[Bulk] Heat treating aluminum header?

[brian young]

Been a long time since I had a metallurgy class so a google search finds:
 
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLD,GGLD:2004-42,GGLD:en&q=annealing+aluminum
 
http://www.evergreengardenworks.com/copperwi2.htm
 
http://www.tinmantech.com/html/aluminum_alloys_continued.html

Bill Glaze <billglaze at triad.rr.com> wrote:
This is getting to be a rather absorbing thread; at least for me.  I had always been taught that aluminum anneals like brass and copper; that is, opposite to steel.  I had been taught that to anneal aluminum, (or brass, as in cartridge cases, or copper, as in cold worked bullet jackets) that one heats the material, then chills it rapidly.  In fact, even with lead, which most people would think is, well, just lead, that lead in its pure state, or alloyed with the common metals, (tin, antimony, others) can be hardened.  In fact, by heating lead bullets in an oven to just below deformation temperatures, (just below where the bullets would begin to "slump") for an hour, then rapidly immersing them in cold water, I have been able to raise the Brinnell of the bullets from 9-10 to over 20.
What I am wondering is if the aluminum headers are being hardened to brittleness by "work hardening" caused by minute vibrations, repeated thousands of times.
Because the applied exhaust heat would, it seems, tend to put the aluminum in a continual annealing condition.
I was in the aluminum window manufacturing business for many years.  We used several hardnesses of aluminum, and several different hardening processes; heat treating, artificial aging, artificial hardening, etc.
Of course, when flying for United Airlines, in severe turbulence, I found myself hoping that the wing spars hadn't been work hardened to the brittleness stage!
Sorry for the long posting, but, as I said, it is an extremely interesting thread.

Bill Glaze

Karl G. Mueller wrote:
Jon,
 
The problem with the aluminum being heated and cooled every time
you run the engine acts like an artificial aging (hardening). In time the 
material will get very brittle and therefore break very easy. Here is a little
trick you can try that I know works: If you have a self cleaning electric oven
at home, put the header in the oven run the cleaning cycle. Do that at night
before you go to bed and the next morning you header will be annealed.
It has to cool of slowly.This is the opposite process of hardening. This makes
the aluminum more flexible and less prone to breakage.
 
Karl G. Mueller
kgamueller at rogers.com

----- Original Message ----- 
From: JonLowe at aol.com 
To: discussion at nsrca.org 
Sent: Wednesday, September 07, 2005 8:39 PM
Subject: [Bulk] Heat treating aluminum header?


After many many flights, I had an aluminum header break for my OS 1.60.  I had it welded up by a very good welder, but the header broke again after one flight in an area removed from the weld, but close enough that it would have gotten pretty hot.  I suspect that the heat treat of the header got changed.  Any ideas on how to try to heat treat a second pipe that has benn welded to try to at least get more than one flight?  I've odered a new header, but it is not here yet.
 
Thanks
 
Jon Lowe


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