What is a primary cause of intergranular corrosion in aluminum alloys?

• A. Exposure to UV light
• B. Improper heat treatment
• C. High surface finish
• D. Adequate passivation

Answer: (B)

Intergranular corrosion travels along grain boundaries where heat-treatment changes create regions with different electrochemical behavior than the surrounding grains. In aluminum alloys that are precipitation-h Hardened, improper heat treatment (wrong temperatures or aging schedules) can cause boundary precipitates to form or grow at the grain boundaries, depleting solute in adjacent grains and establishing a galvanic couple between the boundary and the grain interior. In a corrosive environment, this makes the grain boundaries preferentially corrode, producing intergranular attack. The other factors listed don’t induce this specific path of attack: UV light doesn’t trigger it, a high-quality surface finish helps reduce it, and adequate passivation protects rather than promotes it.