Electrochemical behaviour of a Mg-rich primer in the protection of Al alloys

Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Full Immersion: a Galvanic Throwing Power Investigation Using a Scanning Vibrating Electrode Technique

“…10 While the exact configurations such as electrolyte thickness, concentration and polymer resistances differ from this work, several configurations were chosen for comparison and the results are summarized in Table I where the results show good correlation. It is to be noted that while FEA predicts the galvanic current for fixed conditions, such as fixed electrolyte chemistry and thickness, SVET can be utilized to study the current density distributions as a function of actual position and time dependent electrolyte solution chemistry and pH and also surface modifications such as formation of Mg(OH) 2 and effects of inhibitor leaching from the pretreatment. The FEA model uses fixed Elogi boundary conditions and predicts the quasi-steady state galvanic current and galvanic couple potential distribution.…”

“…Anionic species leaching from the pretreatment might also bring down the anodic activity at defect by acting as cathodic inhibitor. The protection of the defect by Mg(OH) 2 and anionic species leaching in both lab accelerated life testing (LALT) and field exposures for pretreated systems has been previously reported. 4,7,8 Further investigation of the chemical protection mechanism and the conditions required for chemical protection will be reported in future work.…”

“…1 Over the past few years, a commercial organic coating system containing a Mg-rich primer (MgRP) has been developed for the active corrosion protection of aerospace aluminum alloys. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The commercial MgRP coating system consists of a surface pretreatment, an epoxy resin with metallic Mg pigment and, where applicable, a polyurethane topcoat. The active corrosion protection of any Al alloy is provided by galvanic coupling of more active Mg pigment in the primer which is active compared to the more noble AA2024-T351 substrate.…”

Chromate replacement: what does the future hold?

“…120,121 On the other hand, in the case of Mg-rich primers, the corrosion potential of the underlying metal (such as an Al alloy~−0.64 V SCE in 3% NaCl) could also be maintained well below its pitting potential during contact with Mg-rich particles in the primer (~−0.93 V SCE in 3%NaCl). 120,122 The oxides/hydroxides of the active metal particles (with an approximate size of 30-40 µm 122 ) could also serve to provide long-term protection to the underlying metal substrate as reported by Bierwangen et al Indeed, the Mg-rich primer system was reported to provide protection after a 3000 h Prohesion exposure and up to 6000 h under ASTM B117 salt spray testing when a top coat was applied. 120 However, the "self-corrosion" of active metal particles within the primer itself has proven to be a major drawback of metal-rich primer systems.…”

Influence of magnesium nitrate on the corrosion performance of sol–gel coated AA2024-T3 aluminium alloy

“…This technique has been exploited with zinc-rich primers on metal surfaces whereby the formation of corrosion product precipitates inside a coating, occur around zinc particles, blocking the pores thereby increasing its barrier resistance [16]. Recently increased attention, particularly from North Dakota State University, has focused on magnesium as a corrosion inhibitor in epoxy primers and some sol-gels for protecting aerospace alloys [17,18,19,20]. The researchers have found that magnesium can provide sacrificial protection and also form a protective oxide layer at the alloy surface thereby enhancing barrier protection.…”