Liquid-Solid Equilibrium and Intermediate Phase Formation during Solidification in Mg-1.3 at%Zn-1.7 at%Y Alloy

Abstract

Mg-Y-Zn alloys have attracted much attention in recent years due to their excellent mechanical properties, which are said to be the effect of the intermediate phase (X phase) in the Mg solid solution ( phase). The formation behavior of the X phase has been reported to be a eutectic type reaction in the Mg-Y-Zn pseudo-binary system. However, the phase diagram of this system still requires clarification. In the present study, the 97.0Mg-1.3Zn-1.7Y (at%) alloy was prepared to clarify the liquidus and solidus in the liquid-solid coexistence region, and the solubility limit in the phase. The chemical compositions of the alloy were analyzed by electron probe X-ray microanalysis after isothermal heat treatment. The results indicate that the Mg-Y-Zn ternary system can be represented as a pseudo-binary system between the and X phases. In addition, the solidus line for the phase has been clarified. The solubility limit for the phase is not much different from that of the previous report, whereas the formation behavior of the X phase is not in the manner of a eutectic reaction, but rather that of a peritectic one.

Experimental Study on Phase Equilibria in the Vicinity of <i>X</i>, <i>W</i> and <i>H</i> Phases in the Mg&ndash;Zn&ndash;Y Ternary System

“…6) On the other hand, an intermetallic compound (W phase; Mg 3 Zn 3 Y 2 ) has also received attention in recent years as a new strengthening phase in MgZnY ternary alloys in addition to the ¡ and X phases. 7,8) Authors have reported 9) that the X phase is not solidified in a manner of eutectic reaction as reported previously, 10) but in a manner of peritectic reaction. Moreover, the W phase is transiently formed from the liquid phase in high temperatures, and is disappeared after the subsequent isothermal heat treatment.…”

“…The analyzed chemical compositions of nominal Mg 97.0 -Zn (at%), respectively, which were adopted to distinguish the alloys. Figure 2 shows backscattered electron images (BEIs) and analyzed chemical compositions of the black and gray regions obtained by EPMA for the Mg 97.2 Zn 1.3 Y 1.5 alloy after the isothermal heat treatment at 833 K. The authors have already reported 9) from the resultant chemical compositions that the black and gray regions in Fig. 2 are the ¡ and X phases, respectively.…”

Compositional Transition Layer around Growing LPSO in Mg₉₇Zn₁Y₂ Cast Alloys

“…The concentration ratio of Y/Zn in the LPSO is almost equivalent, and that in the matrix is 3, and that in the transition layer increases from 0.5 (as-cast) to 1. 3,4,7,12,14) The LPSO in the rapid solidification processes shows 18R-type LPSOs with an especially dilute composition. These facts indicate that nonstoichiometric 18R-type LPSO can exist metastably.…”

Microstructure Simulation for Solidification of Magnesium–Zinc–Yttrium Alloy by Multi-phase-field Method Coupled with CALPHAD Database

“…[1][2][3][4] Recently, one of our authors has investigated the solubility limit for the a phase and the chemical composition of the X phase in the a phase. 8) In the study we revealed that the W phase has non-stoichiometry for the Mg and Zn at 25 at% Y composition with L2 1 crystal structure, which has different thermodynamic model proposed by previous literature. 8) Thus it is necessary to re-build a thermodynamic database to simulate the system by means of CALPHAD technique.…”

“…8) In the study we revealed that the W phase has non-stoichiometry for the Mg and Zn at 25 at% Y composition with L2 1 crystal structure, which has different thermodynamic model proposed by previous literature. 8) Thus it is necessary to re-build a thermodynamic database to simulate the system by means of CALPHAD technique. The solid solubility range in the W phase and melting point of the X phase and the I phase were evaluated based on our experimental results.…”