Porosity is an area of sponge-like texture in an otherwise sound metal casting. There are two types of porosity:
• Micro-porosity: Very small (almost invisible) interconnected air filled cells.
• Macro-porosity: Larger flaws in the casting visible to the naked eye.
Porosity is typically caused during the casting process by internal shrinkage, gas cavitation, oxide films and inclusions and the many combinations thereof.