Understanding solute segregation to the dislocation loops in Al-Cu-Mg alloys

Dislocation loops are important microstructural features that are present in the quenched microstructure of Al alloys after solution treatment. Like other basic microstructural features such as constituent particles and grain boundaries, dislocation loops can attract a significant amount of solute atoms and as a result, they can affect the overall solute balance in the alloy. Quantitative information about solute segregation levels at the dislocation loops is important for a better estimation of the amount of solute in matrix, which is available for clustering/precipitation during ageing treatment. In this contribution, quenched-in dislocation loops in Al-Cu-Mg alloys have been characterized carefully for their size and number density evolution using transmission electron microscopy. The large-angle convergent beam electron diffraction (LACBED) technique has been employed to characterize their Burger’s vector and habit plane precisely. The loop size evolution during the ageing process has been used to deduce the amount of vacancies migrating to form these dislocation loops. A theoretical calculation has been conducted to assess the level of segregation of solute atoms around the dislocation loops due to vacancy migration and vacancy–solute interactions as dislocation loop size increases by the adsorption of vacancies.