Analyzing time series of serrated flow and the dependence on structural heterogeneity in Al-Mg-Sc alloy

Friction stir processing was applied to Al-Mg-Sc alloy, improving the mechanical properties and causing the serrated heterogeneity due to structural fluctuations in stirred zone (SZ). We found that the serrated behavior can be dominated by microstructure, not necessarily initiated under the intervention of temperature and strain rate, which stimulated the exploration of the dependence between structural heterogeneity and serrated heterogeneity. The time series of strain and strain rate were used to explain the formation and transformation of Portevin-Le Chatelier types in serrated heterogeneity. Since the time series of strain rate possessed intense periodicity and the peaks were at similar levels, serrated flow was inclined to Type A. Once the periodicity was broke or/and the peaks sharply increased, it would induce the failure of Type A and promote the transformation to the Type B with discontinuous propagation. In addition, we found that the serrated heterogeneity decreased with the increase of texture strength, while the increase of precipitated heterogeneity would strengthen serrated heterogeneity. Ultimately, the dependence between structural heterogeneity and serrated heterogeneity was discussed, which is beneficial to understand the nature of the material within SZ and the uniformity of processing area.