Strain-induced clustering in Al alloys

Solute clusters represent the start of decomposition during aging of aluminum alloys and can generate strengthening while keeping the strain hardening high in comparison with shearable precipitates. In this study, clusters in a pre-aged AlMgSiCu 6xxx-series and a recently developed AlMgZnCu crossover alloy were investigated by atom probe tomography (APT) tensile testing before and after straining. Pre-aging was performed at 100°C and 60°C respectively, and a tensile strain of 5 % was applied. The key feature detected was the formation of clusters during plastic deformation, referred to here as "strain-induced clustering". It is explained based on diffusion enhancement by the strain-induced formation of excess vacancies during tensile testing, and evaluated by means of a simple modeling approach. In addition to the significant intrinsic contribution of clusters to strain hardening via dislocations, strain-induced clustering adds a hypothetical non-dislocation-based component to strain hardening.