Dramatic enhancement of the corrosion resistance of dilute Mg–Al–Mn–Ca alloy through Gd alloying

Dilute Mg–Al–Mn–Ca–Gd alloy with extraordinary corrosion resistance (PH = 0.21 mm/year) comparable to that of high-purity Mg was prepared. The Gd addition promoted the second phase transformation from the Al–Mn phase to the Al8Mn4Gd and Al2Gd phases with decreased potential difference with Mg matrix, thus weakening the micro-galvanic corrosion. The homogeneous distribution of nano-sized second phases effectively inhibited localised corrosion, contributing to the integrity of surface film. Furthermore, Gd alloying promoted the formation of compact corrosion products mixed with Gd2O3 and embedded with the nano-sized Al2Gd phase, resulting in a stable and protective surface film.