ORALS

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:
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