Where the
world gathers for metal finishing
Q&As since 1989


-----

Problem of soft anodic coatings

 

Soft anodizing

I am experiencing soft anodic coatings. They tend to scratch easily. I am anodizing with a current density of 1.5amps per square decimeter, with the anodizing time of around 40-45 minutes which should be giving me about a 25 micron layer. My bath temperature varies between 18-21 °C. This is for type II sulfuric anodize. I seal the anodic coating with straight de ionized water for about a hour. What am I doing wrong!

Steve Power
- Nelson, New Zealand

---

Steve...you didn't mention the alloy you are working with, or the electrolyte composition.. both of which could be contributing to your problem. Is this a new problem for you.. are you an experienced anodizer? Do you regularly monitor your DI water for conductivity/resistivity, and pH? Is your Al content of your bath ok? There are alot of variables to check.

Marc Green
anodizer - Boise, Idaho
 

---

Your temperature is correct, your current is correct, but probably your acid concentration is too high. Get it down to 15 %/wt which is 12 fluid ounces per gal of 66 degree Baumé Sulfuric Acid which is 165.3 grams per liter.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina