Strain-induced microstructural and precipitation behavior of Al-Mg-Si-Mn alloys: Effects of Si content under controlled thermomechanical conditions

• Resolved shear stress promoted DDRX nucleation during hot deformation. • Deformation band-precipitate interactions triggered local CDRX at 300-350 °C. • Stress-assisted precipitation of B′ and U1 phases occurred during deformation. • Higher Si content resulted in enhanced Copper texture and reduced ductility at elevated temperatures. • Formation of coherent βʺ precipitates along the [001] Al direction controlled by lattice mismatch. This study investigates the microstructural evolution of Al-Mg-Si-Mn alloys, focusing on the influence of Si content on mechanical properties, deformation mechanisms, and precipitate evolution during high-temperature tensile testing. Tensile tests were performed at 200, 250, 300, and 350°C with strain rates of 0.1, 1, and 10%/s, showing significant variations in mechanical response as a function of Si content. Microstructural characterization was performed using electron backscatter diffraction, energy-dispersive X-ray spectrometry, and a transmission electron microscope to analyze deformation mechanisms, precipitate evolution, and texture formation. The results show a progressive decrease in tensile strength and yield strength with increasing deformation temperature, with the most pronounced reduction occurring at 350°C in alloys with higher Si content. This increased Si level promotes the strengthening of the Copper texture while progressively suppressing the Cube texture during deformation at elevated temperatures. At 200°C, deformation bands are formed primarily by interaction with dislocations, while precipitates drive deformation band formation by effectively impeding dislocation motion. Resolved shear stress analysis indicates a direct influence on the initiation and progression of discontinuous dynamic recrystallization (DDRX), with higher Si levels promoting more pronounced DDRX. Deformation at elevated temperatures of 300 and 350°C enhances dynamic recrystallization and accelerates continuous dynamic recrystallization, leading to increased grain boundary formation and a reduction in deformation band density. Furthermore, the evolution of β′, B′, and U1 phases at 300°C and 0.1%/s strain rate highlights the heterogeneous nucleation and growth mechanisms of precipitates. These results underscore the critical role of Si content in controlling the mechanical response and microstructural evolution of Al-Mg-Si-Mn alloys, providing valuable insights for optimizing alloy design and performance at elevated temperatures.