After the experiments, the prepared modified samples were cut and mechanically polished from the T6-treated samples. The chemical compositions of the samples were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and the results indicated that its compositions fit well with its nominal compositions. The microstructures of the samples were examined using optical microscope (OM; Olympus PMG), scanning electron microscopy (SEM; Tescan Vega II), and energy dispersive spectrum (EDS; Oxford Inca 350). The following parameters, i.e. mean diameter, aspect ratio, and roundness, were used to describe the characteristics of eutectic silicon in the T6 treated samples magnified at 200 times using Image Pro Plus 6.0 software. The above parameters were defined as follows: