Magnesium Technology 2017: Solidification and Processing I
Sponsored by: TMS Light Metals Division, TMS: Magnesium Committee
Program Organizers: Kiran Solanki, Arizona State University; Dmytro Orlov, Lund University; Alok Singh, National Institute for Materials Science; Neale Neelameggham, Ind LLC

Tuesday 2:00 PM
February 28, 2017
Room: 5A
Location: San Diego Convention Ctr

Session Chair: Neale Neelameggham, Ind LLC; Tracy Berman, University of Michigan

2:00 PM  
Microsegregation in High Pressure Die Cast Mg Alloys: Tracy Berman1; Mei Li2; John Allison1; 1University of Michigan; 2Ford Motor Company
    Expanding Integrated Computational Materials Engineering (ICME) capabilities for high pressure die cast (HPDC) and super vacuum die cast (SVDC) magnesium alloys will result in significant reductions in the time and cost required to develop components and optimize the casting and heat treatment processes. In this work, a description of segregation in SVDC Mg-Al binary and Mg-Al-Mn ternary alloys is obtained by combining quantitative electron probe micro-analysis (EPMA) mapping in conjunction with an EPMA forward simulation model. High precision MagmaSoft SVDC simulations are coupled with EPMA segregation profiles to develop a location-dependent microsegregation model that accounts for solute trapping. This approach successfully describes the macrosegregation and eutectic phase fraction observed through the casting thickness. Additionally, eutectic phase dissolution kinetics and changes in microsegregation after solution treatment are studied using EPMA mapping and DICTRA simulations. Approaches for incorporating these results into the emerging ICME capabilities for HPDC Mg will be described.

2:30 PM  
Numerical Simulations of TRC Equipped with a Core: Jong-Jin Park1; 1Hongik University
    TRC(Twin-roll casting) has been used for production of sheets of aluminum alloys for a long time. Recently, this technology began to be applied to production of sheets of magnesium alloys. In the present investigation, horizontal type TRC is analyzed by the rigid-thermo-viscoplastic FEM to investigate differences between AA3003 and Mg-AZ31. The result of the present investigation is expected to help determine properly process parameters of TRC for magnesium alloys. In addition, a core is introduced at the roll gap for the purpose of enhancing cooling of the melt by reducing not only the vortex development but also the volume of the melt in the melt pool.

2:50 PM  
Growth of Al8Mn5 Intermetallic in AZ91: Christopher Gourlay1; Guang Zeng1; Jingwei Xian1; 1Imperial College London
    Primary Al8Mn5 intermetallic is crucial for Fe impurity control of AZ91, and consequently corrosion resistance of magnesium alloys. Therefore, better understanding of the nucleation and growth mechanisms of Al8Mn5 during solidification process, as influenced by the Fe impurity level, is needed. In this paper, we study the faceted growth morphology, crystal structure, composition and growth orientation of Al8(Mn,Fe)5 intermetallic, using electron microscopy techniques. The results provide insights of nucleation and growth of primary Al8Mn5 intermetallic as well as its interaction with (Mg) dendrite growth in AZ91 solidification.

3:10 PM  Cancelled
Influence of CaO Grain Refiner Addition on the Microstructure and Mechanical Properties of As-cast Mg Alloys: Yahia Ali1; Dong Qiu1; Ming-Xing Zhang1; 1University of Queensland
    In the last couple of decades, magnesium and its alloys have been involved in more and more applications, especially, in automotive industry. Hence, research is continuously seeking higher mechanical properties Mg alloys. Grain refinement by inoculation has been a well-known process in the industry due to its low cost and successful reproducible results. However, zirconium inoculation has its limitations such as incompatibility with Mg-Al alloys, and thus a new Mg grain refiner is highly needed. In this work, based on E2EM crystallographic model calculations, CaO has been discovered as a new grain refiner for Mg alloys. Optical micrographs showed outstanding grain refinement efficiency of the new grain refiner. Mechanical properties of the as-cast alloys have been improved by the addition of CaO. SEM and TEM have been used to study the nature of the nucleating particle in the grains centre.

3:30 PM Break

3:50 PM  
Grain Refinement of Mg and Its Alloy by Inoculation of In-situ MgO Particles: Yun Wang1; Guosheng Peng1; Zhongyun Fan1; Chamini Mendis1; 1Brunel University London
    Significant grain refinement of Mg and its alloy was achieved by intensive melt shearing without addition of any grain refiner. It was demonstrated that the grain refinement was resulted from promoted heterogeneous nucleation by inoculation of in-situ MgO particles, which had been effectively dispersed by melt shearing. It was shown that MgO formed in pure Mg and AZ91D alloy melts were {100} and {111} faceted, respectively. For pure Mg, high resolution TEM revealed two orientation relationships (OR), (100)[0-11] MgO//(0-112)[01-11]Mg, and (100)[0-11] MgO//(1-102)[-24-23]Mg. For AZ91D alloy, however, Mg nucleated on (111) plane of MgO according to OR: (111)[0-11]MgO//(0001)[11-20]Mg. Small lattice misfits at MgO/Mg interfaces along the three ORs indicated that heterogeneous nucleation of Mg occurred on MgO substrate in specific ways for atomic attachment to minimise the interfacial energy. The large numbers of dispersed MgO particles were potent to promote the heterogeneous nucleation process, resulting in grain refinement.

4:10 PM  
Numerical Study of Magnesium Production by Pidgeon Process and Pre-prepared Pellets Silicothermic Process: Comparison of Heat Transfer: Daxue Fu1; Zhang Ting'an1; Zhihe Dou1; Lukui Guan1; 1Northeastern University
    A novel process of magnesium production has been developed by changing the preparation method of pellets of silicothermic process. For the method, the pellets consist of dolomite, ferrosilicon, fluorite and binder, which need to be roasted before reduction. After calcinations, porous pellets were obtained due to the decomposition of dolomite in the pellets. Heat transfer of the porous pellets is different from that of pellets used in Pidgeon process. In the present paper, a comparative study on heat transfer of the novel process and Pidgeon process was carried out by numerical method. The results indicated that heat transfer of Pidgeon pellets is slightly better than that of the porous pellets. For the novel process, the temperature in the center of a retort of 300mm-diameter reaches 1473K after heating the retort at 1523K for 2.3h (without considering reaction heat), which needs 4.8h for the Pidgeon process.

4:30 PM  
On the Age Hardening Response of Aluminum Containing Magnesium Sheets with Zinc or Manganese (AZ- and AM Series Alloys): Jan Bohlen1; Ander Telleria Iparragirre2; Gurutze Arruebarrena2; Dietmar Letzig1; 1Helmholtz-Zentrum Geesthacht; 2Mondragon University
    A higher content of aluminum in magnesium alloys leads to the formation of the precipitation hardening intermetallic compound Mg17Al12. However, the rollability and the resulting ductility and formability of sheets of such alloys are reduced with increasing Al content. In this study, magnesium alloys of the AZ- and AM- series were used to investigate the impact of the aluminum content on the rollability, the resulting sheet properties and the precipitation strengthening of the sheets subsequent to the rolling process. Alloys with 6 wt.% and 8 wt.% aluminum were used. The higher content of aluminum leads to a decrease of rollability as well as a decrease of the ductility of the sheets after rolling and annealing. Alloys of the AM series perform more advantageous compared to AZ series alloys. However, Mn limits the ability to precipitation strengthening. The ability to balance both properties is discussed.

4:50 PM  
Performance Evaluation of High-pressure Ddie-cast Magnesium Alloys: Mark Easton1; Suming Zhu1; Mark Gibson2; Trevor Abbott3; Hua Qian Ang1; Xiaobo Chen4; Nick Birbilis4; Gary Savage2; 1RMIT University; 2CSIRO; 3Magontec; 4Monash University
    Over 90% of the magnesium alloys in commercial applications are produced by high-pressure die-casting. This paper presents our efforts in evaluating castability and properties of commercial and near-commercial magnesium alloys to demonstrate how the currently available alloys can be applied to different situations across a range of property space. For high temperature applications, i.e. 175C and above, Mg-RE and Mg-Al-Ca based alloys have creep properties at least comparable to aluminium alloy A380 although these alloys have some challenges with casting. For moderate temperatures, Mg-Al-RE based alloys, especially AE44, are most attractive due to an excellent combination of creep resistance, strength and castability. For automotive structural applications where a good combination of strength and ductility is required, Mg-Al alloys provide the baseline, but Mg-Al-RE based alloys can provide outstanding performance with age hardening during the paintbake cycle. Therefore, high-pressure die-cast magnesium alloys hold great promise in automotive applications.

5:10 PM  
Simulation Study on Direct Desulfurization of Molten Iron by Magnesium Vapor: Yan Liu1; Yongkun Yang1; Dongxing Wang1; Xiaolong Li1; Zhang Ting'an1; 1Northeastern University
    A new technique of bottom blown method was proposed for desulfurization of molten iron using inert gas to carry magnesium vapor combined with mechanical stirring. A water model was established based on the similarity principle. Experimental phenomena were recorded by high-speed camera, combining with image processing method, the influence factors on bubble disintegration and dispersion of molten pool were researched. By the stimulus response technique, measuring the changes of conductivity in the molten pool, influence factors of mixing time were studied. Results show that: the new technique is conducive to the bubble disintegration and dispersion of the molten pool, shorten the mixing time, prolong the residence time of the bubble in the molten pool. The desulfurization efficiency can be enhanced and the removal time of sulfur is shortened. It can also reduce the temperature drop during desulphurization and benefit to efficiency utilization of magnesium in iron industrial.