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Sulfur difference in aluminum stock

We use 1" sections of aluminum tubing stock as retaining weights to hold punched disks of film flat in an analytical instrument. I needed to have more of the aluminum rings made by our shop department and did a quick comparative analysis of the new aluminum stock to the rings we have on hand. I found that the new aluminum stock has a fairly high sulfur level whereas the old rings have none. Both aluminum pieces have a shiny silver appearance, however the new stock (with the sulfur) has a slightly "grainy" look to it. Would the sulfur we found in the new material most likely be from hardening with a sulfuric acid treatment?

Mark Morse
consumer imaging - Rochester, New York
2003

It is almost a certainty that the sulfur is not a constituent of the bulk alloy. The maximum sulfur content of an alloy is likely to be in the range of 0.2-20 ppm. Sources of sulfur would be lubricants/coolants or possibly from a sulfuric acid anodizing treatment.

Toby Padfield
Automotive suspension modules - Michigan
2003

Yes Mark, there is a difference between alloys and there are subtle differences in lot numbers from the same source in the same alloy. Normally they do not make any great difference, but every now and then it comes up with an absolutely unusable batch for someone's needs. I would go to an 1100 alloy as it has the least alloying materials in it. I would be very curious as to the cutting fluid that your machinist used. Aluminum does not like several commonly used ones.

James Watts
- Navarre, Florida
2003