Roof panel corrosion?

[Busterboo]

1 E89 roof panels are aluminium, aren't they? (Well, my 'Hello Kitty' fridge magnet says they're not ferrous, anyway.)
2 Assuming they are, is the prime suspect for damage galvanic corrosion?
3 If it is, are all our E89s in danger of such damage, then?
4 If it isn't, is there another known cause?

 

[AnubisZed]

1 E89 roof panels are aluminium, aren't they? (Well, my 'Hello Kitty' fridge magnet says they're not ferrous, anyway.)
2 Assuming they are, is the prime suspect for damage galvanic corrosion?
3 If it is, are all our E89s in danger of such damage, then?
4 If it isn't, is there another known cause?

1, Yes
2, :idunno:
3, Yes
4,

 

[pvr]

Like with alloy wheels, corrosion normally start where there was a stone chip.

 

[Pondy]

BeardyJon summed it up well on the other roof corrosion thread IMHO:

Quote:
“Rust” is another name for Iron Oxide, which is produced by the chemical reaction of Iron and Oxygen. The process of Oxidation is also known as corrosion and Aluminium is also susceptible to corrosion when exposed to Oxygen. So, no Aluminium can’t “rust” (because it is not Iron) but it can corrode and if its not properly sealed and protected it will react with atmospheric oxygen to produce Aluminium Oxide. That’s why there are a lot of cases of this happening to z4 owners. If your car hasn't suffered then you're one of the lucky ones I guess but it doesn't mean it can’t happen.

The roof panels are folded at the edges and more so in the corners. The roof panels sit against rubber seals when closed. Moisture seems to sit in the gaps and gets into the folds of the ally. If the paint hasn't sealed the folds on the underside, the moisture tracks under the paint and causes corrosion to the metal which gives the paint nothing to adhere to, so bubbles. That's how I see it happening anyway.

 

[Busterboo]

My aluminium bonnet has plenty of stone chips, but zero corrosion. The wings are aluminium, too, but (chip and) corrosion free.

Accordingly, I'm tempted to believe galvanic corrosion is the culprit on other owners' roof panels.

That said, whatever the cause, it can happen to all of us, of course, and, when it does, 'money out of BMW' and 'blood out of a stone' will sound identical.

 

[AnubisZed]

My aluminium bonnet has plenty of stone chips, but zero corrosion. The wings are aluminium, too, but (chip and) corrosion free.

Accordingly, I'm tempted to believe galvanic corrosion is the culprit on other owners' roof panels.

That said, whatever the cause, it can happen to all of us, of course, and, when it does, 'money out of BMW' and 'blood out of a stone' will sound identical.

Agreed, my roof paintwork was not damaged from the outside, the bubbling came from the inside and, surprisingly, at the same place as most others have. Up to that point no issues at all, rubbers hadn't been touched and no chips, so no reason for it to happen from an outside source.

It did take a bit of time for BMW to agree it, but I do think that the manager at Nottingham Sytners wasn't exactly bothering to give it any attention whats-so-ever, in fact I'd go as far as to say he was totally £*$&ing useless!