Composition optimization of high-strength Mg-Gd-Y-Zr alloys based on the structural unit of Mg-Gd solid solution

doi:10.1016/j.jmst.2020.08.041

Abstract

Abstract:

Mg-Gd-Y-Zr alloys with high strength fall within narrow composition range. The present paper explains their composition rule by establishing the cluster-plus-glue-atom unit of Gd-containing Mg solid solution with the aid of Mg matrix and Mg₅Gd precipitate phase. First, based on the structural homologue between Gd-containing Mg solid solution and Mg₅Gd precipitate phase and in combination with our previously established method for calculating the glue atoms, [Gd-Mg₁₂]Mg₅ is obtained as the chemical unit of Gd-containing Mg solid solution. Then, seven compositions are designed using different combinations of this unit and that of pure Mg [Mg-Mg₁₂]Mg₃. After a systematic experimental investigation on the microstructure and mechanical property evolutions as a function of the unit proportions, it is revealed that the Mg-10.1Gd-3.3Y-0.9Zr alloy, being issued from equi-proportion mixing of the two units, shows the strongest tendency of precipitation and reaches the highest strength of 374 MPa after aging. The composition and strength of this alloy are quite close to GW103K which is well recognized for its general mechanical performance in Mg-Gd-Y-Zr system.

Key words: Mg-Gd solid solution, Chemical unit, Cluster-plus-glue-atom unit, Mg-Gd-Y-Zr cast alloys

Rui Jiang, Shengnan Qian, Chuang Dong, Ying Qin, Yujuan Wu, Jianxin Zou, Xiaoqin Zeng. Composition optimization of high-strength Mg-Gd-Y-Zr alloys based on the structural unit of Mg-Gd solid solution[J]. J. Mater. Sci. Technol., 2021, 72: 104-113.

Figures/Tables 19

Fig. 1. Correlation between tensile strength (in color depth) and Mg-Gd-Y alloy compositions. Most of the existing alloys fall close to a composition line (dotted line) of Gd/Y = 2/1, along which seven compositions (marked with dot symbols) are designed in the present work and following experimental results are marked with star symbols.

Fig. 2. Pair distribution function (a) and corresponding effective electronic potentialφ(r)∝-sin(2kF r)/ r3 arising from Friedel oscillation (b). The central positions of the negative (red-shaded) and positive (green shaded) potential zones are labeled with rn and rn+0.5, respectively. The radial distance r is scaled with Friedel wavelength λFr.

Fig. 3. Structures of [Mg-Mg12] (a) and [Gd-Mg14] (b) in Mg5Gd, where three atom-shells are Mg1, Mg2 and Mg3, respectively.

Table 1 Structure data of [Gd-Mg14] in Mg5Gd phase, where the nearest neighbor Mg atoms are distributed at three shells.

Central atom	The nearest neighbor shells	Number of atoms	The distance(nm) between Gd and Mg
Gd	Mg¹	4	0.3274
	Mg²	6	0.3517
	Mg³	4	0.3305

Table 2 The designed composition and experimental composition of seven cast alloys and corresponding formulas.

Designed	Experimental
{Gd}_n{Mg}_m	Weight%	Formulas	{Gd}_n{Mg}_m	Remark
{Gd}₃{Mg}₁	Mg-13.5Gd-3.3Y-0.2Zr	3[Gd_0.70Y_0.30-Mg₁₂]Mg_4.98Zr_0.05 + 2{Mg}	{Gd}₃{Mg}₂	GW133K
{Gd}₃{Mg}₂	Mg-11.6Gd-2.7Y-0.3Zr	1[Gd_0.69Y_0.29-Mg₁₂]Mg_4.99Zr_0.03 + 1{Mg}	{Gd}₁{Mg}₁	GW123K
{Gd}₁{Mg}₁	Mg-10.1Gd-3.3Y-0.9Zr	1[Gd_0.60Y_0.35-Mg₁₂]Mg_4.86Zr_0.09 + 1{Mg}	{Gd}₁{Mg}₁	GW103K
{Gd}₂{Mg}₃	Mg-9.1Gd-2.8Y-0.5Zr	3[Gd_0.61Y_0.34-Mg₁₂]Mg_4.99Zr_0.06 + 4{Mg}	{Gd}₃{Mg}₄	GW93K
{Gd}₁{Mg}₂	Mg-7.3Gd-2.1Y-0.3Zr	1[Gd_0.62Y_0.31-Mg₁₂]Mg_5.03Zr_0.05 + 2{Mg}	{Gd}₁{Mg}₂	GW72K
{Gd}₁{Mg}₃	Mg-5.9Gd-1.6Y-0.4Zr	1[Gd_0.64Y_0.31-Mg₁₂]Mg_4.97Zr_0.07 + 3{Mg}	{Gd}₁{Mg}₃	GW62K
{Gd}₁{Mg}₄	Mg-6.0Gd-0.7Y-0.5Zr	1[Gd_0.91Y_0.16-Mg₁₂]Mg_4.91Zr_0.11 + 4{Mg}	{Gd}₁{Mg}₄	GW61K

Fig. 4. Position in the mold and size of rectangle-shaped specimens for tensile tests.

Fig. 5. Microstructures of the Mg-Gd-Y-Zr alloys in as-cast state (a (OM), b (SEM)) and after solution heat treatment (c (OM), d (SEM)). GW62 K, GW72 K, GW93 K, and GW103 K are heated to 525℃ for 6 h and GW133 K, GW123 K and GW61 K are heated to 500 ℃ for 6 h.

Fig. 6. XRD patterns of as-cast Mg-Gd-Y-Zr alloys (a) and Mg-Gd-Y-Zr alloys after solution heat treatment (b), where the standard phase is Mg (PDF#35-0821) and Mg24Y5 (PDF#65-7687), respectively.

Fig. 7. Grain sizes of Mg-Gd-Y-Zr alloys after solution heat treatments as functions of solution heating temperature (red and black lines represent 525 °C and 500 °C, respectively), holding time (square, circle and triangle represent 6, 12 and 18 h, respectively), and the content of (Gd + Y) and Zr.

Fig. 8. Aging curves of cast-T4 specimens aged at 200 ℃ (a), and 225 ℃ (b).

Table 3 Incubation period, time to peak hardness and hardness during ageing at 200 and 225 ℃.

Alloys	Incubation period (h)		Time to peak hardness (h)		Peak hardness (HV)
Alloys	200 ℃	225 ℃	200 ℃	225 ℃	200 ℃	225 ℃
GW61K	8	16	128	128	89.3 (3.4)	75.2 (3.6)
GW62K	8	16	64	64	93.5 (3.2)	83.0 (4.6)
GW72K	8	2	64	64	114.0 (3.9)	101.6 (4.5)
GW93K	2	0	64	32	127.0 (4.1)	121.4 (4.8)
GW103K	2	0	64	32	135.2 (3.1)	133.1 (3.6)
GW123K	2	0	64	32	135.4 (3.3)	133.4 (3.0)
GW133K	2	0	64	32	143.0 (4.2)	139.2 (3.5)

Fig. 9. SEM microstructures of the studied Mg-Gd-Y-Zr alloys after peak-ageing treatment at 200 ℃ and 225 ℃.

Fig. 10. XRD patterns of specimens after peak ageing at 200 (a) and 225 ℃ (b), where the standard phase is Mg (PDF#35-0821) and Mg24Y5 (PDF#65-7687), respectively.

Table 4 Room temperature mechanical properties of the studied Mg-Gd-Y-Zr alloys.

Alloys	State	HV	σ_0.2 (MPa)	UTS (MPa)	Elongation (%)
GW133K
	As-cast	104	209	251	0.47
	T4-500 ℃-6 h	102.8	192	257	1.61
	T6-200 ℃-64 h	143	230	230	0.14
	T6-225 ℃-32 h	139.2	271 (78)	274 (17)	0.22
GW123K
	As-cast	92.9	169	259	3.52
	T4-500 ℃-6 h	88	185	252	4.88
	T6-200 ℃-64 h	135.2	259 (74)	314 (62)	0.48
	T6-225 ℃-32 h	133	241 (56)	331 (79)	0.82
GW103K
	As-cast	91.8	166	238	1.76
	T4-500 ℃-6 h	88.3	153	247	6.37
	T6-200 ℃-64 h	135.2	248 (95)	315 (68)	0.55
	T6-225 ℃-32 h	133	230 (77)	347 (100)	1.02
GW93K
	As-cast	82.4	176	234	6
	T4-500 ℃-6 h	78.8	138	210	6.72
	T6-200 ℃-64 h	127	208 (70)	318 (118)	1.15
	T6-225 ℃-32 h	121.4	220 (82)	327 (117)	1.79
GW72K
	As-cast	75.2	130	232	13.2
	T4-500 ℃-6 h	70.2	68	157	6.81
	T6-200 ℃-64 h	114	183 (115)	244 (87)	1.31
	T6-225 ℃-32 h	101.6	170 (102)	245 (88)	2.18
GW62K
	As-cast	69.8	89	212	15.6
	T4-500 ℃-6 h	65.5	93	185	14.35
	T6-200 ℃-64 h	93.5	185 (92)	305 (120)	8.86
	T6-225 ℃-32 h	95	114 (21)	209 (24)	16.65
GW61K
	As-cast	61.4	107	213	18.28
	T4-500 ℃-6 h	57.1	86	196	18.38
	T6-200 ℃-64 h	89.3	199 (113)	297 (101)	10.6
	T6-225 ℃-32 h	75.2	111 (25)	205 (9)	16.65

Fig. 11. Correlation between of mechanical properties and composition of Mg-Gd-Y-Zr alloys.

Fig. 12. Compositions of the cuboid-shaped phase.

Fig. 13. Relative change of lattice parameters a (a) and c (b) and unit cell volume (c) of matrix Mg solid solution in the states of T4 to peak T6 at 200 ℃ and 225 ℃.

Fig. 14. Correlation between incubation period, peak hardness and UTS in peak ageing condition.

Fig. 15. Correlation between elongations (in color depth) and compositions of Mg-Gd-Y-Zr alloys.

References 36

[1]	B.L. Mordike, Mater. Sci. Eng. A 324 (1) (2002) 103-112. DOI URL
[2]	F.S. Pan, M.B. Yang, X.H. Chen, J. Mater. Sci. Technol. 32 (2016) 1211-1221. DOI URL
[3]	M. Hakamada, T. Furuta, Y. Chino, Y. Chen, H. Kusuda, M. Mabuchi, Energy 32 (2007) 1352-1360. DOI URL
[4]	N. Stanford, D. Atwell, A. Beer, C. Davies, M.R. Barnett, Scr. Mater. 59 (2008) 772-775. DOI URL
[5]	Y. Huang, W. Gan, K.U. Kainer, N. Hort, J. Magnes, Alloy 2 (2014) 1-7.
[6]	Q. Luo, Y. Guo, B. Liu, Y. Feng, J. Zhang, Q. Li, K. Chou, J. Mater. Sci. Technol. 44 (2020) 171-190. DOI URL
[7]	P.H. Fu, L.M. Peng, H.Y. Jiang, W.J. Ding, C.Q. Zhai, China Foundry 11 (4) (2014) 277-286.
[8]	I.A. Anyanwu, S. Kamado, Y. Kojima, Mater. Trans. 42 (2001) 1206-1211. DOI URL
[9]	L.K. Jiang, W.C. Liu, G.H. Wu, W.J. Ding, Mater. Sci. Eng. A-Struct.Mater. Prop. Micros. Pro. 612 (2014) 293-301.
[10]	L.L. Rokhlin, N.I. Nikitina, Zeitschrift Fur Metallkunde 85 (1994) 819-823.
[11]	S.M. He, X.Q. Zeng, L.M. Peng, X. Gao, J.F. Nie, W.J. Ding, J. Alloys Compd. 427 (2007) 316-323. DOI URL
[12]	S.M. He, X.Q. Zeng, L.M. Peng, X. Gao, J.F. Nie, W.J. Ding, J. Alloys Compd. 421 (2006) 309-313. DOI URL
[13]	J.F. Nie, Scr. Mater. 48 (8) (2003) 1009-1015. DOI URL
[14]	H.R.J. Nodooshan, W.C. Liu, G.H. Wu, Y. Rao, C.X. Zhou, S.P. He, W.J. Ding, R. Mahmudi, Mater. Sci. Eng. A-Struct. Mater. Prop. Micros. Proc. 615 (2014) 79-86.
[15]	J. Wang, J. Meng, D.P. Zhang, D.X. Tang, Mater. Sci. Eng. A-Struct.Mater. Prop. Micros. Proc. 456 (2007) 78-84.
[16]	J.H. Zhang, S.J. Liu, R.Z. Wu, L.G. Hou, M.L. Zhang, J. Magnes, Alloy 6 (2018) 277-291.
[17]	J.F. Nie, Metall. Mater. Tran. A-Phys.Metall. Mater. Sci. 43a (2012) 3891-3939.
[18]	D.H. Stjohn, M.A. Easton, M. Qian, J.A. Taylor, Metall. Mater. Tran. A-Phys.Metall. Mater. Sci. 44a (2013) 2935-2949.
[19]	S. Kamado, Y. Kojima, R. Ninomiya, K. Kubota, Proceedings of the Third International Magnesium Conference, Manchester, UK, 1996, 10-12 April.
[20]	H. Shangming, Shanghai Jiao Tong University, 2007 (in Chinese).
[21]	S.N. Qian, C. Dong, T.Y. Liu, Y. Qin, Q. Wang, Y.J. Wu, L.D. Gu, J.X. Zou, X.W. Heng, L.M. Peng, X.Q. Zeng, J. Mater. Sci. Technol. 34 (2018) 1132-1141. DOI URL
[22]	C. Dong, Q. Wang, J.B. Qiang, Y.M. Wang, N. Jiang, G. Han, Y.H. Li, J. Wu, J.H. Xia, J. Phys. D Appl. Phys. 40 (2007) R273-R291.
[23]	L.J. Luo, H. Chen, Y.M. Wang, J.B. Qiang, Q. Wang, C. Dong, P. Haussler, Philos Mag 94 (2014) 2520-2540. DOI URL
[24]	G. Han, J.B. Qiang, F.W. Li, L. Yuan, S.G. Quan, Q. Wang, Y.M. Wang, C. Dong, P. Haussler, Acta Mater. 59 (2011) 5917-5923. DOI URL
[25]	D.D. Dong, Composition Origin of Metallic Glasses and Solid Solution Alloys: Short-range-order Structural Unit, Ph.D. Thesis, Dalian University of Technology, 2017 (in Chinese).
[26]	D.D. Dong, C. Dong, Q. Wang, Acta Metall. Sin. 54 (2) (2018) 293-300 (in Chinese).
[27]	J. Friedel, Adv. Phys. 3 (1954) 446-507. DOI URL
[28]	J. Barzola-Quiquia, M. Lang, D. Decker, P. Haussler, J. Non-Cryst. Solids 334 (2004) 352-355.
[29]	B.B. Jiang, Q. Wang, C. Dong, P.K. Liaw, Sci. Rep. 9 (2019) 3404. DOI URL
[30]	S. Zhang, C. Dong, Mater. Lett. 233 (2018) 71-73. DOI URL
[31]	A. Takeuchi, A. Inoue, Mater. Trans. 46 (2005) 2817-2829. DOI URL
[32]	H. Abrams, Metallography 4 (1971) 59-78. DOI URL
[33]	K.Y. Zheng, J. Dong, X.Q. Zeng, W.J. Ding, Mater. Sci. Technol. 24 (2008) 320-326. DOI URL
[34]	Q.M. Peng, Y.D. Huang, J.A. Meng, Y.D. Li, K.U. Kainer, Intermetallics 19 (2011) 382-389. DOI URL
[35]	S.M. Zhu, J.F. Nie, M.A. Gibson, M.A. Eastona, Scr. Mater. 77 (2014) 21-24. DOI URL
[36]	J.L. Li, R.S. Chen, W. Ke, Trans. Nonferr. Met. Soc. China 21 (4) (2011) 761-766. DOI URL