Dave Long dl at silcom.com
Fri Sep 26 14:21:05 PDT 2003

> For  decades, 6061-T6 has been the alloy most often used to make
> sailboat spars.  Googling on the terms "6061," "T6," and "mast"
> returns over 1,500 hits. Walk to a nearby marina, and you can gaze
> at dozens or hundreds of tubes made from this alloy.

... and not only that, but aluminum is not
too terribly difficult to weld with devices
that go for a few hundred bucks.

Between that, and my shop instructor saying
that a weld always ought to be stronger than
the parent metal, I was figuring that there
was misdirection involved, with journalists
being told 6061-T6 instead of a stronger,
lighter, more difficult to weld metal such
as Bolcer mentioned.

However, after a little research, it seems
that Rogers is correct about 6061-T6: the
T6 stands for "heat treated, artificially
aged" (in oaken casks, no doubt), and the
welding process seriously weakens alloys
like this, so it may be that the limiting
factor is tooling to scale up processes
like aluminum can extrusion to centrifuge
scale. [0,1,2]

That would be especially reassuring if it 
turned out that extrusion gets very tough
very quickly for increased cross section.
Does it?


:: :: ::

(I have no idea how precisely one would
have to manufacture something to spin at
that many g's.  Even a nice bicycle frame
TIG weld might be the equivalent of a few
bowling balls in the dryer. [3])

[0] http://www.alcotec.com/atfas.htm
[1] http://www.lincolnelectric.com/knowledge/articles/content/comistakes.asp
[2] http://www.cancentral.com/canc/nontext/manuf.htm
[3] http://www.straightdope.com/mailbag/mspincycle.html

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