Here's a brief article, of uncertain provenance, that says "Most original equipment aluminum wheels are clear coated for corrosion resistance." http://autos.yahoo.com/maintain/repairqa/vehicle_exterior/ques129_0.html Here's a reference that looks more trustworthy: http://www.detailsupplyoutlet.com/pdf_files/tips.pdf It says "Most aftermarket wheels are made of aluminum alloy, whether they are polished, chromed, painted, cleared or powder coated & cleared." A brief discussion follows of various finishes. From the context, it appears that clear-coating is not universal.
@Charles Murray: There's no question aluminum wheels are more expensive than steel wheels. If they were cheaper, do you think Alcoa would go to the trouble of paying for a study to show how environmentally friendly they are?
@William K.: I could be wrong, but I'm pretty sure that most OEM aluminum wheels have at least a clear chromate conversion coating on them. This will not actually prevent corrosion, but the wheel would corrode a lot faster if it didn't have it.
Many aluminum wheels have multiple layers of coating: chromate, primer, silver topcoat, and clearcoat. They may look like bare aluminum, but they're not.
Ann, for many years steel wheels were painted inside and outside because that was the cheapest possible way to make them look good for a while. They would rust when the paint was scratched off, but there were very seldom any leaks due to corrosion.
Today I had to take the new tire on it's rim back to Belle Tire as it had gone flat overnight. The problem was that they had not properly cleaned and sealed the rim on the aluminum wheel. So the problem is alive and well today.
So it sounds like the available coatings are not being applied by automotive OEMs. Considering how long the salt problem has been going on, and how well publicized it's been, you'da thunk by now it would be common--and cheaper.
Ann, my guess is that any coating at all will add to the cost and therefore not be added tp OEM wheels on passenger cars. But some fancy appearance treatment would probably be added if it was not too expensive. I have not seen any originally applied coating on Chrysler product aluminum rims since they have been making them, which is quite a few years. It seems that the management does not accept that corrosion exists. Of course, for Chrysler upper management, vehicle problems don't exist. Cars serviced daily seldom suffer problems.
I tend to think that quality consists of remaining able to meet the service specifications of a product, while it seems that to many others quality equates to the number of features. "What we have here is a failure to commu8nicate", it seems. Unfortunately the marketing wonks all seem to follow those who seek features, regardless of how useless they are.
Mydesign, I'm not sure I understand your question. There was no discussion of changing either the number of wheels or trailer dimensions. The point of the aluminum vs steel wheels, as we state in the article, is that they both weigh less and are strong enough to support tires that can bear heavier loads. This is all part of CAFE-type regulations for commercial vehicles for lowering carbon emissions. Does that answer your question?
@Ann: Looking forward to seeing your new article. Replacing chromate conversion coatings with less environmentally-harmful alternatives is a topic that is very important to me.
We are currently transitioning from a traditional chromate to Alodine EC² to protect aluminum die castings from corrosion. It's a great coating, but, like everything, it has some limitations. One of the biggest is that, since it's an electrodeposited coating, it's very difficult to coat internal passages.
I've often thought that an LCA comparing the environmental impacts of chromate vs. EC² would be interesting. Chromating creates a hazardous waste stream -- but the large amounts of electricity required to apply electrodeposited coatings like EC² don't come without environmental costs, either. It would be interesting to see how they balance out.
(By the way, now that you mention it, Alcoa's LCA for the aluminum wheels doesn't include the environmental impacts of the chromating process, either).
William, funny you should ask that question. I just filed an article--it should publish soon--on a new non-toxic substance for preventing salt corrosion on wrought aluminum–zinc–magnesium–copper AA7000 alloys commonly used in aerospace and automotive apps. Inorganic and organic corrosion inhibitors already exist, but they tend to be either toxic or potentially toxic. Stay tuned.
Oak Ridge National Laboratory has developed a surface preparation method to improve joining carbon composites with aluminum, with potentially far-reaching ramifications for high-volume industrial applications.
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