Study of an Mg₉₀Y₇Zn₃ alloy (WZ73) in sodium chloride solution — An analysis by correlated polarization and climate chamber testing

Abstract

In the present work, the corrosion behavior of a twin‐roll cast WZ73 magnesium alloy is investigated by potentiodynamic polarization and climate chamber tests in different sodium chloride solutions. The corrosion parameters Ecorr and jcorr are extracted from the polarization curves, and the critical concentration for the initiation of pitting corrosion is thus identified. The critical concentration for the initiation of pitting is confirmed by means of climate chamber tests. As a consequence, the WZ73 magnesium alloy is found to be highly susceptible to pitting corrosion in sodium chloride solutions of concentrations higher than 10−4 mol/L. Moreover, when the NaCl concentration increases, the corrosion mechanism changes from pitting to filiform corrosion, which is attributed to micro‐galvanic effects. At low NaCl concentrations, the corrosion attack remains localized. When the NaCl concentration increases, pitting occurs and, in addition to the pits that form, micro‐galvanic corrosion leads to filiform corrosion attack. This is caused by the electrochemical potential of the long period stacking ordered phase, which is higher than that of the α‐Mg matrix. Consequently, the corrosion attack is focused on the phase boundary between the α‐matrix and LPSO phases.

Effect of Fluoride Coatings on the Corrosion Behavior of Mg–Zn–Ca–Mn Alloys for Medical Application

“…The NaCl solution is adequate for Mg-based alloy degradation investigations because, inside the human body, there is a high quantity of chloride ions due to human nutrition or air because salt is used for road management and is present in marine environments. Hornig et al [ 18 ] observed in the case of Mg–Y–Zn alloy that for low NaCl concentration solutions, the corrosion effects are localized since at higher concentrations pitting appears and, supplementary to the pits, the micro galvanic corrosions conduct a filiform corrosion attack. It was concluded that, based on NaCl concentration, the corrosion process can vary from pitting to filiform corrosion [ 18 ].…”

“…Hornig et al [ 18 ] observed in the case of Mg–Y–Zn alloy that for low NaCl concentration solutions, the corrosion effects are localized since at higher concentrations pitting appears and, supplementary to the pits, the micro galvanic corrosions conduct a filiform corrosion attack. It was concluded that, based on NaCl concentration, the corrosion process can vary from pitting to filiform corrosion [ 18 ]. The type of solution is important, and it must be chosen in accordance with the medical application in which the Mg-based implant will be used because different degradation rates of the alloy can be obtained [ 19 ].…”