Vacancy-solute interactions during ageing of a cold worked Mg-RE alloy

Abstract

Abstract The vacancy–solute interactions during artificial ageing at 250ºC of cold worked samples of a commercial alloy WE54 (Mg-RE) was studied by coincidence Doppler broadening of the positron annihilation radiation and positron annihilation lifetime spectroscopy. The results show that in the as-cold-worked state the vacancies are associated with dislocations that are introduced by the cold work. After artificial ageing at 250ºC the vacancies are stabilised by their association with solute elements and help the formation of precipitate precursors. The present study demonstrates that the stronger hardening response achieved in the cold worked samples comes from the presence of a higher concentration of retained vacancies that have formed during the cold work and not annealed during the first minutes of ageing. These vacancies are stabilised by association with solute elements and they help the formation of the precipitates precursors. This mechanism accelerates the formation of hardening precipitates without any apparent changes in the precipitation sequence and in the products of the decomposition of the initial supersaturated solid solution.