Corrosion-resistant electric connector terminal and electroplating method thereof

Abstract

The invention relates to a corrosion-resistant electric connector terminal and an electroplating method thereof, and relates to the technical field of metal surface treatment, and the terminal comprises a copper alloy base material and a nickel-tungsten-rhenium ternary alloy coating covering the surface of the copper alloy base material. According to the electroplating method, an electroplating solution containing nickel sulfate, sodium tungstate, ammonium perrhenate and ethylenediamine tetramethylenephosphonic acid is adopted, and deposition is carried out through a variable-temperature gradient pulse electroplating process; the process sequentially comprises three stages of interface layer low-temperature deposition, main body layer high-temperature deposition and surface layer stress regulation and control deposition. A special coordination agent and a gradient temperature control strategy are utilized, stable co-deposition of multi-component metal is achieved, the internal stress of a plating layer is effectively eliminated, and micropores are sealed. The obtained terminal has excellent corrosion resistance, extremely low contact resistance and good matrix binding force, and the problems that a high-hardness alloy coating is prone to embrittlement and insufficient in corrosion resistance are solved.

Description

Technical Field

[0001] This application relates to the field of metal surface treatment technology, and in particular to a corrosion-resistant electrical connector terminal and its electroplating method. Background Technology

[0002] Electrical connectors, as key components for transmitting signals and electrical energy in electronic devices, are widely used in consumer electronics, automotive electronics, and communication base stations. Their core component, the contact terminals, typically uses copper alloy as the base material. To ensure the conductivity stability of the contact interface and prevent oxidation and corrosion of the base material, a protective plating layer is usually prepared on the copper alloy surface. Traditional electrical connector terminal protection systems mainly rely on gold plating or palladium-nickel alloy plating. Although these precious metal plating layers have excellent conductivity and corrosion resistance, their raw material costs are extremely high, and the relatively soft pure gold plating layer is prone to wear during insertion and removal.

[0003] To reduce costs and improve wear resistance, nickel-tungsten alloys are considered a promising alternative to gold or chromium due to their high hardness, high melting point, and good wear resistance. However, existing nickel-tungsten alloy electroplating technologies still face significant technical bottlenecks when applied to electrical connector terminals. On the one hand, nickel-tungsten alloy platings often present a contradiction between high hardness and high brittleness. To achieve excellent corrosion resistance, a high tungsten content is usually required, but this leads to the accumulation of enormous tensile stress within the plating. When the terminals are crimped or bent in subsequent processing, the high-stress plating is prone to brittle fracture, forming microcracks that allow corrosive media to penetrate the plating and erode the substrate, resulting in contact failure.

[0004] On the other hand, conventional constant-temperature DC electroplating processes struggle to balance deposition efficiency and coating quality. While high-temperature deposition can increase the co-deposition rate of refractory tungsten, it exacerbates grain coarsening and internal stress accumulation; low-temperature deposition, while yielding finer grains, suffers from slow deposition rates and low alloying degrees. Furthermore, traditional nickel-tungsten binary alloy coatings often fail to completely eliminate grain boundaries in their microstructure. These grain boundaries, acting as preferential channels for corrosive media penetration, limit their long-term protective capabilities under harsh salt spray or acidic environments. Existing complexing agent systems, when handling multi-component metal ion co-deposition, often suffer from uneven coating composition or poor plating solution stability due to excessively large differences in reduction potential. Therefore, developing a novel alloy coating and its preparation process that maintains high corrosion resistance, overcomes brittle cracking, and possesses excellent electrical properties has become a pressing technical challenge for the industry.

[0005] In view of the above-mentioned related technologies, a corrosion-resistant electrical connector terminal and its electroplating method are provided. Summary of the Invention

[0006] The purpose of this application is to provide a corrosion-resistant electrical connector terminal and its electroplating method, aiming to improve the problems faced by the existing nickel-tungsten alloy gold plating technology when applied to electrical connector terminals, such as high internal stress leading to processing brittleness, difficulty in balancing deposition efficiency and quality in traditional processes, and grain boundary corrosion limiting long-term protection capabilities.

[0007] By adopting the above technical solution, a corrosion-resistant electrical connector terminal includes:

[0008] Copper alloy substrate;

[0009] A nickel-tungsten-rhenium ternary alloy coating covering the surface of the copper alloy substrate;

[0010] The chemical composition of the nickel-tungsten-rhenium ternary alloy coating, by weight percentage, is: nickel 50-60 wt%, tungsten 30-40 wt%, and rhenium 5-10 wt%.

[0011] Preferably, the copper alloy substrate is grade C7025 or C194.

[0012] Preferably, an electroplating method for corrosion-resistant electrical connector terminals includes the following steps:

[0013] S1. Pretreatment of copper alloy substrate;

[0014] S2. Prepare a ternary alloy electroplating solution, wherein the ternary alloy electroplating solution comprises: nickel sulfate, sodium tungstate, ammonium perrhenate, and ethylenediaminetetramethylenephosphonic acid;

[0015] S3. A nickel-tungsten-rhenium ternary alloy coating is deposited on the surface of the copper alloy substrate using a variable temperature gradient pulse electroplating process.

[0016] The variable temperature gradient pulse electroplating process includes, in sequence, a low-temperature deposition stage for the interface layer, a high-temperature deposition stage for the main body layer, and a stress-controlled deposition stage for the surface layer.

[0017] Preferably, the concentrations of each component in the ternary alloy electroplating solution are: nickel sulfate 20-30 g / L, sodium tungstate 40-60 g / L, ammonium perrhenate 3-6 g / L, and ethylenediaminetetramethylenephosphonic acid 60-80 g / L.

[0018] Preferably, the ternary alloy electroplating solution further comprises gluconolactone at a concentration of 15-20 g / L and sodium sulfate at a concentration of 20-30 g / L.

[0019] Preferably, the pH value of the ternary alloy electroplating solution is 7.5 to 8.5.

[0020] Preferably, the temperature of the low-temperature deposition stage of the interface layer is 45-50°C, and the average current density is 3-5 A / dm²; the temperature of the high-temperature deposition stage of the main layer is 70-75°C, and the average current density is 8-12 A / dm²; the temperature of the stress-controlled deposition stage of the surface layer is 45-50°C, and the average current density is 4-6 A / dm².

[0021] Preferably, the heating rate from the low-temperature deposition stage of the interface layer to the high-temperature deposition stage of the main layer is 3 to 5 °C / min.

[0022] Preferably, the cooling rate from the high-temperature deposition stage of the main layer to the stress-controlled deposition stage of the surface layer is 3-5°C / min.

[0023] Preferably, the variable temperature gradient pulse electroplating process uses a pulsed reverse power supply, wherein:

[0024] In the low-temperature deposition stage of the interface layer and the stress-controlled deposition stage of the surface layer, the forward pulse time is 80-100 ms and the reverse pulse time is 5-10 ms.

[0025] During the high-temperature deposition stage of the main layer, the forward pulse time is 50–80 ms and the reverse pulse time is 10–20 ms.

[0026] In summary, this application includes at least one of the following beneficial technical effects:

[0027] 1. This application fundamentally eliminates grain boundaries, the main channel for corrosive media penetration, by introducing rhenium into the coating and inducing the formation of a fully amorphous structure using EDTMP ligand. Rhenium can spontaneously form a dense oxide semiconductor film in a corrosive environment, producing a synergistic shielding effect with tungsten oxide, significantly improving the corrosion resistance of the terminals in salt spray, acidic and humid environments, and solving the defect of traditional crystalline coatings being prone to grain boundary corrosion.

[0028] 2. The initial low-temperature deposition stage set in this application, combined with pulsed reverse current technology, makes the initial nucleation of the coating on the copper alloy substrate surface fine and uniform; the low-temperature environment reduces the nucleation growth rate at the interface, avoids the formation of coarse grains, significantly reduces interface stress, ensures excellent adhesion between the coating and the substrate, and prevents the coating from peeling or falling off during the use of the terminal.

[0029] 3. In the high-temperature main deposition stage of this application, thermal energy is used to provide the activation energy required for the deposition of refractory metals, which greatly improves the deposition rate and the content of tungsten and rhenium in the alloy. At the same time, since the Ni-W-Re amorphous coating itself has extremely low contact resistance and extremely high wear resistance, the thickness of the subsequent expensive gold plating layer can be greatly reduced or even eliminated, which significantly reduces the raw material production cost of electrical connectors while improving performance. Detailed Implementation

[0030] Examples 1-3:

[0031] Example 1:

[0032] This embodiment provides an electroplating method for corrosion-resistant electrical connector terminals, including the following steps:

[0033] Preparation of ternary alloy electroplating solution:

[0034] Prepare an aqueous electroplating solution with the following components:

[0035] Nickel sulfate: 25g / L

[0036] Sodium tungstate: 50g / L

[0037] Ammonium perrhenate: 4.5 g / L

[0038] Ethylenediaminetetramethylenephosphonic acid: 70 g / L

[0039] Gluconolactone: 17.5 g / L

[0040] Sodium sulfate: 25g / L

[0041] pH value: Adjust to 8.0

[0042] Variable temperature gradient pulse electroplating process:

[0043] The pretreated copper alloy substrate is used as the cathode, and the platinum-titanium plated mesh is used as the anode. The substrate is placed in the above electroplating solution, and stirring is started. Electroplating is carried out continuously in the following three stages:

[0044] Low-temperature deposition of the interface layer:

[0045] The temperature of the plating solution is controlled at 48℃.

[0046] The average current density is set to 4 A / dm².

[0047] Pulse parameters: forward pulse time 90ms, reverse pulse time 8ms.

[0048] Deposition time: 90 seconds.

[0049] High-temperature deposition of the main layer:

[0050] Turn on the heating and raise the temperature of the plating solution to 72°C at a rate of 4°C / min and maintain the temperature.

[0051] The average current density is set to increase to 10A / dm².

[0052] Pulse parameters: forward pulse time 65ms, reverse pulse time 15ms.

[0053] Deposition time: 8 minutes.

[0054] Surface stress-controlled deposition:

[0055] Turn on the cooling system and reduce the temperature of the plating solution back to 48°C at a rate of 4°C / min.

[0056] The average current density was set to be reduced to 5 A / dm².

[0057] Pulse parameters: forward pulse time 90ms, reverse pulse time 8ms.

[0058] Deposition time: 90 seconds.

[0059] Post-processing:

[0060] After electroplating, the terminals are removed, soaked and cleaned in a deionized water recovery tank, then ultrasonically rinsed with 65℃ hot deionized water for 2 minutes, and finally dried under 110℃ hot air circulation to obtain the finished product.

[0061] Example 2:

[0062] This embodiment provides an electroplating method for corrosion-resistant electrical connector terminals, including the following steps:

[0063] Preparation of ternary alloy electroplating solution:

[0064] Prepare an aqueous electroplating solution with the following components:

[0065] Nickel sulfate: 20 g / L

[0066] Sodium tungstate: 40g / L

[0067] Ammonium perrhenate: 3g / L

[0068] Ethylenediaminetetramethylenephosphonic acid: 60 g / L

[0069] Gluconolactone: 15g / L

[0070] Sodium sulfate: 20g / L

[0071] pH value: Adjust to 7.5

[0072] Variable temperature gradient pulse electroplating process:

[0073] The operating steps are the same as in Example 1, but the specific process parameters are set as follows:

[0074] Low-temperature deposition of the interface layer:

[0075] The temperature of the plating solution is controlled at 45℃.

[0076] The average current density is set to 3A / dm².

[0077] Pulse parameters: forward pulse time 80ms, reverse pulse time 5ms.

[0078] Deposition time: 60 seconds.

[0079] High-temperature deposition of the main layer:

[0080] Turn on the heating and raise the temperature of the plating solution to 70°C at a rate of 3°C / min and maintain the temperature.

[0081] The average current density is set to increase to 8A / dm².

[0082] Pulse parameters: forward pulse time 50ms, reverse pulse time 10ms.

[0083] Deposition time: 6 minutes.

[0084] Surface stress-controlled deposition:

[0085] Turn on the cooling system and reduce the temperature of the plating solution back to 45°C at a rate of 3°C / min.

[0086] The average current density was set to be reduced to 4 A / dm².

[0087] Pulse parameters: forward pulse time 80ms, reverse pulse time 5ms.

[0088] Deposition time: 60 seconds.

[0089] Post-processing:

[0090] Same as Example 1.

[0091] Example 3:

[0092] This embodiment provides an electroplating method for corrosion-resistant electrical connector terminals, including the following steps:

[0093] Preparation of ternary alloy electroplating solution:

[0094] Prepare an aqueous electroplating solution with the following components:

[0095] Nickel sulfate: 30g / L

[0096] Sodium tungstate: 60g / L

[0097] Ammonium perrhenate: 6g / L

[0098] Ethylenediaminetetramethylenephosphonic acid: 80 g / L

[0099] Gluconolactone: 20g / L

[0100] Sodium sulfate: 30g / L

[0101] pH value: Adjust to 8.5

[0102] Variable temperature gradient pulse electroplating process:

[0103] The operating steps are the same as in Example 1, but the specific process parameters are set as follows:

[0104] Low-temperature deposition of the interface layer:

[0105] The temperature of the plating solution should be controlled at 50℃.

[0106] The average current density is set to 5 A / dm².

[0107] Pulse parameters: forward pulse time 100ms, reverse pulse time 10ms.

[0108] Deposition time: 120 seconds.

[0109] High-temperature deposition of the main layer:

[0110] Turn on the heating and raise the temperature of the plating solution to 75°C at a rate of 5°C / min and maintain the temperature.

[0111] The average current density is set to increase to 12A / dm².

[0112] Pulse parameters: forward pulse time 80ms, reverse pulse time 20ms.

[0113] Deposition time: 10 minutes.

[0114] Surface stress-controlled deposition:

[0115] Turn on the cooling system and reduce the temperature of the plating solution back to 50°C at a rate of 5°C / min.

[0116] The average current density was set to be reduced to 6 A / dm².

[0117] Pulse parameters: forward pulse time 100ms, reverse pulse time 10ms.

[0118] Deposition time: 120 seconds.

[0119] Post-processing:

[0120] Same as Example 1.

[0121] Comparative Examples 1-5:

[0122] Comparative Example 1:

[0123] The difference compared to Example 1 is as follows:

[0124] In the preparation of the electroplating solution, no ammonium perrhenate was added, and the other components of the plating solution and the electroplating process parameters were exactly the same as in Example 1.

[0125] Comparative Example 2:

[0126] The difference compared to Example 1 is as follows:

[0127] In the preparation of the electroplating solution, ethylenediaminetetramethylenephosphonic acid was not used; instead, an equal mass of sodium citrate was used as a complexing agent. The remaining components of the plating solution and the electroplating process parameters were exactly the same as in Example 1.

[0128] Comparative Example 3:

[0129] The difference compared to Example 1 is as follows:

[0130] In the electroplating process, the variable temperature gradient operation was eliminated, and constant high-temperature electroplating was adopted throughout the entire process. Specifically, the plating solution temperature was kept constant at 72°C, the current density was kept constant at 10A / dm², the total electroplating time was the same as that in Example 1, and all other aspects were the same.

[0131] Comparative Example 4:

[0132] The difference compared to Example 1 is as follows:

[0133] In the electroplating process, the variable temperature gradient operation was eliminated, and constant low-temperature electroplating was adopted throughout the entire process. Specifically, the plating solution temperature was kept constant at 48°C, the current density was kept constant at 4A / dm², the total electroplating time was the same as that in Example 1, and all other aspects were the same.

[0134] Comparative Example 5:

[0135] The difference compared to Example 1 is as follows:

[0136] In the electroplating process, a DC power supply was used instead of a pulsed reverse power supply. The current density of each stage was set to the average current density value of the corresponding stage in Example 1, and the temperature control program was exactly the same as in Example 1.

[0137] Test Example 1-3:

[0138] Test Example 1: Neutral Salt Spray Corrosion Performance Test

[0139] This test case aims to determine the resistance of the electrical connector terminal plating prepared in Examples 1 to 3 and Comparative Examples 1 to 5 to neutral salt spray corrosion.

[0140] The experimental equipment used was a standard salt spray corrosion test chamber. The experimental medium was a salt solution prepared using analytical grade sodium chloride and distilled water, with the sodium chloride concentration controlled within the range of 50 g / L ± 5 g / L. The pH value of the collected solution was measured using a precision pH meter and adjusted to between 6.5 and 7.2 by adding analytical grade hydrochloric acid or sodium hydroxide solution. The temperature inside the test chamber was set and maintained at 35℃ ± 2℃.

[0141] The specific experimental steps are as follows:

[0142] Sample pretreatment. All terminal samples to be tested were ultrasonically cleaned for 2 minutes with anhydrous ethanol to remove adsorbed dust or fingerprints from the surface, and then dried with cold air.

[0143] Sample placement. Fix the dried terminal samples on the plastic bracket inside the test chamber. The plated surface of the sample is tilted at an angle of 15 to 30 degrees to the vertical direction to ensure that the samples do not touch each other and do not obstruct salt spray deposition.

[0144] Spraying operation. Start the test chamber and spray continuously. Set the spray pressure to 0.1 MPa to 0.15 MPa to achieve a salt spray deposition rate of 1.0 mL / (80 cm²·h) to 2.0 mL / (80 cm²·h).

[0145] Observation and Recording. Open the chamber lid every 24 hours to quickly observe the surface condition of the samples. The focus of observation is to identify whether reddish-brown rust spots appear on the sample surface. Record the time when visible red rust first appears on each sample as the corrosion failure time of that sample. For samples that have not shown red rust after 168 hours, record it as >168h and stop the test.

[0146] The specific data obtained from the test are recorded in Table 1.

[0147] Table 1: Statistical Table of Neutral Salt Spray Corrosion Test Results

[0148] Group number Sample Description Time of first appearance of red rust (h) Example 1 intermediate parameter preparation >168 Example 2 Preparation of lower limit parameters 154 Example 3 Upper limit parameter preparation 162 Comparative Example 1 No perrhenate ammonium component 88 Comparative Example 2 Use sodium citrate instead of EDTMP 52 Comparative Example 3 Constant high temperature process (72℃) 28 Comparative Example 4 Constant low temperature process (48℃) 65 Comparative Example 5 DC power supply electroplating 82

[0149] Results analysis and mechanism explanation:

[0150] The test results of Examples 1 to 3 show that the coating obtained using the electroplating solution formulation containing ammonium perrhenate and ethylenediaminetetramethylenephosphonic acid has a significantly longer corrosion resistance time than Comparative Example 1 and Comparative Example 2. This difference stems from the fact that the oxide film induced by rhenium in the coating blocks the contact path between the corrosive medium and the copper substrate. Simultaneously, EDTMP, as a multidentate phosphonate coordinating agent, alters the reduction kinetics of nickel, tungsten, and rhenium ions due to its significant steric hindrance effect, inhibiting the orderly stacking and growth of crystal nuclei and promoting an amorphous or nanocrystalline structure in the coating. Compared to the crystalline structure formed by the sodium citrate system in Comparative Example 2, the amorphous structure in these examples eliminates grain boundaries, thereby blocking the diffusion channels for chloride ions to penetrate inward along the grain boundaries.

[0151] Data from Comparative Examples 3 and 4 show that a single isothermal electroplating process leads to a decrease in the corrosion resistance of the coating. Comparative Example 3, using constant high-temperature deposition, while beneficial for the co-deposition of tungsten and rhenium, suffers from high tensile stress accumulation within the coating due to the lack of stress control at low temperatures. This results in microcracks, allowing chloride ions to rapidly corrode the substrate through these cracks, leading to the shortest corrosion resistance time. Comparative Example 4, using constant low-temperature deposition, suffers from low co-deposition rates of refractory metals tungsten and rhenium due to reaction activation energy limitations. This results in insufficient alloy element content in the coating, failing to form an effective passivation protective layer. The variable temperature gradient process used in the examples combines the low-stress characteristics of low-temperature deposition with the high alloy content of high-temperature deposition. While ensuring alloy composition, the mutual cancellation of stress gradients reduces structural defects such as microcracks, thereby maintaining the integrity of the coating.

[0152] A comparison of Comparative Example 5 and the Examples shows that the application of pulsed reverse current contributes to improved corrosion resistance. Under DC electroplating conditions, concentration polarization easily occurs at the cathode interface, leading to increased surface roughness and pinhole defects in the coating. The pulsed reverse current technology used in the Examples periodically dissolves microscopic protrusions and adsorbed impurities on the coating surface using reverse pulses, refining the deposited particles and improving the density of the coating. This dense microstructure further reduces porosity and enhances the physical shielding effect of the coating against corrosive media.

[0153] Test Example 2: Coating Adhesion and Flexibility Test

[0154] This test case aims to evaluate the bonding strength and resistance to brittle cracking of the electrical connector terminal plating prepared in Examples 1 to 3 and Comparative Examples 1 to 5 under mechanical deformation conditions.

[0155] The experimental equipment used was a bending tester equipped with a standard V-groove and indenter, as well as an optical magnifying glass with a magnification of 10x. The auxiliary material was 3M 600 pressure-sensitive adhesive tape with good adhesion.

[0156] The specific experimental steps are as follows:

[0157] Sample fixation. Select a strip terminal sample with dimensions of 10mm × 50mm, place it horizontally above the V-shaped mold of the bending tester, and adjust its position so that the area to be tested is located at the center of the bending axis.

[0158] Bending operation. The indenter of the testing machine descends at a rate of 10 mm / min, applying pressure to the sample until the sample undergoes a 90-degree plastic deformation. The bending radius R is set to 1 times the thickness of the sample substrate.

[0159] Tape peeling. Remove the bent sample. Cut a piece of 3M 600 tape approximately 50mm long and ensure the adhesive side tightly covers the bent edges and stretched areas of the sample. Press back and forth three times with your fingers to remove air bubbles and ensure complete adhesion. Then, holding one end of the tape, quickly peel it off perpendicular to the sample surface within 0.5 to 1 second.

[0160] Microscopic observation. A 10x optical magnifying glass was used to observe the curved ridge areas of the sample. The observation indicators included two aspects: first, checking whether there were transverse or network cracks on the coating surface; second, checking whether there were coating fragments adhering to the adhesive surface of the torn-off tape, or whether the substrate was exposed on the sample surface.

[0161] The specific data obtained from the test are recorded in Table 2.

[0162] Table 2: Record of Bending Bond Strength and Flexibility Test Results

[0163] Group number Surface condition of the curved area (10X magnification observation) Tape removal result Comprehensive judgment Example 1 Surface is continuous and crack-free. No adhering substances on the adhesive surface qualified Example 2 The surface is continuous, with occasional minor dents. No adhering substances on the adhesive surface qualified Example 3 Surface is continuous and crack-free. No adhering substances on the adhesive surface qualified Comparative Example 1 A small number of transverse microcracks appeared There is a very small amount of powder on the adhesive surface. Barely qualified Comparative Example 2 Obvious through-cracks appeared There are chunks of peeling off the adhesive surface. Failure (high brittleness) Comparative Example 3 Multiple deep cracks appeared at the edge. No adhering substances on the adhesive surface Failure (high brittleness) Comparative Example 4 No cracks on the surface Large areas of the adhesive surface are peeling off in flakes. Failure (poor binding) Comparative Example 5 The surface is rough and has microcracks. A small number of particles adhered to the adhesive surface. Unqualified

[0164] Results analysis and mechanism explanation:

[0165] The samples from Examples 1 to 3 exhibited continuous and non-peeling coatings in bending tests, attributed to the stress-compensating structure constructed by the low-temperature-high-low-temperature deposition sequence in the variable temperature gradient process. Comparative Example 3 employed constant high-temperature deposition; the co-deposition of tungsten and nickel was accompanied by volume shrinkage, leading to the accumulation of unidirectional tensile stress within the coating. When the sample was subjected to bending forces, the internal tensile stress superimposed on the external deformation stress, exceeding the material's fracture limit, resulting in deep cracks as shown in Table 2. The Examples, by implementing low-temperature deposition in the final stage, utilized the slight differences in lattice deposition parameters at different temperatures to introduce a surface layer with compressive stress characteristics on the outermost layer of the coating. This surface compressive stress layer vector-canceled the tensile stress of the inner main layer, reducing the overall residual stress level of the coating and thus improving its ability to withstand mechanical deformation.

[0166] The test results of Comparative Example 4 showed large-area peeling, indicating that constant low-temperature deposition cannot form sufficient bonding strength on the surface of the copper alloy substrate. In the first stage, the embodiment used low-temperature, low-current-density deposition parameters. This reduced the reduction rate of metal ions at the cathode interface, allowing crystal nuclei to preferentially form a high-density of fine crystal nuclei at high-energy sites on the substrate, increasing the physical anchoring points between the coating and the substrate. Furthermore, the instantaneous dissolution effect of the pulsed reverse current on the initial deposited layer removed the loose layer at the interface, achieving atomic-level metallic bonding. In contrast, although Comparative Example 4 used low temperatures throughout, the lack of subsequent high-temperature stages to promote thermal diffusion of the interface layer and the stress support of the main layer resulted in insufficient overall bonding strength.

[0167] The network cracks observed in Comparative Example 2 are directly related to the choice of components. When using conventional sodium citrate as a ligand, the coating tends to form a large-grained crystalline structure, with dislocations easily accumulating at grain boundaries, leading to increased material brittleness. The combination of ethylenediaminetetramethylenephosphonic acid and ammonium perrhenate used in the examples promotes the accumulation of nickel, tungsten, and rhenium atoms in a disordered amorphous or nanocrystalline manner. The amorphous structure lacks long-range ordered slip planes. Although it has high hardness, its isotropic structural characteristics prevent stress concentration at specific grain boundaries. Combined with the solid solution strengthening effect of rhenium, the coating maintains high hardness while possessing the toughness to adapt to the plastic deformation of the substrate.

[0168] Test Example 3: Contact Resistance Stability Test

[0169] This test case aims to quantitatively evaluate the electrical transmission stability of the electrical connector terminals prepared in Examples 1 to 3 and Comparative Examples 1 to 5 before and after aging in a high temperature and high humidity environment.

[0170] The experiment used a precision micro-ohmmeter equipped with a Kelvin four-wire test fixture to measure low-level contact resistance, and a programmable constant temperature and humidity test chamber for environmental aging treatment.

[0171] The specific experimental steps are as follows:

[0172] Initial resistance measurement. Fix the terminal sample to be tested onto the insulation test bench. Use a four-wire probe of a precision micro-ohmmeter to contact the crimping area and contact area of ​​the terminal respectively. Set the test mode to dry circuit mode, limit the open circuit voltage to 20mV, and limit the test current to 10mA to prevent electrothermal effects from damaging the surface oxide film during the measurement process. After the readings stabilize, record the initial contact resistance value of each sample (denoted as ). ).

[0173] Environmental aging treatment. The samples, after initial measurements, were suspended in a constant temperature and humidity test chamber. The chamber parameters were set according to EIA-364-31 standard: temperature controlled at 85℃±2℃, relative humidity controlled at 85%±3%RH. The samples were left to stand continuously under this environment for 168 hours.

[0174] Recovery and drying. After the aging time is over, the sample is taken out and left to stand for 2 hours in a standard atmospheric environment (temperature 25℃±2℃, relative humidity 50%±5%RH) to allow the sample to cool naturally and dry the condensation on the surface.

[0175] Final resistance measurement. Using the same equipment, parameters, and probe contact position as in the first step, perform a second contact resistance measurement on the aged sample and record the final contact resistance value (denoted as ). ).

[0176] Data calculation. Calculate the change in contact resistance. .

[0177] The specific data obtained from the test are recorded in Table 3.

[0178] Table 3: Data on changes in contact resistance before and after high temperature and high humidity aging

[0179] Group number Initial contact resistance Contact resistance after aging Change in resistance Example 1 1.24 1.58 0.34 Example 2 1.35 1.92 0.57 Example 3 1.18 1.65 0.47 Comparative Example 1 1.42 5.86 4.44 Comparative Example 2 1.29 8.43 7.14 Comparative Example 3 1.55 12.67 11.12 Comparative Example 4 2.86 21.35 18.49 Comparative Example 5 1.68 4.15 2.47

[0180] Results analysis and mechanism explanation:

[0181] Resistance changes in Examples 1 to 3 All samples maintained low resistance levels, while Comparative Examples 1 and 2 showed a more significant increase in resistance. This phenomenon indicates that the synergistic effect of rhenium and the EDTMP ligand in the coating has a decisive influence on maintaining electrical stability. In the system of the examples, the amorphous structure induced by EDTMP eliminated grain boundaries, making it difficult for oxygen and water molecules to diffuse inward through the grain boundary channels. At the same time, the doping of rhenium caused a dense and conductive composite oxide film to form on the coating surface under high temperature and high humidity conditions. In contrast, Comparative Example 1, lacking rhenium, had a relatively loose structure of pure tungsten-nickel oxide on its surface; Comparative Example 2, using a sodium citrate system, formed a crystalline structure, with the grain boundaries becoming preferential channels for the diffusion of corrosive media, leading to oxidation of the substrate or underlying metal, and thus causing a significant increase in contact resistance.

[0182] The high resistance changes in Comparative Examples 3 and 4 verify the role of the variable temperature gradient process in ensuring coating integrity. Comparative Example 3, due to constant high-temperature deposition, exhibits significant tensile stress within the coating, leading to the formation of microcracks. In the aging environment, moisture directly corrodes the copper alloy substrate through these microcracks, generating copper oxides, a high-resistivity material, which directly causes a sharp increase in the resistance of the measurement circuit. Comparative Example 4, employing constant low-temperature deposition, suffers from insufficient coating thickness and high porosity due to the low deposition efficiency of refractory metals, failing to effectively isolate the substrate from the external environment. This embodiment, through a gradient construction of a low-temperature interface – high-temperature substrate – low-temperature surface layer, not only ensures coating thickness and alloy content during the high-temperature stage but also seals penetrating pores with the low-temperature surface layer, constructing an effective physical shielding layer, thereby maintaining low resistance characteristics during aging tests.

[0183] Comparative Example 5 shows that the resistance stability of the DC electroplated sample is inferior to that of the example using pulsed reverse current. During DC electroplating, the uneven distribution of metal ion concentration on the cathode surface leads to a microscopic roughness on the deposited layer surface, increasing the specific surface area and thus increasing the active sites for surface oxidation reactions. The pulsed reverse current technology used in the example selectively dissolves surface protrusions using reverse pulses, achieving a surface leveling effect. The smooth and dense surface not only reduces the actual area for adsorbing water vapor but also improves the contact state between the test probe and the coating surface, reducing contact resistance fluctuations caused by differences in surface microstructure.

Claims

1. A corrosion-resistant electrical connector terminal, characterized in that, include: Copper alloy substrate; A nickel-tungsten-rhenium ternary alloy coating covering the surface of the copper alloy substrate; The chemical composition of the nickel-tungsten-rhenium ternary alloy coating, by weight percentage, is: nickel 50-60 wt%, tungsten 30-40 wt%, and rhenium 5-10 wt%.

2. The corrosion-resistant electrical connector terminal according to claim 1, characterized in that, The copper alloy substrate is graded C7025 or C194.

3. A method for electroplating corrosion-resistant electrical connector terminals, wherein the corrosion-resistant electrical connector terminal according to any one of claims 1-2 is characterized in that, Includes the following steps: S1. Pretreatment of copper alloy substrate; S2. Prepare a ternary alloy electroplating solution, wherein the ternary alloy electroplating solution comprises: nickel sulfate, sodium tungstate, ammonium perrhenate, and ethylenediaminetetramethylenephosphonic acid; S3. A nickel-tungsten-rhenium ternary alloy coating is deposited on the surface of the copper alloy substrate using a variable temperature gradient pulse electroplating process. The variable temperature gradient pulse electroplating process includes, in sequence, a low-temperature deposition stage for the interface layer, a high-temperature deposition stage for the main body layer, and a stress-controlled deposition stage for the surface layer.

4. The electroplating method for corrosion-resistant electrical connector terminals according to claim 3, characterized in that, The concentrations of each component in the ternary alloy electroplating solution are as follows: nickel sulfate 20-30 g / L, sodium tungstate 40-60 g / L, ammonium perrhenate 3-6 g / L, and ethylenediaminetetramethylenephosphonic acid 60-80 g / L.

5. The electroplating method for corrosion-resistant electrical connector terminals according to claim 4, characterized in that, The ternary alloy electroplating solution also contains gluconolactone at a concentration of 15-20 g / L and sodium sulfate at a concentration of 20-30 g / L.

6. The electroplating method for corrosion-resistant electrical connector terminals according to claim 4, characterized in that, The pH value of the ternary alloy electroplating solution is 7.5 to 8.

5.

7. The electroplating method for corrosion-resistant electrical connector terminals according to claim 3, characterized in that, The temperature of the low-temperature deposition stage of the interface layer is 45-50℃, and the average current density is 3-5A / dm². The temperature during the high-temperature deposition stage of the main layer is 70-75℃, and the average current density is 8-12A / dm². The temperature of the surface stress-controlled deposition stage is 45–50°C, and the average current density is 4–6 A / dm².

8. The electroplating method for corrosion-resistant electrical connector terminals according to claim 7, characterized in that, The heating rate from the low-temperature deposition stage of the interface layer to the high-temperature deposition stage of the main layer is 3-5℃ / min.

9. The electroplating method for corrosion-resistant electrical connector terminals according to claim 7, characterized in that, The cooling rate from the high-temperature deposition stage of the main layer to the stress-controlled deposition stage of the surface layer is 3-5℃ / min.

10. The electroplating method for corrosion-resistant electrical connector terminals according to claim 7, characterized in that, The variable temperature gradient pulse electroplating process uses a pulsed reverse power supply, wherein: In the low-temperature deposition stage of the interface layer and the stress-controlled deposition stage of the surface layer, the forward pulse time is 80-100 ms and the reverse pulse time is 5-10 ms. During the high-temperature deposition stage of the main layer, the forward pulse time is 50–80 ms and the reverse pulse time is 10–20 ms.