Deformation instabilities in Al-Li based alloys

The Portevin - Le Chatelier effect (PLC effect) was observed in various Al systems. In precipitation hardenable solutions the so called ''inverse PLC effect'' occurred and was often attributed to the interplay between dynamic strain ageing and precipitation. Recently discontinuous yielding was observed also in Al-Li binary alloys and in Al-Li based complex alloys. These alloys contain shearable precipitates of delta' (Al3Li) phase. At present it is still not clear whether the discontinuous yielding in these materials occurs due to the precipitate shearing or due to the dynamic interaction of Li atoms with dislocations. This contribution deals with serrated yielding occurring in concentrated Al and Al-Li based alloys. Specimens were first solution treated and afterwards step-by-step isochronally annealed to appropriate temperatures in order to obtain required initial phase composition and distribution of precipitates. The evolution of the microstructure was monitored by electrical resistivity measurements and TEM observations. Mechanical test with constant stress rate was used and on selected specimens was combined with simultaneous ''in situ'' electrical resistivity measurements.