Some Physicochemical Phenomena Observed During Fabrication of Mg-C Cast Composites

Abstract

Some effects acquired in composites processed under industrial conditions were presented. Glassy carbon particles (GCp) and short carbon fibers were applied in magnesium matrix composites fabricated by suspension casting. As the matrix magnesium alloys with Al and without Al but with Zn, Zr and rare earth elements (RE) were used. The main interest was focused on the behavior of the reinforcing components, depending on the magnesium alloying elements. The observation of the stirred suspensions during their industrial processing detected an effect of carbon components’ migration to the top of the crucible, suggesting segregation processes. Experiments with unmixed suspensions performed by way of remelting the composites with uniformly distributed reinforcement showed that the segregation effect depends on the magnesium matrix composition. In the case of the alloy with Al, two zones with (top) and without reinforcement can be formed. For the alloys with Zn, Zr, and RE, an additional zone of segregated carbon reinforcement can appear directly at the bottom of the crucible. The SEM/EDS examination also showed some differences in the influence of the magnesium matrix on the carbon reinforcement dependent on the applied alloying elements. The most destructive effect was detected for the Al-containing alloy and minor defects in GCp were formed when Gd with Nd were applied.