automotive corrosion

[Salvatio]

there're quite some questions which i'd love to ask regarding to the title. Hope you guys could help me out. where could i find the best resources of these?

1. which part of a car corrode the most? i.e. the bottom corner of the door, or even around the wheel. And why does it happen?

2. what is the best way to prevent the latter from happening? metallurgically or by coating?

3. any particular manufacturer in mind, which provides the longest-lasting car? Volvo?

Thank you.

 

[TheBlacksmith]

Areas that trap dirt and road chemicals and remain damp. Hardly a definitive answer, but its true. Many cars have a lip around the fenders that holds stuff and the fenders rust right around the opening, some have traps in reinforcement ribs underneath, some doors have leaky window seals and plugged drain holes...

Blacksmith

 

[rorschach]

in any corrosion situation four things needed to exist in order for corrosion to take place. you need an anode, you need a cathode (these can be different grains or a grain and an inclusion of the same part), you need an electrolyte (water is almost always the electrolyte) for the generated hydroxyl ions to flow through, and you need an electrical return path for the electrons to flow in. remove/disrupt any of those four and no corrosion will take place. paint serves as both an insulator (between different parts but not when both anode and cathode are the same part) and a barrier to the electrolyte. zinc serves as a sacrificial anode that will corrode preferentially to surrounding steel but it's life is limited. corrosion in autos is almost always due to design tradeoffs that trap moisture and chlorides (road salt)which in the presence of water increase the production of hydroxyl ions if my corrosion training is being remembered correctly.

 

[JEB66]

In addition to all the items above, I feel the owner plays a role as well.

The people who wash their automobiles often will greatly delay the onset of rust compaired to those who never wash their cars.

 

[EdStainless]

There are some inintended issues as well. If you live in a location that uses a lot of road salt in the winter you will see that cars parked outside have less corrosion than ones that are in garages. The frozen road slush in not corrosive (no electolyte) but when it melts at night it can do a lot of damage.

Other locations that rust a lot are anywhere that the standard protection has been damaged. Holes where trim is attacked aren't protected like the inside and outside surfaces.

I will say that lot has changed in the last 15 years. It used to common to see cars less than 6 years old with noticable 'edge' or door bottom rusting. Any more it is rare on cars less than 15 years old. My '92 Carprice was spotless when I sold it last year. My '96 Ford and '96 Volvo are both spotless (at least as far as rust goes). And this is all in the upper mid-west.
This is largely attributable to plastic trim (no holes and no galvanic action), stainless trim and exhaust, two side galvanized bodys, and better paints.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[mshimko]

I think finding and reading a few articles on automotive corrosion, and what's been improved upon the last 20-30 years would be worthwhile, especially since much of what the average person is concerned with may have been significantly improved in recent years.

Just off the top of my head; I recall corrosion of autos becoming a major issue in the 1970s when two things occured: (1) cars were made suddenly lighter which meant thinner sheet metal, and (2) a significant increase of salts to improve winter driving.

But as bad as things were around that time (including the many designed-in corrosion helpers), the auto industry has made great strides to improve. Autos today have fewer crevices, allow for drainage, and are optimally primed.

 

[MetalsInc]

EdStainless brings up a good point. I live far enough north that we actually don't use salt that often on roads - it is not worth it. A garage that is kept around 50F is murder on your car. Warm enough to melt the snow/slush/ice, but not really warm enough to get good evaporation. This is the most common heated garage I run into. I leave my car out all winter, just plugged in. Keeps everything but the engine frozen - except that one time the engine froze.... not a fun experience.