There are two most commonly used anodizing types: anodizing (type Ⅱ) and hard anodizing (type Ⅲ).
Different from aluminum profile, the anodizing of aluminum castings has more difficulties, limited thickness, dark colors, lower hardness, and higher costs.
Thickness & characteristics
for Aluminum Castings
Anodizing (Type Ⅱ)
Thickness: 5-15 μm
Color: Natural/Grey/Black
Hardness: HV 200-350
Benefits: improved corrosion resistance, lower cost
Hard Anodizing (Type Ⅲ)
Thickness: 25-50 μm
Color: Dark grey/Black
Hardness: HV 350-500
Benefits: Excellent corrosion resistance, good wear resistance
Cast Aluminum Material & Anodizing Performance
Anodizing performance for die castings (ADC12/A380, 9%-12% Si content):
- Anodizing (Type Ⅱ): can only do dark grey or black anodizing, thickness 5-10 μm, can do uniform anodizing but is challenging and price is high
- Hard Anodizing (Type Ⅲ): can only do black anodizing, thickness 25-40 μm. Anodizing is uneven, flow marks on the surface as the picture.
Anodizing performance for gravity castings (A356/AlSi7Mg, 6%-7% Si content):
- Anodizing (Type Ⅱ): can do natural, dark grey or black anodizing, thickness 5-15 μm, perfect anodizing finish, cost-effective.
- Hard Anodizing (Type Ⅲ): can do dark grey or black anodizing, thickness 25-50 μm. Uniform color surface, no flow marks.
Casting Process Selection for Different Anodizing Requirements
- For excellent surface, choose gravity casting (also known as permanent mold casting);
- For good wear resistance, choose die casting if flow marks are acceptable and order quantity is large, or choose gravity casting;
- For only corrosion resistance with large-scale orders, die casting will be cheaper;
- For only corrosion resistance with medium-small orders, choose gravity casting, mold cost will be lower.
