Although thixoforming complex near net shaped products in aluminium alloys is now an established technology in many automotive applications, current developments are taking place in a number of fronts: dynamic applications for load bearing components; alloy development-expanding the existing portfolio of thixoformable alloys; in materials recycling and in thixoforming of high melting point alloys.
  In the automotive industry, the drive for materials' development stems from the necessity of weight reduction in cars (more use of light alloys, including aluminium, magnesium, and metal matrix composites) and reduced costs. Most of the major automotive producers are currently using or are experimenting with thixoformed products. In Europe, Italian, French, German, and Spanish manufactures all have invested in the technology. In the United States, Ford is the main investor.
  The current manufacturing routes involve either 1) the use of non-dendritic alloy feedstock, which is cut to slugs of appropriate size before re-heating the slugs to the semi-solid state by a carousel of induction heaters and once the slugs have reached the required liquid fraction, robots automatically transfer them to the shot chamber of the thixoforming press (an adapted form of die-casting machine) to inject them into a die, or 2) cooling from the liquid to the semi-solid state before directly injecting into the die (New Rheocasing Method NRC). The production route is very similar to diecasting, however, the resulting properties of the parts are of much higher quality.
  Thixoforming has seen commercialisation around existing alloy composition based on aluminium-silicon 356 and 357 materials. A number of players are undertaking research to expand the portfolio of existing alloys, both in low and high temperature alloys.
  Current research in the later field is concentrating on the development of high melting point alloys such as steels, iron-alloys, copper-alloys, superalloys and other exotic materials, to further exploit the potential benefits of this under-utilised metal forming technique. However, although thixoforming of high melting point alloys offers exciting possibilities and tremendous potential, and has already been part of the original work of over thirty years ago, it is currently still in the research stage of development.
  This paper will concentrate on the later strand and will review past and current developments and offer insights to as yet unforeseen possibilities.

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  The influence of Duplex Casting and agitation on the refinement of primary silicon crystals in a hypereutectic Al-Si alloy was investigated. The molten alloys were cast in the space between concentric cylinders composed of a graphite mold and cylindrical alumina stirrer. Conventional single casting without agitation produced coarse primary silicon crystals, and the primary silicon size decreased monotonously as the rotation speed of the stirrer increased. On the other hand, agitation by the stirrer inhibited the proper refinement mechanism of Duplex Casting.

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  The microstructure control and formation behavior of the characteristic microstructures in high Fe content aluminum cast alloy of Al-7%Si-3%Cu-1%Fe during the deformation-semi-solid casting process (D-SSC process) proposed in this work were investigated. The mechanical properties of the fabricated alloy by the D-SSC process were also examined. In the microstructures, the size and shape of the primary α-Al phase and the Fe containing intermetallic compound of the β-Al₅FeSi phase were evaluated. The refined distribution of the β phase and finely spheroidized α-Al phase were simultaneously achieved by the D-SSC process which includes hot-deformation, heating to the semi-solid temperatures and casting. The increased total deformation ratio by the hot-rolling and final deformation ratio result in the decreased size of the α-Al phase after heating at temperatures of the semi-solid state. The β phase decreases mores as the total deformation ratio increases The continuous in-situ observation of the microstructure changes during heating to the semi-solid temperature after hot-deformation was performed using a laser microscope. The recrystallized microstructure of the α-Al phase is first formed and the preferential dissolution of the recrystallized grain boundaries occurs shortly before the dissolution of the eutectic phase with increasing temperature. After dissolution of the grain boundaries, the separation and spheroidization of the α-Al phase occur, after which the characteristic semi-solid microstructure is formed. Deformation by hot-forging and the subsequent semi-solid casting process produce the more refined β phase, which is very effective for achieving excellent mechanical properties of the proof stress of 120 MPa, tensile strength of 265 MPa and elongation of 20%. The proposed D-SSC process is found to be useful for modifying the high amount of Fe into a harmless impurity.

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  In order to develop the near net shaping process of austenitic stainless steels (UNS : s30400) by semi-solid extrusion forming process, microstructure controlling technology and forming technology of this material in the semi-solid state were investigated. Effects of forming temperature, forming rate, and forming pressure on the form ability of its slurry into a metallic mold were studied. Rapid heating of the material before forming into the mold is needed to avoid coarsening of grains in the semi-solid state, but no homogeneous temperature distribution and homogeneous microstructure are obtained. In the case of rapid forming, the liquid phase is injected into the mold preferentially and segregation of the solid and liquid phases occurs. In the case of slow forming, such segregation does not occur, but good fulfillment is not obtained because of rapid cooling caused by sufficient contact with the metallic mold. When these parameters are optimized, defect-free formings are obtained, as are good surface products. By using a stainless steel wire net in place of a multi-hole die, high fluidity and homogeneous microstructures are obtained even at low forming rates. Two- or three-dimensional shape plates can also be formed by optimizing these parameters.

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