Anodisation of an anodized sample

[kapot]

Is it possible to anodize a sample which has been already anodized?

 

[swall]

No, you will need to strip the part and re-anodize.

 

[kapot]

What will be the consequence if it will be done? A supplier did anodise a casted aluminum part. However the dimensioning was not conform specification, so he anodised it a second time, which resulted in acceptable dimensions.
The purpose of this anodisation is mainly to increase corrosion resistance (no aesthetic purpose).

 

[swall]

Anodize is a self limiting process in that once the film thickness builds to a certain point, the re-dissolution by the acid will remove film faster than it will build. So, if you put the part back in the acid (you of course would have to re-establish your electrical contact point), the film will start to dissolve. The anodizing will be slow and uneven, as the only way the bath can reach the substrate to build more film is via the pores in the anodize cells. Not only will this be slow until the process gets re-started, but in the meantime you will be continuing to remove the film you already have.