Posted by Matt Wilson on Thursday, April 05, 2001 at 11:46PM :
In Reply to: Another rivet question posted by ROB ROSE on Thursday, April 05, 2001 at 9:06AM :
Aluminum expands anywhere from 1.8 to 2.5 times as much as plain carbon and low-alloy steels for a given temperature change, so one would initially think that the aluminum would contract a lot more than steel when it cools after riveting. However, when you consider that steel may have to be heated a lot more to achieve an appreciable amount of ductility, the amount of contraction that occurs may be similar to that of the aluminum.
On the other hand, some rivets are not even heated, but are simply installed cold.
As for keeping the DD aluminum rivets on ice, there are many aluminum alloys that "age" after heat treatment, when stored above a certain temperature. The temperature varies from alloy to alloy. Some require much colder temperatures than others, in order to prevent or slow down the aging process. Aging allows these aluminum alloys to become harder as time passes. Aluminum alloys that are not heat-treatable are hardenable only by cold-working.
To my knowledge, there are no steels that behave as the age hardening aluminum alloys that I have just described. After heat-treating, steels are already as hard as they are going to get, and they don't require any aging. You wouldn't gain anything as far as retention of softness by chilling your steel parts. To the contrary, when exposed to cold enough temperatures, that is, cryogenic temperatures (on the order of -200 to -350 degrees or so), steels do achieve some additional wear resistance, strength and toughness. I believe this can be done with other types of metals, as well.
Matt
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