Formation Behavior of 14H Long Period Stacking Ordered Structure in Mg-Y-Zn Cast Alloys with Different α-Mg Fractions

doi:10.1016/j.jmst.2016.01.005

Abstract

Abstract:

Phase compositions and microstructure evolutions of three Mg-Y-Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14H long period stacking ordered (LPSO) structure from α-Mg grains. The annealed microstructure characteristics indicate that the 18R phase is thermal stable in Mg₈₆Y₈Zn₆ alloy where 18R serves as matrix, and 14H lamellar phase only forms within tiny α-Mg slices (less than 1% for volume fraction). The α-Mg grains in Mg₈₈Y₈Zn₄ and Mg₈₉Y₈Zn₃ alloys exhibit cellular shape, and 14H phase forms and develops into lamellar shape in these cellular grains after annealing. The results suggest that the presence of α-Mg grains is a requirement for the generation of 14H phase. The nucleation and growth rates of 14H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms. Moreover, the 14H lamellas are parallel to adjacent 18R plates in Mg₈₆Y₈Zn₆ alloy, but the 14H phase precipitated in cellular α-Mg grains of Mg₈₈Y₈Zn₄ and Mg₈₉Y₈Zn₃ alloys exhibits random orientation relationship with surrounding 18R phase, indicating that the orientation relationship between 14H and 18R phases depends on the relationship between α-Mg grains and 18R phase.

Key words: Mg-Y-Zn, α-Mg grain, Long period stacking ordered phase, Annealing, 14H

Liu Huan,Xue Feng,Bai Jing,Ma Aibin,Jiang Jinghua. Formation Behavior of 14H Long Period Stacking Ordered Structure in Mg-Y-Zn Cast Alloys with Different α-Mg Fractions[J]. J. Mater. Sci. Technol., 2016, 32(12): 1267-1273.

Figures/Tables 9

Table 1. Analyzed chemical compositions of as-cast alloys (at.%)

Alloy code	Alloy	Mg	Y	Zn
I	Mg₈₆Y₈Zn₆	85.93	7.95	6.12
II	Mg₈₈Y₈Zn₄	87.83	8.13	4.04
III	Mg₈₉Y₈Zn₃	88.70	8.04	3.26

Fig. 1. XRD patterns of as-cast alloys I-III.

Fig. 2. Optical micrographs of as-cast alloys: (a) alloy I, (b) alloy II, and (c) alloy III.

Fig. 3. SEM images of as-cast alloys: (a) alloy I, (b) alloy II, and (c) alloy III.

Table 2. EDS results of the test points marked in Fig. 3

Test point	Chemical composition (at.%) ---------------------------
Test point	Mg	Y	Zn
A	96.59	2.60	0.81
B	87.58	7.10	5.32
C	34.21	20.28	45.51
D	84.13	13.25	2.42
E	69.92	25.74	4.34
F	95.90	3.24	0.86
G	95.04	3.98	0.98

Fig. 4. (a) TEM image of Mg12YZn phase in alloy III, (b) SAED patterns of Mg12YZn phase in (a), (c) TEM image of α-Mg grain with lamellar contrasts in alloy III, (d) SAED patterns of α-Mg phase in (c); (e) TEM image of α-Mg grain in alloy II.

Fig. 5. (a) SEM image of alloy I annealed at 773 K for 100 h and (b) SAED patterns of matrix in alloy I.

Fig. 6. Microstructures of as-cast alloy I annealed for (a) 1 h, (d) 5 h, (g) 40 h, (j) 100 h; alloy II annealed for (b) 1 h, (e) 5 h, (h) 25 h, (k) 50 h; alloy III annealed for (c) 0.5 h, (f) 2 h, (i) 6 h, (l) 25 h.

Fig. 7. (a) TEM image of 14H lamellas in alloy I annealed for 100 h, (b) SAED patterns of 14H lamellas in (a), (c) TEM image of 14H lamellas in alloy III annealed for 100 h, (d) SAED patterns of 14H lamellas in (c).

References

[1]	Z.G. Su, R.G. Li, J. An, Y. Lu,J. Mater. Eng. Perform. 19(2010) 70-76.
[2]	H. Liu, F. Xue, J. Bai, Y.S. Sun, Mater. Sci. Eng. A. 585(2013) 261-267.
[3]	J.F.Wang, P.F. Song, S. Gao, Y.Y.Wei, F.S. Pan, J. Mater. Sci. 47(2012) 2005-2010.
[4]	Z.P. Luo, S.Q. Zhang, Y.L. Tang, D.S. Zhao, J. Alloy. Compd. 209(1994) 275-278.
[5]	Z.P. Luo, S.Q. Zhang,J. Mater. Sci. Lett. 19(2000) 813-815.
[6]	M. Matsuda, S. Ii, Y. Kawamura, Y. Ikuhara, M. Nishida, Mater. Sci. Eng. A. 393(2005) 269-274.
[7]	T. Itoi, T. Seimiya, Y. Kawamura, M. Hirohashi, Scr. Mater. 51(2004) 107-111.
[8]	Y.M. Zhu, A.J. Morton, J.F. Nie, Acta Mater. 58(2010) 2936-2947.
[9]	J.S. Zhang, C.J. Chen, Z.P. Que, W.L. Cheng, J.D. Xu, J.J. Kang, Mater. Sci. Eng. A.552(2012) 81-88.
[10]	M. Yamasaki, T. Anan, S. Yoshimoto, Y. Kawamura, Scr.Mater. 53(2005) 799-803.
[11]	J.S. Zhang, C. Xin,W.L. Cheng, L.P. Bian, H.X.Wang, C.X. Xu, J. Alloy. Compd. 558(2013) 195-202.
[12]	M. Matsuura, K. Konno, M. Yoshida, M. Nishijima, K. Hiraga, Mater. Trans. 47(2006) 1264-1267.
[13]	M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura, Acta Mater. 55(2007) 6798-6805.
[14]	C. Xu, S.W. Xu, M.Y. Zheng, K. Wu, E.D. Wang, S. Kamado, G.J. Wang, X.Y. Lv,J. Alloy. Compd. 524(2012) 46-52.
[15]	D.D. Yin, Q.D. Wang, Y. Gao, C.J. Chen, J. Zheng, J. Alloy. Compd. 509(2011)1696-1704.
[16]	H.Z. Li, H.T. Liu, F.B. Li, H.J. Wang, X.P. Liang, C.M. Liu,J. Mater. Eng. Perform.21(2012) 1056-1060.
[17]	Y.M. Zhu, M. Weyland, A.J. Morton, K. Oh-ishi, K.Hono, J.F. Nie, Scr. Mater. 60(2009) 980-983.
[18]	E. Abe, Y. Kawamura, K. Hayashi, A. Inoue, Acta Mater. 50(2002) 3845-3857.
[19]	Y.M. Zhu, A.J. Morton, J.F. Nie, Acta Mater. 60(2012) 6562-6572.
[20]	G.L. Bi, D.Q. Fang,W.C. Zhang, J. Sudagar, Q.X. Zhang, J.S. Lian, Z.H. Jiang,J. Mater.Sci. Technol. 28(2012) 543-551.
[21]	G.L. Bi, D.Q. Fang, L. Zhao, Q.X. Zhang, J.S. Lian, Q. Jiang, Z.H. Jiang, J. Alloy. Compd.509(2011) 8268-8275.
[22]	W.J. Ding, Y.J.Wu, L.M. Peng, X.Q. Zeng, G.Y. Yuan, D.L. Lin, J. Mater. Res. 24(2009)1842-1854.
[23]	Y.J.Wu, L.M. Peng, X.Q. Zeng, D.L. Lin,W.J. Ding, Y.H. Peng, J. Mater. Res. 24(2009)3596-3602.
[24]	J. Grobner, A. Kozlov, X.Y. Fang, J. Geng, J.F. Nie, R. Schmid-Fetzer, Acta Mater.60(2012) 5948-5962.
[25]	S.Q. Luo, A.T. Tang, F.S. Pan, K. Song,W.Q.Wang, Trans.Nonferrous Metal.Soc China 21 (2011) 795-800.
[26]	K. Liu, J.H. Zhang, H.Y. Lu, D.X. Tang, L.L. Rokhlin, F.M. Elkin, J. Meng, Mater. Des.31(2010) 210-219.
[27]	J.F.Wang, P.F. Song, S. Gao, X.F. Huang, Z.Z. Shi, F.S. Pan, Mater. Sci. Eng. A. 528(2011) 5914-5920.
[28]	M. Suzuki, T. Kimura, J. Koike, K. Maruyama, Scr. Mater. 48(2003) 997-1002.
[29]	M. Suzuki, T. Kimura, J. Koike, K. Maruyama, Mater. Sci. Eng. A.387-389(2004)706-709.
[30]	E. Onorbe, G. Garces, P. Perez, P. Adeva, J. Mater. Sci. 47(2012) 1085-1093.
[31]	H. Liu, F. Xue, J. Bai, J. Zhou, Y.S. Sun,J. Mater. Sci. Technol. 30(2014) 128-133.
[32]	K. Hagihara, A. Kinoshita, Y. Fukusumi, M. Yamasaki, Y. Kawamura, Mater. Sci.Eng. A. 560(2013) 71-79.