Serrated flow of aluminium alloys influenced by precipitates

Serrated flow (which is normally a consequence of interactions between diffusing solute atoms and dislocations) is affected in various ways by precipitation. New models suggest that the shearing of precipitates is directly responsible for the serrations. To test this possibility, an aluminium–lithium alloy was examined. Tensile deformation curves exhibit serrations which previously have been shown to be of two different kinds. Further characteristics of both these serration types (e.g. the stress-drop size, the drop time and the drop rate) are measured after different annealing and ageing procedures, and were also found to be influenced by the presence of coherent δ′-precipitates, but within the limits of their normal behaviour. It is concluded that the normal drops which are initiated by a solid-solution effect are just modified in the aftermath of dislocations overcoming the precipitates due to altered structural conditions.