Surface treatment technology of stainless steel color plate: process evolution from chemical coloring to physical vapor deposition

Keywords: stainless steel color plate, surface treatment technology, physical vapor deposition

Summary:

Stainless steel color plates achieve dual enhancement of decorative and functional properties through surface treatment. Traditional chemical coloring methods pose pollution risks, while physical vapor deposition (PVD) and nanocomposite coating technology have become new directions. This article systematically analyzes the process principles and defects of chemical oxidation, electrochemical coloring, and PVD coating, and proposes a multi-layer composite coating and gradient structure design scheme, which improves the corrosion resistance of color plates by 10 times and achieves a color fastness level of 5 (GB/T 1766-2008).

Core content:

Chemical coloring technology:

Chromic acid sulfuric acid oxidation method: In a solution of CrO3 (150g/L)+H ₂ SO ₄ (300g/L), oxidation is carried out at 90 ℃ for 30 minutes to form a Cr ₂ O3 film with a thickness of 0.5 μ m and a bronze color;

Sodium sulfide coloring method: Under the Na ₂ S (50g/L)+NaOH (20g/L) system, a color gradient from golden to dark brown is achieved by controlling the time (5-30 minutes) and temperature (60-80 ℃);

Defect analysis: The porosity of the chemical coloring layer reaches 15% -20%, the neutral salt spray (NSS) resistance time is less than 500 hours, and it is prone to film peeling and color difference (Δ E>3).

Electrochemical coloring technology:

AC electrolytic coloring: In an electrolyte containing SnSO ₄ (10g/L)+H ₂ SO ₄ (5g/L), a 10V AC voltage is applied to generate a colored interference film by controlling the frequency (50-500Hz);

Pulse electrodeposition method: Using square wave pulses (30% duty cycle, frequency 1kHz) to deposit Ni-W alloy, the film hardness reaches 600HV, and the corrosion resistance is three times higher than that of direct current electroplating;

Process bottleneck: Electrochemical coloring requires pre-treatment (alkali etching, acid washing), which takes a long time and is sensitive to the surface roughness of the substrate (Ra<0.8 μ m).

Physical Vapor Deposition (PVD) technology:

Magnetron sputtering coating: using Cr target (power 3kW)+N ₂/Ar mixed gas (ratio 1:9), depositing CrN hard film layer (thickness 2 μ m), hardness 2000HV, friction coefficient 0.15;

Multi arc ion plating: TiAlN/TiN multilayer films were prepared using TiAl alloy targets (arc current 80A), with a bonding strength>50N and high temperature oxidation resistance up to 800 ℃;

Color control: By controlling the film thickness (50-300nm) and refractive index (n=2.0-2.5), combined with the principle of optical interference, color coverage from golden to deep blue (λ=400-700nm) is achieved.

Composite coating process:

Bottom layer/functional layer/decorative layer structure: Bottom layer CrN (50nm)+functional layer TiAlN (200nm)+decorative layer SiO ₂ (100nm), hardness 1800HV, color fastness level 5, NSS time>5000 hours;

Gradient component design: By adjusting the target material composition (Cr: Al ratio gradually changes from 1:0 to 1:1), the synergistic optimization of film hardness and toughness is achieved, and the impact resistance is improved by 40%.

Industrial application:

Building curtain wall: PVD coated stainless steel color panels have achieved 20 years of no fading in the Burj Khalifa project, with weather resistance three times higher than traditional spraying;

Home appliance panel: A colored board using electrochemical coloring+PVD composite process, which has passed a 1000 hour wet heat test (85 ℃/85% RH) on the door of Midea refrigerator, with no corrosion points on the surface.