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The effect of heating rate on the microstructural breakdown required for thixoformability

Cecília T. W. Proni and Eugênio J. Zoqui

Abstract

Thixoforming processes depend upon three basic features of the semisolid slurry: the thermodynamics of the liquid-to-solid transition; the morphology of the microstructure; and the slurry's rheological properties. By studying the thermodynamics of the solid-to-liquid transition of a specific alloy, one can determine whether the entire thixoforming process can be controlled when the alloy is used as the raw material. The rheology of the semisolid material is determined not only by the morphology of the microstructure of the primary solid phase immersed in the liquid, but also by the relative amounts of liquid and solid. In thixoforming operations the raw material is heated up to the semisolid state and injected into the die. Hence, the heating procedure has a significant impact on the morphology of the remaining solid and, consequently, its viscous behaviour, as shown in this paper. A heating rate close to 50 K min−1 was found to produce the most suitable morphology for semisolid processing as the mechanisms involved (Ostwald ripening and coalescence) were present to an equal extent.


*Correspondence address, Cecília Tereza Weishaupt Proni, PhD, Eugênio José Zoqui, Professor, Materials and Manufacturing Department, Faculty of Mechanical Engineering, University of Campinas – UNICAMP, R. Mendelev 200, Campinas, SP, 13083-860, Brazil, Tel.: +551935213296, Fax: +551935213722, E-mail: , E-mail: , Web: http://lattes.cnpq.br/5094974411402019

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Received: 2016-08-04
Accepted: 2016-12-21
Published Online: 2017-02-22
Published in Print: 2017-03-13

© 2017, Carl Hanser Verlag, München