Performance of a Magnesium-Rich Primer on Pretreated AA2024-T351 in Selected Laboratory and Field Environments: Conversion Coating Pretreatments

The effect of conversion coatings on the corrosion protection of AA2024-T351 by magnesium-rich primer (MgRP) was evaluated in topcoated and non-topcoated, scribed conditions. Protection of remote scratches and global protection by the coating after exposure in selected laboratory and field environments was investigated. Exposure studies focused on chromate conversion coating, trivalent chromium pretreatment (TCP), and non-chromium pretreatment, and compared to non-film forming (NFF) surface pretreatment. Exposures were conducted in the field under two different environments: at a coastal marine site and at an inland rural site. ASTM B117 with 5 wt% NaCl, modified ASTM B117 with acidified ASTM substitute ocean water and UV light, as well as full immersion in ambiently aerated 5 wt% NaCl solution were compared to field environments. Mg pigment depletion rate, global galvanic protection potential, coating barrier properties, and scribe protection were investigated. In systems without a topcoat, full immersio...

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