What is the proper nondestructive inspection to locate surface cracks in an aluminum alloy casting or forging?

• A. Eddy Current inspection.
• B. Zyglo or dye penetrant.
• C. X-Ray Inspection.
• D. Magnetic Particle inspection.

Answer: (B)

The ability to reveal cracks that break the surface is what this question focuses on. Dye penetrant inspection is designed specifically for finding surface-breaking flaws on nonferrous metals like aluminum. The process is simple: apply a liquid penetrant, let it seep into any surface crack, wipe away the excess, and apply a developer so the penetrant trapped in the crack is drawn out and becomes visible (often glowing under UV). This method is highly sensitive to very fine surface cracks and works well on complex-shaped castings or forgings, because you just need access to the exterior surface.

Magnetic particle inspection wouldn’t apply here because aluminum isn’t magnetic, so it can’t reveal surface cracks with this method. Eddy current can detect surface and near-surface flaws in conductive materials, but it’s more equipment-intensive and can be less practical for irregular aluminum parts. Radiography can show internal features but isn’t as straightforward for tiny surface cracks and involves more safety and cost considerations.