Transcript Anodize Aluminum - University of Arizona

Aluminum Anodize
By: Randall Marks
Aluminum Oxide
• Amorphous aluminum oxide (alumina,
Al2O3) forms in a layer 2-3 nm thick when
bare aluminum is exposed to oxygen
• Protects from further oxidation
• Stress causes fractures in the surface, but
not peeling
• How can this natural coating be improved
upon?
Anodize Process
Types of Anodize
• Barrier Anodize
– Near neutral electrolyte solution
– Max 1um thick
• Porous Anodize
– Acidic electrolyte solution
– Can be several hundred um thick
Barrier Anodize
• Forms oxide on both
sides
• Dielectric, which
supports up to 1 V/nm
• Too thin for most
mechanical
applications
Porous Anodize Formation
Porous Anodize Sealing
• Hot water forms
hydrous oxide
crystals, sealing the
pores.
• Dyes or electroplated
metals can be sealed
inside the pores for
various colorations
Hard Anodize
• Hard Anodize Formation
– Low temperature
– Low acidity
• Applications
– Durable protective layer
– Bearings
• Not sealed to hold lubricants in the pores
• Surface is second hardest material known
Optics Applications
• Reduction of stray light/spectral reflections
– Bead blasted black anodize
– No outgassing
– Black anodize not good for bearing type
surfaces
• Adhesive preparation
– Phosphoric acid preparation
– Left unsealed
• Corrosion resistance
Important Application
Considerations
• AMS governing specs:
– AMS 2469-AMS 2474
• Part grows by approximately half the oxide
thickness
• Surface Young’s Modulus around 300
MPa.
• Does not protect against all chemicals
– Highly susceptible to strong acids and bases
References
• Case Western Reserve University
Electrochemistry Encyclopedia
– http://electrochem.cwru.edu/ed/encycl/arta02-anodizing.htm
• AACOA Inc. Anodizing Presentation
– http://www.aacoa.com/presentations/anodizin
g_presentation-c.pdf