Outstanding thermal stability of cold-rolled Al–Y alloy revealed using in-situ synchrotron X-ray diffraction and ex-situ microscopy

Abstract

This paper describes the main results from an experimental investigation into the thermal stability of a cold-rolled Al–Y alloy. Tensile tests performed on specimens of the alloy and pure Al in annealed states reveal superior anti-softening properties of the former specimens relative to the latter counterparts. Origins of such thermal stability and underlying recovery and recrystallization kinetics are studied using electron microscopy and high energy X-ray diffraction (HEXRD) techniques. Microscopic observations reveal that recovery and recrystallization begin in the specimens of pure Al at a much lower temperature than in the specimens of Al–Y alloy. Onset of the recovery process in the Al–Y alloy is observed to begin with dislocation rearrangements in the β-Al3Y phases. The onset is followed by more substantial reduction in dislocation density, shrinkage of the β-Al3Y phases, and coarsening of the α-Al grains. The alloy contains stacking faults, which interestingly remain stable during the annealing treatments contributing to the thermal stability. The observed mechanisms are further confirmed by tracking the evolution of peaks under the in-situ synchrotron X-ray diffraction with heating. Onset of recovery was observed at 280 °C in both α-Al and β-Al3Y phases, while substantial shrinkage and spheroidization of β-Al3Y phases and decrease in dislocation density were detected at 400 °C causing loss of the alloy strength. Thermodynamic calculation showed that solubility of Y rapidly increases in α-Al at temperatures above 400 °C explaining the spheroidization and shrinkage of the β-Al3Y phases by diffusion of Y into the Al matrix.

Keywords

• Al-RE alloys
• Eutectic phases
• Strength
• Ductility
• Synchrotron X-ray diffraction