Correlated impacts of deformation-induced precipitation and precipitates dissolution on mechanical properties in Al-Mg-Si alloys

To enhance the strength of Al alloys while maintaining appreciable ductility, engineering nano-sized precipitates via tailored deformation is one of the most promising strategies. Deformation-induced precipitation (DIP) and precipitates dissolution (DIPD) are thus vital. There have been numerous studies on the microstructural evolutions and mechanical properties associated with precipitation during deformation and/or aging. However, the distinct roles and quantifiable contributions of DIP and DIPD on mechanical properties remain ambiguous. In this study, two thermo-mechanical processing routes were employed in Al-0.53Mg-0.64Si-0.13Fe alloy: (1) DIP achieved by cold rolling the solution-treated samples, where high density Guinier-Preston zones‌ are introduced; (2) DIPD via cold rolling the peak aged samples, where the precipitates partially exhibit structural signatures of ‌metastable β″ phase‌. Geometric phase analyses were successfully applied to the lattice misfits along the precipitate/matrix interfaces, which are obtained to be 0.64 % and 0.85 % for the DIP and DIPD, respectively. The slight difference of interface strains is identified to exert predominant impacts on precipitation strengthening, although the number density and size of precipitates are comparable in these two processes. The contributions of precipitates to the yield strength are calculated as 33.1 and 68.7 MPa for DIP and DIPD, respectively. This systematic study pioneers the comparative analysis of precipitation strengthening in the DIP and DIPD processed Al alloys. Moreover, it leads to quite different mechanical properties during subsequent re-aging after DIP and DIPD. Our work provides new insights to correlate the impacts of different types of precipitation on the performance for all heat-treatable Al alloys.