The porosity formed due to simultaneous nucleation of solid grains and gas bubbles at the first moment that metal freezes at the mold walls is called__________?
Correct answer: C. Subsurface porosity
- A. Pinhole porosity
- B. Gas inclusion porosity
- C. Subsurface porosity
- D. Micro porosity
Explanation
Subsurface porosity forms just beneath the casting surface when gas bubbles nucleate at the advancing solidification front as metal first freezes against the mold wall. This distinguishes it from pinhole porosity, which usually appears as small surface openings.
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