Effect of Heat Treatment on Microstructure and Corrosion Resistance of Al-Si-Mg-Zr-Cu-Sc Alloy

Aluminum–silicon (Al-Si) alloys are widely used in aerospace, automotive manufacturing, power electronics, marine engineering and other fields due to their excellent physical properties. However, their corrosion resistance is insufficient in harsh service environments. In this study, a variety of characterization methods were adopted, including scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical measurements (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization), immersion corrosion tests, and scanning vibrating electrode technique (SVET). The results show that the appropriate heat treatment regime can significantly enhance the corrosion resistance of the alloy, while improper aging parameters will aggravate the corrosion tendency. The optimal heat treatment regime is solution treatment at 500 °C for 4 h followed by aging at 200 °C for 48 h. Under this condition, the corrosion current density (icorr) is as low as 79.30 μA/cm2, and the low-frequency impedance modulus and phase angle in EIS tests are optimal. The as-extruded alloy exhibits severe localized corrosion, while the heat-treated alloy transforms into mild and uniform corrosion. The underlying mechanism is that heat treatment induces the formation of uniformly distributed nanoscale Mg2Si and Al3(Sc,Zr) precipitates, which synergistically improve the corrosion resistance of the alloy by weakening micro-galvanic coupling and facilitating the formation of a stable passive film.