What is the recommended action when coating damage exposes bare magnesium?

• A. Apply MIL-S-24521
• B. Apply MIL-M-3170
• C. Apply MIL-M-3172
• D. MIL-M-3171

Answer: (D)

When coating damage exposes bare magnesium, the first step is to restore a protective barrier with a primer formulated specifically for magnesium surfaces. Magnesium is highly reactive and readily corrodes when exposed to moisture and contaminants, so quickly re-establishing a compatible, adherent coating is essential to prevent localized corrosion and maintain the integrity of the coating system.

MIL-M-3171 is the primer designed for magnesium substrates in this context. It provides good adhesion to the magnesium surface and compatibility with the topcoat, creating a continuous protective film that blocks moisture and electrolytes from reaching the metal.

The other specifications are not ideal for this situation because they are not tailored to magnesium substrates or may not ensure the proper adhesion and barrier properties required after exposure of bare magnesium. Using them could compromise protection and lead to faster corrosion or coating failure.