A comparative investigation of microstructure and mechanical properties in a deformed and aged Al-Mg-Si alloy with high Cu content

• Artificial aging without deformation produces uniform precipitates. • Deformation and aging accelerate diffusion and promote diverse precipitates. • Dislocation-assisted precipitates improve strength while maintaining ductility. A thermomechanical processing (TMP) route was employed for an Al-0.98 Mg-0.36Si-1.0Cu (wt. %) alloy. The alloy was first pre-aged (PA) at 70 °C for 1 week followed by 30 % cold rolling (CR) and final aging (FA) at 160 °C for up to 1 week in an oil bath. Microstructure evolution was examined by scanning transmission electron microscopy (STEM), and mechanical properties were evaluated through hardness and tensile tests. The results demonstrated that while PA treatment typically formed GPB zones, pre-deformation introduced a high dislocation density (0.9 × 10 15 m −2 ) with dislocation cell structures (0.3 μm) in the sample. During FA treatment, the dislocations were partially rearranged to form subgrain structures, providing fast diffusion paths and abundant heterogeneous nucleation sites that accelerated precipitation. This resulted in a hardening rate of 1.5 HV × h −1 and a peak hardness of 140 HV at 16 h. Furthermore, pre-deformation induced a complex precipitate structure after FA, including GPB/β” composites, precursor Q’/L phases and precipitate-decorated dislocations (i.e. S’, Q’, C and E phases). This microstructural feature significantly enhanced the yield strength and ultimate tensile strength (270 MPa and 320 MPa, respectively) compared to those of the non-deformed sample (132 MPa and 200 MPa, respectively) while maintaining rather good elongation (9 %).