Effect of aging time on precipitation behavior, mechanical and corrosion properties of a novel Al-Zn-Mg-Sc-Zr alloy

The precipitation behavior, mechanical properties and corrosion resistance of a novel Al-Zn-Mg-Sc-Zr alloy aged at different time were studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile tests, potentiodynamic polarization and electrochemical impedance spectroscopy. The results revealed that with increasing aging time at 120 degrees C, the hardness and tensile strength of the alloy increased rapidly at first and then slightly decreased. The resistance of exfoliation corrosion (EXCO) and intergranular corrosion (IGC) increased gradually with increasing aging time. The same trend of corrosion properties was demonstrated by electrochemical polarization curves and EIS test. The characteristics of grain boundary precipitates and precipitate free zone (PFZ) had a significant influence on the mechanical and corrosion behaviors of the studied alloy. On the basis of TEM observations, the size of grain boundary precipitates and the width of PFZ became larger, and the distributed spacing of grain boundary precipitates was enhanced with increasing aging time.