Galvanic Compatibility of Coated Steel Fasteners with Magnesium

Abstract

<div class="htmlview paragraph">Selected metallic platings and insulating coatings on steel fasteners were evaluated for ability to reduce galvanic corrosion of die cast magnesium in a modified salt spray test. Proprietary electroplate systems based on zinc, zinc-nickel, zinc-cobalt and tin-zinc were tested, along with a commercial 50-50 tin lead alloy electroplate without supplementary coating. A proprietary liquid-applied zinc-rich inorganic coating successfully used on automotive fasteners was also tested for compatibility with magnesium.</div> <div class="htmlview paragraph">Encapsulation of bolt heads with plastic insulating coatings or special molded caps was evaluated.</div> <div class="htmlview paragraph">Interruption of the continuous salt spray by rinse and bake cycles was investigated as a likely exposure condition for magnesium assemblies in powertrain or underhood applications.</div> <div class="htmlview paragraph">Several of the protection schemes were found to effectively eliminate galvanic corrosion of the magnesium.</div>