Abstract：Steel is a particularly challenging material to semi-solid process because of the high temperatures involved and the potential for surface oxidation. Here the experience of semi-solid processing will be reviewed and the current situation in relation to commercial application assessed. The review will include discussion of the range of potential steel materials which are amenable to thixoformingn and identification of suitable steels; modelling of die fill and rheological properties of semi solid steel; technology considerations for industrialisation; die development and the properties of thixoformed products.

Thixoforming of steel offers the advantages of casting technology in combination with high mechanical strength that can only be achieved by forging. The progress in establishing this technology in industry depends on the success in the development of suitable steel grades. Recent investigations dealt with the development of steel grades that are especially adapted to the thixoforming process. For this, alloys were developed with a lower solidus temperature and a wider process temperature range compared to classic forging steels. In consequence, the inductive heating process is more tolerant to inaccuracies and for a given liquid fraction the process temperature window is easier to handle. It is desired to obtain great degrees of deformation at rather low forming forces as these parameters determine the size of the needed presses. This behaviour is affected by the present liquid fraction in the slug and the heat transfer between work piece and die. It was detected that variations of the forming force have a direct influence on the quality of the thixoformed parts. In order to make the thixoforming technology of steels competitive versus other forming technologies, the parts must show a favourable microstructure and thus, good in-use properties. In this paper various solutions are compared. The main results obtained in the optimization research, namely, the steel grades adapted to semi-solid forming, the resulting process parameters and the mechanical properties of thixoforming parts will be presented for two exemplary steel grades. By producing a real automotive part, thixoforging of steels with regard to the adapted materials and to the ongoing industrial implementation of this process is proved.

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Abstract. Thixoforging is a type of semi-solid metal processing at high solid fraction (0.5

Through different papers [1,2], authors shown that the influence of thermal exchanges was a first order parameter on the semi-solid steel behaviour, and certainly for every semi-solid metallic materials. These thermal exchanges hide other parameters effect like, for example, the strain rate influence. This paper tries to determine the influence of these two parameters by using a new extrusion device on a hydraulic press. This new tools conception annihilated the influence of the decrease of the punch speed before stopping and permitted to have a constant speed during the experiment. This work also deals with the homogeneous flow during thixoforming of steel and shows the importance to couple initial temperature of the slug with punch speed. This paper presents different conditions which permitted to have a homogeneous flow by keeping a low load.

Steel is a particularly challenging material to semi-solid process because of the high temperatures involved and the potential for surface oxidation. Here the experience of semi-solid processing will be reviewed and the current situation in relation to commercial application assessed. The review will include discussion of the range of potential steel materials which are amenable to thixoforming including thermodynamic prediction of suitable alloy compositions.

Abstract. Thixoforging involves shaping alloys with a globular microstructure in the semi-solid state. To reach this kind of material, the Recrystallisation and Partial Melting (RAP) process can be used to obtain a globular microstructure from extruded material with liquid penetrating the recrystallised boundaries. Induction heating is used to apply the RAP process to slugs. One of the benefits of using this method of heating is the fast heating rate (20°C/s). This paper will help to improve heating parameters by showing their influence on 7075 aluminium alloy recrystallisation. These parameters are the heating rate; heating frequencies-power; presence or not of protective gas; position of the slug in the inductor; energy stored inside the slug; oxide layer on the slug side; chamfer of the slug upper corner.