In Situ Formation and Refinement of Mg2Si in Fiber-Reinforced AZ91D Magnesium Alloy*

In order to obtain a lightweight material having an excellent high-temperature strength, Mg alloy composites reinforced with short alumina fibers and in situ Mg2Si particles were fabricated. The composites were fabricated by pressureless infiltration of the Mg alloy melt into the preform consisting of the fibers and attached Si particles. The volume fraction of Si particles in the preform, the melting temperature of the Mg alloy, and the cooling rate after the infiltration were varied. P and CaF2 particles were also used as refiners of the Mg2Si. Based on the results, the conditions dispersed the Mg2Si particles finely and homogeneously and the formation and dispersion mechanism of the Mg2Si were clarified. Although the Si content exceeds its equilibrium solubility in the Mg melt when the volume fraction of the Si particles was 9.5 vol%, all of the Si particles reacted with the Mg alloy melt to form Mg2Si particles. The Mg2Si particles were homogeneously dispersed in the matrix, because the segmentation of Mg2Si particles in the infiltration was prevented due to the presence of fibers. As the melting temperature decreased or the cooling rate after the infiltration increased, the Mg2Si particles became finer. The introduction of P or CaF2 further promoted the refinement of the Mg2Si particles. [doi:10.2320/matertrans.F-MRA2007834]