What is the Corrosion of steel car bodies?

Answer 1

Put simply if you take a sheet of ordinary steel like they make car bodies out of, and leave it exposed to the weather, within a year all you'll have is a pile of rusty bits on the floor.

So whats going on here? Well the main component of steel is Iron, and its the iron that's turning to rust. Iron on itself is a fairly reactive metal, and as it combines atom by atom with the oxygen in the air you get iron oxide or rust.

However if you stick a piece of the same steel in a tank of pure oxygen the rate at which it rusts will be slower.

So whats going on there? Rain! you see the rain contains loads of impurities that make it slightly acidic, and as such its perfect for speeding up that chemical reaction of turning the steel into rust.

So what do manufacturers of cars do to stop this? There are several ways of stopping this from happening. They all are basicly doing the same thing, putting some form of barrier between the steel and the air/rain.

The first and most obvious is to paint the car, once upon a time the undercoat was done on the production line by men with sprayguns, now they dip the cars in baths of paint, this ensures that every nook and cranny of the car gets painted and stops the car from being exposed to the elements. They also apply sealants to keep water out of the seams on the body.

Finally there's the wax polish many people use, a lot of people think that the polish is for the shine, but no, its to protect the car from the elements. When a well waxed car gets rained on you will see the characteristic 'beading' of the rain on the bodywork. This is because the raid can not physically bond to the surface of the paint. In an unwaxed car, the rain forms a sheet which is the rain bonding to the surface of the car.

So how does the corrosion start? The first route is when you get holes in the paintwork, for example stone chips these allow the corrosion to form under the paint, often displaying itself as a rust 'bubble' under the surface of the paint. Secondly and often more critically is bad design, If the rain finds within the seams of the bodywork a natural point where it can collect next to bare metal, from either inferior paint application, or cheap materials used then you will get corrosion points where all cars of a certain design will normally start to corrode at first.