A process for improving 6XXX alloys, such as 6013, preferably includes heating,
hot rolling, inter-rolling thermal treatment at a very high temperature such as
1020 F. or more, again hot rolling (with or without subsequent continuous
hot rolling or cold rolling or both), solution heat treating and artificial aging.
The initial heating, inter-rolling, thermal treatment and solution treatment, especially
the latter two, are carried out at very high temperatures such as 1030 F.
Each aforesaid hot rolling stage produces substantial metal thickness reduction.
The improved sheet or plate product has a substantially reduced occurrence of reduced
density features revealed in scanning electron microscope examination at 500X and
exhibits improved (reduced) fatigue crack growth rate providing an advantage in
aerospace applications such as fuselage skin, especially fuselage belly skin.
