@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.
@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?
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.
William, here's a link to the corrosion inhibitor blog we just posted: http://www.designnews.com/document.asp?doc_id=252049 There's already a lively discussion going about corrosion and aluminum wheel coatings.
Although there is undoubtedly some sort of anti-corrosion treatment applied to most OEM wheels, "the proof is in the performance." It certainly seems that the treatment is intended to last long enough for the car to be sold, and probably for th first year after that. But the person who gets the year-old trade-in is the one afflicted with the leaks. Of course, one other cause factor is the balance weights that are always installed, with the sharp-edged steel anchor tabs that will cut through any protective coating. Perhaps we need a new method of attaching balance weights to replace a system that came into use in the 1950's? Most other automotive technology has advanced a bit since then, after all.
My last vehicle with steel wheels was a 1985 Dodge van that I finally donated in 2003. The one time that I had to replace a damaged tire I did not see any rust or corrosion on the wheel except for the lug-bolt holes, which the paint came off when the nuts were torqued down. And I never had any rim leaks on those wheels, even after all of those years.The paint finish still was a good protector. And it probably was cheaper than whatever the aluminum wheels get.
Ann, how the wheels are relating to carbon emissions? Irrespective of wheel type (Steel or Aluminum), majority of carbon emissions are coming from Engine and type of fuels, am I right. In my previous comment I had raised another concern about weight bearing capacity per cubic cm.
Mydesign, the aluminum wheels are part of lightweighting efforts to reduce carbon emissions. Lighter weight vehicles use less fuel per mile, thus reducing carbon emissions produced per vehicle, per given time period. This is in response to US and European regulations for both consumer and commercial vehicles. Her are a couple of DN articles on US efforts: http://www.designnews.com/author.asp?section_id=1366&doc_id=249877 http://www.designnews.com/author.asp?section_id=1392&doc_id=250828
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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