Cathodic Protection of Mild Steel Using Aluminium-Based Alloys

Typically, steel is protected from corrosion by employing sacrificial anodes or coatings based on Zn, Mg, Al or Cd. However, stricter environmental regulations require new environmentally friendly alternatives to replace Cd. Traditionally, Al-based anodes have been employed to cathodically protect steel in marine applications or as ion vapour deposition (IVD)-Al sacrificial coatings for aerospace applications. However, Al tends to passivate, thus losing its protective effect. Therefore, it is important to identify possible alloys that can provide a constantly sufficient current. In this study, Al-X alloys (X = Ag, Bi, Ca, Cr, Cu, Ga, Gd, In, Mg, Mn, Ni, Sb, Si, Sn, V, Ti, Zn and Zr) were firstly tested for a screening of the sacrificial properties of binary systems. Al-0.5Cr, Al-1Sn, Al-0.2Ga, Al-0.1In, Al-2Si and Al-5Zn alloys were suggested as promising sacrificial Al-based alloys. Suitable heat treatments for each system were implemented to reduce the influence of the secondary phases on the corrosion properties by minimising localised attack. extensive evaluation of the corrosion properties, including galvanic coupling of these alloys to steel, was performed in the NaCl electrolyte. A comparative analysis was conducted in order to choose the most promising alloy(s) for avoiding the passivation of Al and for efficient cathodic protection to steel.