Plating layer structure for plating zinc-nickel alloy on cyanide-free copper-zinc alloy bottom plating layer

Abstract

The utility model discloses a plating layer structure for plating a zinc-nickel alloy on a cyanide-free copper-zinc alloy bottom plating layer, which comprises a zinc alloy substrate, and a cyanide-free copper-zinc alloy plating layer, a zinc-nickel alloy plating layer and a trivalent chromium blue passivation film which are sequentially prepared on the zinc alloy substrate from inside to outside. According to the plating layer structure with the zinc-nickel alloy plated on the cyanide-free copper-zinc alloy bottom plating layer, the binding force of the plating layer is measured through a thermal shock test method according to GB / T 5270-2005 Metal Covering Layer Electro-Deposition and Chemical Deposition Layer Adhesive Strength Test Method on Metal Matrix, and the measurement result meets the standard requirement. The corrosion resistance is tested according to GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Mist Test, the surface of a plated part is free of white corrosives after being subjected to a neutral salt spray test for 480 h, and a plated layer has good corrosion resistance.

Description

Technical Field

[0001] This utility model belongs to the field of metal electroplating, specifically relating to a coating structure for a zinc-nickel alloy plating layer on a cyanide-free copper-zinc alloy base layer. Background Technology

[0002] Zinc-nickel alloy plating offers superior corrosion resistance and is widely used as a protective coating in automotive parts, aerospace, and hardware products. The traditional process for electroplating zinc-nickel alloy onto zinc alloy die-cast parts typically involves sequentially preparing a zinc-nickel alloy plating layer and a trivalent chromium passivation film on a zinc alloy substrate. However, the zinc-nickel alloy plating layer is cathodic relative to the zinc alloy die-cast substrate, offering no electrochemical protection. When the plating layer is damaged, corrosive media can rapidly destroy the zinc alloy die-cast substrate through galvanic corrosion. Furthermore, when using alkaline zinc-nickel alloy plating solutions, the highly alkaline solution can penetrate the pores on the surface of the zinc alloy die-cast part, corroding both the substrate and the plating layer, potentially causing the plating to peel off completely.

[0003] The industry has done a lot of research and development on cyanide-free copper plating processes, but no new breakthroughs have been achieved in cyanide-free copper plating technology for divalent copper. [1] Polymeric thiocyanate copper-zinc alloy plating is a newly developed cyanide-free copper-zinc alloy plating process. This process uses polymeric cuprous thiocyanate and polymeric zinc thiocyanate as the main salts and polymeric sodium thiocyanate as the complexing agent. Its process performance is close to that of cyanide copper-zinc alloy plating. It is currently in the trial stage and is mainly used as a top coating.

[0004] References: [1]. Qin Zuzu, Li Jiansan, Xu Jinlai, Research progress of cyanide-free copper plating process at home and abroad [J], Electroplating & Finishing, 2015, 34(3): 149-152. Summary of the Invention

[0005] To address the issue that direct zinc-nickel alloy plating on zinc alloy die-cast parts lacks electrochemical protection, this invention provides a plating structure for zinc-nickel alloy plating on a cyanide-free copper-zinc alloy undercoat. To achieve the above objective, this invention employs the following technical solution:

[0006] A coating structure for a zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base coating includes a zinc alloy die-cast substrate, and a cyanide-free copper-zinc alloy coating, a zinc-nickel alloy coating, and a trivalent chromium blue passivation film sequentially prepared from the inside to the outside on the zinc alloy die-cast substrate.

[0007] The cyanide-free copper-zinc alloy coating is prepared using a polymeric thiocyanate copper-zinc alloy plating process.

[0008] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 3–9 μm.

[0009] Preferably, the thickness of the zinc-nickel alloy coating is 5–20 μm.

[0010] The electrode potential of the zinc-nickel alloy coating is significantly negative than that of the copper-zinc alloy coating. Compared with the copper-zinc alloy coating, the zinc-nickel alloy coating is an anodic coating. This coating structure can effectively prevent the corrosive medium from eroding towards the substrate.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. The coating structure of zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base coating disclosed in this utility model has an electrochemical protective effect on the copper-zinc alloy coating, overcoming the defect that direct zinc-nickel alloy plating on the zinc alloy surface does not have an electrochemical protective effect.

[0013] 2. The coating structure of zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base layer disclosed in this utility model is a cyanide-free copper-zinc alloy plating on the surface of zinc alloy die castings. The corrosiveness of the plating solution remaining in the pores on the surface of the plating part is weak, and it has no destructive effect on the substrate and the coating. This overcomes the residual corrosion problem that exists when directly plating alkaline zinc-nickel alloy onto zinc alloy die castings. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of the present invention and form part of this application, do not constitute an undue limitation of the present invention. In the drawings:

[0015] Figure 1 This is a schematic diagram of the coating structure of Embodiment 1 and Embodiment 2 of this utility model. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0017] A coating structure for a zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base coating includes a zinc alloy die-cast substrate, and a cyanide-free copper-zinc alloy coating, a zinc-nickel alloy coating, and a trivalent chromium blue passivation film sequentially prepared from the inside to the outside on the zinc alloy die-cast substrate.

[0018] Zinc alloy die castings are subjected to dewaxing, degreasing, and activation according to the current pretreatment process.

[0019] After pretreatment, zinc alloy die-cast parts are coated with a cyanide-free copper-zinc alloy using a polymeric thiocyanate copper-zinc alloy plating process.

[0020] Preferably, the thickness of the cyanide-free copper-zinc alloy coating is 3–9 μm.

[0021] Preferably, the cyanide-free copper-zinc alloy coating is prepared using the following polymeric thiocyanate copper-zinc alloy plating process:

[0022] Polymeric cuprous thiocyanate 18–25 g / L, polymeric zinc thiocyanate 8–12 g / L, polymeric sodium thiocyanate 125–175 g / L, ammonium chloride 3–5 g / L, plating bath pH 9.5–11.5, plating bath temperature 35℃–45℃, cathode current density 0.5–1.5 A / dm³ 2 The cathode moves at a speed of 3-5 m / min, and a brass plate is used as the anode.

[0023] After cyanide-free copper-zinc plating, zinc-nickel alloy coatings are prepared using the existing zinc-nickel alloy plating process for zinc alloy die castings.

[0024] Preferably, the thickness of the zinc-nickel alloy coating is 5–20 μm.

[0025] Preferably, the zinc-nickel alloy plating is prepared using the Detronzin 1215 alkaline zinc-nickel alloy electroplating process from Chaobang Chemical Co., Ltd.

[0026] Zinc 5.5–8.5 g / L, Nickel 1.0–1.8 g / L (provided by DETRONZIN 1215 Ni nickel supplement 13–22 mL / L), Sodium hydroxide 120–135 g / L, DETRONZIN 1215 Base auxiliary agent 90–110 mL / L, DETRONZIN 1215 Brightener master brightener 1.0–5.0 mL / L, DETRONZIN 1215 Purifier R purifying agent 0.1–0.8 mL / L, plating bath temperature 21℃–28℃, cathode current density 1.0–3.0 A / dm³ 2 The cathode moves at a speed of 4–6 m / min.

[0027] Preferably, the zinc-nickel alloy coating is prepared using the DETRONZIN 1377 acidic zinc-nickel alloy electroplating process from Chaobang Chemical Co., Ltd.

[0028] Zinc 22-30 g / L, Nickel 22-30 g / L, Potassium Chloride 160-190 g / L, Ammonium Chloride 45-75 g / L, DETRONZIN 1377A Base additive 10-20 mL / L, DETRONZIN 1377B Bri brightener 0.5-1.5 mL / L, DETRONZIN 1377C Complexing agent 10-20 mL / L, DETRONZIN 1377D Additive additive 8-12 mL / L, plating bath temperature 27℃-31℃, plating solution pH 4.6-5.2, cathode current density 0.5-3.5 A / dm³ 2 The cathode moves at a speed of 3–5 m / min.

[0029] After zinc alloy die castings are plated with zinc-nickel alloy, a trivalent chromium blue passivation film is prepared using the current trivalent chromium blue passivation process.

[0030] Preferably, the trivalent chromium blue passivation film is prepared using TRIROS 344 zinc-nickel blue passivating agent from Chaobang Chemical Co., Ltd.

[0031] TRIROS 344A zinc-nickel blue passivating agent 15-75 mL / L, TRIROS 344B zinc-nickel blue passivating agent 25-100 mL / L, passivation temperature 25℃-30℃, passivation solution pH 4.0-4.8, passivation time 45-90 s, air residence 15-35 s, weak air agitation.

[0032] Preferably, the trivalent chromium blue passivation film is prepared using TRIROS 343 zinc-nickel blue passivating agent from Chaobang Chemical Co., Ltd.

[0033] TRIROS 343 zinc-nickel blue passivating agent 135~175mL / L, passivation solution pH 1.8~2.6, operating temperature 30℃~60℃, immersion time 45~75s, air agitation.

[0034] The specific process is as follows: "1% sulfuric acid for film removal → water washing → passivation → water washing → draining after removal from the tank → blowing away residual droplets on the surface of the plated parts with high-pressure air".

[0035] After passivation, zinc alloy die-cast parts are dried at 60°C for 15–20 minutes. Example 1

[0036] like Figure 1 As shown, a coating structure for a zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base coating includes a zinc alloy die-cast substrate 1, and a cyanide-free copper-zinc alloy coating 2, a zinc-nickel alloy coating 3, and a trivalent chromium blue passivation film 4, which are sequentially prepared from the inside to the outside on the zinc alloy die-cast substrate 1.

[0037] 1. Pre-processing:

[0038] The zinc alloy die casting substrate 1 is subjected to the following pretreatment process according to the current zinc alloy pretreatment process: "chemical dewaxing → water washing → ultrasonic dewaxing → water washing → ultrasonic degreasing → water washing → acid salt activation → water washing".

[0039] 2. Copper-zinc alloy plating:

[0040] After pretreatment, the zinc alloy die-casting parts were coated with a cyanide-free copper-zinc alloy coating 2 using a polymeric thiocyanate copper-zinc alloy plating process, with a coating thickness of 6μm.

[0041] The plating solution contained 22 g / L of polycuprous thiocyanate, 10 g / L of polyzinc thiocyanate, 150 g / L of polysodium thiocyanate, and 4 g / L of ammonium chloride. The pH of the plating bath was 11.5, the bath temperature was 45℃, and the cathode current density was 1.0 A / dm³. 2 The cathode moves at a speed of 4 m / min, and a brass plate is used as the anode.

[0042] 3. Zinc-nickel alloy plating:

[0043] After copper-zinc plating, zinc alloy die-cast parts were coated with copper and zinc using Detronzin 1215 alkaline zinc-nickel alloy electroplating process from Chaobang Chemical to prepare zinc-nickel alloy coating 3, with a coating thickness of 12μm.

[0044] Zinc 7.5 g / L, Nickel 1.4 g / L (provided by DETRONZIN 1215 Ni nickel supplement 16 mL / L), Sodium hydroxide 128 g / L, DETRONZIN 1215 Base additive 100 mL / L, DETRONZIN 1215 Brightener 3.0 mL / L, DETRONZIN 1215 Purifier R 0.5 mL / L, plating bath temperature 25℃, cathode current density 2.5 A / dm³ 2 The cathode moves at a speed of 5 m / min.

[0045] 4. Passivation:

[0046] After zinc alloy die castings are plated with zinc-nickel alloy, trivalent chromium blue passivation film is prepared using TRIROS 344 zinc-nickel blue passivating agent from Chaobang Chemical Co., Ltd. 4.

[0047] TRIROS 344A zinc-nickel blue passivating agent 45 mL / L, TRIROS 344B zinc-nickel blue passivating agent 60 mL / L, passivation temperature 28℃, passivation solution pH 4.4, passivation time 60 s, air residence 25 s, weak air agitation.

[0048] The specific process is as follows: "1% sulfuric acid for film removal → water washing → passivation → water washing → draining after removal from the tank → blowing away residual droplets on the surface of the plated parts with high-pressure air".

[0049] 6. Drying:

[0050] After passivation, the zinc alloy die-cast parts are dried and cured at 60°C for 18 minutes. Example 2

[0051] like Figure 1 As shown, a coating structure for a zinc-nickel alloy plating on a cyanide-free copper-zinc alloy base coating includes a zinc alloy die-cast substrate 1, and a cyanide-free copper-zinc alloy coating 2, a zinc-nickel alloy coating 3, and a trivalent chromium blue passivation film 4, which are sequentially prepared from the inside to the outside on the zinc alloy die-cast substrate 1.

[0052] 1. Pre-processing:

[0053] The zinc alloy die casting substrate 1 is subjected to the following pretreatment process according to the current zinc alloy pretreatment process: "chemical dewaxing → water washing → ultrasonic dewaxing → water washing → ultrasonic degreasing → water washing → acid salt activation → water washing".

[0054] 2. Copper-zinc alloy plating:

[0055] After pretreatment, the zinc alloy die-casting parts were coated with a cyanide-free copper-zinc alloy coating 2 using a polymeric thiocyanate copper-zinc alloy plating process, with a coating thickness of 6μm.

[0056] The plating solution contained 25 g / L of polycuprous thiocyanate, 12 g / L of polyzinc thiocyanate, 175 g / L of polysodium thiocyanate, and 5 g / L of ammonium chloride. The pH of the plating bath was 10, the bath temperature was 40℃, and the cathode current density was 1.0 A / dm³. 2 The cathode moves at a speed of 4 m / min, and a brass plate is used as the anode.

[0057] 3. Zinc-nickel alloy plating:

[0058] After copper-zinc plating, zinc alloy die-cast parts were coated with copper and zinc using Chaobang Chemical's DETRONZIN 1377 acidic zinc-nickel alloy electroplating process to prepare zinc-nickel alloy coating 3, with a coating thickness of 12μm.

[0059] Zinc 26g / L, Nickel 26g / L, Potassium Chloride 175g / L, Ammonium Chloride 60g / L, DETRONZIN 1377A Base Additive 15mL / L, DETRONZIN 1377B Bri Brightener 1.0mL / L, DETRONZIN 1377C Complexing Agent 15mL / L, DETRONZIN 1377D Additive Additive 10mL / L, plating bath temperature 29℃, plating solution pH 4.9, cathode current density 2.5A / dm³ 2 The cathode moves at a speed of 4 m / min.

[0060] 4. Passivation:

[0061] After zinc alloy die castings are plated with zinc-nickel alloy, trivalent chromium blue passivation film is prepared using TRIROS 343 zinc-nickel blue passivating agent from Chaobang Chemical Co., Ltd. 4.

[0062] TRIROS 343 zinc-nickel blue passivating agent 150mL / L, passivation solution pH 2.2, operating temperature 45℃, immersion time 60s, air agitation.

[0063] The specific process is as follows: "1% sulfuric acid for film removal → water washing → passivation → water washing → draining after removal from the tank → blowing away residual droplets on the surface of the plated parts with high-pressure air".

[0064] 6. Drying:

[0065] After passivation, the zinc alloy die-cast parts are dried and cured at 60°C for 18 minutes.

[0066] Experimental Example 1:

[0067] Zinc alloy die casting zinc-nickel alloy samples were prepared according to the process of Examples 1 and 2. The samples were heated to 150°C and held for 30 minutes in a heating furnace according to GB / T5270-2005 "Review of Test Methods for Adhesion Strength of Electrodeposition and Chemical Deposition of Metallic Coatings on Metal Substrates". They were then taken out and placed in water at room temperature for rapid cooling. No blistering or peeling of the coating was observed, and the coating adhesion was good.

[0068] Experimental Example 2:

[0069] Zinc alloy die castings were prepared according to the process described in Examples 1 and 2. The corrosion resistance was tested according to GB / T10125–2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". No white corrosion products were generated on the surface of the samples after 480 hours of neutral salt spray test, indicating that the coating has good corrosion resistance.

[0070] The technical solutions provided by the embodiments of this utility model have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of this utility model. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of this utility model. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this utility model, but all should fall within the protection scope of this utility model.

Claims

1. A plating structure in which a zinc-nickel alloy is plated on a cyanide-free copper-zinc alloy undercoat layer, characterized by: The zinc alloy die casting base body, and the cyanide-free copper-zinc alloy plating layer, the zinc-nickel alloy plating layer, and the trivalent chromium blue passivation film prepared in sequence from inside to outside on the zinc alloy die casting base body. The cyanide-free copper-zinc alloy plating layer is prepared by using a polymeric thiocyanate copper-zinc alloy plating process.

2. The plating layer structure of zinc-nickel alloy over cyanide-free copper-zinc alloy underlayer plating layer according to Claim 1, characterized by: The thickness of the cyanide-free copper-zinc alloy plating layer is 3-9 μm.

3. The plating layer structure of zinc-nickel alloy over cyanide-free copper-zinc alloy underlayer plating layer according to Claim 1, wherein: The thickness of the zinc-nickel alloy plating layer is 5-20 μm.

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