Journal of Alloys and Compounds - Encsusers.encs.concordia.ca/~mmedraj/papers/Mg-Zn-Zr.pdf ·...

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Experimental investigation of the MgeZneZr ternary system at 450 C Xin Zhang a , Yi-Nan Zhang a, b , Dmytro Kevorkov a , Mamoun Medraj a, c, * a Department of Mechanical and Industrial Engineering, Concordia University,1455 de Maisonneuve Boulevard West, Montreal, QC, H3G 1M8, Canada b Institute of Biomaterials and Biomedical Engineering, University of Toronto,164 College Street, Toronto, ON, M5S 3G9, Canada c Department of Mechanical and Materials Engineering, Masdar Institute, Masdar City P.O. Box 54224, Abu Dhabi, United Arab Emirates article info Article history: Received 30 December 2015 Received in revised form 7 April 2016 Accepted 9 April 2016 Available online 13 April 2016 Keywords: MgeZneZr system Magnesium alloys Ternary compounds Diffusion couple Phase diagram SEM abstract The MgeZneZr ternary system was experimentally investigated at 450 C using six diffusion couples and 16 key alloys. Four new ternary compounds, IM1, IM2, IM3 and IM4 were detected. The compositions, homogeneity ranges, phase relationships and the X-ray diffraction patterns of these compounds were identied using scanning electron microscopy coupled with energy-dispersive x-ray spectrometer and x- ray diffraction techniques. The homogeneity ranges of IM1, IM2, IM3 and IM4 are Mg (23e26) Zn 66 Zr (8e11) , Mg (15e16) Zn 66 Zr (18e19) , Mg (10e11) Zn 66 Zr (23e24) , and Mg (9e13) Zn (79e87) Zr (5e8) , respectively. IM1 compound crystallizes in an MgZn 2 structure type with hexagonal structure and P6 3 /mmc space group. The MgeZn and ZneZr binary compounds do not have extended solid solubility into the ternary system. The phase boundaries of MgeZneZr liquid phase at 450 C were determined by several key alloys. The single phase liquid region extended into the ternary phase diagram only to around 1 at.% Zr. However, phase regions containing liquid along with other phases existed in the vicinity of the MgeZn side up to 10 at% Zr. Based on the current experimental results, the isothermal section of the MgeZneZr ternary system at 450 C was constructed. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Due to light weight, high specic strength and superior cast- ability, Mg alloys have great potential for increased use in auto- motive and aerospace industries [1,2]. To date, many series of Mg alloys have been developed [3,4] and are under study [5]. MgeZ- neZr (ZK series) based alloys are one of the most important com- mercial Mg alloys [2]. Zn is one of the common alloying elements added in Mg alloys to improve castability, yield strength, as well as creep resistance [6,7]. On the other hand, Zr is helpful to obtain ne grain size that ensures good room temperature mechanical prop- erties and corrosion resistance [8]. Zr is an excellent grain rener for Mg alloys [9,10] because Zr has close lattice parameters to Mg, which means that Zr is easy to form heterogeneous nucleation for Mg grains [11,12]. Zn contributes to grain size renement of Mg alloys through the constitutional undercooling effect [13]. There- fore, Mg alloys containing Zn and Zr have better mechanical properties than pure Mg due to grain renement [13,14], and the signicantly improved ductility at room temperature by introducing cross slips to non-basal planes [14]. As a ternary sys- tem, because of the benets of Zn and Zr elements in Mg alloys, MgeZneZr alloys have relatively high specic strength and good corrosion resistance [15]. For example, ZK60 (Mge6Zne0.7Zr wt%) alloy has been widely used in industry due to high specic strength and improved plasticity [16]. ZK51 (Mge4.6Zne0.75Zr wt%) alloy has excellent room temperature strength and ductility, enabling it to be used in military and aerospace applications [17]. Besides, ZK61, ZK31 and ZK40 alloys were reported to have good plasticity and are used for different purposes [18e20]. Apart from structural applications, Mg, Zn and small amount of Zr are non-toxic elements for the human body, which is promising as biomaterials [21e23]. Mg exists in the human body as fourth most prevalent cation and is found in bone tissue naturally [21]. Zn is an essential element for the human body (estimated 15 mg/day) [22] and has physiologi- cally important inuence in bone formation [23]. A small amount of Zr in the human body (<250 mg) shows good biocompatibility and low toxicity [24]. Understanding the phase relations in the MgeZneZr system is essential for developing new Mg alloys and for understanding the behavior and the processing of the current ZK Mg alloys. A brief literature review of the MgeZn, MgeZr and ZneZr binary systems and the MgeZneZr ternary system are presented. The * Corresponding author.. E-mail address: [email protected] (M. Medraj). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2016.04.081 0925-8388/© 2016 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 680 (2016) 212e225

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lable at ScienceDirect

Journal of Alloys and Compounds 680 (2016) 212e225

Contents lists avai

Journal of Alloys and Compounds

journal homepage: http: / /www.elsevier .com/locate/ ja lcom

Experimental investigation of the MgeZneZr ternary system at 450 �C

Xin Zhang a, Yi-Nan Zhang a, b, Dmytro Kevorkov a, Mamoun Medraj a, c, *

a Department of Mechanical and Industrial Engineering, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, QC, H3G 1M8, Canadab Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON, M5S 3G9, Canadac Department of Mechanical and Materials Engineering, Masdar Institute, Masdar City P.O. Box 54224, Abu Dhabi, United Arab Emirates

a r t i c l e i n f o

Article history:Received 30 December 2015Received in revised form7 April 2016Accepted 9 April 2016Available online 13 April 2016

Keywords:MgeZneZr systemMagnesium alloysTernary compoundsDiffusion couplePhase diagramSEM

* Corresponding author..E-mail address: [email protected] (M. M

http://dx.doi.org/10.1016/j.jallcom.2016.04.0810925-8388/© 2016 Elsevier B.V. All rights reserved.

a b s t r a c t

The MgeZneZr ternary systemwas experimentally investigated at 450 �C using six diffusion couples and16 key alloys. Four new ternary compounds, IM1, IM2, IM3 and IM4 were detected. The compositions,homogeneity ranges, phase relationships and the X-ray diffraction patterns of these compounds wereidentified using scanning electron microscopy coupled with energy-dispersive x-ray spectrometer and x-ray diffraction techniques. The homogeneity ranges of IM1, IM2, IM3 and IM4 are Mg(23e26)Zn66Zr(8e11),Mg(15e16)Zn66Zr(18e19), Mg(10e11)Zn66Zr(23e24), and Mg(9e13)Zn(79e87)Zr(5e8), respectively. IM1 compoundcrystallizes in an MgZn2 structure type with hexagonal structure and P63/mmc space group. The MgeZnand ZneZr binary compounds do not have extended solid solubility into the ternary system. The phaseboundaries of MgeZneZr liquid phase at 450 �C were determined by several key alloys. The single phaseliquid region extended into the ternary phase diagram only to around 1 at.% Zr. However, phase regionscontaining liquid along with other phases existed in the vicinity of the MgeZn side up to 10 at% Zr. Basedon the current experimental results, the isothermal section of the MgeZneZr ternary system at 450 �Cwas constructed.

© 2016 Elsevier B.V. All rights reserved.

1. Introduction

Due to light weight, high specific strength and superior cast-ability, Mg alloys have great potential for increased use in auto-motive and aerospace industries [1,2]. To date, many series of Mgalloys have been developed [3,4] and are under study [5]. MgeZ-neZr (ZK series) based alloys are one of the most important com-mercial Mg alloys [2]. Zn is one of the common alloying elementsadded in Mg alloys to improve castability, yield strength, as well ascreep resistance [6,7]. On the other hand, Zr is helpful to obtain finegrain size that ensures good room temperature mechanical prop-erties and corrosion resistance [8]. Zr is an excellent grain refinerfor Mg alloys [9,10] because Zr has close lattice parameters to Mg,which means that Zr is easy to form heterogeneous nucleation forMg grains [11,12]. Zn contributes to grain size refinement of Mgalloys through the constitutional undercooling effect [13]. There-fore, Mg alloys containing Zn and Zr have better mechanicalproperties than pure Mg due to grain refinement [13,14], and thesignificantly improved ductility at room temperature by

edraj).

introducing cross slips to non-basal planes [14]. As a ternary sys-tem, because of the benefits of Zn and Zr elements in Mg alloys,MgeZneZr alloys have relatively high specific strength and goodcorrosion resistance [15]. For example, ZK60 (Mge6Zne0.7Zr wt%)alloy has beenwidely used in industry due to high specific strengthand improved plasticity [16]. ZK51 (Mge4.6Zne0.75Zr wt%) alloyhas excellent room temperature strength and ductility, enabling itto be used in military and aerospace applications [17]. Besides,ZK61, ZK31 and ZK40 alloys were reported to have good plasticityand are used for different purposes [18e20]. Apart from structuralapplications, Mg, Zn and small amount of Zr are non-toxic elementsfor the human body, which is promising as biomaterials [21e23].Mg exists in the human body as fourth most prevalent cation and isfound in bone tissue naturally [21]. Zn is an essential element forthe human body (estimated 15 mg/day) [22] and has physiologi-cally important influence in bone formation [23]. A small amount ofZr in the human body (<250 mg) shows good biocompatibility andlow toxicity [24]. Understanding the phase relations in theMgeZneZr system is essential for developing new Mg alloys andfor understanding the behavior and the processing of the currentZK Mg alloys.

A brief literature review of theMgeZn, MgeZr and ZneZr binarysystems and the MgeZneZr ternary system are presented. The

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Fig. 1. Partial isothermal section of the MgeZneZr ternary system at 345 �C [57].

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 213

MgeZn system was investigated both experimentally and ther-modynamically over the years [25e35]. The most recent thermo-dynamically modeled phase diagram of the MgeZn system wasrecently reported by Ghosh et al. [36]. It shows good agreementwith the experimental data reported by several research groups[27e35]. Two eutectic reactions, L4Mg51Zn20þMg12Zn13 (341 �C)and L4Mg2Zn11 þMg (368 �C), take place at 28.7 at.% and 92.2 at.%Zn, respectively. One eutectoid reaction ofMg51Zn204Mg þ Mg12Zn13 takes place at 321 �C. There are fourperitectic reactions: L þ Mg 4 Mg51Zn20 (342 �C),L þMg2Zn3 4Mg12Zn13 (347 �C), L þ (MgZn2)4Mg2Zn3 (410 �C),and L þ (MgZn2) 4Mg2Zn11 (380 �C). Five intermediate com-pounds, Mg51Zn20, Mg12Zn13, Mg2Zn3, MgZn2 and Mg2Zn11, arefound in the binary phase diagram. In addition, the metastablephase of Mg51Zn20 only exists in a narrow temperature range be-tween 321 �C and 345 �C.

To date, only partial experimental data in theMg-rich part of theMgeZr phase diagram is available [37e41]. Thermodynamiccalculation for the full composition range of this systemwas carriedout by H€am€al€ainen and Zeng [42] and Arroyave et al. [43]. In theMgeZr system, the maximum solubility of Zr in Mg is 0.766 at.%,and the solid solubility of Mg in Zr is negligible. The peritectic re-action (L1þhcp(Zr)4 hcp(Mg)) occurs at 654.6 �C. Zr undergoes anallotropic phase transformation at 864 �C from bcc(Zr) to hcp(Zr).The phase transformation reaction in the Zr-rich side is:L 4 L1 þ bcc(Zr) (1848 �C) and L1 þ bcc(Zr) 4 hcp(Zr) (864 �C). Lstands for Zr-rich liquid and L1 stands for the Mg-rich liquid. Thereare no intermediate compounds in the MgeZr system.

The ZneZr phase diagram is not well established because of thelimited experimental data in the Zr-rich side [44e52]. Dutkiewicz[46] summarized previous experimental findings [44e47] andconstructed the ZneZr phase diagram. Arroyave and Liu [53]thermodynamically modeled this system for the whole composi-tion range considering the previous experimental data [47e49].According to Arroyave and Liu [53], there are the following twoeutectic reactions: L 4 Zr þ ZnZr (1015 �C); L 4 Zn þ Zn22Zr(419 �C). Three eutectoid reactions take place according to:Zn2Zr3 4 b(Zr) þ ZnZr (1000 �C), b(Zr) 4 a(Zr)þZnZr2 (718 �C),and ZnZr2 4 a(Zr) þ ZnZr (705 �C). There are five peritectic re-actions: L þ Zn2Zr 4 Zn3Zr (1110 �C), L þ Zn2Zr 4 ZnZr (1110 �C),L þ ZnZr4Zn2Zr3 (1015 �C), L þ Zn3Zr 4 Zn39Zr5 (750 �C), andL þ Zn39Zr5 4 Zn22Zr (545 �C). One peritectoid reaction takesplaces according to: b(Zr) þ ZnZr 4 ZnZr2 (750 �C). Seven inter-mediate compounds, Zn22Zr, Zn39Zr5, Zn3Zr, Zn2Zr, ZnZr Zn2Zr3 andZnZr2 are detected in the binary phase diagram. Arroyave et al. [53]indicated that ZnZr2 and Zn2Zr3 are found to be stable at705e750 �C and 1000e1015 �C, respectively.

To date, the MgeZneZr ternary system has not been wellstudied. Lashkoi [54] identified the (Zn, Mg)2Zr and Zn2(Mg, Zr)phases in cast alloys. Babkin [55] studied the solubility of Zr inMgeZn alloy, and found that Zn did not affect Zr solubility in liquidMg. Afterward, Lohberg et al. [56] determined the liquidus in theMg-rich corner of the MgeZneZr system. The latest experimentalisothermal section of the MgeZneZr ternary system was carriedout by Ren et al. [57]. A partial isothermal section at 345 �C is shownin Fig. 1. Five three-phase triangulations of Zr þ Zn2Zr3 þ Mg,Mg þ ZnZr þ Zn2Zr3, Lþ(Mg,Zn)2Zr þ Mg, L þ MgZn þ (Mg,Zn)2Zrand MgZn þ Mg2Zn3þ(Mg, Zr)Zn2 were reported. (Mg, Zn)2Zr is asubstitutional solid solution where Mg replaces around 3 at.% of Znin Zn2Zr. The (Mg, Zr)Zn2 is a substitutional solid solution of MgZn2,

in which around 15 at.% of Mg is replaced by Zr. However, the Zn-rich corner was not studied. Even in the Mg-rich corner, no alloyswere prepared in the L þ MgZn þ (Mg, Zn)2Zr andMgZnþMg2Zn3þ (Mg, Zr)Zn2 regions. Therefore, morework is stillneeded for this system.

2. Experimental procedures

In this research, 450 �C was chosen as the annealing tempera-ture, because the phase diagram of theMgeZneZr system at 450 �Cis useful for high temperature processes for Mg production such assemi-solid casting. In addition, this temperature is high enough tocause diffusion and to reach equilibrium for the key alloys.

In order to establish a systematic experimental investigation ofthe MgeZneZr ternary system, 6 diffusion couples and 12 key al-loys were prepared using high purity Mg (99.8%), Zn (99.9%) ingotsand Zr slugs (99.95%) supplied by Alfa Aesar (USA) and Mg-33 wt%Zr master alloy from Richest Group Company (China). Due to thesignificant differences in melting temperatures of the three ele-ments, an intensive evaporation of Mg and Zn happened duringmelting, which led to composition shifting problem. Also, becausethe miscibility gap between Mg and Zr, it is difficult to preparehomogeneous samples. Therefore, the sample preparation methodof directly melting the three elements is abandoned, and animproved experimental procedure using ZneZr and MgeZr masteralloys was designed to prepare homogeneous key alloys. ZneZrmaster alloys were prepared using an arc melting furnace andwater-cooled Cu crucible using a non-consumable tungsten elec-trode. Before melting, Zr slugs were cut to around 1 mm thick andwere pressed to increase the contact area with Zn ingot. Then theassembly was melted in the arc melting furnace. After melting, themaster alloys were cut into small pieces that were remelted 3e4times to make sure all the Zr mixed with Zn. Before every meltingprocess, around 0.50 g of Zinc was added to compensate for theevaporation of Zn during melting. The details of the sample prep-aration can be found in Zhang's Master's thesis [58]. Afterward,ternary alloys were prepared in an induction furnace by addingdifferent amount of Mg and Zn to ZneZr and MgeZr master alloys.After melting, ternary key alloys were cut into two pieces. Onepiece was used for ICP (Inductively Coupled Plasma mass spec-trometry) test and SEM study in the as-cast condition. The otherpiece was wrapped in tantalum foil, sealed in argon-purged quartztube and annealed in a box furnace for different time ranging from2 to 28 days depending on the composition.

Diffusion couple technique is an advanced tool that is often used

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Fig. 2. Location of the diffusion couples in the isothermal section of the ternarysystem.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225214

to study the formation of phases in binary, ternary and multicom-ponent systems [59,60]. To prepare diffusion couples, two end-members, which were prepared from pure metals or alloys, weregrinded down to 1200 grit SiC paper and were polished using 1 mmcolloidal silica polishing suspensions (OPeS suspension). Then thetwo end-members were clamped together using a clamping ring.The diffusion couples were wrapped in tantalum foil and annealedat 450 �C in a quartz tube filled with Ar for different time rangingfrom 2 to 10 days. The annealing period of diffusion couples wasadjusted based on the appearance of the quartz tubes. If the quartztube turned black, the diffusion couple was taken out to avoidintensive evaporation.

After annealing, the quartz tube was quenched in water and thesamples weremounted in epoxy. Then it was grinded down to 1200grit SiC papers and was polished by 1 mm colloidal silica. Duringgrinding and polishing, ethanol was used as a lubricant. HitachiSe3400 N (SEM) coupled with Oxford energy dispersive spec-trometer (EDS) was used to analyse the diffusion couples and keyalloys. Because of the overlapping of peaks, there is an estimated2e3 at.% error of EDS results. Therefore, for the chemical compo-sition identification, 3e5 measurements were carried out ondifferent locations for each phase and the average compositionwastaken as the actual composition. The area EDS was also used toidentify the overall composition of the key alloys.

X-ray scans using a PANalytical X-ray Diffractometer with aCuKa radiation at 45 kV and 40 mA were performed on key alloys.The crystal structure information of the pure elements and binaryphases in this system were taken from the Pearson's Crystal Data-base [61]. The majority of the peaks of the pure elements and bi-nary compounds are located in the range from 20� to 90�. Hence,spectra were acquired in this range with a 0.02� step size. Siliconpowder was added to the samples for calibrating the zero shift aswell as specimen displacement. X'Pert HighScore Plus Rietveldanalysis software was used for XRD patterns analysis.

3. Results and discussion

3.1. Experimental investigation through diffusion couples

Diffusion couple technique is one of the main methods used inthis research to map the phase diagram of the MgeZneZr system.Six diffusion couples were prepared and analyzed. The composi-tions of the end-members and the annealing conditions of thediffusion couples are summarized in Table 1. Fig. 2 shows thelocation of the diffusion couples in the ternary system.

3.1.1. Diffusion couple #1: ZreMg36Zn64Backscattered electron (BSE) images of diffusion couple #1:

ZreMg36Zn64 are presented in Fig. 3. The first end-member wasmade from Zr, and the second end-member was made from a two-phase alloy that is composed of MgZn2 and Mg2Zn3 as shown inFig. 3 (c). After 7 days annealing at 450 �C, seven diffusion zoneswere observed in this diffusion couple. As shown in Fig. 3 (a) and(b), the diffusion zones were colored for clearer illustration. The

Table 1List of the diffusion couples.

Diffusion couple End-member 1 End-member 2 Annealing condition

#1 Zr 36 Mg 64 Zn at.% 450 �C 7 days#2 Zr 20 Mg 80 Zn at.% 450 �C 2 days#3 Zr 45 Mg 55 Zn at.% 450 �C 3 days#4 Zr 45 Mg 55 Zn at.% 450 �C 7 days#5 Zr 43 Mg 57 Zn at.% 450 �C 7 days#6 Zr 30 Mg 70 Zn at.% 450 �C 10 days

EDS spot analysis results for each phase are summarized in Table 2.Fig. 3 (b) represents the magnified image of this diffusion couplenear the Zr end-member side. EDS line scan was carried out acrossthis diffusion couple. The results, shown in Fig. 3 (d), indicate thatthe IM1 and IM2 ternary compounds are substitutional solid so-lutions, where Mg is substituted by Zr at constant Zn concentrationof 66 at.%. The homogeneity range of IM1 and IM2 are estimated asMg(22e26)Zn66Zr(8e12) and Mg(14e16)Zn66Zr(18e20), respectively. Thehomogeneity range of IM3 phase could not be determined from thisdiffusion couple because its layer was too thin to acquire severalEDS points across the layer. However, the average composition of 6points of IM3 along the layer is Mg10Zn66Zr24. A very thin layer wasobserved between Zone 1 (Zr) and Zone 3 (Zn2Zr), which could notbe analyzed but is thought to be ZnZr, because this the only com-pound stable between Zr and Zn2Zr at 450 �C based on the ZneZrbinary phase diagram [53].

In the current work, IM3, IM2 and IM1 are considered as sepa-rate ternary compounds based on the clear phase boundariesobserved in the EDS line scan in Fig. 3 (d). The binary homogeneityrange of MgZn2 was estimated as Mg(32e34)Zn(66e68). Fig. 3 (c)represents the microstructure of the second end-member ofdiffusion couple #1 before annealing, where Mg2Zn3 is located inthe matrix of MgZn2. According to the binary phase diagram of theMgeZn system [36], the Mg2Zn34Lþ(MgZn2) peritectic reactionoccurs at 410 �C. Therefore, the Mg36Zn64 alloy transforms to liquidandMgZn2 while annealing at 450 �C. The composition of the liquidcould be obtained from the binary phase diagram [36] which wasfound to be aroundMg60Zn40. The interdiffusion started between Zrand the semi-solid end-member that contained liquid and MgZn2.Layers of ZnZr, Zn2Zr, IM3, IM2, and IM1 formed during diffusion.Some liquid evaporated from the MgeZn end-member, because theannealing time was relatively long.

The diffusion path of this diffusion couple can be depicted asfollows:Zr / ZnZr / Zn2Zr / IM3 / IM2 / IM1 / MgZn2 þ Liquid(Mg60Zn40). The phase equilibria obtained from diffusion couple #1are represented in Fig. 3 (e). The two end-members of diffusioncouple #1 are connected by a dashed line. Numbers in the blackboxes represent the diffusion layers in Fig. 3 (a).

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Fig. 3. (a) SEM micrograph of diffusion couple #1; (b) magnified SEM micrograph of the diffusion layers; (c) SEM micrograph of the Mg36Zn64 end-member before annealing; (d)EDS line scan across diffusion couple #1; (e) diffusion path depicted from diffusion couple #1 where the numbers refer to the diffusion layers in part (a) of this Figure.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 215

3.1.2. Diffusion couple #2: ZreMg20Zn80Diffusion couple #2 was prepared to determine the phase

equilibria in the Zn-rich side. The BSE images of this diffusioncouple are presented in Fig. 4. The first end-member was made

from Zr, and the second was made from Mg20Zn80 binary alloycontaining MgZn2 and Mg2Zn11 compounds. This diffusion couplewas annealed at 450 �C for 2 days. After annealing, EDS spotanalysis was used to identify the seven diffusion zones observed in

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Table 2EDS spot analysis of diffusion couple #1.

Zone Composition (at.%) Corresponding phase

Mg Zn Zr

1 0 0 100 Zr2 0 50 50 ZnZr3 0 67 33 Zn2Zr4 11 65 24 IM35 14e16 66 18e20 IM26 22e26 66 8e12 IM17 32e34 66e68 0 MgZn2

Fig. 4. (a) SEM micrographs of diffusion couple #2; (b) magnified SEM image of the diffusion layer; (c) EDS line scan across diffusion layers; (d) diffusion path depicted fromdiffusion couple #2 where the numbers refer to the diffusion layers in (a).

Table 3EDS spots analysis of diffusion couple #2.

Zone Composition (at.%) Corresponding phase

Mg Zn Zr

1 0 0 100 Zr2 0 50 50 ZnZr3 0 64 36 Zn2Zr4 0 74 26 Zn3Zr5 0 87 13 Zn39Zr56 10e15 77e81 7e9 IM47 33 67 0 MgZn2

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225216

Fig. 4 (a). Chemical compositions and the corresponding phases aresummarized in Table 3. A new ternary compound (IM4) wasobserved in zone 6. Besides, the equilibrium between IM4 (zone 6)and Zn39Zr5 (zone 5) could be established from this diffusioncouple. Fig. 4 (b) is a magnified part of this diffusion couple. Zr,ZnZr, Zn2Zr and Zn3Zr were detected by EDS spot analysis. Duringannealing, Mg2Zn11 transforms into liquid and MgZn2 according tothe peritectic reaction: L þ (MgZn2) 4 Mg2Zn11 (380 �C) [36]. Thecomposition of the liquid is about Mg12.5Zn87.5, which was obtainedfrom the binary phase diagram [36]. Mg and Zn atoms from thesemi-solid end-member side diffused to Zr side, and Zr atoms from

the Zr end-member diffused to the semi-solid end-member side.The diffusion rate was high due to the presence of liquid. Therefore,the annealing period of this diffusion couple was short. ZnZr, Zn2Zr,Zn3Zr, Zn39Zr5 and IM4 layers formed during annealing. Afterannealing, the MgeZn end-member created a porous structure dueto the liquid evaporation. EDS line scan was carried out across thisdiffusion couple to determine the homogeneity ranges of theternary and binary phases and the results are presented in Fig. 4 (c).It can be seen from this Figure that in the IM4 ternary compound,Mg was substituted by both Zr and Zn. Hence, the homogeneityrange of IM4 was estimated as Mg(10e15)Zn(77e81)Zr(7e9).

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Fig. 5. (a) SEM image from diffusion couple #3; (b) EDS line scan across diffusion layers of diffusion couple #3; (c) SEM image from diffusion couple #4; (d) EDS line scan acrossdiffusion layers of diffusion couple #4; (e) SEM image from diffusion couple #5; (f) EDS line scan across diffusion layers of diffusion couple #5; (g) SEM image from diffusion couple#6; (h) EDS line scan across diffusion layers of diffusion couple #6.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 217

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Fig. 6. A partial isothermal section of the MgeZneZr ternary system at 450 �C con-structed based on the diffusion couples results.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225218

The sequence of diffusion layers in this diffusion couple can bedepicted as follows:Zr/ ZnZr/ Zn2Zr/ Zn3Zr/ Zn39Zr5 / IM4/MgZn2þ Liquid(Mg12.5Zn87.5). The phase equilibria obtained from diffusion couple#2 are represented in Fig. 4 (d). The two end-members of diffusioncouple #2 are connected by a dashed line.

3.1.3. Summary of the diffusion couples resultsThe other four diffusion couples were analyzed using the same

method. The SEM images and the EDS line scan results of diffusioncouples #3 e #6 are summarized in Fig. 5. The diffusion pathsdepicted from these diffusion couples are listed as follows:

Diffusion couple #3: Zr / ZnZr / Zn2Zr / IM3 / IM2 / IM1

Diffusion couple #4:Zr/ Zn2Zr/ IM3/ IM2/ IM1/MgZn2 þ Liquid (Mg60Zn40)

Diffusion couple #5:Zr / Zn2Zr / Zn3Zr / IM1 / MgZn2 þ Liquid (Mg60Zn40)

Diffusion couple #6:Zr / Zn2Zr / Zn3Zr / IM2 / IM1 / MgZn2 þ Liquid(Mg12.5Zn87.5)

An isothermal section of the MgeZneZr ternary system at450 �Cwas constructed by combining the results of the six diffusioncouples. Phase relations are demonstrated in Fig. 6. Four ternarycompounds which were labeled as IM1, IM2, IM3 and IM4 weredetected in the diffusion couples. The compositions of the ternaryphases detected by EDS in diffusion couples #1 to #6 are summa-rized in Table 4. IM1 and IM2 ternary compounds have substitu-tional solid solubilities where Mg is substituted by Zr at a constantZn concentration (66 at.%). The homogeneity range of IM1 and IM2were Mg(23e25)Zn66Zr(8e11) and Mg(15e16)Zn66Zr(18e19), respectively.No solid solubility of IM3was observed in the diffusion couples, andthe composition of IM3 compound was determined asMg10Zn66Zr24.

3.2. Experimental investigation through key alloys

A partial isothermal section of the MgeZneZr ternary system at450 �C, shown in Fig. 6, was constructed based on the results ob-tained from the diffusion couples. However, the phase equilibria inthe MgeZn side is still not clear. 12 key alloys were designed andprepared to improve the understanding of the phase relations inthis region and to verify the results obtained by diffusion couples.The actual composition, corresponding phases of the key alloyswere summarized in Table 5. Fig. 7 shows the locations of the keyalloys in the isothermal section of the MgeZneZr system.

3.2.1. Structure and composition of the IM1, IM2, IM3 and IM4ternary compounds

Four ternary compounds, IM1, IM2, IM3 and IM4, were observedby diffusion couples technique. The key alloys No. 1e4 were pre-pared to study the crystal structure of the ternary compounds andto verify the formation of these ternary compounds. The use ofsingle-phase samples is preferred for the crystal structure identi-fication of new compounds. In the present work, single-phasesamples of IM1 and IM4 were successfully prepared after severalattempts. Although the single-phase IM2 and IM3 alloys were notsuccessful, two-phase samples that contain Mg þ IM2 andMg þ IM3 were successfully prepared. The annealed key sampleswere studied by XRD using Rietveld analysis. The XRD patterns ofIM1 and IM4 are illustrated in Fig. 8 (a) and (b), respectively. It wasfound that IM1 compound crystallizes in an MgZn2 structure typewith the hexagonal structure and P63/mmc space group. As shownin Fig. 8 (c), the refined XRD pattern of the MgZn2 is perfectlycorresponding to IM1 pattern. In the refined MgZn2 pattern, 30% ofMg was replaced by Zr. This substitution did not shift the peaksbecause there is no large difference in the atomic size between Mg(r ¼ 0.16 nm) and Zr (r ¼ 0.159 nm). The calculated chemicalcomposition of IM1 was Mg24Zn66Zr10, which was consistent withthe EDS results obtained from the key alloys and diffusion couples.The crystallographic parameters of the IM1 compound are pre-sented in Table 6. The crystal structure and prototype of the IM4have not been determined yet.

The other two new ternary compounds (IM2 and IM3) weredetected from the diffusion couples. Although the crystal structuresof these two ternary compoundswere not determined in this study,the XRD patterns of IM2 and IM3 were obtained. The equilibratedsamples 3 and 4 are analyzed by XRD, and SEM coupled with EDS.Two-phase equilibria of Mg þ IM2 and Mg þ IM3 were inferredfrom key alloys 3 and 4 by SEM/EDS. The XRD patterns of thesesamples with the identified phases are shown in Fig. 9 (a) and (b).The XRD patterns of IM2 and IM3 could be obtained by subtractingthe Mg patterns from the patterns of the two phase alloys. The XRDpatterns of the IM2 and IM3 were shown in Fig. 9 (c) and (d),respectively. The crystal structure and prototype of IM2 and IM3have not been determined yet. Studies regarding the crystalstructure of these ternary compounds are still needed and will becarried in a future work.

To study the phase transformations of the IM1, IM2 and IM3ternary compounds, key alloys 5e7 were prepared and annealed intwo steps. The first step involved heating the alloys up to 450 �Cand holding them for 2 weeks. Then they were analyzed using SEMand XRD. The second step involved annealing the same alloys for 2more weeks at 450 �C, followed by SEM and XRD analysis. The keyalloy 6 (Mg75Zn23Zr2) is presented here as an example. The back-scattered images of this key alloy are shown in Fig. 10. Fig. 10 (a)represents the micrograph of this alloy in the as-cast condition. Mg,Mg2Zn3, IM3, and Zn2Zr phases were identified by EDS spot anal-ysis. Around 3 at.% of Zr was substituted by Mg in the Zn2(Zr, Mg)solid solution. A peritectic morphology containing Zn2Zr as a

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Fig. 7. The locations of the key alloys in the isothermal section of the MgeZneZrsystem.

Table 5Actual compositions and corresponding phases of the key alloys.

Sample number Actualcomposition(at.%)

EDS composition(at.%)

Correspondingphases

Mg Zn Zr Mg Zn Zr By EDS By XRD

1 27 65 8 27 65 8 IM1 IM12 9 84 7 8 84 8 IM4 IM43 91 6 3 17 65 18 IM2 IM2

97 3 0 (Mg) (Mg)4 72 20 8 13 64 23 IM3 IM3

98 2 0 (Mg) (Mg)22 66 12 IM1 IM135 65 0 MgZn2 MgZn2

5 41 57 2 40 60 0 Mg2Zn3 Mg2Zn3

77 23 <1 Eutectic Eutectic6 75 23 2 26 65 9 IM1 IM1

96 4 0 (Mg) (Mg)72 28 <1 Eutectic Eutectic16 65 18 IM2 IM2

7 77 20 3 24 65 11 IM1 IM197 3 0 (Mg) (Mg)0 49 51 ZnZr ZnZr

8 85 9 6 0 0 100 Zr Zr98 2 0 (Mg) (Mg)

9 17 80 3 11 84 5 IM4 IM413 87 <1 Liquid Liquid33 67 0 MgZn2 MgZn2

10 20 75 5 11 82 7 IM4 IM433 67 0 MgZn2 MgZn2

11 23 71 6 23 67 10 IM1 IM113 79 8 IM4 IM432 68 0 MgZn2 MgZn2

0 88 12 Zn39Zr5 Zn39Zr512 5 88 7 9 85 6 IM4 IM4

0 95 5 Zn22Zr Zn22Zr

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 219

primary phase and surrounded by the peritectic phase IM3 wasobserved. Upon annealing Zn2Zr decomposes to form IM3. Mean-while, Mg and Mg2Zn3 were observed in the as-cast alloy. AlthoughMg2Zn3 is not stable at 450 �C, it forms in the as-cast conditionsindicating that the as-cast sample is not at equilibrium. Fig. 10 (b)represents the sample after 2 weeks annealing at 450 �C. Mg, IM2and eutectic structure were observed. During annealing, IM3 phasedecomposed forming the IM2 compound. During quenching inwater after annealing, remaining liquid solidified to eutecticmicrostructure of Mg and MgZn2. The BSE images of the samesample after 4 weeks annealing are shown in Fig.10 (c) and (d). IM1,Mg and eutectic morphologywere observed in the SEM images. TheMg solid solution dissolves around 4 at.% Zn.With longer annealing,all IM2 decomposed to form IM1 and Mg. This key sample wasfinally brought to equilibrium after 4 weeks annealing because themetastable phases were not observed, and the Mg þ IM1 þ Liquidthree-phase equilibrium has been obtained. The composition of theeutectic area identified by EDS area mapping was Mg72Zn28. The Zramount in the eutectic composition was less than 1 at.%.

The actual chemical compositions and the corresponding con-stituent phases of key alloy 6 are listed in Table 7. The phase re-lationships could be inferred from this alloy at different conditionsand they are shown in Fig. 11. Four phases ofMgþ Zn2Zrþ IM3þMg2Zn3 were observed in the as-cast alloy, andZn2Zr is decomposing to form IM3. MgZn2 þ IM2 þ Liquid exist inthe annealed alloy after 2 weeks annealing at 450 �C. After 2 weeks

Table 4Compositions of the ternary compounds based on diffusion couples analysis.

Diffusion couple IM1 IM2

Composition (at.%) Composition (at.%)

Mg Zn Zr Mg Zn

#1 22e26 66 8e12 14e16 66#2#3 22e26 66 8e12 16 66#4 24e27 66 7e10 15e17 66#5 23e25 67 8e10#6 23e25 66 9e11 15e16 66

annealing at 450 �C, IM3 phase decomposed to form the IM2compound. The three-phase equilibrium of MgZn2 þ IM1 þ Liquidwas determined in the alloy annealed for 4 weeks, which indicatesIM2 decomposed to form IM1 andMg upon longer annealing. Theseresults indicate that the equilibrium process may occur throughperitectic reactions. Fig. 12 represents the XRD patterns and iden-tified phases of key alloy 6. The XRD results confirmed that the IM2decomposed to IM1 and Mg when the alloy was subjected to longannealing, which agrees well with the EDS results. The existence ofMgZn2 indicates that the eutectic structure was composed of Mgand MgZn2, which confirms the SEM/EDS analysis.

3.2.2. Phase equilibrium in the Zn-rich cornerThe composition of IM4 in key alloy 4 is Mg8.6Zn84Zr7.4. IM4 was

found to have solid solubility in the diffusion couples #2. Key alloys9e12 were selected to study the phase relations in the Zn-rich re-gion and the solid solubility range of IM4. The actual compositionsof the key alloys and the phases confirmed by EDS and XRD are

IM3 IM4

Composition (at.%) Composition (at.%)

Zr Mg Zn Zr Mg Zn Zr

18e20 11 65 247e9 77e81 10e15

18 10 66 2417e19 10 66 24

18e19

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Fig. 8. (a) XRD pattern of IM1 obtained from key alloy No. 1; (b) XRD pattern of IM4 obtained from key alloy No. 2 (both samples were annealed at 450 �C for 4 weeks); (c) XRDpattern of IM1 and refined MgZn2 phase.

Table 6Crystal structure of the IM1 phase.

IM1 composition by EDS Mg(23e26)Zn66Zr(8e11)

IM1 phase composition identified by Rietveld analysis Mg24Zn66Zr10Prototype MgZn2

Space group P63/mmcUnit cell parameters and lattice volume Atomic coordinates Occupancy (%) x y z Bisoa ¼ 5.23 Zn1-6h Zn 100 0.1697 0.3394 0.25 0.50b ¼ 5.23 Zn2-2a Zn 100 0 0 0 0.50c ¼ 8.51 Mg, Zr1-4f Mg 68.5%

Zr 31.5%0.3333 0.6666 0.5629 0.50

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225220

summarized in Table 5. Examples of the micrographs of the as-castand equilibrated alloys are presented in Fig. 13.

The as-cast sample No. 9 (Mg17Zn80Zr3) along with the equili-brated sample after 2 days annealing at 450 �C are demonstrated inFig. 13 (a) and (b). After 2 days annealing at 450 �C, the quartz tubeturned black, therefore the alloy was taken out to avoid intensiveevaporation. The sample reached equilibrium relatively fast due tothe presence of large amount of liquid for this composition at thistemperature due to its proximity to the MgeZn side. Zn39Zr5, IM4,MgZn2 and eutectic of MgZn2 and Zn were observed in the as-castsample as shown in Fig. 13 (a). IM4, MgZn2 and the MgZn2 þ Zneutectic were detected by EDS spot analysis in Fig.13 (b). The binaryZn39Zr5 compound was observed in the as-cast sample, and it wasnot observed in the sample after 2 days annealing at 450 �C. Zn39Zr5is a metastable compound in this key alloy that is expected to have

MgZn2 þ IM4 þ liquid three-phase at equilibrium. Zn39Zr5 formedat around 750 �C during melting and it did not decompose becausethe melting time in the arc melting furnace was short. Duringannealing, Zn39Zr5 reacted with Mg to form IM4. MgZn2 is a stablephase in the key alloy, showing no Zr solubility. MgeZn liquidoccurred at this temperature and formed MgeMgZn2 eutecticstructure upon quenching. The composition of IM4 was identifiedas Mg11Zn84Zr5, and the liquid composition was determined asMg13Zn87 by EDS area analysis. The Zr amount in the eutecticcomposition was less than 1 at.%. Based on the results of this keyalloy, a three-phase equilibrium of MgZn2 þ IM4 þ liquid wasdetermined.

Fig.13 (c) shows the two-phase equilibrium ofMgZn2 and IM4 inkey alloy 10 (Mg20Zn75Zr5). The composition of the IM4 wasdetermined as Mg11Zn82Zr7. The black spots were porosities, which

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Fig. 9. (a) XRD pattern of sample No. 3; (b) XRD pattern of sample No. 4; (c) XRD pattern of IM2; (d) XRD pattern of IM3.

Fig. 10. SEM micrographs of (a) As-cast sample No. 6; (b) Sample after 2 week annealing at 450 �C; (c), (d) Sample after 4 weeks annealing at 450 �C.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 221

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Table 7Actual composition and corresponding phases of key alloy 6 (Mg75Zn23Zr2).

Sample condition EDS composition (at.%) Corresponding phases

Mg Zn Zr

As-cast 3 65 32 Zn2(Zr,Mg)100 <1 <1 Mg40 60 0 Mg2Zn3

11 65 24 IM3450 �C 2weeks 16 66 18 IM2

96 4 0 (Mg)64 30 6 Eutectic

450 �C 4weeks 26 65 9 IM196 4 0 (Mg)72 28 <1 Eutectic

450oC 4 weeks

Liquid

IM1

IM2

Zn Zr

MgZn

MgZn

ZnMg

Zn Zr

Zn Zr

Zn Zr6

IM3

As-cast450oC 2 weeks

Fig. 11. Phase relationships of key alloy 6 at as-cast, after 2 weeks and 4 weeksannealing. The actual composition of this key alloy is labeled by number 6 on thediagram.

Fig. 12. XRD results of key alloy 6 annealed

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225222

were caused by liquid evaporation. This alloy shows that IM4 is inequilibrium with MgZn2 at 450 �C. This means that there is a twophase region between these two compounds in the 450 �Cisothermal section.

Fig. 13 (d) represents the three-phase key alloy 11 (Mg23Zn71Zr6)after 4weeks annealing at 450 �C. IM4, IM1 andMgZn2 phases wereobserved in the micrograph. The composition of IM4 was deter-mined as Mg13Zn79Zr8. The composition of IM1 was detected asMg23Zn67Zr10. Therefore a three-phase equilibrium ofMgZn2 þ IM4 þ IM1 was determined.

After 4 weeks annealing, sample 12 (Mg5Zn88Zr7) was broughtto equilibrium. As shown in Fig. 13 (e), Zn39Zr5, Zn22Zr and IM4demonstrated equilibrium three-phase relationship in this alloy at450 �C. This means that there is a triangulation between these threecompounds in the 450 �C isothermal section. The composition ofIM4 was detected as Mg9Zn85Zr6.

Based on these four key alloys, the phase relationships in the Zn-rich part are presented in Fig. 13 (f). The homogeneity range of theternary compound IM4 was obtained from the EDS results of keyalloys 9e12 and diffusion couples #2. IM4 has a homogeneity rangeof 9e13 at.% Mg, 79e87 at.% Zn and 5e8 at.% Zr.

X-ray diffraction was performed on the key alloys in the Zn-richcorner. The full pattern refinement along with the identified phasesof alloys 10 and 11 are illustrated in Fig. 14 (a) and (b), respectively.The XRD results are consistent with the SEM results. In key alloy No.10, MgZn2 and IM4 phases were detected in the XRD results. Thepeaks of IM4 in key alloy No.10matched well with the key alloy No.4 which was composed of a single phase of IM4. MgZn2, IM1 andIM4 phases were detected in key alloy No. 11, which was consistentwith the SEM results.

at 450 �C for (a) 2 weeks (b) 4 weeks.

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Fig. 13. SEMmicrographs of (a) as-cast key alloy 9; (b) key alloy 9 after 2 days annealing at 450 �C; (c) alloy 10 after 2 weeks annealing at 450 �C; (d) alloy 11 after 4 weeks annealingat 450 �C; (e) alloy 12 after 4 weeks annealing at 450 �C; (f) partial phase diagram in the Zn corner of the MgeZneZr system at 450 �C based on the results of key alloys 9 to 12.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 223

3.3. Isothermal section of the Zn-rich corner of the MgeZneZrsystem at 450 �C

The isothermal section of the MgeZneZr system at 450 �C, asshown in Fig. 15, was constructed by 6 diffusion couples and 12 keyalloys. The solid lines represent the phase boundaries and the solidsolubility of the ternary compounds obtained experimentally. A fewboarder lines that are expected between certain phases but havenot been verified experimentally have been drawn as dotted lines.

In the current work, no ternary solid solubilities were observed

for the binary compounds, which contradicts the work of Ren et al.[57], who suggested a Mg/Zr atomic substitution such as (Mg,Zr)Zn2. The composition they reported in this context isMg17.54Zn67.11Zr15.35 which is close to the composition of IM2compound observed in the current work. In addition, Ren et al. [57]reported a three phase equilibrium between MgeZnZreZn2Zr3 at345 �C. The existence of the Zn2Zr3 at 345 �C, has a contradictionwith the binary ZneZr phase diagram [53], where the Zn2Zr3 phaseonly exists within a very limited temperature range(1000e1015 �C). In this work, the Zn2Zr3 compound is not detected

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Fig. 14. (a) XRD results of sample 10 annealed at 450 �C for 4 weeks. (b) XRD results of sample 11 annealed at 450 �C for 4 weeks.

Fig. 15. Isothermal section of the MgeZneZr system at 450 �C.

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225224

in the diffusion couples and key alloys. The three phase equilibriumof MgeZreZnZr has been observed in key alloy 8 and supported theconclusion that the Zn2Zr3 compound is not stable at 450 �C. Singlephase liquid is found at 450 �C in this system. This is consistent withthe MgeZr and ZneZr binary systems, which have steep liquiduslines in the Mg- and Zn-rich regions. The single phase liquid regionextended up to 1 at.% into the ternary phase diagram. The binaryhomogeneity range of MgZn2 was estimated as Mg(32e34)Zn(66e68),which agrees well with the literature [36].

4. Conclusions

The isothermal section of the MgeZneZr ternary system at450 �C has been studied and constructed experimentally in thiswork. Four new ternary compounds were detected in this system.The phase equilibria were determined based on the phase analysisof 6 diffusion couples and 12 key alloys. The homogeneity ranges ofIM1, IM2, IM3 and IM4 phases were found to beMg(23e26)Zn66Zr(8e11), Mg(15e16)Zn66Zr(18e19),Mg(10e11)Zn66Zr(23e24), and Mg(9e13)Zn(79e87)Zr(5e8), respectively.Based on these ranges, IM2 and IM3 have been considered stoi-chiometric, whereas IM4 was found to have complex ternary sol-ubility. IM1 compound has 3% Mg/Zr atomic exchange while Znatomic ratio remains constant at around 66%. It crystallizes in

MgZn2 structure type with a hexagonal structure and P63/mmcspace group. Sixteen three-phase equilibria have been revealed inthis system, among them five triangulations contain Mg. Eighteentwo-phase regions have been observed majority of them involvethe newly discovered ternary compounds. Although large region ofliquid exists in the MgeZn phase diagram at 450 �C, single phaseliquid region extended only up to 1 at.% into the ternary phasediagram at this temperature. However, Two and three-phase re-gions that contain liquid phase along other phases extende up toaround 10 at.% Zr. No ternary solubility of binary compounds couldbe observed in this system at 450 �C.

Acknowledgements

Financial support from the Natural Sciences and EngineeringResearch Council (NSERC) (RGPIN 261704) is grateful acknowl-edged. The authors also would like to thank Dr. AhmadMostafa andMr. Yogesh Iyer Murthy for their help during the experimentalwork.

References

[1] B.L. Mordike, T. Ebert, Magnesium properties-applications-potential, Mater.Sci. Eng. A 302 (2001) 37e45.

[2] E. Aghion, B. Bronfin, Magnesium alloys development towards the 21st cen-tury, Mater. Sci. Forum 350e351 (2000) 19e28.

[3] M. Avedesian, H. Baker, ASM specialty handbook-magnesium and magnesiumalloys, ASM. Mat. Db (1999) 1681e1683.

[4] Y.N. Zhang, D. Kevorkov, X.D. Liu, F. Bridier, P. Chartrand, M. Medraj, Homo-geneity range and crystal structure of the Ca2Mg5Zn13 compound, J. AlloysCompd. 523 (2012) 75e82.

[5] A. Gil-Santos, N. Moelans, N. Hort, O. Van der Biest, Identification anddescription of intermetallic compounds in Mg-Si-Sr cast and heat-treatedalloys, J. Alloys Compd. 669 (2016) 123e133.

[6] F.W. Bach, M. Schaper, C. Jaschik, Influence of lithium on hcp magnesium al-loys, Mater. Sci. Forum 419e422 (2) (2003) 1037e1042.

[7] Z.H. Yu, H.G. Yan, J.H. Chen, Y.Z. Wu, Effect of Zn content on the microstruc-tures and mechanical properties of laser beam-welded ZK series magnesiumalloys, J. Mater. Sci. 45 (2010) 3797e3803.

[8] M.P. Staiger, A.M. Pietak, J. Huadmai, G. Dias, Magnesium and its alloys asorthopedic biomaterials: a review, Biomaterials 27 (2006) 1728e1734.

[9] Z. Zhang, J.P. Li, J.X. Zhang, G.W. Lorimer, J. Robson, Review on research anddevelopment of magnesium alloys, Acta Metall. Sin. 21 (5) (2008) 313e328.

[10] M. Shahzad, L. Wagner, The role of Zr-rich cores in strength differential effectin an extruded Mg-Zn-Zr alloy, J. Alloys Compd. 486 (2009) 103e108.

[11] E.F. Emely, Principles of Magnesium Technology, Pergamon, Oxford, 1966, pp.127e130.

[12] Y.C. Lee, A.K. Dahle, D.H. St John, The role of solute in grain refinement ofmagnesium, Metall. Mater. Trans. A 31 (2000) 2895e2906.

[13] A. Becerra, M. Pekguleryuz, Effects of zinc, lithium, and indium on the grainsize of magnesium, J. Mater. Res. 24 (5) (2009) 1722e1730.

[14] J. Koike, T. Kobayashi, T. Mukai, H. Watanabe, M. Suzuki, K. Maruyama,K. Higashi, The activity of non-basal slip systems and dynamic recovery atroom temperature in fine-grained AZ31b magnesium alloys, Acta Mater 51 (7)(2003) 2055e2065.

[15] C.Y. Wang, X.J. Wang, H. Chang, K. Wu, M.Y. Zheng, Processing maps for hotworking of ZK60 magnesium alloy, Mater. Sci. Eng. A 464 (2007) 52e58.

Page 14: Journal of Alloys and Compounds - Encsusers.encs.concordia.ca/~mmedraj/papers/Mg-Zn-Zr.pdf · alloys was designed to prepare homogeneous key alloys. ZneZr master alloys were prepared

X. Zhang et al. / Journal of Alloys and Compounds 680 (2016) 212e225 225

[16] A. Bussiba, A.B. Artzy, A. Shtechman, S. Ifergan, M. Kupiec, Grain refinement ofAZ31 and ZK60 Mg alloys towards superplasticity studies, Mater. Sci. Eng. A302 (2001) 56e62.

[17] I.J. Polmear, Overview magnesium alloys and applications, Mater. Sci. Tech. 10(1994) 1e16.

[18] H. Watanabe, T. Mukai, M. Mabuchi, K. Higashi, High-strain-rate super-plasticity at low temperature in a ZK61 magnesium alloy produced by powdermetallurgy, Scr. Mater 41 (1999) 209e213.

[19] R. Pinto, M.G.S. Ferreira, M.J. Carmezim, M.F. Montemor, The corrosionbehaviour of rare-earth containing magnesium alloys in borate buffer solu-tion, Electrochim. Acta 56 (2011) 535e545.

[20] L. Lin, Z. Liu, L. Chen, T. Liu, S. Wu, Microstructure evolution and low tem-perature superplasticity of ZK40 magnesium alloy subjected to ECAP, Met.Mater. Int. 10 (6) (2004) 501e506.

[21] A. Hartwig, Role of magnesium in genomic stability, Mutat. Res.-Fund. Mol. M.475 (2001) 113e121.

[22] H. Tapiero, K.D. Tew, Trace elements in human physiology and pathology: zincand metallothioneins, Biomed. Pharmacother. 57 (2003) 399e411.

[23] M. Yamaguchi, Role of zinc in bone formation and bone resorption, J. TraceElem. Exp. Med. 11 (1998) 119e135.

[24] L. Salda~n, A. M�endez-Vilas, L. Jiang, M. Multigner, J.L. Gonz�alez-Carrasco,M.T. P�erez-Prado, In vitro biocompatibility of an ultrafine grained zirconium,Biomaterials 28 (2007) 43e54.

[25] O. Boudouard, Alloys of zinc and magnesium, Comptes Rendus Hebdomad-aires des Seances de l'Academie des Sciences, 139, 1904, pp. 424e426.

[26] G. Grube, Alloys of magnesium with cadmium, zinc, bismuth and antimony,Z. Anorg. Chem. 49 (1906) 72e92.

[27] G. Bruni, C. Sandonnini, The ternary of magnesium, zinc and cadmium II,Z. Anorg. Chem. 78 (1913) 273e297.

[28] R.J. Chadwick, The constitution of the alloys of magnesium and zinc, J. I. Met.449 (1928) 285e299.

[29] G. Grube, A. Burkhardt, The electrical conductivity, thermal expansion andhardness of magnesium-zinc, Z. Elek. Anorg. Phy. Chem. 35 (1929) 315e331.

[30] J.J. Park, L.L. Wyman, Phase relationship in Mg alloys, WADC Tech. Rep. (1957)1e27.

[31] W. Hume-Rothery, E.D. Rounsefell, The system magnesium-zinc, J. I. Met. 41(1929) 119e138.

[32] S. Samson, The crystal structure of Mg2Zn11: isomorphism between Mg2Zn11and Mg2Cu6Al5, Acta Chem. Scand. 3 (1949) 835e843.

[33] T. Takei, The equilibrium diagram of the system magnesium-zinc, KinzokunoKenkyu, J. Jpn. I. Met. 6 (1929) 177e183.

[34] R. Agarwal, S.G. Fries, H.L. Lukas, G. Petzow, F. Sommer, T.G. Chart,G. Effenberg, Assessment of the Mg-Zn system, Z. Met. 83 (1992) 216e223.

[35] I. Higashi, N. Shotani, M. Uda, T. Mizoguchi, H. Katoh, The crystal structure ofMg51Zn20, J. Solid State Chem. 36 (1981) 225e233.

[36] P. Ghosh, M. Mezbahul-Islam, M. Medraj, Critical assessment and thermody-namic modeling of Mg-Zn, Mg-Sn, Sn-Zn and Mg-Sn-Zn systems, CALPHAD 36(2012) 28e43.

[37] G.A. Mellor, The constitution of magnesium-rich alloys of magnesium andzirconium, J. I. Met. 77 (1950) 163e174.

[38] J.H. Schaum, H.C. Burnett, Magnesium-rich side of the magnesium-zirconiumconstitution diagram, J. Res. Nat. Bur. Stand 49 (3) (1952) 155e162.

[39] A.A. Nayeb-Hashemi, J.B. Clark, The Mg-Zr (magnesium-zirconium) system,Bull. Alloy Phase Diagr. 6 (3) (1985) 246e250.

[40] I.M. Vesey, H.J. Bray, An investigation of the magnesium-zirconium system, J. I.Met. 92 (1964) 383e384.

[41] E.F. Emley, P. Duncumb, The maximum solid solubility of zirconium in mag-nesium, J. I. Met. 90 (1962) 360e361.

[42] M. H€am€al€ainen, K. Zeng, Thermodynamic evaluation of the Mg-Zr system,CALPHAD 22 (3) (1998) 375e380.

[43] R. Arroyave, D. Shin, Z.K. Liu, Modification of the thermodynamic model forthe Mg-Zr system, CALPHAD 29 (2005) 230e238.

[44] E. Gebbhardt, On the partial systems of zinc with titanium and zirconium,Z. Met. 33 (1941) 355e357.

[45] P. Chiotti, G.R. Kilp, Zinc-zirconium system, Trans. Tms. AIME 215 (1959)892e900.

[46] X. Chen, W. Jeitschko, Preparation, properties, and crystal structure of Zr5Zn39,a vacancy variant of the Ce5Mg41-type, and structure refinement of ZrZn22,J. Solid State Chem. 121 (1996) 95e104.

[47] P. Pietrokowsky, A cursory investigation of intermediate phases in the sys-tems Ti-Zr, Ti-Hg, Zr-Zn, Zr-Cd and Zr-Hg by X-Ray powder diffractionmethods, Trans. AIME 200 (1954) 219e226.

[48] J. Dutkiewicz, The Zn-Zr (Zinc-Zirconium) system, J. Phase Equilib. 13 (14)(1992) 430e433.

[49] P. Villars, L.D. Calvert, Pearson's Handbook of Crystallographic Data forIntermetallic Phases, 4, ASM International, Materials Park, OH, 1991, pp.53e65.

[50] W. Rossteutscher, I.C. Schubert, Titanium-zinc and titanium-cadmium alloys,Z. Met. 56 (10) (1965) 730e734.

[51] D.R. Petersen, H.W. Rinn, A new phase in the zinc-zirconium system, ActaCrystallogr. 14 (1961) 328e337.

[52] M.E. Williams, W.J. Boettinger, U.R. Kattner, Contribution to the Zr-rich part ofthe Zn-Zr phase diagram, J. Phase Equilib. Diff 25 (4) (2004) 355e367.

[53] R. Arroyave, Z.K. Liu, Thermodynamic modelling of the Zn-Zr system, CAL-PHAD 30 (2006) 1e13.

[54] N.E. Lashko, G.I. Morozova, E.S. Andreeva, V.V. Thonova, M.A. Gerasimova,Phase composition of cast magnesium-zinc-zirconium alloys, Izv, Akad. Nauk.SSSR Mat. 2 (1969) 159e163.

[55] V.M. Babkin, Solubility of Zirconium in liquid magnesium and the ML5 alloy,Metalloved. Termicheskaya Obrab. Met. 3 (1968) 61e64.

[56] K. Lohberg, G. Schmidt, Grain refuting effect of zirconium in magnesium al-loys, Giessereiforschung 27 (3) (1975) 75e82.

[57] Y.P. Ren, Y. Guo, D. Chen, S. Li, W.L. Pei, G.W. Qin, Isothermal section of Mg-Zn-Zr ternary system at 345�C, CALPHAD 35 (2011) 411e415.

[58] X. Zhang, Experimental Investigation of the Ternary Mg-Zn-Zr System, M.A.Scthesis, Concordia University, Montreal, 2015 (Print).

[59] J. Wang, Y.N. Zhang, P. Hudon, I.H. Jung, M. Medraj, P. Chartrand, Experimentalstudy of the phase equilibria in the Mg-Zn-Ag ternary system at 300 �C,J. Alloys Compd. 639 (2015) 593e601.

[60] A.A. Kodentsov, G.F. Bastin, F.J.J. van Loo, The diffusion couple technique inphase diagram determination, J. Alloys Compd. 320 (2001) 207e217.

[61] H. Putz and K. Brandenburg, Pearson's Crystal Data, Crystal Structure Databasefor Inorganic Compounds, CD-ROM Software Version 1.3.