Comparison of the Corrosion Behaviors of Mg–Gd–Y–Zn–Zr Alloys Fabricated by Different Preparation Methods

The corrosion behaviors of a Mg–5Gd–4Y–1Zn–0.5Zr (wt%) alloy treated with different processing methods were studied. The AE sample (hot extrusion), the AA sample (hot extrusion + annealing) and the AR sample (hot extrusion + annealing + hot rolling) were prepared. The microstructures of the AE sample included dynamically recrystallized grains and deformation grains with an average size of 26.1 μm. In contrast, the AA and AR samples had homogeneous microstructures with average grain sizes of separately 41.2 μm and 36.7 μm. The corrosion behaviors of the samples were different, and the corrosion resistance decreased in the order of AR sample > AA sample > AE sample. The micro-galvanic corrosion consisted of numerous long-period stacking orderly phases and Mg matrix, and the heterogeneously distributed dislocations accelerated the corrosion rate of the AE sample. In contrast, the homogeneous microstructures with increased grain sizes led to better corrosion resistance in the AA and AR samples. The corrosion products were determined to be Mg(OH)₂ and MgO. However, the increased number of Gd and Y atoms helped form compact corrosion product films decorated with Gd₂O₃ and Y₂O₃ in the AR and AA samples. In addition, the relatively concentrated prismatic planes also slowed the corrosion rate, resulting in the highest corrosion resistance in the AR sample.