A cyanide-free cadmium plating method for aerospace alloy steel forging machine parts

Abstract

The application discloses a cyanide-free cadmium plating method for aerospace alloy steel forging machine parts, which comprises sequentially performing polythiocyanate copper-zinc alloy plating, potassium chloride cyanide-free cadmium plating, hydrogen removal and hexavalent chromium passivation on the alloy steel base body. The prepared potassium chloride cyanide-free cadmium plating combined coating is free of rust after neutral salt spray test for 1000h according to GB / T 10125-2012 "Artificial Atmosphere Corrosion Test Salt Spray Test", and the coating adhesion is determined by the thermal shock test method according to GB / T 5270-2005 "Metal Coating on Metal Substrates - Adhesion by Electrodeposited and Chemically Deposited Coatings - Test Methods - Review", and the adhesion meets the standard requirements. The prepared potassium chloride cyanide-free cadmium plating combined coating overcomes the defect that the current aerospace alloy steel forging machine parts are prone to black spots during potassium chloride cyanide-free cadmium plating.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, specifically relating to a cyanide-free cadmium plating method for aerospace alloy steel forgings. Background Technology

[0002] Forged and machined parts made of 25Cr3MoA alloy steel were subjected to cyanide-free cadmium plating. Black spots frequently appeared on the cadmium plating layer of the forged surface, but these spots did not appear on the machined surface. After the problem occurred, the factory had to send personnel to the user to re-passivate the problematic cadmium-plated parts. The re-passivated parts did not show the recurrence of the black spots. This problem caused dissatisfaction from the user, who strongly demanded that the processing unit and supplier provide a solution and resolve the issue.

[0003] The chromium content of 25Cr3MoA alloy steel is 3% to 3.5%, and even after sandblasting, some sintered chromium trioxide film may still remain on the surface of its forgings. Based on the chemical properties of chromium trioxide... [1] Short-term pickling using conventional hydrochloric acid pickling and activation processes is insufficient to effectively remove the chromium trioxide film from the forged surface of 25Cr3MoA alloy steel. Directly applying potassium chloride cyanide-free cadmium plating to the alloy steel forging surface with residual chromium trioxide film results in a porous cadmium plating layer. These pores may penetrate the plating layer or become trapped within it once the plating reaches a certain thickness. The potassium chloride cadmium plating solution remaining in these pores causes residual corrosion to the cadmium plating layer; once the corrosion penetrates the plating, it leads to black spots on the surface.

[0004] References: [1] Beijing Chemical Reagent Company, ed., Chemical Reagents and Fine Chemicals Handbook, Chemical Industry Press, 2002, p. 293. Summary of the Invention

[0005] To address the problem of black spots easily forming on the cadmium plating layer of forged alloy steel machined parts, this invention provides a cyanide-free cadmium plating method for aerospace alloy steel forged machined parts. To achieve the above objective, this invention adopts the following technical solution:

[0006] A cyanide-free cadmium plating method for aerospace alloy steel forgings, characterized by the following steps:

[0007] (1) Sandblast the surface of the alloy steel forging blank to remove the oxides on its surface;

[0008] (2) Machining is performed on a portion of the surface of the alloy steel forging blank processed in step (1) to obtain an alloy steel forging machined part;

[0009] (3) The alloy steel forging machined part substrate prepared in step (2) is subjected to degreasing and activation treatment;

[0010] (4) A cyanide-free copper-zinc alloy coating is prepared on the alloy steel forging machined substrate after step (3) using a polymer thiocyanate copper-zinc alloy plating process.

[0011] (5) A cyanide-free cadmium plating layer is prepared on the cyanide-free copper-zinc alloy plating layer prepared in step (4) using a cyanide-free cadmium plating process.

[0012] (6) Dehydrogenation treatment is performed on the alloy steel forging machined parts that have undergone cyanide-free cadmium plating in step (5);

[0013] (7) A passivation layer is prepared by a hexavalent chromium passivation process on the cyanide-free cadmium plating layer after hydrogen removal in step (6);

[0014] The polymeric thiocyanate copper-zinc alloy plating process described in step (4) is as follows:

[0015] Polymeric cuprous thiocyanate 17–25 g / L, polymeric zinc thiocyanate 12–16 g / L, polymeric sodium thiocyanate 125–175 g / L, brightener 8–12 mL / L, plating bath pH 9.5–11.5, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode.

[0016] The brightener in the polymeric thiocyanate copper-zinc alloy plating process includes 60-100 g / L of N,N'-di-n-propylethylenediamine and 80-120 g / L of polyacrylamide with a molecular weight of less than 8000.

[0017] In some embodiments, the activation treatment in step (3) employs a sulfuric acid anodic electrolysis process:

[0018] Concentrated sulfuric acid 150–250 g / L, anolyte current density 0.5–1.5 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1-2 minutes. The cathode is made of lead plate.

[0019] In some embodiments, the polymer thiocyanate copper-zinc alloy plating process described in step (4) uses anode movement to avoid anode surface passivation, and the anode movement speed is 3 to 5 m / min.

[0020] In some embodiments, the area ratio of the anode to the cathode in the polymer thiocyanate copper-zinc alloy plating process described in step (4) is (1-2):1.

[0021] In some embodiments, the copper mass fraction in the copper-zinc alloy coating described in step (4) is 58% to 78%.

[0022] In some embodiments, the thickness of the copper-zinc alloy coating in step (4) is 3 to 10 μm.

[0023] In some embodiments, the cyanide-free cadmium plating layer described in step (5) is prepared using a potassium chloride cyanide-free cadmium plating process:

[0024] Cadmium chloride 25–35 g / L, potassium chloride 100–140 g / L, PULIZIER NCC-617 AC complexing agent 100–140 g / L, PULIZIER NCC-617 Base auxiliary agent 25–30 mL / L, PULIZIER NCC-617 Bri brightener 1.5–2.5 mL / L, PULIZIER NCC-617 HCD high-zone brightener 5–10 mL / L, plating bath temperature 20–35℃, plating solution pH 7–9, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min.

[0025] In some embodiments, the thickness of the cyanide-free cadmium plating layer in step (5) is 5–30 μm.

[0026] In some embodiments, the hexavalent chromium passivation process in step (7) employs a hexavalent chromium low-chromium color passivation process:

[0027] The volume concentration of HC-5 high-protection low-chromium colored passivating agent is 2% to 4%, the passivation temperature is 20 to 35℃, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and it is carried out with weak air agitation or workpiece oscillation.

[0028] In some embodiments, the hexavalent chromium passivation process in step (7) employs a hexavalent chromium military green passivation process:

[0029] OVG-31 military green passivating agent 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air agitation or oscillation of the plated parts, passivation time 30~90s.

[0030] This invention employs sulfuric acid anodic electrolytic activation to activate the surface of alloy steel forgings. In the sulfuric acid medium, the metal on the workpiece surface undergoes an anodic electrolytic oxidation reaction and dissolves in the electrolyte, thereby effectively removing the oxide film from the workpiece surface. During this process, no hydrogen evolution reaction occurs in the metal matrix.

[0031] Potential activation theory posits that: 1) Higher cathodic polarization shifts the deposition potential of the metal more positively, which is beneficial for the reduction of the oxide film on the substrate surface; 2) The slow deposition rate of the plating solution provides sufficient time for oxide film reduction. The combination of these two factors ensures that the oxide film on the substrate surface is reduced to the substrate metal, and the resulting coating, after the oxide film is removed, forms a strong bond with the substrate metal.

[0032] The polymeric thiocyanate copper-zinc alloy plating process described in this invention has plating solution properties similar to those of cyanide copper-zinc alloy plating solutions, exhibiting high cathodic polarization and activation capabilities. When plating using this process, chromium trioxide on the alloy steel forging surface preferentially reacts and is reduced to metallic chromium, which then bonds with the substrate. Subsequently, copper and zinc ions in the plating solution begin electrodeposition to form a copper-zinc alloy coating.

[0033] A cadmium plating layer was prepared on a copper-zinc alloy coating. The electrode potential of the cadmium plating layer was significantly more negative than that of the copper-zinc alloy coating, and the cadmium plating layer provided electrochemical protection for the copper-zinc alloy coating.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The cyanide-free cadmium plating method for aerospace alloy steel forgings of the present invention uses sulfate electrolytic activation method instead of pickling activation method, which can effectively remove the chromium trioxide oxide film on the forging surface of alloy steel forgings and overcome the defect of hydrogen embrittlement of the workpiece substrate caused by the current pickling activation process.

[0036] 2. The cyanide-free cadmium plating method for aerospace alloy steel forgings of the present invention involves polymerizing thiocyanate to plate copper-zinc alloy on an alloy steel substrate, which can further remove the residual chromium trioxide oxide film on the forging surface of aerospace alloy steel forgings.

[0037] 3. The cyanide-free cadmium plating method for aerospace alloy steel forgings of the present invention prepares a cadmium plating layer on a copper-zinc alloy coating, effectively overcoming the defect that the cadmium plating layer prepared directly on the alloy steel substrate does not have an electrochemical protective effect. Attached Figure Description

[0038] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, do not constitute an undue limitation of the invention. In the drawings:

[0039] Figure 1 These are schematic diagrams of the coating structures in Embodiments 1, 2, 3, and 4 of the present invention;

[0040] Figure 2 The image shows a cadmium-plated sample made of alloy steel forging surface according to this scheme after undergoing a damp heat test.

[0041] Figure 3 The image shows a cadmium-plated sample made according to this scheme with an alloy steel forging surface after a mold test.

[0042] Figure 4 The image shows the microstructure of the cadmium-plated layer prepared on the alloy steel forging surface according to this scheme.

[0043] Figure 5 This is a microscopic morphology image of a cadmium-plated layer directly prepared from an alloy steel forging surface using current technology.

[0044] Figure 6 This is a photo of an alloy steel forging sample that has been directly cadmium-plated using current technology and left for 6 months. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0046] A cyanide-free cadmium plating method for aerospace alloy steel forgings includes: sandblasting, machining, degreasing, sulfuric acid anodic electrolytic activation, polymeric thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blank.

[0047] The coating structure prepared by the above method includes an alloy steel forged machined part substrate, and a cyanide-free copper-zinc alloy coating, a cyanide-free cadmium plating layer, and a hexavalent chromium passivation layer sequentially prepared from the inside to the outside on the alloy steel forged machined part substrate.

[0048] The surface of alloy steel forging blanks is sandblasted using traditional sandblasting techniques.

[0049] Alloy steel forging blanks are sandblasted and then partially machined to obtain alloy steel forging machined parts.

[0050] The alloy steel forging machined parts are subjected to the following pretreatment process: "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0051] After degreasing, alloy steel forging machined parts are activated using a sulfuric acid anodic electrolytic activation process. Preferably, the sulfuric acid anodic electrolytic activation process employs the following method:

[0052] Concentrated sulfuric acid 150–250 g / L, anolyte current density 0.5–1.5 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1-2 minutes. The cathode is made of lead plate.

[0053] After electrolytic activation, the alloy steel forging machined parts are prepared with a cyanide-free copper-zinc alloy coating using the polymer thiocyanate copper-zinc alloy plating process of the present invention.

[0054] Preferably, the mass fraction of copper in the cyanide-free copper-zinc alloy coating is 58% to 78%.

[0055] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 3–10 μm.

[0056] Polymeric cuprous thiocyanate 17–25 g / L, polymeric zinc thiocyanate 12–16 g / L, polymeric sodium thiocyanate 125–175 g / L, brightener 8–12 mL / L, plating bath pH 9.5–11.5, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min. A brass plate with a copper mass fraction of 68% is used as the anode. The anode moves at a speed of 3-5 m / min. The area ratio of the anode to the cathode is (1-2):1.

[0057] After the alloy steel forging machined parts are polymerized with thiocyanate and copper-zinc alloy, a cyanide-free cadmium plating layer is prepared using the current cyanide-free cadmium plating process.

[0058] Preferably, the thickness of the cyanide-free cadmium plating layer is 5–30 μm.

[0059] Preferably, the cyanide-free cadmium plating layer is prepared using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process from Chaobang Chemical Co., Ltd.

[0060] Cadmium chloride 25–35 g / L, potassium chloride 100–140 g / L, PULIZIER NCC-617 AC complexing agent 100–140 g / L, PULIZIER NCC-617 Base auxiliary agent 25–30 mL / L, PULIZIER NCC-617 Bri brightener 1.5–2.5 mL / L, PULIZIER NCC-617 HCD high-zone brightener 5–10 mL / L, plating bath temperature 20–35℃, plating solution pH 7–9, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min.

[0061] After cadmium plating, alloy steel forging machined parts undergo hydrogen removal treatment at 190–210℃ for 10–24 hours.

[0062] After hydrogen removal treatment, the alloy steel forging machined parts are prepared with a hexavalent chromium passivation layer using the current hexavalent chromium passivation process.

[0063] Preferably, the hexavalent chromium passivation layer is a hexavalent chromium colored passivation layer.

[0064] Preferably, the hexavalent chromium colored passivation layer is prepared using HC-5 high-protection low-chromium colored passivation agent from Chaobang Chemical Co., Ltd.

[0065] The volume concentration of HC-5 high-protection low-chromium colored passivating agent is 2% to 4%, the passivation temperature is 20 to 35℃, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and it is carried out with weak air agitation or workpiece oscillation.

[0066] Preferably, the hexavalent chromium passivation layer is a hexavalent chromium military green passivation layer.

[0067] Preferably, the military-green passivation layer is prepared using OVG-31 military-green passivating agent from Chaobang Chemical Co., Ltd.

[0068] OVG-31 military green passivating agent 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air agitation or oscillation of the plated parts, passivation time 30~90s.

[0069] Alloy steel forgings are passivated and then washed and dried.

[0070] Example 1:

[0071] The material type of the aerospace alloy steel forging machined parts is 25Cr3MoA. Its cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anodic electrolytic activation, polymeric thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0072] like Figure 1 As shown, the cyanide-free cadmium plating layer structure prepared by the cyanide-free cadmium plating method includes: an alloy steel forging machined part substrate 1, and a cyanide-free copper-zinc alloy plating layer 2, a cyanide-free cadmium plating layer 3, and a hexavalent chromium color passivation layer 4 sequentially prepared on the alloy steel forging machined part substrate 1.

[0073] 1. Sandblasting:

[0074] The surface of alloy steel forging blanks is sandblasted using traditional sandblasting techniques.

[0075] 2. Machining:

[0076] Alloy steel forging blanks are sandblasted and then partially machined to obtain alloy steel forging machined parts.

[0077] 3. Degreasing:

[0078] The alloy steel forging machined part substrate 1 is subjected to the following pretreatment process: "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0079] 4. Anodic electrolytic activation:

[0080] The degreased alloy steel forging machining substrate 1 was activated using the sulfuric acid anodic electrolytic activation process.

[0081] Concentrated sulfuric acid 200 g / L, anolyte current density 1.0 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1.5 minutes. The cathode is made of lead plate.

[0082] 5. Polymerized thiocyanate copper-zinc alloy plating:

[0083] After electrolytic activation, the alloy steel forging machined parts are prepared using the polymer thiocyanate copper-zinc alloy plating process of the present invention to prepare a cyanide-free copper-zinc alloy coating 2. The mass fraction of copper in the coating is 66% to 70%, and the coating thickness is 7 μm.

[0084] Polymeric cuprous thiocyanate 21 g / L, polymeric zinc thiocyanate 14 g / L, polymeric sodium thiocyanate 150 g / L, brightener 10 mL / L, plating bath pH 10.5, plating bath temperature 45℃, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode. The anode moving speed is 4 m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0085] 6. Cyanide-free cadmium plating:

[0086] After the alloy steel forging machined parts are polymerized with thiocyanate and copper-zinc alloy, a cyanide-free cadmium plating layer 3 is prepared using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical. The plating layer thickness is 12μm.

[0087] Cadmium chloride 30 g / L, potassium chloride 120 g / L, PULIZIER NCC-617 AC complexing agent 120 g / L, PULIZIER NCC-617 Base auxiliary agent 28 mL / L, PULIZIER NCC-617 Bri brightener 2.0 mL / L, PULIZIER NCC-617 HCD high-zone brightener 8 mL / L, plating bath temperature 28℃, plating solution pH 8, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0088] 7. Hydrogen removal:

[0089] Alloy steel forgings are machined after cyanide-free cadmium plating and then subjected to hydrogen removal treatment at 200℃ for 24 hours.

[0090] 8. Hexavalent chromium color passivation:

[0091] After hydrogen removal treatment, hexavalent chromium colored passivation layer 4 is prepared using HC-5 high-protection low-chromium colored passivating agent from Chaobang Chemical.

[0092] The volume concentration of HC-5 high-protection low-chromium colored passivating agent is 3%, the passivation temperature is 28℃, the pH of the passivation solution is 1.7, the passivation time is 8s, and the workpiece is oscillating.

[0093] The specific process is as follows: "2% nitric acid for brightening → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0094] Example 2:

[0095] The material grade of the aerospace alloy steel forging machined parts is ZGCr15. Its cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anodic electrolytic activation, polymeric thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0096] like Figure 1 As shown, the cyanide-free cadmium plating layer structure prepared by the cyanide-free cadmium plating method includes: an alloy steel forging machined part substrate 1, and a cyanide-free copper-zinc alloy plating layer 2, a cyanide-free cadmium plating layer 3, and a hexavalent chromium color passivation layer 4 sequentially prepared on the alloy steel forging machined part substrate 1.

[0097] 1. Sandblasting:

[0098] The surface of the alloy steel forging blank is sandblasted using the traditional sandblasting process.

[0099] 2. Machining:

[0100] Alloy steel forging blanks are sandblasted and then partially machined to obtain alloy steel forging machined parts.

[0101] 3. Degreasing:

[0102] The alloy steel forging machined part substrate 1 is subjected to the following pretreatment process: "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0103] 4. Anodic electrolytic activation:

[0104] The degreased alloy steel forging machining substrate 1 was activated using the sulfuric acid anodic electrolytic activation process.

[0105] Concentrated sulfuric acid 220 g / L, anolyte current density 1.2 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1.2 minutes. The cathode is made of lead plate.

[0106] 5. Polymerized thiocyanate copper-zinc alloy plating:

[0107] After electrolytic activation, the alloy steel forging machined parts are prepared using the polymer thiocyanate copper-zinc alloy plating process of the present invention to prepare a cyanide-free copper-zinc alloy coating 2. The mass fraction of copper in the coating is 66% to 70%, and the coating thickness is 7 μm.

[0108] Polymeric cuprous thiocyanate 23 g / L, polymeric zinc thiocyanate 15 g / L, polymeric sodium thiocyanate 168 g / L, brightener 11 mL / L, plating bath pH 9.8, plating bath temperature 40℃, cathode current density 1.2 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode. The anode moving speed is 4 m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0109] 6. Cyanide-free cadmium plating:

[0110] After the alloy steel forging machined parts are polymerized with thiocyanate and copper-zinc alloy, a cyanide-free cadmium plating layer 3 is prepared using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical. The plating layer thickness is 12μm.

[0111] Cadmium chloride 33 g / L, potassium chloride 110 g / L, PULIZIER NCC-617 AC complexing agent 135 g / L, PULIZIER NCC-617 Base auxiliary agent 28 mL / L, PULIZIER NCC-617 Bri brightener 2.0 mL / L, PULIZIER NCC-617 HCD high-zone brightener 8 mL / L, plating bath temperature 22℃, plating solution pH 8, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0112] 7. Hydrogen removal:

[0113] Alloy steel forgings are machined after cyanide-free cadmium plating and then subjected to hydrogen removal treatment at 200℃ for 24 hours.

[0114] 8. Hexavalent chromium color passivation:

[0115] After hydrogen removal treatment, hexavalent chromium colored passivation layer 4 is prepared using HC-5 high-protection low-chromium colored passivating agent from Chaobang Chemical.

[0116] The HC-5 high-protection, low-chromium colored passivating agent has a volume concentration of 3.5%, a passivation temperature of 22℃, a passivation solution pH of 1.5, a passivation time of 8s, and is subjected to weak air agitation.

[0117] The specific process is as follows: "2% nitric acid for brightening → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0118] Example 3:

[0119] The material type of the aerospace alloy steel forging machined parts is 30CrMnSiA. Its cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anodic electrolytic activation, polymeric thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0120] like Figure 1 As shown, the cyanide-free cadmium plating layer structure prepared by the cyanide-free cadmium plating method includes: an alloy steel forging machined part substrate 1, and a cyanide-free copper-zinc alloy plating layer 2, a cyanide-free cadmium plating layer 3, and a hexavalent chromium military green passivation layer 4 sequentially prepared on the alloy steel forging machined part substrate 1.

[0121] 1. Sandblasting:

[0122] The surface of alloy steel forging blanks is sandblasted using traditional sandblasting techniques.

[0123] 2. Machining:

[0124] Alloy steel forging blanks are sandblasted and then partially machined to obtain alloy steel forging machined parts.

[0125] 3. Degreasing:

[0126] The alloy steel forging machined substrate 1 is subjected to the following pretreatment process: "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0127] 4. Anodic electrolytic activation:

[0128] The degreased alloy steel forging machining substrate 1 was activated using the sulfuric acid anodic electrolytic activation process.

[0129] Concentrated sulfuric acid 170 g / L, anolyte current density 0.8 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1.8 minutes. The cathode is made of lead plate.

[0130] 5. Polymerized thiocyanate copper-zinc alloy plating:

[0131] After electrolytic activation, the alloy steel forging machined parts are prepared using the polymer thiocyanate copper-zinc alloy plating process of the present invention to prepare a cyanide-free copper-zinc alloy coating 2. The mass fraction of copper in the coating is 66% to 70%, and the coating thickness is 7 μm.

[0132] Polymeric cuprous thiocyanate 18 g / L, polymeric zinc thiocyanate 13 g / L, polymeric sodium thiocyanate 140 g / L, brightener 8 mL / L, plating bath pH 11.3, plating bath temperature 50℃, cathode current density 1.0 A / dm³ 2The cathode moves at a speed of 4 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode. The anode moving speed is 4 m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0133] 6. Cyanide-free cadmium plating:

[0134] After the alloy steel forging machined parts are polymerized with thiocyanate and copper-zinc alloy, a cyanide-free cadmium plating layer 3 is prepared using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical. The plating layer thickness is 12μm.

[0135] Cadmium chloride 27 g / L, potassium chloride 130 g / L, PULIZIER NCC-617 AC complexing agent 110 g / L, PULIZIER NCC-617 Base auxiliary agent 28 mL / L, PULIZIER NCC-617 Bri brightener 2.2 mL / L, PULIZIER NCC-617 HCD high-zone brightener 8 mL / L, plating bath temperature 28℃, plating solution pH 8.5, cathode current density 1.0 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0136] 7. Hydrogen removal:

[0137] Alloy steel forgings are machined after cyanide-free cadmium plating and then subjected to hydrogen removal treatment at 200℃ for 24 hours.

[0138] 8. Hexavalent chromium military green passivation:

[0139] After hydrogen removal treatment, the alloy steel forging machined parts are prepared with military green passivation layer 4 using OVG-31 military green passivating agent from Chaobang Chemical.

[0140] OVG-31 military green passivating agent 90mL / L, passivation solution pH 1.2, passivation temperature 28℃, air stirring, passivation time 60s.

[0141] The specific process is as follows: "2% nitric acid for brightening → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0142] Example 4:

[0143] The material type of the aerospace alloy steel forging machined parts is 33Cr3MoWV. Its cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anodic electrolytic activation, polymeric thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0144] like Figure 1As shown, the cyanide-free cadmium plating layer structure prepared by the cyanide-free cadmium plating method includes: an alloy steel forging machined part substrate 1, and a polymeric thiocyanate copper-zinc alloy plating layer 2, a cyanide-free cadmium plating layer 3, and a hexavalent chromium military green passivation layer 4 sequentially prepared on the alloy steel forging machined part substrate 1.

[0145] 1. Sandblasting:

[0146] The surface of the alloy steel forging blank is sandblasted using the traditional sandblasting process.

[0147] 2. Machining:

[0148] After sandblasting, some surfaces of the alloy steel forging blank are machined to obtain the alloy steel forging machined part.

[0149] 3. Degreasing:

[0150] The alloy steel forging machined substrate 1 is subjected to the following pretreatment process: "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0151] 4. Anodic electrolytic activation:

[0152] The degreased alloy steel forging machining substrate 1 was activated using the sulfuric acid anodic activation electrolysis process.

[0153] Concentrated sulfuric acid 250 g / L, anolyte current density 1.5 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1 minute. The cathode is made of lead plate.

[0154] 5. Polymerized thiocyanate copper-zinc alloy plating:

[0155] After electrolytic activation, the alloy steel forging machined parts are prepared using the polymer thiocyanate copper-zinc alloy plating process of the present invention to prepare a cyanide-free copper-zinc alloy coating 2. The mass fraction of copper in the coating is 66% to 70%, and the coating thickness is 7 μm.

[0156] Polymeric cuprous thiocyanate 25 g / L, polymeric zinc thiocyanate 16 g / L, polymeric sodium thiocyanate 175 g / L, brightener 9 mL / L, plating bath pH 10, plating bath temperature 38℃, cathode current density 1.4 A / dm³ 2 The cathode moves at a speed of 4 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode. The anode moving speed is 4 m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0157] 6. Cyanide-free cadmium plating:

[0158] After the alloy steel forging machined parts are polymerized with thiocyanate and copper-zinc alloy, a cyanide-free cadmium plating layer 3 is prepared using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical. The plating layer thickness is 12μm.

[0159] Cadmium chloride 25 g / L, potassium chloride 140 g / L, PULIZIER NCC-617 AC complexing agent 100 g / L, PULIZIER NCC-617 Base auxiliary agent 28 mL / L, PULIZIER NCC-617 Bri brightener 1.6 mL / L, PULIZIER NCC-617 HCD high-zone brightener 8 mL / L, plating bath temperature 35℃, plating solution pH 9, cathode current density 0.8 A / dm³ 2 The cathode moves at a speed of 3 m / min.

[0160] 7. Hydrogen removal:

[0161] Alloy steel forgings are machined after cyanide-free cadmium plating and then subjected to hydrogen removal treatment at 200℃ for 24 hours.

[0162] 8. Hexavalent chromium military green passivation:

[0163] After hydrogen removal treatment, the alloy steel forging machined parts are prepared with military green passivation layer 4 using OVG-31 military green passivating agent from Chaobang Chemical.

[0164] OVG-31 military green passivating agent 110mL / L, passivation solution pH 1.3, passivation temperature 23℃, oscillating plated parts, passivation time 50s.

[0165] The specific process is as follows: "2% nitric acid for brightening → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0166] Experimental Example 1:

[0167] The cadmium-plated colored passivated and military green passivated samples of alloy steel forgings prepared in Examples 1 to 4 showed no white rust after 1000 hours of neutral salt spray testing according to GB / T 10125–2012 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The salt spray resistance of the coatings far exceeds the requirement of 96 hours of neutral salt spray testing without white rust as specified in GB / T 13346-2012 "Metallic and Other Inorganic Coatings - Treated Cadmium Electroplating on Steel".

[0168] Experimental Example 2:

[0169] The cadmium-plated color passivated alloy steel forgings prepared in Examples 1 and 2 were subjected to a 20-day damp heat test according to GJB150.9A-2009 "Laboratory Environmental Testing Methods for Military Equipment Part 9: Damp Heat Test". The test results are as follows: Figure 2As shown, no visible changes occurred on the surface of any of the samples, which meets the requirements of environmental testing.

[0170] Experimental Example 3:

[0171] The cadmium-plated color passivated alloy steel forgings prepared in Examples 1 and 2 were subjected to a mold test for 28 days according to GJB150.9A-2009 "Laboratory Environmental Testing Methods for Military Equipment Part 10: Mold Test". The test results are as follows: Figure 3 As shown, the mold growth on the surface of all samples was grade 0, which meets the environmental testing requirements.

[0172] Experimental Example 4:

[0173] The cadmium-plated passivated samples of alloy steel forgings prepared in Examples 1 to 4 were tested for coating adhesion according to GB / T 5270–2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Coatings on Metal Substrates". The coated parts were heated to 300°C in a furnace and held for 60 minutes, then removed and rapidly cooled in room temperature water. No blistering or peeling of the coating occurred. The tests demonstrate that the composite coating prepared in this invention has excellent adhesion.

[0174] Experimental Example 5:

[0175] Cadmium-plated samples of alloy steel forgings were prepared according to the process in Example 1. After pretreatment, the alloy steel forgings were plated with a copper-zinc alloy and then with cadmium, without passivation. The microstructure of the cadmium plating layer on the forging surface was characterized using scanning electron microscopy. The resulting microstructure image is shown below. Figure 4 The results show that there are no pores on the cadmium plating layer.

[0176] Experimental Example 6:

[0177] Cadmium-plated samples of alloy steel forgings were prepared using traditional processes. After degreasing and hydrochloric acid activation, the alloy steel forgings were directly plated with potassium chloride without cyanide, without passivation. The microstructure of the cadmium plating layer on the forging surface was characterized using scanning electron microscopy. The resulting microstructure images are shown below. Figure 5 The cadmium plating layer shows pores.

[0178] Experimental Example 7:

[0179] After cadmium plating, the alloy steel forging machined parts prepared in Experimental Example 5 were subjected to color passivation. The samples were placed in a laboratory environment for 1 year, and no black spots appeared on the plating surface of the forging surface of the parts.

[0180] Experimental Example 8:

[0181] The alloy steel forging machined parts prepared in Example 6 were cadmium-plated and then subjected to color passivation. After being placed in a laboratory environment for 6 months, black spots appeared on the plating surface of the forging side of the parts. The results are as follows: Figure 6 As shown.

[0182] Experimental Example 9:

[0183] The effect of brightener concentration in the polymeric thiocyanate copper-zinc alloy plating bath on the coating was tested.

[0184] The plating solution contained 20 g / L of polycuprous thiocyanate, 14 g / L of polyzinc thiocyanate, and 145 g / L of polysodium thiocyanate. The pH of the plating bath was 10.5, the bath temperature was 45℃, and the cathode current density was 1.0 A / dm³. 2 A brass plate was used as the anode. The addition amount of N,N'-di-n-propylethylenediamine was 0.2–1.4 g / L, and the addition amount of polyacrylamide with a molecular weight less than 8000 was 0.5–2.0 g / L. Experiments showed that the addition range of N,N'-di-n-propylethylenediamine was relatively narrow, while the addition range of polyacrylamide with a molecular weight less than 8000 was wider. The experimental results indicated that, calculated based on the upper and lower limits of the concentration of the components in the brightener, a good copper-zinc alloy coating could generally be obtained when the addition amount of the brightener was in the range of 7–13 mL / L.

[0185] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts, characterized in that, Includes the following steps: (1) Sandblast the surface of the alloy steel forging blank to remove the oxides on its surface; (2) Machining is performed on a portion of the surface of the alloy steel forging blank processed in step (1) to obtain an alloy steel forging machined part; (3) The alloy steel forging machined part substrate prepared in step (2) is subjected to degreasing and activation treatment; (4) A cyanide-free copper-zinc alloy coating is prepared on the alloy steel forging machined substrate after step (3) using a polymer thiocyanate copper-zinc alloy plating process. Chromium trioxide on the alloy steel forging surface can preferentially react and be reduced to metallic chromium, which combines with the substrate. Then, copper and zinc ions in the plating solution begin to electrodeposit to form a copper-zinc alloy coating. (5) A cyanide-free cadmium plating layer is prepared on the cyanide-free copper-zinc alloy plating layer prepared in step (4) using a cyanide-free cadmium plating process. (6) Dehydrogenation treatment is performed on the alloy steel forging machined parts that have undergone cyanide-free cadmium plating in step (5); (7) A passivation layer is prepared by a hexavalent chromium passivation process on the cyanide-free cadmium plating layer after hydrogen removal in step (6); The polymeric thiocyanate copper-zinc alloy plating process described in step (4) is as follows: Polymeric cuprous thiocyanate 17–25 g / L, polymeric zinc thiocyanate 12–16 g / L, polymeric sodium thiocyanate 125–175 g / L, brightener 8–12 mL / L, plating bath pH 9.5–11.5, plating bath temperature 35–55℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode. The brightener in the polymeric thiocyanate copper-zinc alloy plating process includes 60-100 g / L of N,N'-di-n-propylethylenediamine and 80-120 g / L of polyacrylamide with a molecular weight of less than 8000. The activation treatment described in step (3) employs a sulfuric acid anodic electrolysis process: Concentrated sulfuric acid 150–250 g / L, anolyte current density 0.5–1.5 A / dm³ 2 At room temperature, the alloy steel forging machined part is hung on the anode and electrolyzed for 1-2 minutes. The cathode is made of lead plate.

2. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that: The polymer thiocyanate copper-zinc alloy plating process described in step (4) uses anode movement to avoid anode surface passivation, and the anode movement speed is 3-5 m / min.

3. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that: In step (4), the area ratio of the anode to the cathode in the polymer thiocyanate copper-zinc alloy plating process is (1-2):

1.

4. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that: The copper-zinc alloy coating prepared in step (4) has a copper mass fraction of 58% to 78%.

5. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that: The thickness of the copper-zinc alloy coating in step (4) is 3 to 10 μm.

6. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that, The cyanide-free cadmium plating layer described in step (5) is prepared using a potassium chloride cyanide-free cadmium plating process. Cadmium chloride 25–35 g / L, potassium chloride 100–140 g / L, PULIZIER NCC-617 AC complexing agent 100–140 g / L, PULIZIER NCC-617 Base auxiliary agent 25–30 mL / L, PULIZIER NCC-617 Bri brightener 1.5–2.5 mL / L, PULIZIER NCC-617 HCD high-zone brightener 5–10 mL / L, plating bath temperature 20–35℃, plating solution pH 7–9, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 2–4 m / min.

7. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that: The thickness of the cyanide-free cadmium plating layer described in step (5) is 5–30 μm.

8. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that, The hexavalent chromium passivation process described in step (7) adopts a hexavalent chromium low-chromium color passivation process: The volume fraction of HC-5 high-protection low-chromium colored passivating agent is 2% to 4%, the passivation temperature is 20 to 35℃, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15 seconds, and it is carried out with weak air agitation or workpiece oscillation.

9. The cyanide-free cadmium plating method for aerospace alloy steel forgings and machined parts as described in claim 1, characterized in that, The hexavalent chromium passivation process described in step (7) adopts the hexavalent chromium military green passivation process: OVG-31 military green passivating agent 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air agitation or oscillation of the plated parts, passivation time 30~90s.

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