Fluidity, Microstructure, and Tensile Properties of Sub-rapidly Solidified Mg-6Al-4Zn-xSn (x = 0, 0.6, 1.2, 1.8) Alloy

doi:10.1007/s40195-021-01247-9

Abstract

Abstract:

In this paper, the influence of the Sn element on the melt viscosity, grain size, shrinkage, and tensile properties of the sub-rapidly solidified Mg-6Al-4Zn alloy was studied. The results showed that the melt viscosity of the Mg-6Al-4Zn alloy was greatly decreased because of the addition of Sn. As the content of Sn increased from 0 to 1.8 wt.%, the grain size of the alloy was refined, and the dendrite microstructure was changed to rose-shaped ones simultaneously. The decreased melt viscosity and refined microstructure were conductive to the feeding of melt, which contributed to the reduction in volume fraction of shrinkage. The volume fraction of shrinkage of the Mg-6Al-4Zn-1.2Sn alloy was reduced by 30.8%, compared with that of the alloy without Sn addition. Tensile properties of the Mg-6Al-4Zn-xSn alloys were increased firstly and then decreased with the augmented Sn content. The yield strength, ultimate tensile strength, and elongation of the alloy containing 1.2 wt.% Sn were 21.4%, 39.5%, and 259.0% higher than those of the alloy without Sn addition, respectively. The addition of Sn was considered to reduce the shrinkage of the sub-rapidly solidified Mg-6Al-4Zn magnesium alloy and thus improved its tensile properties. To identify the mechanism, the effect of Sn on the volume fraction of shrinkage was discussed from three aspects of melt viscosity, grain refinement, and volume fraction of eutectic phases.

Key words: Magnesium alloy, Melt viscosity, Grain size, Shrinkage, Tensile properties

Jie Cui, Tianjiao Luo, Yingju Li, Xiaohui Feng, Qiuyan Huang, Yuansheng Yang. Fluidity, Microstructure, and Tensile Properties of Sub-rapidly Solidified Mg-6Al-4Zn-xSn (x = 0, 0.6, 1.2, 1.8) Alloy[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(9): 1265-1276.

Figures/Tables 15

Table 1 Chemical composition of the Mg-6Al-4Zn-xSn alloys (wt.%)

Alloy	Al	Zn	Sn	Mg
Mg-6Al-4Zn	6.02	4.03	0	Balance
Mg-6Al-4Zn-0.6Sn	5.97	3.97	0.62	Balance
Mg-6Al-4Zn-1.2Sn	5.95	3.98	1.22	Balance
Mg-6Al-4Zn-1.8Sn	6.05	4.04	1.78	Balance

Fig. 1 a Length of the spiral specimens for Mg-6Al-4Zn alloys with different contents of Sn, b relationship between fluidity and melt viscosity

Fig. 2 Melt kinematic viscosity for Mg-xAl alloys (x = 5.07, 7.09, 11.13 wt.%)

Fig. 3 a Melt dynamic viscosity for the Mg-6Al-4Zn alloy with different contents of Sn, b enlarged position of the box in (a)

Fig. 4 Optical micrographs of dendrite microstructures for sub-rapidly solidified Mg-6Al-4Zn alloy with different contents of Sn: a 0, b 0.6 wt.%, c 1.2 wt.%, d 1.8 wt.%

Fig. 5 Average grain size for sub-rapidly solidified Mg-6Al-4Zn alloy with different contents of Sn

Table 2 Mean content of alloy elements in the dendrite center and inter-dendrite region (average value of five measurements, wt.%)

Alloy	Dendrite center			Inter-dendrite region
	Al	Zn	Sn	Al	Zn	Sn
Mg-6Al-4Zn	2.71	1.61	-	6.42	8.36	-
Mg-6Al-4Zn-0.6Sn	2.67	1.58	0.24	6.60	8.50	0.83
Mg-6Al-4Zn-1.2Sn	2.56	1.53	0.51	6.91	8.98	1.68
Mg-6Al-4Zn-1.8Sn	2.54	1.52	0.62	6.98	9.23	2.24

Fig. 6 Calculated phase diagram of Mg-6Al-4Zn-xSn alloy

Fig. 7 Element distribution in the Mg-6Al-4Zn alloy with 1.8 wt.% Sn addition: a Mg, b Al, c Zn, d Sn

Fig. 8 SEM images of eutectic phases for the Mg-6Al-4Zn alloys with different contents of Sn: a 0, b 0.6 wt.%, c 1.2 wt.%, d 1.8 wt.%

Fig. 9 Volume fraction of eutectic phases for sub-rapidly solidified Mg-6Al-4Zn alloy with different contents of Sn

Fig. 10 Optical micrographs of shrinkages for the Mg-6Al-4Zn alloy with different contents of Sn: a1-a4 0, b1-b4 0.6 wt.%, c1-c4 1.2 wt.%, d1-d4 1.8 wt.%

Fig. 11 a Volume fraction of shrinkage for the Mg-6Al-4Zn alloy with different contents of Sn, b relationship between fluidity and volume fraction of shrinkage

Fig. 12 a Engineering stress vs. strain curves of the Mg-6Al-4Zn alloy with different contents of Sn, b tensile properties of the Mg-6Al-4Zn alloy with different contents of Sn

Fig. 13 Fractographies of the Mg-6Al-4Zn alloy with different contents of Sn: a 0, b 0.6 wt.%, c 1.2 wt.%, d 1.8 wt.%

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