Failure of adhesion of powder coating over hard anodizing.

Good Powdercoat adhesion over anodised surfaces is notoriously difficult if not impossible.
The best way to understand this is to regard Anodising as a surface inwards process and powder as a surface outwards process.
You basically have no "key" to promote adhesion.
It is not good practice.
Hope this helps,
Regards,
Bill

Hi Terry,

Hard anodising is a thick dense aluminium oxide layer on the aluminium substrate. The pores that occur in the structure of the anodising are much smaller than you normally get with either chromic or sulfuric anodising. This means that there is less of the mechanical key to get the coating to stick. It also means that the anodising is more sensitive to surface contamination. Your paint applicator may want to look at the cleaning regimen prior to powder coating.

One other thing is that the hard anodising may have porosity in it (as opposed to pores in the aluminium oxide cells, this is intercellular porosity, sometimes called the "Christmas Tree effect", as when you section through the porosity it looks very much like a christmas tree pattern), this may have trapped sulfuric acid in from the anodising process which may be leaching out during the curing process for the powder coating and this may well be causing adhesion problems.