Porosity is a phenomenon that
occurs in materials, especially castings, as they change from liquid to
solid during the manufacturing process.
Porosity is when holes or defects are
created that are too small to be seen by the naked eye, and if these are
permeated by gas or fluid, significant and costly quality problems can
arise, even leading to the failure of the component in service through
leaks or surface defects.
Porosity can be found in many materials
but is particularly prevalent in aluminium die castings, where three
main types may be identified:
Flow Porosity- resulting in surface or internal defects caused by poor pressure conditions in the process.
Gas Porosity- usually internal, caused by trapped gasses of various kinds in the die.
Shrink Porosity- the most common and most difficult to control, caused by the change in volume as the metal changes state from liquid to solid.