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Salt Spray Test v/s Salt Bath Test after Hard Anodising  

June 14, 2008

Does anybody know what is the equivalent comparison between exposing a Hard Anodised Sample to a Salt Spray Test in a Lab as opposed to keeping the sample immersed in a 5% Aqueous Solution in Salt inhouse- or is there no comparison at all?!
I am informed that 24 hour in a salt bath equals 160 hours in a salt spray chamber.Is this correct?
I am keeping 6061-T6 Hard Anodised Sample as per MIL-A-8625,Type3,Class1 in Salt Bath for 51 hours as a n equivalent for 336 hours in Salt Spray as per the standard requirement.
Samples do come out spotless.

Ravi Rao
Hard Anodising Facility Owner-Mechanical Engineer - Belgaum, Karnataka, India

Check your requirements as, in general, hardcoat Type III coatings do not require salt spray testing! There is a statement in the specification that "unless otherwise specified Type III coatings will be unsealed." Obviously unsealed coatings wouldn't stand a chance of passing 336 hours of salt spray. Also, it's not surprising that 6061 will pass - try 2024 as the specification default for corrosion panels suggests. As for the correlation between hours of salt spray and hours of immersion in a salt bath, I've never seen a requirement or standard for salt bath immersion. I've worked with finishing standards for 30 years the last 15 with both ASTM B8 committee and SAE's Committee B which over sees AMS specifications. I can't see why a salt bath immersion would be more corrosive that an elevated temperature, oxygen laden salt spray test. The bottom line is that regardless of what persons respond here, you're bound to comply with the requirements of Mil-A-8625 [link is to spec at TechStreet] and it dictates 336 hours of ASTM B-117 [link is to spec at TechStreet] salt spray.

Milt Stevenson, Jr. Anoplate Corp Syracuse, NY, USA

Dear Milt,
Thanks for your comments!Our Customer's drawings specify Nickel Acetate sealing after Hard Anodising as per MIL-A-8625,Type 3,Class 1.Hence Amendment 1 to Rev.F ,page 2-correction with footnote, is applicable to us,
" Type 3 coatings shall be tested for corrosion only when it is specified that the coating is sealed."
Min.5 specimens need to be Salt Spray tested every month and it is quite expensive.Besides, it takes at least 15 days to get a report from the Lab.If I am processing 40000 sq.in. of material every day,I do not have any indication of the product quality(other than thickness and visual)for 45 days!18,00,000 sq.inches later,it would be too late!So far my Salt Sprays have come out OK(spotless)-but I am paranoid.Salt Bath immersion idea was my only consolation (however misplaced(?!))until you threw it out!!
Any Suggestions?Will be grateful!
Ravi

Ravi Rao
- Belgaum, India