Impact of microgalvanic corrosion on the degradation morphology of WE43 and pure magnesium under exposure to simulated body fluid

Corrosion of magnesium alloys was studied during exposure to simulated body fluid (SBF). Microgalvanic processes dominate degradation morphology and formation of the corrosion/conversion layer. Localized corrosion with vigorous hydrogen evolution was observed at zirconium- and iron-rich precipitates that act as micro-cathodes. These are surrounded by volcano-shaped deposits of Mg(OH)2. Circular areas around cathodic centers were found to be protected from corrosion, while bulk degradation takes place in between. In SBF, conversion to a corrosion double layer was demonstrated. Differences observed for WE43 and pure magnesium (Mg) are discussed within the framework of a comprehensive model of the mechanisms of corrosion.

► Localized Corrosion of WE43 and pure magnesium under static exposure to SBF.
► Vigorous hydrogen evolution at particles, which act as micro-cathodes.
► Zr at WE43 and Fe at pure magnesium are dominant micro-cathodes.
► Protection of surrounding bulk and volcano-shaped depositions.
► A comprehensive corrosion model including a corrosion double-layer is proposed.