Summary for hard anodized finish Discussion
hard anodized finish is the focus of this thread, but the answers are cautious rather than definitive. Jeff Kaloski asks whether Lukon 24 type III hard anodize on 6061-T6 aluminum can survive up to two months of continuous saltwater immersion on a naval mast with a sonar attachment, noting only a mil-spec salt-spray requirement of 14 days and five or fewer pits. Todd Osmolski says he does not know how hard anodize will perform, but points out that painted cast-aluminum outboard engines with sacrificial zinc anodes can last for years. A later answer explains that many hard anodize coatings will not meet 14-day salt-spray demands without extra protection such as sealing. It adds that hard anodize is often left non-sealed to preserve abrasion resistance, but sealing is recommended for this application and can push corrosion resistance well beyond 1,000 hours on some alloys.
Q. I’m working with a naval contractor attempting to extend an 6061_T6 aluminum mast into salt water with a sonar piece attached to the end. To comply with periods of up to 2 months of continuous saltwater immersion, we are planning on using a Lukon 24 hard anodized finish. The mil-spec states this type III finish must survive 14 days under a constant salt water spray with 5 or fewer salt induced pits. This is the only corrosion analysis I have on this type of finish. Does an anyone have any experience or knowledge pertaining to this finish’s corrosion resistance?
Jeff Kaloski
– Pasadena, California
2003
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A. I have no idea how hard anodize will work. I do know that paint on cast aluminum outboard engines with sacrificial zinc anodes holds up for years.
Todd Osmolski
– Charlotte, North Carolina, USA
2003
A. Not many “hard anodize” coatings will withstand the rigors of 14-day salt spray without additional treatments such as sealing. As “sealing” can lower the abrasion resistance of hard anodic coatings, hard anodize is typically provided NON-SEALED. Your applications calls for the added protection afforded by sealing; some work better than others extending corrosion resistance to well over 1,000 hours on some alloys.
Milt Stevenson, Jr.
Plating shop technical manager – Syracuse, New York
2003