Posted by CK on February 05, 2001 at 14:51:41:
In Reply to: Re: Re: Re: Re: Re: Re: thin vs thick metal horns posted by Rick Denney on February 05, 2001 at 14:08:14:
From http://www.biowheels.com/Article.asp?PostID=91
..."The net result is a stronger, harder, and stiffer material. The growth of these local concentrations of copper in the case of 2xxx alloys, is the fundamental strengthening mechanism of heat treatable aluminum alloys. It is called age hardening. Age hardening carried out at or near room temperature is called natural age hardening.
If external heating is used the process is called artificial age hardening. Higher temperatures allow more atomic mobility and larger disks of copper can be formed. In addition, the intermetallic Cu2Al phase can be formed. The higher the temperature the faster the growth, too fast if one is not careful. If the alloy is heated for too long or too hot, then it will become soft again. This is because Cu2Al precipitates fully form into a separate phase and coalesce into significantly fewer particles. An abrupt discontinuity occurs between the parent phase lattice and large Cu2Al precipitates, and dislocation can pass around the particles unhindered. The net result is a soft, unstrained parent matrix with hard particles here and there. The Cu2Al particles are large enough that you can see them with an optical microscope.
The highest hardness from age hardening aluminum alloys is usually obtained by artificial age hardening. Very careful temperature control and heating times can result in an alloy with finely dispersed GP-Zones and just barely formed Cu2Al particles. This alloy seems to have the highest values of strength, hardness, and stiffness.
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Also: http://129.115.20.102/materials/Experiment7.html
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Also: Check out pp. 161-162 of "Metals in the Service of Man" by W. Alexander & A. Street. All about age hardening of aluminum.