Complexing agent and potassium chloride-based zinc-iron alloy plating solution containing the same, and zinc-iron electroplating method

Abstract

A complexing agent for zinc-iron alloy electroplating, including component A selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof, component B being sodium sulfosalicylate. An electroplating solution is provided, including 50-70 g / L of zinc chloride, 2-12 g / L of ferrous chloride tetrahydrate, 160-240 g / L of potassium chloride, 25-35 g / L of boric acid, 6-55 g / L of the complexing agent, 0.1-0.2 mL / L of a brightener and 20-30 mL / L of an electroplating additive, with a pH of 4.5-5.6. During the electroplating process, a temperature of a plating bath is controlled at 15-30° C., a cathode current density is 1-3 A / dm2 and a swept rate of cathode is 3-5 m / min.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from Chinese Patent Application No. 202411964288.4, filed on Dec. 30, 2024. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This application relates to electroplating, and more particularly to a complexing agent and a potassium chloride-based zinc-iron alloy plating solution containing the same, and a zinc-iron alloy electroplating method.BACKGROUND

[0003] With the industrial development in China, the traditional zinc plating process has been extensively replaced with a zinc-nickel alloy electroplating process. However, the zinc-nickel plating solution contains highly oxidation-resistant complexing agents such as diethylenetriamine, which pose significant challenges for the electroplating wastewater treatment (Guo et al., Combined process for treating alkaline zinc-nickel alloy electroplating and passivation wastewater, Electroplating & Finishing, 2021, 40(7):579-583). In view of this, extensive attempts have been made to develop a zinc-iron electroplating process to replace the zinc-nickel electroplating process, but no breakthrough has been achieved so far.

[0004] Iron is a cost-effective metal that can form high-performance alloys with commonly used metals. In the field of electroplating, alkaline zinc-iron alloy electroplating has been widely adopted. However, in China, due to the low iron content in the alkaline zinc-iron alloy plating solution, a weight percentage of the iron in the coating typically ranges from 0.3% to 0.7% (Zhang et al., Status of Zn-Fe Electroplating, 1998, 18(5):7-11), and the coating performance does not yet meet the requirements for zinc-nickel alloy coatings. In an acidic zinc-iron alloy plating solution, ferrous ions are easily oxidized by oxygen molecules into ferric ions, leading to the formation of ferric hydroxide precipitates. This is particularly evident in a chloride-based acidic zinc-iron alloy plating solution, where ferric hydroxide precipitation can occur after just five days of storage (Zhou et al., Study of zinc-iron electrodeposition in light acid solution containing (NH4)2Fe(SO4)2, 2010, 29(1):32-27). The stability issues have greatly limited the application of the acidic zinc-iron alloy plating solution, and it has been rarely reported about the industrial application of the acidic zinc-iron alloy electroplating to date.

[0005] Hydroxy-graphene-modified sealants recently developed have significantly improved the corrosion resistance and other properties of coatings. The prepared sealing layer exhibits a self-healing capability. When applied to seal zinc and zinc-nickel alloy coatings that have been passivated with trivalent chromium, these sealants effectively remedy the deficiency that the trivalent chromium passivation films cannot offer the self-repairing property (Guo et al., Study on properties of graphene oxide in sealant for plated coatings, 2021, 40(9):696-700).SUMMARY

[0006] To improve the stability of an acidic zinc-iron alloy plating solution, the present disclosure provides a complexing agent and a potassium chloride-based zinc-iron alloy plating solution containing the same, and a zinc-iron alloy electroplating method.

[0007] A complexing agent for a potassium chloride-based zinc-iron alloy plating solution, comprising:

[0008] a component A; and

[0009] a component B;

[0010] wherein the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof;

[0011] the component B is sodium sulfosalicylate;

[0012] a weight ratio of the component A to the component B is 3:1-3; and

[0013] a weight concentration of the complexing agent in the potassium chloride-based zinc-iron alloy plating solution is 6-55 g / L.

[0014] In some embodiments, a potassium chloride-based zinc-iron alloy plating solution, comprising:

[0015] 50-70 g / L of zinc chloride;

[0016] 2-12 g / L of ferrous chloride tetrahydrate or 3-17 g / L of ferrous sulfate heptahydrate;

[0017] 160-240 g / L of potassium chloride;

[0018] 25-35 g / L of boric acid;

[0019] 6-55 g / L of a complexing agent;

[0020] 0.1-0.2 mL / L of a brightener;

[0021] 20-30 mL / L of an electroplating additive; and

[0022] wherein the potassium chloride-based zinc-iron alloy plating solution has a pH of 4.5-5.6;

[0023] the complexing agent comprises a component A and a component B; the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof; the component B is sodium sulfosalicylate; and the component A and the component B are mixed according to a weight ratio of 3:1-3;

[0024] the brightener comprises o-chlorobenzaldehyde and formic acid in a weight ratio 1:0.8-1.2;

[0025] the electroplating additive comprises 17-23 parts by weight of a sulfonation product of a fatty alcohol polyoxyethylene ether and sulfamic acid, 5-7 parts by weight of sodium benzoate, 0.4-0.6 part by weight of nicotinic acid and 80-90 parts by weight of water.

[0026] In some embodiments, the brightener is prepared through steps of:

[0027] mixing o-chlorobenzaldehyde with formic acid in the weight ratio of 1:0.8-1.2 under stirring to obtain the brightener; and

[0028] the electroplating additive is prepared through steps of:

[0029] adding 17-23 kg of the sulfonation product, 5-7 kg of sodium benzoate and 0.4-0.6 kg of nicotinic acid to 70 kg of water, followed by stirring for complete dissolution and dilution to 100 L with water, so as to obtain the electroplating additive.

[0030] In some embodiments, the sulfonation product is derived from an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid.

[0031] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution has a pH of 4.5-5.6.

[0032] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is prepared through steps of:

[0033] adding water to a plating bath followed by addition of zinc chloride, potassium chloride, boric acid, and complexing agent and stirring for dissolution, wherein the water added to the plating bath is 70% of a predetermined volume of the potassium chloride-based zinc-iron alloy plating solution;

[0034] adding ferrous chloride tetrahydrate to the plating bath followed by stirring for dissolution;

[0035] adding the brightener and the electroplating additive to the plating bath, followed by stirring, adjustment to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, and addition of water to the predetermined volume to produce a mixture; and

[0036] electrolyzing the mixture at a current density of 0.1-0.2 A / dm2 for 30-90 minutes to produce the potassium chloride-based zinc-iron alloy plating solution.

[0037] A zinc-iron electroplating method is also provided, comprising:

[0038] preparing the potassium chloride-based zinc-iron alloy plating solution;

[0039] preprocessing a workpiece;

[0040] in the potassium chloride-based zinc-iron alloy plating solution, electroplating zinc-iron alloy on a preprocessed workpiece to give an electroplated workpiece;

[0041] subjecting the electroplated workpiece to trivalent chromium passivation to form a passivation film-coated workpiece; and

[0042] sealing the passivation film-coated workpiece with a graphene-modified sealant to form a graphene-modified sealing film, thereby obtaining a finished workpiece;

[0043] wherein a temperature of a plating bath is controlled at 15-30° C., a current density of a cathode is 1-3 A / dm2, and a swept rate of cathode is 3-5 m / min.

[0044] In some embodiments, an anode is a zinc plate with a weight percentage of 99.99%.

[0045] In some embodiments, an area ratio of the cathode to an anode is 2:0.7-1.3.

[0046] In some embodiments, a 30 wt. % ferrous chloride tetrahydrate solution is supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate at 2-12 g / L.

[0047] Compared to the prior art, the present disclosure has the following beneficial effects.

[0048] (1) In the zinc-iron alloy electroplating method disclosed herein, the component A in the complexing agent (e.g., sodium glucoheptonate) can form stable complex ions with ferrous ions, effectively inhibiting their oxidation to ferric ions.

[0049] (2) The sodium sulfosalicylate in the complexing agent provided herein exhibits unique complexing ability toward ferric ions, with a log K3 of 32.12. The small amount of ferric ions in the plating solution forms stable complex ions with sodium sulfosalicylate, which then undergo co-deposition with zinc to produce a high-performance plating coating, without adversely affecting the plating solution.

[0050] (3) The present disclosure overcomes the poor stability of traditional chloride-based acidic zinc-iron alloy plating solutions.

[0051] (4) A zinc-iron alloy coating prepared by the method provided herein has significantly better salt spray resistance than the current potassium chloride zinc plating layers.

[0052] (5) In the process method disclosed herein, the formic acid is used as a solvent to dissolve o-chlorobenzaldehyde, significantly increasing the content of o-chlorobenzaldehyde in the brightener and improving the cost-effectiveness of the brightener.

[0053] (6) In the process method disclosed herein, the formic acid in the brightener exhibits a strong reducing property, which can inhibit the formation of ferric ions in the plating solution.BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying figures described herein are for further understanding of the disclosure, which form a part of this application, and should not be construed as limitation to the present disclosure.

[0055] FIG. 1 schematically shows a coating of Embodiment 1 of the present disclosure;

[0056] FIG. 2 schematically shows a coating of Embodiment 2 of the present disclosure;

[0057] FIG. 3 schematically shows a coating of Embodiment 3 of the present disclosure; and

[0058] FIG. 4 schematically shows a coating of Embodiment 4 of the present disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[0059] The illustrative embodiments and the descriptions provided herein are used to elaborate the technical solutions of this disclosure to facilitate understanding this disclosure, and are not intended to limit the present disclosure.

[0060] The present disclosure provides a plating solution, including a complexing agent, a brightener and an electroplating additive. The electroplating process provided herein includes pretreatment, zinc-iron alloy electroplating, passivation and sealing.

[0061] In some embodiments, the complexing agent includes a component A and a component B. The component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof. The component B is sodium sulfosalicylate. The component A and the component B are mixed according to a weight ratio of 3:1-3.

[0062] In some embodiments, the brightener includes o-chlorobenzaldehyde and formic acid in a weight ratio of 1:0.8-1.2. The o-chlorobenzaldehyde and the formic acid are mixed, stirred, and dissolved to give the brightener.

[0063] In some embodiments, the electroplating additive includes a sulfonation product of a fatty alcohol polyoxyethylene ether and sulfamic acid, sodium benzoate, nicotinic acid and water. 17-23 kg of the sulfonation product, 5-7 kg of the sodium benzoate and 0.4-0.6 kg of the nicotinic acid are added to 70 kg of the water, followed by stirring for complete dissolution and dilution to 100 L with water, so as to obtain the electroplating additive.

[0064] In some embodiments, the sulfonation product is derived from an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid.

[0065] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is prepared through the following steps.

[0066] 70% water is added to a plating bath followed by addition of zinc chloride, potassium chloride, boric acid, and the complexing agent and stirring for dissolution, where the water added to the plating bath is 70% of a predetermined volume of the potassium chloride-based zinc-iron alloy plating solution.

[0067] Ferrous chloride tetrahydrate is added to the plating tank, followed by stirring for dissolution.

[0068] The brightener and the electroplating additive are added to the plating bath followed by stirring, adjustment to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution and addition of water to the predetermined volume to produce a mixture.

[0069] The mixture is electrolyzed at a current density of 0.1-0.2 A / dm2 for 30-90 minutes to produce the potassium chloride-based zinc-iron alloy plating solution.

[0070] In some embodiments, the zinc-iron electroplating method provides an electroplating solution with a pH 4.5-5.6 for an electroplating process. The electroplating solution includes 50-70 g / L of zinc chloride, 2-12 g / L of ferrous chloride tetrahydrate, 160-240 g / L of potassium chloride, 25-35 g / L of boric acid, 6-55 g / L of complexing agent, 0.1-0.2 mL / L of brightener and 20-30 mL / L of electroplating additive. During the electroplating process, a temperature of a plating bath is controlled at 15-30° C., a cathode current density is 1-3 A / dm2 and a swept rate of cathode is 3-5 m / min.

[0071] In some embodiments, an anode is a zinc plate with a weight percentage of 99.9%.

[0072] In some embodiments, an area ratio of the cathode to an anode is 2:0.7-1.3.

[0073] In some embodiments, a 30 wt. % ferrous chloride tetrahydrate solution is supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate at 2-12 g / L.

[0074] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution includes 2-12 g / L of ferrous chloride tetrahydrate or 3-17 g / L of ferrous sulfate heptahydrate.

[0075] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is filtered circularly by a filter machine during production.

[0076] In some embodiments, the zinc-iron alloy electroplating method is performed through the following steps.

[0077] The potassium chloride-based zinc-iron alloy plating solution is prepared.

[0078] A pretreatment is performed on a workpiece to give a pre-treated workpiece.

[0079] A zinc-iron alloy coating is electrodeposited onto the pretreated workpiece to give an electroplated workpiece.

[0080] The electroplated workpiece is subjected to trivalent chromium passivation to form a passivated workpiece.

[0081] The passivation film-coated workpiece is sealed with a graphene-modified sealant to form a graphene-modified sealing film, thereby obtaining a finished workpiece.

[0082] In some embodiments, an aluminium-based alloy workpiece is coated with a zinc layer by chemical zinc immersion.

[0083] In some embodiments, the trivalent chromium passivation is performed by using a TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd). The TRIROS 348 zinc-iron blue-white passivation is performed in a passivating solution including 135-175 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 1.8-2.6; passivating temperature: 30-60° C.; passivating time: 30-60 s; and air stirring.

[0084] In some embodiments, the graphene-modified sealing film is prepared by using a PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd). The PRODICO 480 graphene-modified sealant is diluted with water to 2.5-3.2 times to prepare a sealing solution. The passivation film-coated workpiece is immersed in the sealing solution for 8-15 s. After taking it out of the sealing solution, the passivation film-coated workpiece is drained and blown off the residual sealing solution on the surface of the passivation film-coated workpiece with high-pressure air to give the finished workpiece. After sealing, the finished workpiece is dried and solidified at 70-85° C. for 20-35 minutes.

[0085] In some embodiments, the zinc immersion layer is prepared by using a ALBUME AS-699 cyanide-free zinc immersion method for aluminum (Guangzhou Ultra Union Chemicals Co., Ltd). The ALBUME AS-699 cyanide-free zinc immersion for aluminum is performed in an immersion solution including 150-175 mL / L of ALBUME AS-699 cyanide-free zinc immersion agent for aluminum, 6-9 g / L of zinc ion and 0.16-0.20 g / L cupric ion under the following conditions: immersion temperature: 20-30° C.; and immersion time: 60-120 s.Embodiment 1

[0086] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0087] Referring to FIG. 1, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a steel substrate 01, a zinc-iron alloy coating 02, a trivalent chromium blue-white passivation film 03, and a graphene-modified sealing film 04 sequentially arranged from inside to outside.(1) Pretreatment

[0088] The steel substrate 01 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation and water rinsing to complete the pretreatment process and give a pretreated steel substrate 01.(2) Zinc-Iron Alloy Plating

[0089] The pretreated steel substrate 01 was plated with the zinc-iron alloy coating 02 with a thickness of 12 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated steel substrate 01. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0090] Sodium gluconate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0091] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0092] 20 kg of a sulfonation product of an OX- 105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0093] Water was added to a plating bath, to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 5 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume, and electrolyzed at a current density of 0.15 A / dm2 for 60 minutes to produce the plating solution.Plating Operation

[0094] The plating operation was performed in a plating solution including 60 g / L of zinc chloride, 10 g / L of ferrous chloride tetrahydrate, 200 g / L of potassium chloride, 30 g / L of boric acid, 35 g / L of the complexing agent, 0.15 mL / L of the brightener, and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5; plating temperature: 20° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(3) Passivation

[0095] The electroplated steel workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 03. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 150 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.4; passivating temperature: 45° C.; passivating time: 45 s; and air stirring, so as to form a passivation film-coated steel workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation and water rinsing.(4) Sealing

[0096] The passivation film-coated steel workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 04, thereby obtaining a finished steel workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated steel workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed steel workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished steel workpiece. After sealing, the finished steel workpiece was dried and solidified at 80° C. for 25 minutes.Embodiment 2

[0097] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0098] Referring to FIG. 2, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a zinc alloy substrate 11, a zinc-iron alloy coating 12, a trivalent chromium blue-white passivation film 13, and a graphene-modified sealing film 14 sequentially arranged from inside to outside.(1) Pretreatment

[0099] The zinc alloy substrate 11 was sequentially subjected to chemical dewaxing, water rinsing, ultrasonic dewaxing, water rinsing, ultrasonic degreasing, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated zinc alloy substrate 11.(2) Zinc-Iron Alloy Plating

[0100] The pretreated zinc alloy substrate 11 was plated with the zinc-iron alloy coating 12 with a thickness of 16 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated zinc alloy substrate 11. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0101] Sodium glucoheptonate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0102] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0103] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water, so as to obtain the electroplating additive.Preparation of the Plating Solution

[0104] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 4.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.15 A / dm2 for 60 minutes to produce the plating solution.Plating Operation:

[0105] The plating operation was performed in a plating solution including 70 g / L of zinc chloride, 10 g / L of ferrous chloride tetrahydrate, 220 g / L of potassium chloride, 35 g / L of boric acid, 55 g / L of the complexing agent, 0.15 mL / L of the brightener and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 4.6; plating temperature: 25° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution with a weight percentage of 30% was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the platng bath to a predetermined concentration.(3) Passivation Process

[0106] The electroplated zinc alloy workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 13. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 175 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of passivating solution: 2.4; passivating temperature: 40° C.; passivating time: 40 s; and air stirring, so as to form a passivation film-coated zinc alloy workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation, and water rinsing.(4) Sealing

[0107] The passivation film-coated zinc alloy workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 14, thereby obtaining a finished zinc alloy workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated zinc alloy workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed zinc alloy workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished zinc alloy workpiece. After sealing, the finished zinc alloy workpiece was dried and solidified at 85° C. for 20 minutes.Embodiment 3

[0108] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0109] Referring to FIG. 3, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a cast iron substrate 21, a zinc-iron alloy coating 22, a trivalent chromium blue-white passivation film 23 and a graphene-modified sealing film 24 sequentially arranged from inside to outside.(1) Pretreatment

[0110] The cast iron substrate 21 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated cast iron substrate 21.(2) Zinc-iron Alloy Plating

[0111] The pretreated cast iron substrate 21 was plated with the zinc-iron alloy coating 22 with a thickness of 16 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated cast iron substrate 21. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0112] Potassium sodium tartrate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0113] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0114] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0115] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 5.3 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.1 A / dm2 for 90 minutes to produce the plating solution.Plating Operation

[0116] The plating operation was performed in a plating solution including 50 g / L of zinc chloride, 8 g / L of ferrous chloride tetrahydrate, 180 g / L of potassium chloride, 25 g / L of boric acid, 25 g / L of the complexing agent, 0.15 mL / L of the brightener and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5.3; plating temperature: 23° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(3) Passivation

[0117] The electroplated cast iron workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 23. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 135 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.0; passivating temperature: 50° C.; passivating time: 45 s; and air stirring, so as to form a passivation film-coated cast iron workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation, and water rinsing.(4) Sealing

[0118] The passivation film-coated cast iron workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 24, thereby obtaining a finished cast iron workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated cast iron workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed cast iron workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished cast iron workpiece. After sealing, the finished cast iron workpiece was dried and solidified at 70° C. for 35 minutes.Embodiment 4

[0119] Provided herein was a plating solution, including a complexing agent, a brightener, and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0120] Referring to FIG. 4, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included an aluminum alloy substrate 1, a zinc immersion layer 2, a zinc-iron alloy coating 3, a trivalent chromium blue-white passivation film 4, and a graphene-modified sealing film 5 sequentially arranged from inside to outside.(1) Pretreatment

[0121] The aluminum alloy substrate 1 was sequentially subjected to chemical degreasing, water rinsing, ultrasonic degreasing, water rinsing, alkaline etching, water rinsing, bright dipping, water rinsing, micro-etching, water rinsing to complete the pretreatment process and give a pretreated aluminum alloy substrate 1.(2) Chemical Zinc Immersion

[0122] The pretreated aluminum alloy substrate 1 was subjected to a zinc immersion by using the ALBUME AS-699 cyanide-free zinc immersion (Guangzhou Ultra Union Chemicals Co., Ltd) to form the zinc immersion layer 2. The ALBUME AS-699 cyanide-free zinc immersion was performed in an immersion solution including 160 mL / L of ALBUME AS-699 cyanide-free zinc immersion agent, 7.5 g / L of zinc ion and 0.18 g / L cupric ion under the following conditions: immersion temperature: 25° C.; and immersion time: 90 s to give an immersed aluminum alloy substrate 1. The specific process includes first chemical zinc immersion, water rinsing, zinc stripping, water rinsing, second chemical zinc immersion, and water rinsing.(3) Zinc-Iron Alloy Plating

[0123] The immersed aluminum alloy substrate 1 was plated with the zinc-iron alloy coating 3 with a thickness of 12 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated aluminum alloy substrate 1. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0124] Sodium citrate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0125] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0126] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0127] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.2 A / dm2 for 30 minutes to produce the plating solution.Plating Operation

[0128] The plating operation was performed in a plating solution including 65 g / L of zinc chloride, 10 g / L of ferrous sulfate, 240 g / L of potassium chloride, 30 g / L of boric acid, 40 g / L of the complexing agent, 0.15 mL / L of the brightener, and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5.4; plating temperature: 25° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was circulated and filtered by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating tank during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(4) Passivation

[0129] The electroplated aluminum alloy workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 4. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 160 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.2; passivating temperature: 50° C.; passivating time: 35 s; and air stirring, so as to form a passivation film-coated aluminum alloy workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation and water rinsing.(5) Sealing Process

[0130] The aluminum alloy workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 5, thereby obtaining a finished aluminum alloy workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare the sealing solution. The passivated aluminum alloy workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed aluminum alloy workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished aluminum alloy workpiece. After sealing, the finished aluminum alloy workpiece was dried and solidified at 75° C. for 30 minutes.Example 1

[0131] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were subjected to a neutral salt spray test according to GB / T 10125-2021 “Corrosion tests in artificial atmospheres-Salt spray tests”. After 480 hours of testing, no white rust was observed on the surfaces of the zinc-iron alloy samples. The corrosion resistance of the coating prepared in the present disclosure far exceeded the requirement of 216 hours without white rust specified in GB / T 41950-2022 “Metallic coatings-Electroplated coatings of zinc and zinc alloys on iron or steel with without hexavalent chromium conversion coatings”.Example 2

[0132] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were tested for coating adhesion according to GB / T 5270-2005 “Metallic coatings on metallic substrates-Review of methods for testing adhesion of electrodeposited and chemically deposited coatings”. A steel workpiece and a cast iron workpiece were heated to 250° C. for 60 minutes in a heating furnace. A zinc alloy workpiece was heated to 150° C. for 60 minutes. An aluminum alloy workpiece was heated to 220° C. for 60 minutes. After heating, these workpieces were immediately taken out and quenched in water at room temperature. No blistering or peeling of their coatings was observed. It was demonstrated that the coating prepared by the present disclosure exhibited an excellent adhesion.Example 3

[0133] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were subjected to a 28-day mold test according to GJB 150.10A-2009 “Laboratory Environmental Test Methods for Military Materiel-Part 10: Mold Test”. No mold growth was observed on the surface of the zinc-iron alloy samples, confirming compliance with environmental test requirements.Example 4

[0134] 1000 mL of potassium chloride-based zinc-iron alloy plating solution was prepared, including 70 g / L of zinc chloride, 12 g / L of ferrous chloride tetrahydrate, 220 g / L of potassium chloride, 35 g / L of boric acid, 35 g / L of the complexing agent, 0.2 mL / L of the brightener, and 30 mL / L of the electroplating additive. The pH of the plating solution was adjusted to 5.6. After storing the plating solution in a laboratory for one month, no precipitate formation was observed.Example 5

[0135] 250 mL of potassium chloride-based zinc-iron alloy plating solution prepared in Example 4 was continuously subjected to a Hull cell test. Specifically, each panel was plated under the condition: 1 A current for 10 minutes. Based on practical conditions, the brightener, the electroplating additive, the complexing agent, the ferrous chloride, and the potassium chloride were supplemented as needed. Finally, a total of 120 panels were plated. Throughout the testing, no iron hydroxide precipitate formed in the plating solution. The plating solution exhibited a good covering ability, deposited a bright coating, and no significant changes in coating appearance were observed during continuous plating.Comparative Example 1

[0136] According to the method provided in the Embodiment 1, the zinc-iron alloy electroplating method in the Embodiment 1 was replaced with a ZINLITE 401 potassium chloride-based zinc electroplating method (Guangzhou Ultra Union Chemicals Co., Ltd). A steel workpiece was sequentially plated with zinc, passivated through a trivalent chromium blue-white passivation and sealed with a graphene-modified sealant to obtain a zinc-plated sample. The zinc-plated sample was subjected to a neutral salt spray test according to GB / T 10125-2021 “Corrosion tests in artificial atmospheres—Salt spray tests”. No white rust was observed on the surface after 320 hours.

[0137] The technical solutions provided in the embodiments of the present disclosure have been described in detail above. The principle and the implement method of the embodiments of the present disclosure have been elaborated with reference to some specific examples. The introductions of the above embodiments are used to facilitate understanding the principle of the embodiments of the present disclosure. It should be noted that any modifications and improvements made by those skilled in the art without departing from the spirit of the disclosure shall fall within the scope of the disclosure defined by the appended claims.

Examples

embodiment 1

[0086]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0087]Referring to FIG. 1, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a steel substrate 01, a zinc-iron alloy coating 02, a trivalent chromium blue-white passivation film 03, and a graphene-modified sealing film 04 sequentially arranged from inside to outside.

(1) Pretreatment

[0088]The steel substrate 01 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation and water rinsing to complete the pretreatment process and give a pretreated steel substrate 01.

(2) Zinc-Iron Alloy Plating

[0089]The pretre...

embodiment 2

[0097]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0098]Referring to FIG. 2, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a zinc alloy substrate 11, a zinc-iron alloy coating 12, a trivalent chromium blue-white passivation film 13, and a graphene-modified sealing film 14 sequentially arranged from inside to outside.

(1) Pretreatment

[0099]The zinc alloy substrate 11 was sequentially subjected to chemical dewaxing, water rinsing, ultrasonic dewaxing, water rinsing, ultrasonic degreasing, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated zinc alloy substrate 11.

(2) Zinc-Iron Alloy Plating

[0100]The pretreated zinc alloy substrate 11 was plated...

embodiment 3

[0108]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0109]Referring to FIG. 3, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a cast iron substrate 21, a zinc-iron alloy coating 22, a trivalent chromium blue-white passivation film 23 and a graphene-modified sealing film 24 sequentially arranged from inside to outside.

(1) Pretreatment

[0110]The cast iron substrate 21 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated cast iron substrate 21.

(2) Zinc-iron Alloy Plating

[011...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from Chinese Patent Application No. 202411964288.4, filed on Dec. 30, 2024. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This application relates to electroplating, and more particularly to a complexing agent and a potassium chloride-based zinc-iron alloy plating solution containing the same, and a zinc-iron alloy electroplating method.BACKGROUND

[0003] With the industrial development in China, the traditional zinc plating process has been extensively replaced with a zinc-nickel alloy electroplating process. However, the zinc-nickel plating solution contains highly oxidation-resistant complexing agents such as diethylenetriamine, which pose significant challenges for the electroplating wastewater treatment (Guo et al., Combined process for treating alkaline zinc-nickel alloy electroplating and passivation wastewater, Electroplating & Finishing, 2021, 40(7):579-583). In view of this, extensive attempts have been made to develop a zinc-iron electroplating process to replace the zinc-nickel electroplating process, but no breakthrough has been achieved so far.

[0004] Iron is a cost-effective metal that can form high-performance alloys with commonly used metals. In the field of electroplating, alkaline zinc-iron alloy electroplating has been widely adopted. However, in China, due to the low iron content in the alkaline zinc-iron alloy plating solution, a weight percentage of the iron in the coating typically ranges from 0.3% to 0.7% (Zhang et al., Status of Zn-Fe Electroplating, 1998, 18(5):7-11), and the coating performance does not yet meet the requirements for zinc-nickel alloy coatings. In an acidic zinc-iron alloy plating solution, ferrous ions are easily oxidized by oxygen molecules into ferric ions, leading to the formation of ferric hydroxide precipitates. This is particularly evident in a chloride-based acidic zinc-iron alloy plating solution, where ferric hydroxide precipitation can occur after just five days of storage (Zhou et al., Study of zinc-iron electrodeposition in light acid solution containing (NH4)2Fe(SO4)2, 2010, 29(1):32-27). The stability issues have greatly limited the application of the acidic zinc-iron alloy plating solution, and it has been rarely reported about the industrial application of the acidic zinc-iron alloy electroplating to date.

[0005] Hydroxy-graphene-modified sealants recently developed have significantly improved the corrosion resistance and other properties of coatings. The prepared sealing layer exhibits a self-healing capability. When applied to seal zinc and zinc-nickel alloy coatings that have been passivated with trivalent chromium, these sealants effectively remedy the deficiency that the trivalent chromium passivation films cannot offer the self-repairing property (Guo et al., Study on properties of graphene oxide in sealant for plated coatings, 2021, 40(9):696-700).SUMMARY

[0006] To improve the stability of an acidic zinc-iron alloy plating solution, the present disclosure provides a complexing agent and a potassium chloride-based zinc-iron alloy plating solution containing the same, and a zinc-iron alloy electroplating method.

[0007] A complexing agent for a potassium chloride-based zinc-iron alloy plating solution, comprising:

[0008] a component A; and

[0009] a component B;

[0010] wherein the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof;

[0011] the component B is sodium sulfosalicylate;

[0012] a weight ratio of the component A to the component B is 3:1-3; and

[0013] a weight concentration of the complexing agent in the potassium chloride-based zinc-iron alloy plating solution is 6-55 g / L.

[0014] In some embodiments, a potassium chloride-based zinc-iron alloy plating solution, comprising:

[0015] 50-70 g / L of zinc chloride;

[0016] 2-12 g / L of ferrous chloride tetrahydrate or 3-17 g / L of ferrous sulfate heptahydrate;

[0017] 160-240 g / L of potassium chloride;

[0018] 25-35 g / L of boric acid;

[0019] 6-55 g / L of a complexing agent;

[0020] 0.1-0.2 mL / L of a brightener;

[0021] 20-30 mL / L of an electroplating additive; and

[0022] wherein the potassium chloride-based zinc-iron alloy plating solution has a pH of 4.5-5.6;

[0023] the complexing agent comprises a component A and a component B; the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof; the component B is sodium sulfosalicylate; and the component A and the component B are mixed according to a weight ratio of 3:1-3;

[0024] the brightener comprises o-chlorobenzaldehyde and formic acid in a weight ratio 1:0.8-1.2;

[0025] the electroplating additive comprises 17-23 parts by weight of a sulfonation product of a fatty alcohol polyoxyethylene ether and sulfamic acid, 5-7 parts by weight of sodium benzoate, 0.4-0.6 part by weight of nicotinic acid and 80-90 parts by weight of water.

[0026] In some embodiments, the brightener is prepared through steps of:

[0027] mixing o-chlorobenzaldehyde with formic acid in the weight ratio of 1:0.8-1.2 under stirring to obtain the brightener; and

[0028] the electroplating additive is prepared through steps of:

[0029] adding 17-23 kg of the sulfonation product, 5-7 kg of sodium benzoate and 0.4-0.6 kg of nicotinic acid to 70 kg of water, followed by stirring for complete dissolution and dilution to 100 L with water, so as to obtain the electroplating additive.

[0030] In some embodiments, the sulfonation product is derived from an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid.

[0031] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution has a pH of 4.5-5.6.

[0032] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is prepared through steps of:

[0033] adding water to a plating bath followed by addition of zinc chloride, potassium chloride, boric acid, and complexing agent and stirring for dissolution, wherein the water added to the plating bath is 70% of a predetermined volume of the potassium chloride-based zinc-iron alloy plating solution;

[0034] adding ferrous chloride tetrahydrate to the plating bath followed by stirring for dissolution;

[0035] adding the brightener and the electroplating additive to the plating bath, followed by stirring, adjustment to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, and addition of water to the predetermined volume to produce a mixture; and

[0036] electrolyzing the mixture at a current density of 0.1-0.2 A / dm2 for 30-90 minutes to produce the potassium chloride-based zinc-iron alloy plating solution.

[0037] A zinc-iron electroplating method is also provided, comprising:

[0038] preparing the potassium chloride-based zinc-iron alloy plating solution;

[0039] preprocessing a workpiece;

[0040] in the potassium chloride-based zinc-iron alloy plating solution, electroplating zinc-iron alloy on a preprocessed workpiece to give an electroplated workpiece;

[0041] subjecting the electroplated workpiece to trivalent chromium passivation to form a passivation film-coated workpiece; and

[0042] sealing the passivation film-coated workpiece with a graphene-modified sealant to form a graphene-modified sealing film, thereby obtaining a finished workpiece;

[0043] wherein a temperature of a plating bath is controlled at 15-30° C., a current density of a cathode is 1-3 A / dm2, and a swept rate of cathode is 3-5 m / min.

[0044] In some embodiments, an anode is a zinc plate with a weight percentage of 99.99%.

[0045] In some embodiments, an area ratio of the cathode to an anode is 2:0.7-1.3.

[0046] In some embodiments, a 30 wt. % ferrous chloride tetrahydrate solution is supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate at 2-12 g / L.

[0047] Compared to the prior art, the present disclosure has the following beneficial effects.

[0048] (1) In the zinc-iron alloy electroplating method disclosed herein, the component A in the complexing agent (e.g., sodium glucoheptonate) can form stable complex ions with ferrous ions, effectively inhibiting their oxidation to ferric ions.

[0049] (2) The sodium sulfosalicylate in the complexing agent provided herein exhibits unique complexing ability toward ferric ions, with a log K3 of 32.12. The small amount of ferric ions in the plating solution forms stable complex ions with sodium sulfosalicylate, which then undergo co-deposition with zinc to produce a high-performance plating coating, without adversely affecting the plating solution.

[0050] (3) The present disclosure overcomes the poor stability of traditional chloride-based acidic zinc-iron alloy plating solutions.

[0051] (4) A zinc-iron alloy coating prepared by the method provided herein has significantly better salt spray resistance than the current potassium chloride zinc plating layers.

[0052] (5) In the process method disclosed herein, the formic acid is used as a solvent to dissolve o-chlorobenzaldehyde, significantly increasing the content of o-chlorobenzaldehyde in the brightener and improving the cost-effectiveness of the brightener.

[0053] (6) In the process method disclosed herein, the formic acid in the brightener exhibits a strong reducing property, which can inhibit the formation of ferric ions in the plating solution.BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying figures described herein are for further understanding of the disclosure, which form a part of this application, and should not be construed as limitation to the present disclosure.

[0055] FIG. 1 schematically shows a coating of Embodiment 1 of the present disclosure;

[0056] FIG. 2 schematically shows a coating of Embodiment 2 of the present disclosure;

[0057] FIG. 3 schematically shows a coating of Embodiment 3 of the present disclosure; and

[0058] FIG. 4 schematically shows a coating of Embodiment 4 of the present disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[0059] The illustrative embodiments and the descriptions provided herein are used to elaborate the technical solutions of this disclosure to facilitate understanding this disclosure, and are not intended to limit the present disclosure.

[0060] The present disclosure provides a plating solution, including a complexing agent, a brightener and an electroplating additive. The electroplating process provided herein includes pretreatment, zinc-iron alloy electroplating, passivation and sealing.

[0061] In some embodiments, the complexing agent includes a component A and a component B. The component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof. The component B is sodium sulfosalicylate. The component A and the component B are mixed according to a weight ratio of 3:1-3.

[0062] In some embodiments, the brightener includes o-chlorobenzaldehyde and formic acid in a weight ratio of 1:0.8-1.2. The o-chlorobenzaldehyde and the formic acid are mixed, stirred, and dissolved to give the brightener.

[0063] In some embodiments, the electroplating additive includes a sulfonation product of a fatty alcohol polyoxyethylene ether and sulfamic acid, sodium benzoate, nicotinic acid and water. 17-23 kg of the sulfonation product, 5-7 kg of the sodium benzoate and 0.4-0.6 kg of the nicotinic acid are added to 70 kg of the water, followed by stirring for complete dissolution and dilution to 100 L with water, so as to obtain the electroplating additive.

[0064] In some embodiments, the sulfonation product is derived from an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid.

[0065] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is prepared through the following steps.

[0066] 70% water is added to a plating bath followed by addition of zinc chloride, potassium chloride, boric acid, and the complexing agent and stirring for dissolution, where the water added to the plating bath is 70% of a predetermined volume of the potassium chloride-based zinc-iron alloy plating solution.

[0067] Ferrous chloride tetrahydrate is added to the plating tank, followed by stirring for dissolution.

[0068] The brightener and the electroplating additive are added to the plating bath followed by stirring, adjustment to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution and addition of water to the predetermined volume to produce a mixture.

[0069] The mixture is electrolyzed at a current density of 0.1-0.2 A / dm2 for 30-90 minutes to produce the potassium chloride-based zinc-iron alloy plating solution.

[0070] In some embodiments, the zinc-iron electroplating method provides an electroplating solution with a pH 4.5-5.6 for an electroplating process. The electroplating solution includes 50-70 g / L of zinc chloride, 2-12 g / L of ferrous chloride tetrahydrate, 160-240 g / L of potassium chloride, 25-35 g / L of boric acid, 6-55 g / L of complexing agent, 0.1-0.2 mL / L of brightener and 20-30 mL / L of electroplating additive. During the electroplating process, a temperature of a plating bath is controlled at 15-30° C., a cathode current density is 1-3 A / dm2 and a swept rate of cathode is 3-5 m / min.

[0071] In some embodiments, an anode is a zinc plate with a weight percentage of 99.9%.

[0072] In some embodiments, an area ratio of the cathode to an anode is 2:0.7-1.3.

[0073] In some embodiments, a 30 wt. % ferrous chloride tetrahydrate solution is supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate at 2-12 g / L.

[0074] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution includes 2-12 g / L of ferrous chloride tetrahydrate or 3-17 g / L of ferrous sulfate heptahydrate.

[0075] In some embodiments, the potassium chloride-based zinc-iron alloy plating solution is filtered circularly by a filter machine during production.

[0076] In some embodiments, the zinc-iron alloy electroplating method is performed through the following steps.

[0077] The potassium chloride-based zinc-iron alloy plating solution is prepared.

[0078] A pretreatment is performed on a workpiece to give a pre-treated workpiece.

[0079] A zinc-iron alloy coating is electrodeposited onto the pretreated workpiece to give an electroplated workpiece.

[0080] The electroplated workpiece is subjected to trivalent chromium passivation to form a passivated workpiece.

[0081] The passivation film-coated workpiece is sealed with a graphene-modified sealant to form a graphene-modified sealing film, thereby obtaining a finished workpiece.

[0082] In some embodiments, an aluminium-based alloy workpiece is coated with a zinc layer by chemical zinc immersion.

[0083] In some embodiments, the trivalent chromium passivation is performed by using a TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd). The TRIROS 348 zinc-iron blue-white passivation is performed in a passivating solution including 135-175 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 1.8-2.6; passivating temperature: 30-60° C.; passivating time: 30-60 s; and air stirring.

[0084] In some embodiments, the graphene-modified sealing film is prepared by using a PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd). The PRODICO 480 graphene-modified sealant is diluted with water to 2.5-3.2 times to prepare a sealing solution. The passivation film-coated workpiece is immersed in the sealing solution for 8-15 s. After taking it out of the sealing solution, the passivation film-coated workpiece is drained and blown off the residual sealing solution on the surface of the passivation film-coated workpiece with high-pressure air to give the finished workpiece. After sealing, the finished workpiece is dried and solidified at 70-85° C. for 20-35 minutes.

[0085] In some embodiments, the zinc immersion layer is prepared by using a ALBUME AS-699 cyanide-free zinc immersion method for aluminum (Guangzhou Ultra Union Chemicals Co., Ltd). The ALBUME AS-699 cyanide-free zinc immersion for aluminum is performed in an immersion solution including 150-175 mL / L of ALBUME AS-699 cyanide-free zinc immersion agent for aluminum, 6-9 g / L of zinc ion and 0.16-0.20 g / L cupric ion under the following conditions: immersion temperature: 20-30° C.; and immersion time: 60-120 s.Embodiment 1

[0086] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0087] Referring to FIG. 1, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a steel substrate 01, a zinc-iron alloy coating 02, a trivalent chromium blue-white passivation film 03, and a graphene-modified sealing film 04 sequentially arranged from inside to outside.(1) Pretreatment

[0088] The steel substrate 01 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation and water rinsing to complete the pretreatment process and give a pretreated steel substrate 01.(2) Zinc-Iron Alloy Plating

[0089] The pretreated steel substrate 01 was plated with the zinc-iron alloy coating 02 with a thickness of 12 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated steel substrate 01. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0090] Sodium gluconate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0091] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0092] 20 kg of a sulfonation product of an OX- 105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0093] Water was added to a plating bath, to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 5 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume, and electrolyzed at a current density of 0.15 A / dm2 for 60 minutes to produce the plating solution.Plating Operation

[0094] The plating operation was performed in a plating solution including 60 g / L of zinc chloride, 10 g / L of ferrous chloride tetrahydrate, 200 g / L of potassium chloride, 30 g / L of boric acid, 35 g / L of the complexing agent, 0.15 mL / L of the brightener, and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5; plating temperature: 20° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(3) Passivation

[0095] The electroplated steel workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 03. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 150 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.4; passivating temperature: 45° C.; passivating time: 45 s; and air stirring, so as to form a passivation film-coated steel workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation and water rinsing.(4) Sealing

[0096] The passivation film-coated steel workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 04, thereby obtaining a finished steel workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated steel workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed steel workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished steel workpiece. After sealing, the finished steel workpiece was dried and solidified at 80° C. for 25 minutes.Embodiment 2

[0097] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0098] Referring to FIG. 2, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a zinc alloy substrate 11, a zinc-iron alloy coating 12, a trivalent chromium blue-white passivation film 13, and a graphene-modified sealing film 14 sequentially arranged from inside to outside.(1) Pretreatment

[0099] The zinc alloy substrate 11 was sequentially subjected to chemical dewaxing, water rinsing, ultrasonic dewaxing, water rinsing, ultrasonic degreasing, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated zinc alloy substrate 11.(2) Zinc-Iron Alloy Plating

[0100] The pretreated zinc alloy substrate 11 was plated with the zinc-iron alloy coating 12 with a thickness of 16 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated zinc alloy substrate 11. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0101] Sodium glucoheptonate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0102] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0103] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water, so as to obtain the electroplating additive.Preparation of the Plating Solution

[0104] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 4.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.15 A / dm2 for 60 minutes to produce the plating solution.Plating Operation:

[0105] The plating operation was performed in a plating solution including 70 g / L of zinc chloride, 10 g / L of ferrous chloride tetrahydrate, 220 g / L of potassium chloride, 35 g / L of boric acid, 55 g / L of the complexing agent, 0.15 mL / L of the brightener and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 4.6; plating temperature: 25° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution with a weight percentage of 30% was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the platng bath to a predetermined concentration.(3) Passivation Process

[0106] The electroplated zinc alloy workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 13. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 175 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of passivating solution: 2.4; passivating temperature: 40° C.; passivating time: 40 s; and air stirring, so as to form a passivation film-coated zinc alloy workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation, and water rinsing.(4) Sealing

[0107] The passivation film-coated zinc alloy workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 14, thereby obtaining a finished zinc alloy workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated zinc alloy workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed zinc alloy workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished zinc alloy workpiece. After sealing, the finished zinc alloy workpiece was dried and solidified at 85° C. for 20 minutes.Embodiment 3

[0108] Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0109] Referring to FIG. 3, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a cast iron substrate 21, a zinc-iron alloy coating 22, a trivalent chromium blue-white passivation film 23 and a graphene-modified sealing film 24 sequentially arranged from inside to outside.(1) Pretreatment

[0110] The cast iron substrate 21 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated cast iron substrate 21.(2) Zinc-iron Alloy Plating

[0111] The pretreated cast iron substrate 21 was plated with the zinc-iron alloy coating 22 with a thickness of 16 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated cast iron substrate 21. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0112] Potassium sodium tartrate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0113] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0114] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0115] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 5.3 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.1 A / dm2 for 90 minutes to produce the plating solution.Plating Operation

[0116] The plating operation was performed in a plating solution including 50 g / L of zinc chloride, 8 g / L of ferrous chloride tetrahydrate, 180 g / L of potassium chloride, 25 g / L of boric acid, 25 g / L of the complexing agent, 0.15 mL / L of the brightener and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5.3; plating temperature: 23° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was filtered circularly by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(3) Passivation

[0117] The electroplated cast iron workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 23. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 135 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.0; passivating temperature: 50° C.; passivating time: 45 s; and air stirring, so as to form a passivation film-coated cast iron workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation, and water rinsing.(4) Sealing

[0118] The passivation film-coated cast iron workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 24, thereby obtaining a finished cast iron workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare a sealing solution. The passivated cast iron workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed cast iron workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished cast iron workpiece. After sealing, the finished cast iron workpiece was dried and solidified at 70° C. for 35 minutes.Embodiment 4

[0119] Provided herein was a plating solution, including a complexing agent, a brightener, and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0120] Referring to FIG. 4, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included an aluminum alloy substrate 1, a zinc immersion layer 2, a zinc-iron alloy coating 3, a trivalent chromium blue-white passivation film 4, and a graphene-modified sealing film 5 sequentially arranged from inside to outside.(1) Pretreatment

[0121] The aluminum alloy substrate 1 was sequentially subjected to chemical degreasing, water rinsing, ultrasonic degreasing, water rinsing, alkaline etching, water rinsing, bright dipping, water rinsing, micro-etching, water rinsing to complete the pretreatment process and give a pretreated aluminum alloy substrate 1.(2) Chemical Zinc Immersion

[0122] The pretreated aluminum alloy substrate 1 was subjected to a zinc immersion by using the ALBUME AS-699 cyanide-free zinc immersion (Guangzhou Ultra Union Chemicals Co., Ltd) to form the zinc immersion layer 2. The ALBUME AS-699 cyanide-free zinc immersion was performed in an immersion solution including 160 mL / L of ALBUME AS-699 cyanide-free zinc immersion agent, 7.5 g / L of zinc ion and 0.18 g / L cupric ion under the following conditions: immersion temperature: 25° C.; and immersion time: 90 s to give an immersed aluminum alloy substrate 1. The specific process includes first chemical zinc immersion, water rinsing, zinc stripping, water rinsing, second chemical zinc immersion, and water rinsing.(3) Zinc-Iron Alloy Plating

[0123] The immersed aluminum alloy substrate 1 was plated with the zinc-iron alloy coating 3 with a thickness of 12 μm by using the potassium chloride-based zinc-iron alloy plating solution to give an electroplated aluminum alloy substrate 1. The potassium chloride-based zinc-iron alloy electroplating method was performed through the following steps.Preparation of the Complexing Agent

[0124] Sodium citrate and sodium sulfosalicylate were mixed at a weight ratio of 3:2 and stirred evenly to obtain the complexing agent.Preparation of the Brightener

[0125] o-Chlorobenzaldehyde and formic acid were mixed at a weight ratio of 1:1 and stirred for complete dissolution to yield the brightener.Preparation of the Electroplating Additive

[0126] 20 kg of a sulfonation product of an OX-105 type fatty alcohol polyoxyethylene ether and sulfamic acid (JadeChem New Materials Co., Ltd), 6 kg of sodium benzoate, and 0.5 kg of nicotinic acid were added to 70 kg of water, stirred for dissolution, and diluted to 100 L with water to obtain the electroplating additive.Preparation of the Plating Solution

[0127] Water was added to a plating bath to which the zinc chloride, the potassium chloride, the boric acid, and the complexing agent were added and stirred to dissolve, where the water is 70% of a predetermined volume of the plating solution. The ferrous chloride tetrahydrate was added to the plating bath and stirred for dissolution. The brightener and the electroplating additive were added to the plating bath, and stirred evenly. The mixture in the plating bath was adjusted to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, added with water to the predetermined volume and electrolyzed at a current density of 0.2 A / dm2 for 30 minutes to produce the plating solution.Plating Operation

[0128] The plating operation was performed in a plating solution including 65 g / L of zinc chloride, 10 g / L of ferrous sulfate, 240 g / L of potassium chloride, 30 g / L of boric acid, 40 g / L of the complexing agent, 0.15 mL / L of the brightener, and 25 mL / L of the electroplating additive under the following conditions: pH of the plating solution: 5.4; plating temperature: 25° C.; cathodic current density: 2 A / dm2; and swept rate of cathode: 4 m / min. The anode was a zinc plate with a weight percentage of 99.99 %. The area ratio of the cathode to the anode was 2:1. The plating solution was circulated and filtered by a filter machine during production. 30 wt. % ferrous chloride tetrahydrate solution was supplemented to a plating tank during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate in the plating bath to a predetermined concentration.(4) Passivation

[0129] The electroplated aluminum alloy workpiece was passivated by using the TRIROS 348 zinc-iron blue-white passivation (Guangzhou Ultra Union Chemicals Co., Ltd) to form the trivalent chromium blue-white passivation film 4. The TRIROS 348 zinc-iron blue-white passivation was performed in a passivating solution including 160 mL / L of TRIROS 348 zinc-iron blue-white passivator under the following conditions: pH of the passivating solution: 2.2; passivating temperature: 50° C.; passivating time: 35 s; and air stirring, so as to form a passivation film-coated aluminum alloy workpiece. The specific process includes removing membrane on the surface of zinc-iron alloy coating with 0.2% sulfuric acid, water rinsing, passivation and water rinsing.(5) Sealing Process

[0130] The aluminum alloy workpiece was sealed with the PRODICO 480 graphene-modified sealant (Guangzhou Ultra Union Chemicals Co., Ltd) to form the graphene-modified sealing film 5, thereby obtaining a finished aluminum alloy workpiece. The PRODICO 480 graphene-modified sealant was diluted with water to 2.8 times to prepare the sealing solution. The passivated aluminum alloy workpiece was immersed in the sealing solution for 10 s. After taking it out of the sealing solution, the sealed aluminum alloy workpiece was drained and blown off the residual sealing solution on the surface of the passivation film with high-pressure air to give the finished aluminum alloy workpiece. After sealing, the finished aluminum alloy workpiece was dried and solidified at 75° C. for 30 minutes.Example 1

[0131] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were subjected to a neutral salt spray test according to GB / T 10125-2021 “Corrosion tests in artificial atmospheres-Salt spray tests”. After 480 hours of testing, no white rust was observed on the surfaces of the zinc-iron alloy samples. The corrosion resistance of the coating prepared in the present disclosure far exceeded the requirement of 216 hours without white rust specified in GB / T 41950-2022 “Metallic coatings-Electroplated coatings of zinc and zinc alloys on iron or steel with without hexavalent chromium conversion coatings”.Example 2

[0132] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were tested for coating adhesion according to GB / T 5270-2005 “Metallic coatings on metallic substrates-Review of methods for testing adhesion of electrodeposited and chemically deposited coatings”. A steel workpiece and a cast iron workpiece were heated to 250° C. for 60 minutes in a heating furnace. A zinc alloy workpiece was heated to 150° C. for 60 minutes. An aluminum alloy workpiece was heated to 220° C. for 60 minutes. After heating, these workpieces were immediately taken out and quenched in water at room temperature. No blistering or peeling of their coatings was observed. It was demonstrated that the coating prepared by the present disclosure exhibited an excellent adhesion.Example 3

[0133] The samples of plated zinc-iron alloy prepared in Embodiments 1-4 were subjected to a 28-day mold test according to GJB 150.10A-2009 “Laboratory Environmental Test Methods for Military Materiel-Part 10: Mold Test”. No mold growth was observed on the surface of the zinc-iron alloy samples, confirming compliance with environmental test requirements.Example 4

[0134] 1000 mL of potassium chloride-based zinc-iron alloy plating solution was prepared, including 70 g / L of zinc chloride, 12 g / L of ferrous chloride tetrahydrate, 220 g / L of potassium chloride, 35 g / L of boric acid, 35 g / L of the complexing agent, 0.2 mL / L of the brightener, and 30 mL / L of the electroplating additive. The pH of the plating solution was adjusted to 5.6. After storing the plating solution in a laboratory for one month, no precipitate formation was observed.Example 5

[0135] 250 mL of potassium chloride-based zinc-iron alloy plating solution prepared in Example 4 was continuously subjected to a Hull cell test. Specifically, each panel was plated under the condition: 1 A current for 10 minutes. Based on practical conditions, the brightener, the electroplating additive, the complexing agent, the ferrous chloride, and the potassium chloride were supplemented as needed. Finally, a total of 120 panels were plated. Throughout the testing, no iron hydroxide precipitate formed in the plating solution. The plating solution exhibited a good covering ability, deposited a bright coating, and no significant changes in coating appearance were observed during continuous plating.Comparative Example 1

[0136] According to the method provided in the Embodiment 1, the zinc-iron alloy electroplating method in the Embodiment 1 was replaced with a ZINLITE 401 potassium chloride-based zinc electroplating method (Guangzhou Ultra Union Chemicals Co., Ltd). A steel workpiece was sequentially plated with zinc, passivated through a trivalent chromium blue-white passivation and sealed with a graphene-modified sealant to obtain a zinc-plated sample. The zinc-plated sample was subjected to a neutral salt spray test according to GB / T 10125-2021 “Corrosion tests in artificial atmospheres—Salt spray tests”. No white rust was observed on the surface after 320 hours.

[0137] The technical solutions provided in the embodiments of the present disclosure have been described in detail above. The principle and the implement method of the embodiments of the present disclosure have been elaborated with reference to some specific examples. The introductions of the above embodiments are used to facilitate understanding the principle of the embodiments of the present disclosure. It should be noted that any modifications and improvements made by those skilled in the art without departing from the spirit of the disclosure shall fall within the scope of the disclosure defined by the appended claims.

Examples

embodiment 1

[0086]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0087]Referring to FIG. 1, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a steel substrate 01, a zinc-iron alloy coating 02, a trivalent chromium blue-white passivation film 03, and a graphene-modified sealing film 04 sequentially arranged from inside to outside.

(1) Pretreatment

[0088]The steel substrate 01 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation and water rinsing to complete the pretreatment process and give a pretreated steel substrate 01.

(2) Zinc-Iron Alloy Plating

[0089]The pretre...

embodiment 2

[0097]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0098]Referring to FIG. 2, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a zinc alloy substrate 11, a zinc-iron alloy coating 12, a trivalent chromium blue-white passivation film 13, and a graphene-modified sealing film 14 sequentially arranged from inside to outside.

(1) Pretreatment

[0099]The zinc alloy substrate 11 was sequentially subjected to chemical dewaxing, water rinsing, ultrasonic dewaxing, water rinsing, ultrasonic degreasing, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated zinc alloy substrate 11.

(2) Zinc-Iron Alloy Plating

[0100]The pretreated zinc alloy substrate 11 was plated...

embodiment 3

[0108]Provided herein was a plating solution, including a complexing agent, a brightener and an electroplating additive. A potassium chloride-based zinc-iron alloy electroplating method was also provided, including pretreatment, zinc-iron alloy plating, passivation, and sealing.

[0109]Referring to FIG. 3, an electroplated product prepared by the potassium chloride-based zinc-iron alloy electroplating method included a cast iron substrate 21, a zinc-iron alloy coating 22, a trivalent chromium blue-white passivation film 23 and a graphene-modified sealing film 24 sequentially arranged from inside to outside.

(1) Pretreatment

[0110]The cast iron substrate 21 was sequentially subjected to chemical degreasing, water rinsing, acid rinsing, water rinsing, alkaline cathodic electrocleaning, water rinsing, alkaline anodic electrocleaning, water rinsing, activation, and water rinsing to complete the pretreatment process and give a pretreated cast iron substrate 21.

(2) Zinc-iron Alloy Plating

[011...

Claims

1. A complexing agent for a potassium chloride-based zinc-iron alloy plating solution, comprising:a component A; anda component B;wherein the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof;the component B is sodium sulfosalicylate;a weight ratio of the component A to the component B is 3:1-3; anda weight concentration of the complexing agent in the potassium chloride-based zinc-iron alloy plating solution is 6-55 g / L.

2. A potassium chloride-based zinc-iron alloy plating solution, comprising:50-70. g / L of zinc chloride;2-12. g / L of ferrous chloride tetrahydrate or 3-17 g / L of ferrous sulfate heptahydrate;160-240. g / L of potassium chloride;25-35. g / L of boric acid;6-55. g / L of a complexing agent;0.1-0.2 mL / L of a brightener; and20-30. mL / L of an electroplating additive;wherein the potassium chloride-based zinc-iron alloy plating solution has a pH of 4.5-5.6; andthe complexing agent comprises a component A and a component B; the component A is selected from the group consisting of sodium gluconate, sodium glucoheptonate, potassium sodium tartrate, sodium citrate and a combination thereof;the component B is sodium sulfosalicylate; and the component A and the component B are mixed according to a weight ratio of 3:1-3.

3. The potassium chloride-based zinc-iron alloy plating solution of claim 2, wherein the brightener comprises o-chlorobenzaldehyde and formic acid in a weight ratio of 1:0.8-1.2; andthe electroplating additive comprises 17-23 parts by weight of a sulfonation product of a fatty alcohol polyoxyethylene ether and sulfamic acid, 5-7 parts by weight of sodium benzoate, 0.4-0.6 part by weight of nicotinic acid and 80-90 parts by weight of water.

4. The potassium chloride-based zinc-iron alloy plating solution of claim 2, wherein the brightener is prepared through steps of:mixing o-chlorobenzaldehyde with formic acid in the weight ratio of 1:0.8-1.2 under stirring to obtain the brightener.

5. The potassium chloride-based zinc-iron alloy plating solution of claim 2, wherein the electroplating additive is prepared through steps of:adding 17-23 kg of the sulfonation product, 5-7 kg of sodium benzoate and 0.4-0.6 kg of nicotinic acid to 70 kg of water, followed by stirring for complete dissolution and dilution to 100 L with water, so as to obtain the electroplating additive.

6. The potassium chloride-based zinc-iron alloy plating solution of claim 2, wherein the potassium chloride-based zinc-iron alloy plating solution is prepared through steps of:adding water to a plating bath followed by addition of zinc chloride, potassium chloride, boric acid, and the complexing agent and stirring for dissolution, wherein the water added to the plating bath is 70% of a predetermined volume of the potassium chloride-based zinc-iron alloy plating solution;adding ferrous chloride tetrahydrate to the plating bath followed by stirring for dissolution;adding the brightener and the electroplating additive to the plating bath followed by stirring, adjustment to pH 4.5-5.6 with a 10 wt. % sodium hydroxide solution or a 3 wt. % hydrochloric acid solution, and addition of water to the predetermined volume to produce a mixture; andelectrolyzing the mixture at a current density of 0.1-0.2 A / dm2 for 30-90 minutes to produce the potassium chloride-based zinc-iron alloy plating solution.

7. A zinc-iron electroplating method, comprising:preparing the potassium chloride-based zinc-iron alloy plating solution of claim 2;preprocessing a workpiece;in the potassium chloride-based zinc-iron alloy plating solution, electroplating zinc-iron alloy on a preprocessed workpiece to give an electroplated workpiece;subjecting the electroplated workpiece to trivalent chromium passivation to form a passivation film-coated workpiece; andsealing the passivation film-coated workpiece with a graphene-modified sealant to form a graphene-modified sealing film, thereby obtaining a finished workpiece;wherein a temperature of a plating bath is controlled at 15-30° C., a current density of a cathode is 1-3 A / dm2, and a swept rate of cathode is 3-5 m / min.

8. The zinc-iron electroplating method of claim 7, wherein an anode is a zinc plate with a weight percentage of 99.99%.

9. The zinc-iron electroplating method of claim 7, wherein an area ratio of a cathode to an anode is 2:0.7-1.3.

10. The zinc-iron electroplating method of claim 7, wherein a 30 wt. % ferrous chloride tetrahydrate solution is supplemented to the plating bath during production, so as to maintain a weight concentration of ferrous chloride tetrahydrate at 2-12 g / L.

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