| Summary: | The goals of this research are to develop deeper understanding of the corrosion protection mechanism of Mg-rich primer (MgRPs), improve corrosion protection performance of MgRPs, and extend the application of MgRPs. To address these research goals, the following studies were performed:
1. Early blistering problems encountered during constant immersion or ASTM B117 exposure of top-coated MgRPs over AA2024-T3 substrate were investigated. The results suggest that hydrogen entrapment by topcoat, instead of Al corrosion, contributes significantly to the formation of early blistering. Meanwhile, simultaneous real-time hydrogen collection and open circuit potential measurement was 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.
2. Degradation behaviors of MgRP in 1% NaCl solution and Dilute Harrison Solution (DHS) were compared through scanning electron microscopy, hydrogen volume collection and electrochemical tests. The effects of connection modes between Mg pigment and Al substrate, different ions on the formation and stability of Mg oxidation products, and cathodic reaction sites on the microstructure of MgRP were discussed. In addition, an in situ method for the estimation of remaining Mg pigment in MgRP was developed based on H2 volume collection.
3. The effects of adding sodium benzoate (SB), sodium dodecylbenzenesulfonate (SDBS), and 8-hydroxyquinoline (HQ) to MgRP on its corrosion protection of AA 2024-T3 were investigated. The results show that addition of SB, SDBS and HQ into MgRP improved the corrosion protection performance of MgRP by decelerating the oxidation rate of Mg, improving coating barrier properties and inhibiting the corrosion of Al alloy substrate. 4. The (MgRP-powder topcoat) coating system was developed and characterized in this research for the corrosion protection of Al alloys. The results show that powder topcoat can be applied on top of MgRP through both fluidized bed and electrostatic spray methods. Moreover, this (MgRP-powder topcoat) coating system provided much longer corrosion protection time to Al substrate than the powder coat by itself, without degrading other coating properties. === AkzoNobel, US DOD, OSD, Technical Corrosion Collaboration (TCC) and NDSU Center for Surface Protection
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