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Corrosion of Type 3003-H14 Perforated Anodized Aluminum

Q. We had an Anodizer clear anodize some perforated 1/8" 3003 H14 aluminum panels. The job looked good until the were installed inside an airport in Corpus Christi Texas after being up for three to four weeks they started showing white growing out of the holes. I feel not knowing anything about anodizing that the panels where not sealed completely and that allowed for oxidization to form. The anodizer is telling me now he can not get a seal at the edges of the perforated holes why not?

Jeff Boucher
- Hudson, New Hampshire

A. Jeff,

The pore structure of the oxide in anodizing grows from the surface outward at a right angle (straight) If you have a sharp edge it will not cover that area. A radius is the only way of compensating for this. If the parts are thin that may be impractical or impossible. Lacquering the holes may be an option.

Drew Nosti CEF
Member AESF Light Metal Committee
Member AAC Hard Coat Committee

drew nosti
Drew Nosti, CEF
Anodize USA
supporting advertiser
Ladson, South Carolina

A. Another option here could be anodizing the part, then clear chromate conversion coat the holes of the part with a artists brush and some patience. If the chromate gets on the anodized finish it should not harm it in any way that I know of. And this should delay or eliminate the problem you've seen occur. The chromated holes will not take much in terms of physical abuse, but in terms of corrosion resistance, you'll be just fine.

Matthew Stiltner
plating company - Toledo, Ohio

A. Drew may be perfectly right with the "edge effect" explanation, however, I'd suspect that it's more than that. For instance, a dull punch can rip the metal and create crevices or fissures that can entrap sulfuric and other corrosive agents. As such, no anodic film can form around or over the cracks. Both "edge effect" and ripped metal can be overcome by heavy etching and moving the panel so the etchant moves through and around the edge. Anodically speaking, good luck!

milt stevenson jr.
Milt Stevenson, Jr.
Syracuse, New York

Q. An architect has asked us if 3003-H14 perforated metal, .125" thick with 3/8-1/2" dia holes needs to be anodized for a rooftop application to hide mechanical components and as an architectural detail?

Michael Wiebeck
- Toronto, Ontario, Canada
November 1, 2016

A. Hi Michael. Something has to be done to it: A fluoropolymer paint like Kynar, or powder coating, or anodizing. Leaving it uncoated would probably prove to be a corrosion problem and an aesthetic issue.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
November 2016

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