ORALS

SESSION: MagnesiumThuAM-R4	Intl Symp. on Next Generation Magnesium Alloys and Their Applications for Sustainable Development
Thu Oct, 24 2019 / Room: Adonis
Session Chairs: TBA Session Monitor: TBA

12:10: [MagnesiumThuAM03] Invited
Strengthening using the Deformation Kink Band in Mg-Based LPSO-Phase Alloys
Koji Hagihara¹ ; Takayoshi Nakano¹ ; Michiaki Yamasaki² ; Yoshihito .kawamura³ ; ¹Osaka university, Suita, Japan; ²Kumamoto university, Kumamoto, Japan; ³Kumamoto University, Kumamoto, Japan;
Paper Id: 300 [Abstract]

The long-period stacking ordered phase, the so-called LPSO phase, is strongly focused as a suitable strengthening phase of Mg alloys[1-4]. One of the hot topics found in Mg-alloys containing a large amount of LPSO phase is the unusual increase in strength by the extrusion [5]. Concerning this, we recently clarified the mechanisms which induce the drastic strengthening of the LPSO-phase alloys by extrusion, on the basis of the quantitative analysis [6]. This is one of the main purposes in this presentation and the details of this are discussed. In order to achieve this, the temperature and loading orientation dependence of the deformation behavior of the Mg₈₈Zn₄Y₇ extruded alloy, which contains a ~86 vol.% of LPSO-phase, were examined. Using several extruded alloys with different extrusion ratios, the influence of the extrusion ratio to the microstructure formation and the following mechanical properties were examined by compression tests. The tests were conducted in a temperature range between room temperature and 400 °C in a vacuum. Two loading orientations were selected for the compression test; one orientation is parallel to the extrusion direction (0° orientation) and the other is inclined at an angle of 45° from the extrusion direction (45° orientation) which clarifies the anisotropic mechanical properties of the extruded alloys. As a result, the yield stress of the LPSO phase alloy was found to exhibit a strong orientation dependence varied with the extrusion ratio. Especially, the yield stress of the extruded alloy with the reduction ratio of 10 showed an extremely high value of ~460 MPa when loaded at 0° orientation while it was largely reduced when loading at 45° orientation. This strong anisotropy of the plastic deformation behavior was considered to be derived from the variation in the deformation mechanisms depending on the loading orientation because of the development of strong {10-10} fiber texture along the extrusion direction. The basal slip was found to govern the deformation behavior at 45° orientation while the predominate deformation mechanism varied from the basal slip to the formation of deformation of the kink band at 0° orientation as the extrusion ratio increased. In addition, it was found that the introduction the deformation kink band boundary during the extrusion process effectively acts as a strong obstacle against the motion of the basal slip. That is, "the kink band strengthening" was first quantitatively elucidated, which contributes to the drastic increase in the yield stress of the extruded LPSO-phase alloys in the wide temperature range below 400 ºC.

References:
1) Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Mater. Trans. 42, 1172-1176 (2001).
2) K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H.Y. Yasuda, Y. Umakoshi, Acta Mater. 58, 6282-6293 (2010).
3) M. Yamasaki, K. Hashimoto, K. Hagihara, Y. Kawamura, Acta Mater. 59, 3646-3658 (2011).
4) K. Hagihara, A. Kinoshita, Y. Fukusumi, M. Yamasaki, Y. Kawamura, Mater. Sci. Eng. A 560, 71-79 (2013).
5) K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi, Intermetallics 18, 1079-1085 (2010).
6) K. Hagihara, Z. Li, M. Yamasaki, Y. Kawamura, T. Nakano, Acta Materialia, 15, 226-239 (2019).

SESSION: MagnesiumFriAM-R4	Intl Symp. on Next Generation Magnesium Alloys and Their Applications for Sustainable Development
Fri Oct, 25 2019 / Room: Adonis
Session Chairs: Eiji Abe; Session Monitor: TBA

12:35: [MagnesiumFriAM04]
Development of Incombustible Mg-Zn-Y Alloys
Shin-ichi Inoue¹ ; Michiaki Yamasaki² ; Yoshihito .kawamura³ ; ¹Kumamto University, Kumamoto, Japan; ²Kumamoto university, Kumamoto, Japan; ³Kumamoto University, Kumamoto, Japan;
Paper Id: 348 [Abstract]

Mg alloys have been attracting keen attention as promising lightweight materials for aerospace, automobile, and railway applications. On the other hand, it is often pointed out that Mg alloys have poor oxidation resistance and burn easily. The flammability of Mg alloys is a problem to be solved when we consider using Mg alloys as structural materials of mass transportation vessels. In fact, the Federal Aviation Administration (FAA) in the USA has banned the use of Mg alloys for aircraft cabins. From the point of view of reducing aircraft weight, however, the FAA decided to lift the ban on using the Mg alloy in an aircraft cabin and set up a flammability test for Mg alloys. As a part of the development of non-flammable Mg alloys, some metal elements have been added into Mg. It has long been known that the addition of rare earth elements can improve incombustibility of the surface of the oxide film on Mg alloys [1-6]. Among the RE-containing Mg alloys, Mg-Zn-Y with a long period stacking order (LPSO) phase has excellent mechanical properties and is expected to be used in aircraft components. Mg-Zn-Y alloys produced by rapid solidification powder metallurgy have extremely high yield strengths of ~600 MPa. Mg-Zn-Y alloys produced by ingot metallurgy and extrusion have a multimodal microstructure and high yield strengths of ~340 MPa [7, 8]. The Mg₉₇Zn₁Y₂ alloy, however, exhibits an ignition temperature of ~1150 K. This ignition temperature is lower than the flame temperature (~1200 K) of the oil burner of the FAA flammability test. Therefore, to use this alloy safely in an aircraft cabin, it is necessary to increase the ignition temperature of the Mg-Zn-Y alloy. In this study, to increase the ignition temperature, a fourth element was added in the Mg-Zn-Y alloy. Mg-Zn-Y alloys were prepared using high-frequency induction melting in Ar atmosphere. Specimens were heated at 973 K in a muffle furnace in the air. For investigating the structure of oxide films, XRD measurement, SEM, and TEM observations were conducted on the cross section of the film formed on the Mg-Zn-Y alloys. XRD measurement and SEM observation revealed that the surface film of the Mg-Zn-Y alloy was mainly composed of Y₂O₃. An inhomogeneous and thick Y₂O₃ layer was formed by internal oxidation of Y. Cracks were often observed in the inhomogeneous Y₂O₃. Furthermore, the metallic Mg was observed in gaps between the coarse Y₂O₃ crystal gains. Therefore, suppression of internal oxidation of Y will help to form a uniform and thin Y₂O₃ film on the surface of the Mg-Zn-Y alloy and prevent crack formation in the Y₂O₃ layer. On the other hand, Mg-Zn-Y alloys with fourth elements exhibit an ignition temperature of ~1320 K. Furthermore, the thin and homogeneous Y₂O₃ film is formed on the surface of Mg-Zn-Y alloys with the fourth element.

References:
[1] B. S. You et al., Scr Mater. 42 (2000) 1089-1094.\n[2] M. Sakamoto et al., J. Mater Sci. Lett. 16 (1997) 1048-1050.\n[3] B. H. Choi et al., Met Mater. Int. 9 (2003) 395-398.\n[4] D.B. Lee, Mater. Sci. Forum 419-422.\n[5] X. Zenget al., Mater. Sci. Eng. A 301 (2001) 154-644.\n[6] Q. Tan et al., Scr. Mater. 115 (2016) 38-41.\n[7] Y. Kawamura et al., Mater.Trans. 42 (2001) 1172-1176.\n[8] Y. Kawamura et al., Mater. Trans. 48 (2007) 2986-2992

SESSION: MagnesiumFriPM1-R4	Intl Symp. on Next Generation Magnesium Alloys and Their Applications for Sustainable Development
Fri Oct, 25 2019 / Room: Adonis
Session Chairs: Takao Tsumuraya; Session Monitor: TBA

15:15: [MagnesiumFriPM108]
Deformation Behavior of Directionally Solidified Mg/LPSO Alloy with Respect to its Lamellar Structure
Daria Drozdenko¹ ; Kristián Máthis² ; Michiaki Yamasaki³ ; Stefanus Harjo⁴ ; Wu Gong⁵ ; Kazuya Aizawa⁶ ; Yoshihito .kawamura⁷ ; ¹Magnesium Research Center, Kumamoto University, Kumamoto, Japan; ²Department of Physics of Materials, Charles University, Prague, Czech Republic; ³Kumamoto university, Kumamoto, Japan; ⁴Japan Atomic Energy Agency, Naka-gun, Japan; ⁵Kyoto University, Tokai-mura, Japan; ⁶Japan Atomic Energy Agency, Tokai-mura, Japan; ⁷Kumamoto University, Kumamoto, Japan;
Paper Id: 308 [Abstract]

Recently, a new generation of Mg alloys with an LPSO phase have received considerable attention due to their enhanced mechanical and promising high-temperature properties compared to the conventional Mg alloys. Nevertheless, those alloys still suffer from anisotropy of mechanical properties. It is generally agreed that besides the dislocation slip, deformation kinking and twinning contribute to the plastic deformation of those alloys. The materials’ parameters (shape and orientation of LPSO phase, grain size, texture) as well as the experimental conditions (loading direction, temperature etc.) are factors on which deformation kinking depends for it to be considered common for Mg/LPSO alloys. The conditions for kink formation in Mg-LPSO alloys and their dependence on temperature, however, are still under consideration. In this present work, a directionally solidified Mg -24 wt.% Y- 12wt.% Zn alloy having a lamellar structure elongated along the solidification direction was investigated. In order to reveal the effect of orientation on deformation behavior, uniaxial compression tests were performed parallel and perpendicular to the LSPO lamellae. Active deformation mechanisms were revealed by combination of two advanced in-situ techniques: acoustic emission and neutron diffraction. Detailed microscopy observations by optical and scanning electron microscopy (including EBSD, BSD imaging and IGMA) were performed for getting information about microstructure changes (e.g. twin and kink formation) with respect to a lamellar structure and crystallographic orientation. Kinking was found to be a dominant deformation mechanism during compression along the lamellar structure, resulting in high yield strength. In the case of loading perpendicular to lamellae, kinking was limited to well oriented lamellae and rather higher activity of the <c+a> dislocation slip was observed. IGMA analysis has shown that all observed kinks in both orientations were found to be of <1-100>-and <1-210>-rotation types.

References:
[1] Kawamura et al. Mater Trans 42(7) 2001 1172-1176
[2] Hagihara et al. Intermetallics 18 (2010) 267-276
[3] Yamasaki et al. Acta Mater, 61 (2013) 2065-2076
[4] Garces et al. Int. J. Plast. 106 (2018) 107-128
[5] W.Gong et al. Int J Plast 111 (2018) 288-306