Porosity in metals

Porosity is the formation of holes and channels in materials. Porosity is particularly found in castings. The small holes and channels are formed by gases which may evolve during the casting process. Porosity can affect the mechanical properties of the components. It can cause fractures and other defects.

Porosity is usually discovered when a casting is being machined. As layers of metal are removed, voids and channels will become obvious. Porosity can be classified into three main categories Gas Porosity caused by gas formation and trapped air during the casting process. 

Flow Porosity caused by unequal pressure on the molten metal during the casting process which causes flow porosity Shrink Porosity caused by changes in volume as the metal solidifies. One technique of addressing porosity is by impregnating the pores with an inert material which can withstand high temperature and vibration.