Corrosion-resistant and thermal-shock-resistant composite layer based on tin layer, corrosion-resistant and thermal-shock-resistant treatment method for aluminum substrate, and aluminum terminal

Abstract

The present application provides a corrosion-resistant and thermal-shock-resistant composite layer based on a tin layer, a corrosion-resistant and thermal-shock-resistant treatment method for an aluminum substrate, and an aluminum terminal. The corrosion-resistant and thermal-shock-resistant composite layer based on a tin layer comprises an alkaline copper layer, a pyrophosphate copper layer, a chemical nickel layer, and a tin layer; 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 chemical nickel layer is 1-30 μm, and the thickness of the tin layer is 3-30 μm. The corrosion-resistant treatment method for an aluminum substrate comprises the step of providing the corrosion-resistant and thermal-shock-resistant composite layer based on a tin layer on the surface of an aluminum substrate. The surface of the corrosion-resistant aluminum terminal is provided with the corrosion-resistant and thermal-shock-resistant composite layer based on a tin layer. The composite layer in the present application has excellent performance, and can still have a good corrosion resistance after experiencing cyclic thermal shocks; the present application can still meet 240H salt spray corrosion resistance requirements after experiencing cyclic thermal shocks.

Description

Tin-based corrosion-resistant and temperature-shock-resistant composite layer, aluminum substrate corrosion-resistant and temperature-shock-resistant treatment method, and aluminum terminal

[0001] Related applications

[0002] This application claims priority to the Chinese invention patent application with application number 202310934974.6 filed on July 27, 2023, and cites the entire contents disclosed in the above patent application as part of this application. Technical Field

[0003] The present invention relates to a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, a corrosion-resistant and temperature-shock-resistant treatment method for an aluminum substrate, and an aluminum terminal, and belongs 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-mentioned object, the present disclosure first provides a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, which comprises: an alkaline copper layer, a char copper layer, a chemical nickel layer, and a tin layer;

[0011] The thickness of the alkaline copper layer is 1-10 μm, the thickness of the char copper layer is 2-18 μm, the thickness of the chemical nickel layer is 1-30 μm, and the thickness of the tin layer is 3-30 μm.

[0012] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the alkaline copper layer, the char copper layer, the chemical nickel layer, and the tin layer are provided in sequence.

[0013] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the alkaline copper layer is illustratively 1-6 μm, and further illustratively 2-4 μm.

[0014] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the charred copper layer is exemplarily 5-15 μm, and further exemplarily 8-10 μm.

[0015] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the chemical nickel layer is exemplarily 4-15 μm, and further exemplarily 5-10 μm.

[0016] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the tin layer can have different thicknesses according to the different corrosion resistance requirements of the applicable position. 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 tin layer can be set. Exemplarily, the thickness of the tin layer (thin tin layer) is 3-10μm, and further exemplarily 3-6μm; in the completely exposed area where the aluminum terminal has a large contact area with the environment, the requirements for corrosion resistance are high, and a thicker tin layer needs to be set. Exemplarily, the thickness of the tin layer (thick tin layer) is 10-25μm, and further exemplarily 14-18μm.

[0017] In the aforementioned tin-based corrosion-resistant and temperature-shock-resistant composite layer, the tin-based corrosion-resistant and temperature-shock-resistant composite layer further comprises, for example, a transition layer disposed on a side of the alkali copper layer that is not in contact with the char copper layer. The transition layer is disposed between the alkali copper layer and the substrate requiring corrosion resistance treatment to serve as a transition, and can be achieved using an appropriate surface treatment method.

[0018] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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 tin layer are arranged in sequence. The zinc layer and the secondary zinc deposition layer serve as a transition to the subsequent electroplating layer, which can ensure its 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 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 and vacuum plating.

[0019] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the zinc layer is exemplarily 0.1-10 μm, and further exemplarily 0.5-1 μm.

[0020] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the thickness of the secondary zinc deposition layer is 0.1-10 μm, and further illustratively is 1.5-2.5 μm.

[0021] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the zinc layer, the secondary zinc deposition layer, the alkaline copper layer, the char copper layer, the chemical nickel layer, and the tin layer are electroplated layers respectively.

[0022] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further includes a chemical copper layer (or chemically plated copper layer).

[0023] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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.

[0024] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the chemical copper layer is exemplarily 3-25 μm, and further exemplarily 5-15 μm.

[0025] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further includes an acid copper layer.

[0026] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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.

[0027] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the acid copper layer is illustratively 1-20 μm, and further illustratively 3-10 μm.

[0028] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further includes a Watt nickel layer.

[0029] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the Watt nickel layer is arranged on the surface of the chemical nickel layer, that is, the Watt nickel layer can be arranged in the following ways: (1) between the chemical nickel layer and the char copper layer; (2) between the chemical nickel layer and the silver layer.

[0030] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, the thickness of the Watt nickel layer is exemplarily 1-20 μm, and further exemplarily 3-9 μm.

[0031] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, for example, the corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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 choose 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.

[0032] 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. During temperature shock testing, the thermal expansion volume of the aluminum substrate is greater than that of the electroplated film. 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.

[0033] The alkali copper layer, the char copper layer and the tin layer of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer provided in the present invention have a similar expansion coefficient 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 the electroplating film layer from being damaged by temperature shock test, and effectively protects the workpiece from corrosion.

[0034] The chemical nickel layer of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer provided by the present disclosure is chemical nickel plating. Under the action of the catalyst iron ions, the hypophosphite in the solution catalyzes dehydrogenation to form an active hydride, which undergoes a reduction reaction with the nickel ions in the solution, thereby chemically depositing nickel on the surface of the workpiece to form a chemical nickel layer. The thickness of the nickel layer deposited by the chemical reaction is very uniform, and since there is no additional current, it is not affected by the current size and the tip discharge effect. There is no internal stress generated by electroplating between the chemical nickel layer and the workpiece, and it is truly stress-free. In general electroplated layers, during hot and cold shocks, temperature changes will lead to the release of internal stress between the coating and the substrate. At the same time, tensile stress caused by the difference in expansion coefficients also appears, that is, the dual effect of "internal stress + tensile stress", which makes the coating under electroplating more likely to be torn and lose its protective effect on the workpiece. The chemical nickel layer is chemically deposited. Since there is no internal stress, that is, it only withstands tensile stress in the temperature shock test. Compared with other electroplated coatings, it is less stressed and has a smaller risk of being torn due to stress. It can withstand the impact of temperature shock and prevent subsequent corrosion.

[0035] The present disclosure also provides a method for preparing the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, which includes the following steps: forming an alkali copper layer, a char copper layer, a chemical nickel layer, and a tin layer on the surface of the substrate in sequence by electroplating.

[0036] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin 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.

[0037] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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.

[0038] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, the electroplating solution used for the pyrophosphate 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 remaining component in the electroplating solution is water.

[0039] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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).

[0040] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the chemical plating solution used for the chemical nickel layer contains, based on the total volume of the chemical plating solution, 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.

[0041] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, the temperature of the electroless nickel plating is 85-95°C, and the electroless plating time is 5-150 minutes (exemplarily 20-100 minutes, further exemplary 40 minutes). The electroless nickel plating reaction rate is stable. According to the method disclosed herein, the general nickel plating rate is 1 μm / 5 minutes, i.e., 5 minutes to 1 μm, i.e., 20 minutes to 4 μm, and 40 minutes to 8 μm.

[0042] In the above-mentioned method for preparing a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, the electroplating solution used for the tin layer illustratively contains, based on the total volume of the electroplating solution, 10-50 g / L of stannous sulfate, 60-190 ml / L of sulfuric acid, 1-10 g / L of gelatin, 5-10 ml / L of formaldehyde, and 5-30 g / L of benzalkonium chloride. The remaining component in the electroplating solution is water.

[0043] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the temperature of the electroplated tin layer is 10-40°C, the anode and cathode area ratio is 1:1-2 (illustratively 1:1.5), and the current density is 0.5-2A / dm 2 (Example is 0.7-1.2A / dm 2 ), the plating time is 15-120min (exemplary 60min).

[0044] The tin layer disclosed herein may be a matte tin layer or a bright tin layer, both of which may achieve good corrosion resistance. The specific electroplating preparation process may be determined as needed.

[0045] In the above-mentioned preparation method of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, for example, the electroplated alkali copper layer, the electroplated coke copper layer, the electroplated tin 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.

[0046] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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.

[0047] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer, illustratively, the zinc layer and the secondary zinc deposition layer can be prepared by a conventional electroplating method.

[0048] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin 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.

[0049] The present disclosure also provides a method for treating an aluminum substrate for corrosion resistance and temperature shock resistance, which includes the step of providing a corrosion-resistant and temperature shock-resistant composite layer based on a tin 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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 a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer provided by the present disclosure.

[0054] 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.

[0055] 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:

[0056] The front surface of the aluminum terminal is rolled and polished;

[0057] Stamping the sides of the aluminum terminals;

[0058] A zinc layer, a secondary zinc layer, an alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin layer are sequentially formed on the front and side surfaces of the treated aluminum terminal by electroplating to achieve corrosion-resistant and temperature-shock-resistant aluminum terminals.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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%).

[0064] 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.

[0065] 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). It optimizes the corrosion resistance of aluminum terminals after temperature shock cycles, and can achieve 100 cycles of maintaining the temperature at -40°C for 30 minutes and 140°C for 30 minutes while still having good corrosion resistance. The fully exposed area with a thick tin layer can achieve a salt spray time of up to 240 hours, and the semi-exposed area with a thin tin layer can achieve salt spray resistance for 44 hours. It still has a long mechanical life in harsh environments with rapid temperature changes and high corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] FIG1 is a schematic diagram of an exemplary overall structure of the aluminum terminal provided by the present disclosure.

[0067] FIG2 is a schematic diagram of an exemplary electroplating process of the aluminum terminal provided in the present disclosure.

[0068] Figure 3 shows the morphology of the side of the aluminum terminal obtained by ordinary stamping and precision stamping.

[0069] Figure 4 shows the SEM images of conventional aluminum sheets and rolled aluminum sheets.

[0070] Figure 5 shows the morphology of the samples before and after the temperature shock test.

[0071] FIG6 is a surface SEM image and a side cross-sectional metallographic image of a conventional coating (nickel plating) before and after temperature shock.

[0072] FIG7 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

[0073] 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.

[0074] The aluminum terminal provided by the present disclosure is an aluminum terminal with an electroplated film layer, comprising an aluminum terminal material and an electroplated film layer, wherein the aluminum terminal material is an unprocessed aluminum substrate in the shape of a terminal without an electroplated film layer. 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 chemical nickel layer, and a tin layer. An exemplary overall structure of an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer is shown in FIG1 , wherein a zinc layer 2, an alkali copper layer 3, a charred copper layer 4, an chemical nickel layer 5, and a tin 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.

[0075] An exemplary electroplating process for aluminum terminals is shown in Figure 2. The electroplating 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, chemical nickel plating, tin electroplating, post-treatment, pure water washing, and drying. The secondary zinc deposition step can be selected as needed. For example, the electroplating process may or may not include the secondary zinc deposition step based on requirements. Terminal corrosion principle: Common corrosion of metal materials is oxidative corrosion and electrochemical corrosion.

[0076] The principle of oxidative corrosion is the oxidation reaction of metal in the air. The more active the metal, the more susceptible it is to oxidative corrosion. Generally, the following two methods are adopted to avoid corrosion: 1. Surface treatment. A thin film is covered on the metal surface through surface treatment to isolate the air and prevent the metal from reacting with the air; 2. Convert oxidative corrosion into electrochemical corrosion. Protect the workpiece by corroding another metal, that is, the cathodic protection method of sacrificial anode: a metal with stronger reducing properties is used as the protective electrode and connected to the protected metal to form a primary battery. The metal with stronger reducing properties will be consumed by oxidation reaction as the negative electrode, and the protected metal can be used as the positive electrode to avoid corrosion.

[0077] The principle of electrochemical corrosion is the galvanic cell reaction of metals in the marine atmosphere. Metals, impurities, water and ionic salts such as sodium chloride form a galvanic cell, which undergoes an oxidation reaction on the anode (metal), causing the anode to dissolve (i.e., the metal is corroded), and a reduction reaction occurs on the cathode, transferring electrons and discharging. The corrosion time and process are extremely long. Generally, the salt spray test method is used to verify the corrosion resistance of metal materials. The salt spray test is a simulation experiment that simulates metal materials in the marine atmosphere or humid air. It uses the artificial simulated salt spray environment conditions created by the salt spray test equipment to assess the corrosion resistance of products or metal materials. Electrochemical corrosion under salt spray is generally prevented from contacting the metal material by a surface treatment covering film layer. However, the penetration ability of chloride ions in a salt spray environment is very strong, and they can penetrate into the substrate through the pores of the metal surface film layer, thereby causing corrosion. The present disclosure is designed from two aspects: the terminal material and the electroplating film layer, so that the electroplating film layer of the terminal can effectively prevent the penetration of chloride ions, greatly improving the corrosion resistance of the aluminum terminal.

[0078] Corrosion principle after terminal temperature shock test: Due to the difference in expansion coefficient between the workpiece itself and the electroplated film layer, and the difference in expansion coefficient between the electroplated film layers, the expansion coefficient of the aluminum workpiece is 23.21×10 -6 / K, the expansion coefficient of nickel electroplating 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 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 workpiece substrate and causing electrochemical corrosion.

[0079] The present invention is designed from the selection of electroplating film layer, using copper electroplating film layer with a coefficient of expansion close to that of aluminum, tin layer (copper's coefficient of expansion is 17×10 -6 / K, the expansion coefficient of tin is 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 chemical nickel layer without internal stress can reduce the tensile stress it bears without being torn, while still maintaining its original density. It can effectively protect the workpiece from corrosion in salt spray tests.

[0080] The disclosed technical solution also incorporates design considerations from the terminal material, ensuring that the electroplated film effectively blocks chloride ion penetration, significantly enhancing the corrosion resistance of the aluminum terminal. The front of the terminal is roller-pressed and polished, achieving a roughness of less than Ra 3.6, and typically less than Ra 0.8. The side of the terminal is precision-stamped, resulting in a bright band greater than 50%, and typically greater than 98%, and a roughness less than Ra 3.6, and typically less than Ra 0.8.

[0081] The roll-pressing process increases the surface density of the aluminum material by applying pressure mechanically, 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 protectiveness. SEM images of conventional and roll-pressed aluminum sheets are shown in Figure 4. In Figure 4, Figure a shows the conventional aluminum sheet, and Figure b shows the roll-pressed aluminum sheet. As can be seen from Figure 4, the roll-pressing process reduces the surface roughness of the aluminum sheet and significantly improves its flatness.

[0082] The polishing process adopts 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.

[0083] Polishing and precision stamping processes are all used to improve the smoothness and flatness of the terminal material surface and sides.

[0084] 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.

[0085] Ultrasonic degreasing removes oil from the workpiece surface through both physical ultrasonic vibration and chemical esterification. The oil on the workpiece surface must be thoroughly treated; otherwise, the remaining oil on the workpiece surface will affect the effective coverage of the subsequent electroplating layer, causing the electroplating layer to fall off or cause plating to be missed.

[0086] The purpose of alkaline cleaning is that aluminum is an amphoteric metal and reacts with both acids and alkalis. This process uses a strong alkaline solution (such as NaOH and KOH) to dissolve the aluminum oxide and some aluminum on the surface of the workpiece, providing a good surface for the subsequent electroplating layer to cover and ensure its adhesion.

[0087] The functions of pickling are: 1. Neutralize the alkaline solution that remains on the workpiece surface from the previous alkaline wash. 2. Further dissolve the aluminum oxide and some aluminum on the workpiece surface, providing a good surface for subsequent electroplating and ensuring adhesion. 3. Activate the aluminum metal on the workpiece surface, making the aluminum atoms active, reducing the activation energy of subsequent reactions and facilitating subsequent processing steps.

[0088] The purpose of electroless zinc deposition is that the electrode potential difference between aluminum and copper is too large (aluminum is -1.662V (standard electrode potential) and copper is +0.34V (standard electrode potential). Therefore, copper cannot be directly electroplated on the aluminum surface. A layer of zinc must be chemically deposited on the aluminum before subsequent metal layers can be electroplated. The zinc layer deposited in this process is very rough and uneven, which greatly affects subsequent electroplating.

[0089] The function of chemical zinc 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 seed. The surface of the zinc seed is very flat after being dissolved by the strong acid, and can be used for subsequent electroplating.

[0090] The function of secondary zinc deposition is to chemically deposit a layer of zinc on the surface of the workpiece again. At this time, the zinc layer is flat and dense. The surface of the aluminum workpiece has been modified into zinc, which is easy to electroplate other metals.

[0091] The effects of activation are as follows: 1. Zinc is chemically very active and easily oxidized by oxygen in the air, forming an oxide film. This oxide film, formed when the workpiece is exposed to oxygen between processes, needs to be removed during this process. 2. Activating the zinc surface activates the zinc atoms, reducing the activation energy of subsequent reactions and facilitating subsequent processes.

[0092] 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.

[0093] 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.

[0094] 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 disclosed herein. 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 precipitation 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.

[0095] 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.

[0096] 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 minutes, and electroplating thickness 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Watt nickel layer (i.e. Watt nickel plating, bright nickel plating) is a nickel sulfate electroplating layer. It 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.

[0102] 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.

[0103] Electroless Nickel Plating: Electroless nickel is deposited chemically. Under the action of catalytic iron ions, hypophosphite ions in the solution undergo catalytic dehydrogenation, forming active hydrides. These react with nickel ions in the solution to form a reduction reaction, chemically depositing nickel onto the workpiece surface. The resulting nickel layer is very uniform in thickness. Because there is no additional current, it is unaffected by current magnitude or the tip discharge effect. There is no internal stress between the electroless nickel layer and the workpiece, making it truly stress-free. In typical electroplated coatings, temperature fluctuations during thermal shock release internal stress between the coating and the substrate. This simultaneous effect of tensile stress caused by differences in expansion coefficients also creates a dual effect of "internal stress + tensile stress," making the underlying coating more susceptible to tearing, thus losing its protective effect on the workpiece. Electroless nickel is chemically deposited, and because it is free of internal stress, it experiences only tensile stress during temperature shock tests. Compared to other electroplated coatings, it experiences less stress and is less likely to tear due to stress. It can withstand temperature shocks and effectively block chloride ion penetration, preventing corrosion in salt spray tests.

[0104] At the same time, during the deposition process of conventional electroplated films, hydrogen evolution occurs as a side reaction. The generation and overflow of hydrogen creates microscopic pores in the nickel layer, so the amount of hydrogen evolution directly affects the density of the film. Since electroless nickel plating is a simple chemical reaction, it does not involve the influence of current density and hydrogen atomic overpotential on its reaction. The hydrogen generated by the side reaction is far less than that of electroplated nickel layers. Therefore, the porosity of the electroless nickel layer is lower, the density is better, and it can more effectively prevent the penetration of chloride ions, greatly improving the corrosion resistance of the workpiece.

[0105] The parameters for chemical nickel plating are as follows: based on the total volume of the chemical plating solution, the chemical plating solution used for the chemical nickel layer contains nickel sulfate: 15-25g / L, sodium hypophosphite: 15-25g / L, sodium acetate: 20-30g / L, succinic acid: 5-10g / L, and lactic acid: 10-20g / L; the remaining component in the plating solution is water. The temperature for chemical nickel plating is 85-95°C, and the chemical plating time is 5-150min (exemplarily 20-100min, further exemplary 40min). The reaction rate of chemical nickel plating is stable. According to the method disclosed herein, the general nickel plating rate is 1μm / 5min, that is: 5min-1μm, that is, 20min-4μm, 40min-8μm.

[0106] Electroplated tin: Compared to silver plating, electroplated tin offers greater density and a softer film, enabling close connections with other workpieces and providing superior electrical performance. Furthermore, tin is significantly less expensive than silver, making it the optimal choice for corrosion-resistant aluminum terminals.

[0107] The electroplating parameters are as follows:

[0108] Plating solution composition: stannous sulfate: 10-50g / L, sulfuric acid: 60-190ml / L, gelatin: 1-10g / L, formaldehyde: 5-10ml / L, benzyl acetone: 5-30g / L; temperature: 10-40°C, cathode and anode area ratio: 1:1.5, current density: 0.7-1.2A / dm 2 , electroplating time: 15-120min; the coating thickness can be controlled by controlling the parameters of chemical copper plating as needed.

[0109] The functions of post-treatment are: 1. Prevent the tin electroplated film layer on the surface of the workpiece from changing color due to high temperature, which affects the appearance; 2. It can initially fill some of the pores in the tin electroplated film layer to enhance its corrosion resistance.

[0110] The purpose of pure water washing is to thoroughly clean the workpiece with flowing deionized water. Tap water contains a large amount of metal ions, such as calcium and sodium, which will remain on the surface of the workpiece during cleaning, making the workpiece more susceptible to corrosion in a salt spray environment. Therefore, flowing deionized water must be used for cleaning.

[0111] The purpose of drying is to use an oven at 85°C to dry the moisture on the surface of the workpiece in time to prevent the residual water from the previous process from adhering to the workpiece, forming watermarks that affect the appearance and prevent corrosion and oxidation of the workpiece.

[0112] After the impact test, the aluminum terminal provided by the present invention can still achieve a salt spray resistance of 240 hours when a thick tin layer is used, meeting the corrosion resistance requirements of the fully exposed area of ​​the aluminum terminal; when a thin tin layer is used, it can achieve salt spray resistance of 44 hours, meeting the corrosion resistance requirements of the semi-exposed area of ​​the aluminum terminal; the expansion coefficient of the alkali copper layer and the coke copper layer used in the present invention is close to that 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 is smaller, and the volume change has less impact on the coating; at the same time, the ductility of the alkali copper, coke copper and tin layers is also excellent, and they can effectively withstand tensile stress in the temperature shock cycle (on the one hand, they can reduce the tensile stress, and on the other hand, they can withstand the applied tensile stress) without damage.

[0113] The chemical nickel layer used in the present disclosure has good ductility and toughness, and can easily withstand the stress caused by volume changes without causing microscopic damage to the coating. It can continue to maintain its good density and still have a good protective effect.

[0114] The present disclosure can achieve the following technical effects by cooperating with each other through the alkaline copper layer, the char copper layer, the chemical nickel layer, the tin layer, etc.:

[0115] 1. During the temperature cycle, the increase in temperature will lead to the release of stress in the electroplating layer, resulting in the failure of the bonding force between the plating layers. The alkaline copper layer, as the bottom layer, has good bonding force, which can ensure the bonding force of the terminal in the temperature shock and will not cause problems such as blistering and peeling.

[0116] 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 optimal. Therefore, the present disclosure exemplarily adopts a combination of alkaline copper + coke copper, which can effectively improve the corrosion resistance of the workpiece.

[0117] 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 choice of the char copper layer is between 2-18μm. The thicker the coating, the more it can cover its own pores. However, considering the influence of the electroplating time, the exemplary solution can choose 5-15μm. The thickness of the chemical nickel layer is 3-28μm. Too thick a coating will still lead to an increase in its internal stress and a decrease in ductility. The exemplary solution can choose 4-15μm.

[0118] In the corrosion-resistant composite layer provided by the present invention, the electroplated film layers such as the alkali copper layer, the calcined copper layer, the chemical nickel layer, and the tin 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.

[0119] Example 1

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

[0121] 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. The first image (shown on the left) in Figure 3 shows the side of the aluminum terminal produced by conventional stamping, while the second image (shown on the right) shows the side of the aluminum terminal produced by precision stamping. As shown in Figure 3, the side of the aluminum terminal produced by conventional stamping has a higher proportion of rough bands, while the side of the aluminum terminal produced by precision stamping is essentially glossy, with a proportion greater than 98%. The glossy bands were determined using a projector and the proportion of glossy bands was determined by calculating their length or area. The roughness of the front 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 finish. The filter sampling cutoff wavelength λc used in the roughness test is 0.8mm×5, where 0.8mm is the sampling length and 5 is the magnification factor.

[0122] The tin-based corrosion-resistant and temperature-shock-resistant composite layer consists of a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a calcined copper layer, an electroless nickel layer, and a tin layer, located on the fully exposed surface of the aluminum terminal material. The thicknesses are 0.5μm, 2μm, 2μm, 10μm, 8μm, and 15μm, respectively. The formation of the tin-based corrosion-resistant and temperature-shock-resistant composite layer also improves the surface roughness of the aluminum terminal, reducing it to 0.168μm.

[0123] Example 2

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

[0127] Example 3

[0128] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer based on a tin 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 corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin layer arranged in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 2μm, 2μm, 1μm, and 3μm respectively.

[0131] Example 4

[0132] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, wherein:

[0133] 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;

[0134] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin layer arranged in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 5μm, and 7μm, respectively.

[0135] Example 5

[0136] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, wherein:

[0137] 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;

[0138] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin layer arranged in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 25μm, and 7μm, respectively.

[0139] Example 6

[0140] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, wherein:

[0141] 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;

[0142] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin 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 29μm, respectively.

[0143] Example 7

[0144] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, wherein:

[0145] 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;

[0146] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, an chemical nickel layer, and a tin layer arranged in the fully exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 10μm, and 20μm respectively.

[0147] The present disclosure also provides comparative examples 1 to 10, wherein the thickness of each comparative example is kept constant with that of Example 1, and the total thickness of each layer remains unchanged.

[0148] Comparative Example 1

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

[0150] Comparative Example 2

[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 only includes a zinc layer, a secondary zinc deposition layer, and a charred copper layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0152] Comparative Example 3

[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 only includes a zinc layer, a secondary zinc deposition layer, and an electroless nickel layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0154] Comparative Example 4

[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 only includes a zinc layer, a secondary zinc deposition layer, and a tin layer, with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0156] Comparative Example 5

[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 alkaline copper layer and only has a zinc layer, a secondary zinc deposition layer, a charred copper layer, a chemical nickel layer, and a tin layer with thicknesses of 0.5 μm, 2 μm, 12 μm, 8 μm, and 15 μm.

[0158] Comparative Example 6

[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 charred copper layer and only has a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a chemical nickel layer, and a tin layer with thicknesses of 0.5 μm, 2 μm, 12 μm, 8 μm, and 15 μm.

[0160] Comparative Example 7

[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 chemical nickel layer and only has a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, and a tin layer with thicknesses of 0.5 μm, 2 μm, 2 μm, 10 μm, and 23 μm.

[0162] Comparative Example 8

[0163] 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 deposition layer, an alkaline copper layer, a charred copper layer, and an chemical nickel layer with thicknesses of 0.5 μm, 2 μm, 2 μm, 10 μm, and 23 μm.

[0164] Comparative Example 9

[0165] 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.

[0166] Comparative Example 10

[0167] 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 been subjected to a rolling process.

[0168] Comparative Examples 11-14

[0169] 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.

[0170] Comparative Example 15

[0171] 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.

[0172] Comparative Example 16

[0173] This comparative example provides an aluminum terminal, the surface of which is provided with a transition layer and a conventional chemical nickel layer.

[0174] 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 the comparative example after the temperature shock cycle test.

[0175] Table 1

[0176] The temperature shock test was conducted in accordance with the national standard GB / T 2423.22-2012. Specifically, 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 "holding at -40°C for 30 minutes" and "holding at 140°C for 30 minutes," the salt spray corrosion resistance test was conducted in accordance with the national standard GB / T 2423.17-2008. Acceptance criteria: The coating showed no corrosion, no surface pitting, peeling, blistering, etc., and no spots or color changes.

[0177] Test results:

[0178] The following performance comparisons were made with conventional electroplated terminals: 1. SEM images after temperature cycling (to examine coating damage); 2. Salt spray images after temperature cycling (to examine corrosion resistance). The test results are shown in Figure 5 , where Panel (a) shows the conventional coating after 100 temperature shocks, Panel (b) shows the coating of Example 1 of the present disclosure after 100 temperature shocks, Panel (c) shows the conventional coating without temperature shocks, and Panel (d) shows the coating of Example 1 of the present disclosure without temperature shocks.

[0179] As can be seen from Figure 5, the corrosion resistance of the aluminum terminal after the temperature shock is significantly reduced, and the number of corrosion points is significantly more than that of the sample without the temperature shock. The conventional coating (only tin plating or only nickel plating) has worse corrosion resistance than the coating disclosed in this invention, regardless of whether the temperature shock test is performed or not, and more serious corrosion occurs.

[0180] Comparative Example 16 is a 3 μm thick chemical nickel layer plated on the transition layer by chemical plating. After temperature cycling, the sample showed corrosion within 12 hours of the salt spray resistance test.

[0181] The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer of the embodiment of the present invention was subjected to a salt spray corrosion resistance test after being subjected to 100 temperature shocks. The test found that after the temperature shock, the corrosion-resistant and temperature-shock-resistant composite layer based on the thick tin layer of Example 1 was still able to remain in a good state without corrosion in the 240H salt spray test, while the corrosion-resistant and temperature-shock-resistant composite layer based on the thin tin layer of Example 3 was still able to remain in a 44H salt spray test without corrosion.

[0182] Figure 6 shows surface SEM images and side cross-sectional metallographic images of a conventional coating (nickel plating) before and after the temperature shock. Figures (a) and (b) show the surface SEM image and side cross-sectional metallographic image of the conventional coating (nickel plating) before the temperature shock, respectively. Figures (c) and (d) show the surface SEM image and side cross-sectional metallographic image of the conventional coating (nickel plating) after the temperature shock, respectively.

[0183] As can be seen in Figure 6, after the temperature shock, the conventional nickel plating has obvious cracks under the SEM. After the cross-section metallographic test, obvious cracks can be observed on the side, indicating that the temperature shock has a great impact on the plating, causing the plating to fail and thus lose protection for the terminal.

[0184] FIG7 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, wherein the left image is the conventional coating and the right image is the coating according to Example 1 of the present disclosure.

[0185] As can be seen from FIG. 7 , the coating 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.

[0186] Adhesion test: The aluminum terminal obtained in Example 1 of the present disclosure was baked at 220° C. for 30 minutes and then quenched in water. No peeling, blistering, or other poor adhesion was observed.

[0187] The semi-exposed area of ​​the aluminum terminal provided in Example 3 of the present disclosure has a corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer, and the salt spray corrosion resistance of the terminal can reach 44H. 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. During the actual use of the aluminum terminal, this area is not completely exposed to the environment. Therefore, the corrosion resistance time obtained in 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 and temperature-shock-resistant composite layer based on the tin layer will still play 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 and temperature-shock-resistant composite layer based on the tin layer in Example 3, the service life of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer in the semi-exposed area will not be lower than the service life of the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer in the exposed area, and the overall corrosion resistance of the aluminum terminal is also guaranteed.

[0188] Based on this, the present disclosure can set different corrosion-resistant and temperature-shock-resistant composite layers based on tin layers at different positions of aluminum terminals 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.

[0189] Experiment on the influence of surface roughness and bright band on corrosion resistance:

[0190] In Example 8, 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 varying surface roughness (surface roughness before the corrosion-resistant layer was formed) and varying bright band percentages. 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 percentage on salt spray corrosion resistance. Acceptance criteria included: no corrosion, no surface pitting, peeling, or blistering, and no spots or color changes in the coating. The experimental results are shown in Table 2.

[0191] Table 2

[0192] 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 of the aluminum terminal with the corrosion-resistant composite layer on the surface, and the better the salt spray corrosion resistance;

[0193] According to the experimental data of Example 8, 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.

[0194] The technical solution disclosed in this disclosure has the following advantages:

[0195] 1. Low cost and simple process; 2. The composite layer has excellent performance and can still have good corrosion resistance after experiencing temperature cycling shock; after experiencing temperature cycling shock, when a thicker tin layer is used, it can still meet the 240H salt spray corrosion resistance requirement, and when a thinner tin layer is used, it can meet the 44H 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 based on a tin layer, comprising: Alkaline copper layer, char copper layer, chemical nickel layer, tin 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 chemical nickel layer is 1-30 μm, and the thickness of the tin layer is 3-30 μm; Preferably, the alkaline copper layer, the calcined copper layer, the chemical nickel layer and the tin layer are arranged in sequence.

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

5. The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer according to claim 1, wherein: The thickness of the tin layer is 3-10 μm or 10-25 μm.

6. The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer according to claim 1, wherein: The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further comprises a transition layer, wherein the transition layer is arranged on a side of the alkali copper layer that is not in contact with the coke copper layer; Preferably, the transition layer is a zinc layer, or 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 based on a tin layer according to any one of claims 1 to 6, wherein: The alkaline copper layer, the char copper layer, the chemical nickel layer and the tin layer are electroplated layers respectively.

8. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer according to any one of claims 1 to 7, wherein: The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further includes a chemical copper layer, which is arranged 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 based on a tin layer according to any one of claims 1 to 8, wherein: The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer also includes an acid copper layer, which is arranged 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 based on a tin layer according to any one of claims 1 to 9, wherein: The corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer further includes a Watt nickel layer, and the Watt nickel layer is arranged on the surface of the chemical 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 based on the tin layer according to any one of claims 1 to 10, comprising the following steps: An alkaline copper layer, a charred copper layer, a chemical nickel layer, and a tin 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, 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, based on the total volume of the chemical plating solution; the temperature of the chemical nickel plating is 85-95° C., and the chemical plating time is 5-150 min; Preferably, 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, benzalkyne acetone 5-30 g / L, based on the total volume of the electroplating solution; the temperature of the electroplated tin layer is 10-40°C, the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the current density is 0.5-2 A / dm 2 , preferably 0.7-1.2A / dm 2 , the electroplating time is 15-120min.

12. A method for treating an aluminum substrate against corrosion and temperature shock, comprising the step of providing a corrosion-resistant and temperature shock-resistant composite layer based on a tin layer as claimed in any one of claims 1 to 10 on a partial area or the entire area of ​​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, preferably less than Ra 0.

8.

15. 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 corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer as claimed in 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 scorched copper layer, a chemical nickel layer, and a tin 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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