Thixoforming of Aluminium-Silicon Alloys in a Mechanical Eccentric Press

Abstract:

The semisolid processing technology is not widely used due to the high cost of raw material and the equipment it requires. New low-cost raw materials and processes could be the key to expand the use of this technology. This paper describes an initial effort to develop new Al-Si-Mg in terms of raw material production and processing. The morphological evolution of all the alloys produced was characterized during their reheating to the semisolid state at 45 and 60% solid fraction, as well as the semisolid behaviour in terms of viscosity versus shear rate. The adaptation of the semisolid technology to the thixoforming process via eccentric press was tested using an equipment up to 25 tons. This type of equipment is not commonly employed in this kind of processing. Results indicate that alloys with low silicon content, e.g., 2 or 4wt%Si, behave similarly to alloys with 7wt%Si, which are normally used in the thixoforming process, with a viscosity of about 2 * 105 Pa.s. The semisolid behaviour of low silicon alloys indicates the potential expansion of the range of raw materials for this application. Thixoforming of semisolid materials in an eccentric press appears to be a very promising technology, yielding parts that, despite their simplicity and restricted shape, display a very good final mechanical behaviour.