The segregation phenomena in structure forming process of composites by plastic working
Grzegorz Skorulski, Jan Piwnik, Piotr Baranowski
Quarterly No. 3, 2010 pages 235-239
DOI:
keywords: segregation, structure of composities, semi-solid extrusion
abstract Thixotrophy is a property shear-thinning fluids have to show a time-dependent change in viscosity, the longer the fluid undergoes shear stress, the lower its viscosity. The most important problem regarding the thixoforming process is the prevention of the liquid segregation phenomena during deformation. So, it is take place during forming process of composities by plastic working. Since the liquid is of eutectic composition in materials, the liquid segregation will result in significant or undesirable situation. In this work, thus, the thixoforming experiments with a die designed to modelling extrusion process using substitute materials were carried out successfully. The die filling patterns of semisolid materials by varying the process parameters, such as geometry of the die and pressing force, have been investigated. During hot extrusion of complex profiles the billet is split into separate metal streams by the bridges of the die. Behind the bridges the metal streams join and are welded together to form the required profile. Welds formed this way lie along the product length and are referred as longitudinal welds. Since the majority of profiles are produced in continuous length, the extrusion products apart from longitudinal welds contain also transversal welds representing pints between successive billets. To produce a successful extrusion it is necessary to assure stress, flow and temperature conditions such that sound welds can be obtained. In general the weld quality is considerably influenced many factors relating to the die design, billet material and extrusion conditions (ram velocity, billet and die temperature).The segregation phenomena and formation of agglomerate have the basic influence on structure of the final product. The aim of this work is analyzing the phenomena of segregation in semi-solid extrusion process, using several kind of substitute materials, which can simulate the thixotrophic fluid behavior and displacement of solid particles. The experimental researches are made to investigation of segregation in the near-wall layers and the formation of agglomerate. Especially, the distribution of the solid particles at the end of extrusion process have been taken into consideration.