Study On Synergistic Effects Between Pigments In Modified Magnesium-Rich Primer On AZ91D Magnesium Alloy

Because of the high strength to weight ratio, Magnesium alloys are good materials for automobiles, electronics and aerospace industries. However, in many environments the application of magnesium alloys is limited because of the corrosion problems. In previous work, an epoxy coating with pure magnesium particles was prepared and applied on AZ91D alloy. However, the adhesion and cathodic protection of the primer to the magnesium alloy substrate is to be further improved. In this paper, several kinds of Mg-rich primer were prepared and synergistic effects between pigments were investigated.A Mg-HQ-rich primer was prepared by adding8-hydroxyquinoline in an epoxy coating. The synergistic effects between8-HQ and Mg particles in the Mg-HQ-rich primer are suggested as follows:the additive8-HQ combines with Mg2+in the coating to form a highly insoluble complexes, MgQ2, instead of Mg(OH)2. A protective layer of MgQ2may retard dissolution of the magnesium particles and prolong the cathodic protection effect of the Mg-HQ-rich primer. Additionally, the corrosion products of magnesium particles, which are composed of MgQ2and brucite, may block the defects in the primer and the active sites on the substrate surface, thereby further increase the corrosion resistance of the Mg-HQ-rich primer.Zinc oxide particles were dispersed in epoxy resin, and zinc oxide modified Mg-rich epoxy primer were prepared. The addition of10wt.%ZnO in the primer instead of10wt.%Mg effectively decreased the dissolution rate of Mg particles and prolonged the time of cathodic protection. This could be because the well dispersed zinc oxide particles could play a role in electrical conduction instead of Mg particles. And, the additives zinc oxide particles improved the physical crosslink density of the epoxy resin matrix, which could reduce the porosity or defects and enhance the barrier property and adhesion of the primer.Aluminium fluoride, aluminium fluoride trihydrate, glass ionomer cement and trisodium hexafluoroaluminate were adding to Mg-rich primer to reduce the formation of blister, respectively. These additives partly lowered activity of magnesium particles in the Mg-rich primer, but decreased the barrier property greatly. In addition, the corrosion inhibition of trisodium hexafluoroaluminate for magnesium was discussed. The study indicates that the generation of MgF2enhanced the corrosion resistance of magnesium. And furthermore, trisodium hexafluoroaluminate facilitated the formation of passive film on magnesium surface, lowered the donor concentration and instability of the film.