A method for nickel plating a magnesium alloy part

Abstract

The present application relates to alloy nickel plating technical field, disclose a kind of nickel plating method of magnesium alloy parts, comprising: magnesium alloy raw material is sequentially sandblasted, cleaning, first baking, hang, ultrasonic oil removal, four-stage water washing, pickling, four-stage water washing, acid activation, four-stage water washing, alkali activation, four-stage water washing, zinc deposition, four-stage water washing, nickel pre-deposition, four-stage water washing, chemical nickel deposition, four-stage water washing, passivation, hang down, spin-dry and second baking, obtain nickel-plated magnesium alloy parts.The present application can reduce the influence of surface residue, zinc deposition fluctuation and uneven plating on subsequent chemical nickel layer during magnesium alloy nickel plating, thereby improving the stability of nickel plating process and coating consistency under the condition of relatively thin coating.

Description

Technical Field

[0001] This invention relates to the field of nickel plating technology, and more specifically, to a method for nickel plating magnesium alloy parts. Background Technology

[0002] Magnesium alloys are characterized by low density, high specific strength, and significant weight reduction, making them commonly used in electronic product brackets, housings, lightweight automotive components, and other structural parts. However, magnesium alloys have high chemical reactivity, and their natural oxide film has poor stability, making them prone to corrosion in humid, salt spray, or electrochemically corrosive environments. For magnesium alloy parts that require a balance of conductivity, corrosion resistance, appearance stability, and assembly adaptability, surface treatment processes such as nickel plating are typically used to improve their surface properties.

[0003] Existing technologies have proposed pretreatment processes for electroless nickel plating on magnesium alloy surfaces. For example, patent CN103898505A discloses a pre-electroplated zinc-nickel alloy electroless nickel plating process for magnesium alloy surfaces. This process includes alkaline washing, acid washing, activation, zinc immersion, zinc-nickel electroplating, and electroless nickel plating, using zinc immersion and zinc-nickel electroplating to provide a foundation for subsequent electroless nickel plating. In this scheme, after zinc immersion, zinc-nickel alloy electroplating is required before electroless nickel plating. Therefore, it mainly relies on the interlayer transition route of "zinc immersion layer—zinc-nickel alloy pre-plating layer—electroless nickel layer" to improve the nickel plating conditions on the magnesium alloy surface.

[0004] However, for magnesium alloy die-cast parts, their surfaces typically contain micropores, depressions, corner areas, and mold release agent residue. Ordinary degreasing and fixed-time pretreatment can easily lead to inconsistent surface conditions in certain areas. Furthermore, if pickling, acid activation, alkali activation, and water washing are performed as independent processes without control over the conductivity and transition time of the final water wash, the surface condition before zinc plating can easily fluctuate. In addition, if the zinc plating process ends at a fixed time, it is difficult to reflect the actual displacement reaction state of different batches of magnesium alloy materials, potentially resulting in insufficient or excessive zinc plating. If the subsequent nickel plating process proceeds directly after zinc plating, sudden current changes during the initial plating stage can cause localized hydrogen evolution, uneven plating, or interface disturbances.

[0005] Therefore, it is necessary to propose a nickel plating method for magnesium alloy parts to improve the stability of the nickel plating process for magnesium alloy parts under thinner plating conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a method for nickel plating magnesium alloy parts to solve the above-mentioned technical problems.

[0007] To achieve the above objectives, the present invention provides the following solution: A method for nickel plating magnesium alloy parts includes the following steps: The magnesium alloy material is subjected to the following steps in sequence: sandblasting, cleaning, first baking, hanging, ultrasonic degreasing, four-stage water washing, pickling, four-stage water washing, acid activation, four-stage water washing, alkali activation, four-stage water washing, zinc immersion, four-stage water washing, nickel pre-deposition, four-stage water washing, chemical nickel deposition, four-stage water washing, passivation, hanging, spin drying, and second baking to obtain nickel-plated magnesium alloy parts. The ultrasonic degreasing includes alternating ultrasonic on-state and ultrasonic off-state immersion states, and the ultrasonic on-state and ultrasonic off-state immersion states are alternated at least twice. The pickling is carried out using a composite pickling solution including organic acid, fluoride salt and corrosion inhibitor; the acid activation is carried out using a fluorinated acid activation solution with a pH of 3.0-5.5; and the alkali activation is carried out using an alkali activation solution with a pH of 10.5-12.5. In the four-stage water washing process, which is located after alkali activation and before zinc precipitation, the conductivity of the last water washing tank is ≤80μS / cm, and the interval between the end of the four-stage water washing after alkali activation and the start of zinc precipitation is ≤90s. The zinc precipitation is carried out using a non-cyanide zinc precipitation solution. The zinc precipitation is a single-displacement zinc precipitation. During the zinc precipitation process, the open circuit potential of the magnesium alloy material in the non-cyanide zinc precipitation solution is collected. The zinc precipitation ends when the change in open circuit potential does not exceed a preset potential stabilization threshold within 10s-30s. The preset potential stabilization threshold is 5mV-20mV. The nickel pre-deposition includes a current density increasing plating stage and a constant current thickening stage. In the current density increasing plating stage, the current density increases from 0.2A / dm²-0.5A / dm² to 0.8A / dm²-1.2A / dm². In the constant current thickening stage, the current density is 1.0A / dm²-3.0A / dm². The total thickness of the plating layer on the surface of the nickel-magnesium alloy parts is 5μm-10μm.

[0008] Preferably, the magnesium alloy material is a magnesium alloy die-cast part; The sandblasting is carried out using alumina sand, ceramic sand or glass microspheres, with a sandblasting pressure of 0.15MPa-0.35MPa, a sandblasting distance of 80mm-150mm, and a sandblasting time of 10s-60s. The surface roughness Ra of the sandblasted magnesium alloy material is 0.9μm-1.8μm.

[0009] Preferably, the cleaning is performed by at least one of spray cleaning, soaking cleaning, or running water cleaning, and the cleaning time is 30s-180s; The temperature of the first baking is 80℃-130℃, and the time is 10min-60min; After the first baking is completed, the magnesium alloy material is cooled to ≤45℃ before being hung up; The interval between the end of the first baking and the completion of the hanging process is ≤30 minutes, and the interval between the completion of the hanging process and the start of the ultrasonic degreasing process is ≤20 minutes.

[0010] Preferably, the ultrasonic degreasing is performed using an alkaline degreasing solution; the alkaline degreasing solution includes sodium carbonate, sodium phosphate, sodium silicate, a complexing agent, and a nonionic surfactant. The total processing time for ultrasonic degreasing is 2-8 minutes, the ultrasonic frequency is 25kHz-45kHz, the ultrasonic power density is 0.3W / cm²-1.2W / cm², and the degreasing temperature is 45℃-65℃. The duration of the ultrasonic activation phase is 20s-90s, and the duration of the ultrasonic deactivation phase is 10s-60s.

[0011] Preferably, the four-stage water washing is a four-stage counter-current water washing, with each stage of water washing lasting 10s-60s; The four-stage water washing process, which occurs after pickling, acid activation, alkali activation, zinc precipitation, nickel pre-deposition, and electroless nickel deposition, all employs a four-stage countercurrent water washing method. In the four-stage water wash that occurs after zinc precipitation and before nickel pre-deposition, the conductivity of the last water wash tank is ≤80μS / cm, and the interval between the end of the four-stage water wash after zinc precipitation and the start of nickel pre-deposition is ≤120s.

[0012] Preferably, the composite pickling solution includes citric acid, tartaric acid, ammonium fluoride, and a corrosion inhibitor; The concentration of citric acid in the composite pickling solution is 20 g / L-80 g / L, the concentration of tartaric acid is 5 g / L-30 g / L, the concentration of ammonium fluoride is 5 g / L-25 g / L, and the corrosion inhibitor is one or more of thiourea, hexamethylenetetramine, and ethylene thiourea, with a concentration of 0.1 g / L-2 g / L. The pickling temperature is 20℃-35℃, and the time is 10s-90s; The interval between the end of pickling and the start of the fourth-stage water rinse after pickling is ≤120s.

[0013] Preferably, the fluoride-containing activation solution includes ammonium hydrofluoride, citric acid, and deionized water, and the acid activation time is 10s-60s; The alkaline activation solution includes sodium hydroxide, sodium carbonate, phosphate and nonionic surfactant, and the alkaline activation temperature is 35℃-65℃, and the alkaline activation time is 30s-5min. The interval between the end of acid activation and the start of alkali activation is ≤120s.

[0014] Preferably, the non-cyanide zinc precipitation solution includes a zinc source, fluoride salts, a complexing agent, and a pH adjuster; The zinc source is one or more of zinc sulfate, zinc acetate, and zinc oxide; The fluoride salt is one or more of sodium fluoride, potassium fluoride, ammonium fluoride, and ammonium hydrofluoride; The complexing agent is one or more of potassium pyrophosphate, sodium pyrophosphate, sodium citrate, and potassium sodium tartrate. The non-cyanide zinc precipitation solution has a zinc ion concentration of 2 g / L-10 g / L, a fluoride salt concentration of 5 g / L-30 g / L, a complexing agent concentration of 20 g / L-80 g / L, and a pH value of 9.5-11.5. The zinc immersion temperature is 20℃-35℃, and the maximum zinc immersion time is ≤120s; The zinc plating process ends when the open circuit potential change is reached or the maximum zinc plating time is reached.

[0015] Preferably, the nickel pre-deposition is performed using a nickel salt electroplating solution based on a nickel sulfate system, a nickel aminosulfonate system, or a nickel chloride system; The nickel salt electroplating solution has a nickel ion concentration of 40 g / L-120 g / L, a boric acid concentration of 20 g / L-45 g / L, a pH value of 3.5-5.5, and a temperature of 35℃-60℃. The duration of the current density increasing plating stage is 30s-120s, and the duration of the constant current thickening stage is 1min-5min. The current density increasing plating stage and the constant current thickening stage are performed continuously.

[0016] Preferably, the electroless nickel deposition is performed using an electroless nickel plating solution; The electroless nickel plating solution includes nickel salt, hypophosphite reducing agent, complexing agent, and stabilizer; the complexing agent is one or more of lactic acid, sodium citrate, malic acid, sodium acetate, and sodium succinate, and the stabilizer is one or more of thiourea, sodium thiosulfate, and potassium iodate. The pH value of the electroless nickel plating solution is 4.5-5.2, and the temperature is 80℃-90℃; The passivation is performed using a chromium-free passivation solution, and the passivation time is 20s-90s. The second baking temperature is 80℃-130℃, and the time is 10min-60min.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The ultrasonic degreasing of this invention is a pulsed degreasing process that alternates between an ultrasonic on-state segment and an ultrasonic immersion segment with an ultrasonic stop segment. For micropores, depressions, corners, and areas with residual mold release agent on the surface of magnesium alloy die-cast parts, the ultrasonic immersion segment with the ultrasonic stop segment allows the alkaline degreasing liquid to re-enter the local structural area, while the ultrasonic on-state segment utilizes cavitation to promote the removal of contaminants, thereby reducing the problem of uneven degreasing caused by bubble shielding or insufficient local liquid renewal during continuous ultrasonication.

[0018] Composite pickling, fluorinated acid activation, alkali activation, the conductivity of the final stage of four-stage water washing, and the transfer time were used as surface condition control conditions before zinc immersion. Controlled treatment of the magnesium alloy surface was achieved through composite pickling, while a continuous acid-alkali surface conditioning process was formed through fluorinated acid activation and alkali activation. The conductivity of the final stage water washing and the transfer time limited the influence of residual ions and prolonged exposure on the zinc immersion reaction, thereby improving the consistency of the magnesium alloy material's surface condition before entering the zinc immersion process.

[0019] The zinc plating process is set as a single-stage displacement zinc plating process, with the endpoint determined based on the change in open-circuit potential. During the zinc plating process, a displacement reaction occurs on the surface of the magnesium alloy material, and its open-circuit potential changes with the surface reaction state. When the change in open-circuit potential does not exceed the preset potential stability threshold within a certain period of time, it indicates that the zinc plating reaction is stabilizing. At this point, the zinc plating process is terminated, which can reduce the problems of insufficient or excessive zinc plating caused by relying solely on zinc plating for a fixed time.

[0020] After zinc plating, nickel pre-deposition is performed, and the nickel pre-deposition is set up as a continuous process of increasing current density initial plating stage and constant current thickening stage. The increasing current density initial plating stage avoids the surface of the magnesium alloy material after zinc plating from being directly subjected to a high current density, reducing the risk of local hydrogen evolution, local burning, or uneven deposition in the initial plating stage; the constant current thickening stage is used to form a nickel-based transition deposition state suitable for receiving electroless nickel deposition.

[0021] This invention employs a continuous control method—pulsed ultrasonic degreasing, composite pickling and acid-base activation, low-conductivity water washing and time-limited sequence transition, open-circuit potential endpoint zinc immersion, segmented nickel pre-deposition, and electroless nickel deposition—to ensure that magnesium alloy materials undergo contaminant removal, surface activation state adjustment, endpoint control of displacement zinc immersion, and nickel-based transition deposition buffering before electroless nickel deposition. This helps reduce the impact of pretreatment residues, zinc immersion fluctuations, and uneven plating on the subsequent electroless nickel layer.

[0022] The total coating thickness is controlled within the range of 5μm-10μm, and the stability of the thin coating formation process is improved through pretreatment state control, zinc immersion endpoint control, and nickel pre-deposition segmented control. Compared with process routes that rely on thicker electroplated zinc layers, zinc-nickel alloy layers, or copper transition layers, this invention is more suitable for nickel plating of magnesium alloy parts with requirements for weight, dimensional tolerances, conductivity, and surface consistency. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The above are external views of the magnesium alloy double ear support parts of Embodiments 1-15 of the present invention; Figure 2 The figures show the external appearance of the magnesium alloy double ear support parts of Comparative Examples 1-12 of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, in the following examples and comparative examples, the magnesium alloy materials are all AZ91D magnesium alloy die-cast parts, and the processing flow is carried out in the following order: sandblasting, cleaning, first baking, hanging, ultrasonic degreasing, four-stage water washing, pickling, four-stage water washing, acid activation, four-stage water washing, alkali activation, four-stage water washing, zinc immersion, four-stage water washing, nickel pre-deposition, four-stage water washing, electroless nickel deposition, four-stage water washing, passivation, hanging, spin drying, and second baking.

[0027] The change in open-circuit potential is used to characterize the extent of the zinc displacement reaction on the magnesium alloy surface. When the open-circuit potential enters a relatively stable range, it indicates that the displacement reaction is approaching equilibrium. The preset potential stability threshold is used to characterize the allowable range of fluctuations in the open-circuit potential as it enters the stable plateau region.

[0028] Example 1: This embodiment provides a method for nickel plating magnesium alloy parts, including the following steps.

[0029] S1. The magnesium alloy material is sandblasted with alumina sand as the sandblasting medium, the sandblasting pressure is 0.25MPa, the sandblasting distance is 120mm, the sandblasting time is 30s, and the surface roughness Ra of the sandblasted magnesium alloy material is 1.2μm.

[0030] S2. Clean the sandblasted magnesium alloy material with running water for 90 seconds.

[0031] S3. The cleaned magnesium alloy material is baked for the first time at a temperature of 100℃ for 30 minutes. After the first baking, the magnesium alloy material is cooled to 40℃ and then hung up. The interval between the end of the first baking and the completion of the hanging is 20 minutes, and the interval between the completion of the hanging and the start of the ultrasonic degreasing process is 10 minutes.

[0032] S4. Perform ultrasonic degreasing on the magnesium alloy material after it has been mounted. Ultrasonic degreasing uses an alkaline degreasing solution, which includes sodium carbonate, sodium phosphate, sodium silicate, sodium gluconate, and fatty alcohol polyoxyethylene ether. The degreasing temperature is 55℃, the ultrasonic frequency is 35kHz, the ultrasonic power density is 0.8W / cm², and the total treatment time is 5 minutes. Ultrasonic degreasing includes alternating ultrasonic on-state and ultrasonic off-state immersion phases. The ultrasonic on-state phase lasts for 50 seconds, and the ultrasonic off-state immersion phase lasts for 30 seconds, with the ultrasonic on-state and ultrasonic off-state immersion phases alternating at least twice.

[0033] S5. Perform a four-stage countercurrent water wash on the magnesium alloy material after ultrasonic degreasing, with each stage lasting 30 seconds.

[0034] S6. The magnesium alloy material after the fourth-stage water washing is pickled. Pickling is carried out using a composite pickling solution, which includes citric acid, tartaric acid, ammonium fluoride, and a corrosion inhibitor; wherein, the concentration of citric acid is 50 g / L, the concentration of tartaric acid is 15 g / L, the concentration of ammonium fluoride is 15 g / L, and the corrosion inhibitor is thiourea with a concentration of 0.8 g / L; the pickling temperature is 25℃, the pickling time is 45 s, and the interval between the end of pickling and the start of the fourth-stage water washing after pickling is 60 s.

[0035] S7. Perform a four-stage counter-current water wash on the pickled magnesium alloy material, with each stage lasting 30 seconds.

[0036] S8. Acid activation is performed on the magnesium alloy material after the fourth-stage water washing. The fluorinated acid activation solution includes ammonium fluoride, citric acid, and deionized water. The pH value of the acid activation solution is 4.2, and the acid activation time is 35 seconds.

[0037] S9. Perform a four-stage countercurrent water wash on the acid-activated magnesium alloy material, with each stage lasting 30 seconds.

[0038] S10. Alkali activation is performed on the magnesium alloy material after the fourth-stage water washing. The alkali activation solution includes sodium hydroxide, sodium carbonate, sodium phosphate, and fatty alcohol polyoxyethylene ether. The pH value of the alkali activation solution is 11.5, the alkali activation temperature is 50℃, and the alkali activation time is 2 min. The interval between the end of acid activation and the start of alkali activation is 90 s.

[0039] S11. The alkali-activated magnesium alloy material is subjected to a four-stage countercurrent water wash, with each stage lasting 30 seconds. The conductivity of the final water wash tank is 55 μS / cm. The interval between the end of the four-stage water wash after alkali activation and the start of zinc precipitation is 60 seconds.

[0040] S12. Zinc precipitation is performed on the magnesium alloy material. A non-cyanide zinc precipitation solution is used, which includes a zinc source, fluoride salt, complexing agent, and pH adjuster. The zinc source is zinc sulfate, the fluoride salt is potassium fluoride, the complexing agent is potassium pyrophosphate, and the pH adjuster is sodium hydroxide. The zinc ion concentration in the non-cyanide zinc precipitation solution is 6 g / L, the fluoride salt concentration is 15 g / L, the complexing agent concentration is 50 g / L, the pH value is 10.5, and the precipitation temperature is 25℃. Zinc precipitation is a single-displacement precipitation. During the precipitation process, the open-circuit potential of the magnesium alloy material in the non-cyanide zinc precipitation solution is collected. Zinc precipitation ends when the change in open-circuit potential is no greater than 10 mV within 20 consecutive seconds. If the above condition is not met, the zinc precipitation ends when the maximum precipitation time reaches 120 seconds.

[0041] S13. Perform four-stage countercurrent water washing on the zinc-plated magnesium alloy material, with each stage lasting 30 seconds. The conductivity of the final water washing tank is 60 μS / cm. The interval between the end of the four-stage water washing after zinc plating and the start of nickel pre-deposition is 90 seconds.

[0042] S14. Nickel pre-deposition was performed on the magnesium alloy material. Nickel pre-deposition was carried out using a nickel salt plating solution based on a nickel sulfate system. The nickel ion concentration in the solution was 80 g / L, the boric acid concentration was 35 g / L, the pH value was 4.5, and the temperature was 45℃. Nickel pre-deposition included a current density increasing initial plating stage and a constant current thickening stage. The current density increasing initial plating stage lasted for 80 seconds, with the current density increasing from 0.35 A / dm² to 1.0 A / dm². The constant current thickening stage lasted for 3 minutes, with a current density of 2.0 A / dm².

[0043] S15. Perform a four-stage countercurrent water wash on the magnesium alloy material after nickel pre-deposition, with each stage lasting 30 seconds.

[0044] S16. Perform electroless nickel deposition on magnesium alloy materials. The electroless nickel plating solution includes nickel salt, hypophosphite reducing agent, complexing agent, and stabilizer, wherein the complexing agent is lactic acid and sodium citrate, and the stabilizer is thiourea; the pH value of the electroless nickel plating solution is 4.8, and the temperature is 85℃.

[0045] S17. Perform a four-stage countercurrent water wash on the magnesium alloy material after electroless nickel deposition, with each stage lasting 30 seconds.

[0046] S18. Perform chromium-free passivation treatment on the magnesium alloy material after the fourth-level water washing, with a passivation time of 60s.

[0047] S19. The passivated magnesium alloy material is hung up, spun dry, and baked a second time. The second baking temperature is 100℃ and the time is 30 minutes to obtain nickel-plated magnesium alloy parts.

[0048] The total thickness of the plating layer on the surface of the nickel-magnesium alloy parts obtained in this embodiment is 7.8μm-8.5μm.

[0049] Example 2: The difference between this embodiment and Embodiment 1 is as follows: the sandblasting medium is glass microspheres, the sandblasting pressure is 0.15MPa, the sandblasting distance is 80mm, the sandblasting time is 10s, and the surface roughness Ra of the magnesium alloy material after sandblasting is 0.9μm; the cleaning is spray cleaning, and the cleaning time is 30s; the first baking temperature is 80℃, and the time is 10min; after the first baking, the material is cooled to 45℃ before being hung up, the interval between the end of the first baking and the completion of the hanging is 30min, and the interval between the completion of the hanging and the entry into the ultrasonic degreasing process is 20min.

[0050] Example 3: The difference between this embodiment and Embodiment 1 is as follows: the sandblasting medium is ceramic sand, the sandblasting pressure is 0.35 MPa, the sandblasting distance is 150 mm, the sandblasting time is 60 s, and the surface roughness Ra of the magnesium alloy material after sandblasting is 1.8 μm; the cleaning method is immersion cleaning, and the cleaning time is 180 s; the first baking temperature is 130℃, and the time is 60 min; after the first baking is completed, the material is cooled to 38℃ before being hung up, the interval between the end of the first baking and the completion of the hanging is 15 min, and the interval between the completion of the hanging and the entry into the ultrasonic degreasing process is 8 min.

[0051] Example 4: The difference between this embodiment and Embodiment 1 is that: the ultrasonic degreasing temperature is 45℃, the total processing time is 2min, the ultrasonic frequency is 25kHz, and the ultrasonic power density is 0.3W / cm²; the duration of the ultrasonic on-state is 20s, and the duration of the ultrasonic stop immersion state is 10s; the ultrasonic on-state and ultrasonic stop immersion states are alternated at least twice.

[0052] Example 5: The difference between this embodiment and Embodiment 1 is that: the ultrasonic degreasing temperature is 65℃, the total processing time is 8min, the ultrasonic frequency is 45kHz, and the ultrasonic power density is 1.2W / cm²; the duration of the ultrasonic on-state is 90s, and the duration of the ultrasonic stop immersion state is 60s; the ultrasonic on-state and ultrasonic stop immersion states are alternated at least twice.

[0053] Example 6: The difference between this embodiment and Embodiment 1 is as follows: the concentration of citric acid in the composite pickling solution is 20 g / L, the concentration of tartaric acid is 5 g / L, the concentration of ammonium fluoride is 5 g / L, the corrosion inhibitor is hexamethylenetetramine with a concentration of 0.1 g / L; the pickling temperature is 20°C, the pickling time is 10 s; and the interval between the end of pickling and the start of the fourth-stage water rinse after pickling is 120 s.

[0054] Example 7: The difference between this embodiment and Embodiment 1 is as follows: the concentration of citric acid in the composite pickling solution is 80 g / L, the concentration of tartaric acid is 30 g / L, the concentration of ammonium fluoride is 25 g / L, the corrosion inhibitor is ethylene thiourea, and the concentration of the corrosion inhibitor is 2 g / L; the pickling temperature is 35℃, the pickling time is 90 s; and the interval between the end of pickling and the start of the fourth-stage water rinse after pickling is 50 s.

[0055] Example 8: The difference between this embodiment and Embodiment 1 is as follows: the pH value of the fluoride activation solution is 3.0, and the acid activation time is 10s; the pH value of the alkali activation solution is 10.5, the alkali activation temperature is 35℃, and the alkali activation time is 30s; the interval between the end of acid activation and the start of alkali activation is 120s; in the four-stage water washing after alkali activation, the conductivity of the last water washing tank is 80μS / cm, and the interval between the end of the four-stage water washing after alkali activation and the start of zinc precipitation is 90s.

[0056] Example 9: The difference between this embodiment and Embodiment 1 is as follows: the pH value of the fluoride activation solution is 5.5, and the acid activation time is 60s; the pH value of the alkali activation solution is 12.5, the alkali activation temperature is 65℃, and the alkali activation time is 5min; the interval between the end of acid activation and the start of alkali activation is 80s; in the four-stage water washing after alkali activation, the conductivity of the last water washing tank is 50μS / cm, and the interval between the end of the four-stage water washing after alkali activation and the start of zinc precipitation is 45s.

[0057] Example 10: The difference between this embodiment and Embodiment 1 is as follows: the zinc source in the non-cyanide zinc precipitation solution is zinc acetate, the fluoride salt is sodium fluoride, the complexing agent is sodium citrate, and the pH adjuster is sodium carbonate; the zinc ion concentration is 2 g / L, the fluoride salt concentration is 5 g / L, the complexing agent concentration is 20 g / L, the pH value is 9.5, and the zinc precipitation temperature is 20°C; during the zinc precipitation process, the zinc precipitation ends when the change in open circuit potential is no greater than 5 mV within 10 consecutive seconds, and the longest zinc precipitation time is 120 seconds.

[0058] Example 11: The difference between this embodiment and Example 1 is as follows: the zinc source in the non-cyanide zinc precipitation solution is zinc oxide, the fluoride salt is ammonium fluoride, the complexing agent is potassium sodium tartrate, and the pH adjuster is potassium hydroxide; the zinc ion concentration is 10 g / L, the fluoride salt concentration is 30 g / L, the complexing agent concentration is 80 g / L, the pH value is 11.5, and the zinc precipitation temperature is 35°C; during the zinc precipitation process, the zinc precipitation ends when the change in open circuit potential within 30 seconds is not greater than 20 mV, and the longest zinc precipitation time is 120 seconds.

[0059] When zinc oxide is used as the zinc source, zinc oxide is first added to an aqueous solution containing a complexing agent and a pH adjuster and stirred to dissolve, forming a zinc complex system, and then the pH value of the non-cyanide zinc precipitation solution is adjusted.

[0060] Example 12: The difference between this embodiment and Embodiment 1 is that: nickel pre-deposition is carried out using a nickel salt electroplating solution with a nickel chloride system, the nickel ion concentration is 40 g / L, the boric acid concentration is 20 g / L, the pH value is 3.5, and the temperature is 35°C; the duration of the current density increasing plating stage is 30 s, and the current density increases from 0.2 A / dm² to 0.8 A / dm²; the duration of the constant current thickening stage is 1 min, and the current density is 1.0 A / dm².

[0061] Example 13: The difference between this embodiment and Example 1 is that: nickel pre-deposition is carried out using a nickel salt electroplating solution with a nickel sulfamate system, the nickel ion concentration is 120 g / L, the boric acid concentration is 45 g / L, the pH value is 5.5, and the temperature is 60℃; the duration of the current density increasing plating stage is 120 s, and the current density increases from 0.5 A / dm² to 1.2 A / dm²; the duration of the constant current thickening stage is 5 min, and the current density is 3.0 A / dm².

[0062] Example 14: The difference between this embodiment and Embodiment 1 is that the complexing agent in the electroless nickel plating solution is malic acid and sodium acetate, and the stabilizer is sodium thiosulfate; the pH value of the electroless nickel plating solution is 4.5, and the temperature is 80℃; the passivation time is 20s; and the second baking temperature is 80℃ for 10min.

[0063] Example 15: The difference between this embodiment and Embodiment 1 is that the complexing agent in the electroless nickel plating solution is sodium succinate and sodium citrate, and the stabilizer is potassium iodate; the pH value of the electroless nickel plating solution is 5.2, and the temperature is 90℃; the passivation time is 90s; and the second baking temperature is 130℃ and the time is 60min.

[0064] Comparative Example 1: The difference between this comparative example and Example 1 is that the ultrasonic degreasing is performed continuously without a pause in the ultrasonic wetting process. Specifically, the ultrasonic frequency is 35 kHz, the power density is 0.8 W / cm², the degreasing temperature is 55°C, and the continuous ultrasonic treatment lasts for 5 minutes.

[0065] Comparative Example 2: The difference between this comparative example and Example 1 is that the ultrasonic degreasing method uses ordinary immersion degreasing without applying ultrasound, the immersion temperature is 55°C, and the immersion time is 5 minutes.

[0066] Comparative Example 3: The difference between this comparative example and Example 1 is that the pickling solution used is not a composite pickling solution, but only a fluorinated pickling solution; the concentration of ammonium fluoride in the fluorinated pickling solution is 15 g / L, and no citric acid, tartaric acid and corrosion inhibitors are added.

[0067] Comparative Example 4: The difference between this comparative example and Example 1 is that after the four-stage water washing following pickling, acid activation is not performed; instead, the process proceeds directly to alkali activation.

[0068] Comparative Example 5: The difference between this comparative example and Example 1 is that: after the four-stage water washing following acid activation, no alkali activation is performed, and the sample directly proceeds to the four-stage water washing and zinc precipitation before zinc precipitation.

[0069] Comparative Example 6: The difference between this comparative example and Example 1 is that the conductivity of the last water washing tank is not controlled after the four-stage water washing after alkali activation, and the interval between the end of the four-stage water washing after alkali activation and the start of zinc precipitation is 180s.

[0070] Comparative Example 7: The difference between this comparative example and Example 1 is that the zinc immersion does not use the change in open circuit potential as the endpoint criterion, but uses a fixed zinc immersion time of 120s.

[0071] Comparative Example 8: The difference between this comparative example and Example 1 is that the zinc immersion is carried out in a two-stage zinc immersion process. After the first zinc immersion, the zinc is washed with water and subjected to acid stripping treatment before the second zinc immersion. After the second zinc immersion, the subsequent nickel pre-deposition is carried out.

[0072] Comparative Example 9: The difference between this comparative example and Example 1 is that after the four-stage water wash following zinc precipitation, nickel pre-deposition is not performed, but the process proceeds directly to chemical nickel deposition.

[0073] Comparative Example 10: The difference between this comparative example and Example 1 is that the nickel pre-deposition does not have a current density increment plating stage, but directly uses a constant current of 2.0 A / dm² for nickel pre-deposition, and the deposition time is 4 min.

[0074] Comparative Example 11: The difference between this comparative example and Example 1 is that the nickel pre-deposition uses a single low-current deposition without a constant current thickening stage; specifically, the current density is 0.5 A / dm² and the deposition time is 4 min.

[0075] Comparative Example 12: The difference between this comparative example and Example 1 is that the four-stage water wash after nickel pre-deposition does not control the washing time, and the interval between the end of the four-stage water wash after nickel pre-deposition and the start of chemical nickel deposition is 180s.

[0076] Performance tests and results are shown in Tables 1 and 2. Figure 1 , Figure 2 As shown.

[0077] Table 1 Example 1 7.8-8.5, average 7.99 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 2 5.4-6.2, average 5.8 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 3 8.7-9.8, average 9.2 0.1-0.2 0.2-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 4 5.8-6.8, average 6.3 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 5 8.4-9.6, average 9.0 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 6 5.5-6.4, average 6.0 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 7 8.2-9.7, average 8.9 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 8 5.6-6.5, average 6.1 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 9 8.3-9.6, average 9.1 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 10 5.2-6.3, average 5.8 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 11 8.8-10.0, average 9.4 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 12 5.0-5.9, average 5.5 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 13 8.9-10.0, average 9.5 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 14 5.2-6.0, average 5.7 0.2-0.3 0.2-0.4 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Example 15 8.8-10.0, average 9.3 0.1-0.2 0.1-0.3 No contraction within 5 seconds No shedding, ≥4B 20 / 20 qualified Table 2 Comparative Example 1 7.4-8.7 0.2-0.4 0.4-0.9 Passed on 18 / 20 Passed on 17 / 20 Three pieces showed slight discoloration or localized corrosion spots in the corner areas. Comparative Example 2 7.2-8.6 0.3-0.6 0.5-1.2 15 / 20 passed Passed on 14 / 20 Increased uneven deposition in micropores and depressions Comparative Example 3 7.1-8.4 0.2-0.5 0.5-1.0 Passed on 16 / 20 15 / 20 passed Localized surface darkening, with pinpoint abnormalities observed in individual samples. Comparative Example 4 7.3-8.5 0.2-0.4 0.4-0.8 Passed on 17 / 20 Passed on 16 / 20 Increased local color difference after zinc plating Comparative Example 5 7.2-8.5 0.2-0.5 0.5-1.1 Passed on 16 / 20 15 / 20 passed Increased surface condition fluctuations before zinc plating Comparative Example 6 7.0-8.6 0.3-0.6 0.6-1.3 Passed on 14 / 20 Passed on 13 / 20 Acid and alkali residues and exposure time lead to a decrease in the uniformity of zinc precipitation. Comparative Example 7 7.3-8.8 0.2-0.5 0.4-1.0 Passed on 17 / 20 Passed on 16 / 20 Some samples had excessive or insufficient zinc deposition. Comparative Example 8 7.5-9.0 0.2-0.4 0.3-0.8 Passed on 18 / 20 Passed on 17 / 20 Increased process steps, local interlayer state fluctuations Comparative Example 9 6.8-8.3 0.4-0.8 0.8-1.5 Passed on 12 / 20 Passed on 11 / 20 Uneven electroless nickel plating and decreased localized coating adhesion stability Comparative Example 10 7.1-8.6 0.3-0.6 0.6-1.2 15 / 20 passed Passed on 14 / 20 Increased local electrochemical shock during the initial plating stage Comparative Example 11 6.9-8.1 0.3-0.6 0.5-1.1 Passed on 16 / 20 15 / 20 passed Nickel pre-deposition reduces the ability to accept chemical nickel. Comparative Example 12 7.2-8.7 0.2-0.5 0.5-1.0 Passed on 16 / 20 15 / 20 passed Increased fluctuations in the surface state of nickel pre-deposited surfaces Experimental Results Analysis The test results from Examples 1-15 show that magnesium alloy parts treated with nickel plating can achieve a plating thickness in the range of 5μm-10μm. The resistance after electroplating is less than 1Ω, and the resistance remains less than 1Ω after 8 hours of salt spray testing. Both the water boiling cross-cut adhesion test and the 8-hour salt spray test meet the requirements for nickel plating of magnesium alloy parts. These results demonstrate that the present invention, within a continuous process chain consisting of sandblasting, cleaning, baking, pulsed ultrasonic degreasing, composite pickling, acid activation, alkali activation, zinc immersion, nickel pre-deposition, and electroless nickel deposition, enables the plating layers to maintain good conductivity, adhesion stability, and salt spray resistance under different parameter boundaries.

[0078] As can be seen from Examples 2 and 3, when the sandblasting pressure, sandblasting distance, sandblasting time, and first baking parameters are set to low and high limits respectively, the resulting coating can still be maintained within the range of 5μm-10μm and meet the requirements of resistance, water boiling cross-cut adhesion, high temperature and high humidity, and 8h salt spray tests. This result indicates that sandblasting and the first baking can provide an acceptable initial surface condition for subsequent degreasing, pickling, and zinc immersion, avoiding a decrease in subsequent nickel plating stability due to insufficient surface roughness or residual moisture in the pretreatment.

[0079] As can be seen from Examples 4 and 5, when the pulsed ultrasonic degreasing parameters are set to low and high boundaries respectively, the resulting coatings can meet the requirements of subsequent tests. Combining the test results of Comparative Examples 1 and 2, it can be seen that when ultrasonic degreasing is changed to continuous ultrasonic degreasing or ordinary immersion degreasing, the number of qualified salt spray tests after 8 hours decreases, the number of qualified water-boiling cross-cut tests decreases, and the probability of localized blooming, uneven deposition, or corrosion points in corners, micropores, or recessed areas increases. This result indicates that for magnesium alloy die-cast parts, ordinary continuous ultrasonic or ordinary immersion degreasing is insufficient to fully address the problems of insufficient local liquid renewal, bubble shielding, or contaminant residue in micropores. The pulsed degreasing process of this invention, which alternates between ultrasonic on-state and ultrasonic off-state immersion, is beneficial to improving the cleanliness consistency of local areas of die-cast parts, thereby improving the stability of subsequent pickling, zinc immersion, and nickel deposition.

[0080] As can be seen from Examples 6 and 7, when the citric acid, tartaric acid, ammonium fluoride, and corrosion inhibitor in the composite pickling solution are set at low and high boundaries, respectively, the resulting coating can still pass the salt spray test (8 hours), cross-cut corrosion test, and resistance test. Combined with Comparative Example 3, it can be seen that when only a fluorinated pickling solution is used without the addition of organic acids and corrosion inhibitors, the number of qualified samples in the cross-cut corrosion test and the number of qualified samples in the salt spray test (8 hours) decrease, and local darkening, pinpoint abnormalities, or increased differences in surface condition appear. This result indicates that simple fluorinated pickling easily leads to excessively strong local reactions or uneven pickling conditions. The composite pickling solution of organic acids, fluoride salts, and corrosion inhibitors used in this invention can reduce the risk of local over-corrosion during the pickling process while removing the oxide film and weakly bonded surface layer of magnesium alloys, making subsequent acid activation, alkali activation, and zinc deposition reactions more stable.

[0081] Examples 8 and 9 show that when the pH of the fluorinated acid activation solution, the acid activation time, the pH of the alkali activation solution, the alkali activation temperature, and the alkali activation time are set to low and high limits respectively, the resulting coatings can maintain good nickel plating effects. Comparative Examples 4 and 5 show that after omitting acid activation or alkali activation, the surface condition adjustment before zinc immersion is insufficient, the local color difference increases after zinc immersion, and the number of qualified samples after 8 hours of salt spray and 100-cross cross-cut adhesion tests decreases. These results indicate that acid activation and alkali activation are not simply repetitive pretreatment steps, but rather play the roles of fluorinated activation and alkaline surface conditioning respectively; their combination with composite pickling and four-stage water washing helps reduce surface condition fluctuations of magnesium alloy materials before entering the zinc immersion process.

[0082] As can be seen from Examples 8, 9, and Comparative Example 6, when the conductivity of the final stage of the four-stage water rinse after alkali activation is controlled to be no greater than 80 μS / cm, and the interval between the end of the four-stage water rinse after alkali activation and the start of zinc plating does not exceed 90 s, the zinc plating and subsequent nickel plating results are more stable. However, in Comparative Example 6, the conductivity of the final stage water rinse before zinc plating was not controlled, and the transition time was extended to 180 s, resulting in a decrease in the number of qualified salt spray tests after 8 hours, the number of qualified cross-cut tests after boiling, and the resistance stability after salt spraying. These results indicate that the surface condition before zinc plating depends not only on the pickling and activation processes themselves but also on residual ions from the water rinse and the exposure time. This invention, by limiting the conductivity of the final stage water rinse and the transition time, can reduce the interference of acid and alkali residues, ion residues, and surface re-oxidation on the displacement zinc plating reaction.

[0083] Examples 10 and 11 show that when the zinc ion concentration, fluoride salt concentration, complexing agent concentration, pH value, and zinc deposition temperature in the non-cyanide zinc deposition solution are set to low and high limits respectively, the zinc deposition endpoint can still be determined by the change in open-circuit potential, and satisfactory nickel plating results can still be obtained. Comparative Example 7 shows that when zinc deposition is controlled by a fixed time of 120 seconds without using the change in open-circuit potential as the endpoint criterion, some samples show a tendency for insufficient zinc deposition or excessive displacement, resulting in a decrease in the number of samples passing the 8-hour salt spray test and the number passing the 100-cross cross-section test. This result indicates that the surface state of different batches of magnesium alloy materials may vary, and relying solely on a fixed time for zinc deposition cannot accurately reflect the actual displacement reaction state. This invention uses whether the change in open-circuit potential is lower than a preset potential stability threshold within a continuous period as the zinc deposition endpoint, thus linking the zinc deposition termination condition with the displacement reaction state and improving the consistency of zinc deposition.

[0084] As can be seen from Comparative Example 8, although secondary zinc plating is a common approach to improving zinc plating coverage, it requires additional zinc stripping and re-zinc plating steps, resulting in a longer process path and potentially introducing additional interface fluctuations. This invention employs a single-stage replacement zinc plating method combined with open-circuit potential endpoint determination. This reduces process steps while making the zinc plating endpoint predictable, making it more suitable for continuous batch processing of magnesium alloy parts.

[0085] Examples 12 and 13 show that when the nickel pre-deposition electroplating solution and current parameters are set to low and high limits respectively, the resulting coatings still meet the requirements for thin coating, resistance, cross-cut adhesion test, and 8-hour salt spray test. Comparative Example 9 shows that when nickel pre-deposition is omitted and the magnesium alloy material after zinc plating directly enters the electroless nickel plating process, the stability of the electroless nickel plating process decreases, resistance fluctuations increase, and the number of qualified samples in the cross-cut adhesion test and 8-hour salt spray test is significantly reduced. These results indicate that nickel pre-deposition plays a transitional role between the zinc plating layer and the electroless nickel plating layer, reducing the direct dependence of electroless nickel plating on the surface uniformity and activity state of the zinc plating layer.

[0086] As can be seen from Comparative Example 10, when nickel pre-deposition does not have a current density incrementing initial plating stage and instead uses a higher constant current for nickel pre-deposition, the local electrochemical shock during the initial plating stage increases. The number of qualified salt spray tests after 8 hours, the number of qualified cross-cut adhesion test tests, and the resistance stability after salt spray are all lower than in Example 1. This result indicates that the surface after zinc plating should not be directly subjected to high current densities. The present invention, by gradually increasing the current density from a lower value to the target value, can reduce the risk of local hydrogen evolution, scorching, or uneven deposition during the initial plating stage.

[0087] As can be seen from Comparative Example 11, when nickel pre-deposition uses only low-current deposition without a constant-current thickening stage, although the initial electrochemical shock can be reduced, the resulting nickel pre-deposition state is insufficient to stably support subsequent electroless nickel deposition, leading to lower resistivity results in water boiling, salt spraying for 8 hours, and after salt spraying compared to Example 1. This result indicates that the present invention sets the nickel pre-deposition to a continuous process of increasing current density during the initial plating stage plus a constant-current thickening stage, which balances the gentleness of the initial plating stage with ensuring a sufficiently stable nickel-based transition state before subsequent electroless nickel deposition.

[0088] As shown in Comparative Example 12, when the four-stage water washing after nickel pre-deposition is not controlled in terms of washing time and the interval between the end of the four-stage water washing and the start of electroless nickel deposition is extended to 180 s, the surface state fluctuation of the nickel pre-deposition increases, and the stability of subsequent electroless nickel deposition decreases. This result indicates that after nickel pre-deposition, timely water washing and time-limited sequence transition are still necessary to maintain the surface state to avoid the impact of nickel pre-deposition surface contamination or activation state decay on electroless nickel deposition.

[0089] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for nickel plating magnesium alloy parts, characterized in that, The steps include the following: The magnesium alloy material is subjected to the following steps in sequence: sandblasting, cleaning, first baking, hanging, ultrasonic degreasing, four-stage water washing, pickling, four-stage water washing, acid activation, four-stage water washing, alkali activation, four-stage water washing, zinc immersion, four-stage water washing, nickel pre-deposition, four-stage water washing, chemical nickel deposition, four-stage water washing, passivation, hanging, spin drying, and second baking to obtain nickel-plated magnesium alloy parts. The ultrasonic degreasing includes alternating ultrasonic on-state and ultrasonic off-state immersion states, and the ultrasonic on-state and ultrasonic off-state immersion states are alternated at least twice. The pickling is carried out using a composite pickling solution including organic acid, fluoride salt and corrosion inhibitor; the acid activation is carried out using a fluorinated acid activation solution with a pH of 3.0-5.5; and the alkali activation is carried out using an alkali activation solution with a pH of 10.5-12.

5. In the four-stage water washing process, which is located after alkali activation and before zinc precipitation, the conductivity of the last water washing tank is ≤80μS / cm, and the interval between the end of the four-stage water washing after alkali activation and the start of zinc precipitation is ≤90s. The zinc precipitation is carried out using a non-cyanide zinc precipitation solution. The zinc precipitation is a single-displacement zinc precipitation. During the zinc precipitation process, the open circuit potential of the magnesium alloy material in the non-cyanide zinc precipitation solution is collected. The zinc precipitation ends when the change in open circuit potential does not exceed a preset potential stabilization threshold within 10s-30s. The preset potential stabilization threshold is 5mV-20mV. The nickel pre-deposition includes a current density increasing plating stage and a constant current thickening stage. In the current density increasing plating stage, the current density increases from 0.2A / dm²-0.5A / dm² to 0.8A / dm²-1.2A / dm². In the constant current thickening stage, the current density is 1.0A / dm²-3.0A / dm². The four-stage water washing is a four-stage counter-current water washing, with each stage of water washing lasting 10s-60s. The four-stage water washing process, which occurs after pickling, acid activation, alkali activation, zinc precipitation, nickel pre-deposition, and electroless nickel deposition, all employs a four-stage countercurrent water washing method. In the four-stage water wash that is located after zinc precipitation and before nickel pre-deposition, the conductivity of the last water wash tank is ≤80μS / cm, and the interval between the end of the four-stage water wash after zinc precipitation and the start of nickel pre-deposition is ≤120s. The total thickness of the plating layer on the surface of the nickel-magnesium alloy parts is 5μm-10μm; The interval between the end of the four-stage water wash after nickel pre-deposition and the start of chemical nickel deposition is less than 180 seconds.

2. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The magnesium alloy material is a magnesium alloy die-cast part; The sandblasting is carried out using alumina sand, ceramic sand or glass microspheres, with a sandblasting pressure of 0.15MPa-0.35MPa, a sandblasting distance of 80mm-150mm, and a sandblasting time of 10s-60s. The surface roughness Ra of the sandblasted magnesium alloy material is 0.9μm-1.8μm.

3. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The cleaning method is at least one of spray cleaning, soaking cleaning or running water cleaning, and the cleaning time is 30s-180s. The temperature of the first baking is 80℃-130℃, and the time is 10min-60min; After the first baking is completed, the magnesium alloy material is cooled to ≤45℃ before being hung up; The interval between the end of the first baking and the completion of the hanging process is ≤30 minutes, and the interval between the completion of the hanging process and the start of the ultrasonic degreasing process is ≤20 minutes.

4. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The ultrasonic degreasing is performed using an alkaline degreasing solution; the alkaline degreasing solution includes sodium carbonate, sodium phosphate, sodium silicate, a complexing agent, and a nonionic surfactant. The total processing time for ultrasonic degreasing is 2-8 minutes, the ultrasonic frequency is 25kHz-45kHz, the ultrasonic power density is 0.3W / cm²-1.2W / cm², and the degreasing temperature is 45℃-65℃. The duration of the ultrasonic activation phase is 20s-90s, and the duration of the ultrasonic deactivation phase is 10s-60s.

5. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The composite pickling solution includes citric acid, tartaric acid, ammonium fluoride, and corrosion inhibitors. The concentration of citric acid in the composite pickling solution is 20 g / L-80 g / L, the concentration of tartaric acid is 5 g / L-30 g / L, the concentration of ammonium fluoride is 5 g / L-25 g / L, and the corrosion inhibitor is one or more of thiourea, hexamethylenetetramine, and ethylene thiourea, with a concentration of 0.1 g / L-2 g / L. The pickling temperature is 20℃-35℃, and the time is 10s-90s; The interval between the end of pickling and the start of the fourth-stage water rinse after pickling is ≤120s.

6. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The fluoride-containing activation solution includes ammonium hydrofluoride, citric acid and deionized water, and the acid activation time is 10s-60s. The alkaline activation solution includes sodium hydroxide, sodium carbonate, phosphate and nonionic surfactant, and the alkaline activation temperature is 35℃-65℃, and the alkaline activation time is 30s-5min. The interval between the end of acid activation and the start of alkali activation is ≤120s.

7. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The non-cyanide zinc precipitation solution includes a zinc source, fluoride salts, complexing agents, and pH adjusters; The zinc source is one or more of zinc sulfate, zinc acetate, and zinc oxide; The fluoride salt is one or more of sodium fluoride, potassium fluoride, ammonium fluoride, and ammonium hydrofluoride; The complexing agent is one or more of potassium pyrophosphate, sodium pyrophosphate, sodium citrate, and potassium sodium tartrate. The non-cyanide zinc precipitation solution has a zinc ion concentration of 2 g / L-10 g / L, a fluoride salt concentration of 5 g / L-30 g / L, a complexing agent concentration of 20 g / L-80 g / L, and a pH value of 9.5-11.

5. The zinc immersion temperature is 20℃-35℃, and the maximum zinc immersion time is ≤120s; The zinc plating process ends when the open circuit potential change is reached or the maximum zinc plating time is reached.

8. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The nickel pre-deposition is carried out using nickel salt electroplating solutions based on nickel sulfate, nickel sulfamate, or nickel chloride systems. The nickel salt electroplating solution has a nickel ion concentration of 40 g / L-120 g / L, a boric acid concentration of 20 g / L-45 g / L, a pH value of 3.5-5.5, and a temperature of 35℃-60℃. The duration of the current density increasing plating stage is 30s-120s, and the duration of the constant current thickening stage is 1min-5min. The current density increasing plating stage and the constant current thickening stage are performed continuously.

9. The method for nickel plating magnesium alloy parts according to claim 1, characterized in that, The electroless nickel deposition is performed using an electroless nickel plating solution; The electroless nickel plating solution includes nickel salt, hypophosphite reducing agent, complexing agent, and stabilizer; the complexing agent is one or more of lactic acid, sodium citrate, malic acid, sodium acetate, and sodium succinate, and the stabilizer is one or more of thiourea, sodium thiosulfate, and potassium iodate. The pH value of the electroless nickel plating solution is 4.5-5.2, and the temperature is 80℃-90℃; The passivation is performed using a chromium-free passivation solution, and the passivation time is 20s-90s. The second baking temperature is 80℃-130℃, and the time is 10min-60min.

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