THE Materials Oracle
Join Date: Feb 2006
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Fatigue is a microplastic yielding phenomenon. It affects all materials (yes, even those ones that are claimed to have a fatigue life limit, like steel and titanium. It only visibily exhibits in them under ultraherzian loadings, though). At grain triple points and other such extremely high energy internal defects - ones that magnify applied stress locally so significantly that the point loadings are above the macroscopic yield strength of the material, work is built up by repeated sub-macroscopic yield loadings that at tiny points, the local work causes miniscule fractures. Once those fractures have occurred, the only way to heal them is by incipient melting.
So no, unfortunately, while solution treating and aluminium alloy frame and then re-aging it may remove almost all the plastic work done to the frame by a recrystallisation process, it won't weld the microcracks up, unless you take it high enough for them to melt together. You'll get a degree of sintering, but not proper melting.