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Semisolid metal processing is a well-known technology that can be used to enhance manufacturing product quality in broad industries. The technology controls the thixotropic properties of alloys within their solidus and liquidus temperature ranges. In general, most known alloys can generate semisolid slurries at high solid fractions, and the remaining can form slurries at low solid fractions. This has provided opportunities for many metals and alloys to be processed as semisolid slurries in today’s casting industry. However, only a few researchers studied this technology potentially for a new metal-based additive manufacturing or 3D printing process. This article reviewed literature and findings from thixotropy rheology and semisolid metal processing methods, finally to thixotropic metal 3D printing. The survey shows that more future work is needed, including the investigation of thixotropic metal flow mechanics, the modelling and simulation of semisolid metal extrusion and further development of a fully thixotropic 3D printing system. 

Compared with current powder-based 3D metal printing, thixotropic metal 3D printing has great potentials and advantages in equipment cost, product quality, and process efficiency. In this paper, detailed problem statement, technique challenge, and development method regarding thixotropic metal 3D printing are discussed. A shear mixing and extruding prototype machine for thixotropic alloy fabrication was designed. We developed a direct thixotropic metal 3D printing machine and conducted a modeling and simulation process for the system. The printability of this direct metal 3D printing machine was studied. At the end, conclusions and future directions are also presented.