On the silicon spheroidization in Al–Si alloys

It is commonly known that eutectic silicon spheroidizes during a T6 solution heat treatment in Al–Si cast alloys. This spheroidization of the brittle silicon is the main reason for the good fracture elongation values in peak hardened T6 condition. As the silicon spheroidization is known as a side effect of common T6 treatment, there is little known about the influence of sole silicon spheroidization on the mechanical properties. The following paper presents fundamental aspects of the spheroidization process of eutectic silicon in Al–Si cast alloys. It is theoretically as well as experimentally found that the disintegration and spheroidization of well modified eutectic silicon is finished within minutes of exposure to temperatures above 500 °C. The application of this new silicon spheroidization treatment (SST) to thixoformed components results in outstanding fracture elongation values (up to 18%) at good yield strength level (∼230 MPa). FEM simulations of the short high temperature heat treatment confirm a short process time for successful SST even for components with notably variable wall thicknesses.