Glossary
Porosity — definition
Voids in the section from gas trapped during filling — it weakens the part and can create leak paths.
Gas porosity comes from air that did not get out of the cavity, or from gas released by vaporising release agent. In high pressure die casting it is unavoidable to some degree, because filling happens in milliseconds.
There are three consequences: reduced tensile strength, an initiation point for fatigue cracks, and possible leak paths through the section in parts that must be pressure tight.
Porosity is also the reason high pressure die castings normally cannot be heat treated: during solution treatment the trapped gas expands and raises blisters under the surface.
Porosity can be reduced through gating design, venting and overflows, but it cannot be machined away. Say in the enquiry which sections cannot tolerate porosity, and the fill will be designed for it.