Anodizing is the electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide finish. We call it a finish that makes a project pop with color, better wear resistance and no electric conductivity.
Which materials are best for anodizing? Aluminum is the recommended metal best suited for anodizing, although other nonferrous metals, such as magnesium and titanium, can also be anodized. Aluminum can be anodized in a range of colors, including gold, bronze, blue, green, red, copper, black and silver. Unsure whether or not a metal’s been anodized? Simply test the conductivity of the surface with a digital multimeter. If the part is anodized, it is not conductive and has high resistance.
The Pros
- Very durable, abrasion-resistant and long-lasting
- Much harder surface than paint that doesn’t peel or chip
- Some are fade-resistant in sunlight
- Excellent corrosion protection, withstanding salt spray
- Environmentally friendly
- Good electrical insulator
IT’S SIMILAR TO OXIDATION, ONLY BETTER
Here’s how it works:
- The aluminum is immersed in an acid electrolyte bath with an electric current passed through the bath
- A cathode is mounted inside the anodizing tank
- The aluminum acts as an anode through which electricity moves into
- Oxygen ions are released from the acid electrolyte to combine with the aluminum atoms at the surface of the metal being anodized.
After anodizing, raw aluminum becomes harder and stronger. According to IQS® Directory, a leading manufacturing directory, “The anodizing process creates a stable aluminum oxide layer that is integrated with the underlying aluminum. The added anodic layer is porous, making it suitable for applying dyes, paints, lubricants, and adhesives.”
TYPES AND APPLICATIONS OF ANODIZING
There are many types of anodizing, but the most common are Type I, Type II and Type III.
- Chromic Acid Anodizing or Type I:
- Good for tight tolerance parts, will not change dimensions
- It can be black dyed; other colors are not practical
- Good for bonding
- Applications include:
- Precision machined components
- Aerospace components
- Welded components and assemblies
- As a paint/prime base
Sulfuric Acid Anodizing or Type II:
- More alloys can be finished
- Clearer finish allows dying with a greater variety of colors
- Waste treatment is easier than chromic anodize, reducing costs
Applications include:
- Optical components
- Hydraulic valve bodies
- Military weapons
- Computer and electronic enclosures
- Mechanical hardware
Hard Anodizing (Hardcoat) or Type III:
- Typically done in a sulfuric acid-based electrolyte
- Improved wear resistance
- Can repair worn surfaces on aluminum
- Improves parts surface for slide applications
- It can be dyed black, other colors less decorative
- Finish is harder than tool steel
- It can be ground or lapped
Applications include:
- Valves
- Pistons
- Sliding parts
- Hinge mechanisms
- Cams
- Gears
- Swivel joints
- Insulation plates
- Blasts shield
Boric-Sulfuric Acid Anodizing (BSAA):
- Good for tight tolerance parts, will not change dimensions
- Corrosion protection
- Good for bonding
Applications include:
- Precision machined components
- Aerospace components
- As a paint/prime base
Titanium Anodizing:
- Used in looking for stress cracks in base material
- Improves corrosion resistance
- Improves adhesion of dry film lubricant or paint application
Applications include:
- Aircraft parts
- Medical devices
- Spacecraft components
Electrolytic 2-Step Anodizing – AnoBlack EC:
Applications include:
- Medical devices and instruments
- Aerospace components (space vehicles)
- Optics
Strength, durability, color—and so much more. Anodizing brings many benefits to a variety of industries and applications, from the automotive, medical, aerospace and electronics industries to artisans and jewelers. Ask Latest Metalworks how anodizing can help enhance your next project.