Magnesium Technology 2017: Alloy Development
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 8:30 AM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Michele Manuel, University of Florida; Vineet Joshi, Pacific Northwest National Laboratory
8:30 AM Keynote
Using the Crystal Plasticity Approach to Parse the Effects of Alloying and Aging on the Mechanical Behavior of Wrought Mg Alloys: S.R. Agnew1; J.J. Bhattacharyya1; Fulin Wang1; 1Department of Materials Science and Engineering, University of Virginia
Predicting the collective effects of solid solution alloying, precipitation, and grain size on the mechanical properties of a given alloy is one of the “holy grails” of mechanical metallurgy. For alloys with a cubic crystal structure, this is challenging enough to have been solved only in specific cases, and even there, predicting the anisotropies induced by crystallographic texture is very difficult. In the case of hexagonal close packed Mg alloys, this challenge is even greater and arguably more important. Research over the past decade has also highlighted the significant impact precipitate shape and orientation can have on the strength of Mg alloys. This lecture will show, with examples from conventional and rare earth containing Mg alloys, that the crystal plasticity approach has enabled the level of our predictive capability to rapidly approach the level, which exists in other more mature alloys systems.
Development of High-strength High-speed-extrudable Mg-Al-Ca-Mn Alloy: Taiki Nakata1; Chao Xu1; Taisuke Sasaki2; Yasunobu Matsumoto3; Kazunori Shimizu3; Kazuhiro Hono2; Shigeharu Kamado1; 1Nagaoka University of Technology; 2National Institute for Materials Science; 3Sankyo Tateyama, Inc. Sankyo Material-Company
Poor hot-workability is one reason for the limited applications of wrought magnesium alloys. We have recently reported a precipitation hardenable Mg-Al-Ca-Mn dilute alloy with excellent extrudabilty. In this work, we optimized the composition of the Mg-Al-Ca-Mn alloy to achieve comparable strength and elongation to those of the 6000 series of Al alloys. We found that the Mg-1.3Al-0.3Ca-0.4Mn (wt.%) alloy extruded at high die-exit speed of 24 m/min shows excellent age-hardening response within only 0.5 h of aging at 200oC. The peak aged sample exhibited yield stress of 288 MPa and elongation of 21 % that are superior to those of 6000 series aluminum alloys. This high strength is attributed to the dispersion of Guinier Preston zones in relatively fine grains. If this excellent property is demonstrated in sheet materials, we can open up a possibility to development of “bake hardenable magnesium alloy”.
Development of Ultra-high Strength and Ductile Mg-Gd-Y-Zn-Zr Alloys by Extrusion with Forced-air Cooling: Chao Xu1; Taiki Nakata1; Mingyi Zheng2; Shigeharu Kamado1; 1Nagaoka University of Technology; 2Harbin Institute of Technology
Ultra-high strength Mg-8.2Gd-3.8Y-1Zn-0.4Zr (wt.%) alloys with moderate ductility were successfully developed in this study. The alloy was homogenized at 510oC, then cooled in furnace to ambient temperature or immediately quenched in warm water. Subsequently, hot extrusions at 450oC with and without forced-air cooling were carried out, followed by artificial ageing. The plate-shaped basal long period stacking ordered (LPSO) phases formed in the furnace cooled samples promote dynamic recrystallization (DRX) during extrusion, while the nanoscale basal stacking faults (SFs) formed in the quenched samples restrict the DRX. The forced-air cooling during extrusion refines the DRXed grain size and decreases the DRX ratio of the alloys. After peak-ageing, nanoscale β' phases densely precipitate on the prismatic planes of α-Mg matrix. The peak-aged sample extruded after the quenching and forced-air cooling exhibits ultra-high proof stress of 466 MPa, ultimate tensile strength of 514 MPa and moderate elongation to failure of 14.5%.
Effect of Extrusion Ratio on Microstructure and Resulting Mechanical Properties of Mg Alloys with LPSO Phase: Klaudia Horváth1; Daria Drozdenko1; Gerardo Garcés2; Kristián Máthis1; Patrik Dobroň1; 1Charles University in Prague; 2CENIM-CSIC
Magnesium alloys containing zinc (Zn) and yttrium (Y) were extruded with a different extrusion ratio at 350°C. In all alloys, Zn and Y formed long period stacking ordered phase (LPSO) which was investigated by transmission electron microscopy (TEM). The texture of the alloys was measured by X-ray diffraction. Analysis of the microstructure was done by light microscopy, where LSPO phase in all alloys was found elongated in the extrusion direction (ED). Afterwards, the mechanical properties of extruded Mg alloys were investigated during compression loading at room temperature and at a constant strain rate of 10-3 s-1. The samples with a height of 15mm and a diameter of 10 mm were compressed along extrusion direction. Concurrently with the deformation tests, the acoustic emission (AE) response of the specimens was recorded. The results of the AE experiments were proved by the microstructure investigations.
10:10 AM Break
Mechanically Alloyed Magnesium Based Nanostructured Alloy Powders for Biomedical Applications: Peter Morcos1; Khalil ElKhodary2; Hanadi Salem2; 1Nanotechnology Program, The American University in Cairo, Egypt.; 2Mechanical Engineering Department, The American University in Cairo, Egypt
Mechanical alloying (MA) is one of the most commonly used methods in preparing metallic materials . We are especially interested its ability to produce nanostructured materials. MA has rarely been used, however, in producing magnesium-based alloys of nanostructured grains, due to the complexity of the process . In this work, high energy ball milling of elemental powders; Mg, Zn and Zr, are investigated for the MA of ZK50 alloy. Crystallite size, lattice strain, and total milling energy (required for complete alloying) are characterized using X-ray diffraction. Scanning electron microscopy is also used to determine milling time effect on powder morphology. Consolidation of the milled powders into thin sheets was conducted via hot pipe rolling at 0.4 Tm. Results obtained showed that complete alloying was achieved at 45 milling hours where the particle size reached was was less than 1 µm and crystallite size of 20 nm. References:  J. C. D. V. Michaela FOUSOVA, "MAGNESIUM-ZINC ALLOY PREPARED BY MECHANICAL ALLOYING AND SPARK PLASMA," in Metal, Czech Republic, 2014;  J. L.-S. F. C.-G. a. J. C.-M. A.F. Palacios-Lazcano, "Microstructural study of Mg-Zn alloys prepared by mechanical alloying," REVISTA MEXICANA DE FISICA, p. 72–77, 2007.
Combined Effects of Grain Size Refinement and Dynamic Precipitation on Mechanical Properties of a New Magnesium Alloy: Matthew Vaughan1; Jan Seitz2; Rainer Eifler2; Hans Maier2; Ibrahim Karaman1; 1Texas A&M University; 2Leibniz Universität Hannover
Two well-known methods for enhancing the strength and controlling the anisotropy in magnesium alloys are precipitation hardening and grain size refinement. In this study, both methods are combined in an attempt to achieve optimal strengthening and anisotropy control: this was done via severe plastic deformation using Equal Channel Angular Processing (ECAP) of a precipitation hardenable magnesium alloy, Mg–6Zn–0.6Zr– 0.4Ag–0.2Ca (wt.%), within the temperature range of 125 °C – 200 °C. ECAP specimens were processed along different routes, where mechanically several of the ECAP samples show ultra-high strength levels approaching 400 MPa. The roles of grain size, texture, and precipitate morphology on mechanical properties are systematically investigated. It is shown here that the resulting microstructures generally show a refined grain size around 500 nm with a complex distribution of Mg-Zn enriched precipitates, which via ECAP either dynamically precipitate or are redistributed from the starting condition.
Zn Segregation at Precipitate/Matrix Interface in Mg-Sn-Zn Alloys: Chaoqiang Liu1; Houwen Chen1; Jian-Feng Nie1; 1Chongqing University
Magnesium-tin based alloys have received considerable attention in the past 15 years for developing high strength alloys. Mg-Sn binary alloys are precipitation hardenable, but their age-hardening response is moderate. Additions of Zn can significantly improve the age-hardening response of binary Mg-Sn alloys by refining the distribution of Mg2Sn precipitates. To understand the role of Zn in the precipitation process, the Mg2Sn precipitates with different morphologies and orientations in under-, peak- and over-aged samples of a Mg-9.8Sn-1.2Zn (wt.%) alloy are characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and STEM X-ray mapping. It is found that Zn atoms invariably segregate to the Mg2Sn-Mg interface, irrespective of the interfacial structures and orientation relationships of the Mg2Sn precipitates. This finding provides an insight to the understanding of the enhanced nucleation of Mg2Sn precipitates in Mg-Sn-Zn alloys.
Machinability Investigation in Micro-milling of Mg based MMCs with Nano-sized Particles: Xiangyu Teng1; Dehong Huo1; Eugene Wong1; Manoj Gupta2; 1Newcastle University; 2National University of Singapore
Magnesium based metal matrix composites (MMCs) can be employed in various areas such as automobile and aerospace due to its weight saving potential, high specific mechanical properties and excellent damping capacity. Recently, improved strength and ductility have been observed due to the incorporation of nano-scale reinforcements into magnesium. This paper presents the experimental results on the machinability of Mg based metal matrix composites with nano-sized particles (Mg/BN MMCs & Mg/ZnO MMCs) produced by liquid-state processing using micro-milling process. The effect of reinforcement materials and volume fraction, as well as the varying cutting parameters such as feed per tooth, spindle speed and depth of cut on the cutting force and surface characteristic were studied. Additionally, since the refinement of grain size was recognised as one of the main reason that cause strengthening, the effect of grain size on machining performance was investigated in order to reveal the cutting mechanism.