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

doi:10.1007/s40195-014-0178-4

摘要/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

. [J]. 金属学报英文版, 2015, 28(1): 115-121.

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.

图/表 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

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