Structure effect on the kinetics and staging of the corrosion process of biodegradable ZX10 and WZ31 magnesium alloys

Biodegradable magnesium alloys are one of the most promising materials for osteosynthesis surgical implants due to the combination of unique properties: high strength, low weight, Young’s modulus close to the bone’s one, and low cytotoxicity. The most important performance characteristic is the corrosion rate, which determines the lifetime of an implant. At the moment, the main efforts of the researchers are aimed at finding a material with optimal corrosion properties ensuring the preservation of the operational properties of an implant during the bone healing period. Most of the works on this issue cover the study of the influence of the alloy chemical composition. At the same time, it is widely known that the structure of a material can also have a great effect on corrosion, for example, grain refinement can even change its type. Besides, it is important that the materials with the same quantitative parameters of corrosion can be substantially different in terms of the corrosion process staging. The authors studied the WZ31 and ZX10 magnesium alloys in two states: as-cast (coarse-grained) and after multi-axial isothermal forging and pressing (fine-grained), using the up-to-date in-situ methods that allow monitoring the dynamics of changes in the corrosion rate, as well as the staging of the corrosion damage development on the sample surface. Such methods are the corrosion rate measuring by hydrogen evolution and the sample’s surface video-monitoring during the corrosion attack. The authors carried out tests within the conditions similar to the human body conditions, such as temperature, the corrosion environment composition, and pH level. The obtained results show that the type of corrosion of the WZ31 alloy changes with the decrease in the grain size from a relatively uniform to a highly localized corrosion. In contrast, the ZX10 alloy showed a decrease in the corrosion rate with the decreasing grain size, but the corrosion type did not change.