The difference between Rheocasting and Thixocasting

When it comes to advanced metal-forming techniques, aluminium thixocasting and rheocasting are two innovative processes used to create high-quality, lightweight aluminium components. Both are part of the semi-solid metal (SSM) processing family, sharing several advantages but differing critically.

What Do Thixocasting and Rheocasting Have in Common?

Both techniques involve working with aluminium alloys in a semi-solid state – a “mushy” mix of solid and liquid phases. This semi-solid state allows the metal to flow under pressure while minimising defects.

Thixocasting and Rheocasting utilise the thixotropic behaviour of aluminium alloys, allowing them to flow smoothly during moulding. This results in parts with reduced porosity and enhanced mechanical properties like strength and ductility. This enables a uniform microstructure, making them ideal for applications that require durability and precision.

Both processes aim for a globular microstructure, which improves the metal’s flow and results in components with better overall performance, such as increased fatigue resistance.

Key Differences Between Thixocasting and Rheocasting

While they share several advantages, these processes differ significantly in their methods and applications:

How the Slurry is Prepared:

• Thixocasting starts with a pre-cast billet that is heated to a semi-solid state, then injected into a mold.

• Rheocasting has 87 ways of making the slurry. They all begin with molten aluminium that is cooled and agitated to create a semi-solid slurry, allowing for greater flexibility in adjusting alloy composition. 86 of them have temperature control in the cooling process. The other one is the production-stable Comptech Rheometal process, which is enthalpy-controlled.
  
  

Material Flexibility:

• Thixocasting uses a limited range of specially formulated alloys with specific properties.

• Rheocasting allows for a wider range of alloys, providing more options for manufacturers to choose materials that meet specific needs.
  
  

Cost and Production:

• Thixocasting involves higher initial costs of the thixocasting machine and the need for pre-cast billets and specialised heating equipment.

• Rheocasting is typically more cost-effective. It uses molten metal directly, reducing waste and simplifying logistics. Rheocasting can easily be added to existing HPDC cells.
  
  

Applications:

• Thixocasting is best for applications needing high precision and consistency, such as automotive and aerospace parts.

• Rheocasting is chosen for its closeness to HPDC, which enables cost efficiency and the ability to adapt to different materials. This makes it suitable for diverse industries like automotive, electronics, and consumer goods.

   

Conclusion

Both thixocasting and Rheocasting provide significant advantages in producing high-quality aluminium parts, but the choice depends on specific production needs.

Thixocasting requires specialised machinery and billets, making it expensive. As most of this post’s receivers are in the HPDC foundry industry, Rheocasting is much easier to implement in their foundry, as melt preparation is different from HPDC. Rheocasting works with a wide range of alloys and opens new applications for your foundry.

Check out the Rheocasting Workshop for more information and learn what it can do for your foundry!