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At MI Metals we offer type II capabilities in satin clear anodize finish.  Type II anodizing is by far the most popular form of anodizing aluminum.  Clear benefits of an aluminum anodized finish include durability, color stability, ease of maintenance, dramatic cost savings and aesthetics.

Sulfuric acid anodizing has been defined as “an electrochemical process that intentionally forms a porous anodic oxide on aluminum”.  This oxide, an integral part of the metal, is formed when a current is applied to the aluminum parts in a sulfuric acid anodizing bath.


Under normal circumstances, the aluminum is anodized using a prescribed set of parameters:

  • Typically, Type II anodizing is performed in a sulfuric acid bath containing 180-200 grams per Liter of acid and a small amount of dissolved aluminum. The operating temperature is controlled between 68-72º F. Current densities can range from 5-18 amps per square foot (ASF), but commonly are run at 12-15 ASF.
  • The power supply is a DC rectifier. The aluminum part being anodized is made the anode (or positive pole) in the system. The most efficient cathodes (or negative pole) are 6063-T6 aluminum.
  • Current is applied to the system for a prescribed time, and at the desired current density to achieve the oxide thickness required (oxide thicknesses can range from 0.1 mil to 0.8 mil). The resulting porous oxide can then be sealed.


For many years anodizers used almost any convenient cathode material, from the actual tank wall to the lead coils used for cooling in sulfuric acid anodizing baths. Little attention was paid to the type of material or the anode to cathode ratio. As operations became more sophisticated and research on this subject was accomplished, specific recommendations on the ratio and material became available. The consensus opinion was the best material for the cathodes was aluminum and specifically 6063-T6 alloy.

In addition the ratio of 3 sq feet of anode to 1 sq foot of cathode gave the most consistent anodizing. Attempting to accomplish this ratio in a job shop environment is difficult but the closer you are to this ratio the better your overall anodizing performance will be. We at MI Metals went one step further and designed our own  “cathode system” to insure years of reliable, flexible and easily serviceable cathode design.

It offers the following advantages over other systems:

  1. Lower voltage required to do the same work.
  2. Long life (some cathodes in service over 3 years)
  3. No undesirable metals to contaminate the anodizing bath
  4. High surface area per cathode
  5. Easily replaced
  6. Uses less tank space
  7. Less heat build up
  8. Overall lower operating cost
  9. Simpler to change the cathode area