David Barker wrote:

If I rememeber my limited metalurgy  correctly, I think the hardening
Aluminum to T-6 takes 8-11 hours at ~900 degrees F not 350 degrees.
Dave  Barker

Paul and list,

The July 2003 Custom Planes (the latest issue, I think) has an article
called "Choosing the Right Metal for Various Applications" (p. 62). The
author, Ron Caraway, writes:

"6061 is alloyed with chromium, copper, iron, magnesium, manganese, silicon,
titanium, and zinc. Cold working in the "O" condition is readily performed.
The alloy is notably less easy to cold-form in the T-4 and T-6 condition.
Annealing is a little more complicated than [aluminum grades] 1100 and 5052.
To anneal 6061 it should be brought up to 775 degrees F for two to three
hours, followed by controlled cooling at 50 degrees per hour down to 500
degrees F, then air cool. This material can be hardened by either aging or
solution heat-treat. The aging precipitation heat treatment is done at 350
degrees F for eight hours, followed by air cooling. This produces a T-6
condition and can be done afer annealing and welding, but the welded
material will be somewhat weaker. Solution heat treating is complicated and
requires the material to be heated to 990 degrees F for an adequate time to
allow for thorough heating and then water quenched. Precipitation hardening
is done at 320 F for 18 hours and air cooled, followed by 350 degrees F for
eight hours and then air cooled."

I don't know if Mr. Caraway is an authoritative source but he seems to have
done some research.

Barry Gardner
Wheaton, IL

 
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