Corrosion on aluminum panel - how far will it spread?

[Blue Oval84]

Turns out I own my first aluminium car (Audi TT MK3) and during the first wash, I found a stone chip on the top of the windscreen that has clearly started to corrode.

Is this going to be like rust on a steel car in as much as it will keep spreading, or is aluminium a bit more self-limiting in how far it will go?

I'm assuming it's the former and this will need properly grinding out and respraying?

[paintman]

Check the area with a magnet. That looks a lot like rust.

IME with aluminium or the alloy on Range Rover Classics it does spread, but not with the same speed & does tend to be self limiting.

[Blue Oval84]

Just had a go with the magnet and pretty certain it's aluminium, there was no real grip at all (maybe a tiny attraction from some internal steel reinforcement, or the roof mechanism?), and the magnet slid off down the windscreen.

[Iceblue]

Most panels on the Mk 3 were aluminium for weight saving the corrosion will just spread under the paint if left untreated, if you mask off just above the chip and carefully rub back to clean metal then prime and paint with a rattle can not going over the crease line onto the roof then blend with (Tcut) or similar it will be virtually unnoticeable.

[Blue Oval84]

Yeah I figured it's just going to keep spreading, I think I'll get the bodyshop to do it, every time I've ever tried to use a rattle can on a car the results have been less than pleasing lol. I doubt they'll charge much for such a small area.