A method for trivalent chromium plating of NdFeB workpiece

Abstract

The invention discloses a method for trivalent chromium plating of a NdFeB workpiece, comprising degreasing, rust removal, electrolytic activation, citrate pre-nickel plating, pyrophosphate copper plating, acid copper plating, bright nickel plating, trivalent chromium plating, and rare earth electrolytic protection on the NdFeB substrate. The combined coating prepared by the trivalent chromium plating method for NdFeB workpiece disclosed by the invention is subjected to a neutral salt spray test according to GB / T 10125-2012 "Artificial Atmosphere Corrosion Test Salt Spray Test". The surface of the plated piece is free of rust after 120 hours of sulfate trivalent chromium white chromium plating, the surface of the plated piece is free of rust after 96 hours of chloride trivalent chromium white chromium plating, and the surface of the plated piece is free of rust after 72 hours of sulfate trivalent chromium black chromium plating. The combined coating has high corrosion resistance, and the preparation method thereof has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of metal surface treatment, and in particular relates to a trivalent chromium plating method for a NdFeB workpiece. Background Art

[0002] As the third generation of rare earth permanent magnet materials, NdFeB has excellent magnetic properties and high cost performance. It has been favored by people since its introduction in the 1980s. In recent years, my country has become the global production and market center of NdFeB permanent magnet materials. The material has been widely used in high-tech fields such as computers, network information, aerospace, communications, transportation, home appliances, and health care. In the context of energy conservation, environmental protection and low-carbon economy, the development of new energy vehicles, wind power generation, energy-saving home appliances, small and lightweight vehicles, and variable frequency air conditioners will continue to increase the market demand for NdFeB permanent magnet materials, and at the same time, higher requirements are put forward for the corrosion resistance of NdFeB permanent magnet materials.

[0003] The surface of sintered NdFeB is porous, and the material itself has high chemical activity, which brings many difficulties to the surface treatment of NdFeB. The problem of poor corrosion resistance has not been solved, and various protection methods for NdFeB magnets still have different defects. The domestic NdFeB surface protection technology mainly has the following problems: the existing pre-treatment process has defects such as acid and alkali solution infiltrating into the pores on the surface of NdFeB during oil removal and rust removal, resulting in re-oxidation, which leads to residual corrosion of magnet pores and intergranular phases, seriously affecting the quality of the coating, and the coating is prone to blistering and pitting corrosion; in the electroplating process, there is also the problem of plating solution infiltrating into the pores on the surface of NdFeB and corroding the substrate; the uniformity, bonding strength and corrosion resistance of the coating have not yet met the expected requirements, and the protection capacity is limited. These problems have seriously restricted the development of NdFeB permanent magnet materials and related industries, and restricted the competitiveness of my country's NdFeB permanent magnet industry in the international market. Summary of the invention

[0004] In order to solve the problem that the electroplating layer prepared on the surface of NdFeB workpiece by the current process has poor corrosion resistance, the present invention provides a method for trivalent chromium plating of NdFeB workpiece. In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A method for trivalent chromium plating of a NdFeB workpiece comprises the following steps:

[0006] (1) performing citrate pre-nickel plating on the surface of the NdFeB substrate;

[0007] (2) performing pyrophosphate copper plating on the citrate pre-nickel plating layer prepared in step (1);

[0008] (3) plating acid copper on the pyrophosphate copper plating layer prepared in step (2);

[0009] (4) plating bright nickel on the acid copper coating prepared in step (3);

[0010] (5) plating trivalent chromium on the bright nickel coating prepared in step (4);

[0011] (6) preparing a rare earth electrolytic protection film on the trivalent chromium coating prepared in step (5) using a rare earth cathode electrolytic protection process;

[0012] The rare earth cathode electrolytic protection process described in step (6) is: rare earth salt 1-10 g / L, HEDP complexing agent 5-50 g / L, alkali metal carbonate 80-150 g / L, pH range 11.5-12.5, cathode current density 0.5-1.2 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, titanium plate as anode, electrolyze for 30 to 90 seconds;

[0013] The alkali metal carbonate in the rare earth cathode electrolytic protection process in step (6) includes any one or both of anhydrous sodium carbonate and anhydrous potassium carbonate;

[0014] The rare earth salt in the rare earth cathode electrolytic protection process in step (6) includes any one or two of lanthanum acetate, praseodymium acetate, cerium acetate, lanthanum sulfate, praseodymium sulfate, and cerous sulfate.

[0015] A method for trivalent chromium plating of a NdFeB workpiece, further comprising a pre-treatment step of the NdFeB workpiece: degreasing, derusting and electrolytically activating the NdFeB substrate before pre-nickel plating with citrate;

[0016] The electrolytic activation of the NdFeB matrix adopts a sulfate electrolytic activation process: alkali metal sulfate 80-200 g / L, pH range 6-8, electrolysis temperature 15°C-40°C, cathode current density 0.5-1.2 A / dm 2 , the cathode moves 4-6 m / min, the NdFeB workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is carried out for 20-40 s;

[0017] The alkali metal sulfate includes any one or both of sodium sulfate and potassium sulfate.

[0018] Preferably, the rust removal of the NdFeB matrix adopts a lactic acid rust removal process: 40-80 mL / L of lactic acid, an operating temperature of 20° C. to 35° C., and a rust removal time of 0.5 to 3 min.

[0019] Preferably, the pH required by the rare earth electrolytic protection process or the electrolytic activation process is adjusted with a 10% by mass sodium hydroxide solution or with a 10% by mass sulfuric acid.

[0020] Preferably, the thickness of the citrate pre-nickel plating layer is 1 to 9 μm, and it is prepared by the current citrate nickel plating process: 180 to 250 g / L nickel sulfate hexahydrate, 10 to 12 g / L sodium chloride, 30 to 35 g / L boric acid, 30 to 40 g / L magnesium sulfate, pH range 7.0 to 7.2, plating tank temperature 50°C to 60°C, cathode current density 1 to 1.5 A / dm 2 , the cathode moves 4 to 6 m / min.

[0021] Preferably, the thickness of the pyrophosphate copper plating layer is 4 to 11 μm.

[0022] Preferably, the thickness of the acid copper plating layer is 7 to 19 μm.

[0023] Preferably, the thickness of the bright nickel plating layer is 3 to 13 μm.

[0024] Preferably, the trivalent chromium plating layer has a thickness of 0.05 to 0.35 μm and is prepared by a trivalent chromium white chromium plating process or a trivalent chromium black chromium plating process.

[0025] Preferably, the trivalent chromium white chromium plating process adopts a sulfate trivalent chromium plating process: Trich-9551 M cylinder opener 8-12 mL / L, Trich-9551 B supplement 260-300 mL / L, Trich-9551 CS conductive salt 260-300 g / L, Trich-9551 WA wetting agent 0.5-2.0 mL / L, pH range 3.4-3.8, plating tank temperature 50°C-55°C, cathode current density 8-15 A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

[0026] Preferably, the trivalent chromium white chromium plating process adopts a chloride trivalent chromium plating process: Trich-6561 opening salt 400-450g / L, Trich-6563 complexing agent 60-85mL / L, Trich-6564 stabilizer 1-2mL / L, Trich-6565 wetting agent 1-3mL / L, pH range 2.5-3.0, plating tank temperature 25°C-36°C, cathode current density 8-16A / dm 2 , medium air agitation.

[0027] Preferably, the trivalent chromium black chromium plating adopts the sulfate trivalent chromium black chromium plating process: Trich-7677 S initiator 8-12mL / L, Trich-7677 M cylinder opener 260-300mL / L, Trich-7677 CS conductive salt 260-300g / L, Trich-7677 C stabilizer 3.0-4.0mL / L, Trich-7677 D toner 3.0-8.0mL / L, Trich-7677 WA wetting agent 0.5-2.0mL / L, pH range 3.3-3.7, plating tank temperature 25°C-40°C, cathode current density 8-14A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

[0028] The present invention uses a neutral sodium sulfate / or potassium sulfate electrolyte to perform cathode electrolytic activation on the surface of the NdFeB substrate. The electrons gathered on the surface of the plated substrate reduce the metal oxide to metal, thereby effectively removing the oxide film on the substrate surface. Using sodium sulfate / or potassium sulfate electrolysis to activate the metal surface is an innovative technology. Experiments show that its activation effect is the same as the traditional pickling activation method. The advantage of the electrolytic activation method is that the neutral sodium sulfate / or potassium sulfate electrolyte immerses in the pores on the surface of the NdFeB substrate without damaging the substrate metal, and can overcome the technical defect of the current pickling activation method that causes corrosion to the NdFeB substrate. A neutral citrate nickel plating process is used to prepare the pre-nickel plating layer, and the neutral plating solution immerses in the pores on the substrate surface without damaging the NdFeB substrate. The citrate nickel plating solution has a high deep plating ability, and the use of the citrate nickel plating process for pre-nickel plating is also beneficial to the sealing of the surface of the NdFeB substrate. The pH of the pyrophosphate copper plating solution is 8.6-9.0, which has little corrosion effect on the NdFeB substrate. Pyrophosphate copper plating on the citrate pre-nickel plating layer can eventually close the pores on the surface of the NdFeB substrate, so that the NdFeB substrate is effectively protected. Plating acid copper on the pyrophosphate copper plating layer increases the thickness of the copper plating layer and improves the brightness. Bright nickel is plated on the copper plating layer. The bright nickel plating layer is an anodic plating layer, and there is a high potential difference between the two plating layers. The copper plating layer can effectively prevent the corrosive medium from corroding toward the substrate. Plating trivalent chromium on the bright nickel plating layer and then performing rare earth cathode electrolytic protection can significantly improve the corrosion resistance of the plating layer.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The trivalent chromium plating method of NdFeB workpieces of the present invention adopts a sulfate electrolytic activation method instead of an acid pickling activation method, which can effectively overcome the technical defects of blistering and pitting corrosion of the coating caused by acid pickling activation of the NdFeB substrate according to the current process;

[0031] 2. The trivalent chromium plating method of the NdFeB workpiece of the present invention prepares a citrate pre-plated nickel layer and a pyrophosphate copper plating layer on the NdFeB substrate, which can effectively seal the pores on the surface of the NdFeB;

[0032] 3. The trivalent chromium plating method for NdFeB workpieces of the present invention adopts a rare earth cathode electrolytic protection process to prepare a protective film on the trivalent chromium plating layer, thereby improving the corrosion resistance and anti-discoloration ability of the trivalent chromium plating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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:

[0034] Figure 1 It is a schematic diagram of the coating structure of Example 1, Example 2 and Example 3 of the present invention. DETAILED DESCRIPTION

[0035] 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.

[0036] The NdFeB workpiece substrate is subjected to degreasing, rust removal and electrolytic activation processes.

[0037] The degreasing process adopts the current NdFeB degreasing process.

[0038] The rust removal process is preferably a lactic acid rust removal process: 40-80 mL / L of lactic acid, an operating temperature of 20° C. to 35° C., and a rust removal time of 0.5 to 3 min.

[0039] The electrolytic activation process is preferably a sulfate electrolytic activation process: alkali metal sulfate 80-200 g / L, pH range 6-8, electrolysis temperature 15°C-40°C, cathode current density 0.5-1.2 A / dm 2 The cathode moves at 4-6 m / min, the workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is performed for 20-40 seconds. A 10% sodium hydroxide solution or a 10% sulfuric acid solution is used to adjust the pH required by the electrolytic activation process.

[0040] Preferably, the alkali metal sulfate includes any one or both of sodium sulfate and potassium sulfate.

[0041] After pretreatment of the workpiece, a citrate pre-plated nickel layer, a pyrophosphate copper plating layer, an acid copper plating layer, a bright nickel plating layer, a trivalent chromium plating layer, and a rare earth electrolytic protective film are prepared in sequence.

[0042] The thickness of the citrate pre-nickel plating layer is 1-9 μm and is prepared by using the current citrate nickel plating process.

[0043] Preferably, the citrate nickel plating process is: nickel sulfate hexahydrate 180-250 g / L, sodium chloride 10-12 g / L, boric acid 30-35 g / L, magnesium sulfate 30-40 g / L, pH range 7.0-7.2, plating tank temperature 50°C-60°C, cathode current density 1-1.5 A / dm 2 , the cathode moves 4 to 6 m / min.

[0044] The thickness of the pyrophosphate copper plating layer is 4-11 μm, and the layer is prepared by using the current pyrophosphate copper plating process.

[0045] Preferably, the pyrophosphate copper plating layer is prepared by the PC-1289 pyrophosphate copper plating process of Chaobang Chemical: 60-90 g / L copper pyrophosphate, 230-280 g / L potassium pyrophosphate, 2-5 mL / L ammonia water, 1-3 mL / L PC-1289 pyrophosphate additive, pH range 8.6-9.0, plating tank temperature 50°C-58°C, cathode current density 1-6 A / dm 2 , air stirring.

[0046] The acid copper plating layer has a thickness of 7 to 19 μm and is prepared by using the current acid copper plating process.

[0047] Preferably, the acid copper coating is prepared by the GAFFA M-8000 acid bright copper plating process of Chaobang Chemical: 180-210 g / L of copper sulfate pentahydrate, 60-80 g / L of sulfuric acid, 50-100 mg / L of chloride ions, 3-8 mL / L of GAFFA M-8000 Mu opener, 0.3-0.6 mL / L of GAFFA M-8000 A main light agent, 0.05-0.3 mL / L of GAFFA M-8000 B auxiliary light agent, 18-30 °C of plating tank temperature, 2-7 A / dm 2 , strong and uniform air stirring.

[0048] The bright nickel plating layer has a thickness of 3 to 13 μm and is prepared by using the current bright nickel plating process.

[0049] Preferably, the bright nickel plating layer is prepared by the NINFEA 8003 bright nickel plating process of Chaobang Chemical: 240-320 g / L of nickel sulfate hexahydrate, 45-60 g / L of nickel chloride hexahydrate, 40-50 g / L of boric acid, 15-40 mL / L of NINFEA SC-260 bright nickel softener, 3-7 mL / L of NINFEA AS-250 bright nickel auxiliary, 0.4-0.8 mL / L of NINFEA 8003 bright nickel main brightener, 0.5-1.5 mL / L of NINFEA NI-35 bright nickel wetting agent, pH range 4.2-4.8, plating tank temperature 50°C-60°C, cathode current density 3-6 A / dm2 , uniform air stirring.

[0050] The trivalent chromium plating layer has a thickness of 0.05 to 0.35 μm and is prepared by using the current trivalent chromium white chromium plating process or the current trivalent chromium black chromium plating process.

[0051] Preferably, the trivalent chromium white chromium plating process adopts the Trich-9551 sulfate trivalent chromium plating process of Chaobang Chemical: Trich-9551 M cylinder opener 8-12mL / L, Trich-9551 B supplement 260-300mL / L, Trich-9551 CS conductive salt 260-300g / L, Trich-9551 WA wetting agent 0.5-2.0mL / L, pH range 3.4-3.8, plating tank temperature 50°C-55°C, cathode current density 8-15A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

[0052] Preferably, the trivalent chromium white chromium plating process adopts the Trich-6561 chloride trivalent chromium plating process of Chaobang Chemical: Trich-6561 opening salt 400-450g / L, Trich-6563 complexing agent 60-85mL / L, Trich-6564 stabilizer 1-2mL / L, Trich-6565 wetting agent 1-3mL / L, pH range 2.5-3.0, plating tank temperature 25°C-36°C, cathode current density 8-16A / dm 2 , medium air agitation.

[0053] Preferably, the trivalent chromium black chromium plating process adopts the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical: Trich-7677 S initiator 8-12mL / L, Trich-7677 M cylinder opener 260-300mL / L, Trich-7677 CS conductive salt 260-300g / L, Trich-7677 C stabilizer 3.0-4.0mL / L, Trich-7677 D toner 3.0-8.0mL / L, Trich-7677 WA wetting agent 0.5-2.0mL / L, pH range 3.3-3.7, plating tank temperature 25°C-40°C, cathode current density 8-14A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

[0054] The rare earth electrolytic protection film is prepared by adopting a rare earth cathode electrolytic protection process.

[0055] Preferably, the rare earth cathode electrolytic protection process is: rare earth salt 1-10 g / L, HEDP complexing agent 5-50 g / L, alkali metal carbonate 80-150 g / L, pH range 11.5-12.5, cathode current density 0.5-1.2 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, use titanium plate as anode, electrolyze for 30 to 90 seconds. Use 10% sodium hydroxide solution or 10% sulfuric acid to adjust the pH required by the electrolytic protection process.

[0056] Preferably, the alkali metal carbonate includes any one or both of anhydrous sodium carbonate and anhydrous potassium carbonate.

[0057] Preferably, the rare earth salt includes any one or two of lanthanum acetate, praseodymium acetate, cerium acetate, lanthanum sulfate, praseodymium sulfate, and cerous sulfate.

[0058] Example 1

[0059] like Figure 1 As shown, a method for trivalent chromium plating of NdFeB workpieces includes pre-treatment on the NdFeB substrate 1, and sequentially preparing a citrate pre-nickel plating layer 2, a pyrophosphate copper plating layer 3, an acid copper plating layer 4, a bright nickel plating layer 5, a trivalent chromium white chromium plating layer 6, and a rare earth electrolytic protective film 7.

[0060] 1. Pre-treatment:

[0061] The workpiece substrate 1 is subjected to a pre-treatment process of "alkaline chemical degreasing → water washing → boiling water sealing → water washing → rust removal → water washing → ultrasonic degreasing → water washing → electrolytic activation → water washing".

[0062] The rust removal process is: lactic acid 50mL / L, operating temperature 28°C, and rust removal time 2.5min.

[0063] The electrolytic activation process is: potassium sulfate 140g / L, pH=7, electrolysis temperature 30°C, cathode current density 0.8A / dm 2 The cathode moves 5 m / min, the workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is performed for 20 seconds. A 10% by mass sodium hydroxide solution or a 10% by mass sulfuric acid is used to adjust the pH required by the electrolytic activation process.

[0064] 2. Citrate nickel plating:

[0065] After the workpiece is pre-treated, a pre-plated nickel layer 2 is prepared on the NdFeB substrate 1, and the coating thickness is 5 μm. The current citrate nickel plating process is adopted: 210 g / L nickel sulfate hexahydrate, 11 g / L sodium chloride, 33 g / L boric acid, 35 g / L magnesium sulfate, pH=7.1, plating tank temperature 55°C, cathode current density 1.3 A / dm2 , cathode moves 5m / min.

[0066] 3. Pyrophosphate copper plating:

[0067] A pyrophosphate copper plating layer 3 is prepared on the pre-nickel plating layer 2 of the workpiece, the plating thickness is 7 μm, and the PC-1289 pyrophosphate copper plating process of Chaobang Chemical is adopted: 75 g / L copper pyrophosphate, 250 g / L potassium pyrophosphate, 3 mL / L ammonia water, 2 mL / L PC-1289 pyrophosphate additive, pH=8.8, plating tank temperature 54°C, cathode current density 3 A / dm 2 , air stirring.

[0068] 4. Acid copper plating:

[0069] An acid copper plating layer 4 is prepared on the pyrophosphate copper plating layer 3 of the workpiece, the plating thickness is 11 μm, and the GAFFA M-8000 acid bright copper plating process of Chaobang Chemical is adopted: 195 g / L of copper sulfate pentahydrate, 70 g / L of sulfuric acid, 75 mg / L of chloride ions, 6 mL / L of GAFFA M-8000 Mu opener, 0.5 mL / L of GAFFA M-8000 A main light agent, 0.15 mL / L of GAFFA M-8000 B auxiliary light agent, plating tank temperature of 24°C, cathode current density of 5 A / dm 2 , strong and uniform air stirring.

[0070] 5. Bright nickel plating:

[0071] A bright nickel plating layer 5 is prepared on the acid copper plating layer 4 of the workpiece, the plating thickness is 8 μm, and the NINFEA 8003 bright nickel plating process of Chaobang Chemical is adopted: 280 g / L nickel sulfate hexahydrate, 55 g / L nickel chloride hexahydrate, 45 g / L boric acid, 28 mL / L NINFEA SC-260 bright nickel softener, 5 mL / L NINFEA AS-250 bright nickel auxiliary agent, 0.6 mL / L NINFEA 8003 bright nickel main brightener, 1 mL / L NINFEA NI-35 bright nickel wetting agent, pH=4.5, plating tank temperature 55°C, cathode current density 4.5 A / dm 2 , uniform air stirring.

[0072] 6. Trivalent chromium plating white chrome:

[0073] A trivalent chromium white chromium coating 6 is prepared on the bright nickel coating 5 of the workpiece, the coating thickness is 0.15 μm, and the Trich-9551 sulfate trivalent chromium plating process of Chaobang Chemical is adopted: Trich-9551 M cylinder opener 10 mL / L, Trich-9551 B supplementer 280 mL / L, Trich-9551 CS conductive salt 280 g / L, Trich-9551 WA wetting agent 1 mL / L, pH=3.6, plating tank temperature 52°C, cathode current density 10 A / dm 2 , cathode moves 2m / min.

[0074] 7. Rare earth cathode electrolytic protection:

[0075] A rare earth electrolytic protective film 7 is prepared on the trivalent chromium white chromium coating 6 of the workpiece, using the rare earth cathode electrolytic protection process developed by Chaobang Chemical: 5.5 g / L lanthanum acetate, 28 g / L HEDP complexing agent, 120 g / L anhydrous sodium carbonate, pH = 12, cathode current density 0.8 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, use titanium plate as anode, and electrolyze for 60 seconds. Use 10% sodium hydroxide solution or 10% sulfuric acid to adjust the pH required by the electrolytic protection process.

[0076] 8. Drying:

[0077] After the rare earth electrolytic protection, the workpiece is dried at 80° C. for 25 minutes.

[0078] Example 2

[0079] like Figure 1 As shown, a method for trivalent chromium plating of NdFeB workpieces includes pre-treatment on the NdFeB substrate 1, and sequentially preparing a citrate pre-nickel plating layer 2, a pyrophosphate copper plating layer 3, an acid copper plating layer 4, a bright nickel plating layer 5, a trivalent chromium white chromium plating layer 6, and a rare earth electrolytic protective film 7.

[0080] 1. Pre-treatment:

[0081] The workpiece substrate 1 is subjected to a pre-treatment process of "alkaline chemical degreasing → water washing → boiling water sealing → water washing → rust removal → water washing → ultrasonic degreasing → water washing → electrolytic activation → water washing".

[0082] The rust removal process is: 60 mL / L of lactic acid, an operating temperature of 25° C., and a rust removal time of 2 min.

[0083] The electrolytic activation process is: sodium sulfate 120g / L, pH=6, electrolysis temperature 25°C, cathode current density 0.7A / dm 2The cathode moves at 4 m / min, the workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is performed for 30 seconds. A 10% by mass sodium hydroxide solution or a 10% by mass sulfuric acid is used to adjust the pH required by the electrolytic activation process.

[0084] 2. Citrate pre-nickel plating:

[0085] After the workpiece is pre-treated, a pre-plated nickel layer 2 is prepared on the NdFeB substrate 1, and the coating thickness is 3 μm. The pre-plated nickel layer 2 is prepared by the current citrate nickel plating process: 190 g / L nickel sulfate hexahydrate, 10 g / L sodium chloride, 30 g / L boric acid, 30 g / L magnesium sulfate, pH=7.0, plating tank temperature 50°C, cathode current density 1 A / dm 2 , cathode moves 4m / min.

[0086] 3. Pyrophosphate copper plating:

[0087] A pyrophosphate copper plating layer 3 is prepared on the pre-nickel plating layer 2 of the workpiece, the plating thickness is 9 μm, and the PC-1289 pyrophosphate copper plating process of Chaobang Chemical is adopted: pyrophosphate copper 90 g / L, potassium pyrophosphate 280 g / L, ammonia water 5 mL / L, PC-1289 pyrophosphate copper additive 3 mL / L, pH=9, plating tank temperature 58°C, cathode current density 4.5 A / dm 2 , air stirring.

[0088] 4. Acid copper plating:

[0089] An acid copper plating layer 4 is prepared on the pyrophosphate copper plating layer 3 of the workpiece, the plating thickness is 9 μm, and the GAFFA M-8000 acid bright copper plating process of Chaobang Chemical is adopted: 180 g / L of copper sulfate pentahydrate, 60 g / L of sulfuric acid, 50 mg / L of chloride ions, 4 mL / L of GAFFA M-8000 Mu opener, 0.3 mL / L of GAFFA M-8000 A main light agent, 0.1 mL / L of GAFFA M-8000 B auxiliary light agent, plating tank temperature of 20°C, cathode current density of 4 A / dm 2 , strong and uniform air stirring.

[0090] 5. Bright nickel plating:

[0091] A bright nickel coating 5 is prepared on the acid copper coating 4 of the workpiece, the coating thickness is 12 μm, and the NINFEA 8003 bright nickel plating process of Chaobang Chemical is adopted: 320 g / L nickel sulfate hexahydrate, 60 g / L nickel chloride hexahydrate, 50 g / L boric acid, 30 mL / L NINFEA SC-260 bright nickel softener, 6 mL / L NINFEA AS-250 bright nickel auxiliary agent, 0.8 mL / L NINFEA 8003 bright nickel main brightener, 1.5 mL / L NINFEA NI-35 bright nickel wetting agent, pH=4.8, plating tank temperature 60°C, cathode current density 4.5 A / dm 2 , uniform air stirring.

[0092] 6. Trivalent chromium plating white chrome:

[0093] A trivalent chromium white chromium coating 6 is prepared on the bright nickel coating 5 of the workpiece, the coating thickness is 0.2 μm, and the Trich-6561 chloride trivalent chromium plating process of Chaobang Chemical is adopted: Trich-6561 opening salt 420 g / L, Trich-6563 complexing agent 70 mL / L, Trich-6564 stabilizer 1.5 mL / L, Trich-6565 wetting agent 2 mL / L, pH=2.8, plating tank temperature 30°C, cathode current density 12 A / dm 2 , medium air agitation.

[0094] 7. Rare earth cathode electrolytic protection:

[0095] A rare earth electrolytic protective film 7 is prepared on the trivalent chromium white chromium coating 6 of the workpiece, using the rare earth cathode electrolytic protection process developed by Chaobang Chemical: 5 g / L praseodymium acetate, 20 g / L HEDP complexing agent, 100 g / L anhydrous potassium carbonate, pH = 11.5, cathode current density 0.6 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, use titanium plate as anode, and electrolyze for 80 seconds. Use 10% sodium hydroxide solution or 10% sulfuric acid to adjust the pH required by the electrolytic protection process.

[0096] 8. Drying:

[0097] After the rare earth electrolytic protection, the workpiece is dried at 70° C. for 30 minutes.

[0098] Example 3

[0099] like Figure 1 As shown, a method for trivalent chromium plating of NdFeB workpieces includes pre-treatment on the NdFeB substrate 1, and sequentially preparing a citrate pre-nickel plating layer 2, a pyrophosphate copper plating layer 3, an acid copper plating layer 4, a bright nickel plating layer 5, a trivalent chromium black chromium plating layer 6, and a rare earth electrolytic protective film 7.

[0100] 1. Pre-treatment:

[0101] The workpiece substrate 1 is subjected to a pre-treatment process of "alkaline chemical degreasing → water washing → boiling water sealing → water washing → rust removal → water washing → ultrasonic degreasing → water washing → electrolytic activation → water washing".

[0102] The rust removal process is as follows: 80 mL / L of lactic acid, an operating temperature of 35° C., and a rust removal time of 1 min.

[0103] The electrolytic activation process is: potassium sulfate 150g / L, pH=7, electrolysis temperature 28°C, cathode current density 1A / dm 2 The cathode moves at 6 m / min, the workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is performed for 40 seconds. A 10% by mass sodium hydroxide solution or a 10% by mass sulfuric acid is used to adjust the pH required by the electrolytic activation process.

[0104] 2. Citrate pre-nickel plating:

[0105] After the workpiece is pre-treated, a pre-plated nickel layer 2 is prepared on the NdFeB substrate 1, and the coating thickness is 7 μm. The current citrate nickel plating process is adopted: 250 g / L nickel sulfate hexahydrate, 12 g / L sodium chloride, 35 g / L boric acid, 40 g / L magnesium sulfate, pH=7.2, plating tank temperature 60°C, cathode current density 1.5 A / dm 2 , cathode moves 6m / min.

[0106] 3. Pyrophosphate copper plating:

[0107] A pyrophosphate copper plating layer 3 is prepared on the pre-nickel plating layer 2 of the workpiece, the plating thickness is 7 μm, and the PC-1289 pyrophosphate copper plating process of Chaobang Chemical is adopted: 60 g / L copper pyrophosphate, 230 g / L potassium pyrophosphate, 2.5 mL / L ammonia water, 1.5 mL / L PC-1289 pyrophosphate copper additive, pH=8.6, plating tank temperature 52°C, cathode current density 3 A / dm 2 , air stirring.

[0108] 4. Acid copper plating:

[0109] An acid copper plating layer 4 is prepared on the pyrophosphate copper plating layer 3 of the workpiece, the plating thickness is 13 μm, and the GAFFA M-8000 acid bright copper plating process of Chaobang Chemical is adopted: 210 g / L of copper sulfate pentahydrate, 80 g / L of sulfuric acid, 80 mg / L of chloride ions, 7 mL / L of GAFFA M-8000 Mu opener, 0.5 mL / L of GAFFA M-8000 A main light agent, 0.25 mL / L of GAFFA M-8000 B auxiliary light agent, plating tank temperature of 28°C, cathode current density of 4.5 A / dm 2, strong and uniform air stirring.

[0110] 5. Bright nickel plating:

[0111] A bright nickel coating 5 is prepared on the acid copper coating 4 of the workpiece, the coating thickness is 10 μm, and the NINFEA 8003 bright nickel plating process of Chaobang Chemical is adopted: 300 g / L nickel sulfate hexahydrate, 55 g / L nickel chloride hexahydrate, 50 g / L boric acid, 25 mL / L NINFEA SC-260 bright nickel softener, 6 mL / L NINFEA AS-250 bright nickel auxiliary agent, 0.8 mL / L NINFEA 8003 bright nickel main brightener, 1.5 mL / L NINFEA NI-35 bright nickel wetting agent, pH=4.8, temperature 58°C, cathode current density 5 A / dm 2 , uniform air stirring.

[0112] 6. Trivalent chromium plating black chromium:

[0113] A trivalent chromium black chromium coating 6 is prepared on the bright nickel coating 5 of the workpiece, the coating thickness is 1.5 μm, and the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical is adopted: Trich-7677 S initiator 10 mL / L, Trich-7677 M cylinder opener 280 mL / L, Trich-7677 CS conductive salt 280 g / L, Trich-7677 C stabilizer 3.5 mL / L, Trich-7677D toner 5 mL / L, Trich-7677 WA wetting agent 1.0 mL / L, pH=3.5, plating tank temperature 35°C, cathode current density 10 A / dm 2 , with slight air agitation.

[0114] 7. Rare earth cathode electrolytic protection:

[0115] A rare earth electrolytic protective film 7 is prepared on the trivalent chromium black chromium coating 6 of the workpiece, using the rare earth cathode electrolytic protection process developed by Chaobang Chemical: 5 g / L cerium acetate, 25 g / L HEDP complexing agent, 140 g / L anhydrous sodium carbonate, pH = 12.5, cathode current density 0.8 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, use titanium plate as anode, and electrolyze for 90 seconds. Use 10% sodium hydroxide solution or 10% sulfuric acid to adjust the pH required by the electrolytic protection process.

[0116] 8. Drying:

[0117] After the rare earth electrolytic protection, the workpiece is dried at 90° C. for 20 minutes.

[0118] Test Example 1

[0119] The NdFeB trivalent chromium-plated white chromium composite coating prepared in Example 1 was subjected to a neutral salt spray test for 120 hours according to the standard GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test". The time for the composite coating to be corrosion-free in neutral salt spray is 2.5 times the time for the nickel-copper-nickel composite coating to be rusted in a neutral salt spray test for 48 hours as specified in the standard GB / T 34491-2017 "Sintered NdFeB surface coating".

[0120] Test Example 2

[0121] The NdFeB trivalent chromium-plated white chromium composite coating prepared in Example 2 was subjected to a neutral salt spray test for 96 hours in accordance with the standard GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test". The time for the composite coating to be corrosion-free in neutral salt spray is twice the time for the nickel-copper-nickel composite coating to be rusted in the neutral salt spray test specified in the standard GB / T 34491-2017 "Sintered NdFeB surface coating".

[0122] Test Example 3

[0123] The NdFeB trivalent chromium-plated black chromium composite coating prepared in Example 3 was subjected to a neutral salt spray test for 72 hours in accordance with the standard GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test". The time for the composite coating to be corrosion-free in neutral salt spray is 1.5 times the time for the nickel-copper-nickel composite coating to be rusted in the neutral salt spray test specified in the standard GB / T 34491-2017 "Sintered NdFeB surface coating".

[0124] Test Example 4

[0125] In this test example, the coating adhesion test was conducted on the samples prepared in Example 1, Example 2 and Example 3. The coating adhesion was tested by the thermal shock method according to ISO 2819-2017 standard. The plated parts were placed in a heating furnace and heated to 300°C for 30 minutes. After being taken out, they were placed in water at room temperature and suddenly cooled. The coating did not blister or fall off. The test shows that the combined coating prepared by the present invention has good adhesion.

[0126] Test Example 5

[0127] In this test example, a weather resistance test was conducted on the samples prepared in Example 1, Example 2 and Example 3. The samples were placed in an outdoor environment for 365 days, and the gloss and color of the coatings of the samples did not show obvious changes.

[0128] Comparative Example 1

[0129] Samples 1, 2 and 3 were prepared according to the process described in Example 1, Example 2 and Example 3, but the rare earth electrolytic protection process was deleted. According to the standard GB / T 10125-2012 "Artificial atmosphere corrosion test salt spray test", samples 1, 2 and 3 were subjected to neutral salt spray tests for 120 hours, 96 hours and 72 hours respectively, and white corrosion products appeared on the coating surfaces of the samples.

[0130] Comparative Example 2

[0131] Samples 1, 2 and 3 prepared in Comparative Example 1 were placed in an outdoor environment for 365 days, and mist-like oxide films appeared on the coating surfaces of the samples.

[0132] The technical solutions provided by the embodiments of the present invention are described in detail above. The principles and implementation methods of the embodiments of the present invention are described in detail using specific examples herein. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In short, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for trivalent chromium plating of NdFeB workpieces, characterized in that: The following steps are involved: (1) performing citrate pre-nickel plating on the surface of the NdFeB substrate; (2) performing pyrophosphate copper plating on the citrate pre-nickel plating layer prepared in step (1); (3) plating acid copper on the pyrophosphate copper plating layer prepared in step (2); (4) plating bright nickel on the acid copper coating prepared in step (3); (5) plating trivalent chromium on the bright nickel coating prepared in step (4); (6) preparing a rare earth electrolytic protection film on the trivalent chromium coating prepared in step (5) using a rare earth cathode electrolytic protection process; The rare earth cathode electrolytic protection process described in step (6) is: rare earth salt 1-10 g / L, HEDP complexing agent 5-50 g / L, alkali metal carbonate 80-150 g / L, pH range 11.5-12.5, cathode current density 0.5-1.2 A / dm 2 , operate at room temperature, use trivalent chromium-plated workpiece as cathode, titanium plate as anode, electrolyze for 30 to 90 seconds; The alkali metal carbonate in the rare earth cathode electrolytic protection process in step (6) includes any one or both of anhydrous sodium carbonate and anhydrous potassium carbonate; The rare earth salt in the rare earth cathode electrolytic protection process in step (6) includes any one or two of lanthanum acetate, praseodymium acetate, cerium acetate, lanthanum sulfate, praseodymium sulfate, and cerous sulfate.

2. The method for trivalent chromium plating of NdFeB workpieces according to claim 1, further comprising a pre-treatment step of the NdFeB workpiece: degreasing, derusting and electrolytic activation of the NdFeB substrate before pre-nickel plating with citrate; The electrolytic activation of the NdFeB matrix adopts a sulfate electrolytic activation process: alkali metal sulfate 80-200 g / L, pH range 6-8, electrolysis temperature 15°C-40°C, cathode current density 0.5-1.2 A / dm 2 , the cathode moves 4-6 m / min, the NdFeB workpiece is used as the cathode, the titanium plate is used as the anode, and the electrolysis is carried out for 20-40 s; The alkali metal sulfate includes any one or both of sodium sulfate and potassium sulfate.

3. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 2, characterized in that: The rust removal of the NdFeB matrix adopts a lactic acid rust removal process: 40 to 80 mL / L of lactic acid, an operating temperature of 20° C. to 35° C., and a rust removal time of 0.5 to 3 minutes.

4. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 1 or 2, characterized in that: The pH required by the rare earth electrolytic protection process or electrolytic activation process is adjusted with a 10% by mass sodium hydroxide solution or with a 10% by mass sulfuric acid.

5. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 1 or 2, characterized in that: The thickness of the citrate pre-plated nickel layer is 1 to 9 μm, and it is prepared by the current citrate nickel plating process: 180 to 250 g / L nickel sulfate hexahydrate, 10 to 12 g / L sodium chloride, 30 to 35 g / L boric acid, 30 to 40 g / L magnesium sulfate, pH range 7.0 to 7.2, plating tank temperature 50° C. to 60° C., cathode current density 1 to 1.5 A / dm 2 , the cathode moves 4 to 6 m / min.

6. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 1 or 2, characterized in that: The thickness of the pyrophosphate copper plating layer is 4 to 11 μm, the thickness of the acid copper plating layer is 7 to 19 μm, and the thickness of the bright nickel plating layer is 3 to 13 μm.

7. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 1 or 2, characterized in that: The trivalent chromium plating layer has a thickness of 0.05 to 0.35 μm and is prepared by a trivalent chromium white chromium plating process or a trivalent chromium black chromium plating process.

8. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 7, characterized in that: The trivalent chromium white chromium plating process adopts a sulfate trivalent chromium plating process: Trich-9551 M tank opener 8-12 mL / L, Trich-9551 B supplement 260-300 mL / L, Trich-9551 CS conductive salt 260-300 g / L, Trich-9551 WA wetting agent 0.5-2.0 mL / L, pH range 3.4-3.8, plating tank temperature 50°C-55°C, cathode current density 8-15 A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

9. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 7, characterized in that: The trivalent chromium white chromium plating process adopts the chloride trivalent chromium plating process: Trich-6561 tank salt 400-450g / L, Trich-6563 complexing agent 60-85mL / L, Trich-6564 stabilizer 1-2mL / L, Trich-6565 wetting agent 1-3mL / L, pH range 2.5-3.0, plating tank temperature 25°C-36°C, cathode current density 8-16A / dm 2 , medium air agitation.

10. The method for trivalent chromium plating of NdFeB workpieces as claimed in claim 7, characterized in that: The trivalent chromium black chromium plating adopts a sulfate trivalent chromium black chromium plating process: Trich-7677 S initiator 8-12 mL / L, Trich-7677 M cylinder opener 260-300 mL / L, Trich-7677 CS conductive salt 260-300 g / L, Trich-7677 C stabilizer 3.0-4.0 mL / L, Trich-7677 D toner 3.0-8.0 mL / L, Trich-7677 WA wetting agent 0.5-2.0 mL / L, pH range 3.3-3.7, plating tank temperature 25°C-40°C, cathode current density 8-14 A / dm 2 , the cathode moves 1 to 3 m / min or is slightly stirred by air.

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