Computer simulation of annealing and recovery effects on serrated flow in some Al-Mg alloys

Strain to the onset of serrated flow (epsilon(c)) remains an important meas ure of formability for aluminum alloys, especially in the 5XXX-series (Al-M g) alloys, since serrated flow can signal undesirable surface appearance as well as premature fracture. For this reason, extensive experimental and th eoretical work has been performed in order to identify the key parameters t hat affect the onset of serrated flow. In particular, it has been determine d that thermal treatments applied after cold rolling can favorably impact t he epsilon(c) of an Al-Mg alloy (5182 can end stock). Recent developments of dislocation density-related constitutive modeling pr ovide a unique opportunity to theoretically address this important problem. Using the Ananthakrishna model described and extensively tested previously , results are presented here to show that recovery processes (as simulated by a reduction in the initial density of dislocations) can cause significan t increases in epsilon(c), in agreement with the aforementioned experimenta l results. Smaller initial dislocation densities can result in a considerab le delay of serrated behavior. Using standard computational tools used in n on-linear dynamics (phase portraits and bifurcation diagrams), the influenc e of recovery (as mimicked by initial dislocation density changes) has also been examined on Luders behavior, and results which confirm previous semiq uantitative considerations in the literature have been obtained. The model in its present form is limited to homogeneous straining and, thus, cannot t reat the propagative instabilities often observed in experiments. Therefore , the next step in the theoretical development will be to include effects o f nonhomogeneous strain.