Common Surface Treatment Techniques for Metals

surface treatment

This article provides an overview of surface treatment processes for various metals, including stainless steel, aluminum alloy, magnesium alloy, zinc alloy, and more. Here’s a closer look at each metal type and the treatment options available:

  • Stainless Steel: Electroplating, polishing, brushing, electrophoresis, PVD (Physical Vapor Deposition), etching, colored passivation
  • Aluminum Alloy: Anodizing, electroplating, etching
  • Magnesium Alloy: Electroplating, passivation film
  • Titanium Alloy: Electroplating, anodizing
  • Zinc Alloy: Electroplating, passivation
  • Cast Aluminum: Electroplating, anodizing
  • Steel: Passivation, phosphating

Below are descriptions of several common surface treatment processes:


1. Anodizing

Anodizing is an electrochemical process that forms a protective oxide layer on the surface of aluminum and its alloys. During this process, aluminum serves as the anode and is immersed in an electrolyte solution, generating an alumina (Al₂O₃) film through electrolysis. This oxide layer can range from a few microns to hundreds of microns in thickness, offering enhanced corrosion resistance, wear resistance, and decorative appeal compared to natural oxide films.

Process Flow:

  • Single Color, Gradient Color: Polishing/sandblasting/brushing → Degreasing → Anodizing → Neutralizing → Dyeing → Sealing → Drying
  • Two Colors:
    • Option 1: Polishing/sandblasting/brushing → Degreasing → Masking → Anodizing 1 → Anodizing 2 → Sealing → Drying
    • Option 2: Polishing/sandblasting/brushing → Degreasing → Anodizing 1 → Laser Engraving → Anodizing 2 → Sealing → Drying

Notes: Two-tone anodizing requires higher costs due to the need for masking and double anodizing, resulting in a higher defect rate.


2. Electrophoresis

Electrophoresis is commonly used for materials like stainless steel and aluminum alloy, adding color while preserving a metallic shine and enhancing surface protection, particularly against corrosion.

Process Flow: Pre-treatment → Electrophoresis → Drying

Advantages:

  1. Wide range of color options
  2. Retains metallic sheen, suitable for combining with sandblasting, polishing, or brushing
  3. Allows surface treatment of complex structures in a liquid environment
  4. Mature and efficient process, ideal for mass production

3. Electroplating

Electroplating involves depositing a thin metal layer on a product’s surface through electrolysis, providing corrosion resistance, improved wear resistance, better conductivity, increased reflectivity, and a decorative finish.

Process Flow: Pre-treatment → Cyanide-free alkaline copper → Cyanide-free white bronze-tin → Metal coating


4. Powder Coating

Powder coating uses electrostatic spray equipment to apply powdered paint to the workpiece. Under electrostatic attraction, the powder adheres uniformly to the surface, forming a coating that is cured under high heat to produce a smooth, durable finish.

Process Flow: Loading → Electrostatic dust removal → Spraying → Low-temperature leveling → Baking


Differences Among Processes

  1. Masking Capabilities: Electroplating, electrophoresis, and anodizing do not allow easy masking, while powder coating and painting can.
  2. Re-processability: Once formed, electrophoresis and anodizing create an insulating layer that cannot be reprocessed, while powder coating, painting, and electroplating can undergo multiple treatments.
  3. Material Suitability: Anodizing is suited for magnesium, aluminum, and their alloys. Electrophoresis works on any conductive surface, while electroplating, powder coating, and painting are compatible with almost all metals.
  4. Corrosion Resistance: Corrosion resistance depends on the coating’s quality, with electrophoresis generally offering superior protection.

Advantages and Disadvantages of Key Processes

  1. Electrophoresis
    • Advantages: Environmentally friendly, water-based coatings; high paint utilization (85%); excellent corrosion resistance; efficient for large volumes; low coating cost per unit area.
    • Disadvantages: Limited color options that are harder to modify; high initial setup cost; only suitable for conductive materials; requires high-temperature curing.
  2. Electroplating
    • Advantages: Produces a metallic luster; high hardness; no heat required for curing.
    • Disadvantages: Potential heavy metal pollution; limited color options; relatively high cost.
  3. Anodizing
    • Advantages: Simple process; vibrant colors achievable; low cost.
    • Disadvantages: Limited to magnesium-aluminum products.
  4. Powder Coating
    • Advantages: Eco-friendly coatings; high material utilization; customizable colors.
    • Disadvantages: Thicker film; requires high-temperature curing.
  5. Painting
    • Advantages: Extensive color and coating options; numerous functional coatings available.
    • Disadvantages: Low material utilization; less environmentally friendly; fire risk; requires a dust-free environment.

Thank you for reading. We are looking forward to serving you with our exceptional gear solutions. #BeyondGears

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