosion-resistant and temperature-shock-resistant composite layer as described in claim 1.

40. The method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal according to claim 39, comprising the following steps: The front side of the aluminum terminals is rolled and polished. The sides of the aluminum terminals are stamped. The aluminum terminals are electroplated sequentially on the front and sides to form a zinc layer, a secondary zinc plating layer, an alkaline copper layer, a pyrolytic copper layer, a chemical nickel layer, and a tin layer, thereby achieving the corrosion-resistant and temperature-shock-resistant aluminum terminals.

41. The preparation method according to claim 40, wherein, The surface roughness of aluminum terminals that have undergone roll forming and polishing is less than Ra 3.

6.

42. The preparation method according to claim 41, wherein, The surface roughness of aluminum terminals after roll forming and polishing is less than Ra 0.

8.

43. The preparation method according to claim 40, wherein, The side roughness of the aluminum terminals after roll forming is less than Ra 3.6, and the bright band is greater than 50%.

44. The preparation method according to claim 40, wherein, The side roughness of the aluminum terminals after roll forming is less than Ra 0.

8.

45. The preparation method according to claim 40, wherein, The gloss band of the aluminum terminals after roll forming is greater than 98%.

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