Which condition may not be detectable even by careful visual inspection of the surface of aluminum alloy parts or structures?

Which condition may not be detectable even by careful visual inspection of the surface of aluminum alloy parts or structures?

• A. Intergranular corrosion
• B. Pitting corrosion
• C. Surface cracking
• D. Uniform corrosion

Answer: (A)

The main idea is that some corrosion modes can hide from surface sight and require looking at the interior. Intergranular corrosion in aluminum alloys attacks along the grain boundaries inside the metal, often progressing just beneath the surface or along boundaries where precipitates and impurities make those paths electrochemically active. Because the attack can be subsurface or confined to grain boundaries, the exterior surface can look relatively normal even as damage is developing beneath. Detecting it typically requires examining a cross-section, polishing and etching to reveal the grain structure, or conducting tests that expose grain-boundary attack; regular surface inspection may miss it. In contrast, pitting, surface cracking, and uniform corrosion tend to produce visible surface features— pits, cracks, or thinning—that are detectable by careful surface inspection.

The main idea is that some corrosion modes can hide from surface sight and require looking at the interior. Intergranular corrosion in aluminum alloys attacks along the grain boundaries inside the metal, often progressing just beneath the surface or along boundaries where precipitates and impurities make those paths electrochemically active. Because the attack can be subsurface or confined to grain boundaries, the exterior surface can look relatively normal even as damage is developing beneath. Detecting it typically requires examining a cross-section, polishing and etching to reveal the grain structure, or conducting tests that expose grain-boundary attack; regular surface inspection may miss it. In contrast, pitting, surface cracking, and uniform corrosion tend to produce visible surface features— pits, cracks, or thinning—that are detectable by careful surface inspection.