Cyanide-free cadmium plating method for aerospace alloy steel forging machining part

Abstract

The invention discloses a cyanide-free cadmium plating method for an aerospace alloy steel forging machining part. The cyanide-free cadmium plating method comprises the following steps: sequentially carrying out polythiocyanate copper-zinc alloy plating, potassium chloride cyanide-free cadmium plating, hydrogen removal and hexavalent chromium passivation on an alloy steel matrix. The potassium chloride cyanide-free cadmium plating combined coating prepared by the preparation method disclosed by the invention is free from corrosion after being subjected to a neutral salt spray test for 1000h according to GB / T 10125-2012 Artificial Atmosphere Corrosion Test Salt Spray Test; according to GB / T 5270-2005 < GB / T 5270-2005 < GB / T > 5270-2005 < GB / T > 5270-2005 > < GB / T > 5270-2005 > < GB / T > 5270-2005 > < GB / T > 5270-2005 > < GB / The potassium chloride cyanide-free cadmium plating combined plating layer prepared by the invention overcomes the defect that black spots are easy to appear when the potassium chloride cyanide-free cadmium plating of the existing aerospace alloy steel forging machine workpiece is carried out.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a cyanide-free cadmium plating method for aerospace alloy steel forging machine parts. Background Art

[0003] When the material grade is 25Cr3MoA, a type of alloy steel forging machined parts are subjected to cyanide-free cadmium plating, black spots often appear on the cadmium plating layer of the forged surface, but such black spots do not appear on the machined surface. After the problem occurs, the factory has to send people to the user to re-passivate the problematic cadmium-plated parts. After the re-passivation, the parts have not been found to have the problem of black spots appearing again. This problem has caused dissatisfaction among the users, who strongly request the processing unit and the supplier to propose a solution and solve the problem.

[0004] The chromium content of 25Cr3MoA alloy steel is 3% to 3.5%. After sandblasting, the forged parts will still have a sintered chromium oxide film on the surface. According to the chemical properties of chromium oxide, [3] , according to the industry's conventional hydrochloric acid pickling activation process, a short-term pickling cannot effectively remove the chromium oxide film on the forged surface of 25Cr3MoA alloy steel. When potassium chloride cyanide-free cadmium plating is directly performed on the alloy steel forging surface with residual chromium oxide film, pores will form in the prepared cadmium plating layer, which may penetrate the plating layer or be sealed in the plating layer when the plating layer reaches a certain thickness. The potassium chloride cadmium plating solution remaining in the pores of the plating layer will cause residual corrosion to the cadmium plating layer. After the corrosive products penetrate the plating layer, black spots will appear on the surface of the plating layer.

[0005] References: [1] Guo Chongwu, Research and Development of a New Acidic Cyanide-free Cadmium Plating Process [J], Electroplating and Finishing, Issue 5, 2016, pp. 250-255. [2] Wang Daming, Guo Chongwu, Maintenance of Potassium Chloride Cyanide-free Cadmium Plating Process [J], Issue 23, 2018, pp. 1099-1101. [3] Beijing Chemical Reagent Company, Chemical Reagents·Fine Chemical Handbook, Chemical Industry Press, 2002, pp. 293. Summary of the invention

[0006] In order to solve the problem that the cadmium plating layer on the forging surface of alloy steel forging machine parts is prone to black spots, the present invention provides a cyanide-free cadmium plating method for aerospace alloy steel forging machine parts. In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A cyanide-free cadmium plating method for aerospace alloy steel forging machine parts, characterized in that it comprises the following steps:

[0008] (1) Shot blasting is performed on the surface of the alloy steel forging blank to remove the oxide on the surface;

[0009] (2) machining a portion of the surface of the alloy steel forging blank processed in step (1) to obtain an alloy steel forging machined part;

[0010] (3) degreasing and activating the alloy steel forging machined part substrate prepared in step (2);

[0011] (4) preparing a cyanide-free copper-zinc alloy coating on the alloy steel forging machine workpiece substrate treated in step (3) by using a polymerized thiocyanate copper-zinc alloy plating process;

[0012] (5) preparing a cyanide-free cadmium plating layer on the cyanide-free copper-zinc alloy plating layer prepared in step (4) by using a cyanide-free cadmium plating process;

[0013] (6) performing a dehydrogenation treatment on the alloy steel forging machined parts that have been subjected to cyanide-free cadmium plating in step (5);

[0014] (7) preparing a passivation layer by a hexavalent chromium passivation process on the cyanide-free cadmium-plated layer after dehydrogenation in step (6);

[0015] The process for plating copper-zinc alloy with polymerized thiocyanate in step (4) is as follows:

[0016] 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 solution pH 9.5-11.5, plating tank temperature 35-55 °C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3-5 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode;

[0017] The brightener in the polythiocyanate copper-zinc alloy plating process comprises 60-100 g / L of N,N'-di-n-propylethylenediamine and 80-120 g / L of polyacrylamide with a molecular weight less than 8000.

[0018] In some embodiments, the activation treatment in step (3) is carried out by a sulfuric acid anode electrolysis process:

[0019] Concentrated sulfuric acid 150~250g / L, anode current density 0.5~1.5A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1 to 2 minutes, and make the cathode with lead plate.

[0020] In some of the embodiments, the polythiocyanate copper-zinc alloy plating process described in step (4) uses anode movement to avoid passivation of the anode surface, and the anode movement speed is 3 to 5 m / min.

[0021] In some of the embodiments, the area ratio of the anode to the cathode in the polythiocyanate copper-zinc alloy plating process described in step (4) is (1-2):1.

[0022] In some of the embodiments, the mass fraction of copper in the copper-zinc alloy coating in step (4) is 58% to 78%.

[0023] In some of the embodiments, the copper-zinc alloy coating in step (4) has a thickness of 3 to 10 μm.

[0024] In some embodiments, the cyanide-free cadmium plating layer in step (5) is prepared by a potassium chloride cyanide-free cadmium plating process:

[0025] Cadmium chloride 25-35 g / L, potassium chloride 100-140 g / L, PULIZIER NCC-617AC complexing agent 100-140 g / L, PULIZIER NCC-617Base auxiliary agent 25-30 mL / L, PULIZIER NCC-617Bri brightener 1.5-2.5 mL / L, PULIZIER NCC-617HCD high-zone brightener 5-10 mL / L, plating tank temperature 20-35 ° C, plating solution pH 7-9, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 2 to 4 m / min.

[0026] In some embodiments, the thickness of the cyanide-free cadmium plating layer in step (5) is 5 to 30 μm.

[0027] In some embodiments, the hexavalent chromium passivation process described in step (7) adopts a hexavalent chromium low-chromium color passivation process:

[0028] The volume concentration of HC-5 high protection low chrome color passivator is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15s, and weak air stirring or workpiece swing is used.

[0029] In some embodiments, the hexavalent chromium passivation process described in step (7) adopts a hexavalent chromium military green passivation process:

[0030] OVG-31 military green passivator 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air stirring or swinging the plated parts, passivation time 30~90s.

[0031] The invention adopts a sulfuric acid anodic electrolytic activation method to activate the surface of the alloy steel forging machined part. The metal on the surface of the workpiece undergoes an anodic electrolytic oxidation reaction in a sulfuric acid medium and dissolves in an electrolyte, thereby effectively stripping off the oxide film on the surface of the workpiece. In the process, no hydrogen evolution reaction occurs in the metal matrix.

[0032] Potential activation theory believes that: 1) the higher cathode polarization makes the metal deposition potential shift more positively, which is conducive to the reduction of the oxide film on the substrate surface; 2) the slow deposition rate of the plating solution can provide enough time for the oxide film to be reduced. The combination of these two factors can ensure that the oxide film on the substrate surface is reduced to the substrate metal, and the coating formed after the oxide film on the substrate surface is eliminated can form a good bonding force with the substrate metal.

[0033] The polymerized thiocyanate copper-zinc alloy plating process of the present invention has a plating solution performance similar to that of the cyanide copper-zinc alloy plating solution, and has a high cathode polarization and activation ability. When the plating process is adopted, the chromium trioxide on the forging surface of the alloy steel can react first and be reduced to metal chromium and combined with the substrate, and then the copper and zinc ions in the plating solution begin to be electrodeposited to form a copper-zinc alloy plating layer.

[0034] A cadmium plating layer is prepared on the copper-zinc alloy plating layer. The electrode potential of the cadmium plating layer is obviously more negative than that of the copper-zinc alloy plating layer. The cadmium plating layer has an electrochemical protective effect on the copper-zinc alloy plating layer.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts of the present invention adopts a sulfate electrolytic activation method instead of a pickling activation method, which can effectively remove the chromium trioxide oxide film on the forging surface of the alloy steel forging machine parts and overcome the defect that the existing pickling activation process causes hydrogen embrittlement of the workpiece matrix;

[0037] 2. The cyanide-free cadmium plating method for aerospace alloy steel forging machine additions of the present invention is to perform polymerized thiocyanate copper-zinc alloy plating on the alloy steel substrate, which can further remove the chromium trioxide oxide film remaining on the forging surface of the aerospace alloy steel forging machine additions;

[0038] 3. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts of the present invention prepares a cadmium plating layer on a copper-zinc alloy plating layer, which effectively overcomes the defect that the cadmium plating layer directly prepared on an alloy steel substrate does not have an electrochemical protection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute an improper limitation of the present invention. In the drawings:

[0040] Figure 1 Schematic diagram of the coating structure of Embodiment 1, Embodiment 2, Embodiment 3 and Embodiment 4 of the present invention;

[0041] Figure 2This is a photo of the alloy steel forging surface cadmium-plated sample prepared according to this scheme after the wet heat test;

[0042] Figure 3 This is a photo of the cadmium-plated sample of the alloy steel forging surface prepared according to this scheme after the mold test;

[0043] Figure 4 This is a microscopic morphology of the cadmium-plated layer prepared on the alloy steel forging surface according to this scheme;

[0044] Figure 5 It is a microscopic morphology of the cadmium-plated layer directly prepared on the forged surface of alloy steel according to the current process;

[0045] Figure 6 This is a photo of the alloy steel forging surface that was directly cadmium-plated according to the current process after being placed for 6 months. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0047] A cyanide-free cadmium plating method for aerospace alloy steel forging machine parts comprises: sandblasting, machining, degreasing, sulfuric acid anode electrolytic activation, polymerized thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying the alloy steel forging blank.

[0048] The coating structure prepared by the method comprises an alloy steel forging machine addition substrate, and a cyanide-free copper-zinc alloy coating, a cyanide-free cadmium coating layer, and a hexavalent chromium passivation layer which are sequentially prepared from inside to outside on the alloy steel forging machine addition substrate.

[0049] The surface of the alloy steel forging blank is sandblasted according to the traditional sandblasting process.

[0050] After the alloy steel forging blank is sandblasted, part of the surface is machined to obtain the alloy steel forging machined part.

[0051] According to the current pre-treatment process, the alloy steel forging machine parts are subjected to "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0052] After the alloy steel forging parts are degreased, the activation treatment is carried out by sulfuric acid anode electrolysis activation process. Preferably, the sulfuric acid anode electrolysis activation process adopts the following process method:

[0053] Concentrated sulfuric acid 150~250g / L, anode current density 0.5~1.5A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1 to 2 minutes, and make the cathode with lead plate.

[0054] After the alloy steel forging machine parts are electrolytically activated, the polymerized thiocyanate copper-zinc alloy plating process of the invention is adopted to prepare a cyanide-free copper-zinc alloy plating layer.

[0055] Preferably, the mass fraction of copper in the cyanide-free copper-zinc alloy coating is 58% to 78%.

[0056] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 3 to 10 μm.

[0057] 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 solution pH 9.5-11.5, plating tank temperature 35-55 °C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3 to 5 m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the anode moving speed is 3 to 5 m / min, and the area ratio of the anode to the cathode is (1 to 2):1.

[0058] After the alloy steel forging parts are plated with copper-zinc alloy by polymerized thiocyanate, the current cyanide-free cadmium plating process is used to prepare the cyanide-free cadmium plating layer.

[0059] Preferably, the thickness of the cyanide-free cadmium plating layer is 5 to 30 μm.

[0060] Preferably, the cyanide-free cadmium plating layer is prepared by using the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of SuperBang Chemical:

[0061] Cadmium chloride 25-35 g / L, potassium chloride 100-140 g / L, PULIZIER NCC-617AC complexing agent 100-140 g / L, PULIZIER NCC-617Base auxiliary agent 25-30 mL / L, PULIZIER NCC-617Bri brightener 1.5-2.5 mL / L, PULIZIER NCC-617HCD high-zone brightener 5-10 mL / L, plating tank temperature 20-35 ° C, plating solution pH 7-9, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 2 to 4 m / min.

[0062] Alloy steel forging machine parts are subjected to dehydrogenation treatment after cadmium plating at 190-210℃ for 10-24h.

[0063] The alloy steel forging machined parts are treated with dehydrogenation and then the hexavalent chromium passivation layer is prepared by the current hexavalent chromium passivation process.

[0064] Preferably, the hexavalent chromium passivation layer is a hexavalent chromium color passivation layer.

[0065] Preferably, the hexavalent chromium color passivation layer is prepared using HC-5 high protection low chromium color passivation agent produced by Chaobang Chemical:

[0066] The volume concentration of HC-5 high protection low chrome color passivator is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15s, and weak air stirring or workpiece swing is used.

[0067] Preferably, the hexavalent chromium passivation layer is a hexavalent chromium military green passivation layer.

[0068] Preferably, the military green passivation layer is prepared using the OVG-31 military green passivation agent of Chaobang Chemical:

[0069] OVG-31 military green passivator 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air stirring or swinging the plated parts, passivation time 30~90s.

[0070] Alloy steel forging machined parts are passivated and then washed and dried.

[0071] Embodiment 1:

[0072] The material model of aerospace alloy steel forging machine parts is 25Cr3MoA, and the cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anode electrolytic activation, polymerized thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0073] 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 machine addition 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 machine addition substrate 1.

[0074] 1. Sand blasting:

[0075] The surface of the alloy steel forging blank is sandblasted according to the traditional sandblasting process.

[0076] 2. Machining:

[0077] After the alloy steel forging blank is sandblasted, part of the surface is machined to obtain the alloy steel forging machined part.

[0078] 3. Oil removal:

[0079] According to the current pre-treatment process, the alloy steel forging machine addition substrate 1 is subjected to "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0080] 4. Anodic electrolytic activation:

[0081] The degreased alloy steel forging machine part substrate 1 is activated according to the sulfuric acid anode electrolytic activation process.

[0082] Concentrated sulfuric acid 200g / L, anode current density 1.0A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1.5 minutes, and make the cathode with lead plate.

[0083] 5. Polythiocyanate copper-zinc alloy plating:

[0084] After electrolytic activation of alloy steel forging parts, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, wherein the mass fraction of copper in the coating is 66% to 70% and the coating thickness is 7 μm.

[0085] Polymerized cuprous thiocyanate 21g / L, polyzinc thiocyanate 14g / L, polysodium thiocyanate 150g / L, brightener 10mL / L, plating solution pH 10.5, plating tank temperature 45℃, cathode current density 1.0A / dm 2 , the cathode moves at 4m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the anode moving speed is 4m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0086] 6. Cyanide-free cadmium plating:

[0087] After the alloy steel forging machine parts are plated with copper-zinc alloy by polymerized thiocyanate, the cyanide-free cadmium plating layer 3 is prepared by the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical, and the coating thickness is 12μm.

[0088] Cadmium chloride 30g / L, potassium chloride 120g / L, PULIZIER NCC-617AC complexing agent 120g / L, PULIZIER NCC-617Base auxiliary agent 28mL / L, PULIZIER NCC-617Bri brightener 2.0mL / L, PULIZIER NCC-617HCD high zone brightener 8mL / L, plating tank temperature 28℃, plating solution pH 8, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0089] 7. Hydrogen removal:

[0090] Alloy steel forging machine parts are subjected to dehydrogenation treatment after cyanide-free cadmium plating at 200℃ for 24h.

[0091] 8. Hexavalent chromium color passivation:

[0092] After dehydrogenation treatment, the alloy steel forging machine parts are treated with Chaobang Chemical's HC-5 high-protection low-chromium color passivation agent to prepare a hexavalent chromium color passivation layer 4.

[0093] The volume concentration of HC-5 high protection low chrome color passivator is 3%, the passivation temperature is 28℃, the pH of the passivation solution is 1.7, the passivation time is 8s, and the workpiece swings.

[0094] The specific process is: "light irradiation with 2% volume fraction nitric acid → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0095] Embodiment 2:

[0096] The material model of aerospace alloy steel forging machine parts is ZGCr15, and the cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anode electrolytic activation, polymerized thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0097] 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 machine addition 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 machine addition substrate 1.

[0098] 1. Sand blasting:

[0099] The surface of the alloy steel forging blank substrate is sandblasted according to the traditional sandblasting process.

[0100] 2. Machining:

[0101] After the alloy steel forging blank is sandblasted, part of the surface is machined to obtain the alloy steel forging machined part.

[0102] 3. Oil removal:

[0103] According to the current pre-treatment process, the alloy steel forging machine addition substrate 1 is subjected to "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0104] 4. Anodic electrolytic activation:

[0105] The degreased alloy steel forging machine part substrate 1 is activated according to the sulfuric acid anode electrolytic activation process.

[0106] Concentrated sulfuric acid 220g / L, anode current density 1.2A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1.2 minutes, and make the cathode with lead plate.

[0107] 5. Polythiocyanate copper-zinc alloy plating:

[0108] After electrolytic activation of alloy steel forging parts, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, wherein the mass fraction of copper in the coating is 66% to 70% and the coating thickness is 7 μm.

[0109] Polymerized cuprous thiocyanate 23g / L, polyzinc thiocyanate 15g / L, polysodium thiocyanate 168g / L, brightener 11mL / L, plating solution pH 9.8, plating tank temperature 40℃, cathode current density 1.2A / dm 2 , the cathode moves at 4m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the anode moving speed is 4m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0110] 6. Cyanide-free cadmium plating:

[0111] After the alloy steel forging machine parts are plated with copper-zinc alloy by polymerized thiocyanate, the cyanide-free cadmium plating layer 3 is prepared by the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical, and the coating thickness is 12μm.

[0112] Cadmium chloride 33g / L, potassium chloride 110g / L, PULIZIER NCC-617AC complexing agent 135g / L, PULIZIER NCC-617Base auxiliary agent 28mL / L, PULIZIER NCC-617Bri brightener 2.0mL / L, PULIZIER NCC-617HCD high zone brightener 8mL / L, plating tank temperature 22℃, plating solution pH 8, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0113] 7. Hydrogen removal:

[0114] Alloy steel forging machine parts are subjected to dehydrogenation treatment after cyanide-free cadmium plating at 200℃ for 24h.

[0115] 8. Hexavalent chromium color passivation:

[0116] After dehydrogenation treatment, the alloy steel forging machine parts are treated with Chaobang Chemical's HC-5 high-protection low-chromium color passivation agent to prepare a hexavalent chromium color passivation layer 4.

[0117] The volume concentration of HC-5 high protection low chrome color passivator is 3.5%, the passivation temperature is 22°C, the pH of the passivation solution is 1.5, the passivation time is 8s, and weak air stirring is used.

[0118] The specific process is: "light irradiation with 2% volume fraction nitric acid → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0119] Embodiment 3:

[0120] The material model of aerospace alloy steel forging machine parts is 30CrMnSiA, and the cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anode electrolytic activation, polymerized thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0121] 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 machine addition 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 machine addition substrate 1.

[0122] 1. Sand blasting:

[0123] The surface of the alloy steel forging blank is sandblasted according to the traditional sandblasting process.

[0124] 2. Machining:

[0125] After the alloy steel forging blank is sandblasted, part of the surface is machined to obtain the alloy steel forging machined part.

[0126] 3. Oil removal:

[0127] According to the current pre-treatment process, the alloy steel forging machine add-on substrate 1 is subjected to "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0128] 4. Anodic electrolytic activation:

[0129] The degreased alloy steel forging machine part substrate 1 is activated according to the sulfuric acid anode electrolytic activation process.

[0130] Concentrated sulfuric acid 170g / L, anode current density 0.8A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1.8 minutes, and make the cathode with lead plate.

[0131] 5. Polythiocyanate copper-zinc alloy plating:

[0132] After electrolytic activation of alloy steel forging parts, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, wherein the mass fraction of copper in the coating is 66% to 70% and the coating thickness is 7 μm.

[0133] Polymerized cuprous thiocyanate 18g / L, polyzinc thiocyanate 13g / L, polysodium thiocyanate 140g / L, brightener 8mL / L, plating solution pH 11.3, plating tank temperature 50℃, cathode current density 1.0A / dm 2, the cathode moves at 4m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the anode moving speed is 4m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0134] 6. Cyanide-free cadmium plating:

[0135] After the alloy steel forging machine parts are plated with copper-zinc alloy by polymerized thiocyanate, the cyanide-free cadmium plating layer 3 is prepared by the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical, and the coating thickness is 12μm.

[0136] Cadmium chloride 27g / L, potassium chloride 130g / L, PULIZIER NCC-617AC complexing agent 110g / L, PULIZIER NCC-617Base auxiliary agent 28mL / L, PULIZIER NCC-617Bri brightener 2.2mL / L, PULIZIER NCC-617HCD high zone brightener 8mL / L, plating tank temperature 28℃, plating solution pH 8.5, cathode current density 1.0A / dm 2 , cathode moves 3m / min.

[0137] 7. Hydrogen removal:

[0138] Alloy steel forging machine parts are subjected to dehydrogenation treatment after cyanide-free cadmium plating at 200℃ for 24h.

[0139] 8. Hexavalent chromium military green passivation:

[0140] After dehydrogenation treatment, the alloy steel forging machined parts were treated with Chaobang Chemical's OVG-31 military green passivating agent to prepare a military green passivation layer 4.

[0141] OVG-31 military green passivator 90mL / L, passivation solution pH 1.2, passivation temperature 28℃, air stirring, passivation time 60s.

[0142] The specific process is: "light irradiation with 2% volume fraction nitric acid → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0143] Embodiment 4:

[0144] The material model of aerospace alloy steel forging machine parts is 33Cr3MoWV, and the cyanide-free cadmium plating method includes: sandblasting, machining, degreasing, sulfuric acid anode electrolytic activation, polymerized thiocyanate copper-zinc alloy plating, cyanide-free cadmium plating, hydrogen removal, passivation, and drying of the alloy steel forging blanks.

[0145] like Figure 1As shown, the cyanide-free cadmium plating layer structure prepared by the cyanide-free cadmium plating method includes: an alloy steel forging machine addition substrate 1, and a polymerized 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 machine addition substrate 1.

[0146] 1. Sand blasting:

[0147] The surface of the alloy steel forging blank substrate is sandblasted according to the traditional sandblasting process.

[0148] 2. Machining:

[0149] After the alloy steel forging blank is sandblasted, part of the surface is machined to obtain the alloy steel forging machined parts.

[0150] 3. Oil removal:

[0151] According to the current pre-treatment process, the alloy steel forging machine add-on substrate 1 is subjected to "alkaline chemical degreasing → water washing → alkaline anodic electrolytic degreasing → water washing".

[0152] 4. Anodic electrolytic activation:

[0153] The degreased alloy steel forging machine part substrate 1 is activated by sulfuric acid anode activation electrolysis process.

[0154] Concentrated sulfuric acid 250g / L, anode current density 1.5A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1 minute, and make the cathode with lead plate.

[0155] 5. Polythiocyanate copper-zinc alloy plating:

[0156] After electrolytic activation of alloy steel forging parts, the polymerized thiocyanate copper-zinc alloy plating process of the present invention is used to prepare a cyanide-free copper-zinc alloy coating 2, wherein the mass fraction of copper in the coating is 66% to 70% and the coating thickness is 7 μm.

[0157] Polymeric cuprous thiocyanate 25 g / L, polymeric zinc thiocyanate 16 g / L, polymeric sodium thiocyanate 175 g / L, brightener 9 mL / L, plating solution pH 10, plating tank temperature 38 ° C, cathode current density 1.4 A / dm 2 , the cathode moves at 4m / min, a brass plate with a copper mass fraction of 68% is used as the anode, the anode moving speed is 4m / min, and the area ratio of the anode to the cathode is 1.5:1.

[0158] 6. Cyanide-free cadmium plating:

[0159] After the alloy steel forging machine parts are plated with copper-zinc alloy by polymerized thiocyanate, the cyanide-free cadmium plating layer 3 is prepared by the PULIZIER NCC-617 potassium chloride cyanide-free cadmium plating process of Chaobang Chemical, and the coating thickness is 12μm.

[0160] Cadmium chloride 25g / L, potassium chloride 140g / L, PULIZIER NCC-617AC complexing agent 100g / L, PULIZIER NCC-617Base auxiliary agent 28mL / L, PULIZIER NCC-617Bri brightener 1.6mL / L, PULIZIER NCC-617HCD high zone brightener 8mL / L, plating tank temperature 35℃, plating solution pH 9, cathode current density 0.8A / dm 2 , cathode moves 3m / min.

[0161] 7. Hydrogen removal:

[0162] Alloy steel forging machine parts are subjected to dehydrogenation treatment after cyanide-free cadmium plating at 200℃ for 24h.

[0163] 8. Hexavalent chromium military green passivation:

[0164] After dehydrogenation treatment, the alloy steel forging machined parts were treated with Chaobang Chemical's OVG-31 military green passivating agent to prepare a military green passivation layer 4.

[0165] OVG-31 military green passivator 110mL / L, passivation solution pH 1.3, passivation temperature 23℃, swing plated parts, passivation time 50s.

[0166] The specific process is: "light irradiation with 2% volume fraction nitric acid → water washing → passivation → water washing → drying at 60℃ for 15 minutes".

[0167] Test Example 1:

[0168] The cadmium colored passivation and military green passivation samples of alloy steel forging machine parts prepared in Examples 1 to 4 were subjected to a neutral salt spray test for 1000 hours in accordance with the standard GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test". The salt spray resistance of the coating is much higher than the requirement of no white rust in a neutral salt spray test for 96 hours in GB / T13346-2012 "Treatment of cadmium electroplating on metal and other inorganic coatings on steel".

[0169] Test Example 2:

[0170] The cadmium-plated color passivated samples of alloy steel forging machined parts prepared in Example 1 and Example 2 were subjected to a wet heat test for 20 days according to GJB150.9A-2009 "Military Equipment Laboratory Environmental Test Method Part 9: Wet Heat Test". The test results are as follows: Figure 2As shown, there is no visible change on the surface of all samples, which meets the environmental test requirements.

[0171] Test Example 3:

[0172] The cadmium-plated color passivated samples of alloy steel forging machined parts prepared in Example 1 and Example 2 were subjected to a fungus test for 28 days according to GJB150.9A-2009 "Military Equipment Laboratory Environmental Test Method Part 10: Fungus Test". The test results are as follows: Figure 3 As shown, the mold growth on the surface of all samples is level 0, which meets the environmental test requirements.

[0173] Test example 4:

[0174] The cadmium-plated passivated samples of alloy steel forging machine parts prepared in Examples 1 to 4 were tested for coating adhesion according to GB / T5270-2005 "Review of Test Methods for Adhesion Strength of Electrodeposited and Chemically Deposited Metal Coatings on Metal Substrates". The plated parts were placed in a heating furnace and heated to 300°C for 60 minutes, then taken out and suddenly cooled in water at room temperature. No blistering or shedding occurred in the coating. The test showed that the combined coating prepared by the present invention had good adhesion.

[0175] Test Example 5:

[0176] According to the process of Example 1, a cadmium-plated sample of alloy steel forging machine parts was prepared. After pre-treatment, the alloy steel forging machine parts were plated with copper-zinc alloy and cadmium, and no passivation treatment was performed. The microscopic morphology of the cadmium-plated layer on the forging surface was characterized by a scanning electron microscope. The obtained microscopic morphology of the coating is as follows: Figure 4 , showing that there are no pores in the cadmium plating.

[0177] Test Example 6:

[0178] The alloy steel forging machine parts were cadmium-plated according to the traditional process. After degreasing and hydrochloric acid activation, the alloy steel forging machine parts were directly subjected to potassium chloride cyanide-free cadmium plating without passivation treatment. The cadmium plating layer on the forging surface was characterized by scanning electron microscopy. The obtained coating micromorphology is shown in the figure. Figure 5 , showing that there are pores in the cadmium plating.

[0179] Test Example 7:

[0180] The alloy steel forging machined parts prepared in Test Example 5 were cadmium plated and then color passivated. The samples were placed in a laboratory environment for 1 year, and no black spots appeared on the surface of the coating on the forging surface of the plated parts.

[0181] Test Example 8:

[0182] The alloy steel forging machined parts prepared in Test Example 6 were cadmium plated and then color passivated. The samples were placed in a laboratory environment for 6 months. Black spots appeared on the surface of the coating on the forging surface of the plated parts. The results are as follows: Figure 6 shown.

[0183] Test Example 9:

[0184] The effect of brightener concentration in polythiocyanate copper-zinc alloy plating bath on the coating was tested.

[0185] Polymerized cuprous thiocyanate 20g / L, polyzinc thiocyanate 14g / L, polysodium thiocyanate 145g / L, plating solution pH 10.5, plating tank temperature 45°C, cathode current density 1.0A / dm 2 , using a brass plate as the anode. The amount of N,N'-di-n-propylethylenediamine added is 0.2-1.4 g / L, and the amount of polyacrylamide with a molecular weight less than 8000 added is 0.5-2.0 g / L. The test shows that the range of the amount of N,N'-di-n-propylethylenediamine added is narrow, while the range of the amount of polyacrylamide with a molecular weight less than 8000 is wide. The test results show that the concentration of the components contained in the brightener is calculated according to the upper and lower limits, and the amount of the brightener added in the range of 7-13 mL / L can usually obtain a good copper-zinc alloy coating.

[0186] The technical solutions provided by the embodiments of the present invention are described in detail above. The principles and implementation methods of the embodiments of the present invention are described in detail using specific examples herein. The description of the embodiments above is only applicable to help understand the principles of the embodiments of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A cyanide-free cadmium plating method for aerospace alloy steel forging machine parts, characterized in that: The following steps are involved: (1) Shot blasting is performed on the surface of the alloy steel forging blank to remove the oxide on the surface; (2) machining a portion of the surface of the alloy steel forging blank processed in step (1) to obtain an alloy steel forging machined part; (3) degreasing and activating the alloy steel forging machined part substrate prepared in step (2); (4) preparing a cyanide-free copper-zinc alloy coating on the alloy steel forging machine workpiece substrate treated in step (3) by using a polymerized thiocyanate copper-zinc alloy plating process; (5) preparing a cyanide-free cadmium plating layer on the cyanide-free copper-zinc alloy plating layer prepared in step (4) by using a cyanide-free cadmium plating process; (6) performing a dehydrogenation treatment on the alloy steel forging machined parts that have been subjected to cyanide-free cadmium plating in step (5); (7) preparing a passivation layer by a hexavalent chromium passivation process on the cyanide-free cadmium-plated layer after dehydrogenation in step (6); The process for plating copper-zinc alloy with polymerized thiocyanate 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 solution pH 9.5-11.5, plating tank temperature 35-55 °C, cathode current density 0.5-1.5 A / dm 2 , the cathode moves 3-5 m / min, and a brass plate with a copper mass fraction of 68% is used as the anode; The brightener in the polythiocyanate copper-zinc alloy plating process comprises 60-100 g / L of N,N'-di-n-propylethylenediamine and 80-120 g / L of polyacrylamide with a molecular weight less than 8000.

2. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The activation treatment described in step (3) adopts sulfuric acid anode electrolysis process: Concentrated sulfuric acid 150~250g / L, anode current density 0.5~1.5A / dm 2 , operate at room temperature, hang the alloy steel forging machine parts on the anode, electrolyze for 1 to 2 minutes, and make the cathode with lead plate.

3. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The polythiocyanate 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.

4. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: In the polythiocyanate copper-zinc alloy plating process described in step (4), the area ratio of the anode to the cathode is (1-2):

1.

5. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The mass fraction of copper in the copper-zinc alloy coating prepared in step (4) is 58% to 78%.

6. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The thickness of the copper-zinc alloy coating in step (4) is 3 to 10 μm.

7. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The cyanide-free cadmium plating layer in step (5) is prepared by a potassium chloride cyanide-free cadmium plating process: Cadmium chloride 25-35g / L, potassium chloride 100-140g / L, PULIZIER NCC-617 AC complexing agent 100-140g / L, PULIZIER NCC-617 Base auxiliary agent 25-30mL / L, PULIZIER NCC-617 Bri brightener 1.5-2.5mL / L, PULIZIER NCC-617 HCD high zone brightener 5-10mL / L, plating tank temperature 20-35℃, plating solution pH 7-9, cathode current density 0.5-1.5A / dm 2 , the cathode moves 2 to 4 m / min.

8. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The thickness of the cyanide-free cadmium plating layer in step (5) is 5 to 30 μm.

9. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to 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 concentration of HC-5 high protection low chrome color passivator is 2% to 4%, the passivation temperature is 20 to 35°C, the pH value of the passivation solution is 1.3 to 2.0, the passivation time is 5 to 15s, and weak air stirring or workpiece swing is used.

10. The cyanide-free cadmium plating method for aerospace alloy steel forging machine parts according to claim 1, characterized in that: The hexavalent chromium passivation process described in step (7) adopts a hexavalent chromium military green passivation process: OVG-31 military green passivator 80~120mL / L, passivation solution pH value 1.0~1.6, passivation temperature 20~30℃, air stirring or swinging the plated parts, passivation time 30~90s.

Images