• The serrated chip geometry can be predicted effectively with average value. • The serrated chip formation can be modeled effectively in time domain without measurement of chip geometry. • The critical shear strain rate for the disappear of crack in machining of cast aluminum alloy are presented. The geometry of serrated chip is of paramount importance to the analysis of physical and thermal phenomena in chip formation process, and it can affect tool fatigue life, surface finish and geometric accuracy of the machining part. This paper presents a novel geometry model of serrated chip segment based on chip formation and cutting force in metal cutting by considering the difference between deformation of shear band and primary shear zone. Where, focusing on the high-speed machining, it key points about the geometry of chip segment, shear band angle, secondary shear angle, third shear angle (curvature angle of second shear band), the strain and its rate, and their evolutions in chip formation process are developed, respectively. Finally, the experimental and simulated instances can verify the proposed method. The results can show that this proposed model having a high accuracy can effectively reflect the evolution of chip segment. The shear angle is silent increased with increase of feed rate, while the difference between shear angles is decreasing with increase of feed rate. While the shear strain is increasing with the increasing feed rate and decreasing with increase of cutting depth, the cutting velocity can enlarge the difference. The critical shear strain rate and cutting velocity for the disappear of crack in chip for feed rate of 0.117mm, 0.14mm and 0.187mm are 1.566e 5 1/s and 32.71m/s, 1.486e 5 1/s and 35.98m/s, 1.279e 5 1/s and 39.25m/s, respectively, which decreased with increased of feed rate.