Hydrogen Evolution and Early Blistering from Magnesium-Rich Primers on AA2024-T3

Early blistering was observed on topcoated magnesium-rich primers (MgRPs) over AA2024-T3 substrate under constant immersion or constant salt spray tests. Hydrogen evolution and the cause of early blistering were investigated in this research. Estimates are given for the first time for the amount of H₂ generated from MgRPs with and without topcoats. The measurement results along with blister formation on glass substrate, hydrogen pressure estimation, adhesion testing, and SEM images support the claim that hydrogen entrapment by topcoat, instead of Al corrosion, contributes significantly to the formation of early blistering on topcoated MgRPs. Meanwhile, simultaneous real-time hydrogen collection and open circuit potential measurement were demonstrated as a new method for studying the corrosion protection mechanism of MgRPs. Moreover, the gas generated from MgRPs was unequivocally identified as hydrogen by cyclic voltammetry scanning.