Enhanced grain refinement in AA7050 Al alloy by deformation-induced precipitation

In this study, an improved double-step thermomechanical treatment was proposed for producing fine grain structure of high-strength Al–Zn–Mg–Cu series alloy based on deformation-induced precipitation. The new method composed of a low temperature pre-deformation and a traditional hot rolling. Effects of this proposed treatment on microstructure and properties of the alloy were studied using optical microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests. The microstructural analysis results show that the pre-deformation can accelerate both formation and spheroidization of the fine precipitates. Those deformation-induced precipitates could exert more drag force on migrations of the grain boundaries. So, recovery and coarseness of those deformed grains can be suppressed during subsequent heating and hot rolling, contributing to the final fine-grain structure of the AA7050 alloy. The properties test results reveal that the alloy processed by the double-step thermomechanical treatment displays superior strength and elongation than the conventional hot-rolled alloy because of the fine grain.