Posted by David Sherman on Sunday, July 09, 2006 at 12:11PM :
In Reply to: Any Metallurgists out there? posted by Dale on Saturday, July 08, 2006 at 7:00PM :
The worst deterioration of metal I've seen due to age alone (not stress fatique) is in old pot metal castings. I'm not sure what the exact alloy is, but it's zinc based. Many cast parts in antique (1920s-1930s) radios swell, crack, and then crumble simply due to age. I've never seen it happen to a carburetor so they must be made of a better alloy, although I have seen it happen to small cast parts on automotive panel switches, trim, bezels, etc. The odd thing is that sometimes one part of a given type and age will crystalize and disintegrate while another, apparently identical, part will be fine. There must be either some subtle difference in the alloy that allows one part to age gracefully while another falls apart, or some difference in the environment (heat/cold cycles, chemicals, etc).
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