Polythiocyanate silver-plated coating structure of neodymium iron boron workpiece

Abstract

The utility model discloses a polythiocyanate silver-plated coating structure of a neodymium-iron-boron workpiece, which comprises a neodymium-iron-boron substrate, and a citrate pre-nickel-plated layer, a nickel-copper alloy coating, a nickel-cobalt alloy coating, a polythiocyanate silver-plated layer and a silver electrolysis protective film which are sequentially prepared on the neodymium-iron-boron substrate from inside to outside. The utility model discloses a polythiocyanate silver-plated coating structure of a neodymium iron boron workpiece, which is characterized in that the binding force of a coating is tested by a thermal shock method according to GB / T 5270-2005 Metal Covering Layer Electro-Deposition and Chemical Deposition Layer Adhesive Strength Test Method on Metal Substrate, and the test result meets the standard requirement; the neutral salt spray test is carried out for 158 hours according to GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test, no corrosives are generated on the surface of a plated part, and a plated layer has good corrosion resistance.

Description

Technical Field

[0001] The utility model belongs to the technical field of metal surface treatment, and in particular relates to a coating structure of polymerized thiocyanate silver plating on a neodymium iron boron workpiece. Background Art

[0002] The surface of the NdFeB matrix is ​​porous and the material itself has high chemical activity. During the electroplating process of the NdFeB workpiece, the acidic or alkaline plating solution that penetrates into the pores on the surface of the NdFeB will cause residual corrosion. [1] , seriously affecting the protective properties of the coating. In the past, a copper-nickel-silver process was used to deposit silver coatings on NdFeB surfaces. However, cyanide copper plating is highly contaminating, and its use has been restricted or even banned. The current process typically involves a pre-nickel layer formed by citrate nickel plating on an NdFeB substrate, followed by bright nickel and silver plating. The electrode potential of the nickel layer is positive relative to the NdFeB substrate, while the electrode potential of the silver layer is also positive relative to the nickel layer. This nickel-silver composite coating deposited on an NdFeB substrate is cathodic and provides no electrochemical protection for the substrate. With this coating structure, corrosive media can damage the NdFeB substrate through galvanic corrosion, resulting in a shorter service life for the coated components. GB / T 34491–2017, "Surface Coatings on Sintered NdFeB Magnets," stipulates that the time it takes for a nickel-silver composite coating on an NdFeB substrate to show signs of corrosion in a neutral salt spray test is 72 hours, which is shorter than that of components with similar coatings on steel substrates.

[0003] Nickel-cobalt alloy coatings have many excellent physical, chemical and mechanical properties, and therefore have a wide range of uses. Because they have higher corrosion resistance and wear resistance than bright nickel coatings, they are more suitable for use as protective decorative coatings on high-end products. [2] The corrosion resistance of silver plating on nickel-cobalt alloy coating will be higher than the current nickel + silver combination coating structure.

[0004] Traditionally, the silver plating layer is prepared using the cyanide silver plating process. Due to the high pollution problem, this process is being gradually eliminated.

[0005] References: [1]. Li Hongying, Hao Zhuangzhi, Liu Yuhui, et al., Research progress on corrosion mechanism and surface protection technology of sintered NdFeB permanent magnet materials [J], Mining and Metallurgical Engineering, 2016, 36(6): 118-124. [2]. Zhu Longzhang, Zhang Qingyuan, Chen Yufei, et al., Study on electrodeposition and corrosion resistance of nickel-cobalt alloy coating [J], Materials Protection, 1997, 30(5): 4-6. Utility Model Content

[0006] In order to overcome the technical defect that the nickel + silver combination coating on the surface of NdFeB does not have an electrochemical protective effect, the utility model provides a coating structure of NdFeB workpieces with polymerized thiocyanate silver plating. In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0007] A coating structure for polythiocyanate silver plating of a NdFeB workpiece comprises a NdFeB substrate, and a citrate pre-nickel plating layer, a nickel-copper alloy plating layer, a nickel-cobalt alloy plating layer, a polythiocyanate silver plating layer, and a silver electrolytic protective film, which are sequentially prepared on the NdFeB substrate from the inside out.

[0008] The thickness of the polymerized thiocyanate silver plating layer is 1 to 5 μm.

[0009] Preferably, the thickness of the citrate pre-nickel plating layer is 3 to 7 μm.

[0010] Preferably, the thickness of the nickel-copper alloy plating layer is 8 to 15 μm.

[0011] Preferably, the thickness of the nickel-cobalt alloy coating is 8 to 15 μm.

[0012] A neutral citrate nickel plating process is used to create a pre-nickel layer on the NdFeB surface. This eliminates the residual corrosion caused by the plating solution remaining in the pores of the NdFeB surface. Plating a nickel-cobalt alloy over a nickel-copper alloy layer provides electrochemical protection for the nickel-copper alloy layer, as the electrode potential of the nickel-cobalt alloy layer is significantly negative. This coating structure effectively prevents corrosive media from attacking the NdFeB substrate. Plating silver over a nickel-cobalt alloy layer offers superior corrosion resistance compared to plating silver over a nickel layer.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The coating structure of the polymerized thiocyanate silver plating on the NdFeB workpiece disclosed in the present invention has a nickel-cobalt alloy coating that provides electrochemical protection for the nickel-copper alloy coating, thus overcoming the defect that the current process of directly plating nickel and silver on the NdFeB substrate does not provide electrochemical protection.

[0015] 2. The coating structure of the NdFeB workpiece polymerized thiocyanate silver plating disclosed in the present invention adopts a polymerized thiocyanate silver plating process to prepare the silver plating layer, thus overcoming the high pollution problem of traditional cyanide silver plating. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 It is a schematic diagram of the coating structure of Example 1 and Example 2 of the present utility model. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The schematic embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0019] A coating structure of polythiocyanate silver plating on a NdFeB workpiece is disclosed. The preparation process comprises the following steps: preparing a citrate pre-nickel plating layer, a nickel-copper alloy plating layer, a nickel-cobalt alloy plating layer, a polythiocyanate silver plating layer, and a silver electrolytic protective film on a NdFeB substrate in sequence from the inside out.

[0020] According to the current pre-treatment process, the NdFeB workpiece substrate is degreased, derusted and activated.

[0021] The citrate pre-nickel plating layer is prepared by using the current citrate nickel plating process. Preferably, the thickness of the citrate pre-nickel plating layer is 3 to 7 μm.

[0022] Preferably, the citrate nickel plating process is:

[0023] Nickel sulfate hexahydrate 180-250g / L, sodium chloride 10-12g / L, boric acid 30-35g / L, magnesium sulfate 30-40g / L, plating solution pH 7.0-7.2, plating tank temperature 50℃-60℃, cathode current density 1-1.5A / dm 2 , the cathode moves 4 to 6 m / min.

[0024] The nickel-copper alloy plating layer is prepared by adopting the current nickel-copper alloy plating process. Preferably, the thickness of the nickel-copper alloy plating layer is 8 to 15 μm.

[0025] Preferably, the nickel-copper alloy coating is prepared using the Nistar 6070 bright nickel-copper alloy plating process of Chaobang Chemical:

[0026] Nickel sulfate hexahydrate 180-220 g / L, copper sulfate pentahydrate 8-12 g / L, trisodium citrate 50-70 g / L, disodium hydroxyethylidene diphosphonate 20-30 g / L, boric acid 28-35 g / L, sodium chloride 5-8 g / L, NISTAR 6070 brightener 0.3-0.7 mL / L, NISTAR 6071 auxiliary agent 6-10 mL / L, NI-35 wetting agent 0.3-1.0 mL / L, plating solution pH 4.3-4.8, plating tank temperature 50-55 °C, cathode current density 2.6-3.2 A / dm 2 , the cathode moves 3 to 5 m / min.

[0027] The nickel-cobalt alloy coating is prepared by using the current nickel-cobalt plating process. Preferably, the thickness of the nickel-cobalt alloy coating is 8 to 15 μm.

[0028] Preferably, the nickel-cobalt alloy coating is prepared using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical:

[0029] Nickel sulfate hexahydrate 220-260 g / L, nickel chloride hexahydrate 50-70 g / L, cobalt sulfate heptahydrate 15-20 g / L, boric acid 40-50 g / L, NINFEA SC-230 auxiliary agent 12-20 mL / L, NINFEA 310 primary brightener 0.5-1.5 mL / L, NINFEA 312 leveler 0.5-1.5 mL / L, NINFEA NI-35 wetting agent 0.5-1.5 mL / L, plating solution pH 4.0-4.5, plating tank temperature 55-60 °C, cathode current density 2-6 A / dm 2 , even air stirring.

[0030] The polythiocyanate silver plating layer is prepared by using the current polythiocyanate silver plating process. Preferably, the thickness of the polythiocyanate silver plating layer is 1 to 5 μm.

[0031] Preferably, the polythiocyanate silver plating layer is prepared using Zunyi Huitong's HT-808 polythiocyanate silver plating process:

[0032] Polymeric sodium thiocyanate 100-160 g / L, polymeric silver thiocyanate 15-20 g / L, potassium hydroxide 8-12 g / L, HT-808 brightener A 10-20 mL / L, HT-808 brightener B 6-12 mL / L, room temperature operation, bath pH 12-13, cathode current density 0.3-1.0 A / dm 2 , the cathode moves 4 to 6 m / min, and Ag-1 silver plate is used as the anode.

[0033] The silver electrolytic protective film is prepared by using the current electrolytic protection process.

[0034] Preferably, the silver electrolytic protective film is prepared using Chaobang Chemical's ANTITAR 1127 silver protection process:

[0035] ANTITAR 1127 MUP opener 32-40 mL / L, ANTITAR 1127 ADDITIVE C 75-85 mL / L, bath pH 3.3-4.0, operating temperature 55-65°C, cathode current density 0.005-0.01 A / dm 2 , cathode movement 3~6m / min, electrolysis time 3~8min.

[0036] The NdFeB workpiece is electrolytically protected and then washed and dried. Example 1

[0037] like Figure 1As shown, a coating structure of polythiocyanate silver plating of NdFeB workpiece includes a NdFeB substrate 1, and a citrate pre-nickel plating layer 2, a nickel-copper alloy plating layer 3, a nickel-cobalt alloy plating layer 4, a polythiocyanate silver plating layer 5, and a silver electrolytic protective film 6 prepared in sequence from the inside to the outside on the NdFeB substrate 1.

[0038] 1. Pre-treatment:

[0039] The NdFeB substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → weak alkaline chemical degreasing → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0040] 2. Pre-nickel plating:

[0041] After the NdFeB workpiece is pre-treated, a citrate pre-plated nickel layer 2 is prepared using the current citrate nickel plating process, and the plating thickness is 5 μm.

[0042] Nickel sulfate hexahydrate 230g / L, sodium chloride 12g / L, boric acid 33g / L, magnesium sulfate 33g / L, plating solution pH 7.2, plating tank temperature 55℃, cathode current density 1.2A / dm 2 , cathode moves 5m / min.

[0043] 3. Nickel-plated copper alloy:

[0044] After the NdFeB workpiece is pre-nickel plated, a nickel-copper alloy coating 3 is prepared using the Nistar 6070 bright nickel-copper alloy plating process of Chaobang Chemical. The coating thickness is 12 μm.

[0045] Nickel sulfate hexahydrate 190g / L, copper sulfate pentahydrate 9g / L, trisodium citrate 55g / L, disodium hydroxyethylidene diphosphonate 20g / L, boric acid 30g / L, sodium chloride 6g / L, NISTAR 6070 brightener 0.5mL / L, NISTAR 6071 auxiliary agent 8mL / L, NI-35 wetting agent 0.6mL / L, plating solution pH 4.6, plating tank temperature 53℃, cathode current density 2.8A / dm 2 , cathode moves 4m / min.

[0046] 4. Nickel-cobalt alloy plating:

[0047] After the NdFeB workpiece is plated with nickel-copper alloy, a nickel-cobalt alloy coating 4 is prepared using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical. The coating thickness is 10 μm.

[0048] Nickel sulfate hexahydrate 260g / L, nickel chloride hexahydrate 70g / L, cobalt sulfate heptahydrate 20g / L, boric acid 50g / L, NINFEA SC-230 auxiliary agent 16mL / L, NINFEA 310 main brightener 1mL / L, NINFEA 312 leveler 1mL / L, NINFEA NI-35 wetting agent 1mL / L, plating solution pH 4.2, plating tank temperature 56℃, cathode current density 4A / dm 2 , even air stirring.

[0049] 5. Silver plating:

[0050] After the NdFeB workpiece is plated with nickel-cobalt alloy, a polythiocyanate silver plating layer 5 is prepared using the HT-808 polythiocyanate silver plating process of Zunyi Huitong. The coating thickness is 2 μm.

[0051] Polythiocyanate sodium 160g / L, polythiocyanate silver 20g / L, potassium hydroxide 12g / L, HT-808 brightener A 15mL / L, HT-808 brightener B 9mL / L, room temperature operation, bath pH 12.6, cathode current density 0.8A / dm 2 , the cathode moves 5m / min, and Ag-1 silver plate is used as the anode.

[0052] 6. Electrolytic protection:

[0053] After the NdFeB workpiece is silver-plated, a silver electrolytic protective film 6 is prepared using Chaobang Chemical's ANTITAR 1127 silver protection process.

[0054] ANTITAR 1127 MUP opener 40 mL / L, ANTITAR 1127 ADDITIVE C 85 mL / L, bath pH 3.5, operating temperature 57°C, cathode current density 0.008 A / dm 2 , cathode movement 4m / min, electrolysis time 5min.

[0055] 7. Drying:

[0056] After electrolytic protection, the NdFeB workpiece is subjected to "water washing → pure water washing → drying". Example 2

[0057] like Figure 1 As shown, a coating structure of polythiocyanate silver plating of NdFeB workpiece includes a NdFeB substrate 1, and a citrate pre-nickel plating layer 2, a nickel-copper alloy plating layer 3, a nickel-cobalt alloy plating layer 4, a polythiocyanate silver plating layer 5, and a silver electrolytic protective film 6 prepared in sequence from the inside to the outside on the NdFeB substrate 1.

[0058] 1. Pre-treatment:

[0059] The NdFeB substrate 1 is subjected to the current pre-treatment process of "grinding and chamfering → water washing → weak alkaline chemical degreasing → water washing → weak alkaline ultrasonic degreasing → water washing → lactic acid activation → water washing".

[0060] 2. Pre-nickel plating:

[0061] After the NdFeB workpiece is pre-treated, a citrate pre-plated nickel layer 2 is prepared using the current citrate nickel plating process, and the plating thickness is 5 μm.

[0062] Nickel sulfate hexahydrate 210g / L, sodium chloride 12g / L, boric acid 30g / L, magnesium sulfate 40g / L, plating solution pH 7.1, plating tank temperature 50℃, cathode current density 1.2A / dm 2 , cathode moves 5m / min.

[0063] 3. Nickel-plated copper alloy:

[0064] After the NdFeB workpiece is pre-nickel plated, a nickel-copper alloy coating 3 is prepared using the Nistar 6070 bright nickel-copper alloy plating process of Chaobang Chemical, with a coating thickness of 10 μm.

[0065] Nickel sulfate hexahydrate 210g / L, copper sulfate pentahydrate 11g / L, trisodium citrate 65g / L, disodium hydroxyethylidene diphosphonate 26g / L, boric acid 32g / L, sodium chloride 7g / L, NISTAR 6070 brightener 0.5mL / L, NISTAR 6071 auxiliary agent 8mL / L, NI-35 wetting agent 0.6mL / L, plating solution pH 4.5, plating tank temperature 52℃, cathode current density 3.0A / dm 2 , cathode moves 4m / min.

[0066] 4. Nickel-cobalt alloy plating:

[0067] After the NdFeB workpiece is plated with nickel-copper alloy, a nickel-cobalt alloy coating 4 is prepared using the NINFEA 310 bright nickel-cobalt alloy plating process of Chaobang Chemical. The coating thickness is 12 μm.

[0068] Nickel sulfate hexahydrate 240g / L, nickel chloride hexahydrate 60g / L, cobalt sulfate heptahydrate 17g / L, boric acid 45g / L, NINFEA SC-230 auxiliary agent 16mL / L, NINFEA 310 main brightener 1mL / L, NINFEA 312 leveler 1mL / L, NINFEA NI-35 wetting agent 1mL / L, plating solution pH 4.2, plating tank temperature 58℃, cathode current density 4A / dm 2 , even air stirring.

[0069] 5. Silver plating:

[0070] After the NdFeB workpiece is plated with nickel-cobalt alloy, a polythiocyanate silver plating layer 5 is prepared using the HT-808 polythiocyanate silver plating process of Zunyi Huitong. The coating thickness is 2 μm.

[0071] Polythiocyanate sodium 130g / L, polythiocyanate silver 17g / L, potassium hydroxide 10g / L, HT-808 brightener A 15mL / L, HT-808 brightener B 9mL / L, room temperature operation, bath pH 12.4, cathode current density 0.6A / dm 2 , the cathode moves 5m / min, and Ag-1 silver plate is used as the anode.

[0072] 6. Electrolytic protection:

[0073] After the NdFeB parts are silver-plated, a silver electrolytic protective film 6 is prepared using Chaobang Chemical's ANTITAR 1127 silver protection process.

[0074] ANTITAR 1127 MUP opener 36 mL / L, ANTITAR 1127 ADDITIVE C 80 mL / L, bath pH 3.6, operating temperature 60°C, cathode current density 0.008 A / dm 2 , cathode movement 4m / min, electrolysis time 5min.

[0075] 7. Drying:

[0076] After electrolytic protection, the NdFeB workpiece is subjected to "water washing → pure water washing → drying".

[0077] Test Example 1:

[0078] The silver-plated NdFeB samples prepared in Examples 1 and 2 were subjected to a 158-hour neutral salt spray test according to GB / T 10125–2021, "Artificial Atmosphere Corrosion Test Salt Spray Test," and showed no rust on the plated surfaces. The coating structure prepared by this invention exhibited a rust-free period in neutral salt spray that was 2.19 times longer than the time it took for a nickel-silver combination coating on a NdFeB surface to show rust in a neutral salt spray test as specified in GB / T 34491–2017, "Surface Coatings of Sintered NdFeB."

[0079] Test Example 2:

[0080] The NdFeB silver-plated samples prepared in Examples 1 and 2 were tested for coating adhesion using the thermal shock method in accordance with GB / T 5270–2005 “Review of test methods for adhesion strength of electrodeposited and chemically deposited metal coatings on metal substrates.” The plated parts were heated to 250°C in a heating furnace for 30 minutes, then taken out and quenched in room temperature water. No bubbling or shedding occurred in the coating, indicating that the coating structure prepared by the present invention had good adhesion.

[0081] The technical solutions provided by the embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only intended to help understand the principles of the embodiments of the present invention. It should be noted that those skilled in the art may make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A coating structure of polythiocyanate silver plating on a NdFeB workpiece, characterized by: The invention comprises a neodymium iron boron substrate, and a citrate pre-nickel plating layer, a nickel-copper alloy plating layer, a nickel-cobalt alloy plating layer, a polymerized thiocyanate silver plating layer, and a silver electrolytic protective film, which are sequentially prepared from the inside to the outside of the neodymium iron boron substrate; The thickness of the polymerized thiocyanate silver plating layer is 1 to 5 μm.

2. The coating structure of the NdFeB workpiece polymerized thiocyanate silver plating as claimed in claim 1, characterized in that: The thickness of the citrate pre-nickel plating layer is 3 to 7 μm.

3. The coating structure of the NdFeB workpiece polymerized thiocyanate silver plating as claimed in claim 1, characterized in that: The thickness of the nickel-copper alloy plating layer is 8 to 15 μm.

4. The coating structure of the NdFeB workpiece polymerized thiocyanate silver plating as claimed in claim 1, characterized in that: The thickness of the nickel-cobalt alloy plating layer is 8 to 15 μm.

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