"Rust" is just a very non-technical term for metal oxidization, such as iron, aluminum or even titanium. Here's some interesting reading...
http://www.popsci.com/popsci/how2/article/0,20967,693558,00.html
and
http://www.popsci.com/popsci/how2/article/0,20967,1076497,00.html
By the...