The work-hardening behavior of modified and base alloys is described through the plot of the instantaneous work hardening rate of θ¼ds/dε versus net flow stress increments of s–sy, referred to as the Kocks–Mecking (K–M) plot [44]. The stages of work hardening by Kocks–Mecking, known as stages II,III and IV represent respectively: linear hardening,reduction of hardening rate,and finally saturation. The hardening stages III and IV are generally seen in polycrystalline materials during compression [44,45]. As seen in Fig. 2b, the instantaneous hardening rate of the alloys,tested at room temperatures,reveal only hardening stages III and IV. The nature of the curves indicates that the hardening rate is higher for the modified alloy in the T6 heat treated condition, than for both the modified alloy in the as-cast condition and the base alloy after T6 heat treatment. At the beginning of stage III, forest dislocation hardening occurred due to the dislocation interactions,accumulation and dynamic recovery of dislocations, which caused a linear reduction of the hardening rate.