Microstructural development during equal channel angular pressing of hypo-eutectic Al–Si casting alloy by different processing routes

An as-cast Al–7 wt.% Si alloy was subjected to repetitive equal channel angular pressing (ECAP) using a 90° die at ambient temperature and following either route A, which involves monotonically increasing strain through a sequence of passes, or route BC, wherein the strains are redundant after every four passes. Microstructures were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and orientation imaging microscopy (OIM). The shape changes of the microstructure constituents mirror the idealized straining for repetitive processing by these routes. Thus, the morphology and distribution of the eutectic constituent in processed materials reflect mainly geometrical effects, although elongated Si and Al5FeSi particles in the eutectic are also broken up. Grain refinement in the primary Al constituent is also strain-path dependent: grain subdivision combined with geometric effects is operative in material processed by route A, while grain subdivision alone predominates in material processed by route BC.