Active Corrosion Protection of Sintered AA7075 Aluminum Alloy via Mn Powder Addition

This study demonstrates that the addition of Mn powder to AA7075 is beneficial to the fabrication of AA7075 matrix composites with high corrosion resistance. AA7075 containing Mn‐rich particles is fabricated via spark plasma sintering using mixed AA7075 and Mn powders. The resulting alloy matrix includes large Mn‐rich particles (diameter 70 μm) composed of inner, middle, and outer parts, with the inner region being nearly pure Mn. Fine Cu‐containing intermetallic particles (IMPs, Al–Cu–Mg and Zn–Mg–Cu–Al, <5 μm), originally present in AA7075, are also retained. Corrosion resistance is evaluated using a 20‐cycle dip‐and‐dry test in 0.1 M NaCl (pH 6.0). Increasing Mn addition reduces discoloration and mass loss. During corrosion, Mn‐accumulated films form in situ on the Cu‐containing IMPs. The inner part of the Mn‐rich particles undergoes anodic dissolution during the dip‐and‐dry cycles, supplying Mn ions for the film formation. The films are considered to form because of local alkalization that is induced by cathodic reactions on the Cu‐containing particles. Potentiodynamic polarization shows that the Mn‐accumulated films suppress the oxygen reduction and increase the pitting potential. The role of Mn‐rich particles in corrosion inhibition is discussed.