Semi-solid metal casting

Semi-solid metal casting (SSM) is a near net shape variant of die casting.^[1] The process is used today with non-ferrous metals, such as aluminium, copper,^[2] and magnesium. It can work with higher temperature alloys that lack suitable die materials. The process combines the advantages of casting and forging.The process is named after the fluid property thixotropy, which is the phenomenon that allows this process to work. Thixotropic fluids flow when sheared, but thicken when standing.^[3] The potential for this type of process was first recognized in the early 1970s.^[3] Its three variants are thixocasting, rheocasting, and thixomolding. SIMA refers to a specialized process to prepare aluminum alloys for thixocasting using hot and cold working.^{[clarification needed]}

SSM is done at a temperature that puts the metal between its liquidus and solidus temperature, ideally 30 to 65% solid. The mixture must have low viscosity to be usable, and to reach this low viscosity the material needs a globular primary surrounded by the liquid phase.^[2] The temperature range depends on the material and for aluminum alloys can be as much as 50 °C, but for narrow melting range copper alloys can be only several tenths of a degree.^[4]

SSM is typically used for high-end applications. For aluminum alloys, typical parts include structural medical and aerospace parts, pressure containing parts, defense parts, engine mounts, air manifold sensor harnesses, engine blocks, and oil pump filter housings.^[5]