Application of the Acoustic Emission Technique for Studying Kinetics of Corrosion Processes in the ZK60 Magnesium Alloy

Low corrosion resistance of magnesium alloys is a challenging problem that hinders their wide implementation in industry and medicine. In this regard, the study of the mechanisms and patterns of corrosion processes in magnesium and its alloys, including the analysis of the kinetics of these processes, is an urgent task. However, the set of methods available for studying the kinetics of corrosion with sufficient time resolution is very limited. Several studies have been published that demonstrated the high sensitivity of the acoustic emission (AE) method to corrosion processes occurring on the surface of magnesium alloys. Although these studies suggested that AE is associated with the release of hydrogen bubbles accompanying corrosion, no direct relationship has yet been established between the amount of hydrogen released and the AE characteristics. The present study aims at filling this gap. To conduct the study, a special setup with a corrosion cell was developed that allows monitoring changes in the volume of hydrogen released from the corroding surface of the sample, concurrently with recording AE signals and changes in the open-circuit potential (OCP) accompanying the corrosion process. Using this technique, the corrosion of ZK60 alloy in a 0.9% NaCl solution was examined. It was found that intense AE accompanied the corrosion process of this alloy from the beginning to the end of the test. A correlation was found between the AE characteristics, the volume of released hydrogen, and the OCP values at various intervals of the test. In particular, a linear relationship was discovered between the number of AE signals and the volume of hydrogen released during the corrosion process. The sensitivity of the method based on AE registration to the released hydrogen volume is shown to be several orders of magnitude higher than that of the conventional method of collecting hydrogen using a burette.