MICROSTRUCTURAL CHARACTERIZATION OF SHEAR-BAND FORMATION IN AL-LI ALLOYS

The Al-Li alloy system can provide a unique opportunity to study the thermal history of shear-band formation by following the thermal dissolution of the precipitate phase delta'(Al3Li) as a function of Li concentration and delta' solvus temperature. The metastable delta' solvus increases in temperature with increasing Li concentration. As such, the dissolution of delta' within the shear bands, as a function of Li alloy concentration, can provide an internal temperature probe to study the thermal history of the shear band. Experiments were conducted in which shear bands were produced in specimens at a strain rate of 10(4)/s. It was found that dissolution was a function of strain rate, strain, and Li concentration. The results of this work were used as a means of further differentiating between the two predominant theories on dynamic recrystallization: the classical nucleation and growth with high-angle grain-boundaries model or the subgrain-coalescence model.