[TowerTalk] 6061-T8... new alloy

[Scott MacKenzie]

6061-T8 is not a new alloy, but a relatively new temper.

6061-T6: Solution heat treated and then artificially aged. Mechanical
property limits not affected by cold working. Most alloys in the -w and -T4
conditions artificially aged to -T6.

6061-T8: Solution heat treated, cold worked and then artificially aged.
Applies to products which are cold worked to improve strength, or in which
the effect of cold work in flattening or straightening is recognized in the
mechanical property limits.

This is usually done at a mill.  The basic idea is to create a mass of
dislocations for the precipitates to nucleate upon.

Fatigue data for 6061-T6 is available from
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=E60AF71CD3AE67A22DF4A0B
249C59A92?purl=/10157028-oVWp5b/webviewable/

>From matlib.com:
6061-T6 Fatigue Strength:
96.5 Mpa (14000 psi) @ 5.00e+8 Cycles 
Completely reversed stress; RR Moore machine/specimen

Since the T8 temper has a lower hardness, with corresponding lower yield and
ultimate strength, I would suspect that it would have a crresponding lower
fatigue strength.  

Scott aka KB0FHP

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Thomson
Sent: Friday, July 09, 2010 8:40 AM
To: towertalk at contesting.com
Subject: [TowerTalk] 6061-T8... new alloy

I noticed on DX eng's site that they sell boom material, made from 6061-T8.

Now this T8 version I had not heard of.   It's a full 10 ksi stonger  [in
yield strength]
VS  6061-T6.  That equates to 28.6%  stronger..which is nothing to sneeze
at. 

The boom material they sell is all .120"  wall.    Now this stuff is superb.
It all telescopes
into each other.  IE:  1.50"-1.75"- 2.00" - 2.25" -2.5"-2.75"-3.00" 

I don't know how long the .120" wall has been out for.  it appears to be
only available in the
new  T8 version.    T6 has been available in .125"  wall  for many sizes..
like above, BUT they 
don't telescope, which is a real pain.   You have to turn it down in a
lathe, etc.. to make it fit
inside the next size up.  

The .120" wall has always been available for steel tubing.  Dunno why it
took so long to do the same for AL tubing ? 

How long has this new 6061-T8  been available ??   It would be the answer,
and a quick fix to one of
my new boom projects.

Later.. Jim   VE7RF 
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