Why is a light metal not used to make car bodies?

Audi and a few other manufactures have used aluminum in their cars for the body, however there are some drawbacks. Light metals are often not very strong, and as a result bend and dent very easily, they are also very expensive to manufacture, and nearly impossible to repair. On top of that they are not as strong as steel and have a tendency to crack when impacted at lower temperatures when thinned out to be malleable enough to make auto body panels.