The aforementioned specimens all possessed ridges on their EDMed surfaces and the ridges increased with silicon content. However, it is difficult to distinguish the EDMed surface from the SEM evidence. The craters on the EDMed surface were first investigated with the surface roughness measurer to quantitatively measure the average ridge number of discharge craters, and the moving tracks of the probe were recorded. Figure 7 shows that under specific EDM conditions, a specimen with the highest silicon content (29Si) presents the highest average ridge number following EDM. Figure 8 shows that when the silicon content increased, the ridge density value on the EDMed surface markedly increased with the area fraction of eutectic and primary silicon particles.