COMBINATION OF MECHANICAL AND ELECTROMAGNETIC STIRRING TO DISTRIBUTE NANO-SIZED Al₂O₃ PARTICLES IN MAGNESIUM MATRIX COMPOSITE

Abstract

In this article, a novel stirring method has been developed for producing metal matrix nanocomposites, in which two different stirring methods, i.e. mechanical and electromagnetic stirrings, have been used simultaneously. Mechanical stirring might not be sufficient enough to break nano-agglomerations properly. Moreover, this method makes some unwanted porosities and gas entrapments in the composites. On the other hand, the electromagnetic stirring as a sort of body force (with no considerable shear stresses) could be used up to solidification decreasing the dendrite microstructures, gas entrapments, and undesirable agglomerations and impurities. Applying these both stirring methods simultaneously as an electromagnetic-mechanical stirring method, the distribution of reinforcing nanoparticles throughout the matrix phase would be more desirable due to better stirring conditions. In addition, since it is a simple and applicable approach, it can be used for mass production. Magnesium/Al₂O₃ nanocomposite with volume fractions of 0.5, 1, and 1.5% have been fabricated accordingly and then hot-extruded at 350 °C using 20 : 1 extrusion ratio. According to the scanning electron microscopy (SEM) results, the nanoparticles have an appropriate distribution in the matrix. Also, comparing the results of microstructural evaluation and Vickers microhardness, tension and compression tests, it was observed that the grain size was decreased and the hardness and yield stress (in both tension and compression tests) were improved adding more nanoparticles to magnesium matrix.