Consequently, as shown in Fig. 3, the total quantity of acicular eutectic and primary silicon particles increased with silicon content. Figures 4(a) and 4(b) show that the MRR and the machined surface Ra of both the Al-12Si specimen close to the eutectic composition and the Al-29Si specimen at hypereutectic composition, were significantly affected by the pulse duration, when the fixed EDM current was 20A and the duty factor was 0.67.