Semi-Solid Processing of Metallic Alloys

The semi-solid processing of metallic alloys encompasses a family of manufacturing techniques that exploit the unique rheological properties of alloys in a state between solid and liquid. When heated into the temperature range between solidus and liquidus, alloys form a slurry of near-globular solid particles surrounded by a liquid matrix. This suspension exhibits shear-thinning and thixotropic behaviour, enabling net-shape or near-net-shape forming with improved dimensional accuracy, refined microstructures and enhanced mechanical performance. Control of particle morphology and liquid fraction is crucial, influencing flow behaviour, die filling and final properties such as tensile strength, fatigue resistance and corrosion performance. Techniques such as rheoforming and thixoforming differ primarily in feedstock preparation: rheoforming uses sheared, partially solidified feedstock to achieve a non-dendritic microstructure, while thixoforming relies on reheated billets produced by specialised cooling or stirring routes. Applications span automotive, aerospace and industrial components, where semi-solid routes deliver high production rates and reduced defects. Recent advances target alloy systems beyond aluminium, including steels and high-strength alloys, and integrate process modelling, electromagnetic stirring and additive manufacturing to widen the scope of component complexity and material performance.

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Semi-Solid Processing of Metallic Alloys publication trend

The graph below shows the total number of articles in semi-solid processing of metallic alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Semi-solid processing: Techniques conducted between an alloy’s solidus and liquidus temperatures to form a slurry of solid grains in a liquid matrix.

Thixotropy: Time-dependent shear-thinning behaviour where viscosity decreases under shear and recovers at rest.

Rheoforming: A semi-solid processing route using feedstock sheared during solidification to produce non-dendritic microstructures for forming.

Thixoforming: A process that reheats specialised billets with near-globular solid particles to a semi-solid state for pressing or casting.

Non-dendritic microstructure: Solid particles of equiaxed, near-globular morphology formed under controlled cooling or stirring.

Solidus and liquidus: Temperatures defining the onset of melting and the completion of melting of an alloy.

References

1. Metallic slurry preparation and printability assessment for material extrusion additive manufacturing. Additive Manufacturing Letters (2024).
2. Microstructure and Properties of Semi-Solid Aluminum Alloys: A Literature Review. Metals (2018).
3. Rheological Characterization of Semi-Solid Metals: A Review. Metals (2018).
4. Semisolid Metal Processing Techniques for Nondendritic Feedstock Production. The Scientific World JOURNAL (2013).
5. Current Progress in Rheoforming of Wrought Aluminum Alloys: A Review. Metals (2020).
6. Current State of Semi-Solid Net-Shape Die Casting. Metals (2019).
7. Near Solidus Forming (NSF): Semi-Solid Steel Forming at High Solid Content to Obtain As-Forged Properties. Metals (2020).