Aluminium–silicon casting alloys are widely used in the automotive industry because of their good specific mechanical properties. From these alloys we can produce components by Semisolid Metal processing (SSM), with good surface finish and practically free of porosity. The SSM is a new technology that offers several advantages over liquid processing and solid processing. One of the advantages of SSM processes is that laminar flow during die-filling which avoids the problems of oxide and gas entrapment and also reduces the shrinkage problems during solidification [1]. As a consequence, blistering during heat treatment SSM components can be prevented. For this reason the SSM components are susceptible to be subjected to aging heat treatments that allow increasing their tensile strength and yield strength while preserving a high ductility. The heat treatment principles for conventionally cast aluminium alloys are well understood, but the different microstructure and solidification history of SSM components indicate that heat treatment conditions which were optimized for conventionally cast materials are not applicable to SSM components [2,3]. The main heat treatment procedures are homogenization, annealing and precipitation hardening (T6 heat treatment). The T6 heat