Meltsner, Kenneth Kenneth.Meltsner at ca.com
Fri Sep 26 18:52:49 PDT 2003

T6, IIRC, is:

1.  Solutionize (heat treat) the piece.  This makes all of the hardening precipitates and cold work go away.

2.  Quench.  This creates lots of little point imperfections, which sets up (3).

3.  Age.  Heat it up again (not as hot as (1)) to get strengthening particles to precipitate out.  How hot and how long is the critical detail, because it's possible to get the particles to grow too big (over-aged) or not big enough.

Welding screws up the carefully created microstructure -- some of the material is heated up to (or past) the solutionizing temperature, and after you stop welding, everything cools off pretty fast.  This creates a soft spot near the weld, and you then need to age  (post weld heat treat) the area, I suspect to get some of the strength back.  Of course, this can screw up the microstructure in the rest of the part, so it's non-trivial to make big parts (which are hard enough to heat treat) this way, and you never end up with a homogenous microstructure.  You could solutionize the whole thing, but it's likely to collapse into a distorted mess because aluminum resembles silly putty at elevated temperatures.


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