Thermal stability of model Al–Li alloys after severe plastic deformation—Effect of the solute Li atoms

The results obtained in the present study demonstrate the effect of various modes of severe plastic deformation (SPD) on the thermal stability of model Al–Li alloys (Li atoms in the solid solution). Two aluminium–lithium alloys (Al–0.7 wt.% Li and Al–1.6 wt.% Li) were processed by hydrostatic extrusion (HE) and equal channel angular extrusion (ECAE). The thermal stability was estimated using differential scanning calorimetry (DSC). The DSC analysis confirms that the recovery and grain growth occur systematically at lower temperatures and at reduced activation energies in the alloy with the lower lithium content. The effects of microstructural changes taking place in the deformed aluminium alloys during annealing were evaluated by Vickers micro-hardness measurements. In all the specimens only a weak softening occurs at the lowest (373 K) annealing temperature. In the specimens annealed at 556 K, an intensive hardness decrease was observed after the shortest time of annealing (for example: annealing the HE-treated Al–1.6 Li alloy for 30 s leads to a decrease of HV0.2 by about 8%). The results show that the thermal stability of the alloys increases with increasing solute content.