Effect of cerium addition on corrosion behaviour of AZ61 + XCe alloy under salt spray test

The corrosion behaviour of Mg–6Al–1Zn + XCe (where X = 0.5, 1.0, 1.5 and 2.0 wt% Ce) alloys, aged for 18 h at different temperatures of 180 °C, 200 °C, 220 °C and 240 °C, was studied in 3.5 wt% NaCl solution. The salt spray test was conducted in accordance with ASTM-B117 standard (fog test). The corrosion morphologies, corrosion rate and the composition of the corrosion products were investigated by X-ray Diffraction (XRD), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) techniques. The results show the cerium addition and ageing treatment has significantly influenced the corrosion morphologies and the corrosion rate. In AZ61 alloy, the intermetallic β (Mg17Al12) phase acts as a corrosion barrier and upon ageing the Al4Ce phase precipitates along the α grain boundaries. The precipitation modifies the β phase to form more continuous network which subsequently reduces the corrosion attack in the chlorine environment. Salt spray test result shows the AZ61 alloy with 1.5 wt% Ce aged at 220 °C exhibits the better corrosion resistance.