Direct bonding to the aircraft structure should not be used to bond which material?

• A. Magnesium
• B. Aluminum
• C. Titanium
• D. Stainless

Answer: (A)

Magnesium should not be directly bonded to the aircraft structure because it is the most anodic among common airframe metals. When magnesium is in electrical contact with other metals (like aluminum, steel, or titanium) in the presence of moisture, a galvanic couple forms and the magnesium will corrode at the bond. This accelerates deterioration and can compromise both electrical continuity and structural integrity. To bond safely, magnesium needs to be isolated from direct metal-to-metal contact with structural components or protected with an insulating barrier or coating, whereas bonding to aluminum, titanium, or stainless is routine when proper surface prep is followed.