Cyanide-free cadmium-iron alloy plating process for magnesium alloy

Abstract

The invention discloses a magnesium alloy cyanide-free cadmium-iron alloy plating process. A chemical zinc deposition layer, a cyanide-free copper-zinc alloy plating layer, a high-corrosion-resistance nickel-phosphorus alloy plating layer, a cyanide-free cadmium-iron alloy plating layer and a passivation layer are sequentially prepared on a magnesium alloy matrix from inside to outside. According to the cyanide-free cadmium iron alloy electroplating 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 the prepared magnesium alloy cadmium-plated iron alloy colored passivated sample piece is free of white rust after being subjected to an acetate fog test for 480 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 cyanide-free cadmium-iron alloy plating process for magnesium alloy. Background Art

[0002] Magnesium alloy is the lightest metal structural material in practical application. Due to its high specific strength and specific stiffness, electromagnetic shielding, shock absorption, and good cutting performance, it can be widely used in military, automobile, aircraft, mobile phone, computer, electromechanical and other industrial products, and is known as the "green engineering material of the century". However, magnesium alloy has active chemical properties, and the oxides generated on its surface are loose and porous, which cannot effectively protect the matrix. The phase containing alloy elements in magnesium alloy can usually form local cathode and anode with the magnesium matrix, and aggravate the corrosion tendency through the galvanic cell reaction. Therefore, the development of high corrosion resistance protective layer for magnesium alloy is a research hotspot in the industry.

[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 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. [2-4] 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. This plating structure has poor corrosion resistance, which limits its application.

[0005] Aluminum alloy has the characteristics of low density and high strength. It has been widely used in the preparation of aerospace parts. Aerospace electrical parts need to use electroplating technology to prepare a protective layer. Some parts need to prepare a highly corrosion-resistant cadmium plating layer to meet their technical requirements. The density of metal aluminum is 2.70g / cm 3 , the density of magnesium metal is 1.74g / cm 3 Therefore, magnesium alloys are more suitable for the special requirements of aerospace parts. However, the existing magnesium alloy electroplating and chemical plating technologies are far from meeting the growing technical needs of my country's aerospace field.

[0006] The corrosion resistance, hardness, and wear resistance of nickel-phosphorus alloy coatings are higher than those of nickel coatings. [6]Production practice has proved that the porosity of the nickel-phosphorus alloy coating prepared by electroplating is significantly lower than that of the nickel-plated layer and the chemically plated nickel-phosphorus alloy coating. Therefore, replacing the nickel-plated layer with a nickel-phosphorus alloy coating can effectively improve the corrosion resistance and other properties of the coating.

[0007] The cadmium plating layer prepared by potassium chloride cyanide-free cadmium plating process has achieved a major breakthrough in the corrosion resistance of the plating layer, providing a new solution to the problem of poor corrosion resistance of existing electroplated layers on magnesium alloys [7] .

[0008] 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]. Yu Gang, Yi Xiangrong, Lei Xiping, et al., Research on the formation mechanism and electroplating process of nickel electrodeposition on magnesium alloy [J], Electroplating and Environmental Protection, 2009, 29(1): 21-25. [3]. Zhang Xiaohuan, Feng Lajun, Lu Man, Optimization of chemical nickel-phosphorus plating process and research on coating performance on magnesium alloy surface [J], Materials Protection, 2022, 55(6): 86-91. [4]. Xu Gang, Zhang Xiuzhi, Zhang Yishuai, Preparation and performance research of Ni-P / Ni coating on magnesium alloy surface [J], Surface Technology, 2010, 39(1): 71-73+80. [5]. Qin Zhili, Guo Chongwu, Application of high corrosion resistance zinc-nickel alloy protective layer in aerospace field [J], Electroplating and Finishing, 2023, 42(9): 14-17. [6]. Zhang Chunli, Zhou Qi, Zhao Ping, Preliminary study on the process of electroplating nickel-phosphorus alloy [J], Materials Protection, 2005, 38(2): 31-33. [7]. Lai Huanwen, Guo Chongwu, Chen Mei, et al., Preparation of ultra-high corrosion resistance potassium chloride cadmium plating protective layer [J], Electroplating and Finishing, 2021, 40(23): 1762-1766. Summary of the invention

[0009] In order to solve the problem of poor corrosion resistance of the existing electroplated protective layer of magnesium alloy, the present invention provides a cyanide-free cadmium iron alloy plating process for magnesium alloy. In order to achieve the above purpose, the present invention adopts the following technical solutions: A magnesium alloy cyanide-free cadmium iron alloy plating process comprises the following steps: (1) Degreasing, pickling and activation of magnesium alloy workpieces; (2) After pretreatment of the magnesium alloy workpiece, a chemical zinc deposition layer is prepared using the current sulfate zinc plating process; (3) After the magnesium alloy workpiece is zinc-plated with sulfate, a cyanide-free copper-zinc alloy coating is prepared by a polythiocyanate copper-zinc alloy plating process; (4) After the magnesium alloy workpiece is plated with copper-zinc alloy without cyanide, a cyanide-free cadmium-iron alloy plating process is used to prepare a cyanide-free cadmium-iron alloy coating; (5) The magnesium alloy workpiece is plated with cadmium iron alloy and then post-treated to prepare a passivation layer; 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, and 5-10 g / L of sodium hydroxide; The stabilizer includes sodium gluconate and sodium hydrogen succinate, and the mass ratio of sodium gluconate to sodium hydrogen succinate is 1:(2-3); The complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid. The above components are mixed evenly to obtain the complexing agent; the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6); 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; 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; The auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate composed of ethylenediamine or dimethylpropylamine and epichlorohydrin, and a D component, wherein the D component is consistent with the C component in the brightener; wherein the polyacrylamide with a molecular weight less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20-50 g / L, the sodium salt of 2-ethylhexyl sulfate is 30-80 g / L, and the D component is 30-60 g / L.

[0010] In some of the embodiments, the thickness of the cyanide-free cadmium iron coating is 8-17 μm.

[0011] In some embodiments, the polythiocyanate copper-zinc alloy plating process includes the following components and process parameters: Polymeric cuprous thiocyanate 18-24 g / L, polymeric zinc thiocyanate 9-13 g / L, polymeric sodium thiocyanate 130-170 g / L, copper-zinc alloy electroplating brightener 8-12 mL / L, plating solution pH 10-12, plating tank temperature 35-55 ° C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3 to 5 m / min, a copper-zinc alloy plate with a copper mass fraction of 68% is used as an anode, and the anode moves 3 to 5 m / min; the copper-zinc alloy electroplating brightener comprises the following components by weight: 60 to 100 parts of N,N'-di-n-propylethylenediamine, 10 to 20 parts of water-based polyurethane resin, 80 to 120 parts of polyacrylamide with a molecular weight less than 8000, and 770 to 870 parts of deionized water.

[0012] In some of the embodiments, the thickness of the cyanide-free copper-zinc alloy coating is 8-13 μm.

[0013] In some of the embodiments, the nickel-phosphorus alloy coating is prepared by PROTEXYER 8713 high corrosion resistant nickel-phosphorus alloy coating process: PROTEXYER 8713 MU tank opener 580~620mL / L, nickel sulfate 280~340g / L, plating solution pH 2.6~2.7, plating tank temperature 60~65℃, cathode current density 3~6A / dm 2 , the cathode moves 3 to 5 m / min.

[0014] In some of the embodiments, the thickness of the nickel-phosphorus alloy coating is 6-12 μm.

[0015] 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.

[0016] In some of the embodiments, 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 15 seconds, and weak air stirring or workpiece swinging; In some of the embodiments, 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 1.0-1.6, passivation temperature 20-30° C., passivation time 30-90 s, weak air stirring or swinging the plated piece; In some of the embodiments, the hexavalent chromium black passivation layer is prepared by 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 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40s, weak air stirring or swinging the plated piece; 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.

[0017] In some of the embodiments, the acid activation adopts the current 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.

[0018] In some of the embodiments, the chemical zinc deposition layer is prepared by the following magnesium alloy chemical zinc deposition process: Zinc sulfate heptahydrate 25-35g / L, potassium pyrophosphate 100-120g / L, potassium fluoride 6-9g / L, bath temperature 68-72℃, zinc precipitation time 8-12min.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. The cyanide-free cadmium-iron alloy plating process of magnesium alloy of the present invention sequentially prepares a chemical zinc deposition layer, a copper-zinc alloy plating layer, a nickel-phosphorus alloy plating layer, and a cadmium-iron alloy plating layer on a magnesium alloy substrate. The nickel-phosphorus alloy plating layer is an anodic plating layer relative to the copper-zinc alloy plating layer, and the cadmium-iron alloy plating layer is also an anodic plating layer relative to the nickel-phosphorus alloy plating layer. This plating structure can effectively prevent the corrosion medium from corroding the magnesium alloy substrate, thus overcoming the technical defects of direct nickel plating after chemical zinc deposition on a magnesium alloy substrate or chemical nickel plating having no electrochemical protection effect; 2. The cyanide-free cadmium-iron alloy plating process of the magnesium alloy of the present invention uses a nickel-phosphorus alloy plating layer as an intermediate plating layer. After the cadmium-iron alloy plating layer is damaged, the nickel-phosphorus alloy plating layer has a high corrosion resistance, and the nickel-phosphorus alloy plating layer can still effectively prevent the corrosive medium from corroding the magnesium alloy substrate. If the nickel-phosphorus alloy plating layer in the present plating structure is deleted, when the cadmium-iron alloy plating layer is damaged, the corrosive medium will inevitably directly corrode the copper-zinc alloy plating layer, and then corrode the magnesium alloy substrate. Therefore, the cadmium-iron alloy plating structure prepared by the present invention significantly improves the corrosion resistance of the magnesium alloy plated parts, and overcomes the technical defect that the existing metal covering layer of the magnesium alloy has poor corrosion resistance; 3. The combined coating prepared by the cyanide-free cadmium-iron alloy plating process of magnesium alloy on magnesium alloy parts has excellent corrosion resistance and other properties, meets the technical requirements of the aerospace field, and significantly expands the application range of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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

[0021] 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.

[0022] A magnesium alloy cyanide-free cadmium-iron alloy plating process comprises pre-treatment of a magnesium alloy workpiece, and sequentially preparing a chemical zinc deposition layer, a cyanide-free copper-zinc alloy plating layer, a nickel-phosphorus alloy plating layer, a cyanide-free cadmium-iron alloy plating layer, and a passivation layer on a magnesium alloy substrate from the inside to the outside.

[0023] The magnesium alloy pretreatment process is used to remove oil, pickle and activate the magnesium alloy workpiece.

[0024] 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.

[0025] Preferably, the 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.

[0026] After pretreatment of the magnesium alloy workpiece, the chemical zinc deposition layer is prepared by the following magnesium alloy chemical zinc deposition process.

[0027] Zinc sulfate heptahydrate 25-35g / L, potassium pyrophosphate 100-120g / L, potassium fluoride 6-9g / L, bath temperature 68-72℃, zinc precipitation time 8-12min.

[0028] After chemical zinc deposition on a magnesium alloy workpiece, the polymerized thiocyanate copper-zinc alloy plating process of the invention is adopted to prepare a cyanide-free copper-zinc alloy plating layer.

[0029] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 8 to 13 μm.

[0030] Polymeric cuprous thiocyanate 18-24 g / L, polymeric zinc thiocyanate 9-13 g / L, polymeric sodium thiocyanate 130-170 g / L, copper-zinc alloy electroplating brightener 8-12 mL / L, plating solution pH 10-12, plating tank temperature 35-55 ° C, cathode current density 0.5-1.5 A / dm 2 The cathode moves 3 to 5 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, and the anode moves 3 to 5 m / min.

[0031] Preferably, the copper-zinc alloy electroplating brightener comprises the following components in weight fractions: 60-100 parts of N,N'-di-n-propylethylenediamine, 10-20 parts of waterborne polyurethane resin, 80-120 parts of polyacrylamide with a molecular weight less than 8000, and 770-870 parts of deionized water.

[0032] Preferably, the copper-zinc alloy electroplating brightener is prepared as follows: 770 to 870 parts by weight of deionized water are added to a reaction tank, 60 to 100 parts of N,N'-di-n-propylethylenediamine, 10 to 20 parts of waterborne polyurethane resin, and 80 to 120 parts of polyacrylamide with a molecular weight less than 8000 are added under stirring, and the brightener is obtained by stirring evenly.

[0033] Preferably, the polyacrylamide with a molecular weight less than 8000 includes any one or two of polyacrylamide with a model number of GRO-70, polyacrylamide with a model number of IC-113, polyacrylamide with a model number of IC-125, and polyacrylamide with a model number of IC-213.

[0034] The magnesium alloy workpiece is plated with copper-zinc alloy and then the nickel-phosphorus alloy coating is prepared by the current nickel-phosphorus alloy plating process.

[0035] Preferably, the thickness of the nickel-phosphorus alloy coating is 6 to 12 μm.

[0036] The preferred color, the nickel-phosphorus alloy coating is prepared by the PROTEXYER 8713 high corrosion resistant nickel-phosphorus alloy coating process of Chaobang Chemical: PROTEXYER 8713 MU tank opener 580~620mL / L, nickel sulfate 280~340g / L, plating solution pH 2.6~2.7, plating tank temperature 60~65℃, cathode current density 3~6A / dm 2 , the cathode moves 3 to 5 m / min.

[0037] After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer.

[0038] Preferably, the thickness of the cyanide-free cadmium iron alloy coating is 8 to 17 μm.

[0039] 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.

[0040] Preferably, the leveling agent includes 5-10 g / L of trimercapto-s-triazine, 30-60 g / L of organic amine epoxy derivative, and 5-10 g / L of sodium hydroxide.

[0041] Preferably, the stabilizer includes sodium gluconate and sodium hydrogen succinate, and the mass ratio of sodium gluconate to sodium hydrogen succinate is 1:(2-3).

[0042] Preferably, the complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid, and the above components are mixed evenly to obtain the complexing agent; the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6).

[0043] 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 280-100 g / L.

[0044] Preferably, the auxiliary agent includes 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; wherein the polyacrylamide with a molecular weight less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20-50 g / L, the sodium salt of 2-ethylhexyl sulfate is 30-80 g / L, and the component D is 30-60 g / L.

[0045] After the magnesium alloy workpiece is plated with cadmium iron alloy, a passivation layer is prepared by the current cadmium plating post-treatment process. 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] After passivation, the magnesium alloy workpiece is dried using a conventional drying process.

[0051] Embodiment 1: like Figure 1 As shown, a magnesium alloy cyanide-free cadmium-iron alloy plating process includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper-zinc alloy coating 3, a nickel-phosphorus alloy coating 4, a cyanide-free cadmium-iron alloy coating 5, and a hexavalent chromium color passivation layer 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0052] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0053] 1) Degreasing: The following weak alkaline ultrasonic degreasing process was used: sodium phosphate 20 g / L, sodium carbonate 20 g / L, Jintel NP-10 degreasing agent 1.2 g / L, tank temperature 70°C, and degreasing time 10 min.

[0054] 2) Pickling activation: The following magnesium alloy pickling activation process was adopted: 25 mL / L phosphoric acid, 20 g / L ammonium bifluoride, room temperature operation, and pickling time of 60 s.

[0055] 2. Chemical zinc precipitation: After the magnesium alloy workpiece is pre-treated, the chemical zinc deposition layer 2 is prepared by the following chemical zinc deposition process.

[0056] Zinc sulfate heptahydrate 30g / L, potassium pyrophosphate 110g / L, potassium fluoride 7g / L, bath temperature 70℃, zinc precipitation time 10min.

[0057] 3. Copper-zinc alloy: After chemical zinc deposition on the magnesium alloy workpiece, the polythiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 3, and the thickness of the copper-zinc alloy coating is 10 μm.

[0058] 1) Preparation of copper-zinc alloy electroplating brightener: Calculated by weight, 820 parts of deionized water were added to a reaction tank, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of polyacrylamide with model GRO-70 were added under stirring, and stirred evenly to obtain the brightener.

[0059] 2) Plating: Polymeric cuprous thiocyanate 21g / L, polymeric zinc thiocyanate 11g / L, polymeric sodium thiocyanate 150g / L, copper-zinc alloy electroplating brightener 10mL / L, plating solution pH 10.5, plating tank temperature 45℃, cathode current density 1.0A / dm 2 The cathode moves at 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, and the anode moves at 4 m / min.

[0060] 4. Nickel-phosphorus alloy plating: After the magnesium alloy workpiece is plated with copper-zinc alloy, the nickel-phosphorus alloy coating 4 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Chaobang Chemical. The thickness of the nickel-phosphorus alloy coating is 8 μm.

[0061] PROTEXYER 8713 MU tank opener 600mL / L, nickel sulfate 310g / L, bath pH 2.6, bath temperature 63℃, cathode current density 4A / dm 2 , cathode moves 4m / min.

[0062] 5. Cadmium-plated iron alloy: After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 5, and the thickness of the cadmium-iron alloy plating layer is 12 μm.

[0063] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of an organic amine epoxy derivative with a product model of 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 is added, and water is added to the required volume to obtain the leveling agent.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 6) Plating: Cadmium chloride 30g / L, ferrous chloride tetrahydrate 5g / L, potassium chloride 120g / L, complexing agent 120g / L, leveling agent 2.0mL / L, brightener 2.0mL / L, auxiliary agent 27mL / L, stabilizer 30g / L, plating solution pH 7, plating tank temperature 28℃, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0069] 6. Hexavalent chromium color passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the hexavalent chromium color passivation layer 6 is prepared using the HC-5 low chromium color passivation process of Chaobang Chemical.

[0070] The volume concentration of HC-5 high protection low chrome color passivator is 3%, the passivation temperature is 28℃, the pH of the passivation solution is 1.6, the passivation time is 8s, and the workpiece swings.

[0071] The specific process is "1.5% volume fraction nitric acid polishing → water washing → passivation → water washing → drain after leaving the tank → use high-pressure air to blow away the residual water on the surface of the plated part".

[0072] 7. Drying: The magnesium alloy workpiece was dried at 60°C for 10 min after passivation.

[0073] Embodiment 2: like Figure 1 As shown, a cyanide-free cadmium-iron alloy plating process for magnesium alloy includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper-zinc alloy coating 3, a nickel-phosphorus alloy coating 4, a cyanide-free cadmium-iron alloy coating 5, and a hexavalent chromium military green passivation layer 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0074] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0075] 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.

[0076] 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.

[0077] 2. Chemical zinc precipitation: After the magnesium alloy workpiece is pre-treated, the chemical zinc deposition layer 2 is prepared by the following chemical zinc deposition process.

[0078] Zinc sulfate heptahydrate 35g / L, potassium pyrophosphate 120g / L, potassium fluoride 9g / L, bath temperature 68℃, zinc precipitation time 10min.

[0079] 3. Copper-zinc alloy: After chemical zinc deposition on the magnesium alloy workpiece, the polythiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 3, and the thickness of the copper-zinc alloy coating is 10 μm.

[0080] 1) Preparation of copper-zinc alloy electroplating brightener: Calculated by weight, 820 parts of deionized water were added to a reaction tank, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-113 polyacrylamide were added under stirring, and stirred evenly to obtain the brightener.

[0081] 2) Plating: Polymeric cuprous thiocyanate 24g / L, polymeric zinc thiocyanate 13g / L, polymeric sodium thiocyanate 170g / L, copper-zinc alloy electroplating brightener 10mL / L, plating solution pH 10, plating tank temperature 45℃, cathode current density 1.0A / dm 2 The cathode moves at 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, and the anode moves at 4 m / min.

[0082] 4. Nickel-phosphorus alloy plating: After the magnesium alloy workpiece is plated with copper-zinc alloy, a nickel-phosphorus alloy coating 4 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Chaobang Chemical. The thickness of the nickel-phosphorus alloy coating is 8 μm.

[0083] PROTEXYER 8713 MU tank opener 620mL / L, nickel sulfate 340g / L, bath pH 2.7, bath temperature 60℃, cathode current density 4A / dm 2 , cathode moves 4m / min.

[0084] 5. Cadmium-plated iron alloy: After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 5, and the thickness of the cadmium-iron alloy plating layer is 12 μm.

[0085] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of an organic amine epoxy derivative with a product model of 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 is added, and water is added to the required volume to obtain the leveling agent.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 6) 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.

[0091] 6. Hexavalent chromium military green passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the military green passivation layer 6 is prepared using Chaobang Chemical's OVG-31 military green passivation process.

[0092] OVG-31 military green passivator 100mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 60s, swing plated parts.

[0093] The specific process is "1.5% volume fraction nitric acid polishing → water washing → passivation → water washing → drain after leaving the tank → use high-pressure air to blow away the residual water on the surface of the plated part".

[0094] 7. Drying: The magnesium alloy workpiece was dried at 60°C for 10 min after passivation.

[0095] Embodiment 3: like Figure 1 As shown, a cyanide-free cadmium-iron alloy plating process for magnesium alloy includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper-zinc alloy plating layer 3, a nickel-phosphorus alloy plating layer 4, a cyanide-free cadmium-iron alloy plating layer 5, and a hexavalent chromium black passivation layer 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0096] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0097] 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.

[0098] 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.

[0099] 2. Chemical zinc precipitation: After the magnesium alloy workpiece is pre-treated, the chemical zinc deposition layer 2 is prepared by the following chemical zinc deposition process.

[0100] Zinc sulfate heptahydrate 25g / L, potassium pyrophosphate 100g / L, potassium fluoride 6g / L, bath temperature 72℃, zinc precipitation time 12min.

[0101] 3. Copper-zinc alloy: After chemical zinc deposition on the magnesium alloy workpiece, the polythiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 3, and the thickness of the copper-zinc alloy coating is 10 μm.

[0102] 1) Preparation of copper-zinc alloy electroplating brightener: Calculated by weight, 820 parts of deionized water were added to a reaction tank, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-125 polyacrylamide were added under stirring, and stirred evenly to obtain the brightener.

[0103] 2) Plating: Polymeric cuprous thiocyanate 18g / L, polymeric zinc thiocyanate 9g / L, polymeric sodium thiocyanate 130g / L, copper-zinc alloy electroplating brightener 10mL / L, plating solution pH 11.5, plating tank temperature 55℃, cathode current density 1.0A / dm 2 The cathode moves at 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, and the anode moves at 4 m / min.

[0104] 4. Nickel-phosphorus alloy plating: After the magnesium alloy workpiece is plated with copper-zinc alloy, the nickel-phosphorus alloy coating 4 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Chaobang Chemical. The thickness of the nickel-phosphorus alloy coating is 8 μm.

[0105] PROTEXYER 8713 MU tank opener 580mL / L, nickel sulfate 280g / L, bath pH 2.7, bath temperature 65℃, cathode current density 4A / dm 2 , cathode moves 4m / min.

[0106] 5. Cadmium-plated iron alloy: After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 5, and the thickness of the cadmium-iron alloy plating layer is 12 μm.

[0107] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of an organic amine epoxy derivative with a product model of 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 is added, and water is added to the required volume to obtain the leveling agent.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 6) 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.

[0113] 6. Hexavalent chromium black passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the hexavalent chromium black passivation layer 6 is prepared using the BZ-71 cadmium black passivation process of Chaobang Chemical.

[0114] 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.

[0115] The specific process is "1.5% volume fraction nitric acid polishing → water washing → passivation → water washing → drain after leaving the tank → use high-pressure air to blow away the residual water on the surface of the plated part".

[0116] 7. Drying: The magnesium alloy workpiece was dried at 60°C for 10 min after passivation.

[0117] Embodiment 4: like Figure 1 As shown, a magnesium alloy cyanide-free cadmium-iron alloy plating process includes pre-treatment of a magnesium alloy substrate 1, and sequentially preparing a chemical zinc deposition layer 2, a cyanide-free copper-zinc alloy coating 3, a nickel-phosphorus alloy coating 4, a cyanide-free cadmium-iron alloy coating 5, and a hexavalent chromium olive-drab passivation layer 6 on the pre-treated magnesium alloy substrate 1 from the inside to the outside.

[0118] 1. Pre-treatment: The magnesium alloy workpiece substrate 1 is pre-treated by using the current magnesium alloy pre-treatment process.

[0119] 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.

[0120] 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.

[0121] 2. Chemical zinc precipitation: After the magnesium alloy workpiece is pre-treated, the chemical zinc deposition layer 2 is prepared by the following chemical zinc deposition process.

[0122] Zinc sulfate heptahydrate 33g / L, potassium pyrophosphate 115g / L, potassium fluoride 8g / L, bath temperature 69℃, zinc precipitation time 9min.

[0123] 3. Copper-zinc alloy: After chemical zinc deposition on the magnesium alloy workpiece, the polythiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 3, and the thickness of the copper-zinc alloy coating is 10 μm.

[0124] 1) Preparation of copper-zinc alloy electroplating brightener: Calculated by weight, 820 parts of deionized water were added to a reaction tank, and 80 parts of N,N'-di-n-propylethylenediamine, 15 parts of waterborne polyurethane resin, and 100 parts of IC-213 polyacrylamide were added under stirring, and stirred evenly to obtain the brightener.

[0125] 2) Plating: Polymeric cuprous thiocyanate 23g / L, polymeric zinc thiocyanate 12g / L, polymeric sodium thiocyanate 165g / L, copper-zinc alloy electroplating brightener 10mL / L, plating solution pH 11.8, plating tank temperature 40℃, cathode current density 1.0A / dm 2 The cathode moves at 4 m / min, and a copper-zinc alloy plate with a copper mass fraction of 68% is used as the anode, and the anode moves at 4 m / min.

[0126] 4. Nickel-phosphorus alloy plating: After the magnesium alloy workpiece is plated with copper-zinc alloy, a nickel-phosphorus alloy coating 4 is prepared by using the PROTEXYER 8713 high-corrosion-resistant nickel-phosphorus alloy plating process of Chaobang Chemical. The thickness of the nickel-phosphorus alloy coating is 8 μm.

[0127] PROTEXYER 8713 MU tank opener 610mL / L, nickel sulfate 330g / L, bath pH 2.6, bath temperature 61°C, cathode current density 4A / dm 2 , cathode moves 4m / min.

[0128] 5. Cadmium-plated iron alloy: After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 5, and the thickness of the cadmium-iron alloy plating layer is 12 μm.

[0129] 1) Preparation of leveling agent: The leveling agent includes 7.5 g / L of trimercapto-s-triazine, 45 g / L of an organic amine epoxy derivative with a product model of 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 is added, and water is added to the required volume to obtain the leveling agent.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 6) 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.

[0135] 6. Hexavalent chromium olive color passivation: After the magnesium alloy workpiece is plated with cadmium iron alloy, the hexavalent chromium olive passivation layer 6 is prepared by the UC-91 cadmium hexavalent chromium olive passivation process of Chaobang Chemical.

[0136] 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.

[0137] The specific process is "1.5% volume fraction nitric acid polishing → water washing → passivation → water washing → drain after leaving the tank → use high-pressure air to blow away the residual water on the surface of the plated part".

[0138] 7. Drying: The magnesium alloy workpiece was dried at 60°C for 10 min after passivation.

[0139] Test Example 1: According to 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 384 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 400 hours, the magnesium alloy cadmium iron alloy hexavalent chromium black passivation sample prepared in Example 3 had no white rust on the surface after 352 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 384 hours. The prepared coatings have excellent corrosion resistance.

[0140] 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 / T 5270-2005 "Review of test methods for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates". The samples were placed in a heating furnace and heated to 150°C for 30 minutes. After being taken out, they were immediately placed in room temperature water for cooling. There was no blistering or shedding of the coating, and the coating adhesion met the standard requirements.

[0141] 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 360 hours at a temperature of 40°C and a relative humidity of 93% in accordance with GB / T 2423.3-2016 "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, meeting the technical requirements of the industry.

[0142] 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 requirements of industry standards.

[0143] 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 cyanide-free cadmium-iron alloy plating process for magnesium alloy, characterized in that: The following steps are involved: (1) Degreasing, pickling and activation of magnesium alloy workpieces; (2) After the magnesium alloy workpiece is pre-treated, the chemical zinc deposition layer is prepared by the current chemical zinc deposition process; (3) After chemical zinc deposition on magnesium alloy workpiece, a cyanide-free copper-zinc alloy coating is prepared by using a polymerized thiocyanate copper-zinc alloy plating process; (4) After the magnesium alloy workpiece is plated with copper-zinc alloy without cyanide, the nickel-phosphorus alloy coating is prepared by the existing nickel-phosphorus alloy plating process; (5) After the magnesium alloy workpiece is plated with nickel-phosphorus alloy, a cyanide-free cadmium-iron alloy coating is prepared by a cyanide-free cadmium-iron alloy plating process; (6) The magnesium alloy workpiece is plated with cadmium iron alloy and then post-treated to prepare a passivation layer; 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, and 5-10 g / L of sodium hydroxide; The stabilizer includes sodium gluconate and sodium hydrogen succinate, and the mass ratio of sodium gluconate to sodium hydrogen succinate is 1:(2-3); The complexing agent includes nitrilotriacetic acid, sulfosalicylic acid, and malic acid. The above components are mixed evenly to obtain the complexing agent; the mass ratio of nitrilotriacetic acid, sulfosalicylic acid, and malic acid is 3:(1-2):(4-6); 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; 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; The auxiliary agent comprises polyacrylamide with a molecular weight less than 8000, sodium salt of 2-ethylhexyl sulfate, a condensate composed of ethylenediamine or dimethylpropylamine and epichlorohydrin, and a D component, wherein the D component is consistent with the C component in the brightener; wherein the polyacrylamide with a molecular weight less than 8000 is 50-80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20-50 g / L, the sodium salt of 2-ethylhexyl sulfate is 30-80 g / L, and the D component is 30-60 g / L.

2. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1, characterized in that: The thickness of the cyanide-free cadmium iron plating layer is 8 to 17 μm.

3. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1, characterized in that: The polythiocyanate copper-zinc alloy plating process includes the following components and process parameters: Polymeric cuprous thiocyanate 18-24 g / L, polymeric zinc thiocyanate 9-13 g / L, polymeric sodium thiocyanate 130-170 g / L, copper-zinc alloy electroplating brightener 8-12 mL / L, plating solution pH 10-12, plating tank temperature 35-55 ° C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3 to 5 m / min, a copper-zinc alloy plate with a copper mass fraction of 68% is used as an anode, and the anode moves 3 to 5 m / min; the copper-zinc alloy electroplating brightener comprises the following components by weight: 60 to 100 parts of N,N'-di-n-propylethylenediamine, 10 to 20 parts of water-based polyurethane resin, 80 to 120 parts of polyacrylamide with a molecular weight less than 8000, and 770 to 870 parts of deionized water.

4. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1 or 3, characterized in that: The thickness of the cyanide-free copper-zinc alloy coating is 8 to 13 μm.

5. The magnesium alloy cyanide-free cadmium iron alloy plating process according to claim 1, characterized in that: The nickel-phosphorus alloy coating is prepared by using the PROTEXYER 8713 high corrosion resistant nickel-phosphorus alloy plating process: PROTEXYER 8713 MU tank opener 580~620mL / L, nickel sulfate 280~340g / L, plating solution pH 2.6~2.7, plating tank temperature 60~65℃, cathode current density 3~6A / dm 2 , the cathode moves 3 to 5 m / min.

6. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1 or 5, characterized in that: The thickness of the nickel-phosphorus alloy coating is 6-12 μm.

7. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1, characterized in that: 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.

8. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 7, 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.

9. The cyanide-free cadmium-iron alloy plating process of magnesium alloy according to claim 1, characterized in that: The acid activation adopts the current 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.

10. The magnesium alloy cyanide-free cadmium iron alloy plating process according to claim 1, characterized in that: The chemical zinc deposition layer is prepared by the current magnesium alloy chemical zinc deposition process: Zinc sulfate heptahydrate 25-35g / L, potassium pyrophosphate 100-120g / L, potassium fluoride 6-9g / L, bath temperature 68-72℃, zinc precipitation time 8-12min.

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