Appearance refining process for zinc-aluminum alloy die-casting optical module

Abstract

The invention discloses an appearance refining process for a zinc-aluminum alloy die-casting optical module, which belongs to the technical field of optical modules and comprises the following steps of: firstly, carrying out chemical polishing treatment on the surface of the optical module, and then, placing a zinc-aluminum alloy die-casting piece in an electrolyte containing silicate-phosphate to generate a porous oxide film; an amorphous Ni-P layer is chemically plated on the surface of the oxidation film and permeates into pores of the oxidation film to form a nano rivet structure; depositing a nanocrystalline nickel layer on the Ni-P layer by adopting pulse electroplating; electroplating a Cu-graphene composite sacrificial layer on the surface of the nanocrystalline nickel layer; after the whole body is protected, the Cu-graphene composite sacrificial layer is removed, and meanwhile, the integrity of the nanocrystalline nickel layer at the bottom layer is reserved; after argon plasma pretreatment, magnetorheological fluid containing CeO2 / diamond nanoparticles is adopted for polishing; and forming a super-hydrophobic film on the surface of the optical module by adopting perfluoroalkyl silane vapor deposition. The refining process can meet the ever-increasing surface smoothness requirement of the optical module.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical module surface processing, and specifically relates to a refined appearance process for zinc-aluminum alloy die-cast optical modules. Background Art

[0002] As a core device in modern optical communication systems, optical modules are widely used in fields such as data centers, 5G networks, fiber to the home, and long-distance backbone transmission. Their core function is to achieve efficient conversion and transmission of optical and electrical signals. Zinc-aluminum alloy die-cast optical modules, as core components for 5G communication and high-speed optical interconnection, are mainly used for precision structural parts such as fiber optic interface housings and heat dissipation bases. Their excellent die-casting formability and cost advantages make them play an important role in mass manufacturing. However, the inherent porosity, uneven hard and soft phases, and easy corrosion of the zinc-aluminum alloy surface make it difficult for traditional mechanical polishing or electroless plating processes to meet the strict requirements of optical modules for surface finish, high reflectivity, and long-term weather resistance. In the prior art, direct polishing is prone to produce an "orange peel effect", the adhesion of the electroplated layer is insufficient and easy to peel off, and the high porosity of a single micro-arc oxidation film leads to deterioration of optical performance. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a refined appearance process for zinc-aluminum alloy die-cast optical modules, which can meet the increasing demand for surface finish of optical modules.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] The refined appearance process for zinc-aluminum alloy die-cast optical modules disclosed by the present invention is characterized in that it includes the following steps:

[0006] (1) Micro-arc oxidation substrate treatment: First, perform chemical polishing on the surface of the optical module, and then place the zinc-aluminum alloy die-casting in an electrolyte containing silicate-phosphate to generate a porous oxide film;

[0007] (2) Step-by-step electroplating: Deposit three functional plating layers in sequence;

[0008] (2.1) First, electrolessly plate an amorphous Ni-P layer on the surface of the oxide film, and infiltrate into the pores of the oxide film to form a nano-rivet structure;

[0009] (2.2) Deposit a nanocrystalline nickel layer on the Ni-P layer by pulse electroplating;

[0010] (2.3) Electroplate a Cu-graphene composite sacrificial layer on the surface of the nanocrystalline nickel layer;

[0011] (3) Sacrificial layer stripping: After protecting the whole, remove the Cu-graphene composite sacrificial layer while retaining the integrity of the underlying nanocrystalline nickel layer;

[0012] (4) Plasma-assisted magnetorheological polishing: After argon plasma pretreatment, polishing is carried out using a magnetorheological fluid containing CeO2 / diamond nanoparticles;

[0013] (5) Molecular self-assembly closure: Perfluoroalkylsilane vapor deposition is used to form a superhydrophobic film on the surface of the optical module.

[0014] Furthermore, the parameters for preparing the Cu-graphene layer are as follows: The plating solution composition includes 200 g / L of copper sulfate, 50 g / L of sulfuric acid, 0.8 g / L of modified graphene, the current density is 4 A / dm 2 , the temperature is 25 ± 2 °C, the mechanical stirring rate is 200 rpm. First, ultrasonic fragmentation pretreatment is carried out, and then polyvinylpyrrolidone is added as a dispersant.

[0015] Furthermore, the parameters for plasma-assisted magnetorheological polishing are as follows:

[0016] Plasma parameters: Radio frequency power is 200 W, argon gas flow rate is 20 sccm, and the treatment time is 5 min;

[0017] Polishing fluid formulation: 5 vol% of CeO2 nanoparticles, 5 vol% of diamond nanoparticles, 40 vol% of carbonyl iron powder, and the balance is the base fluid;

[0018] Polishing trajectory planning: An Archimedean spiral path is adopted, and the overlapping rate of adjacent trajectories is 30 - 40%.

[0019] Furthermore, in step (3), the Cu-graphene is peeled off by a laser-induced method. The surface of the copper layer is scanned with a pulsed laser, and microcracks are generated at the interface between the Cu-graphene layer and the nanocrystalline nickel layer through thermal shock, and then ultrasonic-assisted peeling is carried out in dilute nitric acid.

[0020] Furthermore, in step (4), the viscosity of the magnetorheological fluid varies in the range of 50 - 5000 cP with the shear rate.

[0021] The beneficial effects of the present invention are as follows:

[0022] The appearance refinement process of the zinc-aluminum alloy die-cast optical module disclosed by the present invention can greatly improve the surface finish of the product through step-by-step refinement of the Cu-graphene sacrificial layer + laser peeling. After removing the copper layer, the reflectivity of the pure nickel surface is > 92%, and the uniformity in the full wavelength range is ±0.5%, meeting the requirements of the optical module.

[0023] Other advantages, objectives, and features of the present invention will be described in the subsequent specification, and to some extent, they are obvious to those skilled in the art, or those skilled in the art can obtain teachings from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0024] To make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following attached drawings for illustration:

[0025] Figure 1 It is a flowchart of the refinement process of the present invention; Detailed implementation manners

[0026] As Figure 1 shown, the appearance refinement process of the zinc-aluminum alloy die-cast optical module disclosed by the present invention includes the following steps:

[0027] (1) Micro-arc oxidation substrate treatment: First, chemically polish the surface of the optical module, and then place the zinc-aluminum alloy die-casting in an electrolyte containing silicate-phosphate. Generate a porous oxide film at a voltage of 350 - 450V and a frequency of 500Hz, with a film thickness of 20 - 30μm, a porosity of 15 - 20%, and a surface hardness ≥ 800HV; The surface finish of the porous oxide film is poor and cannot meet the requirements of existing product processes. Therefore, electroplating is required to increase the surface finish of the zinc-aluminum alloy.

[0028] The MAO film formed in the alkaline electrolyte, i.e., the silicate-phosphate system, is mainly composed of ZnAl2O4 spinel phase, Al2O3 and ZnO, with a film thickness usually of 10 - 50μm, having a typical porous structure, most pore diameters of 1 - 5μm, and a porosity of 15 - 30%; There are a large number of discharge micropores on the surface of the micro-arc oxidation film. If electroplating is directly carried out, it will cause mechanical anchoring bonding of the coating, and stress concentration is likely to occur. From the experimental data tested by the scratch method, the bonding strength of direct nickel plating is only 8 - 12MPa, and it is easy to delaminate after polishing, which cannot meet the actual requirements.

[0029] (2) Step-by-step electroplating: Deposit three functional coatings in sequence;

[0030] (2.1) First, electrolessly deposit an amorphous Ni-P layer on the surface of the oxide film, where the P content is 10 - 12wt%, the thickness is 8 - 10μm, and it penetrates into the pores of the oxide film to form a nano-rivet structure; The bonding strength is increased to 25 - 30MPa; The surface roughness Ra of the amorphous Ni-P can reach 0.03μm after polishing, and the P content is 9 - 12wt%. By depositing the amorphous Ni-P layer, the pores of the MAO film can also be passivated to prevent acid etching and penetration of subsequent coatings.

[0031] (2.2) Deposit a nanocrystalline nickel layer on the Ni-P layer by pulse electroplating, with a grain size of 30 - 50nm and a peak current density of 5A / dm 2, with a thickness of 5 - 8 μm; by depositing a nanocrystalline nickel layer, the microdefects of the Ni - P layer can also be filled. Nanocrystals with a grain size of 20 - 50 nm can withstand higher polishing pressures. The present invention uses nanocrystalline nickel (n - Ni) as the transition layer, and its grain size can absorb stress through grain boundary slip, enabling a gradient transition of the micro - arc oxidation film. After adding the n - Ni transition layer, the cracking rate of the coating after thermal cycling from - 40 °C to 85 °C is reduced from 35% to < 5%.

[0032] Meanwhile, the nanocrystalline structure of n - Ni can block the diffusion paths of - corrosion media such as Cl -5 , and the corrosion current density is reduced from 3.2×10 2 A / cm -7 to 8.7×10 2 A / cm 2 . When electroplating copper - graphene on the surface of the n - Ni layer, the inert surface of graphene can reduce the interfacial energy between copper and nickel from 1.2 J / m 2 to 0.6 J / m

[0033] (2.3) Electroplate a Cu - graphene composite sacrificial layer on the surface of the nanocrystalline nickel layer, where the graphene content is 0.8 - 1.2 wt%, and the thickness is 15 - 20 μm; the copper layer is softer than the nickel layer, facilitating subsequent selective removal. Embedding 0.5 - 1 wt% of graphene can reduce the interfacial binding energy, and the ultrasonic peeling efficiency is increased by 40%.

[0034] The present invention adopts three - layer coatings. Among them, mechanical - chemical composite bonding is achieved by Ni - P infiltrating into the pores of the oxide film. The nanocrystalline nickel layer provides a super - precision polishing substrate, which can provide a relatively smooth surface of the optical module. The outermost Cu - graphene composite sacrificial layer has the characteristics of being soft and easy to remove, which can absorb the mechanical impact of zinc - aluminum alloy during transportation, storage or intermediate processes, reduce interfacial damage, and enhance the etching uniformity through graphene.

[0035] Meanwhile, if the nanocrystalline nickel layer is directly polished, its high hardness will cause the abrasive to be quickly passivated, resulting in a 50% reduction in the lifespan of diamond abrasive grains. The soft characteristics of the copper layer can first "pre - consume" the sharp corners of the abrasive, making the subsequent polishing of the nickel layer more uniform.

[0036] (3) Laser - induced peeling: Use a pulsed laser with a wavelength of 1064 nm, an energy density of 3 - 5 J / cm 2 , a pulse width of 20 ns to scan the surface of the copper layer. Micro - cracks are generated at the interface between the Cu - graphene layer and the nanocrystalline nickel layer through thermal shock, and then ultrasonic - assisted peeling is carried out in dilute nitric acid with a concentration of 5 vol%, and the peeling time ≤ 3 min;

[0037] (4) Plasma-assisted magnetorheological polishing: After argon plasma pretreatment, a magnetorheological fluid containing CeO2 / diamond nanoparticles with a particle size ratio of 1:1 is used for polishing under a 0.6 T magnetic field, and the surface roughness Ra ≤ 0.03 μm; the phosphorus element in the Ni-P layer forms an amorphous-nanocrystalline composite structure during polishing, and even after removing the copper layer, the surface still retains the ultra-smooth property.

[0038] (5) Molecular self-assembly sealing: Perfluoroalkylsilane vapor deposition is used to form a superhydrophobic film with a thickness of 50 - 100 nm and a contact angle ≥ 155°. Even after magnetorheological polishing, there are still microscopic pores of 0.5 - 2 nm on the surface measured by the BET method. After hydrolysis of the fluorosilane - Si(OCH3)3 group, it condenses with the hydroxyl groups on the nickel surface, and the long-chain fluorocarbon groups are vertically arranged to form a molecular brush, which affects the appearance quality. After sealing, the surface porosity decreases from 0.3% to < 0.01%, completely eliminating the pollution caused by capillary adsorption.

[0039] Table 1 is a comparison table of the zinc-aluminum surface refinement parameters of the present invention and several comparative examples, where:

[0040] Comparative example 1 is to directly form a porous oxide film on the zinc-aluminum alloy surface without any plating layer;

[0041] Comparative example 2 is to only deposit a nanocrystalline nickel layer on the surface of the oxide film without participating in the other two plating layers;

[0042] Comparative example 3 is to first electrolessly deposit an amorphous Ni-P layer on the surface of the oxide film, and then pulse electroplate to deposit a nanocrystalline nickel layer on the Ni-P layer; the other peeling techniques corresponding to the plating layer can be carried out as usual.

[0043] Table 1

[0044]

[0045] Although the introduction of the sacrificial copper-graphene layer in the present invention increases the steps, through the step-by-step refinement of "plating and then removing", the surface quality that cannot be achieved by traditional processes is realized.

[0046] As a further improvement of the embodiment of the present invention, the parameters for preparing the Cu-graphene layer are as follows: the plating solution composition includes 200 g / L of copper sulfate, 50 g / L of sulfuric acid, 0.8 g / L of modified graphene, the current density is 4 A / dm 2 ², the temperature is 25 ± 2 °C, the mechanical stirring rate is 200 rpm. First, ultrasonic fragmentation (power 300 W, 30 min) is used for pretreatment, and then polyvinylpyrrolidone (PVP) is added as a dispersant. Without the dispersant system, the graphene sedimentation rate increases within 4 hours, while after PVP modification, the sedimentation rate < 5% within 72 hours, which can increase the stability of the plating solution. The graphene forms a three-dimensional network structure in the copper layer, enabling the cracks to expand along the graphene network during laser peeling and improving the peeling efficiency.

[0047] By defining the preparation parameters of the Cu-graphene composite coating, the present invention realizes the uniform dispersion of graphene in the copper layer, enables cracks to propagate directionally along the graphene network during laser peeling, and reduces the peeling energy consumption. At the same time, the content of graphene in the coating is maintained stable, enabling precise control of the interfacial binding energy, and laying a foundation for subsequent non-destructive peeling.

[0048] In this embodiment, the parameters of plasma-assisted magnetorheological polishing are as follows:

[0049] Plasma parameters: radio frequency power 200 W, argon gas flow rate 20 sccm, treatment time 5 min;

[0050] Polishing fluid formulation: 5 vol% CeO2 nanoparticles (20 nm), 5 vol% diamond nanoparticles (50 nm), 40 vol% carbonyl iron powder, and the balance is the base fluid;

[0051] Polishing trajectory planning: adopt an Archimedean spiral path, and the overlapping rate of adjacent trajectories is 30-40%. Plasma bombardment generates a 2-3 nm thick NiO activation layer on the surface, promoting abrasive cutting. The composite abrasive of CeO2 and diamond realizes chemical-mechanical synergistic polishing, and the material removal rate is increased to 120 nm / min. The spiral path avoids the directional arrangement of polishing lines, and the isotropic roughness difference <5%.

[0052] In this embodiment, in step (3), laser-induced peeling of Cu-graphene is adopted. A pulsed laser with a wavelength of 1064 nm is used to scan the surface of the copper layer. Among them, the energy density of the pulsed laser is 3-5 J / cm 2 , the pulse width is 20 ns. Microcracks are generated at the interface between the Cu-graphene layer and the nanocrystalline nickel layer through thermal shock, and then ultrasonic-assisted peeling is carried out in a 5 vol% dilute nitric acid solution, and the peeling time ≤ 3 min. Laser-induced peeling can greatly shorten the peeling time, and compared with selective etching, there is no participation of strong acid solutions.

[0053] In this embodiment, in step (4), the viscosity of the magnetorheological fluid varies in the range of 50-5000 cP with the shear rate. The viscosity in the high shear zone is selected to be >4000 cP to ensure effective cutting of the nano-abrasives; the viscosity in the low shear zone <100 cP to reduce fluid resistance.

[0054] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. The fine process for the appearance of zinc-aluminum alloy die-cast optical modules, characterized in that: Including the following steps: (1) Micro-arc oxidation substrate treatment: First, chemically polish the surface of the optical module, and then place the zinc-aluminum alloy die-cast part in an electrolyte containing silicate-phosphate to form a porous oxide film; (2) Step-by-step electroplating: Deposit three functional coatings in sequence; (2.1) First, electrolessly deposit an amorphous Ni-P layer on the surface of the oxide film to penetrate into the pores of the oxide film to form a nano-rivet structure; (2.2) Deposit a nanocrystalline nickel layer on the Ni-P layer by pulse electroplating; (2.3) Electroplate a Cu-graphene composite sacrificial layer on the surface of the nanocrystalline nickel layer; (3) Sacrificial layer stripping: After protecting the whole, remove the Cu-graphene composite sacrificial layer while maintaining the integrity of the underlying nanocrystalline nickel layer; (4) Plasma-assisted magnetorheological polishing: After pretreatment with argon plasma, polish with a magnetorheological fluid containing CeO2 / diamond nanoparticles; (5) Molecular self-assembly sealing: Form a superhydrophobic film on the surface of the optical module by vapor deposition of perfluoroalkylsilane.

2. The refined appearance process of the zinc-aluminum alloy die-cast optical module according to claim 1, characterized in that: The parameters for preparing the Cu-graphene layer are as follows: the plating solution composition includes 200 g / L of copper sulfate, 50 g / L of sulfuric acid, 0.8 g / L of modified graphene, a current density of 4 A / dm 2 , a temperature of 25 ± 2 °C, a mechanical stirring rate of 200 rpm. First, perform ultrasonic fragmentation pretreatment, and then add polyvinylpyrrolidone as a dispersant.

3. The refined appearance process of the zinc-aluminum alloy die-cast optical module according to claim 2, characterized in that: The parameters of plasma-assisted magnetorheological polishing are as follows: Plasma parameters: Radio frequency power 200W, argon flow rate 20sccm, treatment time 5min; Polishing fluid formulation: CeO2 nanoparticles 5vol%, diamond nanoparticles 5vol%, carbonyl iron powder 40vol%, and the balance is the base fluid; Polishing trajectory planning: Adopt an Archimedean spiral path with an adjacent trajectory overlap rate of 30-40%; 4. The refined appearance process of the zinc-aluminum alloy die-cast optical module according to any one of claims 1-3, characterized in that: In step (3), the Cu-graphene is peeled off by a laser-induced method. The surface of the copper layer is scanned by a pulsed laser to generate microcracks at the interface between the Cu-graphene layer and the nanocrystalline nickel layer through thermal shock, and then ultrasonic-assisted peeling is carried out in dilute nitric acid.

5. The refined appearance process of the zinc-aluminum alloy die-cast optical module according to claim 4, characterized in that: In step (4), the viscosity of the magnetorheological fluid varies in the range of 50-5000 cP with the shear rate.

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