Corrosion resistance and degradation behavior of anodized Mg-Gd alloys: A comparative study

A conventional anodic oxidation process was conducted on two Mg-Gd alloys to study the corrosion resistances and degradation behaviors of their anodized films, and a commercial AZ31 alloy was used for comparison. It was found that both the structures and degradation properties of the anodized films of Mg-Gd alloys were quite different from AZ31 alloy. For Mg-Gd alloys, the anodized films contained more crystalline MgO, Mg2SiO4 and Mg-3(PO4)(2) with lower porosity and small pore size compared with anodized AZ31 alloy. Although the anodized AZ31 alloy showed slightly higher initial corrosion resistance, its long-term degradation performance was uncompetitive compared with two anodized Mg-Gd alloys. And the scanning electrochemical microscopy (SECM) tests also pointed to more uniform degradation behaviors of anodized Mg-Gd alloys. The better long-term degradation performances of anodized Mg-Gd alloys, especially anodized Mg-1Zn-1Gd alloy, were believed to benefit from their different structures, compositions and corrosion products of anodized films compared with anodized AZ31 alloy.