Conception of tooling adapted to the thixoforging of high solid fraction hot-crack-sensitive aluminium alloys

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. Tooling has to be adapted to this particular process to benefit of shear thinning and thixotropic behaviour of such semisolid material. Tooling parameters, as the forming speed and tool temperature, have to be accurately controlled because of their influence on thermal exchanges between material flow and tool. These thermal exchanges influence the high-cracking tendency and the rheology of the semisolid material during forming which affect parts properties. This paper shows, thanks to extrusion tests, how thermal exchanges influence surface quality of thixoforged parts made in 7075 aluminium alloys at high solid fraction by modifying process parameters like forming speed, tool temperature and tool thermal protector. A direct application is the evaluation of surface quality of thixoforged thin wall parts made in 7075 aluminium alloys.