Magnesium Technology 2020: Solidification and Production of Magnesium
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: J. Brian Jordon, Baylor University; Victoria Miller, University of Florida; Vineet Joshi, Pacific Northwest National Laboratory; Neale Neelameggham, IND LLC

Thursday 8:30 AM
February 27, 2020
Room: 6C
Location: San Diego Convention Ctr

Session Chair: Neale Neelameggham, IND LLC; Yuan Yuan, Chongqing University


8:30 AM  Invited
Thermodynamic Description and Thermophysical Properties of Mg-Gd Alloys and Quantitative Phase-field Simulation of their Solidification Process: Lijun Zhang1; 1Central South University
     This paper firstly established a set of thermodynamic descriptions for the Mg-Gd system by means of CALPHAD approach, which show better agreement with the experimental phase equilibria and thermochemical data in the literature than the previous assessments. In terms of diffusion coefficients, the HitDIC software (https://hitdic.com/) was employed to evaluate the diffusion coefficients of solutions and compounds, from which the atomic mobilities were obtained by using the DICTRA software. Moreover, based on the obtained thermodynamic descriptions, the composition and temperature-dependent liquid-solid interfacial energies for Mg-Gd system was also evaluated using our developed OpenIEC code (https://github.com/openiec). Subsequently, the established CALPHAD thermodynamic, atomic mobilities and interfacial energy descriptions were coupled with the phase-field model with finite interface dissipation, and three-dimensional phase-field simulations of evolution of the primary (Mg) dendrites during the solidification of Mg-Gd alloy were carried out. The simulation results are in good agreement with the experimental data.

9:00 AM  
Investigation and Modeling of the Influence of Cooling Rates on the Microstructure of AZ91 Alloys: Sarkis Gavras1; Muhammad Umer Bilal1; Domonkos Tolnai1; Norbert Hort1; 1Magic, Helmholtz-Zentrum Geesthacht
    An increasingly important tool in modern experimental investigations is the ability to accurately produce a digital model or “digital twin” of samples and their properties. This goes hand-in-hand with the primary tenant of Industry 4.0 which is to provide advanced manufacturing solutions through the use of cyber-physical systems. A comparison of the effect of various quenching rates using liquid nitrogen, water at 5°C, water at 20°C and in air on the microstructure of permanent mould cast AZ91 was investigated. Particular emphasis was centred on the changes in microstructural features such as grain size and dendrite arm spacing. A phase-field method was used to produce a digital twin and qualitative analysis of the investigated cooling rates on AZ91. The combination of practical microstructural investigations and simulated microstructures will advance the knowledge of cooling rate influences on AZ91 and their ability to be accurately simulated to assist with property and microstructural predictions.

9:20 AM  
The Independent Effects of Cooling Rate and Na Addition on Hydrogen Storage Properties in Hypo-eutectic Mg Alloys: Manjin Kim1; Yahia Ali1; Stuart McDonald1; Trevor Abbott2; Kazuhiro Nogita1; 1The University of Queensland; 2Magontec Ltd.; The University of Queensland
    The addition of trace chemical refiners such as Na and Sr and rapid cooling are well-established methods for modification of the faceted eutectic Si and Ge in Al-Si and Al-Ge systems to improve mechanical properties. There have been some efforts to extend this strategy to Mg-based alloys. For example, it has been reported that trace Na addition to Mg-Ni alloys can also refine the eutectic Mg2Ni phase and facilitate functional property improvements such as hydrogen absorption kinetics. In this work, we have extended this strategy to a variety of other Mg-based alloys such as Mg-La alloys adding chemical refiners to Mg-based alloys and solidifying at several different cooling rates. The modification of the eutectic morphology in these alloys is discussed with regards to alpha parameters which were calculated using Thermo-Calc. The relationship between eutectic modification mechanisms and hydrogen absorption kinetics in these alloys is investigated.

9:40 AM  
Producing High Purity Magnesium (99.99%) Directly by Pidgeon Process: Bo Yang1; Fei Liu1; Bo-Yu Liu1; Zhi-Min Chang1; Lu-Yao Mao1; Jiao Li1; Zhi-Wei Shan1; 1Xi'an Jiaotong University
    Pure magnesium is the foundation of the entire magnesium industry. Over 90% of the pure magnesium on the market is produced in China using Pidgeon process. Even though the quality of pure magnesium has been improved significantly in the past decades, the majority of them is still suffering the following problems: the purity is only ~99.9%; there are still too many kinds of harmful impurity elements with their content fluctuated greatly in an uncontrollable manner. The impurities can be passed to magnesium alloys and degrade their properties significantly, especially their corrosion resistance ability. This leaves people an impression that Pidgeon process cannot produce high purity magnesium directly. As a consequence, it has long been accepted that producing high purity magnesium requires additional processes, which is usually costly and time consuming. Based on the analysis of the source of the impurities and the temperature feature of the reduction retort, we developed a new technique that can produce high purity magnesium (99.99%) directly by Pidgeon process without significantly increasing the costs. The application of this new technique is expected to benefit the entire magnesium industry.

10:00 AM Break

10:20 AM  
Research on Properties of Prefabricated Pellets of Silicothermic Process After Calcination in Flowing Argon Atmosphere: Junhua Guo1; Ting-an Zhang1; Daxue Fu1; Jibiao Han1; Zonghui Ji1; Zhihe Dou1; 1Northeastern University
    In the Pidgeon process, the separation of calcination and reduction process leads to a long production cycle and high energy consumption. Based on the novel preparation method of pellets of silicothermic process, the low-grade magnesite with abundant resources in Liaoning Province was used as raw material, calcium source, reducing agent and fluorite were added to pelletize directly, and then calcined and reduced in flowing argon atmosphere. The properties and micromorphology of prefabricated pellets after calcination were investigated in the work. The experimental results showed that the hydration activity and compressive strength of prefabricate pellets after calcination reached 23.0% and 998 N, respectively. The recovery ratio of magnesium metal was more than 80% in the reduction process. The research on calcination of prefabricated pellets in flowing gas provided a theoretical basis for continuous extraction of magnesium.

10:40 AM  
Producing Pure Magnesium Through Silicothermic under the Atmospheric Pressure: Fei Liu1; Bo Yang1; Bo-Yu Liu1; Jiao Li1; Zhi-Min Chang1; Zhi-Wei Shan; 1Xi'an Jiaotong University
    The majority of pure magnesium produced worldwide are made by using Silicothermic method (Pidgeon process). However, the Pidgeon process suffers poor efficiency, low industrial concentration and intermittent production. The main reason is that Pidgeon process requires to keep the reaction chamber in vacuum state during the entire reduction process. By analyzing the thermodynamic reaction principle, we reveal that it is the low magnesium partial pressure instead of vacuum that is necessary for the Silicothermic process. Based on this understanding, we develop a new technique that can produce pure magnesium under the atmospheric pressure by using silicothermic method. The magnesium production efficiency of this new technique is comparable to the widely used Pidgeon method. The industrialized application of this exciting technique is expected to help the Silicothermic to realize high efficiency, automated and continuous production while at the same time completely change the poor production conditions, reduce energy consumption and pollution.

11:00 AM  
Effect of Temperature on Magnesium Vapor Condensation in Inert Carrier Gas: Jibiao Han1; Ting-an Zhang1; Daxue Fu1; Junhua Guo1; Zonghui Ji1; Zhihe Dou1; 1Northeastern University
    The process of magnesium extraction by silicothermic process is in vacuum, which leads to discontinuous production. The condensation of magnesium vapor in inert gas is an important step to realize continuous magnesium production. In this paper, the condensation behavior of magnesium vapor in inert carrier gas is studied. The effects of temperatures on the condensation phenomenon, condensation area, condensation weight and microstructure of magnesium vapor were investigated. The results show that three different condensation appearance can be obtained by magnesium condensation in argon gas conditions. With the increase of temperature, the condensation temperature of magnesium vapor increases, the mass of large particles of magnesium decreases, the mass of powdered magnesium increases; higher purity of magnesium can be obtained at different temperatures, which can provide theoretical support for continuous magnesium production process.

11:20 AM  Cancelled
Thermodynamic Descriptions of the Quaternary Mg-Al-Zn-Sn System and Their Experimental Validation: Ting Cheng1; Lijun Zhang1; 1Central South University
    A brief review on the thermodynamic descriptions of all the sub-binary and ternary systems in the Mg-Al-Zn-Sn system available in the literature was first performed, from which the most reliable ones were chosen. After that, thermodynamic description of the quaternary Mg-Al-Zn-Sn system was established via the direct extrapolation of the chosen thermodynamic descriptions of the sub-binary and ternary systems in the framework of CALculation of PHAse Diagrams (CALPHAD) approach. The reliability of the established thermodynamic database was finally validated through a comprehensive comparison of the model-predicted solidified microstructure characteristics and phase fractions in different quaternary alloys with the experimental ones.