Mg–Zr母合金によるマグネシウムの結晶粒微細化

抄録

Effects of Zr addition via Mg–Zr master alloy on the grain refinment in the magnesium ingots was investigated in view of grain size and concentration of soluble Zr. Specimens were prepared by adding Zr up to 2.0 mass% at temperatures 993 K, 1033 K and 1073 K, and examined using optical microscope (OM), scanning electron microscope (SEM) and electron-probe micro analyzer (EPMA). It was found that concentration of soluble Zr was almost independent of the melt temperature between 993 K to 1073 K, where the master alloy was introduced. Grain size was decreased with increasing soluble Zr content exponentially and, at 0.4mass%Zr or more, grain size become constant at about 30 μm (permanent molded castings) and 70 μm (shell molded castings), even if the peritectic composition, 0.6 mass%Zr was not reached. SEM and EPMA observation revealed substructure including Zr-enriched cored area, which is formed characteristically; i.e., in the most cases, metallic Zr particle is located at the center of the core, surrounded by several rings, each of which is made up by Zr enriched Mg solid solution. Such experimental results suggest that some undis-solved Zr particles play an important role in the nucleation of the observed ring structure and this grain refinement pro-ceses is based on non-equilibrium solidification.