The Special Role of Anodic Second Phases in the Micro-galvanic Corrosion of EW75 Mg Alloy

It is well known that second phases act as micro-cathodes in the corrosion of traditional Mg alloys. However, the effect of second phases on the corrosion behavior of Mg-rare earth (RE) alloys is ambiguous in view of the second phases consisting of Mg and more active RE elements. The role of second phases in the corrosion of cast EW75 (Mg-5Y-7Gd-1Nd-0.5Zr) was studied by scanning electron microscopy (SEM) observations, Scanning Kelvin Probe Force Microscopy (SKPFM) analysis, immersion and electrochemical tests. It is found that the second phases in EW75 are more active than Mg matrix and preferentially dissolved at the initial corrosion stage. It indicates that the second phases act as micro-anodes, which are greatly different from the role of second phases in traditional Mg alloys.