Corrosion of Black Oxide 1

[securitech]

Sorry if this has been covered before...

I have two steel parts (Aut20 & 18MnCr5) that need to pass a 200 hr salt spray test (ASTM B117). I read that a black oxide finish can withstand 200 hrs of salt spray if the proper sealant is used.

http://www.pfonline.com/articles/pfd0025.html

Is it really possible to obtain this type of corrosion resistance using Black Oxide? If not, can anyone recommend an alternative black plating/coating that is cost effective?

Thank you very much for your help on this!

Securitech

 

[TVP]

As the article mentions, the black oxide does not provide the corrosion resistance, the "sealer" does. In order to achieve several hundred hours of resistance to red rust in a salt spray test one would need to apply ~ 20-50 micrometers of an organic coating (paint) over black oxide or another pretreatment, such as zinc phosphate. If you want something durable, skip the black oxide and specify a high quality zinc phosphate + ecoat or zinc phosphate + powder coat.

 

[securitech]

The tolerances of the parts are critical. What type of dimensional change does the zinc phosphate + e-coat or powder coat cause?

 

[TVP]

~ 20 micrometers is the typical thickness of zinc phosphate + ecoat. Powder coating is more variable, with thickness usually in the range of 35-75 micrometers.