Mg-rich Corner Of Mg Research Articles

Discovery of a giant lattice in Mg97Zn1Yb2 alloy

The Mg-rich corner of Mg–metal (M)–rare earth element (REE) ternary systems results in a long-period stacking-ordered (LPSO) phase that increases the strength and elongation of the Mg alloy. Using Yb at the REE position does not result in the LPSO phase; instead, it forms unique crystalline structures with intriguing properties. In this study, we found a new giant lattice belonging to the P6/mmc space group by quenching the Mg97Zn1Yb2 alloy at 723 K. The giant lattice, which precipitates around the α-Mg matrix with a chemical composition of Mg75Zn7Yb18 (at%), comprises a basic structure and a superlattice. We developed an atomic configuration model that expresses the basic structure as alternating stacking of three types of layers. The observed features indicate that the structure of the giant lattice is similar to that of the approximant quasicrystal reported for Mg–M–REE ternary systems.

Experimental investigation of phase equilibria in the Mg-rich corner of Mg-Nd-Sc system

Phase equilibria in the Mg-rich corner of Mg–Nd–Sc ternary system was studied by using the equilibrated alloys method. The partial isothermal sections at 500 °C, 530 °C, and 550 °C were constructed by analyzing the phase constitution and the chemical compositions of the present phases in 19 alloy samples. The Mg3(Mg, Nd, Sc) phase exhibited noticeable ternary solubility introduced by the solid solution of Mg and Sc in the Mg3Nd lattice. (Mg_hcp) showed a narrow homogeneity range paralleling to Mg–Sc binary boundary, whereas Mg41Nd5 showed negligible ternary solubility at all three temperatures. The three-phase equilibrium region of (Mg_hcp) + Mg41Nd5 + Mg3(Mg, Nd, Sc) dominated the Mg-rich corner and was surrounded by three two-phase equilibrium regions constituted by any two of above three phases. The primary crystals and the solidification pathways of alloys in the Mg-rich corner were analyzed via the as-cast microstructure. The matrix phases of (MgSc_bcc) and/or (Mg_hcp) together with the precipitations of Mg3(Mg, Nd, Sc) and other ordering structures could provide additional space to optimize microstructure and properties of Sc-alloyed Mg–Nd alloys.

Effects of Bi addition on solidification behavior of Mg–Al–Zn casting alloys using experiments and CALPHAD calculations

A comprehensive understanding of solidification behavior of Mg–Al–Zn–Bi alloys is necessary for designing novel casting Bi-modified AZ alloys. In this paper, 21 Mg–Al–Zn–Bi alloys were prepared to investigate the phase constituents, morphologies, grain sizes and area fractions of precipitates in as-cast microstructures, as well as their phase transition temperatures and solidification paths by using X-ray diffraction, scanning electron microscopy, optical microscopy and differential scanning calorimetric techniques. It was found that the Bi addition leads to the formation of α-Mg3Bi2 phase, which became coarse flake as Bi content increased. Besides, the Bi addition can modify the morphology of eutectic γ-Al12Mg17 phase and refine the grain size of primary phase. Moreover, the measured area fractions of precipitates increased steadily as Bi content increased, which were comparable with the model-predicated values. After that, the calculated liquidus projections in the Mg-rich corner of Mg–Al–Zn–Bi quaternary system were employed for demonstrating the effects of Bi addition on the solidification sequences. Additionally, the phase transition temperatures predicted via Scheil solidification simulations agreed well with measured values. The present work indicated that the combination of experimental investigations and thermodynamic calculations can serve as an efficient method to obtain accurate and comprehensive solidification behavior of Bi-modified Mg–Al–Zn alloys.

Experimental evidence of the Mg7(Zn, Ag)3 continuous solid solution in Mg-rich corner of Mg–Zn–Ag ternary system at 335 °C

The phase constituents and compositions of a series of Mg–Zn–Ag ternary alloys held at 335 °C have been determined using X-ray diffraction and scanning electron microscopy assisted X-ray energy dispersive spectroscopy. The results indicate that a continuous solid solution, i.e., Mg7(Zn, Ag)3 phase exists stably in the Mg-rich corner at 335 °C, whose composition range is 65.1–76.9% Mg, 2.3–24.3% Zn, and 2.3–24.6% Ag (mole fraction), instead of the Mg3Ag phase reported in earlier studies. Moreover, the Mg7(Zn, Ag)3 phase is in equilibrium with the α-Mg solid solution in the Mg-rich corner, which is completely different with the presently accepted phase equilibria in the Mg–Zn–Ag ternary system. Additionally, Ag and Zn are simultaneously soluble in the α-Mg solid solution, and the maximum total solubility reaches approximately 3 at.%. Simultaneously, the c/a ratio of α-Mg decreases owing to the common solution of Ag and Zn.

Study on glass-forming ability and hydrogen storage properties of amorphous Mg60Ni30La10 − xCox (x = 0, 4) alloys

Mg60Ni30La10−xCox (x=0, 4) amorphous alloys were prepared by rapid solidification, using a melt-spinning technique. X-ray diffraction and differential scanning calorimetry analysis were employed to measure their microstructure, thermal stability and glass-forming ability, and hydrogen storage properties were studied by means of PCTPro2000. Based on differential scanning calorimetry results, their glass-forming ability and thermal stability were investigated by Kissinger method, Lasocka curves and atomic cluster model, respectively. The results indicate that glass-forming ability, thermal properties and hydrogen storage properties in the Mg-rich corner of Mg–Ni–La–Co system alloys were enhanced by Co substitution for La. It can be found that the smaller activation energy (ΔΕ) and frequency factor (υ0), the bigger value of B (glass transition point in Lasocka curves), and higher glass-forming ability of Mg–Ni–La–Co alloys would be followed. In addition, atomic structure parameter (λ), deduced from atomic cluster model is valuable in the design of Mg–Ni–La–Co system alloys with good glass-forming ability. With an increase of Co content from 0 to 4, the hydrogen desorption capacity within 4000s rises from 2.25 to 2.85wt.% at 573K.

Phase equilibria in Mg-rich corner of Mg–Ca–RE (RE=Gd, Nd) systems at 400 °C

The phase equilibria in Mg-rich corner of Mg–Ca–Gd and Mg–Ca–Nd ternary systems at 400 °C were determined through the equilibrated alloy method by using XRD, SEM, EPMA and DSC. Partial isothermal sections in Mg-rich corner of Mg–Ca–Gd and Mg–Ca–Nd ternary systems at 400 °C were constructed from 13 alloys. A three-phase region of α–Mg, Mg41RE5 and Mg2Ca was determined in both ternary systems. It is formed by a similar ternary eutectic reaction L→α-Mg+Mg2Ca+Mg41RE5 at 499.6 °C and 505.6 °C, respectively. It is found that the maximum solubility of Ca in Mg5Gd is 3.68% (molar fraction) and 3% of Gd can be dissolved in Mg2Ca in the Mg–Ca–Gd system at 400 °C. While in the Mg–Ca–Nd system the maximum solubility of Ca in Mg41Nd5 is 3.57% and 1.24% of Nd can be dissolved in Mg2Ca at 400 °C. Other three-phase equilibria existing in Mg-rich corner of Mg–Ca–Gd system are α-Mg+Mg5Gd+T and Mg5Gd+Mg2Ca+T and the three-phase equilibrium in Mg-rich corner of Mg–Ca–Nd system is Mg3Nd+Mg2Ca+ Mg41Nd5.

Hydrogen storage properties of Mg–Ce–Ni nanocomposite induced from amorphous precursor with the highest Mg content

The effect of Ce and Ni contents on the glass-forming ability (GFA) of Mg–Ce–Ni system in the Mg-rich corner of Mg–Ce–Ni system is revealed. Ce is more advantageous for the GFA of Mg-rich Mg–Ce–Ni system than Ni, and the lowest Ce content is ∼5 at.% to obtain the fully amorphous alloy. Amorphous alloy with the highest Mg content, Mg90Ce5Ni5, was obtained by melt-spinning. With the amorphous alloy as precursor, nanostructure multi-phases compositae was prepared by crystallizing it in hydrogenation process. The compositae with reversible hydrogen storage capacity of 5.3 wt.% shows much faster kinetics and lower MgH2 desorption activation energy than those of induction-melt Mg90Ce5Ni5 alloy. Both in situ formed nanosized Mg2Ni and CeH2.73 act as effective catalysts and significantly improve the hydrogen storage properties of MgH2.

Experimental investigation and thermodynamic assessment of the Mg–Zn–Gd system focused on Mg-rich corner

The phase equilibria in the Mg-rich corner of Mg–Zn–Gd ternary system at 673 K were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA). Three ternary phases, X-(Mg12ZnGd), W-(Mg3Zn3Gd2) and I-(Mg3Zn6Gd1), have been identified, which are in equilibrium with Mg solid solution. A thermodynamic modeling and optimization of Zn–Gd and Mg–Zn–Gd systems has been carried out for the first time using the CALPHAD method. The sublattice model was used to describe the thermodynamic functions of both solution phases and intermetallic phases presented in these systems. In particular, order/disorder transition between BCC_B2 and BCC_A2 has been taken into account, and their Gibbs energies were expressed with identical function. The thermodynamic database was applied to case studies of experimentally observed microstructures and demonstrated that it is a valuable basis for alloy design.

The maximum solubility of Y in α-Mg and composition ranges of Mg 24Y 5 − x and Mg 2Y 1 − x intermetallic phases in Mg–Y binary system

The solid solubility of Y in the α-Mg matrix and composition homogeneity ranges of Mg 24Y 5 − x and Mg 2Y 1 − x phases in the Mg–Y binary system are important parameters to understand solid–solution- and aging-strengthening effects of Mg–Y-based alloys. However, they are different among the various assessed Mg–Y phase diagrams which are based on limited experimental data, especially at temperatures below ∼850 K. Our experimental results by using both diffusion couple technique and alloy method are in good agreement each other, but much different from the presently accepted Mg–Y phase diagram. The results show that the maximum solubility of Y in the α-Mg matrix is 4.7 at.% Y, much larger than the current phase diagram. The determined composition homogeneity ranges of Mg 24Y 5 − x and Mg 2Y 1 − x phases are much wider than the present ones and shift remarkably to the Mg-rich corner of Mg–Y phase diagram.

Phase equilibria on the ternary Mg–Mn–Ce system at the Mg-rich corner

Three isopleths at the Mg-rich corner of Mg–Mn–Ce ternary system were investigated via thermal analysis, SEM/EPMA and XRD. A ternary eutectic reaction was observed at ∼1 wt.% Mn and 23 wt.% Ce and 592 °C. A solid-solution type ternary intermetallic compound, (Mg,Mn) 12Ce, was observed with 0.5 at% solid solubility of Mn in the tetragonal Mg 12Ce. With the aid of thermodynamic modeling and experiments, a revised phase diagram for the binary Mg–Ce system and the isopleths of 0.6, 1.8 and 2.5 wt.% Mn were proposed up to 25 wt.% Ce.

Phase equilibria and solidification of Mg-rich Mg–Al–Zn alloys

Phase equilibria in Mg-rich corner of Mg–Al–Zn system are analyzed in detail. Thermodynamic calculations are compared with literature data and own key experimental results by means of DSC and DTA measurements. The detailed comparison strongly supports the reliability of the selected thermodynamic description. Furthermore, our focus is placed on proper interpretation of experimental results obtained by thermal analysis. Based on thermodynamic calculation, it is clarified that a signal observed in thermal analysis, which was interpreted as end of solidification in the literature, is related to the start of the monovariant eutectic reaction L + (Mg) + γ-Mg 17Al 12 under non-equilibrium condition and the solidification process ends at lower temperature. This fact is supported by our microstructural observation.