Microstructural change in gravity cast Mg−Ni alloys with Ni contents

Abstract

The effects of Ni content on the microstructures of gravity cast Mg-Ni alloys were examined. Different shapes of primary solid particles and microstructures of the eutectic matrix were observed with varying Ni content. The eutectic matrix in the hypoeutectic alloy consisted of rod-like Mg2Ni phase with a small amount of α-Mg phase. The eutectic matrix in the near-eutectic and hypereutectic alloys consisted of eutectic cells oriented in different directions. A transition of lamellae to fiber occurred. The formation of cellular structure and transition of lamellae to fiber resulted from two-phase instability in the coupled region induced by constitutional undercooling.Keywords: Magnesium alloys, Casting, Interface structure, Microstructure, Eutectic solidification Magnesium has strong potential as a hydrogen storage material, because of low density, abundant supply, and low cost. Moreover, it has the highest hydrogen storage capacity among metallic materials. However, poor kinetic properties of hydriding and dehydriding and high working temperature have limited the practical application of Mg-based hydrogen storage materials. Consequently, numerous studies have been carried out in order to improve the hydriding and dehydriding properties of Mg-based materials. In this regard, several methods, including the addition of alloying elements [1][2][3][4][5], intermetallics [6][7][8], and oxides [9][10][11], have been introduced. In particular, a great number of alloy designs based on the Mg-Ni binary alloy have been investigated following the report by Reilly and Wiswall [12] that Ni could improve hydriding-dehydriding kinetics and decrease the working temperature dramatically compared to pure Mg. Many studies focused on the change in hydriding-dehydriding properties of Mg-Ni binary alloys with compositional change and change in processing variables [13][14][15][16]. However, there has been little research on the relationship between microstructure and the hydriding-dehydriding properties of Mg-Ni binary alloys. In this study, the microstructural change in gravity cast Mg-Ni binary alloys with varying Ni content was investigated parting terms of an analysis of change in the hydriding-dehydriding properties of Mg-Ni binary alloys.A pure Mg (99.9 %) ingot was charged into a carbon crucible and heated to 900 o C. After complete melting of the Mg ingot, Ni was added to the molten Mg in chip form in order to be dissolved as quickly as possible so as to minimize the evaporation of Mg at high temperature. Mechanical stirring was carried out in order to homogenize the melt and rapidly dissolve the Ni chips into the Mg melt. A protective gas comprised of CO2 and SF6 gases was blown to the melt surface to prohibit oxidation and ignition of Mg during heating and melting. The alloy melt was poured into a mold of 200 o C after the Ni chips were dissolved into the melt completely.Specimens for microstructural observation were cut into appropriate size from gravity cast Mg-Ni binary alloys and polished mechanically using emery papers ...

Effect of Mn on microstructure, mechanical properties, and corrosion behaviour of Mg-Ni alloys

“…There are many secondary phases observed along the grain boundaries. As per the XRD results and literature survey, the Mg 2 Ni phase is present in Mg-Ni alloys[15,[26][27][28]. As seen in figures 1(a)-(c), with increasing nickel content shapes, the amount and distribution of secondary phases progressively changed.…”

Microstructure Features and Superplasticity of Extruded, Rolled and SPD-Processed Magnesium Alloys: A Short Review

“…Magnesium (Mg) alloys are prospective lightweight (density~1.78 g/cm 3 ) materials and possess a high strength-to-weight ratio and high machinability [1][2][3]. However, these alloys are comprised of hexagonal close packed (HCP) crystal structures and have an inadequate c/a ratio [4][5][6][7][8][9][10]. The complex shape component of thermomechanical-processed wrought alloys cannot be designed due to very complex deformation (different mode of twinning, twinning variants, twinning morphology and twinning types [11]) and limited-slip activity under ambient temperature loading.…”

Hydrogen Absorption/Desorption in Nanostructured Fe- and Ti-Doped Mg₂Ni Alloys

“…In particular, the set up of Mg-Ni binary alloys has continued, as it was reported that Ni improves the hydriding/dehydriding kinetics and decreases the working temperature dramatically compared to that of pure Mg [17]. Several studies have focused on changes in the hydriding/dehydriding properties of Mg-Ni binary alloys with compositional changes as well as with processing variables [18][19][20]. In fact, hydriding properties of nanostructured materials are different from those of crystalline or amorphous ones, with respect to both thermodynamic and kinetic aspects, as reported by Miitschele and Kirchheim [21].…”