Cathodic Corrosion Protection Performance of Mg-Rich Primers: Effect of Pigment Shape and Pigment Volume Concentration

Abstract

In analogy to Zinc-rich coatings technology, Mg-rich primers (MgRPs) have been developed to protect Al alloys, particularly Al 2024-T3. Pigment shape and pigment volume concentration are two important parameters for metal rich coatings and their role in Mg-rich coatings was examined in this report. Two magnesium pigments, spherical Mg 1-11 and irregular shape Mg 3820, were formulated in Mg-rich coatings at different PVC levels. Pigment shape and particle size and were characterized by scanning electron microscopy (SEM), and particle size distribution (Accusizer 780a), respectively. Critical pigment volume concentration (CPVC) values were predicted by the methods of Bierwagen & Johnson(1, 2) , and were experimentally verified via fluorescence microscopy and SEM. Polarization curves, open circuit potential (OCP) and scanning vibrating electrode technique (SVET) were applied to characterize cathodic protection properties of MgRPs. It has been found that most MgRPs provided cathodic protection to Al alloys except for some low PVC MgRPs. These MgRPs were topcoated and then placed in Neutral Salt Spray chamber, and it is seen that Mg 1-11 coatings had less blistering than Mg 3820 coatings.