How do you prevent intergranular and exfoliation corrosion in aluminum alloys?

Intergranular corrosion attacks grain boundaries preferentially. Mechanism: Precipitate-free zones or precipitates at grain boundaries become anodic/cathodic to grain interiors, Corrosion path follows continuous grain boundary network. Susceptibility factors: Alloy composition (high Cu, Zn increase susceptibility), Temper (T6 most susceptible, T7 improved), Grain structure (pancake vs. recrystallized), and Stress (accelerates to stress corrosion). Exfoliation: Severe form in wrought products with elongated grain structure, Corrosion product volume causes layer delamination, Characteristic leafy appearance. Prevention: Temper selection - Overaged (T7) tempers reduce susceptibility; Composition - Lower Cu, controlled impurities; Heat treatment - Proper solution and aging; Surface protection - Anodize, primer, paint; and Design - Drainage, avoid crevices. Testing: ASTM G110 (intergranular), ASTM G34/G66 (exfoliation). Material acceptance may include corrosion testing. Inspection programs target susceptible areas in service.