Magnesium Technology 2017: Magnesium-Rare Earth Alloys II
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

Thursday 8:30 AM
March 2, 2017
Room: 5A
Location: San Diego Convention Ctr

Session Chair: Wim Sillekens, European Space Agency; Dmytro Orlov, Lund University

8:30 AM  
Microstructure and Mechanical Properties of Mg-Zn-Gd Alloys after Rolling or Extrusion Processes: Rongshi Chen1; M.G. Jiang1; J. Luo1; H. Yan1; C. Xu2; S. Kamado2; 1Institute of Metal Research Chinese Academy of Sciences; 2Nagaoka University of Technology
    A series of Mg-Zn-Gd alloys were developed for large strain hot rolling, cold rolling and high-speed extrusion. The hot rolled Mg-2.0Zn-(0.1, 0.3)Gd (wt.%) alloys can be successfully rolled for a sing pass reduction of 80% without any edge cracks, and high room-temperature ductility of 35% can be obtained in the sheet with 0.3%Gd. The hot rolled sheets showed good cold rollability due to the activation of {10-12} extension twins and dislocation slips. Cold rolling followed by annealing treatment could further modify the texture and optimize the strength and ductility. Besides, Mg-1.58Zn-0.52Gd alloy can be successfully extruded at high die-exit speed of 60 m/min without any surface defects in a wide temperature range. Due to rare earth (RE) texture, which favored the operation of both basal slip and {10-12} extension twins, the extrudates showed high ductility of 30%, which was twice than AZ31 alloy.

8:50 AM  
A Comparative Study on the Microstructure, Mechanical Properties, and Hot Deformation of Magnesium Alloys Containing Zinc, Calcium and Yttrium: K.P. Rao1; K. Suresh2; Hajo Dieringa3; Norbert Hort3; 1City University of Hong Kong; 2Bharathiar University; 3Helmholtz-Zentrum Geesthacht
    Some magnesium alloys are considered as biocompatible materials because they are biodegradable or bioabsorable in body fluids without causing health hazards. Zn and Ca are essential micronutrients in the body and their bio-absorption is beneficial when an orthopedic implant corrodes in a controlled manner. Yttrium in small quantity can be added to improve the mechanical properties. Cast alloys are hot worked to obtain wrought microstructures so as to develop components of superior and consistent properties. In this study, the microstructure and mechanical properties of four magnesium alloys containing zinc, calcium and yttrium in different combinations are compared. It is found that calcium is an excellent grain refiner whereas yttrium increases the grain size. While all these elements provide strengthening, calcium is found to be the most effective one in combination with zinc. The hot working of these alloys over broad ranges of temperature and strain rate will also be compared.

9:10 AM  Cancelled
Addition of Holmium & Erbium and Hot-rolling effects on the Microstructure and Mechanical Properties of Mg-Li based Alloys: Charles Muga1; Zhang Zhongwu (Z.W.)1; Zhao Yu1; Hao Guo1; Songsong Xu1; 1Harbin Engineering University
    Magnesium-Lithium Rare Earth based alloys being ultra-light and strong offer suitability for wide industrial applications. This is because they form stable strengthening phases and activate extra deformation modes under optimized conditions. Effects of introducing Holmium and Erbium elements in Mg-8Li-3Al alloy followed by subsequent aging and hot-rolling deformation were studied. The alloys microstructure morphology was examined using scanning electron microscope (SEM) and energy dispersive spectroscopy (XEDS). Phase analysis depicted the presence of both α-and β-phases alongside intermetallic compounds. Mechanical tensile test results showed increased Yield Strength and Ultimate Tensile Strength on introduction of rare earth elements with optimized thermo-mechanical treatment. The as-cast Mg-8Li-3Al alloy exhibited a tensile strength of 148.2MPa. Thermo-mechanically treated Mg-8Li-3Al-3Er and Mg-8Li-3Al-3Ho alloys exhibited increased tensile strength of 284.5MPa and 293.1MPa respectively. Synergistic effects of adding Holmium and Erbium elements, with aging and hot-rolling deformation enhanced the alloys mechanical properties through work hardening and solution strengthening mechanisms.

9:30 AM  
Bonding Environments in a Creep–resistant Mg-RE-Zn Alloy: Deep Choudhuri1; S. Srinivasan1; Mark Gibson2; Rajarshi Banerjee1; 1University of North Texas; 2CSIRO
    Creep behavior is one of the key factors determining the service lifetime of Mg alloy components in automotive applications. Using Mg-Nd and Mg-Nd-Zn as model alloys we demonstrate that creep-resistance can be improved – atleast by an order of magnitude - by forming high volume fraction of fine-scale precipitates on the {0001}-basal planes of Mg. Precipitation on both basal and {01-10}/{11-20} prismatic planes was also found to be very useful. To obtain a deeper understanding of such a creep-resistant microstructure; the electronic structures of precipitates, precipitate/matrix interfaces and solid solutions were examined via density functional theory (DFT) based first principles calculations. Our DFT results indicated that anisotropy of electron charge delocalization, or the bonding character play a vital role in determining the creep-strength of Mg alloys. From the standpoint of our experimental observations, we will discuss the role of differing bonding characters on precipitate phase formation and stacking fault energies.

9:50 AM  
Microstructural and Numerical Investigation on the Shear Response of a Rare-earth Magnesium Alloy Sheet: Michael Nemcko1; Armin Abedini1; Clifford Butcher1; Peidong Wu2; Michael Worswick1; 1University of Waterloo; 2McMaster University
    Shear tests are performed on an anisotropic rare-earth magnesium alloy rolled sheet (ZEK100-O) to study the constitutive plastic behaviour of the material at room temperature, under quasi-static conditions. The shear response is characterized in three orientations by setting the shear loading direction at 45, 90, and 135 with respect to the rolling direction. Each orientation displays unique trends in terms of yielding and the work hardening rates. EBSD analysis is used to analyze the microstructure of the deformed samples and to determine the twinning modes and twin fraction in each specimen. The results suggest that these parameters have a significant impact on the constitutive behavior of the material. Furthermore, the viscoplastic self-consistent (VPSC) model is used to understand the activity of the various deformation mechanisms and validate the experimental observations.

10:10 AM Break

10:30 AM  
Solute Effect on Strength and Formability of Mg: A First-principle Study: Pulkit Garg1; Mehul Bhatia1; Ilaksh Adlakha1; Suveen Mathaudhu2; Kiran Solanki1; 1SEMTE; 2University of California - Riverside
    In wrought magnesium alloys, room temperature plasticity is largely controlled by limited slip systems such as basal slip and tension/compression twins. The insufficient number of active slip systems limits strength and ductility preventing broader structural applicability of Mg-alloys. Hence, we employ first-principle calculations to investigate the effects of different alloying elements (Y, Li, Al, Zn, Zr, Sn and Ce) on low temperature strength and formability of Mg-alloys through ideal shear strength. Li, Al, Sn, Zn and Zr show a strengthening effect, whereas Y and Ce lower dislocation nucleation energetics on all the slip systems. Further, comparing our ideal shear strength calculations with available general stacking fault energy calculations provides an overall understanding of dislocation nucleation and motion and we found that Y and Ce addition improves the formability of Mg-alloys. The profound effects of solute addition result from the charge transfer between the solute atom and surrounding magnesium atoms.

10:50 AM  
Understanding on the Role of Rare earth Elements in Activation of <c+a> Slip in Magnesium: An Atomistic Approach: Hyo-Sun Jang1; Ki-Hyun Kim1; Nack Joon Kim1; Byeong-Joo Lee1; 1Pohang University of Science and Technology
     The effect of Li addition on the slip behavior of Mg has been investigated using a molecular dynamics simulation. Based on a previous study on Mg-Y alloys concluding that a reduction of the anisotropy in critical resolved shear stress (CRSS) among difference slip systems activates the <c + a> slip, the effect of Li, an element known to improve the room temperature ductility of Mg is chosen as an alloying element to examine the robustness of the above-mentioned conclusion. It is found that Li increases the CRSS of the basal slip more than that of the non-basal slip, reducing the difference in the CRSS among different slip systems. The reduced anisotropy in CRSS is believed to activate the non-basal <c+a> slip and eventually improve ductility in Mg-Li alloys. This understanding can be further extended into an alloy design of more cost-effective Mg alloys with improved room temperature formability.

11:10 AM  
Stabilisation of Disordered BCC Phases in Magnesium-rare Earth Alloys: Patrick Conway1; Adam Shaw2; Kevin Laws1; Michael Ferry1; 1The University of New South Wales; 2Harvey Mudd College
    In magnesium-based systems, stable disordered bcc phases are only known to exist in Mg-Li based alloy systems. However, it is known that Mg is an intense stabiliser of high temperature beta-rare earth phases (also disordered bcc) which often have a high solubility of Mg which can be sustained via quenching. This work focuses on stabilising Mg-rich beta-rare earth phases through targeted alloying additions of specific rare earth elements to generate more stable beta and alpha plus beta Mg-based alloys. The mechanical properties present a large variation across small changes to the composition allowing for targeting desired properties for specific light weight applications.

11:30 AM  
The Effects of Ca Addition on Microstructures and Mechanical Properties of Gravity Cast Mg-Zn-Y Alloy: Young-Gil Jung1; Youngkyun Kim1; Shae K. Kim1; Hyunkyu Lim1; Do Hyang Kim1; 1KITECH
     Mg-Zn-Y alloys with I-phase, that is quasicrystalline phase, are well known for wrought Mg alloys. These alloys have exhibited good combination of high strength and large elongation because I-phase has a strong bond and low interfacial energy with matrix. On the other hand, these alloys could be used as the cast alloys because the I-phase exhibits better thermally stability than many other phases, which could enhance creep resistance at elevated temperature. In this study, the effects of Ca addition on microstructures and mechanical properties of Mg-8Zn-1.6Y alloy (ZW82) were investigated to develop non heat-treatable creep resistant Mg alloys. The test specimens were prepared by casting into a steel mold whose size is 90 w × 150 h × 40 t. The tensile tests were performed at room temperature and 150 oC. Also creep tests were carried out at 150 oC under 100 MPa.