Aluminum alloy trivalent chromium black chromium plating coating structure

Abstract

The utility model discloses a plating structure of aluminum alloy trivalent chromium plated black chromium, which comprises an aluminum alloy base body, and a chemical zinc deposition layer, a polythiocyanate copper plating layer, a bright nickel plating layer, a high-corrosion-resistance nickel-tin alloy plating layer, a trivalent chromium black chromium plating layer and a rare earth electrolysis protective film which are sequentially prepared on the aluminum alloy base body from inside to outside. The utility model discloses a plating layer structure for plating black chromium on trivalent chromium of aluminum alloy, which is characterized in that according to GB / T 5270-2005 Metal Cover Electrodeposition and Chemical Deposition Layer Adhesive Strength Test Method on Metal Matrix, the binding force of a plating layer is tested by a thermal shock method, the binding force meets the standard requirement, and according to GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test for 120 hours, the binding force meets the standard requirement, and the binding force meets the standard requirement. No corrosives are generated on the surface of a plated part, and the plating layer structure has good corrosion resistance.

Description

Technical Field

[0001] The utility model belongs to the technical field of metal surface treatment, and particularly relates to a coating structure of trivalent chromium black chromium plating on aluminum alloy. Background Art

[0002] Trivalent chromium electroplating is widely used to replace hexavalent chromium electroplating, and good environmental and social benefits have been achieved. The trivalent chromium black chromium coating has good properties such as light extinction, selective absorption of solar energy, high wear resistance and appearance decoration. As a functional and protective decorative coating, it has attracted more and more attention. At present, it has been widely used in industries such as automotive parts, electronic products, instruments and meters, and solar collectors. The existing technology generally prepares a trivalent chromium black chromium coating on a bright nickel plating layer, but the corrosion resistance of this coating structure is not high. The corrosion resistance of the trivalent chromium black chromium coating depends not only on the performance of the trivalent chromium black chromium coating itself, but also on the performance of the intermediate coating. It has been found that after the trivalent chromium electroplating layer is corroded and pores appear, the corrosion rate of the intermediate nickel plating layer is significantly higher than that of the trivalent chromium black chromium coating. Therefore, improving the corrosion resistance of the intermediate coating is an effective method to improve the corrosion resistance of trivalent chromium electroplated workpieces.

[0003] When preparing a trivalent chromium black chromium coating on a bright nickel plating layer, the neutral salt spray test can pass for 48h [1] , but usually corrosion products will appear on the coating surface after exceeding the above time.

[0004] The nickel-tin alloy coating has good appearance color, relatively high corrosion resistance and anti-discoloration performance, and has relatively high hardness and wear resistance [2] . However, the surface of the nickel-tin alloy coating is prone to passivation, and it is generally suitable for use as a surface coating rather than an intermediate coating. Therefore, there is currently no application case of using a nickel-tin alloy coating to replace a bright nickel coating as an intermediate coating.

[0005] In the traditional process, after chemical zinc deposition on the aluminum alloy surface, a pre-plated copper layer is prepared by cyanide copper plating process, and then pyrophosphate copper plating, acid copper plating, bright nickel plating, etc. are carried out. Under the strict control of the use of cyanide, the industry is actively seeking other processes to replace cyanide copper plating. However, there are still problems with the low bonding strength when using a divalent copper non-cyanide copper plating process to prepare a pre-plated copper layer on the metal surface [3] , which needs to be further studied and improved by the industry.

[0006] The utility model patent "A coating structure of trivalent chromium white chromium plating on aluminum alloy die-castings" with the authorization announcement number CN 214088701 U includes an aluminum alloy substrate, and a zinc immersion layer, an acidic zinc-nickel alloy coating layer, an electroless nickel plating layer, a pyrophosphate copper plating layer, an acid copper coating layer, a bright nickel coating layer, and a trivalent chromium white chromium coating layer prepared on the aluminum alloy substrate in sequence from the inside to the outside. This technical solution uses electroless nickel plating to replace traditional cyanide copper plating, but the process is relatively complex and the cost is also relatively high.

[0007] Recently, the industry has developed a polymer thiocyanate copper plating process, whose performance is relatively close to that of cyanide copper plating, and it is a cyanide-free copper plating process expected to replace cyanide copper plating.

[0008] References: [1]. Guo Chongwu, Lai Huanwen, A room-temperature trivalent chromium black chromium electroplating process in sulfate system [J]. Electroplating & Finishing, 2012, 31(7): 9-11. [2]. Song Zhenxing, Ma Shuyuan, Yao Suwei, et al., Research on the corrosion resistance of electrodeposited nickel-tin alloy [J]. Electroplating & Finishing, 2013, 35(10): 1-4+16. [3]. Qin Zuzu, Li Jiansan, Xu Jinlai, Research progress of cyanide-free copper plating processes at home and abroad [J]. Electroplating & Finishing, 2015, 34(3): 149-152. Content of the utility model

[0009] In order to solve the problem of low corrosion resistance of trivalent chromium plating on a bright nickel coating layer and the high pollution problem of using cyanide copper plating, the utility model provides a coating structure of trivalent chromium black chromium plating on aluminum alloy. To achieve the above purpose, the utility model adopts the following technical solutions:

[0010] A coating structure of trivalent chromium black chromium plating on aluminum alloy includes an aluminum alloy substrate, and a chemical zinc deposition layer, a polymer thiocyanate copper plating layer, a bright nickel plating layer, a high-corrosion-resistant nickel-tin alloy coating layer, a trivalent chromium black chromium coating layer, and a rare earth electrolytic protective film prepared on the aluminum alloy substrate in sequence from the inside to the outside;

[0011] The thickness of the high-corrosion-resistant nickel-tin alloy coating layer is 1-4 μm.

[0012] Preferably, the thickness of the polymer thiocyanate copper plating layer is 5-11 μm.

[0013] Preferably, the thickness of the bright nickel plating layer is 7-15 μm.

[0014] Preferably, the thickness of the trivalent chromium black chromium coating layer is 0.05-0.2 μm.

[0015] The trivalent chromium plating solution has extremely strong activation ability. After electroplating starts, the oxide film on the surface of the nickel-tin alloy coating layer can be preferentially reduced to the coating metal, and then trivalent chromium ions are reduced to metallic chromium and deposited on the nickel-tin alloy coating layer, so that a good bonding force is formed between the two coating layers.

[0016] Compared with the prior art, the utility model has the following beneficial effects:

[0017] 1. The coating structure of trivalent chromium black chromium plating on aluminum alloy disclosed by the utility model prepares a trivalent chromium black chromium coating on a high-corrosion-resistant nickel-tin alloy coating, improving the corrosion resistance of the coating;

[0018] 2. The coating structure of trivalent chromium black chromium plating on aluminum alloy disclosed by the utility model prepares a cyanide-free copper plating layer on the chemical zinc deposition layer on the surface of the aluminum alloy by using a polymer thiocyanate copper plating process, overcoming the high pollution problem of using the traditional cyanide copper plating process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide a further understanding of the utility model, form a part of this application, and do not constitute an improper limitation to the utility model. In the drawings:

[0020] Figure 1 is a schematic diagram of the coating structure of Embodiment 1 and Embodiment 2 of the utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will combine the drawings and specific embodiments to detail the utility model. Here, the schematic embodiments and descriptions of the utility model are used to explain the utility model, but do not constitute a limitation to the utility model.

[0022] A coating structure of trivalent chromium black chromium plating on aluminum alloy includes an aluminum alloy substrate, and a chemical zinc deposition layer, a polymer thiocyanate copper plating layer, a bright nickel plating layer, a high-corrosion-resistant nickel-tin alloy coating, a trivalent chromium black chromium coating, and a rare earth electrolytic protective film sequentially prepared on the aluminum alloy substrate from inside to outside.

[0023] Degrease, alkali-etch, brighten, and micro-etch the aluminum alloy part substrate according to the current pretreatment process.

[0024] After the pretreatment of the aluminum alloy part, prepare a chemical zinc deposition layer by using the current chemical zinc deposition process.

[0025] Preferably, the chemical zinc deposition layer is prepared by using ALBUME AS-699 cyanide-free zinc deposition agent on aluminum from Superbond Chemical Industry:

[0026] 160 - 220 mL / L of ALBUME AS-699 cyanide-free zinc deposition agent on aluminum, the bath solution contains 6 - 9 g / L of zinc ions, 0.16 - 0.20 g / L of copper ions, the working temperature is 20°C - 30°C, and the zinc deposition time is 60 - 120 s.

[0027] Preferably, the chemical zinc deposition layer is prepared by using AZIN-113 acidic zinc deposition agent on aluminum from Superbond Chemical Industry:

[0028] For the zinc deposition agent AZIN-113 on acidic aluminum, the dosage is 150 - 250 mL / L, the working temperature is 15°C - 30°C, the pH value of the bath is 3.4 - 4.5, and the zinc deposition time is 30 - 90 s.

[0029] After chemical zinc deposition on aluminum alloy parts, a poly thiocyanate copper plating layer is prepared by using a poly thiocyanate copper plating process.

[0030] Preferably, the thickness of the poly thiocyanate copper plating layer is 5 - 11 μm.

[0031] Preferably, the poly thiocyanate copper plating layer is prepared by using the HT-810 poly thiocyanate copper plating process of Zunyi Huitong:

[0032] Cuprous poly thiocyanate 17 - 23 g / L, sodium poly thiocyanate 100 - 160 g / L, sodium potassium tartrate 8 - 12 g / L, HT-810 brightener 1 - 2 mL / L, HT-810 leveling agent 2 - 4 mL / L, bath temperature 45°C - 55°C, pH value of the plating solution 12 - 13, cathode current density 0.5 - 1.0 A / dm 2 , cathode movement 4 - 6 m / min, anode current density ≤ 0.5 A / dm 2 , and an oxygen-free electrolytic copper angle (or copper granule) is used as the anode.

[0033] After poly thiocyanate copper plating on aluminum alloy parts, a bright nickel plating layer is prepared by using the current bright nickel plating process.

[0034] Preferably, the thickness of the bright nickel plating layer is 7 - 15 μm.

[0035] After bright nickel plating on aluminum alloy parts, a high anti-corrosion nickel-tin alloy plating layer is prepared by using the current high anti-corrosion nickel-tin alloy plating process.

[0036] Preferably, the thickness of the high anti-corrosion nickel-tin alloy plating layer is 1 - 4 μm.

[0037] Preferably, the high anti-corrosion nickel-tin alloy plating layer is prepared by using the YF-737 high anti-corrosion nickel-tin alloy plating process of Chaobang Chemical:

[0038] Nickel chloride 140 - 180 g / L, YF-737A additive 450 - 600 mL / L, YF-737B additive 30 - 60 mL / L, pH value of the plating solution 3.5 - 4.5, bath temperature 65°C - 70°C, cathode current density 0.5 - 1.5 A / dm 2 , cathode movement 3 - 5 m / min.

[0039] After high anti-corrosion nickel-tin alloy plating on aluminum alloy parts, a trivalent chromium black chromium plating layer is prepared by using the current trivalent chromium black chromium plating process.

[0040] Preferably, the thickness of the trivalent chromium black chromium coating is 0.05 - 0.2 μm.

[0041] Preferably, the trivalent chromium black chromium coating is prepared by using the Trich-7677 sulfate trivalent chromium black chromium plating process of Superbond Chemical Industry:

[0042] Trich-7677 S starter 8 - 12 mL / L, Trich-7677 M bath opener 260 - 300 mL / L, Trich-7677 CS conductive salt 260 - 300 g / L, Trich-7677 C stabilizer 3 - 4 mL / L, Trich-7677 D toner 1 - 4 mL / L, wherein the mass concentration of trivalent chromium is 12 - 18 g / L, the mass concentration of boric acid is 60 - 70 g / L, the pH value of the plating solution is 3.3 - 3.7, the plating bath temperature is 25°C - 40°C, the cathode current density is 8 - 14 A / dm 2 , the cathode moves at 2 - 3 m / min, or there is slight air agitation.

[0043] After trivalent chromium black chromium plating on the aluminum alloy parts, rare earth electrolytic protection is carried out to prepare a rare earth electrolytic protection film.

[0044] Preferably, the rare earth electrolytic protection film is prepared by using the rare earth electrolytic protection process developed by Superbond Chemical Industry:

[0045] Cerium acetate 1 - 5 g / L, HEDP complexing agent 5 - 30 g / L, sodium molybdate 5 - 10 g / L, anhydrous sodium carbonate 100 - 150 g / L, the pH value of the bath is 11.5 - 12.5 (adjust the pH with sodium hydroxide solution), the cathode current density is 0.5 - 1.5 A / dm 2 , operating at room temperature, using the plated parts as the cathode and a titanium plate as the anode, electrolyzing for 60 - 120 s.

[0046] The aluminum alloy parts are subjected to rare earth electrolytic protection, washed clean with water, and then dried. Example 1

[0047] As Figure 1 shown, a coating structure of trivalent chromium black chromium plating on an aluminum alloy includes an aluminum alloy substrate 1, and a chemical zinc deposition layer 2, a polymerized thiocyanate copper plating layer 3, a bright nickel plating layer 4, a high anti-corrosion nickel-tin alloy coating 5, a trivalent chromium black chromium coating 6, and a rare earth electrolytic protection film 7 sequentially prepared on the aluminum alloy substrate 1 from the inside to the outside.

[0048] 1. Pretreatment:

[0049] The aluminum alloy part substrate 1 is subjected to "chemical degreasing → water washing → ultrasonic degreasing → water washing → alkali corrosion → water washing → brightening → water washing → micro-corrosion → water washing".

[0050] 2. Chemical zinc deposition:

[0051] After the pretreatment of the aluminum alloy parts, a chemical zinc deposit layer 2 is prepared using ALBUME AS-699 cyanide-free zinc deposition agent for aluminum from Superbond Chemical Industry Co., Ltd.

[0052] 200 mL / L of ALBUME AS-699 cyanide-free zinc deposition agent for aluminum, the bath solution contains 7 g / L of zinc ions, 0.18 g / L of copper ions, the working temperature is 25 °C, and the zinc deposition time is 90 s.

[0053] The specific process is "the first zinc deposition → water washing → zinc stripping → water washing → the second zinc deposition → water washing".

[0054] 3. Polymerized thiocyanate copper plating:

[0055] After the chemical zinc deposition of the aluminum alloy parts, a polymerized thiocyanate copper plating layer 3 is prepared using the HT-810 polymerized thiocyanate copper plating process from Zunyi Huitong, and the coating thickness is 6 μm.

[0056] 18 g / L of cuprous thiocyanate polymer, 120 g / L of sodium thiocyanate polymer, 10 g / L of potassium sodium tartrate, 1.5 mL / L of HT-810 brightener, 3 mL / L of HT-810 leveling agent, the bath temperature is 53 °C, the pH of the plating solution is 12.3, the cathode current density is 0.7 A / dm 2 , the cathode moves at 5 m / min, and the anode current density is 0.4 A / dm 2 , and an oxygen-free electrolytic copper angle is used as the anode.

[0057] 4. Bright nickel plating:

[0058] After the polymerized thiocyanate copper plating of the aluminum alloy parts, a bright nickel plating layer 4 is prepared using the current bright nickel plating process, and the coating thickness is 12 μm.

[0059] 5. High-corrosion-resistant nickel-tin alloy plating:

[0060] After the bright nickel plating of the aluminum alloy parts, a high-corrosion-resistant nickel-tin alloy plating layer 5 is prepared using the YF-737 high-corrosion-resistant nickel-tin alloy plating process from Superbond Chemical Industry Co., Ltd., and the coating thickness is 3 μm.

[0061] 150 g / L of nickel chloride, 520 mL / L of YF-737A additive, 45 mL / L of YF-737B additive, the pH of the plating solution is 4.2, the bath temperature is 68 °C, the cathode current density is 1.0 A / dm 2 , and the cathode moves at 4 m / min.

[0062] 6. Trivalent chromium black chromium plating:

[0063] After the high-corrosion-resistant nickel-tin alloy plating of the aluminum alloy parts, a trivalent chromium black chromium plating layer 6 is prepared using the Trich-7677 sulfate trivalent chromium black chromium plating process from Superbond Chemical Industry Co., Ltd., and the coating thickness is 0.1 μm.

[0064] Trich-7677 S starter: 10 mL / L, Trich-7677 M bath conditioner: 290 mL / L, Trich-7677 CS conductive salt: 290 g / L, Trich-7677 C stabilizer: 3.5 mL / L, Trich-7677 D toner: 2 mL / L. Among them, the mass concentration of trivalent chromium is 16 g / L, the mass concentration of boric acid is 67 g / L, the pH of the plating solution is 3.5, the operating temperature is 35 °C, and the cathode current density is 10 A / dm 2 , and the cathode moves at 2 m / min.

[0065] 7. Rare earth electrolytic protection:

[0066] After trivalent chromium black chromium plating on aluminum alloy parts, a rare earth electrolytic protection process of Chaobang Chemical Industry is used to prepare the rare earth electrolytic protection film 7.

[0067] Cerium acetate: 3 g / L, HEDP complexing agent: 20 g / L, sodium molybdate: 10 g / L, anhydrous sodium carbonate: 120 g / L, the pH of the bath is 12 (adjusted with sodium hydroxide solution), and the cathode current density is 1 A / dm 2 , operating at room temperature, using the plating part as the cathode and a titanium plate as the anode, and electrolyzing for 100 s.

[0068] 8. Drying: After rare earth electrolytic protection of aluminum alloy parts, perform "water washing → pure water washing → drying". Example 2

[0069] As Figure 1 shown, a coating structure of trivalent chromium black chromium plating on aluminum alloy includes an aluminum alloy substrate 1, and a chemical zinc deposition layer 2, a polymer thiocyanate copper plating layer 3, a bright nickel plating layer 4, a high anti-corrosion nickel-tin alloy coating 5, a trivalent chromium black chromium coating 6, and a rare earth electrolytic protection film 7 sequentially prepared from the inside to the outside on the aluminum alloy substrate 1.

[0070] 1. Pretreatment:

[0071] Perform "chemical degreasing → water washing → ultrasonic degreasing → water washing → alkaline etching → water washing → brightening → water washing → micro-etching → water washing" on the aluminum alloy part substrate 1.

[0072] 2. Chemical zinc deposition:

[0073] After pretreatment of the aluminum alloy parts, use the AZIN-113 acidic zinc deposition agent on aluminum of Chaobang Chemical Industry to prepare the chemical zinc deposition layer 2.

[0074] AZIN-113 acidic zinc deposition agent on aluminum: 200 mL / L, working temperature: 25 °C, pH of the bath: 4.2, zinc deposition time: 60 s.

[0075] The specific process is "the first zinc deposition → water washing → dezincification → water washing → the second zinc deposition → water washing".

[0076] 3. Copper plating with polymeric thiocyanate:

[0077] After chemical zinc deposition on aluminum alloy parts, a polymeric thiocyanate copper plating layer 3 is prepared by using the HT-810 polymeric thiocyanate copper plating process of Zunyi Huitong, and the thickness of the plating layer is 8 μm.

[0078] Cuprous thiocyanate polymer 22 g / L, sodium thiocyanate polymer 150 g / L, potassium sodium tartrate 10 g / L, HT-810 brightener 1.5 mL / L, HT-810 leveling agent 3 mL / L, bath temperature 52 °C, bath pH 12.1, cathode current density 0.8 A / dm 2 , cathode moving speed 5 m / min, anode current density 0.3 A / dm 2 , and oxygen-free electrolytic copper grains are used as the anode.

[0079] 4. Bright nickel plating:

[0080] After polymeric thiocyanate copper plating on aluminum alloy parts, a bright nickel plating layer 4 is prepared by using the current bright nickel plating process, and the thickness of the plating layer is 10 μm.

[0081] 5. High-corrosion-resistant nickel-tin alloy plating:

[0082] After bright nickel plating on aluminum alloy parts, a high-corrosion-resistant nickel-tin alloy plating layer 5 is prepared by using the YF-737 high-corrosion-resistant nickel-tin alloy plating process of Chaobang Chemical Industry, and the thickness of the plating layer is 3 μm.

[0083] Nickel chloride 180 g / L, YF-737A additive 600 mL / L, YF-737B additive 60 mL / L, bath pH 3.7, bath temperature 65 °C, cathode current density 1.0 A / dm 2 , cathode moving speed 4 m / min.

[0084] 6. Trivalent chromium black chromium plating:

[0085] After high-corrosion-resistant nickel-tin alloy plating on aluminum alloy parts, a trivalent chromium black chromium plating layer 6 is prepared by using the Trich-7677 sulfate trivalent chromium black chromium plating process of Chaobang Chemical Industry, and the thickness of the plating layer is 0.1 μm.

[0086] Trich-7677 S starter 10 mL / L, Trich-7677 M bath conditioner 270 mL / L, Trich-7677 CS conductive salt 270 g / L, Trich-7677 C stabilizer 3.5 mL / L, Trich-7677 D toner 3 mL / L, where the mass concentration of trivalent chromium is 14 g / L, the mass concentration of boric acid is 63 g / L, bath pH 3.5, operating temperature 35 °C, cathode current density 10 A / dm 2 , with gentle air stirring.

[0087] 7. Rare earth electrolytic protection:

[0088] After trivalent chromium black chromium plating on aluminum alloy parts, a rare earth electrolytic protection film 7 is prepared by using the rare earth electrolytic protection process of Chaobang Chemical Industry.

[0089] Cerium acetate 5g / L, HEDP complexing agent 30g / L, sodium molybdate 5g / L, anhydrous sodium carbonate 150g / L, the pH of the bath is 12 (adjusted with sodium hydroxide solution), the cathode current density is 1A / dm 2 , operating at room temperature, using the plated parts as the cathode and titanium plates as the anode, electrolyzing for 100s.

[0090] 8. Drying: After rare earth electrolytic protection of aluminum alloy parts, perform "water washing → pure water washing → drying".

[0091] Test Example 1:

[0092] The trivalent chromium black chromium plated aluminum alloy samples prepared in Example 1 and Example 2 were subjected to a neutral salt spray test for 120h in accordance with GB / T 10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", and there was no rust on the surface of the plated parts. The test shows that the present utility model in trivalent chromium plating on a highly corrosion-resistant nickel-tin alloy coating significantly improves the corrosion resistance of the coating.

[0093] Test Example 2:

[0094] The trivalent chromium black chromium plated aluminum alloy samples prepared in Example 1 and Example 2 were tested for the adhesion of the coating by the thermal shock method in accordance with GB / T 5270–2005 "Review of Test Methods for Adhesion of Metallic Coatings on Metallic Substrates - Electrodeposited and Chemically Deposited Coatings". The plated parts were heated in a heating furnace to 220°C and held for 30min, then taken out and cooled in water at room temperature, and no blistering or peeling occurred on the coating. The test shows that the present utility model has good adhesion in preparing a trivalent chromium black chromium coating on a nickel-tin alloy coating.

[0095] The technical solutions provided by the embodiments of the present utility model have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the embodiments of the present utility model. The descriptions of the above embodiments are only applicable to helping understand the principles of the embodiments of the present utility model. It should be noted that for those of ordinary skill in the art, based on the principles of the embodiments of the present utility model, there will be changes in the specific implementation manners and application scopes, and these should all fall within the protection scope of the present utility model.

Claims

1. A coating structure of trivalent chromium-plated black chromium on aluminum alloy, characterized in that: It comprises an aluminum alloy substrate, and a chemical zinc deposition layer, a polymerized thiocyanate copper plating layer, a bright nickel plating layer, a high corrosion resistance nickel-tin alloy plating layer, a trivalent chromium black chromium plating layer, and a rare earth electrolytic protective film which are sequentially prepared from the inside to the outside on the aluminum alloy substrate; The thickness of the high corrosion resistance nickel-tin alloy plating layer is 1 to 4 μm.

2. The aluminum alloy trivalent chromium black chromium plating structure according to claim 1, characterized in that: The thickness of the polymerized thiocyanate copper plating layer is 5 to 11 μm.

3. The aluminum alloy trivalent chromium black chromium plating structure according to claim 1, characterized in that: The thickness of the bright nickel plating layer is 7-15 μm.

4. The aluminum alloy trivalent chromium black chromium plating structure according to claim 1, characterized in that: The thickness of the trivalent chromium black chromium plating layer is 0.05-0.2 μm.

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