Measuring the hardness of the anodized layer

A. Hi Poova. There are two approaches to going for maximum hardness. First is to go strictly "by the book". If you wish to do that, you must actually go to the book -- directly to a hard copy of genuine reference material like The Surface Finishing and Treatment of Aluminum and its Alloys [adv: suggestions on AbeBooks, Amazon & eBay] or Properties of Electrodeposited Metals and Alloys [affil link to Amazon or on AbeBooks] , make a copy of applicable pages, highlight them, open a file documenting exactly what you are doing to follow them. Larry Durney's "Trouble in Your Tank" devotes the entire third chapter to "Follow the Letter of the Law", explaining why seeking quick tips promotes an intellectual laziness that will usually prove unproductive.

But if you want tips to improve what you are doing, please provide some info on the components you are processing and the anodizing parameters you are employing, and people will be able to instruct you on things to improve to increase the hardness. Good luck.

A. A microhardness tester with the appropriate load would probably give you a hardness reading that can be only somewhat be referenced to the more common rockwell hardness.
You increase hardness of a conventional sulfuric acid anodize by lowering the temperature (requires excellent agitation) and raising the voltage. Consider it as moving towards hard anodizing.

A. The hardness of anodic film can be evaluated by the procedure given in "qualanod spesifikasyonlari". The procedure consists of rubbing a specified glass emery paper on to the anodised aluminium surface. The hardness of anodic film is poor if the anodising temperature and sulfuric acid concentration is over 21 °C and 230 g/l respectively. The anodised aluminium must be taken out immediately from the anodising bath and good rinsing with higher pH must be applied not to soften the anodic film by acidic solutions. And a proper sealing is a must.

"And a proper sealing is a must" (quoting the responder above me).

Sealing decreases the hardness of the anodic coating.

Marc Green
anodizer - Boise, Idaho
2006

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"Trouble in Your Tank: Handbook for Solving plating Problems"
by Larry Durney

on AbeBooks

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on eBay)

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Thanks much, all. Timur's closing sentence followed by Marc's rejoinder proves Durney to be the smartest guy in the room even if he's with us only in spirit these days :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2013