Magnesium alloy micro-arc oxidation and cyanide-free cadmium-iron alloy plating process

Abstract

The invention discloses a magnesium alloy micro-arc oxidation and cyanide-free cadmium-iron alloy plating process. The process comprises the step that a micro-arc oxidation layer, a chemical nickel plating layer, a cyanide-free cadmium-iron alloy plating layer, a passivation layer and a hydrophobic protection film are sequentially prepared on a magnesium alloy matrix from inside to outside. According to the cyanide-free cadmium-iron alloy plating process, 25-35 g / L of cadmium chloride, 4-6 g / L of ferrous chloride tetrahydrate, 100-140 g / L of potassium chloride, 100-140 g / L of a coordination agent, 1.5-2.5 mL / L of a leveling agent, 1.5-2.5 mL / L of a brightening agent, 25-30 mL / L of an auxiliary agent and 25-35 g / L of a stabilizer are adopted, the pH value of a plating solution is 6-8, the temperature of a plating tank is 20-35 DEG C, the cathode current density is 0.5-1.5 A / dm < 2 >, and the cathode movement is 2-4 m / min. The surface of a prepared sample piece is free of white rust after being subjected to an acetate fog test for 400 h according to the GB / T 10125-2021 standard, and a plating layer has excellent corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process. Background Art

[0002] Magnesium alloys have the characteristics of low density, high elastic modulus, good shock absorption and high specific strength, and are widely used in the aerospace and automotive industries. However, magnesium is chemically active, resulting in poor corrosion resistance of magnesium alloys. The alloying element phase in magnesium alloys can usually form local cathode and anode with the magnesium matrix, aggravating the corrosion tendency through galvanic cell reaction.

[0003] There are many methods for magnesium alloy surface treatment, mainly electrophoretic coating, surface plating, micro-arc oxidation, anodizing, chemical conversion film, spraying organic coating and other technologies. [1] However, these surface treatment methods have certain limitations, and the protective effect needs to be further improved. At present, in production applications, electrophoretic coating technology is mainly used to prepare protective layers on the surface of magnesium alloy parts, and other protective technologies are less used.

[0004] The micro-arc oxidation conversion film on the surface of magnesium alloy usually contains more pores. This protective layer alone is not enough to prevent the aluminum alloy substrate from corrosion. [2] .

[0005] The technology of preparing protective layer on magnesium alloy surface by electroplating and chemical plating is still in the research stage. The industry has reported some research on electroplating nickel and chemical plating nickel on magnesium alloy. [3-4] The nickel-plated layer and chemical nickel-plated layer prepared on the surface of magnesium alloy have no electrochemical protective effect on the magnesium alloy substrate, and there is a large potential difference between the two. The electroplated nickel layer and chemical nickel-plated layer prepared by the prior art usually contain a certain number of pores. The corrosive medium passes through the pores of the plating layer to cause galvanic corrosion and destroy the magnesium alloy substrate. Therefore, the corrosion resistance of this plating structure is also poor, which limits its application.

[0006] The pore surface of the micro-arc oxidation film on the surface of the magnesium alloy has a negative charge. The nickel ions in the chemical nickel plating solution can be reduced and deposited in the micropores of the micro-arc oxidation layer without sensitization and activation, forming tiny primary nickel particles. Therefore, chemical nickel plating can be directly performed on the micro-arc oxidation layer of the magnesium alloy workpiece to prepare a chemical nickel plating layer. [5] .

[0007] References: [1]. Fu Haifeng, Lv Dongxian, Tan Huachao, et al., Research status and trends of magnesium alloy surface modification technology [J], Heat Treatment, 2015, 30(3): 1-5. [2]. Liu Fengjuan, Sun Lili, Yu Feng, et al., Preparation of micro-arc oxidation thermal control film on LA141 magnesium-lithium alloy surface [J], Corrosion and Protection, 2022, 43(9): 17-22. [3]. Yu Gang, Yi Xiangrong, Lei Xiping, et al., Study on the formation mechanism and electroplating process of electrodeposited nickel on magnesium alloy [J], Electroplating and Environmental Protection, 2009, 29(1): 21-25. [4]. Zhang Xiaohuan, Feng Lajun, Lu Man, Optimization of chemical nickel-phosphorus plating process and coating performance on magnesium alloy surface [J], Materials Protection, 2022, 55(6): 86-91. [5]. Fu Ming, Li Junming, Composite modification effect of micro-arc oxidation / chemical nickel plating on magnesium alloy surface[J], Materials Protection, 2022, 52(6): 79-83. Summary of the invention

[0008] In order to solve the problem of poor corrosion resistance of the existing electroplated protective layer of magnesium alloy, the present invention provides a magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process. In order to achieve the above purpose, the present invention adopts the following technical solutions: A magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process, comprising the following steps: (1) Use the current pre-treatment process to degrease and pickle the magnesium alloy workpiece; (2) After the magnesium alloy workpiece is pre-treated, the micro-arc oxidation layer is prepared by using the current magnesium alloy micro-arc oxidation process; (3) A chemical nickel plating process is used to prepare a chemical nickel plating layer on a magnesium alloy workpiece after micro-arc oxidation; (4) After the magnesium alloy workpiece is electrolessly nickel-plated, a cyanide-free cadmium-iron alloy coating is prepared by a cyanide-free cadmium-iron alloy plating process; (5) The magnesium alloy workpiece is plated with cadmium iron alloy and then passivated to prepare a passivation layer; (6) Preparation of a hydrophobic protective film after passivation of the cadmium-iron alloy coating on a magnesium alloy workpiece; The cyanide-free cadmium iron alloy plating process includes the following components and process parameters: Cadmium chloride 25-35g / L, ferrous chloride tetrahydrate 4-6g / L, potassium chloride 100-140g / L, complexing agent 100-140g / L, leveling agent 1.5-2.5mL / L, brightener 1.5-2.5mL / L, auxiliary agent 25-30mL / L, stabilizer 25-35g / L, plating solution pH 6-8, plating tank temperature 20-35℃, cathode current density 0.5-1.5A / dm 2 , cathode moves 2-4 m / min; The leveling agent includes 5-10 g / L of trimercapto-s-triazine, 30-60 g / L of organic amine epoxy derivative with model number GDX, and 5-10 g / L of sodium hydroxide; The stabilizer comprises sodium glucoheptanoate and sodium hydrogen succinate, and the mass ratio of sodium glucoheptanoate to sodium hydrogen succinate is 1:(2-3); The ligand comprises nitrilotriacetic acid, sulfosalicylic acid and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid and malic acid is 3:(1-2):(4-6).

[0009] In some embodiments, the brightener in the cyanide-free cadmium iron alloy plating process includes three components A, B, and C, component A includes α-vinyl-N-propanesulfonic acid pyridine inner salt, component B includes any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde, and 4-methoxybenzaldehyde, and component C includes any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate, and N,N-diethylpropargylamine sulfate; wherein component A is 30-80 g / L, component B is 30-80 g / L, component C is 60-100 g / L, and isopropyl alcohol is 280-320 g / L.

[0010] In some of the embodiments, the auxiliary agent in the cyanide-free cadmium iron alloy plating process includes polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate composed of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, and component D is consistent with component C in the brightener; 5-8kg of polyacrylamide with a molecular weight less than 8000, 2-5kg of condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 3-8kg of sodium salt of 2-ethylhexyl sulfate, and 3-6kg of component D are added to 70kg of water, stirred to dissolve, and water is added to 100L to obtain the auxiliary agent.

[0011] In some embodiments, the magnesium alloy micro-arc oxidation process includes the following components and process parameters: Sodium phosphate 10-14g / L, potassium hydroxide 1.8-2.2g / L, potassium fluorozirconate 2-3g / L, constant current mode, anode current density 6A / dm 2 , pulse frequency 500Hz, duty cycle 20%, oxidation time 8-12min, electrolyte temperature 20-25℃, magnesium alloy workpiece as anode and titanium plate as cathode.

[0012] In some embodiments, the chemical nickel plating layer is prepared by ERANI GG-186 alkaline chemical nickel plating process: ERANI GG-186 A additive 35~45mL / L, ERANI GG-186 B ​​reducing agent 140~160mL / L, operating temperature 85~92℃, plating solution pH 8~9.5.

[0013] In some of the embodiments, the passivation layer includes a hexavalent chromium color passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a hexavalent chromium olive drab passivation layer.

[0014] In some of the embodiments, the hexavalent chromium color passivation layer is prepared by HC-5 low chromium color passivation process: the volume concentration of HC-5 high protection low chromium color passivator is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15s, and weak air stirring or workpiece swinging is performed.

[0015] In some of the embodiments, the hexavalent chromium military green passivation layer is prepared using the OVG-31 military green passivation process: OVG-31 military green passivator 80-120 mL / L, passivation solution pH 1.0-1.6, passivation temperature 20-30°C, passivation time 30-90s, weak air stirring or swinging the plated piece.

[0016] In some of the embodiments, the hexavalent chromium black passivation layer is prepared by BZ-71 cadmium plating black passivation process: BZ-71A cadmium plating black passivation agent 80-100mL / L, BZ-71B cadmium plating black passivation agent 80-100mL / L, passivation solution pH 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40s, weak air stirring or swinging the plated piece.

[0017] In some of the embodiments, the hexavalent chromium olive drab passivation layer is prepared by the UC-91 cadmium plating olive drab passivation process: chromic anhydride 25-45 g / L, phosphoric acid 8-16 ml / L, UC-91 activator 4-8 ml / L, UC-91 colorant 1-2 g / L, passivation temperature 20-28°C, passivation time 30-60 s, weak air stirring or swinging the workpiece.

[0018] In some of the embodiments, the thickness of the cyanide-free cadmium iron coating is 10-22 μm.

[0019] In some embodiments, the thickness of the chemically plated nickel layer is 8-16 μm.

[0020] In some embodiments, the pickling activation adopts the following magnesium alloy pickling activation process: Phosphoric acid 23-28 mL / L, ammonium bifluoride 18-22 g / L, room temperature operation, pickling time 50-70 s.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process of the present invention prepares a chemical nickel plating layer on the micro-arc oxidation layer on the surface of the magnesium alloy. This technical combination can significantly improve the wear resistance and scratch resistance of the magnesium alloy workpiece; 2. The magnesium alloy micro-arc oxidation and cyanide-free cadmium-iron alloy plating process of the present invention prepares a cadmium-iron alloy plating layer on the chemical nickel plating layer. The cadmium-iron alloy plating layer is an anodic plating layer. This plating structure can effectively prevent the corrosive medium from corroding the magnesium alloy substrate, thus overcoming the technical defect that direct nickel plating or chemical nickel plating on the magnesium alloy substrate does not have an electrochemical protective effect. 3. The combined coating prepared by the magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process of the present invention on magnesium alloy parts has excellent corrosion resistance, which overcomes the problem of poor corrosion resistance of metal coatings prepared on the surface of magnesium alloys in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 It is a schematic diagram of the coating structure of Example 1, Example 2, Example 3 and Example 4 of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0024] A magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process comprises the following steps: pre-treatment of a magnesium alloy workpiece, and sequentially preparing a micro-arc oxidation layer, a chemical nickel plating layer, a cyanide-free cadmium iron alloy plating layer, a passivation layer, and a hydrophobic protective film on a magnesium alloy substrate from the inside to the outside.

[0025] The magnesium alloy pretreatment process is used to remove oil, pickle and activate the magnesium alloy workpiece.

[0026] Preferably, the oil removal adopts a weak alkaline ultrasonic oil removal process: Sodium phosphate 20-25g / L, sodium carbonate 20-25g / L, Jintel NP-10 degreasing agent 0.5-1.5g / L, tank temperature 65-75℃, degreasing time 8-12min.

[0027] Preferably, the pickling activation adopts the following pickling activation process: Phosphoric acid 23-28 mL / L, ammonium bifluoride 18-22 g / L, room temperature operation, pickling time 50-70 s.

[0028] After pretreatment of the magnesium alloy workpiece, the micro-arc oxidation layer is prepared by the following magnesium alloy micro-arc oxidation process.

[0029] Preferably, the magnesium alloy micro-arc oxidation process includes the following components and process parameters: Sodium phosphate 10-14g / L, potassium hydroxide 1.8-2.2g / L, potassium fluorozirconate 2-3g / L, constant current mode, anode current density 6A / dm 2 , pulse frequency 500Hz, duty cycle 20%, oxidation time 8-12min, electrolyte temperature 20-25℃, magnesium alloy workpiece as anode and titanium plate as cathode.

[0030] The magnesium alloy workpiece is subjected to micro-arc oxidation and then an electroless nickel plating layer is prepared by using the existing alkaline electroless nickel plating process.

[0031] Preferably, the thickness of the chemical nickel plating layer is 8 to 16 μm.

[0032] Preferably, the chemical nickel plating layer is prepared by using ERANI GG-186 alkaline chemical nickel plating process: ERANI GG-186 A additive 35~45mL / L, ERANI GG-186 B ​​reducing agent 140~160mL / L, operating temperature 85~92℃, plating solution pH 8~9.5.

[0033] After the magnesium alloy workpiece is chemically nickel-plated, the cyanide-free cadmium-iron alloy plating process of the invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer.

[0034] Preferably, the thickness of the cyanide-free cadmium iron alloy coating is 10 to 22 μm.

[0035] Preferably, the cyanide-free cadmium iron alloy plating process includes the following components and process parameters: Cadmium chloride 25-35g / L, ferrous chloride tetrahydrate 4-6g / L, potassium chloride 100-140g / L, complexing agent 100-140g / L, leveling agent 1.5-2.5mL / L, brightener 1.5-2.5mL / L, auxiliary agent 25-30mL / L, stabilizer 25-35g / L, plating solution pH 6-8, plating tank temperature 20-35℃, cathode current density 0.5-1.5A / dm 2 , the cathode moves 2 to 4 m / min.

[0036] Preferably, the leveling agent includes 5-10 g / L of trimercapto-s-triazine, 30-60 g / L of an organic amine epoxy derivative of model GDX, and 5-10 g / L of sodium hydroxide.

[0037] Preferably, the stabilizer comprises sodium gluconate and sodium hydrogen succinate, and the mass ratio of sodium gluconate to sodium hydrogen succinate is 1:(2-3).

[0038] Preferably, the ligand comprises nitrilotriacetic acid, sulfosalicylic acid, and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6).

[0039] Preferably, the brightener comprises three components A, B and C, wherein component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt, component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde and 4-methoxybenzaldehyde, and component C comprises any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate and N,N-diethylpropargylamine sulfate; wherein component A is 30-80 g / L, component B is 30-80 g / L, component C is 60-100 g / L, and isopropyl alcohol is 280-320 g / L.

[0040] Preferably, the auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, and component D is consistent with component C in the brightener; 5-8kg of polyacrylamide with a molecular weight less than 8000, 2-5kg of condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 3-8kg of sodium salt of 2-ethylhexyl sulfate, and 3-6kg of component D are added to 70kg of water, stirred to dissolve, and water is added to 100L to obtain the auxiliary agent.

[0041] The magnesium alloy workpiece is plated with cadmium-iron alloy and a cadmium-iron alloy coating post-treatment process is used to prepare a passivation layer.

[0042] Preferably, the passivation layer includes a hexavalent chromium color passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a hexavalent chromium olive drab passivation layer.

[0043] Preferably, the hexavalent chromium color passivation layer is prepared by HC-5 low-chrome color passivation process: the volume concentration of HC-5 high-protection low-chrome color passivator is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15s, and weak air stirring or workpiece swinging is performed.

[0044] Preferably, the hexavalent chromium military green passivation layer is prepared by OVG-31 military green passivation process: OVG-31 military green passivator 80-120 mL / L, passivation solution pH 1.0-1.6, passivation temperature 20-30°C, passivation time 30-90s, weak air stirring or swinging the plated piece.

[0045] Preferably, the hexavalent chromium black passivation layer is prepared by BZ-71 cadmium plating black passivation process: BZ-71A cadmium plating black passivation agent 80-100mL / L, BZ-71B cadmium plating black passivation agent 80-100mL / L, passivation solution pH value 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40s, weak air stirring or swinging the plated piece.

[0046] Preferably, the hexavalent chromium olive drab passivation layer is prepared by the UC-91 cadmium plating olive drab passivation process: chromic anhydride 25-45 g / L, phosphoric acid 8-16 mL / L, UC-91 activator 4-8 mL / L, UC-91 colorant 1-2 g / L, passivation temperature 20-28°C, passivation time 30-60 s, weak air stirring or swinging the workpiece.

[0047] After the magnesium alloy workpiece is passivated, a hydrophobic protective film is prepared using the current hydrophobic protective agent.

[0048] Preferably, the hydrophobic protective film is prepared using PROTEZVY RA plating anti-discoloration agent produced by Chaobang Chemical: PROTEZVY RA anti-tarnish agent for plated parts is 5-15 mL / L, the bath temperature is 60-80°C, and the immersion time is 10-20 seconds.

[0049] The magnesium alloy workpiece is naturally dried after hydrophobic protection.

[0050] Embodiment 2: like Figure 1 As shown, a magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a micro-arc oxidation layer 2, a chemical nickel plating layer 3, a cyanide-free cadmium iron alloy plating layer 4, a hexavalent chromium military green passivation layer 5, and a hydrophobic protective film 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0051] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0052] 1) Degreasing: The following weak alkaline ultrasonic degreasing process was used: sodium phosphate 25 g / L, sodium carbonate 25 g / L, Jintel NP-10 degreasing agent 0.8 g / L, tank temperature 65°C, and degreasing time 10 min.

[0053] 2) Pickling activation: The following magnesium alloy pickling activation process was adopted: 28 mL / L phosphoric acid, 22 g / L ammonium bifluoride, room temperature operation, and pickling time of 50 s.

[0054] 2. Micro-arc oxidation: After the magnesium alloy workpiece is pre-treated, the micro-arc oxidation layer 2 is prepared by the following magnesium alloy micro-arc oxidation process.

[0055] Sodium phosphate 14g / L, potassium hydroxide 2.2g / L, potassium fluorozirconate 3g / L, constant current mode, anode current density 6A / dm 2 , pulse frequency 500 Hz, duty cycle 20%, oxidation time 8 min, electrolyte temperature 20 °C, magnesium alloy workpiece as anode, and titanium plate as cathode.

[0056] 3. Chemical nickel plating: After micro-arc oxidation, the magnesium alloy workpiece is subjected to ERANI GG-186 alkaline chemical nickel plating process of Chaobang Chemical to prepare a chemical nickel plating layer 3, and the coating thickness is 12 μm.

[0057] ERANI GG-186 A additive 45mL / L, ERANI GG-186 B ​​reducing agent 160mL / L, operating temperature 85℃, plating solution pH 9.2.

[0058] 4. Cadmium-plated iron alloy: After the magnesium alloy workpiece is electrolessly nickel-plated, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy coating 4, and the coating thickness is 16 μm.

[0059] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of organic amine epoxy derivatives with the product model GDX sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. According to the formula requirements, sodium hydroxide is dissolved in water, and trimercapto-s-triazine is added, stirred to dissolve, and then the organic amine epoxy derivative with the model GDX is added, and water is added to the required volume to obtain the leveling agent.

[0060] 2) Preparation of stabilizer: The stabilizer includes sodium glucoheptanoate and sodium hydrogen succinate, and the mass ratio of sodium glucoheptanoate to sodium hydrogen succinate is 1:2.5. Sodium glucoheptanoate and sodium hydrogen succinate are mixed together according to the formula ratio requirements, and stirred evenly to obtain the stabilizer.

[0061] 3) Preparation of complexing agent: The complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:1.5:5. Nitrilotriacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formula ratio and stirred evenly to obtain the complexing agent.

[0062] 4) Prepare brightener: The brightener comprises three components: A, B and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt, component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde and 4-methoxybenzaldehyde, and component C comprises any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate and N,N-diethylpropargylamine sulfate. 30kg of isopropanol is added to 40kg of water and mixed evenly, 5.5kg of component A, 4kg of component B and 8kg of component C are added, stirred to dissolve, and water is added to 100L to obtain the brightener.

[0063] 5) Preparation of auxiliary agents: The auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and a D component, wherein the D component is consistent with the C component in the brightener; 6.5 kg of polyacrylamide with a molecular weight less than 8000, 3.5 kg of a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium salt of 2-ethylhexyl sulfate, and 4.5 kg of the D component are added to 70 kg of water, stirred to dissolve, and water is added to 100 L to obtain the auxiliary agent.

[0064] 6) Preparation of cadmium iron alloy plating solution: a) Add 4 / 5 of water into the plating tank according to the volume of the plating solution, add sodium hydroxide, potassium chloride and complexing agent according to the process requirements, the mass ratio of sodium hydroxide to complexing agent is 1:2, and stir to dissolve the above substances; b) Add cadmium chloride and ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add leveling agent, brightener, auxiliary agent, and stabilizer according to the process requirements, stir until the stabilizer is completely dissolved, adjust the pH of the plating solution to 6.5 with a 10% sodium hydroxide solution, add water to the specified volume, and heat at 0.1A / dm 2 The electrolysis was carried out for 4 h at the current density.

[0065] 7) Plating: Cadmium chloride 28g / L, ferrous chloride tetrahydrate 4.7g / L, potassium chloride 135g / L, complexing agent 125g / L, leveling agent 2.0mL / L, brightener 2.0mL / L, auxiliary agent 28mL / L, stabilizer 28g / L, plating solution pH 6.5, plating tank temperature 32℃, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0066] 5. Hexavalent chromium military green passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the military green passivation layer 5 is prepared using Chaobang Chemical's OVG-31 military green passivation process.

[0067] OVG-31 military green passivator 100mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 60s, swing plated parts.

[0068] The specific process is "lightening with 1.5% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0069] 6. Hydrophobic protection: After the magnesium alloy workpiece is passivated, a hydrophobic protective film 6 is prepared using PROTEZVY RA plating anti-discoloration agent produced by Chaobang Chemical.

[0070] PROTEZVY RA anti-tarnish agent for plated parts is 15mL / L, the bath temperature is 60℃, and the immersion time is 12s.

[0071] 7. Drying: The magnesium alloy workpiece is naturally dried after hydrophobic protection.

[0072] Embodiment 3: like Figure 1 As shown, a magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a micro-arc oxidation layer 2, a chemical nickel plating layer 3, a cyanide-free cadmium iron alloy plating layer 4, a hexavalent chromium black passivation layer 5, and a hydrophobic protective film 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0073] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0074] 1) Degreasing: The following weak alkaline ultrasonic degreasing process was used: sodium phosphate 25 g / L, sodium carbonate 20 g / L, Jintel NP-10 degreasing agent 1.0 g / L, tank temperature 70°C, and degreasing time 10 min.

[0075] 2) Pickling activation: The following magnesium alloy pickling activation process was adopted: 26 mL / L phosphoric acid, 20 g / L ammonium bifluoride, room temperature operation, and pickling time of 60 s.

[0076] 2. Micro-arc oxidation: After the magnesium alloy workpiece is pre-treated, the micro-arc oxidation layer 2 is prepared by the following magnesium alloy micro-arc oxidation process.

[0077] Sodium phosphate 10g / L, potassium hydroxide 1.8g / L, potassium fluorozirconate 2g / L, constant current mode, anode current density 6A / dm 2, pulse frequency 500 Hz, duty cycle 20%, oxidation time 12 min, electrolyte temperature 25 °C, magnesium alloy workpiece as anode, and titanium plate as cathode.

[0078] 3. Chemical nickel plating: After micro-arc oxidation, the magnesium alloy workpiece is subjected to ERANI GG-186 alkaline chemical nickel plating process of Chaobang Chemical to prepare a chemical nickel plating layer 3, and the coating thickness is 12 μm.

[0079] ERANI GG-186 A additive 35mL / L, ERANI GG-186 B ​​reducing agent 140mL / L, operating temperature 92℃, plating solution pH 9.

[0080] 4. Cadmium-plated iron alloy: After the magnesium alloy workpiece is electrolessly nickel-plated, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy coating 4, and the coating thickness is 16 μm.

[0081] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of organic amine epoxy derivatives with the product model GDX sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. According to the formula requirements, sodium hydroxide is dissolved in water, and trimercapto-s-triazine is added, stirred to dissolve, and then the organic amine epoxy derivative with the model GDX is added, and water is added to the required volume to obtain the leveling agent.

[0082] 2) Preparation of stabilizer: The stabilizer includes sodium glucoheptanoate and sodium hydrogen succinate, and the mass ratio of sodium glucoheptanoate to sodium hydrogen succinate is 1:2.5. Sodium glucoheptanoate and sodium hydrogen succinate are mixed together according to the formula ratio requirements, and stirred evenly to obtain the stabilizer.

[0083] 3) Preparation of complexing agent: The complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:1.5:5. Nitrilotriacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formula ratio and stirred evenly to obtain the complexing agent.

[0084] 4) Prepare brightener: The brightener comprises three components: A, B and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt, component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde and 4-methoxybenzaldehyde, and component C comprises any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate and N,N-diethylpropargylamine sulfate. 30kg of isopropanol is added to 40kg of water and mixed evenly, 5.5kg of component A, 4kg of component B and 8kg of component C are added, stirred to dissolve, and water is added to 100L to obtain the brightener.

[0085] 5) Preparation of auxiliary agents: The auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and a D component, wherein the D component is consistent with the C component in the brightener; 6.5 kg of polyacrylamide with a molecular weight less than 8000, 3.5 kg of a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium salt of 2-ethylhexyl sulfate, and 4.5 kg of the D component are added to 70 kg of water, stirred to dissolve, and water is added to 100 L to obtain the auxiliary agent.

[0086] 6) Preparation of cadmium iron alloy plating solution: a) Add 4 / 5 of water into the plating tank according to the volume of the plating solution, add sodium hydroxide, potassium chloride and complexing agent according to the process requirements, the mass ratio of sodium hydroxide to complexing agent is 1:2, and stir to dissolve the above substances; b) Add cadmium chloride and ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add leveling agent, brightener, auxiliary agent, and stabilizer according to the process requirements, stir until the stabilizer is completely dissolved, adjust the pH of the plating solution to 7.5 with a 10% sodium hydroxide solution, add water to the specified volume, and heat at 0.1A / dm 2 The electrolysis was carried out for 4 h at the current density.

[0087] 7) Plating: Cadmium chloride 35g / L, ferrous chloride tetrahydrate 6g / L, potassium chloride 140g / L, complexing agent 140g / L, leveling agent 2.0mL / L, brightener 2.0mL / L, auxiliary agent 28mL / L, stabilizer 35g / L, plating solution pH 7.5, plating tank temperature 20℃, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0088] 5. Hexavalent chromium black passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the hexavalent chromium black passivation layer 5 is prepared using the BZ-71 cadmium black passivation process of Chaobang Chemical.

[0089] BZ-71A cadmium black passivation agent 90mL / L, BZ-71B cadmium black passivation agent 90mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 28s, swing plated parts.

[0090] The specific process is "lightening with 1.5% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0091] 6. Hydrophobic protection: After the magnesium alloy workpiece is passivated, a hydrophobic protective film 6 is prepared using PROTEZVY RA plating anti-discoloration agent produced by Chaobang Chemical.

[0092] PROTEZVY RA anti-tarnish agent for plated parts 5mL / L, bath temperature 80℃, immersion time 12s.

[0093] 7. Drying: The magnesium alloy workpiece is naturally dried after hydrophobic protection. Example

[0094] like Figure 1 As shown, a magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a micro-arc oxidation layer 2, a chemical nickel plating layer 3, a cyanide-free cadmium iron alloy plating layer 4, a hexavalent chromium olive-drab passivation layer 5, and a hydrophobic protective film 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0095] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0096] 1) Degreasing: The following weak alkaline ultrasonic degreasing process was used: sodium phosphate 20 g / L, sodium carbonate 25 g / L, Jintel NP-10 degreasing agent 1.0 g / L, tank temperature 70°C, and degreasing time 10 min.

[0097] 2) Pickling activation: The following magnesium alloy pickling activation process was adopted: 24 mL / L phosphoric acid, 19 g / L ammonium bifluoride, room temperature operation, and pickling time of 65 s.

[0098] 2. Micro-arc oxidation: After the magnesium alloy workpiece is pre-treated, the micro-arc oxidation layer 2 is prepared by the following magnesium alloy micro-arc oxidation process.

[0099] Sodium phosphate 13g / L, potassium hydroxide 2.1g / L, potassium fluorozirconate 2.8g / L, constant current mode, anode current density 6A / dm 2 , pulse frequency 500 Hz, duty cycle 20%, oxidation time 9 min, electrolyte temperature 21 °C, magnesium alloy workpiece as anode, and titanium plate as cathode.

[0100] 3. Chemical nickel plating: After micro-arc oxidation, the magnesium alloy workpiece is subjected to ERANI GG-186 alkaline chemical nickel plating process of Chaobang Chemical to prepare a chemical nickel plating layer 3, and the coating thickness is 12 μm.

[0101] ERANI GG-186 A additive 42mL / L, ERANI GG-186 B ​​reducing agent 155mL / L, operating temperature 87℃, and plating solution pH 8.8.

[0102] 4. Cadmium-plated iron alloy: After the magnesium alloy workpiece is electrolessly nickel-plated, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy coating 4, and the coating thickness is 16 μm.

[0103] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of organic amine epoxy derivatives with the product model GDX sold by Sefik New Materials Co., Ltd., and 7.5 g / L of sodium hydroxide. According to the formula requirements, sodium hydroxide is dissolved in water, and trimercapto-s-triazine is added, stirred to dissolve, and then the organic amine epoxy derivative with the model GDX is added, and water is added to the required volume to obtain the leveling agent.

[0104] 2) Preparation of stabilizer: The stabilizer includes sodium glucoheptanoate and sodium hydrogen succinate, and the mass ratio of sodium glucoheptanoate to sodium hydrogen succinate is 1:2.5. Sodium glucoheptanoate and sodium hydrogen succinate are mixed together according to the formula ratio requirements, and stirred evenly to obtain the stabilizer.

[0105] 3) Preparation of complexing agent: The complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:1.5:5. Nitrilotriacetic acid, sulfosalicylic acid, and malic acid are mixed together according to the formula ratio and stirred evenly to obtain the complexing agent.

[0106] 4) Prepare brightener: The brightener comprises three components: A, B and C. Component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt, component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde and 4-methoxybenzaldehyde, and component C comprises any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate and N,N-diethylpropargylamine sulfate. 30kg of isopropanol is added to 40kg of water and mixed evenly, 5.5kg of component A, 4kg of component B and 8kg of component C are added, stirred to dissolve, and water is added to 100L to obtain the brightener.

[0107] 5) Preparation of auxiliary agents: The auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, and a D component, wherein the D component is consistent with the C component in the brightener; 6.5 kg of polyacrylamide with a molecular weight less than 8000, 3.5 kg of a condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 5.5 kg of sodium salt of 2-ethylhexyl sulfate, and 4.5 kg of the D component are added to 70 kg of water, stirred to dissolve, and water is added to 100 L to obtain the auxiliary agent.

[0108] 6) Preparation of cadmium iron alloy plating solution: a) Add 4 / 5 of water into the plating tank according to the volume of the plating solution, add sodium hydroxide, potassium chloride and complexing agent according to the process requirements, the mass ratio of sodium hydroxide to complexing agent is 1:2, and stir to dissolve the above substances; b) Add cadmium chloride and ferrous chloride tetrahydrate according to the process requirements and stir until the solid matter is dissolved; c) Add leveling agent, brightener, auxiliary agent, and stabilizer according to the process requirements, stir until the stabilizer is completely dissolved, adjust the pH of the plating solution to 8 with a 10% mass fraction of sodium hydroxide solution, add water to the specified volume, and heat at 0.1A / dm 2 The electrolysis was carried out for 4 h at the current density.

[0109] 7) Plating: Cadmium chloride 25g / L, ferrous chloride tetrahydrate 4g / L, potassium chloride 140g / L, complexing agent 100g / L, leveling agent 2.0mL / L, brightener 2.0mL / L, auxiliary agent 28mL / L, stabilizer 25g / L, plating solution pH 8, plating tank temperature 30℃, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0110] 5. Hexavalent chromium olive color passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the hexavalent chromium olive passivation layer 5 is prepared by using the UC-91 cadmium hexavalent chromium olive passivation process of Chaobang Chemical.

[0111] Chromic anhydride 30g / L, phosphoric acid 12ml / L, UC-91 activator 6ml / L, UC-91 colorant 1.5g / L, passivation temperature 25℃, passivation time 45s, swing the workpiece.

[0112] The specific process is "lightening with 1.5% volume fraction nitric acid → water washing → passivation → water washing → draining after leaving the tank".

[0113] 6. Hydrophobic protection: After the magnesium alloy workpiece is passivated, a hydrophobic protective film 6 is prepared using PROTEZVY RA plating anti-discoloration agent produced by Chaobang Chemical.

[0114] PROTEZVY RA anti-tarnish agent for plated parts is 13mL / L, the bath temperature is 65℃, and the immersion time is 12s.

[0115] 7. Drying: The magnesium alloy workpiece is naturally dried after hydrophobic protection.

[0116] Test Example 1: According to the standard GB / T 10125-2021 "Artificial atmosphere corrosion test salt spray test", the acetic acid salt spray test was carried out. The magnesium alloy cadmium iron alloy hexavalent chromium color passivation sample prepared in Example 1 had no white rust on the surface after 400 hours, the magnesium alloy cadmium iron alloy hexavalent chromium military green passivation sample prepared in Example 2 had no white rust on the surface after 424 hours, the magnesium alloy cadmium iron alloy hexavalent chromium black passivation sample prepared in Example 3 had no white rust on the surface after 376 hours, and the magnesium alloy cadmium iron alloy hexavalent chromium olive drab passivation sample prepared in Example 4 had no white rust on the surface after 398 hours. The prepared coatings have excellent corrosion resistance.

[0117] Test Example 2: The magnesium alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, Example 3, and Example 4 were tested for coating adhesion in accordance with GB / T5270-2005 "Review of test methods for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates". The magnesium alloy cadmium-plated iron alloy was placed in a heating furnace and heated to 150°C for 30 minutes. After being taken out, it was immediately cooled in water at room temperature. There was no blistering or shedding of the coating, and the coating adhesion met the standard requirements.

[0118] Test Example 3: The magnesium alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, Example 3, and Example 4 were tested for 760 hours at a temperature of 40°C and a relative humidity of 93% in accordance with GB / T2423.3-2016 "Basic Environmental Test Procedures for Electrical and Electronic Products Test Ca: Steady State Wet Heat Test Method". There was no visible change in the coating, thus meeting the technical requirements of the industry.

[0119] Test example 4: The magnesium alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, Example 3, and Example 4 were subjected to a mold test for 28 days in accordance with GJB150.9A-2009 "Military Equipment Laboratory Environmental Test Method Part 10: Mold Test". No mold grew on the surface of the samples, which met the environmental test requirements.

[0120] The technical solutions provided by the embodiments of the present invention are described in detail above. The principles and implementation methods of the embodiments of the present invention are described in detail using specific examples herein. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which are also considered to fall within the protection scope of the present invention.

Claims

1. A magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process, characterized in that: The following steps are involved: (1) Use the current pre-treatment process to degrease and pickle the magnesium alloy workpiece; (2) After the magnesium alloy workpiece is pre-treated, the micro-arc oxidation layer is prepared by using the current magnesium alloy micro-arc oxidation process; (3) A chemical nickel plating process is used to prepare a chemical nickel plating layer on a magnesium alloy workpiece after micro-arc oxidation; (4) After the magnesium alloy workpiece is electrolessly nickel-plated, a cyanide-free cadmium-iron alloy coating is prepared by a cyanide-free cadmium-iron alloy plating process; (5) The magnesium alloy workpiece is plated with cadmium iron alloy and then passivated to prepare a passivation layer; (6) Preparation of a hydrophobic protective film after passivation of the cadmium-iron alloy coating on a magnesium alloy workpiece; The cyanide-free cadmium iron alloy plating process includes the following components and process parameters: Cadmium chloride 25-35g / L, ferrous chloride tetrahydrate 4-6g / L, potassium chloride 100-140g / L, complexing agent 100-140g / L, leveling agent 1.5-2.5mL / L, brightener 1.5-2.5mL / L, auxiliary agent 25-30mL / L, stabilizer 25-35g / L, plating solution pH 6-8, plating tank temperature 20-35℃, cathode current density 0.5-1.5A / dm 2 , cathode moves 2-4 m / min; The leveling agent includes 5-10 g / L of trimercapto-s-triazine, 30-60 g / L of organic amine epoxy derivative with model number GDX, and 5-10 g / L of sodium hydroxide; The stabilizer comprises sodium glucoheptanoate and sodium hydrogen succinate, and the mass ratio of sodium glucoheptanoate to sodium hydrogen succinate is 1:(2-3); The ligand comprises nitrilotriacetic acid, sulfosalicylic acid and malic acid, and the mass ratio of nitrilotriacetic acid, sulfosalicylic acid and malic acid is 3:(1-2):(4-6).

2. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The brightener in the cyanide-free cadmium iron alloy plating process comprises three components A, B and C, wherein the component A comprises α-vinyl-N-propanesulfonic acid pyridine inner salt, the component B comprises any one or two of 3-methoxy-4-hydroxybenzaldehyde, 3,4-dimethoxybenzaldehyde and 4-methoxybenzaldehyde, and the component C comprises any one or two of propargyl alcohol ethoxy ether, propargyl alcohol propoxy ether, N,N-diethylpropargylamine, N,N-diethylpropargylamine formate and N,N-diethylpropargylamine sulfate; wherein the component A is 30-80 g / L, the component B is 30-80 g / L, the component C is 60-100 g / L, and the isopropyl alcohol is 280-320 g / L.

3. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The auxiliary agent in the cyanide-free cadmium iron alloy plating process includes polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate composed of ethylenediamine or dimethylpropylamine and epichlorohydrin, and component D, and component D is consistent with component C in the brightener; 5-8kg of polyacrylamide with a molecular weight less than 8000, 2-5kg of condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin, 3-8kg of sodium salt of 2-ethylhexyl sulfate, and 3-6kg of component D are added to 70kg of water, stirred to dissolve, and water is added to 100L to obtain the auxiliary agent.

4. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The magnesium alloy micro-arc oxidation process includes the following components and process parameters: Sodium phosphate 10-14g / L, potassium hydroxide 1.8-2.2g / L, potassium fluorozirconate 2-3g / L, constant current mode, anode current density 6A / dm 2 , pulse frequency 500Hz, duty cycle 20%, oxidation time 8-12min, electrolyte temperature 20-25℃, magnesium alloy workpiece as anode and titanium plate as cathode.

5. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The chemical nickel plating layer is prepared by using ERANI GG-186 alkaline chemical nickel plating process: ERANI GG-186 A additive 35~45mL / L, ERANI GG-186 B ​​reducing agent 140~160mL / L, operating temperature 85~92℃, plating solution pH 8~9.

5.

6. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The passivation layer comprises a hexavalent chromium color passivation layer, a hexavalent chromium military green passivation layer, a hexavalent chromium black passivation layer, and a hexavalent chromium olive drab passivation layer.

7. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 6 is characterized in that: The hexavalent chromium color passivation layer is prepared by HC-5 low-chromium color passivation process: the volume concentration of HC-5 high-protection low-chromium color passivator is 2% to 4%, the passivation temperature is 20 to 35° C., the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and weak air stirring or workpiece swinging is performed; The hexavalent chromium military green passivation layer is prepared by OVG-31 military green passivation process: OVG-31 military green passivation agent 80-120 mL / L, passivation solution pH value 1.0-1.6, passivation temperature 20-30° C., passivation time 30-90 s, weak air stirring or swinging the plated piece; The hexavalent chromium black passivation layer is prepared by using the BZ-71 cadmium black passivation process: BZ-71A cadmium black passivation agent 80-100mL / L, BZ-71B cadmium black passivation agent 80-100mL / L, passivation solution pH value 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40s, weak air stirring or swinging the plated piece; The hexavalent chromium olive-drab passivation layer is prepared by the UC-91 cadmium plating olive-drab passivation process: chromic anhydride 25-45 g / L, phosphoric acid 8-16 ml / L, UC-91 activator 4-8 ml / L, UC-91 colorant 1-2 g / L, passivation temperature 20-28° C., passivation time 30-60 s, weak air stirring or swinging the workpiece.

8. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The thickness of the cyanide-free cadmium iron plating layer is 10 to 22 μm.

9. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1 is characterized in that: The thickness of the chemical nickel plating layer is 8-16 μm.

10. The magnesium alloy micro-arc oxidation and cyanide-free cadmium iron alloy plating process according to claim 1, characterized in that: The pickling activation adopts the following magnesium alloy pickling activation process: Phosphoric acid 23-28 mL / L, ammonium bifluoride 18-22 g / L, room temperature operation, pickling time 50-70 s.

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