Sealing anodized or cc layer ? 2

[freiheitsgrad]

Hi Guys,

first: Nice to be here, this is my first thread !

I'm currently working on a project for ESA and am diving through the requirements for surface finishing of aluminium.

In the requ. there is a passage saying "...anodized layers and CC layers shall be sealed ... when used as the final surface finish of a part."

Maybe one of you can help me with this:

- Why sealing an anodized or chemical conversion layer ? Aren't they supposed to reduce the affect of corrosion on the surface and can be considered being sort of "inert"? (BTW: no corrosive media in space ...)
-If it's really necessary to seal them ... what could be the desired process ?

Thanks a lot in advance,
Bikeit

 

[mcgyvr]

http://en.wikipedia.org/wiki/Anodizing#Sealing

 

[swall]

Unsealed anodic coatings on aluminum are porous, so for corrosion resistance, they need to be sealed. The sealing process closes up the pores in the columnar aluminum oxide structure. Sealing reduces the film hardness, so for wear resistance the coating is left unsealed. Never heard of sealing for chemical conversion processes. Even if your application is in space, the sealing might be beneficial to protect the parts from corrosion during storage and transit.

 

[freiheitsgrad]

Thanks for your informations. Actually i overread this part (sealing) of information in the german wikipedia-article, since the german keyword for this process is more like "compacting" or "densify" the anodized surface.

...learned something important.

Again: thanks a lot for your support!

 

[SixtySpeedTwin]

Hi, I passivate aluminium parts (interlox 338 or iridite NCP) this both protects the surface and allows the part to be conductive. For me this earth bonding is very important (electroincs industry). The passivation coat also provides an enhanced base for painting too.