On the precipitation behaviour in Al-Cu-Mg-(Ag) alloys processed by equal-channel angular pressing

This paper concerns microstructural evolution in two Al-Cu-Mg-(Ag) alloys subjected to atypical thermomechanical treatment. The alloys, supersaturated with Cu and Mg in a solid solution, were processed using equal-channel angular pressing at room temperature (RT-ECAP), followed by artificial ageing. Such an approach allowed for accessing the essential strengthening components of Al alloys, viz. grain boundaries, dislocations and precipitations. A comprehensive EBSD and TEM investigation was conducted in addition to the conventional hardness and tensile tests to elucidate the microstructure-property relationship. The evolution of these alloys' primary strengthening precipitates (theta ' and Omega) was thoroughly illuminated, focusing on quantitative measurements of their sizes, number densities and volume fractions. Using post-deformation ageing treatments, it was found that an RT-ECAP of the Al-Cu-Mg-Ag (AA2139) alloy gives rise to precipitation theta ' at the expense of Omega-phase and, vice versa, in Al-Cu-Mg (AA2519) it dramatically enhances the Omega-plate number density. Heterogeneous Omega-precipitation after pre-deformation and ageing was demonstrated for both alloys. The defined microstructure characteristics can be used for theoretical estimates of the yield strength of these alloys.