Papers by Keyword: Magnesium

Abstract: Magnesium alloys are potential biodegradable implant materials. However, magnesium alloys normally corrode rapidly in the in-vivo fluid, resulting in subcutaneous gas bubbles and alkalisation of the in-vivo solution. The paper presents a new approach to control the degradation rate of magnesium in a simulated body fluid (SBF) through employing a recently developed anodising technique. It was found that the ceramic like anodised coating formed on the surface of magnesium can effectively slow down the biodegradation process and hence result in slow hydrogen evolution and solution alkalisation processes. The results imply that an anodised magnesium alloy may be successfully used as a biodegradable implant material.

Abstract: This paper provides an overview of the key areas of magnesium research and development being undertaken internationally and consideration of the future challenges confronting the further implementation of magnesium components. This paper will also include a description of some of the technologies that the CAST Cooperative Research Centre has developed and licensed for commercialisation which address some of the future challenges. There will also be a brief overview of the extent of Australia’s commitment to magnesium alloy research through the CAST CRC, the Centre of Excellence for Design in Light Metals and the CSIRO including their Light Metals Flagship program.

Abstract: TiB2 particulate reinforced magnesium matrix composites were successfully fabricated by adding a TiB2–Al master alloy processed via the flux-assisted synthesis (FAS) reaction into molten magnesium. X-ray diffraction (XRD) analysis and microstructural characterization of the TiB2–Al master alloy revealed the formation and uniform distribution of TiB2 reinforcements. By stirring, magnesium matrix composites with dispersed homogenously TiB2 particles can be obtained. Microstructural characterization of the TiB2/Mg composites revealed retention of hexagonal or rectangular TiB2 particulates with the size of about 1 μm.

Abstract: The (AlN+Mg2Si)/Mg metal matrix composite was successfully fabricated by adding Si3N4 into Mg-Al alloy. The formation mechanisms of AlN and Mg2Si were analyzed; the effects of synthesizing temperature and holding time were investigated as well.

Abstract: The present paper examines the development of grain size during the recrystallization of magnesium alloys and the influence the grain size has on the mechanical response. In magnesium alloys grain refinement improves the strength-ductility balance. This simultaneous increase in both strength and ductility is ascribed to the impact the grain size has on deformation twinning. The mechanisms by which the grain size is established during hot working are shown to be conventional dynamic recrystallization followed by post-dynamic recrystallization. The role of alloying addition on both of these reactions is briefly considered.

Abstract: “Environmental cell” microscopy was applied for surveying gas reaction of hydrides in magnesium base alloys, which are candidates for hydrogen storage materials in advanced hydrogen energy systems. In order to clarify the mechanism of hydrogenation process, in-situ experiment has been carried out by using a 200 kV transmission electron microscope (TEM) equipped with a newly developed environmental cell, which is capable to 0.1 MPa in the temperature range between R.T. and 200°C. When hydrogen gas reacted with magnesium powders, straightening of surface steps (60~70 nm in height) was observed, indicating that volume expansion occurred. In addition, the formation of MgH2 was indicated in selected-area-diffraction patterns (SADP). The precise study on this in-situ experiment, as well as its improvement, will be continued, with using transparent films.

Abstract: Microstructures and hydrogen storage properties of Mg-Al super laminate composite alloys were investigated. The laminated sample was made by alternately stacking Mg films and Al films. The laminate was subjected to repetition of stacking and cold-rolling under an ambient condition (super lamination technique), combined with final heat treatment under an argon gas atmosphere. The number of films and thickness was nearly 15000 layers and about 50μm, respectivery. Their microstructures and hydrogen storage properties were studied by scanning electron microscopy, X-ray diffractometry and volumetric method by use of a Sieverts-type apparatus. In heat treatment process at 673K, Mg17Al12 intermetallic compound was formed by interdiffusion. This compound absorbed and desorbed hydrogen reversibly through the disproportionation and recombination react at 673K.

Abstract: In order to clarify the effect of alloying elements on the axial ratio of magnesium binary solid solutions, the solid solutions of Mg-Al, Mg-Zn, and Mg-Li with various concentrations were casted and homogenized. Synchrotron X-ray diffraction patterns were then obtained from annealed powder samples and analyzed using the Rietveld method. The effects of solutes concentration on lattice parameters were explained on the basis of atomic size difference and valence electron effect, which changes electron overlap of magnesium. It has been found in this study that Al and Li raise and reduce the c/a ratio, respectively, while Zn has no effect on the c/a ratio.

Abstract: The extruded AZ31B Mg alloy specimens using powders fabricated by roll compaction processing (RCP) was prepared, and their corrosion behavior has been investigated through the polarization test, electrochemical impedance spectroscopy test, immersion test and SEM observation in comparison to that of the conventional AZ31B Mg alloy, hereafter shortened as I/M specimen. The extruded AZ31B Mg alloys using RCP powder showed little change in Ecorr irrespective of number of pass cycles. Both anodic and cathodic current density suppression of the RCP specimens became larger with an increase in number of pass cycles. It was also confirmed that the corrosion characteristics of the RCP specimens depended strongly on their structural morphology and that the corrosion resistance of the RCP specimens subjected to 50 pass cycles was nearly same as that of the I/M specimen.

Abstract: We studied the fatigue strength of lotus-type porous magnesium with cylindrical pores aligned unidirectionally, which was fabricated through unidirectional solidification in pressurized hydrogen atmospheres. The fatigue strength shows anisotropy; the fatigue strength in the direction parallel to the longitudinal axis of pores is higher than that in the perpendicular direction. Not only anisotropic pores but also fiber texture grown along the pore direction contributes to the anisotropy in the fatigue strength.