The strain induced decomposition of super saturated solid solutions of Cu in Al has been experimentally investigated. A solutionized Al-Cu alloy has been severely deformed by high pressure torsion at room temperature at different strain levels. The resulting microstructures have been systematically characterized using transmission electron microscopy and atom probe tomography. It is established that Cu rich particles nucleate and quickly grow along boundaries during deformation, leading to a full decomposition of the solid solution. Besides, a significant and systematic Cu segregation along grain boundaries has been revealed. Based on these experimental data, the contribution of deformation induced vacancies, dislocations and boundaries were considered to account for the strain induced precipitation. It is concluded that the collection of solutes by moving boundaries might be considered as an important mechanism leading to strain induced precipitation.