Aluminium corrosion

[Ex-SolentBoy]

Exposed anodised aluminium.
White, worm-like corrosion, which, I assume is aluminium oxide.

Am I correct?

I can knock the lumps off with a plastic scraper, but there is still a deposit left.

Is there some chemical way of cleaning it off?

I realise it may be a sort term solution, but I am quite happy with that. Anything abrasive scratches the ali.

 

[TradewindSailor]

Some photos would be informative.

It sounds a little peculiar from you description. Anodised aluminium tends to be fairly robust but will corrode if scratched ... but then this is just a way of protecting itself .... the oxide layer does not continue developing into the alloy like rust would on steel.

I hope this aluminium alloy isn't immersed. Galvanic corrosion or electrolysis would be a big problem if so.

 

[macd]

Exposed anodised aluminium.
White, worm-like corrosion, which, I assume is aluminium oxide.

A photo would help, but the worm-like effect you describe is often associated with corrosion creeping under a lacquered surface (common, for instance, on polished engine castings on m/cycles). Aluminium oxide is present on all non-coated aluminium surfaces and forms a stable barrier to further corrosion, unless other factors are present, such as galvanic effects.

This page may give some useful info: http://www.aluminiumdesign.net/design-support/aluminiums-corrosion-resistance/

 

[Bobobolinsky]

The anodising has broken down, the fluffy white oxides are unstable and will not form a barrier to corrosion. You need to remove with an acid wash, used for aluminium wheels, you can then coat with a laquer to keep the moisture out. This is only a stopgap and the only cure is to remove and re-anodise. When refitting, ensure isolation kits are fitted on the fixings or it will re-occur

 

[Neil_Y]

I believe from my limited knowledge of the corrosion treatment that ACF-50 is able to stop the corrosion cell and protect what is left. Have a read of their data, it has certainly solved this type of issue for me in the past on an emergency tiller Al cover threaded into an Al socket.