Investigation and corrosion performance of cast Mg–6Al–1Zn + XCa alloy under salt spray test (ASTM-B117)

The corrosion behavior of cast Mg–6Al–1Zn + XCa (Where X = 0.5,1.0,1.5 and 2.0 wt.% Ca) magnesium alloy, aged at different temperatures of 180 °C, 200 °C, 220 °C and 240 °C was investigated in accelerated corrosion test chamber according to ASTM-B117 Standard (salt spray test). The exposed alloys were characterized by X-Ray Diffraction (XRD), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) techniques. The microstructural refinement due to calcium addition and ageing treatment results in the improvement of corrosion resistance of the experimental alloy. Corrosion rate decreases due to fine precipitation of the β (Mg17Al12) phase distributed along the α-grain boundaries during ageing. Intermetallic phases act as a barrier, which makes the alloy more resistant to corrosion. Results found that better corrosion resistance of the alloy was observed in Mg–6Al–1Zn + 1.5 wt.% Ca with 180 °C ageing temperature. The corrosion behavior of Mg–6Al–1Zn + XCa alloy exhibited by ASTM B117 salt spray testing and electrochemical polarization measurements showed similar trends concluding that the calcium addition and ageing temperature decreases the corrosion rate.