Effects of Sb Content on Solidification Pathways and Grain Size of AZ91 Magnesium Alloy

doi:10.1007/s40195-014-0178-4

Abstract

Abstract:

The phase constitution and solidification pathways of AZ91+xSb (x=0, 0.1, 0.5, 1, in wt%) alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91+xSb (x=0.1, 0.5, 1) is composed of α-Mg matrix, β-Mg₁₇Al₁₂ phase, and intermetallic compound Mg₃Sb₂. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg₃Sb₂ phase forms after α-Mg nucleation, thus impossible acts as heterogeneous nucleus for α-Mg dendrite. Besides, the solid fraction at dendrite coherency point (f _s ^DCP ) determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.

Key words: Mg-Al-Zn-Sb alloy, Solidification pathways, Nucleation, Grain size, Dendrite coherency

Dan-Hui Hou, Song-Mao Liang, Rong-Shi Chen, Chuang Dong, En-Hou Han. Effects of Sb Content on Solidification Pathways and Grain Size of AZ91 Magnesium Alloy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(1): 115-121.

Figures/Tables 11

Table 1 Chemical compositions of the investigated alloys (wt%)

Alloys	Al	Zn	Mn	Sb
AZ91	8.78	0.69	0.30	-
AZ91 + 0.1Sb	8.84	0.65	0.32	0.09
AZ91 + 0.5Sb	9.18	0.92	0.24	0.42
AZ91 + 1.0Sb	8.66	0.90	0.26	1.02

Fig. 1 Determination of dendrite coherency point through thermal analysis result

Fig. 2 SEM images showing the microstructures of AZ91 + xSb alloys: a AZ91 alloy; b AZ91 + 0.1Sb alloy; c AZ91 + 0.5Sb alloy; d AZ91 + 1.0Sb alloy

Fig. 3 XRD patterns of AZ91 + xSb alloys

Fig. 4 EBSD images of AZ91 + xSb alloys: a AZ91 alloy, average grain size is 217 μm; b AZ91 + 0.1Sb alloy, average grain size is 231 μm,; c AZ91 + 0.5Sb alloy, average grain size is 251 μm; d AZ91 + 1.0Sb alloy, average grain size is 246 μm

Fig. 5 Thermal analysis results of AZ91 alloys: a AZ91 alloy; b AZ91 + 0.1Sb alloy; c AZ91 + 0.5Sb alloy; d AZ91 + 1.0Sb alloy

Table 2 Characteristic temperatures obtained from the cooling curves of the central thermocouple

Alloys	Peak A		Peak B
Alloys	T _onset (°C)	T _peak (°C)	T _onset (°C)	T _peak (°C)
AZ91	610	592	435	425
AZ91 + 0.1Sb	607	592	429	423
AZ91 + 0.5Sb	603	594	428	424
AZ91 + 1.0Sb	602	594	426	423

Fig. 6 Comparison of the derivatives of total enthalpy (dH/dT) versus Temperature of AZ91 and AZ91 + 1.0Sb alloy under Scheil solidification simulation condition, a small peak referring to the formation of Mg3Sb2 phase can be easily seen at 546 °C on the curve of AZ91 + 1.0Sb alloy

Table 3 Predicted precipitation temperature of the three main phases under Scheil simulation

Alloys	T _α-Mg (°C)	T _Mg3Sb2 (°C)	T _γ-Mg17Al12 (°C)
AZ91	603	-	432
AZ91 + 0.1Sb	602	477	432
AZ91 + 0.5Sb	598	528	431
AZ91 + 1.0Sb	600	546	430

Fig. 7 Calculated equilibrium vertical section of Mg-9Al-1.0Zn-xSb system

Fig. 8 Effect of Sb concentration on solid fraction at dendrite coherency (f s DCP ) of AZ91 + xSb alloys

References 35

[1]	A.A. Luo,Int. Mater. Rev. 49, 13(2004)
[2]	A.A. Luo, J. Magnes. Alloys 1, 2 (2013)
[3]	C. Zhang, W. Cao, S.L. Chen, J. Zhu, F. Zhang, A.A. Luo, R. Schmid-Fetzer, JOM 66, 389 (2014)
[4]	J. Xu, G. H. Wu, W.C. Liu, Y. Zhang, W. J. Ding, J.Magnesium Alloys 1, (2013)
[5]	J. Liu, S. Lu, X. Dong, X. Xiao, G. Li,Met. Sci. Heat Treat. 55, 427(2013)
[6]	A. Zafari, H.M. Ghasemi, R. Mahmudi,Mater. Des. 54, 544(2014)
[7]	Y.A. Chen, H. Liu, R. Ye, G. Liu, Mater. Sci.Eng.A 587, 262 (2013)
[8]	G. Mao, Q. Liu, Foundry 59, 614 (2010)
[9]	H.L. Zhao, S.K. Guan, F.Y. Zheng, J. Mater.Res. 22, 2423(2007)
[10]	N. Balasubramani, A. Srinivasan, U.T.S. Pillai, B.C. Pai, Mater. Sci.Eng.A 457, 275 (2007)
[11]	Z. Yang, J. Li, J. Chang, H. Wang, X. Zhu, K. Zhang, S. Yu, Y. Cao,Hot Work. Technol. 5, 18(2004)
[12]	G.Y. Yuan, Y.S. Sun, W.J. Ding,Scr. Mater. 43, 1009(2000)
[13]	K.S. Sun, W.M. Zhang, X.G. Min, Acta Metall.Sin. (Engl. Lett.) 14, 330(2001)
[14]	Y.S. Wang, J.Z. Yu, Q.W. Wang, W.J. Ding, Acta Metall.Sin. (Engl. Lett.) 16, 8(2003)
[15]	Z. Yang, J.P. Li, J.X. Zhang, G.W. Lorimer, J. Robson, Acta Metall.Sin. (Engl. Lett.) 21, 313(2008)
[16]	A. Srinivasan, J. Swaminathan, M.K. Gunjan, U.T.S. Pillai, B.C. Pai, Mater. Sci.Eng.A 527, 1395 (2010)
[17]	N. Balasubramani, A. Srinivasan, U.T.S. Pillai, K. Raghukandan, B.C. Pai, J. Alloys Compd. 455, 168(2008)
[18]	G. Nayyeri, R. Mahmudi, Mater. Sci.Eng.A 527, 669 (2010)
[19]	Q.D. Wang, W.H. Chen, W.J. Ding, Y.P. Zhu, M. Mabuchi, Metall. Mater.Trans.A 32, 787 (2001)
[20]	B.S. Wang, R.L. Xin, G.J. Huang, X.P. Chen, Q. Liu, J. Chin.Electron Microsc. Soc. 28, 20(2009)
[21]	N. Gao, S.C. Wang, H.S. Ubhi, M.J. Starink, J. Mater. Sci. 40, 4971(2005)
[22]	H. Jafari, M.H. Idris, A. Ourdjini, S. Farahany,Mater. Des. 50, 181(2013)
[23]	S. Farahany, H.R. Bakhsheshi-Rad, M.H. Idris, M.R.A. Kadir, A.F. Lotfabadi, A. Ourdjini, Thermochim.Acta 527, 180 (2012)
[24]	S.M. Liang, R.S. Chen, J.J. Blandin, M. Suery, E.H. Han, Mater. Sci.Eng.A 480, 365 (2008)
[25]	A.K. Dahle, P.A. Tondel, C.J. Paradies, L. Arnberg, Metall. Mater.Trans.A 27, 2305 (1996)
[26]	M. Malekan, S.G. Shabestari, Metall. Mater.Trans.A 40, 3196 (2009)
[27]	T. Balakumar, M. Medraj, Calphad 29, 24 (2005)
[28]	M. Paliwal, I.H. Jung, Calphad 34, 51 (2010)
[29]	P. Liang, T. Tarfa, J.A. Robinson, S. Wagner, P. Ochin, M.G. Harmelin, H.J. Seifert, H.L. Lukas, F. Aldinger, Thermochim.Acta 314, 87 (1998)
[30]	S. Thompson, S.L. Cockcroft, M.A. Wells,Mater. Sci. Technol. 20, 194(2004)
[31]	M. Ohno, D. Mirković, R. Schmid-Fetzer,Acta Mater. 54, 3883(2006)
[32]	W. Cao, S.L. Chen, F. Zhang, K. Wu, Y. Yang, Y.A. Chang, R. Schmid-Fetzer, W.A. Oates, Calphad 33, 328 (2009)
[33]	W.J. Boettinger, U.R. Kattner, K. W. Moon, J.H. Perepezko,DTA and heat-flux DSC measurements of alloy melting and freezing, (NIST, U.S. Government Printing Office, 2006), p 22
[34]	L. Arnberg, G. Chai, L. Backerud, Mater. Sci.Eng.A 173, 101 (1993)
[35]	D. Emadi, L.V. Whiting, S. Nafisi, R. Ghomashchi, J. Thermal Anal.Calorim. 81, 235(2005)