Grain Refinement of Magnesium Alloy AZ91D Cast in Permanent Mold Using Mechanical Vibrations

摘要

Castings of magnesium alloys having a microstructure composed of uniformly distributed small and equiaxed grains generally possess better overall properties. A more uniform solute distribution is obtained with fine grains and the tendency for hot tearing is reduced. The fine texture resulting from formation of numerous nuclei ultimately leads to stronger alloys having better ductility, improved fatigue resistance and toughness. The application of vibrations during metal solidification produces grain refinement. Numerous papers have been published on this topic for various metals and commercial alloys. However, in foundry operations it is not common. This situation can be partially attributed to a lack of understanding of principles behind mechanically-enhanced nucleation and their application. Technical problems associated with the production and distribution of mechanical vibrations also explain this situation. In this study, AZ91D magnesium alloy has been cast in a preheated permanent steel mold in the presence of mechanical vibrations induced by a simple device. The results presented in this paper include an evaluation of the influence of mechanical vibrations on the microstructure, mechanical properties and surface finish of cast AZ91D alloy.