| Strengthening using the Deformation Kink Band in Mg-Based LPSO-Phase Alloys Koji Hagihara1; Takayoshi Nakano1; Michiaki Yamasaki2; Yoshihito .kawamura2; 1OSAKA UNIVERSITY, Suita, Japan; 2KUMAMOTO UNIVERSITY, Kumamoto, Japan; PAPER: 300/Magnesium/Invited (Oral) SCHEDULED: 12:10/Thu. 24 Oct. 2019/Adonis 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 Mg<sub>88</sub>Zn<sub>4</sub>Y<sub>7</sub> 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). |
