X5 aluminum running board shows rust?

[keroppi]

I got a question and wonder if any of you has any idea:

I can see some very fine dots of rust on the aluminum running board on an X5... can it rust?! I thought the aluminum running board is real aluminum...??

[97'Scort]

It still can be aluminum. If any work was done on the car that involved welding, cutting or grinding, it is possible for tiny bits of slag to be embedded in aluminum, plastic or glass parts (my passenger side window has slag in it from a careless torch cutter).

There is, however, another explanation. Iron is sometimes used as filler in cheap aluminum alloys since aluminum deposits are often found with trace amounts of iron present. Iron is extremely soluable in liquid form in liquid aluminum, and can wind up in the alloy. Usually, however, the aluminum acts as a sacrificial anode and prevents the iron from rusting. However, if other elements, such as nickel, are not added, any iron exposed to the elements will rust like any other iron.

[blinkme_210]

It's probably road tar. Grab some clay bar and work that running board.

[cloud7]

just use some aluminum polish to wipe the rust off.