A corrosion-resistant composite layer based on a tin layer, a method for corrosion-resistant treatment of an aluminum base material, and a corrosion-resistant aluminum terminal

Abstract

The application provides a tin layer-based corrosion-resistant composite layer, an aluminum base material corrosion-resistant treatment method and a corrosion-resistant aluminum terminal. The tin layer-based corrosion-resistant composite layer comprises an alkaline copper layer, a cupric pyrolysis layer and a tin layer. The thickness of the alkaline copper layer is 1-10 microns, the thickness of the cupric pyrolysis layer is 2-18 microns, and the thickness of the tin layer is 3-30 microns. The aluminum base material corrosion-resistant treatment method comprises the step of arranging the corrosion-resistant composite layer on the surface of the aluminum base material. The surface of the corrosion-resistant aluminum terminal is provided with the corrosion-resistant composite layer. The technical scheme of the application has the following advantages: low cost, simple process, excellent corrosion-resistant performance of the composite layer, meeting the 360H salt mist corrosion resistance requirement, excellent adhesion of each layer, no blistering after 10 times of 220 DEG C thermal shock test, and very good conductivity of the aluminum terminal surface although the surface is provided with the corrosion-resistant composite layer.

Description

TECHNICAL FIELD

[0001] The present application relates to a tin layer-based corrosion-resistant composite layer, an aluminum substrate corrosion-resistant treatment method and a corrosion-resistant aluminum terminal, and belongs to the technical field of corrosion resistance. BACKGROUND

[0002] Aluminum and its alloys are widely used in the electrical energy transmission systems of the military, automotive and aerospace industries due to their low density, high electrical conductivity and good formability, but the lack of corrosion resistance in corrosive environments restricts the further application of aluminum and its alloys. The chemical properties of aluminum and its alloys limit their application: 1. Aluminum is easily oxidized in air to form an oxide film layer, which greatly increases the terminal resistance and affects the transmission of electrical energy; 2. When connected to other metals with more positive standard electrode potentials (such as copper), aluminum is prone to potential corrosion, causing connection failure and even short circuits.

[0003] Current electroplating and chemical plating, spraying, laser surface treatment processes can protect the substrate by coating a film layer on the surface of aluminum and its alloys, but the results of salt spray tests are not ideal, and the salt spray time of common aluminum workpieces can only be maintained for 48 hours before corrosion occurs, greatly limiting the service life of aluminum workpieces in assemblies.

[0004] Current electroplating manufacturers have less research on aluminum electroplating processes, and only through secondary zinc deposition and nickel plating to make them proceed to the next step of electroplating. The selection of plating layer scheme is not uniform and the effect is general, which is difficult to meet the requirements of high corrosion-resistant aluminum workpiece electroplating, especially the aluminum workpieces used in harsh environments such as military, aerospace and automotive fields cannot meet the use requirements. SUMMARY

[0005] To solve the above technical problems, the purpose of the present application is to provide a corrosion-resistant composite layer based on a tin layer, which has excellent salt spray corrosion resistance and can be used for corrosion-resistant treatment of aluminum substrates.

[0006] To achieve the above purpose, the present application first provides a corrosion-resistant composite layer based on a tin layer, which comprises: an alkaline copper layer, a cupric pyrophosphate layer and a tin layer.

[0007] In the above corrosion-resistant composite layer based on a tin layer, preferably, the thickness of the alkaline copper layer is 1-10 μm, the thickness of the cupric pyrophosphate layer is 2-18 μm, and the thickness of the tin layer is 3-30 μm.

[0008] In the above corrosion-resistant composite layer based on a tin layer, preferably, the cupric pyrophosphate layer is arranged between the alkaline copper layer and the tin layer, i.e. the alkaline copper layer, the cupric pyrophosphate layer and the tin layer are arranged in sequence.

[0009] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the copper-zinc layer is 1-6 μm, more preferably 2-4 μm.

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

[0011] In the above-mentioned corrosion-resistant composite layer based on tin layer, the thickness of the tin layer can be different according to the different requirements for corrosion resistance in different applicable positions. For example, in the contact area or welding area of the male and female aluminum terminals, the contact area with the environment is small, which belongs to the semi-exposed area, and the requirement for corrosion resistance is low, so a thinner tin layer can be provided. Preferably, the thickness of the tin layer (thin tin layer) is 3-10 μm, more preferably 3-6 μm. In the completely exposed area of the aluminum terminal with a large contact area with the environment, the requirement for corrosion resistance is high, so a thicker tin layer is required. Preferably, the thickness of the tin layer (thick tin layer) is 10-25 μm, more preferably 14-18 μm.

[0012] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the corrosion-resistant composite layer based on tin layer further comprises a transition layer, which is arranged on the side of the copper-zinc layer not in contact with the copper-zinc layer. The transition layer is arranged between the copper-zinc layer and the substrate requiring corrosion-resistant treatment as a transition, which can be realized by a suitable surface treatment method.

[0013] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the transition layer comprises a zinc layer or a combination of zinc layer and secondary zinc plating layer; the zinc layer (or zinc layer, secondary zinc plating layer), copper-zinc layer, copper-zinc layer and tin layer are arranged in sequence. The zinc layer (or zinc layer, secondary zinc plating layer) as a transition for the subsequent electroplated layer can ensure its adhesion. According to the specific embodiments of the present application, the combination of zinc layer and secondary zinc plating layer includes the arrangement mode of zinc layer and secondary zinc plating layer superimposed (up and down superimposed, secondary zinc plating layer covering zinc layer); and the mode of zinc layer and secondary zinc plating layer located in different areas of the same layer, and in this mode, a part of them can be superimposed. The transition layer of the present application is not limited to zinc layer and secondary zinc plating layer, but can also use other metal or alloy materials, as long as it can help to improve the adhesion of the multifunctional composite layer, for example, other metal transition layer or alloy transition layer can be formed on the surface of the aluminum terminal by spraying, vacuum electroplating and other surface treatment processes.

[0014] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the zinc layer is 0.1-10 μm, more preferably 0.5-1 μm.

[0015] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the secondary zinc plating layer is 0.1-10 μm, more preferably 1.5-2.5 μm.

[0016] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the zinc layer, the secondary zinc layer, the alkaline copper layer, the pyrophoric copper layer and the tin layer are respectively electroplated layers.

[0017] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the corrosion-resistant composite layer based on tin layer further comprises a chemical copper layer.

[0018] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the chemical copper layer is arranged on the surface of the alkaline copper layer or the surface of the pyrophoric copper layer, i.e. the chemical copper layer can be arranged in the following manners: (1) on the surface of the alkaline copper layer which is not in contact with the pyrophoric copper layer; (2) between the alkaline copper layer and the pyrophoric copper layer; (3) on the surface of the pyrophoric copper layer which is not in contact with the alkaline copper layer.

[0019] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the chemical copper layer is 3-25 μm, more preferably 5-15 μm.

[0020] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the corrosion-resistant composite layer based on tin layer further comprises an acid copper layer.

[0021] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the acid copper layer is arranged on the surface of the alkaline copper layer or the surface of the pyrophoric copper layer, i.e. the chemical copper layer can be arranged in the following manners: (1) on the surface of the alkaline copper layer which is not in contact with the pyrophoric copper layer; (2) between the alkaline copper layer and the pyrophoric copper layer; (3) on the surface of the pyrophoric copper layer which is not in contact with the alkaline copper layer.

[0022] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the acid copper layer is 1-20 μm, more preferably 3-10 μm.

[0023] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the corrosion-resistant composite layer based on tin layer further comprises a watt nickel layer.

[0024] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the watt nickel layer is arranged on the surface of the alkaline copper layer or the surface of the pyrophoric copper layer, i.e. the watt nickel layer can be arranged in the following manners: (1) on the surface of the alkaline copper layer which is not in contact with the pyrophoric copper layer; (2) between the alkaline copper layer and the pyrophoric copper layer; (3) on the surface of the pyrophoric copper layer which is not in contact with the alkaline copper layer.

[0025] In the above-mentioned corrosion-resistant composite layer based on tin layer, preferably, the thickness of the watt nickel layer is 1-20 μm, more preferably 3-9 μm.

[0026] In the above tin layer-based corrosion-resistant composite layer, preferably, the tin layer-based corrosion-resistant composite layer can simultaneously contain two or three of the chemical copper layer, the acid copper layer, and the watt nickel layer, and for their specific positions, can be arranged at any one, two, or three of the side surface of the alkaline copper layer not in contact with the pyro-copper layer, between the alkaline copper layer and the pyro-copper layer, and the side surface of the pyro-copper layer not in contact with the alkaline copper layer, and when two or three of them select the same position, the order between them can be arbitrary, for example, when the chemical copper layer, the acid copper layer, and the watt nickel layer are all located between the alkaline copper layer and the pyro-copper layer, the chemical copper layer can be located between the acid copper layer and the watt nickel layer, the acid copper layer can be located between the chemical copper layer and the watt nickel layer, or the watt nickel layer can be located between the chemical copper layer and the acid copper layer.

[0027] In a salt spray environment, after the chloride ion penetrates the plating layer and contacts the base material, it will corrode the base material. The tin layer-based corrosion-resistant composite layer provided by the application protects layer by layer through the cooperation of the alkaline copper layer, the pyro-copper layer, and the tin layer, so that when one plating layer is penetrated, the next layer can still hinder the penetration of chloride ions, thereby improving the overall corrosion resistance of the base material and avoiding the penetration of chloride ions into the plating layer and contacting the base material. When a thick tin layer is used, it can withstand 360 hours of salt spray, meeting the corrosion resistance requirements of the full exposed area of the aluminum terminal; when a thin tin layer is used, it can withstand 60 hours of salt spray, meeting the corrosion resistance requirements of the half exposed area of the aluminum terminal.

[0028] The application also provides a preparation method of the above tin layer-based corrosion-resistant composite layer, which comprises the following steps: sequentially forming an alkaline copper layer, a pyro-copper layer, and a tin layer on the surface of a base material by electroplating.

[0029] In the above preparation method of the tin layer-based corrosion-resistant composite layer, preferably, the electroplating solution for the alkaline copper layer contains cuprous cyanide: 40-50 g / L, total sodium cyanide: 40-60 g / L, free sodium cyanide: 8-14 g / L, potassium sodium tartrate: 30-45 g / L, sodium hydroxide: 1-3 g / L, and additives (a mixture of one or more than two of polyethylene glycol, fatty amine polyoxyethylene ether (AEO), and OP series octylphenol polyoxyethylene ether): 3-5 mL / L, based on the total volume of the electroplating solution.

[0030] In the above preparation method of the tin layer-based corrosion-resistant composite layer, preferably, the temperature for electroplating the alkaline copper layer is 40-50℃, the area ratio of the cathode to the anode is 1:1-2 (preferably 1:1.5), the current density is 0.7-1.2 A / dm 2 , and the electroplating time is 5-15 min.

[0031] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, the plating solution used for forming the cupric pyrophosphate layer contains cupric 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 plating solution.

[0032] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, the temperature for plating the cupric pyrophosphate layer is 40-50℃, the current density is 0.7-1.2 A / dm 2 , the area ratio of the cathode to the anode is 1:1-2 (preferably 1:1.5), and the plating time is 50-90 min.

[0033] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, the plating solution used for forming the tin layer contains stannous sulfate: 10-50 g / L, sulfuric acid: 60-190 mL / L, gelatin: 1-10 g / L, formaldehyde: 5-10 mL / L, and benzalacetone: 5-30 g / L, based on the total volume of the plating solution.

[0034] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, the temperature for plating the tin layer is 10-40℃, the area ratio of the cathode to the anode is 1:1-2 (preferably 1:1.5), the current density is 0.5-2 A / dm 2 (preferably 0.7-1.2 A / dm 2 ), and the plating time is 15-120 min.

[0035] The tin layer of the present application can be a dull tin layer or a bright tin layer, both of which can achieve good corrosion resistance, and the specific plating preparation process can be determined as needed.

[0036] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, the plating of the cupric alkali layer, the cupric pyrophosphate layer, the tin layer, etc. can adopt a pulse plating process, which can further improve the original compactness, so that the plating layer is more compact, has fewer pores, and has stronger salt spray resistance.

[0037] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, when the chemical copper layer, the acid copper layer, and the watt nickel layer are included, these layers can be obtained through corresponding methods at appropriate times.

[0038] In the preparation method of the corrosion-resistant composite layer based on the tin layer, preferably, when the transition layer such as the zinc layer and the secondary zinc deposition layer is included, the transition layer is formed first, and then the cupric alkali layer, the cupric pyrophosphate layer, the tin layer, etc. are formed. The zinc layer and the secondary zinc deposition layer can be prepared by using a conventional plating method.

[0039] In the preparation method of the tin layer-based corrosion-resistant composite layer, in order to ensure the electroplating adhesion, other processes can be added to the electroplating process, such as acid activation treatment before each process and pure water cleaning before each process.

[0040] The application further provides an aluminum substrate corrosion-resistant treatment method, which comprises the step of arranging the tin layer-based corrosion-resistant composite layer on the surface of the aluminum substrate.

[0041] In the aluminum substrate corrosion-resistant treatment method, preferably, the corrosion resistance refers to salt spray corrosion resistance.

[0042] In the aluminum substrate corrosion-resistant treatment method, preferably, the surface roughness of the aluminum substrate is less than Ra 3.6, and more preferably less than Ra 0.8.

[0043] The application further provides a corrosion-resistant aluminum terminal, wherein part or all of the surface of the corrosion-resistant aluminum terminal is provided with the tin layer-based corrosion-resistant composite layer.

[0044] In the corrosion-resistant aluminum terminal, the corrosion-resistant composite layer can cover the entire surface of the aluminum terminal, or only cover the surface area that needs corrosion-resistant treatment.

[0045] The application further provides a preparation method of the corrosion-resistant aluminum terminal, which comprises the following steps:

[0046] The front surface of the aluminum terminal is subjected to roll pressing treatment and polishing treatment;

[0047] The side surface of the aluminum terminal is subjected to stamping treatment;

[0048] The front surface and the side surface of the treated aluminum terminal are sequentially subjected to electroplating to form a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a pyrolytic copper layer and a tin layer, thereby obtaining the corrosion-resistant aluminum terminal.

[0049] In the preparation method, the roll pressing treatment, the polishing treatment and the stamping treatment can be performed only on the area that needs corrosion-resistant treatment, and are not limited to the entire surface of the aluminum terminal. By adopting the local area treatment, the welding can be facilitated, and various connection processes such as friction welding, friction stir welding, ultrasonic welding, molecular diffusion welding and resistance welding can be combined, so that the corrosion-resistant terminal with high reliability can be obtained.

[0050] In the preparation method of the corrosion-resistant aluminum terminal, preferably, the roll pressing treatment of the terminal material can enhance the compactness of the terminal surface and the corrosion resistance of the subsequent electroplating treatment.

[0051] In the preparation method of the corrosion-resistant aluminum terminal, preferably, the polishing treatment is performed on the terminal material to enhance the smoothness of the terminal surface and the corrosion resistance of the subsequent electroplating treatment. The polishing treatment can be performed by chemical polishing, mechanical polishing, or the like.

[0052] In the preparation method of the corrosion-resistant aluminum terminal, preferably, the roughness of the front surface of the aluminum terminal after the rolling treatment and the polishing treatment is less than Ra 3.6, and more preferably less than Ra 0.8.

[0053] In the preparation method of the corrosion-resistant aluminum terminal, preferably, the roughness of the side surface of the aluminum terminal after the rolling treatment 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%).

[0054] In the preparation method of the corrosion-resistant aluminum terminal, preferably, when the transition layer is provided, the transition layer is formed on the front surface and the side surface of the treated aluminum terminal before the electroplating of the copper layer.

[0055] The corrosion-resistant composite layer based on the tin layer prepared by the technical scheme has good salt spray corrosion resistance, and the aluminum terminal provided with the corrosion-resistant composite layer based on the tin layer can achieve 360 hours of salt spray resistance in the full-exposed area and 96 hours of salt spray resistance in the half-exposed area. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 An exemplary overall structure of the aluminum terminal provided by the present application is shown in the figure.

[0057] Figure 2 An exemplary electroplating process of the aluminum terminal provided by the present application is shown in the figure.

[0058] Figure 3 The morphology of the side surface of the aluminum terminal obtained by general stamping and precision stamping is shown in the figure.

[0059] Figure 4 The SEM images of the conventional aluminum plate and the rolled aluminum plate are shown in the figure.

[0060] Figure 5 The sample state after the corrosion resistance test is shown in the figure. DETAILED DESCRIPTION

[0061] In order to have a clearer understanding of the technical features, objects and beneficial effects of the present application, the technical scheme of the present application will be described in detail below, but it should not be understood as limiting the scope of the present application.

[0062] The aluminum terminal provided by the present application comprises an aluminum terminal material and an electroplated film layer, wherein the aluminum terminal material has a terminal surface and a terminal side surface; the electroplated film layer (a corrosion-resistant composite layer based on a tin layer) comprises an alkaline copper layer, a pyro-copper layer and a tin layer, and the electroplated film layer can further comprise a zinc layer and a secondary zinc deposition layer. An exemplary overall structure of the aluminum terminal with the corrosion-resistant composite layer is shown in Figure 1 FIG. 1, wherein a zinc layer 2, an alkaline copper layer 3, a pyro-copper layer 4 and a tin layer 5 are sequentially arranged on the surface of an aluminum base material 1; if necessary, a secondary zinc deposition layer can be further arranged between the zinc layer 2 and the alkaline copper layer 3.

[0063] An exemplary electroplating process of the aluminum terminal is shown in Figure 2 FIG. 2, which comprises the following steps: ultrasonic degreasing, alkaline cleaning, acid cleaning, chemical zinc deposition, chemical zinc removal, secondary zinc deposition, activation, electroplating of alkaline copper, electroplating of pyro-copper, electroplating of tin, post-treatment, pure water cleaning and drying; wherein the step of secondary zinc deposition can be selected according to the need.

[0064] Principle of terminal corrosion: common corrosion of metal materials is oxidation corrosion and electrochemical corrosion.

[0065] The principle of oxidation corrosion is the oxidation reaction of metal in air, and the more active the metal is, the easier it is to be oxidized and corroded. Generally, the following two methods are adopted to avoid corrosion: 1. surface treatment, a thin film is formed on the surface of the metal through surface treatment to achieve the effect of air isolation and avoid the reaction of the metal with air; 2. converting oxidation corrosion into electrochemical corrosion, which protects the workpiece by corroding another metal, i.e. the cathodic protection method of sacrificial anode: a metal with stronger reducing property is used as a protection electrode and connected with the protected metal to form a primary battery, and the metal with stronger reducing property will be oxidized and consumed as a negative electrode, and the protected metal as a positive electrode can avoid corrosion.

[0066] The principle of electrochemical corrosion is the primary battery reaction of metal in marine atmospheric environment, and the metal, impurities, water and ionic salt such as sodium chloride form a primary battery, which undergoes oxidation reaction on the anode (metal) to cause dissolution of the anode (i.e. corrosion of the metal), and reduction reaction occurs on the cathode to transfer electrons and discharge. The time and process of corrosion is extremely long, and the salt spray test method is generally used to verify the corrosion resistance of metal materials. The salt spray test is a simulation experiment of metal materials in marine atmosphere or humid air, which uses the artificial simulated salt spray environment created by the salt spray test equipment to test the corrosion resistance of products or metal materials. The electrochemical corrosion under salt spray is generally hindered by the surface treatment film layer to prevent the salt spray from contacting the metal material, however, the chlorine ion in the salt spray environment has very strong penetration ability, which can penetrate into the base material from the pores of the metal surface film layer and cause corrosion.

[0067] The technical scheme of the present application starts from the design of avoiding the contact of chloride ions with the base material, and designs from two aspects of terminal material and electroplated film layer, so that the electroplated film layer of the terminal can effectively hinder the penetration of chloride ions, and greatly improves the corrosion resistance of the aluminum terminal. The front surface of the material terminal is subjected to roll pressing treatment and polishing treatment, and the roughness after treatment is less than Ra 3.6, more preferably less than Ra 0.8; the side surface of the material terminal is processed by precise stamping process, and the brightness after treatment is greater than 50%, preferably greater than 98%, and the roughness is less than Ra 3.6, more preferably less than Ra 0.8.

[0068] The process of roll pressing treatment increases the surface density of the aluminum material by mechanical means, thereby reducing the porosity of the surface of the aluminum terminal material and improving the density, so as to prepare for the covering of the electroplated film layer in the next step. The fewer the pores of the material, the fewer the pores of the electroplated film layer, and the higher the protection. The SEM images of the conventional aluminum plate and the roll-pressed aluminum plate are shown in Figure 4 Figure 4 In Figure 4 , a graph shows a conventional aluminum plate, and a graph shows a roll-pressed aluminum plate. As can be seen from

[0069] The polishing treatment adopts a magnetic polishing method, specifically by generating a magnetic field through electrification, the magnetic field drives the stainless steel needle to move, and in the process of 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 surface of the terminal material.

[0070] The polishing treatment, precise stamping process and the like all improve the smoothness and flatness of the surface and side surface of the terminal material.

[0071] By improving the flatness and smoothness of the terminal material, it can greatly benefit the electroplated film layer. Due to the influence of electric current, the electroplating process will accumulate more electroplated film layer at the position of electron enrichment of the workpiece, which will cause the thickness of the electroplated film layer on the surface of the terminal to be different, and even a large number of pits will appear, causing the aggregation and penetration of chloride ions in the salt mist. When the flatness of the terminal material is insufficient, due to the principle of tip discharge, the more curved the surface of the conductor is, the more charge will be gathered at the place with smaller relative surface area. The protrusions on the uneven surface of the material will gather a large amount of electrons, so that the protrusions on the surface of the workpiece after electroplating will be more protruding, and the recessed positions will be more recessed, which will form small holes, easily gather salt mist, cause the penetration of chloride ions, and further cause corrosion. After the process of the present application, the terminal material can effectively cover the electroplated film layer, and effectively improve the corrosion resistance.

[0072] ​The effect of ultrasonic degreasing is to remove the oil on the surface of the workpiece by physical ultrasonic vibration and chemical esterification reaction. The oil on the surface of the workpiece must be thoroughly treated, otherwise the residual oil on the surface of the workpiece will affect the effective coverage of the subsequent electroplated film layer, causing the electroplated film layer to fall off or miss plating.

[0073] The effect of alkaline cleaning is that aluminum is an amphoteric metal that can react with both acids and bases. This process dissolves the aluminum oxide and part of the aluminum on the surface of the workpiece by strong alkaline solution (NaOH, KOH, etc.), providing a good surface for the coverage of the subsequent electroplated film layer and ensuring its bonding force.

[0074] The effect of acid cleaning is: 1. Neutralizing the alkaline solution attached to the surface of the workpiece in the previous alkaline cleaning step. 2. Further dissolving the aluminum oxide and part of the aluminum on the surface of the workpiece to provide a good surface for the coverage of the subsequent electroplated film layer and ensure its bonding force. 3. Activating the aluminum metal on the surface of the workpiece to make its aluminum atoms in an active state, reducing the activation energy of the subsequent reaction and facilitating the subsequent process.

[0075] The effect of chemical zinc deposition is that the electrode potential difference between aluminum and copper is too large, with aluminum being -1.662V and copper being +0.34V. Therefore, copper cannot be directly electroplated on the surface of aluminum, and a layer of zinc must be chemically deposited on the aluminum first to enable the subsequent electroplated metal layer. The zinc layer deposited in this process is very rough and uneven, which greatly affects the subsequent electroplating.

[0076] The effect of chemical zinc removal is to use a strong acidic solution to dissolve most of the zinc layer on the surface of the workpiece, leaving only a very thin zinc seed layer. The zinc seed layer is very smooth after being dissolved by the strong acid, allowing for subsequent electroplating.

[0077] The effect of secondary zinc deposition is to chemically deposit another layer of zinc on the surface of the workpiece. This time, the zinc layer is smooth and dense, and the aluminum workpiece surface has been modified to zinc, making it easy to electroplate other metals.

[0078] The effect of activation is: 1. Zinc has chemical properties and is active, easily oxidized by oxygen in the air to form an oxide film. In this process, the oxide film produced when the workpiece is exposed to oxygen during the process gap needs to be removed. 2. Activating the surface of the zinc layer to make its zinc atoms in an active state, reducing the activation energy of the subsequent reaction and facilitating the subsequent process.

[0079] Electroplating alkaline copper: Electroplating alkaline copper is cyanide copper plating. Cyanide has a strong complexing ability in water, which greatly increases the cathode polarization of electroplating, allowing copper ions to accumulate on the cathode and deposit together, increasing the density of the electroplated film layer. The cyanide system electroplated layer is dense and the reaction is fast, efficient, and can cover the zinc layer with a dense and smooth copper layer. Moreover, copper has relatively inert chemical properties and low electroplating internal stress, making it an excellent intermediate plating layer that is easy to electroplate subsequent metal layers.

[0080] 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, additive: 3-5 mL / L, temperature: 40-50℃, anode-cathode area ratio: 1:1.5, current density: 0.7-1.2 A / dm 2 , electroplating time: 5-15 min, plating thickness: preferably 1-6 μm.

[0081] To enhance the compactness of the plating layer, the process is optimized: generally, to meet the requirements of electroplating efficiency, faster production, the current density of electroplating alkaline copper in the electroplating plant is 4-10 A / dm 2 , which is much higher than that of the present application. The current density directly affects the compactness of the plating layer, and high current density will weaken the cathode polarization, and it is easier to reach the hydrogen ion evolution overpotential in the solution, causing the occurrence of hydrogen evolution side reaction during electroplating. The hydrogen evolved will leave pores in the plating layer, reducing the compactness of the plating layer. The electroplating alkaline copper process used in the present application reduces the current density while increasing the concentration of the main salt cuprous cyanide and free sodium cyanide, thereby obtaining an alkaline copper plating layer with excellent electroplating efficiency and compactness.

[0082] Electroplating of copper: the electroplated copper layer is electroplated copper pyrophosphate. The complexing ability of pyrophosphate in water is stronger than that of cyanide, and the cathode polarization in the pyrophosphate system is also stronger. Because [Cu(P2O7)2] 6- carries more negative charges, it has a greater impact on the cathode process, and [Cu(P2O7)2] 6- is difficult to discharge and needs to be hydrolyzed to [CuP2O7] 2- to deposit a copper layer. The hydrolysis of [CuP2O7] 2- is slow, so the cathode polarization is increased again. The copper pyrophosphate plating film is more compact and has fewer pores, which can effectively prevent the penetration of chloride ions in the salt spray test and enhance the corrosion resistance of the workpiece.

[0083] 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℃, anode-cathode area ratio: 1:1.5, electroplating time 50-90 min, electroplating thickness: preferably 5-15 μm. Similarly, to improve the compactness of the plating layer, the process used in the present application is optimized to reduce the current density.

[0084] The present application can bring the following advantages through the cooperation of the alkaline copper layer and the copper pyrophosphate layer:

[0085] 1. Strengthen the adhesion between plating layers: As an excellent base plating layer, alkaline copper has good adhesion with the zinc layer of the base material; if the alkaline copper is removed and direct electroplating of copper is performed, poor adhesion is prone to occur, which makes the workpiece more easily corroded.

[0086] 2. Strengthen the salt spray effect: Since the surface state of the base material greatly affects the electroplated layer, it is impossible to directly electroplate a very dense plating layer on the porous surface of aluminum material; the application preferably adopts a scheme of gradually improving the density, the density of the zinc layer is lower than that of the alkaline copper, the density of the alkaline copper is slightly lower than that of the copper, and the density of the three layers is gradually improved, so that the density of the final copper layer is optimal; therefore, the technical scheme of the application adopts 1-6 μm alkaline copper + 5-15 μm copper for combination, which can effectively improve the corrosion resistance of the workpiece.

[0087] When the electroplated alkaline copper layer is thick, rough plating layer is prone to occur; therefore, the application selects electroplating of 1-10 μm (preferably 1-6 μm), and under this plating layer thickness, the adhesion and density can meet the requirements. The copper layer is selected between 2-18 μm, and the thicker the plating layer, the more pores it can cover; however, considering the influence of electroplating time, 5-15 μm is preferably selected.

[0088] The chemical copper layer is formed by self-catalytic plating through chemical reaction, and the addition of the chemical copper layer between the layers can obtain good adhesion; the chemical copper layer is a good intermediate plating layer, which can enhance the adhesion of the overall plating layer. At the same time, since the preparation process of the chemical copper layer is a simple chemical reaction, the thickness and porosity of the plating layer are not affected by the current distribution, therefore, the thickness of the chemical copper layer is more uniform, the porosity is lower, and the chemical copper layer has good corrosion resistance; the addition of this layer in the application can enhance the corrosion resistance of the overall plating layer.

[0089] The parameters of the chemical copper plating are as follows: composition of the chemical plating solution: copper sulfate 5-20 g / L, sodium hypophosphite 20-50 g / L, sodium citrate 5-30 g / L, nickel sulfate 0.1-5 g / L, potassium ferrocyanide 0.5-7 mg / L, boric acid 15-50 g / L; temperature 60-90 ℃, pH 7.8-10.2, electroplating time 40-100 min, and the general plating speed is 1 μm / 6 min, i.e. 6 min-1 μm, 24 min-4 μm, and 48 min-8 μm; the thickness of the plating layer can be controlled by controlling the parameters of the chemical copper plating as needed.

[0090] The acid copper layer (i.e. acid copper plating layer) is sulfuric acid copper electroplating, which has good adhesion with other plating layers and can be used as an excellent intermediate plating layer; in addition, the sulfuric acid copper plating solution used for preparing the acid copper layer is stable and has low cost; the addition of the acid copper between or on both sides of the alkaline copper layer and the copper can enhance the brightness and corrosion resistance of the overall plating layer itself.

[0091] Electroplating acid copper parameters as follows: the composition of the plating solution: copper sulfate pentahydrate: 160-250g / L, sulfuric acid: 25-50mL / L, chloride ion: 40-120ppm, additives (polydithiopropanesulfonic acid sodium, 2-mercaptobenzimidazole, 1,2-ethylene thiourea, polyamine compounds one or more mixture): 4-15mL / L, current density 0.8-2.0A / dm 2 , temperature 20-30℃, anode to cathode area ratio of 1:1.5, plating time 20-80min, plating thickness according to the need to control the plating parameters.

[0092] Watt nickel layer (i.e. watt nickel plating layer, bright nickel plating layer) is a nickel sulfate electroplating layer, which has good adhesion with other plating layers, and can be used as an excellent intermediate plating layer. The watt nickel is added between the alkaline copper layer and the pyrolytic copper layer or on both sides. In the corrosive environment, a potential difference will be generated, which can be corroded first as an anode to protect other plating layers, enhance the brightness and corrosion resistance of the whole plating layer itself.

[0093] Electroplating watt nickel layer parameters as follows: the composition of the plating solution: nickel sulfate hexahydrate: 250-350g / L, nickel chloride hexahydrate: 60-95g / L, boric acid: 40-60g / L, additives (sodium dodecyl sulfate, saccharin, butynediol ethoxy ether one or more mixture): 6-12mL / L; pH 3-5, current density 0.8-2.0A / dm 2 , temperature 50-60℃, anode to cathode area ratio of 1:1.5, plating time 30-70min, plating thickness according to the need to control the plating parameters.

[0094] Electroplating tin: compared with electroplating silver, the compactness of electroplating tin is better, and the tin electroplating film layer is soft, which can realize the close connection with other workpieces, and has good electrical performance. At the same time, the cost of tin is much lower than that of silver, which is the best choice for corrosion-resistant aluminum terminal.

[0095] Electroplating parameters as follows:

[0096] Electroplating solution composition: stannous sulfate: 10-50g / L, sulfuric acid: 60-190ml / L, gelatin: 1-10g / L, formaldehyde: 5-10ml / L, benzylidene acetone: 5-30g / L; temperature: 10-40℃, anode to cathode area ratio: 1:1.5, current density: 0.7-1.2A / dm 2 , plating time: 15-120min, plating thickness according to the need to control the plating parameters.

[0097] The tin layer-based corrosion-resistant composite layer provided by the application has the following advantages: the alkali copper layer, the pyrophoric copper layer, the tin layer and other electroplated film layers have strong compactness, can effectively hinder the penetration of chloride ions in the salt spray test, and the interaction and mutual superposition of the metal / alloy layers can cover the pores originally existing in the single plating layer. Even if the chloride ions penetrate one electroplated film layer in the salt spray test, other compact plating layers can effectively hinder the further penetration of the chloride ions, and the corrosion resistance of the aluminum base material is greatly improved. By increasing the zinc layer, the secondary zinc deposition layer, the chemical copper layer, the acid copper layer, the watt nickel layer and the like, the corrosion resistance can be further improved.

[0098] The existing aluminum workpiece has a salt spray resistance of 48H, that is, corrosion occurs, and cannot be applied to harsh corrosion environments such as humid and marine environments. The technical scheme provided by the application has the following advantages: on the one hand, through the rolling, polishing and stamping processes, an aluminum terminal material with a good surface state is manufactured, which is beneficial to subsequent electroplating treatment (making the subsequent electroplated film layer more compact); on the other hand, by covering the compact electroplated film layer and the interaction of the electroplated film layers, the penetration of chloride ions in the salt spray test can be effectively hindered, and the occurrence of corrosion can be hindered, thereby greatly enhancing the corrosion resistance of the aluminum terminal.

[0099] The post-processing has the following effects: 1. preventing the tin electroplated film layer on the surface of the workpiece from discoloring at high temperature, affecting the appearance; 2. preliminarily filling the pores of the tin electroplated film layer, and enhancing the corrosion resistance.

[0100] The pure water washing has the following effects: using flowing deionized water to thoroughly clean the workpiece. Tap water contains a large amount of metal ions such as calcium and sodium, which will be left on the surface of the workpiece during cleaning, making the workpiece more susceptible to corrosion in a salt spray environment, so flowing deionized water must be used for cleaning.

[0101] The drying has the following effects: using an oven to dry the moisture on the surface of the workpiece at 85°C in a timely manner, preventing the water left after the previous step from adhering to the workpiece and forming water marks affecting the appearance, and preventing the workpiece from being corroded and oxidized.

[0102] Example 1

[0103] The present embodiment provides an aluminum terminal having a tin layer-based corrosion-resistant composite layer, wherein:

[0104] The front surface of the aluminum terminal material has been subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8; the side surface has been processed by a precision stamping process, and the brightness is greater than 98% and the roughness is less than Ra 0.8; Figure 3 The first picture in the figure is a picture of a side surface of ordinary stamping, and the second picture is a picture of a side surface of precision stamping, which can be seen from Figure 3It can be seen that the rough band of the aluminum terminal obtained by ordinary stamping accounts for a high proportion, while the side surface of the aluminum terminal obtained by precise stamping is basically bright band, accounting for more than 98%. The condition of the bright band is determined by a projector detection, and the proportion of the bright band is determined by calculating the length or area. The roughness of the front surface of the aluminum terminal material before and after polishing is 0.315 μm and 0.282 μm respectively, so it can be seen that the surface roughness can be greatly reduced by polishing to improve the smoothness. In the roughness test, the sampling cutoff wavelength of the filter is λc=0.8 mm x 5.

[0105] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a pyro-copper layer, and a tin layer arranged on the fully exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 2 μm, 10 μm, and 15 μm respectively. After the composite corrosion-resistant layer is formed, the roughness of the surface of the aluminum terminal is also improved and reduced to 0.161 μm.

[0106] Embodiment 2

[0107] The embodiment provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, wherein:

[0108] The front surface of the aluminum terminal material is subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8. The side surface is subjected to a precise stamping process, and the bright band is greater than 98% and the roughness is less than Ra 0.8.

[0109] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a pyro-copper layer, and a tin layer arranged on the fully exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 2 μm, 15 μm, and 20 μm respectively.

[0110] Embodiment 3

[0111] The embodiment provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, wherein:

[0112] The front surface of the aluminum terminal material is subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8. The side surface is subjected to a precise stamping process, and the bright band is greater than 98% and the roughness is less than Ra 0.8.

[0113] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a pyro-copper layer, and a tin layer arranged on the fully exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 2 μm, 2 μm, and 3 μm respectively.

[0114] Embodiment 4

[0115] The embodiment provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, wherein:

[0116] The front surface of the aluminum terminal material is subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8, and the side surface is subjected to precise stamping process, and the bright band is greater than 98% and the roughness is less than Ra 0.8.

[0117] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a cuprous copper layer, and a tin layer arranged on the full exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 3 μm, 5 μm, and 30 μm, respectively.

[0118] Example 5

[0119] The present embodiment provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, wherein:

[0120] The front surface of the aluminum terminal material is subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8, and the side surface is subjected to precise stamping process, and the bright band is greater than 98% and the roughness is less than Ra 0.8.

[0121] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a cuprous copper layer, and a tin layer arranged on the full exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 3 μm, 5 μm, and 30 μm, respectively.

[0122] Example 6

[0123] The present embodiment provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, wherein:

[0124] The front surface of the aluminum terminal material is subjected to rolling and polishing treatment, and the roughness is less than Ra 0.8, and the side surface is subjected to precise stamping process, and the bright band is greater than 98% and the roughness is less than Ra 0.8.

[0125] The composite corrosion-resistant layer includes a zinc layer, a secondary zinc deposition layer, an alkaline copper layer, a cuprous copper layer, and a tin layer arranged on the full exposed area of the surface of the aluminum terminal material, and the thicknesses are 0.5 μm, 2 μm, 3 μm, 5 μm, and 30 μm, respectively.

[0126] Comparative Example 1

[0127] The present comparative example provides an aluminum terminal with a tin layer-based corrosion-resistant composite layer, which is different from Example 1 in that the tin layer-based corrosion-resistant composite layer only has a zinc layer, a secondary zinc deposition layer, and an alkaline copper layer, and the thicknesses are 0.5 μm, 2 μm, and 27 μm.

[0128] The thicknesses of each comparative example are kept in contrast with Example 1, and the total thickness of each layer remains unchanged.

[0129] Comparative Example 2

[0130] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0131] Comparative Example 3

[0132] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0133] Comparative Example 4

[0134] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0135] Comparative Example 5

[0136] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0137] Comparative Example 6

[0138] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0139] Comparative Example 7

[0140] This comparative example provides an aluminum terminal having a corrosion-resistant composite layer based on a tin layer, which differs from Example 1 in that the corrosion-resistant composite layer based on a tin layer has only a zinc layer, a secondary zinc deposition layer, a tin layer, with thicknesses of 0.5 μm, 2 μm, and 27 μm.

[0141] Comparative Example 8

[0142] This comparative example provides a wire-cut aluminum material: the plating layer is the same as Example 1, and it is not subjected to precision stamping and polishing treatment.

[0143] Comparative Example 9

[0144] The comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which is different from example 1 in that the plating layer is the same as example 1, and is not subjected to rolling treatment.

[0145] Comparative examples 10-12

[0146] The comparative examples respectively provide an aluminum terminal with a corrosion-resistant composite layer, which is different from example 3 in that the plating layer thickness is different from example 3, and is specifically shown in Table 1.

[0147] Comparative example 13

[0148] The comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which is different from example 1 in that the plating layer thickness is different from example 1, and is specifically shown in Table 1.

[0149] Comparative example 14

[0150] The comparative example provides an aluminum terminal with a corrosion-resistant composite layer, which is different from example 1 in that the plating layer thickness is different from example 1, and is specifically shown in Table 1.

[0151] The salt spray corrosion test results of the aluminum terminals of the examples and comparative examples, and the wire-cut aluminum material of the comparative examples are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Salt spray corrosion test:

[0156] According to the national standard GB / T 2423.17-2008. The qualified standard is that the plating layer has no corrosion, no surface pitting, peeling, blistering, etc., and the plating layer has no spots and color change.

[0157] Test results:

[0158] Comparative example 14 is a 3 μm thick chemical nickel layer plated on the transition layer by chemical plating, and corrosion occurs at 48H in the salt spray resistance time.

[0159] The aluminum terminal of example 1 of the present application has no corrosion points for 360H.

[0160] The salt spray corrosion resistance of the aluminum terminal with a corrosion-resistant composite layer based on the tin layer provided by example 1 of the present application can reach 360H, and no corrosion points and white rust and red rust will occur; specifically as Figure 5As shown in the drawings, the left drawing is the case of a conventional plating layer, and it can be seen that rust and corrosion points have appeared on the plating layer. The right drawing is the case of the plating layer of the embodiment 1 of the present application, and it can be seen that the plating layer obtained by the embodiment 1 of the present application remains in good condition during the entire test period and does not have any corrosion points.

[0161] The salt spray corrosion resistance of the aluminum terminal with the semi-exposed area provided by the embodiment 3 of the present application can reach 96H, which is lower than that of the embodiment 1 in terms of corrosion resistance time, but the test is performed in a completely exposed salt spray environment, and in the actual use of the aluminum terminal, the area is not completely exposed to the environment. Therefore, the corrosion resistance time obtained by the test of the embodiment 3 is lower than that of the embodiment 1, which does not affect the service life of the aluminum terminal. The corrosion resistance composite layer based on the tin layer still has good corrosion resistance effect. That is, if the semi-exposed area of the aluminum terminal of the embodiment 1 is provided with the corrosion resistance composite layer in the embodiment 3, the service life of the corrosion resistance composite layer based on the tin layer in the semi-exposed area will not be lower than that of the corrosion resistance composite layer based on the tin layer in the exposed area, and the corrosion resistance of the entire aluminum terminal is also guaranteed.

[0162] Therefore, the present application can set different corrosion resistance composite layers based on the tin layer at different positions of the aluminum terminal according to the area characteristics (whether exposed to the environment, the high or low requirement for corrosion resistance performance) and use requirements, so as to reduce the cost while guaranteeing the corrosion resistance performance and service life.

[0163] Effect of surface roughness and bright band on corrosion resistance performance experiments:

[0164] The terminals (including wire cutting materials) with different surface roughness (surface roughness before preparing the corrosion resistance layer) and different bright band ratios in the embodiment 7, the comparative example 8 and the comparative examples 15-17 are formed with the same corrosion resistance layer (i.e. the corrosion resistance layer in the embodiment 1), and the salt spray resistance test (according to the national standard GB / T 2423.17-2008) is performed to evaluate the influence of the surface roughness and the bright band ratio on the salt spray corrosion resistance performance. The qualified standard is that the plating layer has no corrosion, no surface pitting, peeling, bubbling and the like, and the plating layer has no spot and color change. The experimental results are shown in Table 2.

[0165] Table 2

[0166]

[0167] According to the experimental data of the embodiment 7, the comparative example 15 and the comparative example 16 given in Table 2, it can be seen that under the same conditions, the smaller the surface roughness of the substrate, the longer the salt spray resistance time of the aluminum terminal with the corrosion resistance composite layer on the surface, and the better the salt spray corrosion resistance.

[0168] From the experimental data of Example 7, Comparative Example 17 and Comparative Example 8 given in Table 2, it can be seen that, under the condition of the same surface roughness and other conditions being the same, the higher the proportion of the bright band on the surface of the substrate, the longer the time of the aluminum terminal with the corrosion-resistant composite layer on the surface to resist salt spray, and the better the ability to resist salt spray corrosion.

[0169] The technical solution of the present application has the following advantages:

[0170] 1. Low cost and simple process;

[0171] 2. The corrosion-resistant composite layer has excellent corrosion resistance. When a thicker tin layer is used, the 360H salt spray corrosion resistance requirement can be met; when a thinner tin layer is used, the 96H salt spray corrosion resistance requirement can be met, which can be applied to different situations and meet different corrosion resistance requirements;

[0172] 3. The adhesion of each layer is excellent, and there is no blistering after 10 times of 220℃ thermal shock test;

[0173] 4. Although the aluminum terminal surface is provided with a corrosion-resistant composite layer based on a tin layer, the conductivity is still very good.

Claims

1. A tin layer based, salt-spray corrosion resistant composite layer comprising: a transition layer, a basic copper layer, a focal copper layer, a tin layer; the thickness of the basic copper layer is 1-10 μm, the thickness of the focal copper layer is 2-18 μm, and the thickness of the tin layer is 3-30 μm; the focal copper layer is arranged between the basic copper layer and the tin layer, and the transition layer is arranged on the side of the basic copper layer not in contact with the focal copper layer; the transition layer comprises a combination of a zinc layer and a secondary zinc layer, the thickness of the zinc layer is 0.1-10 μm, and the thickness of the secondary zinc layer is 0.1-10 μm.

2. The tin layer-based composite layer resistant to salt spray corrosion according to claim 1, wherein, The thickness of the basic copper layer is 1-6 μm.

3. The tin layer-based composite layer resistant to salt spray corrosion according to claim 1, wherein, The thickness of the focal copper layer is 5-15 μm.

4. The tin layer-based composite layer resistant to salt spray corrosion according to claim 1, wherein, The thickness of the tin layer is 3-10 μm or 10-25 μm.

5. The tin layer-based composite layer resistant to salt spray corrosion according to claim 1, wherein, The thickness of the zinc layer is 0.5-1 μm.

6. The tin layer-based composite layer resistant to salt-spray corrosion according to claim 1, wherein, The thickness of the secondary zinc layer is 1.5-2.5 μm.

7. The tin layer based composite layer for salt spray corrosion resistance according to any one of claims 1 to 6, wherein The zinc layer, the secondary zinc layer, the basic copper layer, the focal copper layer, and the tin layer are respectively electroplated layers.

8. The tin layer based composite layer for salt spray corrosion resistance according to any one of claims 1 to 6, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises a chemical copper layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

9. The tin layer based composite layer for salt spray corrosion resistance according to claim 8, wherein, The thickness of the chemical copper layer is 3-25 μm.

10. The tin layer based composite layer for salt spray corrosion resistance according to claim 9, wherein, The thickness of the chemical copper layer is 5-15 μm.

11. The tin layer based composite layer resistant to salt spray corrosion according to any one of claims 1 to 6, 9, 10, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises an acid copper layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

12. The tin layer based composite layer resistant to salt spray corrosion according to claim 11, wherein, The thickness of the acid copper layer is 1-20 μm.

13. The tin layer based composite layer for salt spray corrosion resistance according to claim 12, wherein, The thickness of the acid copper layer is 3-10 μm.

14. The tin layer based composite layer for salt-spray corrosion resistance according to claim 8, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises an acid copper layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

15. The tin layer based composite layer for salt spray corrosion resistance according to claim 14, wherein, The thickness of the acid copper layer is 1-20 μm.

16. The tin layer based composite layer for salt spray corrosion resistance according to claim 15, wherein, The thickness of the acid copper layer is 3-10 μm.

17. The tin layer based, salt-spray corrosion resistant composite layer of any of claims 1-6, 9, 10, 12-16, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises a watt nickel layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

18. The tin layer based composite layer for salt spray corrosion resistance according to claim 17, wherein, The thickness of the watt nickel layer is 1-20 μm.

19. The tin layer based composite layer for salt spray corrosion resistance according to claim 18, wherein, The thickness of the watt nickel layer is 3-9 μm.

20. The tin layer based composite layer for resistance to salt-spray corrosion according to claim 8, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises a watt nickel layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

21. The tin layer based composite layer for salt spray corrosion resistance according to claim 20, wherein, The thickness of the watt nickel layer is 1-20 μm.

22. The tin layer based composite layer for salt spray corrosion resistance according to claim 21, wherein, The thickness of the watt nickel layer is 3-9 μm.

23. The tin layer based composite layer for salt-spray corrosion resistance according to claim 11, wherein, The tin layer-based salt mist corrosion resistant composite layer further comprises a watt nickel layer arranged on the surface of the basic copper layer or the surface of the focal copper layer.

24. The tin layer based composite layer for salt-spray corrosion resistance according to claim 23, wherein, The thickness of the watt nickel layer is 1-20 μm.

25. The tin layer based composite layer for salt spray corrosion resistance according to claim 24, wherein, The thickness of the watt nickel layer is 3-9 μm. The tin layer-based salt mist corrosion resistant composite layer further comprises a watt nickel layer arranged on the surface of the basic copper layer or the surface of the focal copper layer. The thickness of the watt nickel layer is 1-20 μm.

27. The method of claim 26, wherein the tin layer is prepared by a method comprising: The plating solution for the 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, based on the total volume of the plating solution. The temperature of the plating solution is 40-50°C, the area ratio of the cathode to the anode is 1:1-2, the current density is 0.7-1.2 A / dm 2 , and the plating time is 5-15 min.

28. The method of claim 27, wherein the tin layer is prepared by a method comprising: The thickness of the watt nickel layer is 3-9 μm.

29. The method of claim 26, wherein the tin-based layer is prepared by a process comprising: The plating solution for the copper layer contains copper pyrophosphate: 50-70 g / L, potassium pyrophosphate: 300-450 g / L, ammonium citrate: 15-30 g / L, ammonia: 2-5 mL / L, based on the total volume of the plating solution. The temperature for plating the copper layer is 40-50°C, the current density is 0.7-1.2 A / dm 2 , the ratio of anode to cathode area is 1:1-2, and the plating time is 50-90 min.

30. The method of claim 29, wherein the tin-based layer is prepared by a method comprising:

26. A method for preparing the tin layer-based salt mist corrosion resistant composite layer according to any one of claims 1-25, comprising the following steps:

31. The method of claim 26, wherein the tin-based layer is prepared by a process comprising: The plating solution for the tin layer contains, based on the total volume of the plating solution, 10-50 g / L stannous sulfate, 60-190 ml / L sulfuric acid, 1-10 g / L gelatin, 5-10 ml / L formaldehyde, and 5-30 g / L benzylideneacetone, and the plating temperature is 10-40°C, the ratio of anode to cathode area is 1:1-2, the current density is 0.5-2 A / dm 2 , and the plating time is 15-120 min.

32. The method of claim 31, wherein the tin-based layer is prepared by a method comprising: forming a transition layer, a basic copper layer, a focal copper layer, and a tin layer on the surface of a substrate by electroplating.

33. The method of claim 32, wherein the tin-based layer is prepared by a method comprising: The current density is 0.7-1.2 A / dm 2 . The area ratio of the cathode to the anode is 1:1.

5.

35. The aluminum substrate salt-spray corrosion resistant treatment method claim 34, wherein, The area ratio of the cathode to the anode is 1:1.

5.

36. The method of claim 34, wherein, The area ratio of the cathode to the anode is 1:1.

5.

34. A method for treating the salt mist corrosion resistance of an aluminum substrate, comprising the step of arranging the tin layer-based salt mist corrosion resistant composite layer according to any one of claims 1-25 on the surface of an aluminum substrate. The salt mist corrosion resistance refers to the salt mist corrosion resistance. The roughness of the surface of the aluminum substrate is less than Ra 3.

6.

37. The aluminum substrate salt-spray corrosion resistant treatment method claim 36, wherein, The roughness of the surface of the aluminum substrate is less than Ra 0.

8.

38. A salt-fog corrosion resistant aluminum terminal wherein, Part or all of the surface of the salt-fog corrosion resistant aluminum terminal is provided with the tin layer based salt-fog corrosion resistant composite layer according to any one of claims 1-25.

39. The method for preparing the salt-fog corrosion resistant aluminum terminal according to claim 38, comprising the following steps: performing roll processing and polishing processing on the front surface of the aluminum terminal; performing stamping processing on the side surface of the aluminum terminal; sequentially forming a transition layer, an alkaline copper layer, a pyrophoric copper layer and a tin layer on the front surface and the side surface of the processed aluminum terminal by electroplating to obtain the salt-fog corrosion resistant aluminum terminal.

40. The method of making a salt-fog corrosion resistant aluminum terminal of claim 39, wherein, The roughness of the front surface of the aluminum terminal after roll processing and polishing processing is less than Ra 3.

6.

41. The method of making a salt-fog corrosion resistant aluminum terminal of claim 40, wherein, The roughness of the front surface of the aluminum terminal after roll processing and polishing processing is less than Ra 0.

8.

42. The method of making a salt-fog corrosion resistant aluminum terminal of claim 39, wherein, The roughness of the side surface of the aluminum terminal after roll processing is less than Ra 3.6, and the bright band is greater than 50%.

43. The method of making a salt-fog corrosion resistant aluminum terminal of claim 42, wherein, The roughness of the side surface of the aluminum terminal after roll processing is less than Ra 0.

8.

44. The method of making a salt-fog corrosion resistant aluminum terminal of claim 42, wherein, The bright band of the aluminum terminal after roll processing is greater than 98%.

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