Physics and Mechanics of Fluids, Microfluidics

Grain size reduction by electromagnetic stirring inside gold alloys

R. Ernst^a1, N. Mangelinck-Noël^a2, J. Hamburger^a1, C. Garnier^a1 and P. Ramoni^a3

Laboratoire CNRS-EPM, ENSHMG, BP 95, 38400 Saint-Martin-d'Hères Cedex, France

Laboratoire L2MP, Université Paul Cézanne-Aix-Marseille III, Campus de Saint Jérôme, Service 142, 13397 Marseille Cedex 20, France

Metalor Technologies SA, Neuchâtel, Switzerland

Abstract

The final properties of cast materials depend greatly on the solidification process undergone by the material. In this paper, we study gold alloys dedicated to the watch industry and jewellery in the framework of a research collaboration with the Metalor Company. The aim is to improve the concentration homogeneity of the ingots by controlling the solidification step. It can be achieved by reducing segregations by a decrease in the grain size. For this purpose, we set up a multiphase electromagnetic stirring of the melt to favour the growth of finer grains and improve the homogeneity of the composition. We first design an electromagnetic stirrer by numerical simulation. The stirrer is then implemented on a model experiment. Eventually, the alloys are characterised by metallography and etching to evidence the grain structure. As expected, we obtain a substantial reduction of the grain size although, some work remains to be done to attain the final goal of even finer grains.

(Received May 28 2004)

(Revised October 18 2004)

(Accepted December 20 2004)

(Online publication March 4 2005)

PACS:

• 44.27.+g – Forced convection;
• 81.05.Bx – Metals, semimetals, and alloys

Nathalie.mangelinck@l2mp.fr