This study investigates the microstructural behavior of laboratory-produced Al–Mg–Si(X)–Mn aluminum alloys, focusing on the influence of varying Si content during biaxial hot tensile testing. Alloys with Si contents of 0.7%, 0.9%, and 1.3% were subjected to biaxial deformation at temperatures of 200 °C, 300 °C, and 400 °C. Using digital image correlation analysis, the impact of Si content on microstructural evolution under biaxial tensile loading was analyzed. Force–displacement analysis revealed a consistent inverse relationship between temperature and the maximum force required to initiate strain. At the temperature of 200 °C, the Al–Mg–Si(1.3)–Mn alloy required a maximum force of 1500 N, while at the temperature of 400 °C this force decreased to 900 N. The degree of anisotropy varied, with higher Si alloys exhibiting increased resistance to deformation in the transverse direction. In particular, the Al–Mg–Si(1.3)–Mn alloy showed pronounced strain anisotropy, with large major true strain φ1 values reaching up to 0.32 at 400 °C, compared to 0.26 at 300 °C and 0.2 at 200 °C. Microstructural analysis using electron backscatter diffraction (EBSD) and energy dispersive X-ray spectrometry (EDS) showed minimal changes at low temperatures, while increased dislocation density and grain boundary distortion were observed at elevated temperatures. The β-Mg2Si precipitates, influenced by Si content and temperature, significantly affected the mechanical properties. In the Al–Mg–Si(0.7)–Mn alloy, precipitates were predominantly 1–3 µm in diameter, whereas in the Al–Mg–Si(1.3)–Mn alloy, precipitates grew to 4–8 µm at higher Si content. These findings provide critical insights into the mechanical response and deformation mechanisms of aluminum alloys under biaxial tensile conditions, essential for optimizing material performance in engineering applications.
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