Role of the Microstructure on the Deformation Behavior in Mg 12 ZnY with a Long-Period Stacking Ordered Structure
- PDF / 18,242,173 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 30 Downloads / 177 Views
1128-U05-53
Role of the Microstructure on the Deformation Behavior in Mg12ZnY with a Long-Period Stacking Ordered Structure K. Hagihara1, N. Yokotani1, A. Kinoshita1, Y. Sugino1, H. Yamamoto1 M. Yamasaki2, Y. Kawamura2 and Y. Umakoshi3 1
Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-0871, Japan 2 Department of Materials Science, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555, Japan 3 National Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047, Japan ABSTRACT The influence of a heat-treatment on the plastic deformation behavior in Mg12ZnY with a long-period stacking ordered (LPSO) structure was investigated by using crystals grown by the Bridgman method. Annealing of the crystal at 798 K for 3 days induced the change in the crystal structure of Mg12ZnY from the 18-fold rhombohedral structure (18R) to the 14-fold hexagonal structure (14H). The plastic behavior of those LPSO crystals showed a large variation depending on the loading axis in both crystals, because of the limitation of operative deformation modes in them. The change in the stacking sequence in the LPSO crystals did not show a large influence on the plastic deformation behavior at room temperature. INTRODUCTION Recently, new-types of magnesium (Mg) alloys which possess very high strength and relatively good ductility have been developed especially in the Mg-Y-Zn system, eg. see [1, 2].Some of the alloys contain the Mg12ZnY phase which has the long-period stacking ordered (LPSO) structure of the close-packed plane, which corresponds to the (0001) basal plane in Mg (called LPSO-phase hereafter). The role of the LPSO-phase on the superior mechanical properties of these alloys has been focused, but the details are not enough clarified yet. In order to examine this, we prepared the LPSO single-phase alloys with the 18R structure, the detail on the crystal structure will be described later, and the mechanical properties of the LPSO-phase itself have been investigated by using the directionally solidified (DS) crystals [3]. On the crystal structure of the LPSO-phase, it was recently reported by some researchers [47] that in Mg/LPSO two-phase alloys, the stacking sequence in the LPSO-structure was varied by the heat-treatment at high temperatures. In this study we examined the influence of a heattreatment on the plastic behavior of the Mg12ZnY LPSO-phase. By comparing the plastic behavior between the as-DS-grown crystal and the heat-treated crystals, the effect of the change in the stacking sequence on the mechanical properties was investigated.
EXPERIMENTAL PROCEDURE The mother alloy with the composition of Mg88Zn5Y7 (at.%) was prepared by induction melting. Using the alloy, the directional solidification was conducted by means of the Bridgman method at a rate of 5 mm/h under an Ar atmosphere. By X-ray diffraction (XRD) analysis, the gained crystal was confirmed to be almost composed of the LPSO-phase, although small amounts of second phase
Data Loading...
