Metal casting involves pouring liquid metal into a mold containing a hollow cavity of the desired shape, and allowing it to cool and solidify. However, Semi-solid casting is a modified die casting process, in most die castings, which reduces or eliminates the residual porosity present. Apart from using liquid metal as the feed material, Semi-solid casting uses a higher viscosity feed material that is half solid and half liquid. Usually, taking advantage of a modified die casting machine to inject the semi-solid slurry into re-usable hardened steel dies. The high viscosity of the semi-solid metal, with the use of controlled die filling conditions, confirms that porosity in bad condition can be essentially eliminated because the semi-solid metal fills the die in a non-turbulent manner.

In commerce field, it mainly used for aluminum and magnesium alloys, Semi-solid casting can be heated to the T4, T5 or T6 tempers. The combination of heat treatment, fast cooling rates and minimal porosity provides excellent combinations of strength and ductility. Other benefits of Semi-solid casting are the ability to produce complicated shaped parts, pressure tightness, tight dimensional tolerances and casting thin walls. Semi-solid casting is now available in most foundry.