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

Abstract

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. The corrosion-resistant and temperature-shock-resistant composite layer based on a tin layer comprises: an alkaline copper layer (3), a pyrophosphate copper layer (4), a nickel aminosulfonate layer (5) and a tin layer (6), wherein the thickness of the alkaline copper layer (3) is 1-10 μm, the thickness of the pyrophosphate copper layer (4) is 2-18 μm, the thickness of the nickel aminosulfonate layer (5) is 3-28 μm, and the thickness of the tin layer (6) is 3-30 μm. The corrosion-resistant treatment method for the aluminum substrate comprises the step of providing a corrosion-resistant and temperature-shock-resistant composite layer on the surface of an aluminum substrate (1). The surface of the corrosion-resistant aluminum terminal is provided with the corrosion-resistant and temperature-shock-resistant composite layer. The composite layer has good performance, and still has a good corrosion-resistant effect after being subjected to a temperature cycle shock; and after being subjected to the temperature cycle shock, the composite layer can still meet the requirement for 240-hour salt spray corrosion resistance.

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 202310934996.2 filed on July 27, 2023, and cites the entire disclosure of the above patent application as part of this application. Technical Field

[0003] The present 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, which comprises: an alkali copper layer, a char copper layer, a nickel sulfamate 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 nickel sulfamate layer is 0.5-28 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, illustratively, an alkaline copper layer, a char copper layer, a nickel sulfamate layer, and a tin layer are provided in sequence.

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

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

[0016] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, the tin layer may have different thicknesses depending on the different 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 smaller contact area with the environment and are semi-exposed areas. The requirements for corrosion resistance are lower, 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 larger contact area with the environment, the requirements for corrosion resistance are higher, 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 corrosion-resistant and temperature-shock-resistant composite layer, the corrosion-resistant and temperature-shock-resistant composite layer illustratively further includes a transition layer, which is disposed on the 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, 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, illustratively, the thickness of the zinc layer is 0.1-10 μm, and further illustratively is 0.5-1 μm.

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

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

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

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

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

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

[0026] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the acid copper layer is arranged on the surface of the alkali copper layer or the surface of the charred copper layer, that is, the chemical copper layer or the acid copper layer can be arranged in the following ways: (1) arranged on the side surface of the alkali copper layer that is not in contact with the charred copper layer; (2) arranged between the alkali copper layer and the charred copper layer; (3) arranged on the side surface of the charred copper layer that is not in contact with the alkali copper layer.

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

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

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

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

[0031] In the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, for example, the corrosion-resistant and temperature-shock-resistant composite layer can simultaneously include a chemical copper layer and an acid copper layer, and the specific positions of the two can be set at any one or two of the three positions: the surface of the side of the alkali copper layer not in contact with the charred copper layer, between the alkali copper layer and the charred copper layer, and the surface of the side of the charred copper layer not in contact with the alkali copper layer. When two of them are in the same position, their order can be arbitrary. For example, when the chemical copper layer and the acid copper layer are both located between the alkali copper layer and the charred copper layer, the order can be either alkali copper layer, chemical copper layer, acid copper layer, charred copper layer, or alkali copper layer, acid copper layer, chemical copper layer, charred copper layer. On this basis, a Watt nickel layer can also be provided at the same time.

[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 coke copper layer and the tin layer of the corrosion-resistant and temperature-shock-resistant composite layer provided by the present invention have a similar expansion coefficient to that of aluminum (copper 17×10 -6 / K, tin 26.7×10 -6 / K), significantly reducing the tensile stress caused by volume expansion during temperature shock. The tin layer, made of highly ductile and tough nickel sulfamate, withstands tensile stress without tearing and maintains its original density, effectively protecting workpieces from corrosion during salt spray testing. As the outermost coating in the composite, the tin layer effectively prevents salt spray from penetrating the coating and corroding the substrate.

[0034] The present disclosure also provides a method for preparing the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, which includes the following steps: forming an alkali copper layer, a char copper layer, a nickel sulfamate layer, and a tin layer on the surface of a substrate in sequence by electroplating.

[0035] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the alkaline copper layer illustratively contains, based on the total volume of the electroplating solution, 40-50 g / L of cuprous cyanide, 40-60 g / L of total sodium cyanide, 8-14 g / L of free sodium cyanide, 30-45 g / L of potassium sodium tartrate, 1-3 g / L of sodium hydroxide, and 3-5 mL / L of an additive (one or a mixture of two or more selected from the group consisting of polyethylene glycol, fatty amine polyoxyethylene ether (AEO), and OP series octylphenol polyoxyethylene ether). The remainder of the electroplating solution is water.

[0036] In the preparation method of the above-mentioned corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the temperature of the electroplated alkali copper layer is 40-50°C, the anode and cathode area ratio is 1:1-2 (illustratively 1:1.5), and the current density is 0.7-1.2A / dm 2 , the electroplating time is 5-15min.

[0037] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the charcoal copper layer illustratively contains, based on the total volume of the electroplating solution, 50-70 g / L of copper pyrophosphate, 300-450 g / L of potassium pyrophosphate, 15-30 g / L of ammonium citrate, and 2-5 mL / L of aqueous ammonia. The remainder of the electroplating solution is water.

[0038] In the method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, for example, the temperature of the electroplated copper layer is 40-50°C, and the current density is 0.7-1.2A / dm 2 The area ratio of the anode and cathode is 1:1-2 (exemplarily 1:1.5), and the electroplating time is 50-90 min (exemplarily 70 min).

[0039] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, the electroplating solution used for the nickel sulfamate layer illustratively contains, based on the total volume of the electroplating solution, 300-500 g / L of nickel sulfamate, 10-25 g / L of nickel chloride, 30-40 g / L of boric acid, 100-150 g / L of sulfamate, and 5-10 ml / L of an additive (one or a mixture of two or more of a pyridine derivative, a propargyl alcohol derivative, saccharin, etc.). The remainder of the electroplating solution is water.

[0040] In the method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, for example, the temperature of the nickel sulfamate electroplating layer is 50-60° C., and the current density is 0.8-1.2 A / dm 2 The area ratio of the anode and cathode is 1:1-2 (exemplarily 1:1.5), and the electroplating time is 1-80 min (exemplarily 40-60 min, exemplary 50 min).

[0041] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite 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.

[0042] In the preparation method of the above-mentioned corrosion-resistant and temperature-shock-resistant composite 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).

[0043] 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.

[0044] In the above-mentioned preparation method of the corrosion-resistant and temperature-shock-resistant composite layer, for example, the electroplated alkali copper layer, the electroplated coke copper layer, the electroplated 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.

[0045] In the above-mentioned method for preparing the corrosion-resistant composite layer, illustratively, when a chemical copper layer, an acid copper layer, and a Watt nickel layer are contained, these layers can be obtained by corresponding methods at an appropriate time.

[0046] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, illustratively, the zinc layer and the secondary zinc deposition layer can be prepared by a conventional electroplating method.

[0047] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant composite layer, in order to ensure its electroplating bonding strength, other steps can be added to the electroplating process, such as adding acid activation treatment before each step, adding pure water washing and cleaning before each step, etc.

[0048] The present disclosure also provides a method for treating an aluminum substrate to resist corrosion and temperature shock, which includes the step of providing a corrosion-resistant and temperature shock-resistant composite layer provided by the present disclosure on the surface of the aluminum substrate. The aluminum substrate disclosed in the present disclosure includes a pure aluminum substrate and an aluminum alloy substrate.

[0049] 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.

[0050] 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.

[0051] In the above-mentioned method for treating the aluminum substrate for corrosion resistance and temperature shock resistance, the surface roughness of the aluminum substrate is exemplarily less than Ra 3.6, and further exemplarily less than Ra 0.8.

[0052] The present disclosure also provides a corrosion-resistant and temperature-shock-resistant aluminum terminal, wherein a partial area or the entire area of ​​the surface of the corrosion-resistant and temperature-shock-resistant aluminum terminal is provided with the corrosion-resistant and temperature-shock-resistant composite layer provided by the present disclosure.

[0053] 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.

[0054] 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:

[0055] The front surface of the aluminum terminal is rolled and polished;

[0056] Stamping the sides of the aluminum terminals;

[0057] A zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a tin layer are sequentially formed on the front and side surfaces of the treated aluminum terminal by electroplating to achieve a corrosion-resistant and temperature-shock-resistant aluminum terminal.

[0058] In the above-mentioned method for preparing corrosion-resistant and temperature-shock-resistant aluminum terminals, rolling, polishing, and stamping processes can be performed only on the areas requiring corrosion-resistant and temperature-shock-resistant treatment, 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.

[0059] 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.

[0060] 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.

[0061] In the method for preparing the corrosion-resistant and temperature-shock-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.

[0062] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal, exemplarily, the side roughness of the aluminum terminal after rolling treatment is 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%).

[0063] In the above-mentioned method for preparing the corrosion-resistant and temperature-shock-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.

[0064] 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, that is, improves the salt spray corrosion resistance of aluminum terminals after experiencing temperature cycle shocks. It can achieve 100 cycles of maintaining at -40°C for 30 minutes to 140°C for 30 minutes, and still has 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 60 hours. It still has a long mechanical life in harsh environments with rapid temperature changes and high corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG1 is a schematic diagram of an exemplary overall structure of the aluminum terminal provided by the present disclosure.

[0066] FIG2 is a schematic diagram of an exemplary electroplating process of the aluminum terminal provided in the present disclosure.

[0067] Figure 3 shows the morphology of the side of the aluminum terminal obtained by ordinary stamping and precision stamping.

[0068] Figure 4 shows the SEM images of conventional aluminum sheets and rolled aluminum sheets.

[0069] Figure 5 shows the morphology of the samples before and after the temperature shock test.

[0070] FIG6 is a surface SEM image and a side cross-sectional metallographic image of a conventional coating (nickel plating) before and after temperature shock.

[0071] 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

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

[0073] The aluminum terminal provided by the present disclosure is an aluminum terminal with an electroplated film layer, 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 aminosulfonate 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 aminosulfonate 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.

[0074] An exemplary electroplating process for aluminum terminals is shown in FIG2 : the electroplating process includes the following steps: ultrasonic degreasing, alkaline washing, pickling, chemical zinc deposition, chemical zinc stripping, secondary zinc deposition, activation, alkaline copper electroplating, coke copper electroplating, nickel sulfamate electroplating, tin electroplating, post-treatment, pure water washing, and drying; wherein the secondary zinc deposition step can be selected as needed.

[0075] Terminal corrosion principle: Common corrosion of metal materials is oxidation 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 thermal expansion volume of the aluminum workpiece is much larger 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 workpiece substrate and causing electrochemical corrosion.

[0079] The present invention is designed from the selection of electroplating film layer, using copper, tin and other electroplating film layers with similar expansion coefficients to aluminum (copper 17×10 -6 / K, tin 26.7×10 -6 / K), significantly reducing the tensile stress caused by volume expansion during temperature shock. The tin layer, made of highly ductile and tough nickel sulfamate, withstands tensile stress without tearing and maintains its original density, effectively protecting workpieces from corrosion during salt spray testing. As the outermost coating in the composite, the tin layer effectively prevents salt spray from penetrating the coating and corroding the substrate.

[0080] Roll-pressing increases the surface density of the aluminum material by mechanically applying pressure, thereby reducing the porosity of the aluminum terminal material surface and improving its density, preparing it for the next electroplating layer. The less porous the material, the less porous the electroplating layer, resulting in higher protection. SEM images of conventional and roll-pressed aluminum sheets are shown in Figure 3. Figure 3 (a) shows the conventional aluminum sheet, while Figure (b) shows the roll-pressed aluminum sheet. As shown in Figure 3, the roll-pressing treatment reduces the surface roughness of the aluminum sheet and significantly improves its flatness.

[0081] The polishing process is carried out by magnetic polishing. Specifically, a magnetic field is generated by powering on. The magnetic field drives the stainless steel needle to move. During the movement, the stainless steel needle rubs the surface of the terminal material, thereby achieving the effect of mechanical polishing and improving the smoothness and flatness of the terminal material surface.

[0082] Polishing and precision stamping processes are all used to improve the smoothness and flatness of the front and side surfaces of the terminal material.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] Electroplating parameters are as follows: copper pyrophosphate: 50-70 g / L, potassium pyrophosphate: 300-450 g / L, ammonium citrate: 15-30 g / L, ammonia: 2-5 mL / L, current density 0.7-1.2 A / dm 2 , temperature 40-50°C, cathode and anode area ratio: 1:1.5, electroplating time 50-90 min, electroplating thickness: exemplary 5-15 μm. Similarly, to improve the density of the coating, the process used in the present disclosure is optimized to reduce the current density.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] Watt nickel layer (i.e. Watt nickel plating, bright nickel plating) is a nickel sulfate electroplating layer, which has good bonding strength with other plating layers and can be used as an excellent intermediate plating layer. When Watt nickel is added between or on both sides of the alkaline copper layer and the coke copper layer, a potential difference will be generated in a corrosive environment. It can act as an anode and be corroded first, thus protecting other plating layers and enhancing the brightness and corrosion resistance of the overall plating layer itself.

[0094] The parameters for the electroplating of the 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.

[0095] Electroplating nickel sulfamate: nickel sulfamate is used as the main salt and nickel chloride is used as the anode depolarizer. The nickel layer electroplated in this solution system has good ductility. Compared with other electroplated nickel layers, the film layer electroplated with nickel sulfamate is more resilient and has lower internal stress. It can withstand tensile stress generated by temperature shock without being torn, and still maintains its original density. It can effectively protect the workpiece and avoid corrosion in the salt spray test.

[0096] Electroplating parameters are as follows: nickel sulfamate: 300-500g / L, nickel chloride: 10-25g / L, boric acid: 30-40g / L, sulfamate: 100-150g / L, additives: 5-10ml / L; current density: 0.8-1.2A / dm 2 Temperature: 50-60°C, cathode and anode area ratio: 1:1.5, electroplating time: 1-80 minutes; the coating thickness can be controlled by adjusting the parameters of the electroless copper plating as needed. Similarly, to improve the density of the coating, the process used in this disclosure has been optimized to reduce the current density.

[0097] 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 an excellent choice for corrosion-resistant aluminum terminals.

[0098] The electroplating parameters are as follows: 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℃, cathode and anode area ratio: 1:1.5, current density: 0.7-1.2A / dm 2 , electroplating time: 15-120min, the coating thickness is controlled by controlling the electroplating parameters as needed.

[0099] 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 48 hours, meeting the corrosion resistance requirements of the semi-exposed area of ​​the aluminum terminal. The expansion coefficients of the alkali copper layer, charred copper layer and tin layer used in the present invention are close to those of aluminum. During the temperature shock cycle, the expansion volume of these coatings is similar to that of the aluminum material, and the tensile stress is smaller, and the volume change has less impact on the coating; at the same time, the ductility of the alkali copper, charred 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.

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

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

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

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

[0104] When the electroplated alkaline copper layer is thicker, the coating is prone to roughness. Therefore, the present disclosure chooses to electroplate 1-10 μm (exemplary 1-6 μm). At this coating thickness, both the bonding strength and density can meet the requirements. The choice of the char copper layer is between 2-18 μm. The thicker the coating, the more it can cover its own pores. However, considering the influence of the electroplating time, 5-15 μm is selected as an example. If the nickel sulfamate layer is too thick, it will still lead to an increase in its internal stress and a decrease in its ductility. Therefore, considering comprehensive considerations, 4-15 μm is selected as an example.

[0105] In the corrosion-resistant composite layer provided by the present invention, the electroplated film layers such as the alkali copper layer, the char copper layer, the nickel sulfamate layer, and the 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.

[0106] Example 1

[0107] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0108] The front of the aluminum terminal material was rolled and polished to a roughness of less than Ra 0.8. The side was precision stamped to a gloss band greater than 98% and a roughness less than Ra 0.8. Figure 4 (a) shows the side of the aluminum terminal produced by conventional stamping, while the second figure (b) shows the side of the aluminum terminal produced by precision stamping. As shown in Figure 4, 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.

[0109] The composite corrosion-resistant and temperature-shock-resistant layer consists of a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a pyrolysis copper layer, a nickel sulfamate layer, and a tin layer, applied to the fully exposed areas of the aluminum terminal material. The thicknesses are 0.5μm, 2μm, 2μm, 10μm, 8μm, and 15μm, respectively. The formation of the composite corrosion-resistant layer also improves the surface roughness of the aluminum terminal, reducing it to 0.196μm.

[0110] Example 2

[0111] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0112] 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;

[0113] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, an aminosulfonic acid 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.

[0114] Example 3

[0115] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0116] 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;

[0117] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a tin layer provided in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 2μm, 2μm, 1μm, and 3μm, respectively.

[0118] Example 4

[0119] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0120] 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;

[0121] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, an aminosulfonic acid nickel layer, and a tin layer provided 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.

[0122] Example 5

[0123] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0124] 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;

[0125] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, a nickel sulfamate layer, and a tin layer arranged in the semi-exposed area on the surface of the aluminum terminal material, with thicknesses of 0.5μm, 2μm, 3μm, 5μm, 18μm, and 7μm, respectively.

[0126] Example 6

[0127] This embodiment provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, wherein:

[0128] 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;

[0129] The composite corrosion-resistant and temperature-shock-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a charred copper layer, an aminosulfonic acid 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.

[0130] The present disclosure 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.

[0131] Comparative Example 1

[0132] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and an alkaline copper layer with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0133] Comparative Example 2

[0134] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and a charred copper layer with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0135] Comparative Example 3

[0136] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and an aminosulfonate nickel layer with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0137] Comparative Example 4

[0138] This comparative example provides an aluminum terminal with a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and a tin layer with thicknesses of 0.5 μm, 2 μm, and 35 μm.

[0139] Comparative Example 5

[0140] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the alkaline copper layer and only has a zinc layer, a secondary zinc deposition layer, a charred copper layer, an aminosulfonic acid nickel layer, and a tin layer, with thicknesses of 0.5 μm, 2 μm, 12 μm, 8 μm, and 15 μm.

[0141] Comparative Example 6

[0142] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the charred copper layer and only has a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, an aminosulfonic acid nickel layer, and a tin layer, with thicknesses of 0.5 μm, 2 μm, 12 μm, 8 μm, and 15 μm.

[0143] Comparative Example 7

[0144] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the nickel sulfamate layer and only has a zinc layer, a secondary zinc deposition layer, an 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.

[0145] Comparative Example 8

[0146] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the corrosion-resistant and temperature-shock-resistant composite layer omits the tin layer and only has a zinc layer, a secondary zinc deposition layer, an alkali copper layer, a charred copper layer, and an aminosulfonate nickel layer with thicknesses of 0.5 μm, 2 μm, 2 μm, 10 μm, and 23 μm.

[0147] Comparative Example 9

[0148] 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.

[0149] Comparative Example 10

[0150] This comparative example provides an aluminum terminal having a corrosion-resistant and temperature-shock-resistant composite layer, which differs from Example 1 in that the coating is the same as that in Example 1 and has not been subjected to roller pressing.

[0151] Comparative Examples 11-14

[0152] 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.

[0153] Comparative Example 15

[0154] 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.

[0155] Comparative Example 16

[0156] This comparative example provides an aluminum terminal, the surface of which is provided with a transition layer and a conventional chemical nickel layer.

[0157] 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.

[0158] Table 1

[0159] 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.

[0160] Test results:

[0161] 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.

[0162] Figure 5 shows that the corrosion resistance of the aluminum terminals after the temperature shock test significantly decreased, with significantly more corrosion spots than in samples without the temperature shock test. Conventional coatings (tin or nickel only), regardless of whether or not the temperature shock test was performed, exhibited inferior corrosion resistance to the coatings described in this disclosure, exhibiting more severe corrosion.

[0163] 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.

[0164] The corrosion-resistant and temperature-shock-resistant composite layer disclosed herein was subjected to a salt spray corrosion resistance test after being subjected to 100 temperature shocks. The test found that the corrosion-resistant and temperature-shock-resistant composite layer was still able to remain in a good condition without corrosion in a 240H salt spray test.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] The salt spray corrosion resistance of the aluminum terminal provided in Example 3 of the present disclosure, in which the semi-exposed area has a corrosion-resistant and temperature-shock-resistant composite layer, can reach 48H. Although it is not as good as Example 1 in terms of corrosion resistance time, the test is carried out in a completely exposed salt spray environment. In the actual use of the aluminum terminal, this area is not completely exposed to the environment. Therefore, the corrosion resistance time obtained by the test of Example 3 is lower than that of Example 1 and does not affect the service life of the aluminum terminal. This part of the corrosion-resistant and temperature-shock-resistant composite layer will still play a good corrosion-resistant 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 in Example 3, the service life of the corrosion-resistant and temperature-shock-resistant composite layer in the semi-exposed area will not be lower than the service life of the corrosion-resistant and temperature-shock-resistant composite layer in the exposed area, and the overall corrosion resistance of the aluminum terminal is also guaranteed.

[0171] Based on this, the present disclosure can set different corrosion-resistant and temperature-shock-resistant composite layers at different positions of the aluminum terminal according to regional characteristics (whether exposed to the environment, the level of corrosion resistance requirements) and usage requirements, thereby reducing costs while ensuring corrosion resistance and service life.

[0172] Experiment on the influence of surface roughness and bright band on corrosion resistance:

[0173] In Example 7, Comparative Example 9, and Comparative Examples 17-19, the same corrosion-resistant layer (i.e., the corrosion-resistant layer in Example 1) was formed on the surfaces of terminals (including wire-cut materials) with different surface roughness (surface roughness before forming the corrosion-resistant layer) and different bright band ratios. Salt spray resistance tests (performed in accordance with the national standard GB / T 2423.17-2008) were then performed to evaluate the effects of surface roughness and bright band ratio on salt spray corrosion resistance. Acceptance criteria included: no corrosion, no surface pitting, peeling, blistering, etc., and no spots or color changes in the coating. The experimental results are shown in Table 2.

[0174] Table 2

[0175] According to the experimental data of Example 7, Comparative Example 17, and Comparative Example 18 given in Table 2, it can be seen that, under the same conditions, the smaller the surface roughness of the substrate surface, the longer the salt spray resistance of the aluminum terminal with the corrosion-resistant composite layer on the surface, and the better the salt spray corrosion resistance;

[0176] According to the experimental data of Example 7, Comparative Example 19, and Comparative Example 9 given in Table 2, it can be seen that: when other conditions are the same and the surface roughness is similar, the higher the proportion of the bright band on the substrate surface, the longer the salt spray resistance of the aluminum terminal with a corrosion-resistant composite layer on the surface, and the better the salt spray corrosion resistance.

[0177] The technical solution disclosed in this disclosure has the following advantages:

[0178] 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 48H 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: Alkali copper layer, char copper layer, nickel sulfamate 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 nickel sulfamate layer is 0.5-28 μm, and the thickness of the tin layer is 3-30 μm; Preferably, the alkaline copper layer, the charred copper layer, the aminosulfonate nickel layer and the tin layer are arranged in sequence.

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

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

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

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

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

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

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

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

11. The method for preparing the corrosion-resistant and temperature-shock-resistant composite layer based on the tin layer according to any one of claims 1 to 10, comprising the following steps: An alkaline copper layer, a pyrolytic copper layer, an aminosulfonic acid 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 70min; Preferably, the electroplating solution used for the sulfamate nickel layer contains 300-500 g / L of sulfamate nickel, 10-25 g / L of nickel chloride, 30-40 g / L of boric acid, 100-150 g / L of sulfamate acid, and 5-10 ml / L of additives, based on the total volume of the electroplating solution; the temperature for electroplating the sulfamate nickel layer is 50-60° C., and the current density is 0.8-1.2 A / dm 2 , the anode and cathode area ratio is 1:1-2, preferably 1:1.5, and the electroplating time is 1-80min, preferably 40-60min, preferably 50min; 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, benzyl 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 15-120 min, preferably 60 min.

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

16. The method for preparing the corrosion-resistant and temperature-shock-resistant aluminum terminal according to claim 15, comprising the following steps: The front surface of the aluminum terminal is subjected to rolling and polishing treatment. Preferably, the front surface roughness of the aluminum terminal subjected to rolling and polishing treatment is less than Ra 3.6, more preferably less than Ra 0.8; The side of the aluminum terminal is subjected to stamping treatment. Preferably, the side roughness of the aluminum terminal after roll pressing is less than Ra 3.6, more preferably less than Ra 0.8, and the bright band is greater than 50%, more preferably greater than 98%; An alkali copper layer, a char copper layer, an aminosulfonic acid nickel layer, and a 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.

Images