The role of MgH2 in the process of filiform-like corrosion on Mg alloys has been investigated. MgH2 was grown galvanostatically on the Mg ZEK100 alloy at a current density of −5 mA/cm2 for various times in 0.1 M NaOH and the subsequent electrochemical and corrosion behavior compared to that of as-polished specimens. Polarization curves demonstrated cathodic activity under anodic polarization (i.e., the “negative difference effect”) while x-ray diffraction confirmed the presence of MgH2. Dynamic secondary ion mass spectrometry measurements show strong evidence for the presence of MgH2 in aged sections of corrosion filaments, in the leading edge of corrosion filaments, and in the Mg matrix ahead of the leading edge of corrosion filaments in alloys corroded at Ecorr. The presence of these hydrides is linked to the filiform-like corrosion morphology observed on Mg alloys via in situ monitoring. These hydrides are responsible for the filiform-like corrosion by acting as temporary metastable catalysts for hydrogen evolution prior to their decomposition to Mg(OH)2.

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