Semi Solid Die Casting

What Is Semi-Solid Die Casting?

Semi-solid die casting (SSDC), semi-solid metal casting (SSM), or thixoforming, is a variation of die casting. In this process, engineers use non-ferrous metals like copper, magnesium, zinc, and aluminum, to make a cast. 

Keep reading to learn more about what’s involved in semi-solid die casting, the four major SSDC techniques, and the major benefits of this manufacturing process.

Semi-Solid Die Casting Explained

Combining elements of forging and casting, SSDC is a high-pressure manufacturing process that involves injecting semi-solid metal into a mold. The end result is a metal product manufactured to near-net shape. 

The process itself varies depending on which technique is used (we’ll cover that later). The commonality between all of the various techniques is the use of semi-solid material (hence the name semi-solid die casting). Semi-solid refers to any material that is approximately 50% solid and 50% liquid. Sometimes this material is referred to as a “metal slurry.” During the process, the material must maintain this semi-solid form.

The Four Main Semi-Solid Die Casting Processes

As we mentioned earlier, the semi-solid die casting process varies depending on the technique that is used. There are four major SSM techniques: thixocasting, thixoforging, rheocasting, and thixomolding, which we’ve covered below.

Thixocasting & Thixoforging

In thixocasting, a deformed billet is partially reheated until it reaches a semi-solid state. Usually an induction heater is used during the reheating process. Then, the slurry is deformed between two closed or open dies until it reaches its final shape. In this process, the starting raw material must be a billet that’s already been cut to the correct size. 

In thixocasting, the material that can be used is limited. Casting alloys are typically preferred for this method, specifically A356 and A357 aluminum alloys.

Thixoforging and thixocasting are similar processes. The primary difference is how the alloys are deformed. In thixocasting, the slurry is forced under immense pressure into a mold, which is created with two open or closed dies. In thixoforging, the slurry is deformed between two closed or open dies (with precut profiles) which apply consistent pressure to the slurry. 


Unlike thixocasting, the raw material used during the rheocasting process does not need to be  a deformed billet. Usually, the process starts with an alloy (aluminum or copper) which is heated in a casting machine to a predetermined temperature and poured into a mold. The alloys are stirred or pressurized in a runner system, as it cools in the mold, which keeps the material in a semi-solid/slurry state. 

This technique is typically considered less wasteful and costly when compared to thixocasting/thixoforging, as it doesn’t require a billet. Additionally, biscuits and runners (types of overflow) can be easily recycled. The major disadvantage of rheocasting is the level of work and precision involved in maintaining the slurry. 


Generally reserved for magnesium alloys, thixomolding uses special thixomolding machines that are similar to the equipment used in injection molding.

In thixomolding, chips of magnesium alloy are fed into a high-speed and high-pressure thixomolding machine and purged with Argon. As the material is heated to a specific temperature in the machine, it slowly reaches a semi-solid state. Once the material has reached a predetermined size, it’s shot into a mold. The mold must also be kept under a vacuum as it’s filled with the slurry. 

Strain-Induced & Melt-Activated Method (SIMA)

The strain-induced and melt-activated (SIMA) is a less costly and easier variation of the thixomolding process. The molten material is brought to a predetermined temperature in a controlled setting where fine metal globules are added. Typically, the metal globules come from a source material that has been rolled or forged under the material’s recrystallization temperature.

Types of Alloy Used for Semi-Solid Metal Castings

While semi-solid metal castings can be manufactured from many non-ferrous alloys, the most common metals used today are copper, aluminum, and magnesium. 

Copper is used less frequently compared to aluminum and magnesium as it can potentially crack or shrink during the casting process. However, it’s preferred over aluminum and magnesium when the casting requires exceptional electrical conductivity. Aluminum is primarily used because of its low porosity and excellent yield strength/tensile strength. And magnesium is required when the component needs a good strength-to-weight ratio.

Benefits of Semi-Solid Die Casting

All thixoforming/semi-solid die casting techniques provide a wide array of benefits, including:

  • Tighter Tolerances: Some components must be manufactured to extremely tight tolerances. Because all thixoforming techniques utilize molds, it’s possible to mass produce precision components.
  • Reduced Shrinkage: Because alloys are heated at lower temperatures, the risk of shrinkage in the final product is drastically reduced.
  • Lower Porosity: Metals in a semi-solid state resist pinhole formation while being deformed, thus lowering porosity.
  • Robust Mechanical Properties: Alloys that go through the thixoforming process often have mechanical properties comparable to forged components, especially when these casted components are heat treated. Some of the exceptional mechanical properties of semi-solid die-casted components include high tensile and yield strength, higher fatigue resistance, highly resistance to dry wear, and high resistance to corrosion and stress.


Automotive manufacturers, aerospace companies, and defense contractors use the semi-solid metal casting process to produce lightweight, high-strength frames, engine suspension mounts, filter housings, pump frames, manifolds, and various other thin-walled subcomponent parts. Lighter frames and parts help these industries reduce fuel costs and improve efficiencies.

Other applications include medical devices, engine blocks, and high-volume locks, hooks, housings, handles, and pumps.

Learn More About Semi-Solid Die Casting 

Still have questions about semi-solid die casting? Our team at Silver Basis Engineering is ready to help. We’re an award-winning global manufacturing service provider specializing in semi-solid die casting and plastic injection molding. We also help clients in a wide array of industries from aerospace and defense to automotive and medical.

Contact us today to learn more about our services or to schedule a consultation with an expert.