Processing of immiscible metallic alloys by rheomixing process

Mixing immiscible alloys has been a long standing challenge to both materials scientists and processing engineers. Despite great efforts made worldwide, including extensive space experiments, no casting techniques so far can produce the desirable fine and uniform dispersed microstructure. Based on extensive experience in mixing immiscible organic liquids offered by the polymer processing community, the authors have successfully developed a rheomixing process for mixing immiscible alloys. The rheomixing process utilises first the intensive shear stress-strain field offered by a twin screw extruder to create a fine homogeneous liquid dispersion within the miscibility gap and then the viscous force offered by a semisolid slurry at a temperature below the monotectic temperature is used to counterbalance the gravitational force and the Marangoni effect. A laboratory scale rheomixer has been designed and constructed to realise this two step mixing strategy. The Ga–Pb and Zn–Pb systems were selected to demonstrate the principles of rheomixing. The experimental results showed that the rheomixing process developed is capable of creating a fine and uniform microstructure from immiscible alloys. This paper describes the rheomixing process in detail and the preliminary experimental results on rheomixing in the Ga–Pb and Zn–Pb systems are discussed.