The T6 heat treatment produces maximum strength
(hardness) in aluminium alloys. Unfortunately it requires a
relatively long time to be carried out and therefore has significant
financial implications. The heat treatment cycles that
are currently applied to semi-solid processed components are
mostly those that are in use for dendritic casting alloys.
These heat treatments are not necessarily the optimum treatments,
as the difference in solidification history and microstructure
of rheocast components should be considered. No
agreement has been reached on what the optimum heat
treatment conditions are for rheocast components. The optimum
solution temperature would give the best compromise
between energy savings, time savings, lower risk of distortion
and maximum dissolution of alloying elements. It appears
as if 540o
C is the optimum temperature for A356 in
terms of the compromise between shortening heat treatment
time as well as minimising the risk of blistering and distortion
[3,4]. According to Rosso and Actis Grande [4], the
shortest possible time for solution treatment of rheocast
A356 at 540o
C is 1 hour. However, according to Dewhirst
[3], the optimum solution treatment time at 540o
C is 4 hour