Shae-Kwang Kim

Dehydrogenation properties of nano-/amorphous Mg2NiHx by hydrogen induced mechanical alloying

Abstract In recent years, nanocrystalline materials have been of interest for hydrogen storage applications. Especially, the great improvement of the hydrogenation properties of Mg alloys that can be achieved by nanocrystallization. In this study, nanocrystalline Mg2NiHx is fabricated from Mg and Ni chips by hydrogen induced mechanical alloying (MA) for 96 h under a high-pressure hydrogen atmosphere. The balls to chips mass ratios (BCR) are 30:1 and 66:1. The particles obtained are characterized by XRD and TEM, and absorbed hydrogen contents (AHC) were measured by TGA. For dehydrogenation kinetics, activation energies are calculated by isothermal thermogravimetry analysis (ITGA) and pressure–composition-isotherm (PCI) analysis. The results of XRD and TEM revealed that the Mg2NiHx peaks are broadened in the case of high BCR and the particles are composed of the nanocrystalline phases less than 10 nm with the amorphous phase. The results of ITGA and PCI analysis show that the dehydrogenation kinetics are greatly improved by nanocrystallization. The results show that BCR conditions mainly affect the size and fraction of the nanocrystalline phases, the resultant AHC and the dehydrogenation kinetics.

Investment casting of AZ91HP magnesium alloy

This paper describes AZ91HP magnesium alloy investment casting. The aim of this study is to optimize the process for magnesium investment casting. Special attention was given to evaluating the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZr03, and silica bonded A1203 and ZrSi04. Also, the microstructural features of the as-cast alloy were investigated, and the effect of the processing parameters on the microstructure and mechanical properties were evaluated describing the grain size, hardness and ultimate tensile strength of the as-cast alloy.

Rotation-cylinder method for fabrication of SiC particle reinforced magnesium composites

A new molten metal mixing process, RCM (Rotation-Cylinder Method) for incorporating reinforcement particles into molten magnesium, has been developed for manufacturing SiC particle reinforced magnesium composites in an ambient atmosphere. The RCM can be characterized by the U-shaped laminar melt surface with the Rankine vortex, which significantly reduces particle agglomeration and entrapped slags, such that composites of improved microstructure and properties can be manufactured successfully in conjunction with the subsequent fabrication processes. The RCM can incorporate SiC particles (5 urn size and larger) into molten magnesium with particle volume fractions of up to 20 vol.%. In this paper, the development background, the characteristic vortical motions, the optimum manufacturing conditions and the in-process wetting procedures of the RCM are described.