Rust Problems in Cars

An ominous brown stain on the fender, a bubble in the paint at the bottom of a door, suddenly soaked floors after hitting a puddle—these are signs the iron worm has been hard at work. Otherwise-good cars are regularly sent to early graves because of rust, but the problem is preventable. With iron-based metals, battling oxidation can be a Sisyphean task; in spite of the advanced coatings and alloys developed by chemists and engineers, steel's unstable chemical makeup means it will always succumb to rust in a natural environment. This doesn't mean your car is doomed. Understanding the rusting process, the problematic areas, and the ways to address trouble means your pride and joy can stay on the road as long as you do.

Red Dust Redefined

Rust is the layman's term for the electrochemical breakdown of iron-based metals called oxidation. In this process surface molecules react with oxygen in the air and produce a new molecule, Fe₂O₃, otherwise known as iron oxide. Iron and most steel will completely reduce to iron oxide and constituent elements given enough time. Very poorly made cars in the '70s began showing surface rust as soon as they hit the docks, and untreated, raw sheet steel can rust through in a matter of a few years.

Surface Rust -The first signs of a problem pop up in paint nicks, cracks, and scratches. An easy fix.

Rust preys on the structural and chemical impurities in metal alloys at the microscopic and molecular levels. Pure iron doesn't oxidize as aggressively; examine an old iron engine block and you'll see a thin surface layer of rust but little penetration into the metal. Unfortunately, iron isn't a particularly good material to build cars out of. Adding a dollop of carbon to iron creates steel, which offers dramatic improvements in flexibility, tensile strength, and form-ability. But by definition this adds impurities—impurities that accelerate the rusting process.

Scale Rust- The chemical process corrupts the surface and reduces metal strength.Exposed steel rusts at different rates depending on several factors: alloy components, thickness, the environment the steel lives in, and the type of heat treating the steel undergoes. Alloying elements such as nickel and chromium can be added to stave off rust, but nothing is foolproof—everything eventually corrodes. The effect is accelerated by the presence of any kind of salt. Road salts and other contaminants dissolved in water act as electrolytes, and when introduced to the reaction site, they make the exchange of molecular components much faster. In the real world, this means dirty or salty water trapped somewhere in the car's body makes that spot rust faster—no surprise there. It also explains why cars in northern climates, where salt is used in winter, are prone to rot.

How to Fix Rust Spots On a Car

Automakers do a lot to try to prevent corrosion. A huge amount of testing and materials science is dedicated to keeping your car from dissolving away beneath you. Aluminum and magnesium components are becoming popular because of their light weight, but they also corrode at rates that are unnoticeable within a human lifetime.