Microstructures and Mechanical Properties of Mg-6Gd-4Y-xZn Alloys Reinforced with LPSO Phases

doi:10.11901/1005.3093.2017.493

Chinese Journal of Materials Research

2018, Vol. 32

Issue (6): 439-448 DOI: 10.11901/1005.3093.2017.493

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Microstructures and Mechanical Properties of Mg-6Gd-4Y-xZn Alloys Reinforced with LPSO Phases

Rui ZHEN^1,²(

), Yangshan SUN³, Xuewei SHEN¹, Zhixin BA^1,²

1 School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, China
2 Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing 211167, China
3 Jiangsu Key Lab of Advanced Metallic Materials, College of Material Science & Engineering, Southeast University, Nanjing 211189, China;

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Rui ZHEN, Yangshan SUN, Xuewei SHEN, Zhixin BA. Microstructures and Mechanical Properties of Mg-6Gd-4Y-xZn Alloys Reinforced with LPSO Phases. Chinese Journal of Materials Research, 2018, 32(6): 439-448.

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Abstract

Three quaternary Mg-alloys of Mg-6Gd-4Y-xZn (x=1, 2, 3, mass fraction, %) were prepared, while all the alloys contained strengthened phases of long period stacking ordered (LPSO) structure. The effect of Zn-concentration on the microstructure and mechanical property of the alloys, as well as the formation and evolution of LPSO phases in the alloys and their strengthening mechanism were also studied. Results show that the as-cast microstructure of the Mg-6Gd-4Y-3Zn alloy consists of α-Mg matrix and Mg₁₂Y₁Zn₁phase which presents 18R long period staking ordered (18R-LPSO) structure. The Mg₂₄(GdYZn)₅ eutectic was observed in the as cast microstructure of the alloys with lower Zn additions. After homogenizing annealing, the microstructure of all the quaternary alloys consists of a-Mg matrix, 18R-LPSO- and 14H-LPSO-phases. With the increase of Zn content, the volume fraction of 18R-LPSO phase increases and the lamellae of the 14H-LPSO phase in the matrix are thickened. Both T6- and T5-treatments result in the β' precipitation. The tensile strength of Mg-6Gd-4Y-xZn alloys decreases with the increase of Zn content. The ideal strengthening effect can be achieved by the coexistence of 18R-LPSO phase, small and well distributed precipitates of 14H-LPSO phase and β' precipitates in the microstructure.

Key words: metallic materials magnesium alloy hot extrusion aging treatment long period stacking ordered structures (LPSO) strengthening mechanism

Received: 18 August 2017

ZTFLH:

TG146.22

Fund: Supported by Natural Science Foundation of Jiangsu Province for Outstanding Youth (No. BK20160081) and the Research Foundation of Nanjing Institute of Technology (No. ZKJ201604) and Outstanding Scientific and Technological Innovation Team in Colleges and Universities of Jiangsu Province

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	Rui ZHEN
	Yangshan SUN
	Xuewei SHEN
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https://www.cjmr.org/EN/10.11901/1005.3093.2017.493 OR https://www.cjmr.org/EN/Y2018/V32/I6/439

Table 1 Chemical compositions of the alloys (mass fraction, %)

Fig.1 XRD spectra of as-cast GWZ641 (a),GWZ642 (b) and GWZ643 (c) alloys

Fig.2 Microstructures of the as-cast GWZ642 alloy: (a) OM, (b) SEM, (c) microanalysis of the block-shaped phases,(d) microanalysis of the lamella phases

Fig.3 TEM image of the Mg₁₂Y₁Zn₁phase (a) andcorresponding SAED(EB//[11

2 ?

0]_α) pattern in the as-cast GWZ641 alloy (b)

Fig.4 OM images of as-annealed GWZ641 (a), GWZ642 (b) and GWZ643 (c) alloys

Fig.5 TEM image of the lamella phase and corresponding SAED(EB//[11

2 ?

0]_α) pattern in the as-annealed GWZ641 alloy: (a) 14H-LPSO, (b) 18R-LPSO

Fig.6 OM (a) and SEM (b) images of the as-extruded GWZ642 alloy

Fig.7 OM image of the GWZ642 alloy after T4 treatment

Fig.8 Age-hardening response of the alloys GWZ641 (a),GWZ642 (b) and GWZ643 (c) during T6 treatment

Fig.9 Microstructures of the peak-aged extruded-T6 alloy: (a) OM image of GWZ641, (b) TEM image and corresponding SAED pattern of a-Mg matrix and β' phase in GWZ641, (c) OM image of GWZ642, and (d) TEM image of GWZ642

Fig.10 Microstructures of the peak-aged extruded-T5 alloy: (a) OM image of GWZ641, (b) TEM image and corresponding SAED pattern of a-Mg matrix and β' phase in GWZ641, (c) OM image of GWZ643, and (d) TEM image of GWZ643

Table 2 Mechanical properties of the alloys after different heat treatment

Fig.11 TEM micrographs of 18R-LPSO (a) and 14H-LPSO (b) structures in as-extruded GWZ641 alloy after tensile test

Fig.12 TEM micrograph of 14H-LPSO structure of the extruded GWZ641 alloy

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