A complete analysis of black surface treatment technology for different materials

In the fields of industrial manufacturing, precision parts processing and consumer electronics, black surface treatment technology is highly favored because it combines functionality and aesthetics. The black treatment processes of different materials (such as iron, stainless steel, aluminum, and titanium) vary significantly, which directly affects the corrosion resistance, hardness, and cost of the product. This article will systematically analyze 8 mainstream black surface treatment solutions, covering material selection, process characteristics, and industry application scenarios to help you accurately match your needs.

Black surface treatment scheme for iron-based materials

1. Iron + black zinc treatment

Core process: black appearance is achieved by passivation dyeing after electrogalvanizing.

Key parameters:

• Material grade: The mechanical performance grade of iron parts needs to be clarified (grade 4.8, grade 8.8, grade 10.9, grade 12.9). High grades (such as grade 12.9) need to predict the sensitivity of the coating to hydrogen embrittlement.
• Salt spray test: The salt spray test of conventional black zinc treatment is 24 hours, and high-end demand can be increased to 48-120 hours (the passivation liquid formula and sealing process need to be adjusted).

Industry application: automotive fasteners, outdoor hardware (such as fence hinges).

2. Iron + blackening treatment

Process principle: alkaline high temperature oxidation or room temperature chemical oxidation to generate a ferroferric oxide film layer.

Pros and cons analysis:

• Low cost and easy operation, but weak wear resistance (film thickness is only 0.5-1.5μm).
• Suitable for non-high load scenarios, such as tool handles and gear surfaces.

3. Iron + zinc-nickel alloy electroplating

Technical highlights: The salt spray resistance of zinc-nickel alloy (usually containing 12-15% nickel) can reach more than 720 hours, far exceeding ordinary zinc plating.

Design points:

• The pH value and current density of the plating solution need to be controlled to avoid embrittlement of the coating.
• The first choice for military and marine engineering, such as ship valves and oil pipeline joints.

4. Iron + black nickel electroplating

Appearance characteristics: The coating is black-gray and can be customized with matte/semi-gloss effects.

Process difficulties: Sulfur-containing nickel salt electroplating solution is required, and post-treatment needs to close micropores to improve corrosion resistance.

Typical uses: optical instrument brackets, high-end furniture hardware.

Black treatment technology for stainless steel

1. Stainless steel + black oxidation

Process classification:

• Chemical oxidation: A black oxide film is generated through a chromate or molybdate solution, with a film thickness of about 0.2-0.5μm.
• High temperature oxidation: The film is treated in molten dichromate, and the film layer is denser (applicable to 316L surgical instruments).

Material adaptation:

• 303/304 stainless steel (A2 standard) is commonly used in food machinery; 316 stainless steel (A4 standard) is resistant to chloride corrosion and suitable for marine environments.

2. Stainless steel + black electrophoresis

Process advantages:

• The electrophoretic paint film evenly covers complex structures, and can be matte (RAL 9005) or high gloss (RAL 9006).
• Combined with the corrosion resistance of the stainless steel substrate, the overall salt spray resistance can reach 1000 hours.

Cost considerations: The electrophoresis line has a high investment and is suitable for mass production of consumer electronic housings (such as headphone charging boxes).

Black anodizing solution for aluminum alloy

1. Type II ordinary anodizing

Process parameters:

• Sulfuric acid electrolyte, film thickness 3-6μm, hardness about 200-400HV.
• Can be dyed to dark black (need to control dye concentration and sealing temperature).

Applicable scenarios: 3C product shell (such as laptop A side), drone frame.

2. Type III hard anodizing

Performance breakthrough:

• Film thickness 20-50μm, surface hardness 500-800HV (close to ceramic).
• Requires low-temperature electrolysis (-5°C to 10°C), high energy consumption.

Industrial applications: aviation hydraulic components, gun rails.

PVD black coating technology for titanium alloy

1. Process principles and advantages

• Physical vapor deposition (PVD) can generate black ceramic films such as TiN and TiCN on the titanium surface with a hardness exceeding 2000HV.
• No risk of hydrogen embrittlement, good biocompatibility, and meets medical implant standards (such as titanium Gr5 artificial joints).

2. High-end industry application cases

• Aerospace: TC4 titanium alloy engine blade PVD coating, temperature resistance up to 600°C.
• Luxury goods: Titanium TA1 watch case is black-plated, combining lightness and wear resistance.

Selection decision tree: How to choose the best black treatment solution

Black processing technology for non-metallic materials

Surface treatment of engineering plastics

PVD coating technology

• Use medium-frequency magnetron sputtering to deposit CrCN black film on the surface of PEEK, reducing the friction coefficient from 0.3 to 0.12. A semiconductor equipment manufacturer uses this to solve the problem of electrostatic adsorption of wafer transfer arms.

 Laser carbonization modification

• 1064nm fiber laser generates a micro-nanostructured black layer on the surface of ABS, and the VDA 230-209 scratch resistance test reaches level 4. This technology has been successfully applied to the production of automotive interior parts.

Ceramic material processing

Sol-gel method

• The black glaze prepared by tetrabutyl titanate precursor presents a silky luster after sintering at 1300℃. A high-end tableware brand obtains a color-changing effect of cold and warm light by adding 3% cobalt oxide.

Plasma nitriding

• Si₃N₄ ceramics are treated with plasma at 800℃ to form a SiNxOy black layer on the surface, and the hardness is increased by 30%. This technology has been used in the field of precision bearing manufacturing.

Conclusion

The selection of black surface treatment technology needs to comprehensively consider the characteristics of the substrate, the working environment and the cost budget. For example, medical devices prefer titanium + PVD to ensure biosafety, while outdoor iron parts need to be electroplated with zinc-nickel alloy to resist salt spray corrosion. It is recommended to communicate in depth with Honscn about material parameters (such as A2/A4 classification of stainless steel) and test standards (salt spray duration) to ensure the accurate implementation of the technical solution.
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