Cyanide-free cadmium-iron alloy plating process for zinc alloy die casting

Abstract

The invention discloses a cyanide-free cadmium-iron alloy plating process for a zinc alloy die casting, and relates to the field of metal surface treatment. The cyanide-free cadmium-iron alloy plating technology for the zinc alloy die casting comprises the steps that a zinc alloy matrix is pretreated, and a cyanide-free copper plating layer, a cyanide-free cadmium-iron alloy plating layer, a passivation layer and a graphene modified sealing layer are sequentially prepared on the pretreated zinc alloy matrix from inside to outside. The prepared cadmium-iron alloy coating has excellent corrosion resistance, and overcomes the defect that the existing cadmium plating technology of the zinc alloy die casting does not have an electrochemical protection effect; meanwhile, a copper plating layer is prepared on a zinc alloy matrix by adopting a polythiocyanate copper plating process, so that the problem of high pollution of a traditional cyaniding copper plating process is solved; and the corrosion resistance of the prepared cadmium-iron alloy plating layer is higher than that of a potassium chloride cyanide-free cadmium plating layer.

Description

Technical Field

[0001] The invention relates to the field of metal surface treatment, in particular to a cyanide-free cadmium-iron alloy plating process for zinc alloy die castings. Background Art

[0002] Cyanide-free plating interlayers have excellent corrosion resistance and are widely used in the aerospace field, and have achieved good environmental and social benefits. For example, Guo Chongwu's "Development and Research of New Acidic Cyanide-free Cadmium Plating Process" in 2016 and Lai Huanwen, Guo Chongwu, Chen Mei, etc.'s "Preparation of Ultra-high Corrosion Resistance Potassium Chloride Cadmium Plating Protective Layer" in 2021 are all published. When cyanide-free cadmium plating is directly carried out on the zinc alloy substrate, the cadmium ions in the plating solution will undergo a replacement reaction with the zinc alloy substrate and affect the bonding strength of the coating. Therefore, a pre-plating layer needs to be prepared between the zinc alloy substrate and the plating interlayer. In the case that cyanide is strictly prohibited by the state, research and development of new processes to replace cyanide pre-copper plating has become a hot topic in the industry.

[0003] Although the use of divalent copper cyanide-free copper plating process to prepare a pre-plated copper layer on the metal surface has been studied for many years, the bottleneck problem of low bonding strength has not been broken through. Qin Zuzu, Li Jiansan, and Xu Jinlai published in "Research Progress of Cyanide-Free Copper Plating Process at Home and Abroad". This process has been used in production in small quantities, but there are still certain difficulties in achieving mass production.

[0004] The Chinese invention patent "A method for preparing an environmentally friendly zinc alloy cyanide-free cadmium plating structure" with the authorization announcement number CN 108166031B discloses a method for cyanide-free cadmium plating on the surface of a zinc alloy: comprising preparing a zinc-nickel alloy pre-plating layer, a cyanide-free cadmium plating layer, and a rare earth modified chromate low-chromium passivation layer on the surface of a zinc alloy substrate from the inside to the outside. In this plating structure, the electrode potential of the zinc-nickel alloy plating layer is positive to that of the zinc alloy die-casting substrate, and the electrode potential of the cadmium plating layer is positive to that of the zinc-nickel alloy plating layer. This plating structure has no electrochemical protection effect on the zinc alloy substrate. When the cadmium plating layer is damaged, galvanic corrosion will occur and damage the zinc-nickel alloy plating layer and the zinc alloy die-casting substrate. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of this application is to provide a cyanide-free cadmium-iron alloy plating process for zinc alloy die-castings, so as to solve the problem that zinc alloy die-castings plated with zinc-nickel alloy and then plated with cadmium or cadmium alloy do not have electrochemical protection effect, thereby achieving the effect of improving corrosion resistance.

[0006] To achieve the above effects, the present application discloses a cyanide-free cadmium-iron alloy plating process for zinc alloy die castings, comprising the following steps: (1) Dewaxing, degreasing and activating zinc alloy die castings; (2) After pretreatment of zinc alloy die castings, a cyanide-free copper plating layer is prepared by using a polymerized thiocyanate copper plating process; (3) After the zinc alloy die casting is plated with copper by polymerizing thiocyanate, a cyanide-free cadmium-iron alloy plating process is used to prepare a cyanide-free cadmium-iron alloy coating; (4) Zinc alloy die castings are plated with cadmium iron alloy without cyanide and then passivated to prepare a passivation layer; (5) After the zinc alloy die casting is passivated, it is sealed to prepare a graphene-modified sealing 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, 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 comprises 30-80 g / L, the component B comprises 30-80 g / L, the component C comprises 60-100 g / L and the isopropanol comprises 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 to 80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20 to 50 g / L, the sodium salt of 2-ethylhexyl sulfate is 30 to 80 g / L, and the D component is 30 to 60 g / L.

[0007] In some embodiments, the polythiocyanate copper plating process includes the following components and process parameters: Polycuprous thiocyanate 18-24 g / L, polysodium thiocyanate 130-170 g / L, disodium hydroxyethylidene diphosphonate 10-40 g / L, HT-810 brightener 1-2 mL / L, HT-810 moving agent 2-4 mL / L, plating solution pH 12-13, plating tank temperature 25-45°C, cathode current density 0.5-1.5 A / dm 2 The cathode moves 3-5 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is less than 1A / dm 2 , the anode moves 3 to 5 m / min.

[0008] In some embodiments, the thickness of the cyanide-free cadmium iron coating is 8-18 μm.

[0009] In some embodiments, the thickness of the cyanide-free copper plating layer is 4-8 μm.

[0010] In some of the embodiments, the passivation layer includes a hexavalent chromium color passivation layer, a hexavalent chromium military green passivation layer, and a hexavalent chromium black passivation layer.

[0011] 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 15 s, and weak air stirring or workpiece swinging is performed.

[0012] 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 30-90 s, air stirring or swinging the plated piece.

[0013] 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 80-100 mL / L, BZ-71B cadmium plating black passivation agent 80-100 mL / L, passivation solution pH 1.1-1.5, passivation temperature 20-35°C, passivation time 15-40 s, air stirring or swinging the plated piece.

[0014] In some of the embodiments, the graphene-modified sealing layer is prepared using PRODICO 480 graphene sealing agent: Dilute PRODICO 480 graphene-modified sealer with water to 2.5-3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8-15 seconds. Drain the parts after exiting the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure at 70℃-80℃ for 20-30 minutes.

[0015] In some of the embodiments, the thickness of the graphene modified sealing layer is 0.6-1.8 μm.

[0016] The copper plating layer prepared on the zinc alloy die casting by using the polymerized thiocyanate copper plating process is similar to the cyanide copper plating process, and the prepared plating layer can form a good bonding force with the substrate. As time goes by, the zinc atoms in the zinc alloy can diffuse into the copper plating layer, and the copper atoms in the copper plating layer can also diffuse into the zinc alloy substrate, and finally there is no obvious interface between the copper plating layer and the zinc alloy substrate, thereby further improving the bonding force of the plating layer.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings of the present invention has excellent corrosion resistance, which overcomes the defect that the existing cadmium plating technology for zinc alloy die castings does not have electrochemical protection; 2. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings of the present invention adopts a polymerized thiocyanate copper plating process to prepare a copper plating layer on a zinc alloy substrate, thus overcoming the high pollution problem of the traditional cyanide copper plating process; 3. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings of the present invention has a higher corrosion resistance than the cyanide-free cadmium plating layer of potassium chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 It is a schematic diagram of the coating structure of Example 1, Example 2, and Example 3 of the present invention.

[0020] Among them: zinc alloy substrate-1, cyanide-free copper plating layer-2, cyanide-free cadmium iron alloy plating layer-3, passivation layer-4, graphene modified sealing layer 5. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] Embodiment 1: like Figure 1 As shown, the cyanide-free cadmium-iron alloy plating process for zinc alloy die-castings includes pre-treatment of a zinc alloy substrate 1, and sequentially preparing a cyanide-free copper plating layer 2, a cyanide-free cadmium-iron alloy plating layer 3, a hexavalent chromium color passivation layer 4, and a graphene modified sealing layer 5 on the pre-treated zinc alloy substrate 1 from the inside to the outside.

[0023] 1. Pre-treatment: The zinc alloy die-casting substrate 1 is subjected to "chemical dewaxing → water washing → ultrasonic degreasing → water washing → ultrasonic degreasing → water washing → activation → water washing" by using the existing pre-treatment process.

[0024] 2. Cyanide-free copper plating: After pretreatment of the zinc alloy die casting, the polythiocyanate copper plating process of the present invention is used to prepare a cyanide-free copper plating layer 2, and the thickness of the plating layer is 6 μm.

[0025] Polycuprous thiocyanate 21 g / L, polysodium thiocyanate 150 g / L, disodium hydroxyethylidene diphosphonate 25 g / L, HT-810 brightener 1.5 mL / L, HT-810 moving agent 3 mL / L, plating solution pH 12.5, plating tank temperature 35°C, cathode current density 1.0 A / dm 2 The cathode moves at 4 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is 0.8 A / dm 2 , anode movement 4 m / min.

[0026] 3. Cyanide-free cadmium-plated iron alloy: After the zinc alloy die casting is cyanide-free copper plated, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 3, and the plating layer thickness is 12 μm.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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-diethyl propargylamine, N,N-diethyl propargylamine formate and N,N-diethyl propargylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed evenly, 5.5 kg of component A, 4 kg of component B and 8 kg of component C are added, stirred to dissolve, and water is added to 100 L to obtain the brightener.

[0031] 5) Preparation of auxiliary agents: 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 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.

[0032] 6) Plating: Cadmium chloride 30 g / L, ferrous chloride tetrahydrate 5 g / L, potassium chloride 120 g / L, complexing agent 120 g / L, leveling agent 2.0 mL / L, brightener 2.0 mL / L, auxiliary agent 27 mL / L, stabilizer 30 g / L, plating solution pH 7, plating tank temperature 28°C, cathode current density 1.0 A / dm 2 , cathode moves 3 m / min.

[0033] 4. Hexavalent chromium color passivation: The zinc alloy die casting is plated with cadmium iron alloy and then the hexavalent chromium color passivation layer 4 is prepared by using the HC-5 low chromium color passivation process of Chaobang Chemical.

[0034] 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 8 s, and the workpiece swings.

[0035] The specific process is "light irradiation with 1.5% volume fraction nitric acid → water washing → passivation → water washing".

[0036] 5. Closure: After the zinc alloy die casting is passivated, the graphene modified sealing layer 5 is prepared using PRODICO 480 graphene sealant developed by Chaobang Chemical, and the thickness of the sealing layer is 1.2 μm.

[0037] The PRODICO 480 graphene-modified sealer was diluted with water to 2.8 times to prepare the sealing solution. The plated parts were immersed in the sealing solution for 10 s, drained after being taken out of the tank, and the sealing solution remaining on the surface of the plated parts was blown away with high-pressure air.

[0038] 6. Drying: The zinc alloy die castings were sealed and dried at 75°C for 25 min.

[0039] Embodiment 2: like Figure 1 As shown, the cyanide-free cadmium-iron alloy plating process for zinc alloy die-castings includes pre-treatment of a zinc alloy substrate 1, and sequentially preparing a cyanide-free copper plating layer 2, a cyanide-free cadmium-iron alloy plating layer 3, a hexavalent chromium military green passivation layer 4, and a graphene-modified sealing layer 5 on the pre-treated zinc alloy substrate 1 from the inside to the outside.

[0040] 1. Pre-treatment: The zinc alloy die-casting substrate 1 is subjected to "chemical dewaxing → water washing → ultrasonic degreasing → water washing → ultrasonic degreasing → water washing → activation → water washing" by using the existing pre-treatment process.

[0041] 2. Cyanide-free copper plating: After pretreatment of the zinc alloy die casting, the polythiocyanate copper plating process of the present invention is used to prepare a cyanide-free copper plating layer 2, and the thickness of the plating layer is 6 μm.

[0042] Polycuprous thiocyanate 24 g / L, polysodium thiocyanate 170 g / L, disodium hydroxyethylidene diphosphonate 10 g / L, HT-810 brightener 1.5 mL / L, HT-810 moving agent 3 mL / L, plating solution pH 12.5, plating tank temperature 25°C, cathode current density 1.0 A / dm 2 The cathode moves at 4 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is 0.8 A / dm2 , anode movement 4 m / min.

[0043] 3. Cyanide-free cadmium-plated iron alloy: After the zinc alloy die casting is cyanide-free copper plated, the cyanide-free cadmium-iron alloy plating process of the present invention is adopted to prepare a cyanide-free cadmium-iron alloy plating layer 3, and the plating layer thickness is 12 μm.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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-diethyl propargylamine, N,N-diethyl propargylamine formate and N,N-diethyl propargylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed evenly, 5.5 kg of component A, 4 kg of component B and 8 kg of component C are added, stirred to dissolve, and water is added to 100 L to obtain the brightener.

[0048] 5) Preparation of auxiliary agents: 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 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.

[0049] 6) Plating: Cadmium chloride 28 g / L, ferrous chloride tetrahydrate 4.7 g / L, potassium chloride 135 g / L, complexing agent 125 g / L, leveling agent 2.0 mL / L, brightener 2.0 mL / L, auxiliary agent 28 mL / L, stabilizer 28 g / L, plating solution pH 6.5, plating tank temperature 32°C, cathode current density 1.0 A / dm 2 , cathode moves 3 m / min.

[0050] 4. Hexavalent chromium military green passivation: After the zinc alloy die casting is plated with cadmium iron alloy, the hexavalent chromium military green passivation layer 4 is prepared using Chaobang Chemical's OVG-31 military green passivation process.

[0051] OVG-31 military green passivator 100 mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 60 s, swing plated parts.

[0052] The specific process is "light irradiation with 1.5% volume fraction nitric acid → water washing → passivation → water washing".

[0053] 5. Closure: After the zinc alloy die casting was passivated, the graphene-modified sealing layer 5 was prepared using PRODICO 480 graphene sealant developed by Chaobang Chemical, and the thickness of the sealing layer was 1.2 μm.

[0054] The PRODICO 480 graphene-modified sealer was diluted with water to 2.8 times to prepare the sealing solution. The plated parts were immersed in the sealing solution for 10 s, drained after being taken out of the tank, and the sealing solution remaining on the surface of the plated parts was blown away with high-pressure air.

[0055] 6. Drying: The zinc alloy die castings were sealed and dried at 80 °C for 20 min.

[0056] Embodiment 3: like Figure 1As shown, the cyanide-free cadmium-iron alloy plating process for zinc alloy die-castings includes pre-treatment of a zinc alloy substrate 1, and sequentially preparing a cyanide-free copper plating layer 2, a cyanide-free cadmium-iron alloy plating layer 3, a hexavalent chromium black passivation layer 4, and a graphene-modified sealing layer 5 on the pre-treated zinc alloy substrate 1 from the inside to the outside.

[0057] The zinc alloy die-casting substrate 1 is subjected to "chemical dewaxing → water washing → ultrasonic degreasing → water washing → ultrasonic degreasing → water washing → activation → water washing" by using the existing pre-treatment process.

[0058] 2. Cyanide-free copper plating: After pretreatment of the zinc alloy die casting, the polythiocyanate copper plating process of the present invention is used to prepare a cyanide-free copper plating layer 2, and the thickness of the plating layer is 6 μm.

[0059] Polycuprous thiocyanate 18 g / L, polysodium thiocyanate 130 g / L, disodium hydroxyethylidene diphosphonate 40 g / L, HT-810 brightener 1.5 mL / L, HT-810 moving agent 3 mL / L, plating solution pH 12.5, plating tank temperature 45°C, cathode current density 1.0 A / dm 2 The cathode moves at 4 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is 0.8 A / dm 2 , anode movement 4 m / min.

[0060] 3. Cadmium-plated iron alloy: After the zinc alloy die casting is plated with copper-zinc 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 3, and the plating layer thickness is 12 μm.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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-diethyl propargylamine, N,N-diethyl propargylamine formate and N,N-diethyl propargylamine sulfate. 30 kg of isopropanol is added to 40 kg of water and mixed evenly, 5.5 kg of component A, 4 kg of component B and 8 kg of component C are added, stirred to dissolve, and water is added to 100 L to obtain the brightener.

[0065] 5) Preparation of auxiliary agents: 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 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.

[0066] 6) Plating: Cadmium chloride 35 g / L, ferrous chloride tetrahydrate 6 g / L, potassium chloride 140 g / L, complexing agent 140 g / L, leveling agent 2.0 mL / L, brightener 2.0 mL / L, auxiliary agent 28 mL / L, stabilizer 35 g / L, plating solution pH 7.5, plating tank temperature 20°C, cathode current density 1.0 A / dm 2 , cathode moves 3 m / min.

[0067] 4. Hexavalent chromium black passivation: The zinc alloy die casting was plated with cadmium iron alloy and then the hexavalent chromium black passivation layer 4 was prepared by using the BZ-71 cadmium black passivation process of Chaobang Chemical.

[0068] BZ-71A cadmium black passivation agent 90 mL / L, BZ-71B cadmium black passivation agent 90 mL / L, passivation solution pH 1.3, passivation temperature 25℃, passivation time 28 s, swing plated parts.

[0069] The specific process is "light irradiation with 1.5% volume fraction nitric acid → water washing → passivation → water washing".

[0070] 5. Closure: After the zinc alloy die casting was passivated, the graphene-modified sealing layer 5 was prepared using PRODICO 480 graphene sealant developed by Chaobang Chemical, and the thickness of the sealing layer was 1.2 μm.

[0071] The PRODICO 480 graphene-modified sealer was diluted with water to 2.8 times to prepare the sealing solution. The plated parts were immersed in the sealing solution for 10 s, drained after being taken out of the tank, and the sealing solution remaining on the surface of the plated parts was blown away with high-pressure air.

[0072] 6. Drying: The zinc alloy die castings were sealed and dried at 70 °C for 30 min.

[0073] 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 zinc alloy cadmium-plated iron alloy hexavalent chromium color passivation sample prepared in Example 1 had no white rust on the surface after 480 h, the zinc alloy cadmium-plated iron alloy hexavalent chromium military green passivation sample prepared in Example 2 had no white rust on the surface after 508 h, and the zinc alloy cadmium-plated iron alloy hexavalent chromium black passivation sample prepared in Example 3 had no white rust on the surface after 362 h.

[0074] Test Example 2: The zinc alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, and Example 3 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 min. 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.

[0075] Test Example 3: The zinc alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, and Example 3 were tested for 360 h 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, which met the technical requirements of the industry.

[0076] Test example 4: The zinc alloy cadmium-plated iron alloy samples prepared in Example 1, Example 2, and Example 3 were subjected to a mold test for 28 days in accordance with GJB 150.9A-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.

[0077] Test Example 5: The polymerized thiocyanate copper plating process of the present invention is used for plating: Polycuprous thiocyanate 21 g / L, polysodium thiocyanate 150 g / L, disodium hydroxyethylidene diphosphonate 10 g / L, HT-810 brightener 1.5 mL / L, HT-810 moving agent 3 mL / L, plating solution pH 12.5, plating tank temperature 35°C, cathode current density 1.0 A / dm 2 , cathode movement 4 m / min, oxygen-free electrolytic copper particles as anode, anode current density 1.0 A / dm 2 , anode movement 4 m / min.

[0078] After 30 minutes of plating, the anode surface was copper-colored and there was no decrease in the applied current.

[0079] Comparative Example 1: A cyanide-free copper plating layer, a potassium chloride cyanide-free cadmium plating layer, a hexavalent chromium color passivation layer, and a graphene modified sealing layer were sequentially prepared on the zinc alloy die casting according to the process and coating thickness requirements of Example 1. The difference from Example 1 is that this comparative example uses potassium chloride cyanide-free cadmium plating instead of cyanide-free cadmium iron alloy plating.

[0080] The acetic acid salt spray test was carried out in accordance with GB / T 10125-2021 "Salt spray test for corrosion test in artificial atmosphere". White rust appeared on the surface of the sample prepared in the comparative example after 436 hours.

[0081] Comparison of the acetate salt spray test of Example 1 in Test Example 1 with Comparative Example 1 shows that the salt spray resistance of the cadmium-iron alloy coating of the present invention is higher than that of the potassium chloride cyanide-free cadmium coating.

[0082] Comparative Example 2: The following polymeric thiocyanate copper plating process is used for plating: Polythiocyanate cuprous 21 g / L, polythiocyanate sodium 150 g / L, potassium sodium tartrate 10 g / L, HT-810 brightener 1.5 mL / L, HT-810 moving agent 3 mL / L, plating solution pH 12.5, plating tank temperature 50°C, cathode current density 1.0 A / dm 2 The cathode moves at 4 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is 0.5 A / dm 2 , the anode does not move.

[0083] After 10 minutes of plating, the applied current began to decrease, the anode surface turned dark brown, and the applied current gradually decreased to less than 1 / 3 of the initial current.

[0084] Comparison of Test Example 5 with Comparative Example 2 shows that the present invention uses disodium hydroxyethylidene diphosphonate instead of sodium potassium tartrate and adopts anode movement measures, which significantly reduces the plating tank temperature and increases the upper limit of the anode current density. The polymeric thiocyanate copper plating process of the present invention is energy-saving and has a stable plating solution.

[0085] 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 zinc alloy die castings, characterized in that: The following steps are involved: (1) Dewaxing, degreasing and activating zinc alloy die castings; (2) After pretreatment of zinc alloy die castings, a cyanide-free copper plating layer is prepared by using a polymerized thiocyanate copper plating process; (3) After the zinc alloy die casting is plated with copper by polymerizing thiocyanate, a cyanide-free cadmium-iron alloy plating process is used to prepare a cyanide-free cadmium-iron alloy coating; (4) Zinc alloy die castings are plated with cadmium iron alloy without cyanide and then passivated to prepare a passivation layer; (5) After the zinc alloy die casting is passivated, it is sealed to prepare a graphene-modified sealing layer; The cyanide-free cadmium iron alloy plating process includes the following components and process parameters: Cadmium chloride 25-35 g / L, ferrous chloride tetrahydrate 4-6 g / L, potassium chloride 100-140 g / L, complexing agent 100-140 g / L, leveling agent 1.5-2.5 mL / L, brightener 1.5-2.5 mL / L, auxiliary agent 25-30 mL / L, stabilizer 25-35 g / L, plating solution pH 6-8, plating tank temperature 20-35°C, cathode current density 0.5-1.5 A / 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 isopropanol 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 to 80 g / L, the condensate of ethylenediamine or dimethylpropylamine and epichlorohydrin is 20 to 50 g / L, the sodium salt of 2-ethylhexyl sulfate is 30 to 80 g / L, and the D component is 30 to 60 g / L.

2. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1 is characterized in that: The polymerized thiocyanate copper plating process includes the following components and process parameters: Polycuprous thiocyanate 18-24 g / L, polysodium thiocyanate 130-170 g / L, disodium hydroxyethylidene diphosphonate 10-40 g / L, HT-810 brightener 1-2 mL / L, HT-810 moving agent 2-4 mL / L, plating solution pH 12-13, plating tank temperature 25-45°C, cathode current density 0.5-1.5 A / dm 2 The cathode moves 3-5 m / min, oxygen-free electrolytic copper particles are used as anodes, and the anode current density is less than 1 A / dm 2 , the anode moves 3 to 5 m / min.

3. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1, characterized in that: The thickness of the cyanide-free cadmium iron plating layer is 8 to 18 μm.

4. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1, characterized in that: The thickness of the cyanide-free copper plating layer is 4 to 8 μm.

5. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1 is characterized in that: The passivation layer includes a hexavalent chromium color passivation layer, a hexavalent chromium military green passivation layer, and a hexavalent chromium black passivation layer.

6. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 5, characterized in that: 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 s, and weak air stirring or workpiece swinging is performed.

7. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 5, characterized in that: 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, air stirring or swinging the plated piece.

8. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 5, characterized in that: The hexavalent chromium black passivation layer is prepared by using the BZ-71 cadmium black passivation process: BZ-71A cadmium black passivation agent 80-100 mL / L, BZ-71B cadmium black passivation agent 80-100 mL / L, the pH value of the passivation solution is 1.1-1.5, the passivation temperature is 20-35°C, the passivation time is 15-40 s, and the plated piece is stirred or swung by air.

9. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1, characterized in that: The graphene modified sealing layer is prepared using PRODICO 480 graphene sealing agent: Dilute PRODICO 480 graphene-modified sealer with water to 2.5-3.2 times to prepare the sealing solution. Immerse the plated parts in the sealing solution for 8-15 seconds. Drain the parts after leaving the tank, and use high-pressure air to blow away the sealing solution remaining on the surface of the plated parts. After sealing, dry and cure at 70-80°C for 20-30 minutes.

10. The cyanide-free cadmium-iron alloy plating process for zinc alloy die castings according to claim 1, characterized in that: The thickness of the graphene modified sealing layer is 0.6-1.8 μm.

Images