Microstructural Characteristics and Mechanical Properties of Cast Mg-3Nd-3Gd-xZn-0.5Zr Alloys

doi:10.1007/s40195-021-01315-0

Abstract

Abstract:

The microstructure, aging behavior and mechanical properties of cast Mg-3Nd-3Gd-xZn-0.5Zr (x = 0, 0.5, 0.8, 1 wt%) alloys are investigated in this work. Zn-Zr particles with different morphologies form during solution treatment due to the additions of Zn. As the Zn content increases, the number density of Zn-Zr particles also increases. Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior. In the peak-aged Zn-free alloy, β’’ phases are the key strengthening precipitates. When 0.5 wt% Zn is added, besides β’’ precipitates, additional fine β₁ precipitates form. With the addition of 0.8 wt% Zn, the peak-aged 0.8Zn alloy is characterized by predominantly prismatic β₁ and scanty basal precipitate distributions. The enhanced precipitation of β₁ should be primarily attributable to the presence of increased Zn-Zr dispersoids. When Zn content further increases to 1 wt%, the precipitation of basal precipitates is markedly enhanced. Basal precipitates and β₁ phases are the key strengthening precipitates in the peak-aged 1Zn alloy. Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt% Zn addition, whose yield strength, ultimate tensile strength and elongation are 179 MPa, 301 MPa and 5.3%, respectively.

Key words: Mg-Nd-Gd alloy, Zn addition, Competitive precipitation behavior, Microstructural characterization

He Xie, Guohua Wu, Xiaolong Zhang, Zhongquan Li, Wencai Liu, Liang Zhang, Xin Tong, Baode Sun. Microstructural Characteristics and Mechanical Properties of Cast Mg-3Nd-3Gd-xZn-0.5Zr Alloys[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(6): 922-940.

Figures/Tables 21

Table 1 Actual chemical compositions of cast Mg-3Nd-3Gd-xZn-0.5Zr (x = 0, 0.5, 0.8, 1.0 wt%) alloys

Alloys	Actual compositions
Alloys	Nd (wt%)	Gd (wt%)	Zn (wt%)	Zr (wt%)
Base	3.05	3.08	-	0.43
0.5Zn	3.01	3.04	0.48	0.42
0.8Zn	2.99	3.06	0.79	0.42
1Zn	3.08	3.10	1.05	0.46

Fig. 1 Optical microstructure of as-cast alloys: a base alloy, b 0.5Zn alloy, c 0.8Zn alloy, d 1Zn alloy

Fig. 2 SEM micrographs showing the morphology of secondary phases: a base alloy, b 0.5Zn alloy, c 0.8Zn alloy, d 1Zn alloy. The positions for EDS point analysis are indicated by arrows

Table 2 EDS point analysis results of the secondary phases in as-cast alloys

Alloy	Point	Atomic percentage (at.%)
Alloy	Point	Mg	Nd	Gd	Zn	Zr
Base	A	92.80	6.14	1.06	0.00	0.00
0.5Zn	B	81.95	5.85	2.92	9.28	0.00
0.8Zn	C	74.80	8.20	3.20	13.80	0.00
1Zn	D	71.86	8.18	2.43	17.53	0.00

Fig. 3 XRD patterns of as-cast Mg-3Nd-3Gd-xZn-0.5Zr alloys

Fig. 4 Microstructure of as-quenched alloys: a base alloy, b 0.5Zn alloy, c 0.8Zn alloy, d 1Zn alloy. Note that patches with rosette-like shapes appear in the Zn-containing alloys (marked by the arrows)

Fig. 5 Backscattered SEM micrographs illustrating the presence of cuboid-shaped phases and Zn-Zr particles in as-quenched alloys: a base alloy, b 0.5Zn alloy, c 0.8Zn alloy, d 1Zn alloy

Fig. 6 EDS point analysis of cuboid-shaped phases noticed in the as-quenched base alloy

Fig. 7 a HAADF-STEM image showing Zn-Zr particles with different morphologies in the as-quenched 1Zn alloy; b enlarged image corresponding to the region marked by the dotted frame in a; elements map-scanning of c Nd; d Gd; e Zn, f Zr

Fig. 8 Age-hardening characteristics of the base, 0.5Zn, 0.8Zn and 1Zn alloys at 200 °C

Fig. 9 BF images showing the morphology and the distribution of β’’ precipitates in the base alloy subjected to peak-aged treatment. The electron beam is parallel to [0001]α in a, b, and [${2}\stackrel{-}{1}\stackrel{-}{1}{\text{0}}$]α in c, d. The corresponding SAED patterns are inserted in a, c

Fig. 10 TEM micrographs showing precipitate microstructure representative of the peak-aged 0.5Zn alloy: a, b BF images recorded parallel to [0001]Mg direction; c, d BF images recorded parallel to [${2}\stackrel{-}{1}\stackrel{-}{1}{\text{0}}$]Mg direction

Fig. 11 HADDF-STEM images showing the precipitates interaction between β1 and β’’ in the peak-aged 0.5Zn alloy. The magnified region in a, b shows the identical structure of β’’ and β1, respectively. The electron beam is parallel to [0001]Mg direction

Fig. 12 BF micrographs showing the precipitates in sample of 0.8Zn alloy peak-aged at 200 °C: a, b BF micrographs with the incident beam direction of [0001]α, demonstrating the distribution of β1 precipitates; c, d BF micrographs exhibiting the coexistence of prismatic β1 plates and scanty basal plates (B = [${2}\stackrel{-}{1}\stackrel{-}{1}{\text{0}}$]α)

Fig. 13 BF micrographs showing the precipitate microstructure in sample of the 1Zn alloy peak-aged at 200 °C: a, b BF micrographs with the incident beam direction of [0001]α, demonstrating the distribution of β1 precipitates; c, d BF micrographs exhibiting the dense dispersion of basal plates (B = [${2}\stackrel{-}{1}\stackrel{-}{1}{\text{0}}$]α)

Fig. 14 Typical engineering strain-stress curves (left column) and mechanical properties (right column) of Mg-3Nd-3Gd-xZn-0.5Zr alloys under different states: a, b as-cast; c, d as-quenched; e, f peak-aged

Fig. 15 a HAADF-STEM micrograph of the heat-treated 1Zn alloy (peak-aged at 200 °C for 16 h) illustrating a unique interaction between the globular Zn-Zr particle and β1 precipitate, taken along the [0001]α zone axis; elemental maps of b Mg; c Nd; d Gd; e Zn, f Zr correspond to the a

Fig. 16 a HAADF-STEM micrograph of the heat-treated 1Zn alloy (peak-aged at 200 °C for 16 h) illustrating the unique interaction between rod-like Zn-Zr particles and β1 precipitate, taken along the [0001]α zone axis; elemental maps showing the distribution of b Mg; c Nd; d Gd; e Zn, f Zr

Table 3 Primary precipitates in the peak-aged alloys

Condition	Precipitates after aging at 200 °C
Condition	Base	0.5Zn	0.8Zn	1Zn
Peak-aged	β′′	β′′, β₁	β₁, basal plates	β₁, basal plates

Table 4 Comparison of strengthening effects of precipitate microstructures in different peak-aged alloys

Alloys	Base	0.5Zn	0.8Zn	1Zn
YS_peak-aged-YS_as-quenched (△YS, MPa)	45	69	54	58
UTS_peak-aged-UTS_as-quenched (△UTS, MPa)	106	82	56	52
EL_peak-aged-EL_as-quenched (△EL, %)	- 5.6	- 8.0	- 10.7	- 10.1

Table 5 Measured area number density of prismatic precipitates and basal precipitates in peak-aged alloys

	Base alloy	0.5Zn alloy	0.8Zn alloy	1Zn alloy
Area number density of prismatic precipitates (m^-2)	8.32 × 10¹⁵	9.24 × 10¹⁵	3.66 × 10¹⁴	2.63 × 10¹⁴
Area number density of basal precipitates (m^-2)	-	-	1.03 × 10¹³	2.82 × 10¹⁵

References 41

[1]	L.L. Rokhlin (ed.), Magnesium Alloys Containing Rare Earth Metals (CRC Press, London,
[2]	L.Y. Jia, W.B. Du, J.L. Fu, Z.H. Wang, K. Liu, S.B. Li, X. Du, Acta Metall. Sin. Engl. Lett. 34, 39 (2020).
[3]	J.L. Li, N. Zhang, X.X. Wang, D. Wu, R.S. Chen, Acta Metall. Sin. Engl. Lett. 31, 189 (2017).
[4]	J. Kubásek, D. Dvorský, J. Veselý, P. Minárik, M. Zemková, D. Vojtěch, Acta Metall. Sin. Engl. Lett. 32, 321 (2018).
[5]	R.G. Li, F. Asghar, J.H. Zhang, G.Y. Fu, Q. Liu, B.T. Guo, Y.M. Yu, S.G. Guo, Y. Su, X.J. Chen, L. Zong, Acta Metall. Sin. Engl. Lett. 32, 245 (2018).
[6]	B. Li, B.G. Teng, D.G. Luo, Acta Metall. Sin. Engl. Lett. 31, 1009 (2018).
[7]	S. DeWitt, E.L.S. Solomon, A.R. Natarajan, V. Araullo-Peters, S. Rudraraju, L.K. Aagesen, B. Puchala, E.A. Marquis, A. van der Ven, K. Thornton, J.E. Allison, Acta Mater. 136, 378 (2017).
[8]	H. Liu, Y.M. Zhu, N.C. Wilson, J.F. Nie, Acta Mater. 133, 408 (2017).
[9]	E. L.S. Solomon, V. Araullo-Peters, J.E. Allison, E.A. Marquis, Scr. Mater. 128, 14 (2017).
[10]	W.H. Wang, D. Wu, R.S. Chen, X.N. Zhang J. Mater. Sci. Technol. 34, 1236 (2018).
[11]	X. Xia, A. Sanaty-Zadeh, C. Zhang, A.A. Luo, D.S. Stone, Calphad 60, 58 (2018).
[12]	H. Xie, G. Wu, X. Zhang, W. Liu, W. Ding, Mater. Charact. 175, 111076 (2021).
[13]	T. Honma, T. Ohkubo, S. Kamado, K. Hono, Acta Mater. 55, 4137 (2007).
[14]	Y.Q. Chi, C. Xu, X.G. Qiao, M.Y. Zheng, J. Alloys Compd. 789, 416 (2019).
[15]	J.F. Nie, K. Oh-ishi, X. Gao, K. Hono, Acta Mater. 56, 6061 (2008).
[16]	W. Rong, Y. Wu, Y. Zhang, M. Sun, J. Chen, L. Peng, W. Ding, Mater. Charact. 126, 1 (2017).
[17]	K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H.Y. Yasuda, Y. Umakoshi, Acta Mater. 58, 6282 (2010).
[18]	G. Garcés, G. Requena, D. Tolnai, P. Pérez, P. Adeva, A. Stark, N. Schell, J. Mater. Sci. 49, 2714 (2014).
[19]	L.S. Wang, J.H. Jiang, B. Saleh, Q.Y. Xie, Q. Xu, H. Liu, A.B. Ma, Acta Metall. Sin. Engl. Lett. 33, 1180 (2020).
[20]	Y. Xu, D. Xu, X. Shao, E.H. Han, Acta Metall. Sin. Engl. Lett. 26, 217 (2013).
[21]	Y. Zhou, P. Fu, L. Peng, D. Wang, Y. Wang, B. Hu, M. Liu, A.K. Sachdev, W. Ding, J. Magnes. Alloy. 7, 113 (2019).
[22]	G. Jia, E. Guo, L. Wang, Y. Feng, Y. Chen, Results Phys. 11, 152 (2018).
[23]	X. Gao, B.C. Muddle, J.F. Nie, Philos. Mag. Lett. 89, 33 (2009).
[24]	J.F. Nie, Metall. Mater. Trans. A 43, 3891 (2012).
[25]	J. Tan, Y. Dong, H.X. Zhang, Y.H. Sun, B.Z. Sun, Y. Qi, Scr. Mater. 172, 130 (2019).
[26]	Y. Zhang, W. Rong, Y. Wu, L. Peng, J.F. Nie, N. Birbilis, J. Alloys Compd. 777, 531 (2019).
[27]	D. Zhang, Q. Yang, B. Li, K. Guan, N. Wang, B. Jiang, C. Sun, D. Zhang, X. Li, Z. Cao, J. Meng, J. Alloys Compd. 805, 811 (2019).
[28]	W.Z. Wang, D. Wu, R.S. Chen, Y. Qi, H.Q. Ye, Z.Q. Yang, , J. Alloys Compd. 832, 155 (2020).
[29]	H.M. Zhu, G. Sha, J.W. Liu, H.W. Liu, C.L. Wu, C.P. Luo, Z.W. Liu, R.K. Zheng, S.P. Ringer, Nanoscale Res. Lett. 7, 300 (2012).
[30]	H. Xie, G. Wu, X. Zhang, J. Zhang, W. Ding, Mater. Sci. Eng. A 817, 141292 (2021).
[31]	J.F. Nie, B.C. Muddle, Acta Mater. 48, 1691 (2000).
[32]	D. Wang, P. Fu, L. Peng, Y. Wang, W. Ding, Mater. Charact. 153, 157 (2019).
[33]	X. Gao, J.F. Nie Scr. Mater. 58, 619 (2008).
[34]	I. Toda-Caraballo, E.I. Galindo-Nava, P. E.J. Rivera-Díaz-del-Castillo, Acta Mater. 75, 287 (2014).
[35]	Z.M. Li, A.A. Luo, Q.G. Wang, L.M. Peng, P.H. Fu, G.H. Wu, Mater. Sci. Eng. A 564, 450 (2013).
[36]	D. Zhang, D. Zhang, F. Bu, X. Li, B. Li, T. Yan, K. Guan, Q. Yang, X. Liu, J. Meng, J. Alloys Compd. 728, 404 (2017).
[37]	H.S. Jang, B.J. Lee Scr. Mater. 160, 39 (2019).
[38]	D.H. Ping, K. Hono, J.F. Nie, Scr. Mater. 48, 1017 (2003).
[39]	E. L.S. Solomon, E.A. Marquis, Mater. Lett. 216, 67 (2018).
[40]	Z. Huang, C. Yang, L. Qi, J.E. Allison, A. Misra, Mater. Sci. Eng. A 742, 278 (2019).
[41]	J.F. Nie, X. Gao, S.M. Zhu Scr. Mater. 53, 1049 (2005).