Precipitation and serrated flow in AlZn10

Precipitates were analysed for size and amount by means of small-angle X-ray scattering. The results were correlated with the occurrence of serrated flow in tensile tests. A large number of small, coherent precipitates prevents serrated flow by way of trapping vacancies. Larger, and incoherent, particles do not suppress it. Not relevant for the majority of the results is therefore a recently proposed model according to which the cutting of precipitates is the reason for serrated flow. But certain trends are reversed for heat treatments which produce only fine precipitates. Although these data could not be interpreted unambiguously, they might point to a modification of the serration-initiating mechanism.