Magnesium alloy and zinc-iron alloy plating combination process, bottom plating layer preparation and plating layer structure

Abstract

The invention discloses a magnesium alloy and galvanized iron alloy combined process, bottom plating layer preparation and a plating layer structure. The process comprises the step of sequentially preparing a chemical zinc deposition layer, a cyanide-free copper plating layer, a cyanide-free copper-zinc alloy plating layer, a high-corrosion-resistance nickel-phosphorus alloy plating layer, a zinc-iron alloy plating layer, a chromium-free chemical conversion film, a silane chromium-free passivation layer and a graphene modified sealing layer on a magnesium alloy matrix. According to the potassium chloride zinc-iron alloy plating process, 50 g / L to 70 g / L of zinc chloride, 2 g / L to 12 g / L of ferrous chloride tetrahydrate, 180 g / L to 220 g / L of potassium chloride, 25 g / L to 35 g / L of boric acid, 8 g / L to 40 g / L of a coordination agent, 0.1 mL / L to 0.2 mL / L of a brightening agent and 20 mL / L to 30 mL / L of an auxiliary agent are adopted, the pH value of a plating solution is 4.5 to 5.6, the temperature of a plating tank is 15 DEG C to 30 DEG C, and the cathode current density is 1 A / The surface of a plated part is free of white rust after being subjected to a neutral salt spray test for 560 h according to the GB / T 10125-2021 standard. According to the scheme, the corrosion resistance, wear resistance and other performance of the magnesium alloy part protection layer are remarkably improved, and the good market application prospect is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface treatment, and particularly relates to a combined process for galvanizing and iron alloying of magnesium alloy, preparation of an underlying coating, and coating structure. Background Art

[0002] Magnesium alloy is known as the "green engineering material of the century" and has the characteristics of high specific strength and specific stiffness, and can be widely used in industrial products such as military, automotive, aircraft, mobile phones, computers, and electromechanical products. However, magnesium alloy has active chemical properties, and the oxide formed on its surface is loose and porous and has no protective effect on the substrate.

[0003] There are many methods for surface treatment of magnesium alloy, mainly including electrophoretic coating, surface plating, micro-arc oxidation, anodic oxidation, preparation of chemical conversion film, spraying organic coating and other technologies. However, these surface treatment methods all have certain limitations, and the protection effect also needs to be further improved. At present, electrophoretic coating technology is mainly used in production applications to prepare a protective layer on the surface of magnesium alloy, which has a relatively good protection effect.

[0004] The electroplating and electroless plating technologies of magnesium alloy are still in the research stage [1-2] , and there is still a long way to go before actual application. The electroplated nickel layer and electroless nickel layer prepared on the surface of magnesium alloy have no electrochemical protection effect on the magnesium alloy substrate, and there is a large potential difference between the substrate and the coating. Once galvanic corrosion occurs, the magnesium alloy plated parts will soon be scrapped.

[0005] Functional multi-layer electroplating technology is very important for breaking through some difficulties faced in the electroplating field by integrating the coating structure. The multi-layer composite coating not only has a mechanical protection effect, but also has good electrochemical protection function [3] , and can meet the corrosion resistance requirements of various high-grade products.

[0006] The silane chromium-free passivation technology has made great progress. The passivation layer prepared by using a solvent-based silane chromium-free passivating agent has high corrosion resistance and self-healing property [4] .

[0007] The hydroxy graphene modified sealant has made remarkable progress in improving the coating performance. The prepared sealant has properties such as high corrosion resistance, wear resistance, and self-healing property [5] .

[0008] References: [1]. Yu Gang, Yi Xiangrong, Lei Xiping, et al. Research on the formation mechanism and electroplating process of nickel electrodeposited on magnesium alloy [J]. Electroplating & Pollution Control, 2009, 29(1): 21-25. [2]. Zhang Xiaohuan, Feng Lajun, Lu Man. Research on the optimization of electroless nickel-phosphorus plating process and coating properties on magnesium alloy surface [J]. Materials Protection, 2022, 55(6): 86-91. [3]. Dai Pengmin, Guo Chongwu. Multilayer nickel plating process suitable for aerospace aluminum alloy parts [J]. Electroplating & Finishing, 2024, 43(4): 74-78. [4]. Lai Huanwen, Guo Chongwu. High-performance chromium-free passivation technology [J]. Electroplating & Pollution Control, 2012, 32(6): 35-37. [5]. Guo Chongwu, Lai Huanwen, Xia Liang. Performance study of graphene oxide in coating sealant [J]. Electroplating & Finishing, 2021, 40(9): 696-700. Summary of the Invention

[0009] In order to solve the problem of poor corrosion resistance of the existing electroplated protective layer on magnesium alloy, the present invention provides a combined process of zinc-iron alloy plating on magnesium alloy, preparation of the bottom coating and coating structure. To achieve the above purpose, the present invention adopts the following technical solutions: A combined process of zinc-iron alloy plating on magnesium alloy, characterized by comprising the following steps: (1) Degrease and pickling and activation of the magnesium alloy workpiece; (2) After the pretreatment of the magnesium alloy workpiece, a chemical zinc deposition layer is prepared by the current chemical zinc deposition process for magnesium alloy; (3) After the chemical zinc deposition of the magnesium alloy workpiece, a cyanide-free copper plating layer is prepared by the polymer thiocyanate copper plating process; (4) After the polymer thiocyanate copper plating of the magnesium alloy workpiece, a cyanide-free copper-zinc alloy coating is prepared by the polymer thiocyanate copper-zinc alloy plating process; (5) After the polymer thiocyanate copper-zinc alloy plating of the magnesium alloy workpiece, a high-corrosion-resistant nickel-phosphorus alloy coating is prepared by the current high-corrosion-resistant nickel-phosphorus alloy plating process; (6) After the high-corrosion-resistant nickel-phosphorus alloy plating of the magnesium alloy workpiece, a zinc-iron alloy coating is prepared by the potassium chloride zinc-iron alloy plating process; (7) After the zinc-iron alloy plating of the magnesium alloy workpiece, chemical conversion is carried out to prepare a chromium-free chemical conversion film; (8) After the chromium-free chemical conversion of the magnesium alloy workpiece, silane chromium-free passivation is carried out to prepare a silane chromium-free conversion layer; (9) After the silane chromium-free passivation of the magnesium alloy workpiece, sealing is carried out to prepare a sealing layer; The potassium chloride zinc-iron alloy plating process includes the following components and process parameters: Zinc chloride: 50 - 70 g / L, ferrous chloride tetrahydrate: 2 - 12 g / L, potassium chloride: 180 - 220 g / L, boric acid: 25 - 35 g / L, complexing agent: 8 - 40 g / L, brightener: 0.1 - 0.2 mL / L, auxiliary agent: 20 - 30 mL / L, pH value of the plating solution: 4.5 - 5.6, temperature of the plating bath: 15 - 30 °C, cathode current density: 1 - 3 A / dm 2 , cathode moving speed: 3 - 5 m / min, using zinc plate with mass fraction > 99.9% as the anode, area ratio of cathode to anode: 2:1; during production, add ferrous chloride tetrahydrate solution with mass fraction of 30% to the plating bath to maintain its concentration within the process range; The complexing agent includes sodium glucoheptonate and sodium sulfosalicylate, and the mass ratio of sodium glucoheptonate to sodium sulfosalicylate is 3:(1 - 3). Mix sodium glucoheptonate and sodium sulfosalicylate according to the above ratio and stir evenly; The brightener includes o-chlorobenzaldehyde and formic acid, and the mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8 - 1.2). Mix o-chlorobenzaldehyde and formic acid according to the above ratio and stir until all solid substances are dissolved; The auxiliary agent includes the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and aminosulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight fraction, the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and aminosulfonic acid is 17 - 23 parts, sodium benzoate is 5 - 7 parts, nicotinic acid is 0.4 - 0.6 parts, and pure water is 80 - 90 parts. Add the above three intermediates to water according to the above weight fraction and stir until all solid substances are dissolved.

[0010] For the preparation of the bottom coating in a zinc-iron alloy plating process on magnesium alloy, a cyanide-free copper plating layer is prepared by a polymer thiocyanate copper plating process, including the following components and process parameters: Copper(I) thiocyanate polymer: 18 - 24 g / L, sodium thiocyanate polymer: 130 - 170 g / L, 1-hydroxyethylidene-1,1-diphosphonic acid sodium salt: 20 - 30 g / L, copper plating brightener: 8 - 12 mL / L, pH value of the plating solution: 12 - 13, temperature of the plating bath: 30 - 40 °C, cathode current density: 0.5 - 1.5 A / dm 2 , cathode moving speed: 3 - 5 m / min, using oxygen-free electrolytic copper grains as the anode, loading the copper grains into a titanium anode basket, area ratio of anode to cathode > 3:1, anode moving speed: 3 - 5 m / min; The copper plating brightener includes the following components by weight fraction: melamine: 1 - 2 parts, waterborne polyurethane resin: 10 - 20 parts, polyacrylamide with molecular weight less than 8000: 80 - 120 parts, cobalt acetate: 40 - 60 parts, formic acid: 390 - 430 parts, pure water: 390 - 430 parts.

[0011] In some embodiments, the copper plating brightener is prepared by the following method: Add 390 - 430 parts of formic acid into the reaction tank. While stirring, add 1 - 2 parts of melamine and stir until the solid substances are dissolved. Then add 10 - 20 parts of waterborne polyurethane resin, 80 - 120 parts of polyacrylamide with a molecular weight less than 8000, 40 - 60 parts of cobalt acetate, and 390 - 430 parts of pure water, and stir until the solid substances are dissolved to obtain the brightener.

[0012] In some of the embodiments, the cyanide-free copper-zinc alloy coating is prepared by a polymerized thiocyanate copper-zinc alloy plating process: Copper(I) polymerized thiocyanate 18 - 24 g / L, zinc polymerized thiocyanate 9 - 13 g / L, sodium polymerized thiocyanate 130 - 170 g / L, copper-zinc alloy plating brightener 8 - 12 mL / L, pH value of the plating solution 10 - 12, bath temperature 35 - 55 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode moving speed 3 - 5 m / min, using a brass plate with a copper mass fraction of 68% as the anode, the area ratio of the anode to the cathode > 2:1, anode moving speed 3 - 5 m / min.

[0013] In some of the embodiments, the high-corrosion-resistant nickel-phosphorus alloy coating is prepared by a PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process: PROTEXYER 8713 MU bath starter 580 - 620 mL / L, nickel sulfate hexahydrate 280 - 340 g / L, pH value of the plating solution 2.6 - 2.7, bath temperature 60 - 65 °C, cathode current density 3 - 6 A / dm 2 , cathode moving speed 3 - 5 m / min.

[0014] In some of the embodiments, the silane chromium-free passivation layer is prepared by a zinc cote ZECCOAT-888FL silane chromium-free passivation process: Use the undiluted solution of the ZECCOAT-888FL silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after passivating the workpiece, dry and cure at 80 - 100 °C for 20 - 30 min.

[0015] In some of the embodiments, the silane chromium-free passivation layer is prepared by a zinc cote ZEC-COAT 825 chromium-free passivation process: Use the undiluted solution of the zinc cote ZECCOAT-825 silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after passivating the workpiece, dry at 75 - 85 °C and cure for 20 - 30 min.

[0016] In some of the embodiments, the silane chromium-free passivation layer is prepared by a zinc cote ZECCOAT-888 silane chromium-free passivation process: Use the undiluted solution of the ZECCOAT-888 silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after passivating the workpiece, dry at 75 - 85 °C and cure for 20 - 30 min.

[0017] In some of these embodiments, the silane chromium-free passivation layer is prepared by using the zinc cortec ZEC-W silane chromium-free passivation process: using the original solution of ZEC-W silane chromium-free passivation agent, the pH value of the passivation solution is 4.0 - 4.5, operating at room temperature, dipping for 10 - 15 s, and after the workpiece is passivated, it is dried and cured at 115 - 125 °C for 18 - 25 min.

[0018] In some of these embodiments, the sealing layer is prepared by using the PRODICO 480 graphene-modified sealing agent: Dilute the PRODICO 480 graphene-modified sealing agent with water to 2.5 - 3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8 - 15 s, drain after taking out of the tank, and use high-pressure air to blow off the residual sealing solution on the surface of the plated parts. After sealing, dry and cure at 75 - 85 °C for 20 - 35 min.

[0019] A coating structure prepared by a magnesium alloy galvanized iron alloy combined process, including a magnesium alloy substrate, and sequentially preparing a chemical zinc deposition layer, a cyanide-free copper plating layer, a cyanide-free copper-zinc alloy plating layer, a high-corrosion-resistant nickel-phosphorus alloy plating layer, a zinc-iron alloy plating layer, a chromium-free chemical conversion film, a silane chromium-free passivation layer, and a graphene-modified sealing layer on the magnesium alloy substrate.

[0020] In some of these embodiments, the thickness of the zinc-iron plating layer is 9 - 18 μm.

[0021] In some of these embodiments, the thickness of the cyanide-free copper plating layer is 3 - 10 μm.

[0022] In some of these embodiments, the thickness of the cyanide-free copper-zinc alloy plating layer is 3 - 10 μm.

[0023] In some of these embodiments, the thickness of the high-corrosion-resistant nickel-phosphorus alloy plating layer is 7 - 13 μm.

[0024] In this technical solution, a cyanide-free copper-zinc alloy is plated on the cyanide-free copper plating layer, a nickel-phosphorus alloy is plated on the cyanide-free copper-zinc alloy plating layer, and a zinc-iron alloy is plated on the nickel-phosphorus alloy plating layer. The electrode potential of the cyanide-free copper-zinc alloy plating layer is negative to that of the cyanide-free copper plating layer, the electrode potential of the nickel-phosphorus alloy plating layer is negative to that of the cyanide-free copper-zinc alloy plating layer, and the electrode potential of the zinc-iron alloy plating layer is negative to that of the nickel-phosphorus alloy plating layer. In this coating structure, the outer coating is anodic to the inner coating.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. The magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure of the present invention. The cyanide-free copper-zinc alloy coating provides electrochemical protection for the cyanide-free copper coating. The nickel-phosphorus alloy coating provides electrochemical protection for the cyanide-free copper-zinc alloy coating. The zinc-iron alloy coating also provides electrochemical protection for the nickel-phosphorus alloy coating. This triple electrochemical protection can effectively prevent the erosion of corrosive media towards the magnesium alloy substrate. 2. The magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure of the present invention. The prepared coating structure overcomes the defect that direct nickel plating or electroless nickel plating on the magnesium alloy substrate after chemical zinc deposition does not have electrochemical protection. 3. The magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure of the present invention. The high-corrosion-resistant nickel-phosphorus alloy coating has good hardness and corrosion resistance. When combined with the zinc-iron alloy coating, they complement each other and can provide good protection for the magnesium alloy substrate. 4. The magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure of the present invention. A silane-free chromium passivation layer is prepared on the zinc-iron alloy coating by using a silane-free chromium passivation process. The process is green and environmentally friendly and overcomes the defect that the existing trivalent chromium passivation film does not have self-healing properties. 5. The magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure of the present invention. A hydroxyl graphene modified sealant is used to seal the silane-free chromium passivation layer, which can further improve the corrosion resistance, wear resistance, self-healing properties and other properties of the prepared protective layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not constitute an improper limitation of the present invention.

[0027] In the drawings, Figure 1 are schematic diagrams of the coating structures of Example 1, Example 2, Example 3 and Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described in detail below with reference to the drawings and specific embodiments. Here, the schematic embodiments and descriptions of the present invention are used to explain the present invention, but do not limit the present invention.

[0029] A magnesium alloy galvanized iron alloy composite process, preparation of the bottom coating and coating structure, including pretreatment of the magnesium alloy substrate, and sequentially preparing a chemical zinc deposition layer, a cyanide-free copper coating, a cyanide-free copper-zinc alloy coating, a high-corrosion-resistant nickel-phosphorus alloy coating, a zinc-iron alloy coating, a chromium-free chemical conversion film, a silane-free chromium passivation layer, and a sealant layer on the magnesium alloy substrate.

[0030] The magnesium alloy workpiece is degreased and pickled and activated by using a magnesium alloy pretreatment process.

[0031] Preferably, the degreasing is carried out by a weak alkaline ultrasonic degreasing process: Sodium phosphate 20 - 25 g / L, sodium carbonate 20 - 25 g / L, Gintel NP-10 degreasing agent 0.5 - 1.5 g / L, bath temperature 65 - 75 °C, degreasing time 8 - 12 min.

[0032] Preferably, the pickling activation adopts the following pickling activation process: Phosphoric acid 23 - 28 mL / L, ammonium bifluoride 18 - 22 g / L, operating at room temperature, pickling time 50 - 70 s.

[0033] After the pretreatment of the magnesium alloy workpiece, the following magnesium alloy electroless zinc plating process is adopted to prepare an electroless zinc plating layer.

[0034] Zinc sulfate heptahydrate 25 - 35 g / L, potassium pyrophosphate 100 - 120 g / L, potassium fluoride 6 - 9 g / L, bath temperature 68 - 72 °C, zinc plating time 8 - 12 min.

[0035] After the magnesium alloy workpiece is electroless zinc plated, the cyanide-free copper plating process of the present invention is adopted to prepare a cyanide-free copper plating layer.

[0036] Preferably, the thickness of the cyanide-free copper plating layer is 3 - 10 μm.

[0037] Copper(I) thiocyanate polymer 18 - 24 g / L, sodium thiocyanate polymer 130 - 170 g / L, 1-hydroxyethylidene-1,1-diphosphonic acid sodium salt 20 - 30 g / L, copper plating brightener 8 - 12 mL / L, plating solution pH value 12 - 13, plating bath temperature 30 - 40 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode moving speed 3 - 5 m / min, using oxygen-free electrolytic copper grains as the anode, loading the copper grains into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode moving speed 3 - 5 m / min.

[0038] Preferably, the copper plating brightener comprises the following components in weight fractions: melamine 1 - 2 parts, waterborne polyurethane resin 10 - 20 parts, polyacrylamide with a molecular weight less than 8000 80 - 120 parts, cobalt acetate 40 - 60 parts, formic acid 390 - 430 parts, pure water 390 - 430 parts.

[0039] Preferably, the copper plating brightener is prepared according to the following method: Calculated by weight parts, add 390 - 430 parts of formic acid into a reaction tank, add 1 - 2 parts of melamine under stirring, stir until the solid substances are dissolved, then add 10 - 20 parts of waterborne polyurethane resin, 80 - 120 parts of polyacrylamide with a molecular weight less than 8000, 40 - 60 parts of cobalt acetate, and 390 - 430 parts of pure water, and stir until the solid substances are dissolved to obtain the brightener.

[0040] After the magnesium alloy workpiece is copper-plated without cyanide, a cyanide-free copper-zinc alloy coating is prepared by using the copper-zinc alloy plating process of polymerized thiocyanate developed by Chaobang Chemical Industry.

[0041] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 3-10 μm.

[0042] Copper(I) polymerized thiocyanate 18-24 g / L, zinc(I) polymerized thiocyanate 9-13 g / L, sodium polymerized thiocyanate 130-170 g / L, copper-zinc alloy plating brightener 8-12 mL / L, pH value of the plating solution 10-12, plating bath temperature 35-55 °C, cathode current density 0.5-1.5 A / dm 2 , cathode moving at 3-5 m / min, using a brass plate with a copper mass fraction of 68% as the anode, the area ratio of the anode to the cathode > 2:1, and the anode moving at 3-5 m / min.

[0043] After the magnesium alloy workpiece is copper-zinc alloy plated with polymerized thiocyanate, a highly corrosion-resistant nickel-phosphorus alloy coating is prepared by using the PROTEXYER 8713 nickel-phosphorus alloy plating process of Chaobang Chemical Industry.

[0044] Preferably, the thickness of the highly corrosion-resistant nickel-phosphorus alloy coating is 7-13 μm.

[0045] PROTEXYER 8713 MU tank starter 580-620 mL / L, nickel sulfate hexahydrate 280-340 g / L, pH value of the plating solution 2.6-2.7, plating bath temperature 60-65 °C, cathode current density 3-6 A / dm 2 , cathode moving at 3-5 m / min.

[0046] After the magnesium alloy workpiece is nickel-phosphorus alloy plated, a zinc-iron alloy coating is prepared by using the potassium chloride zinc-iron alloy plating process of the present invention.

[0047] Preferably, the thickness of the zinc-iron alloy coating is 9-18 μm.

[0048] Zinc chloride 50-70 g / L, ferrous chloride tetrahydrate 2-12 g / L, potassium chloride 180-220 g / L, boric acid 25-35 g / L, complexing agent 8-40 g / L, brightener 0.1-0.2 mL / L, auxiliary agent 20-30 mL / L, pH value of the plating solution 4.5-5.6, plating bath temperature 15-30 °C, cathode current density 1-3 A / dm 2 , cathode moving at 3-5 m / min, using a zinc plate with a mass fraction > 99.9% as the anode, and the area ratio of the cathode to the anode is 2:1; during production, a 30% ferrous chloride tetrahydrate solution is added to the plating bath to maintain its concentration within the process range.

[0049] The complexing agent described above includes sodium glucoheptonate and sodium sulfosalicylate. The mass ratio of sodium glucoheptonate to sodium sulfosalicylate is 3:(1 - 3). After mixing sodium glucoheptonate and sodium sulfosalicylate according to the above ratio, stir evenly.

[0050] The brightening agent described above includes o-chlorobenzaldehyde and formic acid. The mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8 - 1.2). After mixing o-chlorobenzaldehyde and formic acid according to the above ratio, stir until all the solid substances are dissolved.

[0051] The auxiliary agent described above includes the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and amino sulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight fraction, the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and amino sulfonic acid is 17 - 23 parts, sodium benzoate is 5 - 7 parts, nicotinic acid is 0.4 - 0.6 parts, and pure water is 80 - 90 parts. Add the above three intermediates to water according to the above weight fraction and stir until all the solid substances are dissolved.

[0052] The potassium chloride zinc-iron alloy plating solution is prepared according to the following method: a) Add 70% of water to the plating bath according to the volume of the plating solution, and add zinc chloride, potassium chloride, boric acid, and the complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid substances are dissolved; c) Add the brightening agent and the auxiliary agent according to the process requirements, stir evenly, and adjust the pH of the plating solution to the process range with 10% sodium hydroxide solution or 3% hydrochloric acid by mass fraction, and add water to the specified volume; d) Electrolyze at a current density of 0.15 A / dm 2 for 60 min.

[0053] After the magnesium alloy workpiece is galvanized with zinc-iron alloy, a chromium-free chemical conversion film is prepared using the zinc-free special ZECZEC-11 chromium-free chemical conversion agent of Superbond Chemical Industry.

[0054] The zinc-free special ZECZEC-11 chromium-free chemical conversion agent is 200 - 300 mL / L, operate at room temperature, and the impregnation time is 50 - 70 s.

[0055] The specific process is "descaling with 0.5% sulfuric acid → water washing → chemical conversion → water washing → drying".

[0056] After the magnesium alloy workpiece undergoes chromium-free chemical conversion, a silicon-based chromium-free passivation layer is prepared using the current solvent-based silicon-based chromium-free passivation process.

[0057] Preferably, the silicon-based chromium-free passivation layer is prepared using the zinc-free special ZECCOAT-888FL silicon-based chromium-free passivation process of Superbond Chemical Industry: Use the undiluted ZECCOAT-888FL silane chromium-free passivating agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure it at 80 - 100 °C for 20 - 30 min.

[0058] Preferably, the silane chromium-free passivation layer is prepared by the zinc cote ZEC-COAT 825 chromium-free passivation process of Superb Chemical Industry: Use the undiluted zinc cote ZECCOAT-825 silane chromium-free passivating agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure it at 75 - 85 °C for 20 - 30 min.

[0059] Preferably, the silane chromium-free passivation layer is prepared by the zinc cote ZECCOAT-888 silane chromium-free passivation process of Superb Chemical Industry: Use the undiluted ZECCOAT-888 silane chromium-free passivating agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure it at 75 - 85 °C for 20 - 30 min.

[0060] Preferably, the silane chromium-free passivation layer is prepared by the zinc cote ZEC-W silane chromium-free passivation process of Superb Chemical Industry: Use the undiluted ZEC-W silane chromium-free passivating agent, the pH value of the passivation solution is 4.0 - 4.5, operate at room temperature, immerse for 10 - 15 s, and after the workpiece is passivated, dry and cure it at 115 - 125 °C for 18 - 25 min.

[0061] After the magnesium alloy workpiece is passivated by silane chromium-free passivation, a graphene modified sealing layer is prepared by using the PRODICO 480 graphene modified sealing agent developed by Superb Chemical Industry.

[0062] Dilute the PRODICO 480 graphene modified sealing agent with water to 2.5 - 3.2 times to prepare a sealing solution. Immerse the plated parts in the sealing solution for 8 - 15 s, drain them after taking them out of the tank, and use high-pressure air to blow off the residual sealing solution on the surface of the plated parts. After the plated parts are sealed, dry and cure them at 70 - 80 °C for 20 - 35 min.

[0063] Example 1: As Figure 1 shown, a magnesium alloy galvanized iron alloy composite process, bottom coating preparation and coating structure include pretreatment of the magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper plating layer 3, a cyanide-free copper-zinc alloy plating layer 4, a high-corrosion-resistant nickel-phosphorus alloy plating layer 5, a zinc-iron alloy plating layer 6, a chromium-free chemical conversion film 7, a silane chromium-free passivation layer 8, and a graphene modified sealing layer 9 from the inside to the outside on the pretreated magnesium alloy substrate 1.

[0064] 1. Pretreatment: Pretreat the magnesium alloy workpiece substrate 1 by using the current magnesium alloy pretreatment process.

[0065] 1) Degreasing: Adopt the following weak alkaline ultrasonic degreasing process: sodium phosphate 20 g / L, sodium carbonate 20 g / L, Gentell NP-10 degreasing agent 1.2 g / L, bath temperature 70 °C, degreasing time 10 min.

[0066] 2) Pickling and activation: Adopt the following pickling and activation process for magnesium alloy: phosphoric acid 25 mL / L, ammonium bifluoride 20 g / L, operate at room temperature, pickling time 60 s.

[0067] 2. Chemical zinc deposition: After the pretreatment of the magnesium alloy workpiece, prepare the chemical zinc deposition layer 2 by adopting the following chemical zinc deposition process.

[0068] Zinc sulfate heptahydrate 30 g / L, potassium pyrophosphate 110 g / L, potassium fluoride 7 g / L, bath temperature 70 °C, zinc deposition time 10 min.

[0069] 3. Cyanide-free copper plating: After the chemical zinc deposition of the magnesium alloy workpiece, prepare the cyanide-free copper plating layer 3 by adopting the polymer thiocyanate copper plating process of the present invention, and the coating thickness is 6 μm.

[0070] 1) Preparation of copper plating brightener: Calculated by weight, add 410 parts of formic acid to the reaction tank, add 1.5 parts of melamine under stirring, stir until the solid substances are dissolved, then add 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide with a molecular weight less than 8000, 50 parts of cobalt acetate, and 410 parts of pure water, and stir until the solid substances are dissolved to obtain the brightener.

[0071] 2) Plating: Polymer thiocyanato cuprous 21 g / L, polymer thiocyanato sodium 150 g / L, 2-hydroxyethylidene diphosphonic acid sodium 25 g / L, copper plating brightener 10 mL / L, pH of the plating solution is 12.5, bath temperature 35 °C, cathode current density 1.0 A / dm 2 , cathode moving speed 4 m / min, use oxygen-free electrolytic copper grains as the anode, load the copper grains into the titanium anode basket, the area ratio of the anode to the cathode > 3:1, anode moving speed 4 m / min.

[0072] 4. Cyanide-free copper-zinc alloy plating: After the cyanide-free copper plating of the magnesium alloy workpiece, prepare the cyanide-free copper-zinc alloy coating 4 by adopting the polymer thiocyanate copper-zinc alloy plating process developed by Chaobang Chemical Industry, and the coating thickness is 6 μm.

[0073] Polymer thiocyanato cuprous 21 g / L, polymer thiocyanato zinc 11 g / L, polymer thiocyanato sodium 150 g / L, copper-zinc alloy plating brightener 10 mL / L, pH of the plating solution is 11, bath temperature 45 °C, cathode current density 1 A / dm2 , the cathode moves at 4 m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the area ratio of the anode to the cathode > 2:1, and the anode moves at 3 - 5 m / min.

[0074] 5. Nickel - phosphorus alloy plating: For the magnesium alloy workpiece, a high - corrosion - resistant nickel - phosphorus alloy coating 5 is prepared by using the PROTEXYER 8713 high - corrosion - resistant nickel - phosphorus alloy plating process of Chaobang Chemical Industry. The coating thickness is 10 μm.

[0075] The PROTEXYER 8713 MU bath conditioner is 600 mL / L, nickel sulfate hexahydrate is 320 g / L, the pH of the plating solution is 2.6, the plating bath temperature is 63 °C, and the cathode current density is 4 A / dm 2 , and the cathode moves at 4 m / min.

[0076] 6. Zinc - iron alloy plating: After the magnesium alloy workpiece is plated with nickel - phosphorus alloy, a zinc - iron alloy coating 6 is prepared by using the potassium chloride zinc - iron alloy plating process of the present invention. The coating thickness is 12 μm.

[0077] 1) Preparation of complexing agent: The glucose sodium heptanoate and sodium sulfosalicylate are mixed in a mass ratio of 3:2 and stirred evenly to obtain the complexing agent.

[0078] 2) Preparation of brightening agent: The o - chlorobenzaldehyde and formic acid are mixed in a mass ratio of 1:1 and stirred until all the solid substances are dissolved to obtain the brightening agent.

[0079] 3) Preparation of auxiliary agent: Calculated by weight fraction, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether of model OX - 105 and amino sulfonic acid, 6 parts of sodium benzoate, 0.5 part of nicotinic acid, and 85 parts of pure water. The above three intermediates are added to water according to the said weight fraction and stirred until all the solid substances are dissolved to obtain the auxiliary agent.

[0080] 4) Preparation of potassium chloride zinc - iron alloy plating solution: a) According to the volume of the plating solution, 70% of water is added to the plating bath, and zinc chloride, potassium chloride, boric acid, and the complexing agent are added according to the process requirements, and stirred to dissolve the above substances; b) Ferrous chloride tetrahydrate is added according to the process requirements and stirred until the solid substances are dissolved; c) The brightening agent and the auxiliary agent are added according to the process requirements, stirred evenly, and the pH of the plating solution is adjusted to 5.4 with a 10% sodium hydroxide solution or a 3% hydrochloric acid solution by mass fraction, and water is added to the specified volume; d) Electrolyze for 60 min at a current density of 0.15 A / dm 2 current density.

[0081] 5) Plating: Zinc chloride 65 g / L, ferrous chloride tetrahydrate 11 g / L, potassium chloride 210 g / L, boric acid 30 g / L, complexing agent 37 g / L, brightening agent 0.15 mL / L, auxiliary agent 25 mL / L, pH of the plating solution is 5.4, temperature of the plating bath is 25 °C, cathode current density is 2 A / dm 2 , cathode moving speed is 4 m / min, the anode is made of zinc plate with mass fraction > 99.9%, the area ratio of the cathode to the anode is 2:1; during production, a ferrous chloride tetrahydrate solution with a mass fraction of 30% is added to the plating bath to keep its mass concentration at the required value.

[0082] 7. Chemical conversion: After the magnesium alloy workpiece is galvanized with zinc-iron alloy, a chromium-free chemical conversion film 7 is prepared using the zinc-free special ZECZEC-11 chromium-free chemical conversion agent of Superbond Chemical Industry.

[0083] ZECZEC-11 chromium-free chemical conversion agent 200 mL / L, operating at room temperature, dipping time is 70 s.

[0084] The specific process is "descaling with 0.5% sulfuric acid → water washing → chemical conversion → water washing → drying".

[0085] 8. Chromium-free passivation: After the magnesium alloy workpiece undergoes chromium-free chemical conversion, a silane chromium-free passivation layer 8 is prepared using the ZECCOAT-888FL silane chromium-free passivation process of Superbond Chemical Industry.

[0086] The ZECCOAT-888FL silane chromium-free passivating agent is used as the original solution, operating at room temperature, dipping for 60 s, and after the workpiece is passivated, it is dried and cured at 90 °C for 25 min.

[0087] 9. Sealing: After the magnesium alloy workpiece is chromium-free passivated, a graphene-modified sealing layer 9 is prepared using the PRODICO 480 graphene-modified sealing agent developed by Superbond Chemical Industry.

[0088] The PRODICO 480 graphene-modified sealing agent is diluted with water to 2.8 times to prepare the sealing solution. The plated parts are immersed in the sealing solution for 10 s, drained after taking out of the tank, and the residual sealing solution on the surface of the plated parts is blown off with high-pressure air. After sealing, it is dried and cured at 80 °C for 30 min.

[0089] Example 2: As Figure 1As shown, a combined process of galvanizing and iron alloying on magnesium alloy, preparation of bottom coating and coating structure includes pretreatment of magnesium alloy substrate 1, and sequentially preparing chemical zinc deposition layer 2, cyanide-free copper plating layer 3, cyanide-free copper-zinc alloy plating layer 4, high anti-corrosion nickel-phosphorus alloy plating layer 5, zinc-iron alloy plating layer 6, chromium-free chemical conversion film 7, silane chromium-free passivation layer 8, and graphene-modified sealing layer 9 from inside to outside on the pretreated magnesium alloy substrate 1.

[0090] 1. Pretreatment: The magnesium alloy workpiece substrate 1 is pretreated by the current magnesium alloy pretreatment process.

[0091] 1) Degreasing: The following weak alkaline ultrasonic degreasing process is adopted: sodium phosphate 25g / L, sodium carbonate 25g / L, Gintel NP-10 degreasing agent 0.8g / L, bath temperature 65°C, degreasing time 10min.

[0092] 2) Pickling and activation: The following magnesium alloy pickling and activation process is adopted: phosphoric acid 28mL / L, ammonium bifluoride 22g / L, operating at room temperature, pickling time 50s.

[0093] 2. Chemical zinc deposition: After the pretreatment of the magnesium alloy workpiece, the chemical zinc deposition layer 2 is prepared by the following chemical zinc deposition process.

[0094] Zinc sulfate heptahydrate 35g / L, potassium pyrophosphate 120g / L, potassium fluoride 9g / L, bath temperature 68°C, zinc deposition time 10min.

[0095] 3. Cyanide-free copper plating: After the chemical zinc deposition of the magnesium alloy workpiece, the cyanide-free copper plating layer 3 is prepared by the polymerized thiocyanate copper plating process of the present invention, and the coating thickness is 6μm.

[0096] 1) Preparation of copper plating brightener: Calculated by weight, 410 parts of formic acid are added to the reaction tank, 1.5 parts of melamine are added under stirring until the solid matter is dissolved, then 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide with a molecular weight less than 8000, 50 parts of cobalt acetate, and 410 parts of pure water are added and stirred until the solid matter is dissolved to obtain the brightener.

[0097] 2) Plating: Polymerized cuprous thiocyanate 24g / L, polymerized sodium thiocyanate 170g / L, 2-hydroxyethylidene-1,1-diphosphonic acid sodium salt 25g / L, copper plating brightener 10mL / L, pH of plating solution is 12, bath temperature 30°C, cathode current density 1.0A / dm 2, the cathode moves at 4 m / min. Use oxygen-free electrolytic copper pellets as the anode, and load the copper pellets into a titanium anode basket. The area ratio of the anode to the cathode > 3:1, and the anode moves at 4 m / min.

[0098] 4. Non-cyanide copper-zinc alloy plating: After non-cyanide copper plating on the magnesium alloy workpiece, a non-cyanide copper-zinc alloy coating 4 is prepared by using the polymerized thiocyanate copper-zinc alloy plating process developed by Superbond Chemical Industry. The coating thickness is 6 μm.

[0099] Copper(I) poly(thiocyanate) 24 g / L, zinc poly(thiocyanate) 13 g / L, sodium poly(thiocyanate) 170 g / L, copper-zinc alloy plating brightener 10 mL / L, the pH of the plating solution is 11, the plating bath temperature is 35 °C, the cathode current density is 1 A / dm 2 , the cathode moves at 4 m / min. Use a brass plate with a copper mass fraction of 68% as the anode. The area ratio of the anode to the cathode > 2:1, and the anode moves at 4 m / min.

[0100] 5. Nickel-phosphorus alloy plating: After non-cyanide copper-zinc alloy plating on the magnesium alloy workpiece, a highly corrosion-resistant nickel-phosphorus alloy coating 5 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Superbond Chemical Industry. The coating thickness is 10 μm.

[0101] PROTEXYER 8713 MU bath conditioner 620 mL / L, nickel sulfate hexahydrate 340 g / L, the pH of the plating solution is 2.7, the plating bath temperature is 60 °C, the cathode current density is 4 A / dm 2 , the cathode moves at 4 m / min.

[0102] 6. Zinc-iron alloy plating: After nickel-phosphorus alloy plating on the magnesium alloy workpiece, a zinc-iron alloy coating 6 is prepared by using the potassium chloride zinc-iron alloy plating process of the present invention. The coating thickness is 12 μm.

[0103] 1) Prepare the complexing agent: Mix sodium glucoheptonate and sodium sulfosalicylate in a mass ratio of 3:2 and stir evenly to obtain the complexing agent.

[0104] 2) Prepare the brightener: Mix o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stir until all the solids are dissolved to obtain the brightener.

[0105] 3) Prepare the auxiliary agent: Calculated by weight fraction, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 part of nicotinic acid, and 85 parts of pure water. Add the above three intermediates to water according to the said weight fraction and stir until all the solids are dissolved to obtain the auxiliary agent.

[0106] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% water to the plating bath according to the volume of the plating solution, and add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements, and stir until the solid substances are dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 4.6 with 10% sodium hydroxide solution or 3% hydrochloric acid by mass fraction, and add water to the specified volume; d) Electrolyze for 60 min at a current density of 0.15 A / dm 2

[0107] 5) Plating: Zinc chloride 70 g / L, ferrous chloride tetrahydrate 12 g / L, potassium chloride 220 g / L, boric acid 35 g / L, complexing agent 40 g / L, brightener 0.15 mL / L, auxiliary agent 25 mL / L, pH of the plating solution is 4.6, temperature of the plating bath is 15 °C, cathode current density is 2 A / dm 2 , cathode moving speed is 4 m / min, use zinc plate with mass fraction > 99.9% as the anode, and the area ratio of the cathode to the anode is 2:1; during production, add 30% ferrous chloride tetrahydrate solution by mass fraction to the plating bath to keep its concentration within the process range.

[0108] 7. Chemical conversion: After the magnesium alloy workpiece is plated with zinc-iron alloy, use the ZECZEC-11 chromium-free chemical conversion agent of Chaobang Chemical Industry to prepare a chromium-free chemical conversion film 7.

[0109] ZECZEC-11 chromium-free chemical conversion agent 230 mL / L, operate at room temperature, dipping time is 64 s.

[0110] The specific process is "removing film with 0.5% sulfuric acid → water washing → chemical conversion → water washing → drying".

[0111] 8. Chromium-free passivation: After the magnesium alloy workpiece undergoes chromium-free chemical conversion, use the ZEC-COAT 825 silane chromium-free passivation process of Chaobang Chemical Industry to prepare a silane chromium-free passivation layer 8.

[0112] Use the ZECCOAT-825 silane chromium-free passivation agent stock solution directly, operate at room temperature, dip for 60 s, and dry and cure the workpiece at 80 °C for 25 min after passivation.

[0113] 9. Sealing: After the magnesium alloy workpiece undergoes chromium-free passivation, use the PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical Industry to prepare a graphene-modified sealing layer 9.

[0114] Dilute the PRODICO 480 graphene modified sealing agent with water to 2.8 times to prepare a sealing solution. Immerse the plated parts in the sealing solution for 10 s, drain them after taking them out of the tank, and blow away the residual sealing solution on the surface of the plated parts with high-pressure air. After sealing, dry and cure at 80 °C for 20 min.

[0115] Example 3: As Figure 1 shown, a magnesium alloy galvanized iron alloy composite process, bottom coating preparation and coating structure include pretreatment of the magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper plating layer 3, a cyanide-free copper-zinc alloy plating layer 4, a high-corrosion-resistant nickel-phosphorus alloy plating layer 5, a zinc-iron alloy plating layer 6, a chromium-free chemical conversion film 7, a silane chromium-free passivation layer 8, and a graphene modified sealing layer 9 on the pretreated magnesium alloy substrate 1 from inside to outside.

[0116] 1. Pretreatment: Pretreat the magnesium alloy workpiece substrate 1 using the current magnesium alloy pretreatment process.

[0117] 1) Degreasing: Adopt the following weak alkaline ultrasonic degreasing process: sodium phosphate 25 g / L, sodium carbonate 20 g / L, Gintel NP-10 degreasing agent 1.0 g / L, bath temperature 70 °C, degreasing time 10 min.

[0118] 2) Pickling and activation: Adopt the following magnesium alloy pickling and activation process: phosphoric acid 26 mL / L, ammonium bifluoride 20 g / L, operate at room temperature, pickling time 60 s.

[0119] 2. Chemical zinc deposition: After the pretreatment of the magnesium alloy workpiece, prepare the chemical zinc deposition layer 2 using the following chemical zinc deposition process.

[0120] Zinc sulfate heptahydrate 25 g / L, potassium pyrophosphate 100 g / L, potassium fluoride 6 g / L, bath temperature 72 °C, zinc deposition time 12 min.

[0121] 3. Cyanide-free copper plating: After the chemical zinc deposition of the magnesium alloy workpiece, prepare the cyanide-free copper plating layer 3 using the polymer thiocyanate copper plating process of the present invention, and the coating thickness is 6 μm.

[0122] 1) Prepare the copper plating brightener: Calculated by weight, add 410 parts of formic acid to the reaction tank, add 1.5 parts of melamine under stirring, stir until the solid substance dissolves, then add 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide with a molecular weight less than 8000, 50 parts of cobalt acetate, and 410 parts of pure water, and stir until the solid substance dissolves to obtain the brightener.

[0123] 2) Plating: Copper(I) thiocyanate polymer 18 g / L, sodium thiocyanate polymer 130 g / L, copper plating brightener 10 mL / L, pH of the plating solution is 12.5, plating bath temperature is 40 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, using oxygen-free electrolytic copper grains as anode, loading the copper grains into a titanium anode basket, the area ratio of anode to cathode > 3:1, anode moving speed is 4 m / min.

[0124] 4. Cyanide-free copper-zinc alloy plating: After cyanide-free copper plating on the magnesium alloy workpiece, a cyanide-free copper-zinc alloy plating layer 4 is prepared by using the copper-zinc alloy plating process of polymerized thiocyanate developed by Chaobang Chemical Industry, and the plating layer thickness is 6 μm.

[0125] Copper(I) thiocyanate polymer 18 g / L, zinc thiocyanate polymer 9 g / L, sodium thiocyanate polymer 130 g / L, copper-zinc alloy plating brightener 10 mL / L, pH of the plating solution is 12, plating bath temperature is 55 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min, using a brass plate with a copper mass fraction of 68% as anode, the area ratio of anode to cathode > 2:1, anode moving speed is 4 m / min.

[0126] 5. Nickel-phosphorus alloy plating: After cyanide-free copper-zinc alloy plating on the magnesium alloy workpiece, a high-corrosion-resistant nickel-phosphorus alloy plating layer 5 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Chaobang Chemical Industry, and the plating layer thickness is 10 μm.

[0127] PROTEXYER 8713 MU bath opener 580 mL / L, nickel sulfate hexahydrate 280 g / L, pH value of the plating solution is 2.6, plating bath temperature is 65 °C, cathode current density is 4 A / dm 2 , cathode moving speed is 4 m / min.

[0128] 6. Zinc-iron alloy plating: After nickel-phosphorus alloy plating on the magnesium alloy workpiece, a zinc-iron alloy plating layer 6 is prepared by using the potassium chloride zinc-iron alloy plating process of the present invention, and the plating layer thickness is 12 μm.

[0129] 1) Preparation of complexing agent: Mix sodium glucoheptonate and sodium sulfosalicylate in a mass ratio of 3:2 and stir evenly to obtain the complexing agent.

[0130] 2) Preparation of brightener: Mix o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stir until all the solid substances are dissolved to obtain the brightener.

[0131] 3) Preparation of auxiliary agent: Calculated by weight fraction, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and aminosulfonic acid, 6 parts of sodium benzoate, 0.5 part of nicotinic acid, and 85 parts of pure water. Add the above three intermediates to water according to the said weight fraction and stir until all the solids are dissolved to obtain the said auxiliary agent.

[0132] 4) Preparation of potassium chloride zinc-iron alloy plating solution: The potassium chloride zinc-iron alloy plating solution is prepared by the following method: a) Add 70% of water to the plating bath according to the volume of the plating solution, and add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solid is dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, adjust the pH of the plating solution to 4.8 with 10% sodium hydroxide solution or 3% hydrochloric acid by mass fraction, and add water to the specified volume; d) Electrolyze at a current density of 0.15 A / dm 2 for 60 min.

[0133] 5) Plating: Zinc chloride 50 g / L, ferrous chloride tetrahydrate 8 g / L, potassium chloride 180 g / L, boric acid 25 g / L, complexing agent 28 g / L, brightener 0.15 mL / L, auxiliary agent 25 mL / L, pH of the plating solution is 4.8, temperature of the plating bath is 25 °C, cathode current density is 2 A / dm 2 , cathode moving speed is 4 m / min, use zinc plate with mass fraction > 99.9% as anode, and the area ratio of cathode to anode is 2:1; during production, add 30% ferrous chloride tetrahydrate solution by mass fraction to the plating bath to keep its concentration within the process range.

[0134] 7. Chemical conversion: After the magnesium alloy workpiece is galvanized with zinc-iron alloy, use the zinc-free chemical conversion agent ZECZEC-11 of Superbond Chemical Industry to prepare a zinc-free chemical conversion film 7.

[0135] ZECZEC-11 zinc-free chemical conversion agent 270 mL / L, operating at room temperature, dipping time is 57 s.

[0136] The specific process is "descaling with 0.5% sulfuric acid → water washing → chemical conversion → water washing → drying".

[0137] 8. Chromium-free passivation: After the magnesium alloy workpiece undergoes chromium-free chemical conversion, use the zinc-free passivation process of zinc silane ZECCOAT-888 of Superbond Chemical Industry to prepare a zinc silane chromium-free passivation layer 8.

[0138] Use the undiluted ZECCOAT-888 silane chromium-free passivating agent, operate at room temperature, immerse for 60 s, and after passivating the workpiece, dry and cure it at 80 °C for 25 min.

[0139] 9. Sealing: After chromium-free passivation of the magnesium alloy workpiece, use the PRODICO 480 graphene modified sealing agent developed by Chaobang Chemical Industry to prepare the graphene modified sealing layer 9.

[0140] Dilute the PRODICO 480 graphene modified sealing agent with water to 2.8 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 10 s, drain after taking out of the tank, and use high-pressure air to blow off the residual sealing solution on the surface of the plated parts. After sealing, dry and cure it at 85 °C for 25 min.

[0141] Example 4: As Figure 1 shown, a magnesium alloy galvanized iron alloy composite process, bottom coating preparation and coating structure include pretreatment of the magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposit layer 2, a cyanide-free copper plating layer 3, a cyanide-free copper-zinc alloy plating layer 4, a high-corrosion-resistant nickel-phosphorus alloy plating layer 5, a zinc-iron alloy plating layer 6, a chromium-free chemical conversion film 7, a silane chromium-free passivation layer 8, and a graphene modified sealing layer 9 from the inside to the outside on the pretreated magnesium alloy substrate 1.

[0142] 1. Pretreatment: Pretreat the magnesium alloy workpiece substrate 1 using the current magnesium alloy pretreatment process.

[0143] 1) Degreasing: Use the following weak alkaline ultrasonic degreasing process: sodium phosphate 20 g / L, sodium carbonate 25 g / L, Gentell NP-10 degreasing agent 1.0 g / L, bath temperature 70 °C, degreasing time 10 min.

[0144] 2) Pickling and activation: Use the following magnesium alloy pickling and activation process: phosphoric acid 24 mL / L, ammonium bifluoride 19 g / L, operate at room temperature, pickling time 65 s.

[0145] 2. Chemical zinc deposition: After pretreatment of the magnesium alloy workpiece, use the following chemical zinc deposition process to prepare the chemical zinc deposit layer 2.

[0146] Zinc sulfate heptahydrate 33 g / L, potassium pyrophosphate 115 g / L, potassium fluoride 8 g / L, bath temperature 69 °C, zinc deposition time 9 min.

[0147] 3. Cyanide-free copper plating: After chemical zinc deposition of the magnesium alloy workpiece, use the polymer thiocyanate copper plating process of the present invention to prepare the cyanide-free copper plating layer 3, and the coating thickness is 6 μm.

[0148] 1) Preparation of bright copper plating agent: Calculated by weight, add 410 parts of formic acid to the reaction tank. Under stirring, add 1.5 parts of melamine and stir until the solid dissolves. Then add 15 parts of waterborne polyurethane resin, 100 parts of polyacrylamide with a molecular weight less than 8000, 50 parts of cobalt acetate, and 410 parts of pure water, and stir until the solid dissolves to obtain the brightening agent.

[0149] 2) Plating: Copper(I) thiocyanate polymer 23 g / L, sodium thiocyanate polymer 165 g / L, bright copper plating agent 10 mL / L, pH of the plating solution is 12.3, plating bath temperature is 40 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min. Use oxygen-free electrolytic copper grains as the anode, load the copper grains into a titanium anode basket, the area ratio of the anode to the cathode > 3:1, and the anode moving speed is 4 m / min.

[0150] 4. Non-cyanide copper-zinc alloy plating: After non-cyanide copper plating of the magnesium alloy workpiece, use the copper-zinc alloy plating process of polymerized thiocyanate developed by Chaobang Chemical Industry to prepare a non-cyanide copper-zinc alloy coating 4 with a coating thickness of 6 μm.

[0151] Copper(I) thiocyanate polymer 23 g / L, zinc thiocyanate polymer 12 g / L, sodium thiocyanate polymer 160 g / L, brightening agent 10 mL / L, pH of the plating solution is 11, plating bath temperature is 40 °C, cathode current density is 1 A / dm 2 , cathode moving speed is 4 m / min. Use a brass plate with a copper mass fraction of 68% as the anode, the area ratio of the anode to the cathode > 2:1, and the anode moving speed is 4 m / min.

[0152] 5. Nickel-phosphorus alloy plating: After non-cyanide copper-zinc alloy plating of the magnesium alloy workpiece, use the PROTEXYER 8713 high anti-corrosion nickel-phosphorus alloy plating process of Chaobang Chemical Industry to prepare a high anti-corrosion nickel-phosphorus alloy coating 5 with a coating thickness of 10 μm.

[0153] PROTEXYER 8713 MU bath starter 610 mL / L, nickel sulfate hexahydrate 330 g / L, pH of the plating solution is 2.7, plating bath temperature is 62 °C, cathode current density is 4 A / dm 2 , cathode moving speed is 4 m / min.

[0154] 6. Zinc-iron alloy plating: After nickel-phosphorus alloy plating of the magnesium alloy workpiece, use the potassium chloride zinc-iron alloy plating process of the present invention to prepare a zinc-iron alloy coating 6 with a coating thickness of 12 μm.

[0155] 1) Preparation of complexing agent: The complexing agent is obtained by mixing sodium gluconate and sodium sulfosalicylate in a mass ratio of 3:2 and stirring evenly.

[0156] 2) Preparation of brightener: The brightener is obtained by mixing o-chlorobenzaldehyde and formic acid in a mass ratio of 1:1 and stirring until all the solids are dissolved.

[0157] 3) Preparation of auxiliary agent: Calculated by weight fraction, 20 parts of the sulfonation product of fatty alcohol polyoxyethylene ether of type OX-105 and amino sulfonic acid, 6 parts of sodium benzoate, 0.5 part of nicotinic acid, and 85 parts of pure water. Add the above three intermediates to water according to the said weight fraction and stir until all the solids are dissolved to obtain the auxiliary agent.

[0158] 4) Preparation of potassium chloride zinc-iron alloy plating solution: a) Add 70% of water to the plating bath according to the volume of the plating solution, and add zinc chloride, potassium chloride, boric acid, and complexing agent according to the process requirements, and stir to dissolve the above substances; b) Add ferrous chloride tetrahydrate according to the process requirements and stir until the solids are dissolved; c) Add brightener and auxiliary agent according to the process requirements, stir evenly, and adjust the pH of the plating solution to 5.6 with 10% sodium hydroxide solution or 3% hydrochloric acid by mass fraction, and add water to the specified volume; d) Electrolyze at a current density of 0.10 A / dm 2 for 90 min.

[0159] 5) Plating: Zinc chloride 65 g / L, ferrous chloride tetrahydrate 11 g / L, potassium chloride 210 g / L, boric acid 28 g / L, complexing agent 36 g / L, brightener 0.15 mL / L, auxiliary agent 25 mL / L, pH of the plating solution is 5.6, temperature of the plating bath is 22 °C, cathode current density is 2 A / dm 2 , cathode moving speed is 4 m / min, use zinc plate with mass fraction > 99.9% as anode, and the area ratio of cathode to anode is 2:1; during production, add 30% ferrous chloride tetrahydrate solution by mass fraction to the plating bath to keep its concentration within the process range.

[0160] 7. Chemical conversion: After the magnesium alloy workpiece is plated with zinc-iron alloy, use the zinc-free chemical conversion agent ZECZEC-11 of Chaobang Chemical Industry to prepare a chromium-free chemical conversion film 7.

[0161] ZECZEC-11 chromium-free chemical conversion agent 300 mL / L, operating at room temperature, dipping time 50 s.

[0162] The specific process is "removing the film with 0.5% sulfuric acid → water washing → chemical conversion → water washing → drying".

[0163] 8. Chromium-free passivation: After the chemical conversion of the magnesium alloy workpiece without chromium, a chromium-free passivation layer 8 of silane is prepared by using the zinc-cote ZEC-W silane chromium-free passivation process of Chaobang Chemical Industry.

[0164] The ZEC-W silane chromium-free passivation agent is used as the original solution, the pH of the passivation solution is 4.2, the operation is carried out at room temperature, the impregnation time is 12 s, and the workpiece is dried and cured at 120 °C for 20 min after passivation.

[0165] 9. Sealing: After the chromium-free passivation of the magnesium alloy workpiece, a graphene-modified sealing layer 9 is prepared by using the PRODICO 480 graphene-modified sealing agent developed by Chaobang Chemical Industry.

[0166] The PRODICO 480 graphene-modified sealing agent is diluted with water to 2.8 times to prepare a sealing solution. The plated parts are immersed in the sealing solution for 10 s, drained after leaving the tank, and the residual sealing solution on the surface of the plated parts is blown off with high-pressure air. After sealing, it is dried and cured at 77 °C for 30 min.

[0167] Test example 1: According to GB / T 10125–2021 "Corrosion tests in artificial atmospheres - Salt spray tests", neutral salt spray tests were carried out. There was no white rust on the surface of the magnesium alloy galvanized iron alloy samples prepared in Example 1, Example 2, Example 3 and Example 4 after 560 h, and the prepared coatings had excellent corrosion resistance.

[0168] Test example 2: According to GB / T 5270–2005 "Review of test methods for adhesion of metallic coatings on metallic substrates - Electrodeposited and chemically deposited coatings", the adhesion of the coatings was tested. The magnesium alloy galvanized iron alloy samples prepared in Example 1, Example 2, Example 3 and Example 4 were heated in a heating furnace to 150 °C and kept warm for 30 min, then taken out and immediately cooled in water at room temperature. There was no blistering or peeling of the coatings, and the adhesion of the coatings met the standard requirements.

[0169] Test example 3: According to GJB 150.9A–2009 "Environmental test methods for military equipment - Part 10: Mold tests", mold tests were carried out for 28 days. There was no mold growth on the surface of the magnesium alloy galvanized iron alloy samples prepared in Example 1, Example 2, Example 3 and Example 4, meeting the requirements of industry standards.

[0170] Test example 4: The damp heat, steady state test was carried out in accordance with GB / T 2423.3-2016 "Basic environmental testing procedures for electric and electronic products - Test Ca: Damp heat, steady state". The magnesium alloy galvanized iron alloy samples prepared in Example 1, Example 2, Example 3 and Example 4 were tested for 240 h under the conditions of a temperature of 40 °C and a relative humidity of 93%. There was no visible change in the appearance of the coating, and the damp heat, steady state test met the standard requirements.

[0171] The technical solutions provided by the embodiments of the present invention have been introduced in detail above. Specific examples are used herein to elaborate on the principles and implementation manners of the embodiments of the present invention. The descriptions of the above embodiments are only applicable to help understand the principles of the embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these are also regarded as falling within the protection scope of the present invention.

Claims

1. A combined process for galvanizing a magnesium alloy and an iron alloy, characterized in that, It includes the following steps: (1) Degrease and pickling-activate the magnesium alloy workpiece; (2) After the pretreatment of the magnesium alloy workpiece, prepare a chemical zinc deposit layer by using the current chemical zinc deposition process for magnesium alloy; (3) After the chemical zinc deposition of the magnesium alloy workpiece, prepare a cyanide-free copper plating layer by using a polymeric thiocyanate copper plating process; (4) After the polymeric thiocyanate copper plating of the magnesium alloy workpiece, prepare a cyanide-free copper-zinc alloy coating by using a polymeric thiocyanate copper-zinc alloy plating process; (5) After the polymeric thiocyanate copper-zinc alloy plating of the magnesium alloy workpiece, prepare a highly corrosion-resistant nickel-phosphorus alloy coating by using the current nickel-phosphorus alloy plating process with high corrosion resistance; (6) After the nickel-phosphorus alloy plating with high corrosion resistance of the magnesium alloy workpiece, prepare a zinc-iron alloy coating by using a potassium chloride zinc-iron alloy plating process; (7) After the zinc-iron alloy plating of the magnesium alloy workpiece, conduct a chromium-free chemical conversion to prepare a chromium-free chemical conversion film; (8) After the chromium-free chemical conversion of the magnesium alloy workpiece, conduct a silane chromium-free passivation to prepare a silane chromium-free conversion layer; (9) After the silane chromium-free passivation of the magnesium alloy workpiece, conduct a sealing to prepare a sealing layer; The potassium chloride zinc-iron alloy plating process described above includes the following components and process parameters: Zinc chloride 50 - 70 g / L, ferrous chloride tetrahydrate 2 - 12 g / L, potassium chloride 180 - 220 g / L, boric acid 25 - 35 g / L, complexing agent 8 - 40 g / L, brightening agent 0.1 - 0.2 mL / L, auxiliary agent 20 - 30 mL / L, pH value of the plating solution 4.5 - 5.6, plating bath temperature 15 - 30 °C, cathode current density 1 - 3 A / dm 2 , cathode moving speed 3 - 5 m / min, using zinc plate with mass fraction > 99.9% as anode, area ratio of cathode to anode is 2:1; during production, add ferrous chloride tetrahydrate solution with mass fraction of 30% to the plating bath to keep its concentration within the process range; The complexing agent includes sodium glucoheptonate and sodium sulfosalicylate. The mass ratio of sodium glucoheptonate to sodium sulfosalicylate is 3:(1-3). Mix sodium glucoheptonate and sodium sulfosalicylate according to the above ratio and stir evenly; The brightening agent includes o-chlorobenzaldehyde and formic acid. The mass ratio of o-chlorobenzaldehyde to formic acid is 1:(0.8-1.2). Mix o-chlorobenzaldehyde and formic acid according to the above ratio and stir until all the solids are dissolved; The auxiliary agent includes the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 and amino sulfonic acid, sodium benzoate, and nicotinic acid. Calculated by weight fraction, the sulfonation product of fatty alcohol polyoxyethylene ether of model OX-105 is 17-23 parts, sodium benzoate is 5-7 parts, nicotinic acid is 0.4-0.6 parts, and pure water is 80-90 parts. Add the above three intermediates to water according to the above weight fraction and stir until all the solids are dissolved.

2. Preparation of the bottom coating in the combined process of galvanizing and electroplating an iron alloy on a magnesium alloy, characterized in that, Prepare a cyanide-free copper plating layer by using a polymeric thiocyanate copper plating process, including the following components and process parameters: Copper thiocyanate 18 - 24 g / L, sodium thiocyanate 130 - 170 g / L, 1 - hydroxyethylidene - 1,1 - diphosphonic acid sodium salt 20 - 30 g / L, brightener for copper plating 8 - 12 mL / L, pH value of plating solution 12 - 13, bath temperature 30 - 40 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode moving speed 3 - 5 m / min, using oxygen - free electrolytic copper grains as anode, loading the copper grains into a titanium anode basket, the area ratio of anode to cathode > 3:1, anode moving speed 3 - 5 m / min; The copper plating brightening agent described above includes the following components by weight fraction: 1-2 parts of melamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight less than 8000, 40-60 parts of cobalt acetate, 390-430 parts of formic acid, and 390-430 parts of pure water.

3. Preparation of the bottom coating in the magnesium alloy galvanized iron alloy composite process according to claim 2, characterized in that, The copper plating brightening agent is prepared by the following method: Add 390-430 parts of formic acid to a reaction tank, add 1-2 parts of melamine under stirring, stir until the solids are dissolved, then add 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight less than 8000, 40-60 parts of cobalt acetate, and 390-430 parts of pure water, and stir until the solids are dissolved to obtain the brightening agent.

4. The magnesium alloy galvanized iron alloy combination process according to claim 1, characterized in that, The cyanide-free copper-zinc alloy coating is prepared by using a polymeric thiocyanate copper-zinc alloy plating process: Copper(I) thiocyanate 18 - 24 g / L, zinc thiocyanate 9 - 13 g / L, sodium thiocyanate 130 - 170 g / L, brightener for copper-zinc alloy plating 8 - 12 mL / L, pH value of plating solution 10 - 12, bath temperature 35 - 55 °C, cathode current density 0.5 - 1.5 A / dm 2 , cathode moving speed 3 - 5 m / min, using brass plate with 68% mass fraction of copper as anode, area ratio of anode to cathode > 2:1, anode moving speed 3 - 5 m / min.

5. The magnesium alloy galvanized iron alloy combination process according to claim 1, characterized in that, The highly corrosion-resistant nickel-phosphorus alloy coating is prepared by using the PROTEXYER 8713 nickel-phosphorus alloy plating process with high corrosion resistance: PROTEXYER 8713 Hull Cell conditioner 580 - 620 mL / L, nickel sulfate hexahydrate 280 - 340 g / L, bath pH 2.6 - 2.7, bath temperature 60 - 65 °C, cathode current density 3 - 6 A / dm 2 , cathode movement 3 - 5 m / min.

6. The magnesium alloy zinc-iron alloy combination process according to claim 1, characterized in that: The described silane chromium-free passivation layer is prepared by using the zinc-based ZECCOAT-888FL silane chromium-free passivation process: Use the undiluted ZECCOAT-888FL silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure at 80 - 100 °C for 20 - 30 min; The described silane chromium-free passivation layer is prepared by using the zinc-based ZEC-COAT 825 chromium-free passivation process of Superbond Chemical Industry: Use the undiluted ZECCOAT-825 silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure at 75 - 85 °C for 20 - 30 min; The described silane chromium-free passivation layer is prepared by using the zinc-based ZECCOAT-888 silane chromium-free passivation process of Superbond Chemical Industry: Use the undiluted ZECCOAT-888 silane chromium-free passivation agent, operate at room temperature, immerse for 30 - 90 s, and after the workpiece is passivated, dry and cure at 75 - 85 °C for 20 - 30 min; The described silane chromium-free passivation layer is prepared by using the zinc-based ZEC-W silane chromium-free passivation process of Superbond Chemical Industry: Use the undiluted ZEC-W silane chromium-free passivation agent, the pH value of the passivation solution is 4.0 - 4.5, operate at room temperature, immerse for 10 - 15 s, and after the workpiece is passivated, dry and cure at 115 - 125 °C for 18 - 25 min.

7. The magnesium alloy galvanized iron alloy combination process according to claim 1, characterized in that, The described sealing layer is prepared by using the PRODICO 480 graphene-modified sealing agent; Dilute the PRODICO 480 graphene-modified sealing agent with water to 2.5 - 3.2 times to prepare a sealing solution. Immerse the plated parts in the sealing solution for 8 - 15 s, drain after taking out of the tank, and use high-pressure air to blow off the residual sealing solution on the surface of the plated parts. After sealing, dry and cure at 75 - 85 °C for 20 - 35 min.

8. A plating structure prepared by a combined process of magnesium alloy and zinc-iron alloy, characterized in that: It includes a magnesium alloy substrate, and a chemical zinc deposition layer, a cyanide-free copper plating layer, a cyanide-free copper-zinc alloy plating layer, a high-corrosion-resistant nickel-phosphorus alloy plating layer, a zinc-iron alloy plating layer, a chromium-free chemical conversion film, a silane chromium-free passivation layer, and a graphene-modified sealing layer are sequentially prepared on the magnesium alloy substrate.

9. The coating structure prepared by the magnesium alloy galvanized iron alloy combination process according to claim 8, characterized in that: The thickness of the described zinc-iron plating layer is 9 - 18 μm.

10. The coating structure prepared by the magnesium alloy galvanized iron alloy combination process according to claim 8, characterized in that: The thickness of the described cyanide-free copper plating layer is 3 - 10 μm, the thickness of the described cyanide-free copper-zinc alloy plating layer is 3 - 10 μm, and the thickness of the described high-corrosion-resistant nickel-phosphorus alloy plating layer is 7 - 13 μm.

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