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Effect of yttrium addition on microstructures, damping properties and mechanical properties of as-cast Mg−based ternary alloys
Journal of Alloys and Compounds 785 (2019) 1270e1278
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Effect of yttrium addition on microstructures, damping properties and mechanical properties of as-cast Mgbased ternary alloys Rui-long Niu a, b, Fang-jia Yan a, b, Dong-ping Duan a, b, *, Xue-min Yang a, b, ** a b
CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China University of Chinese Academy of Sciences, Beijing, 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 October 2018 Received in revised form 22 January 2019 Accepted 24 January 2019 Available online 25 January 2019
In order to reveal the functions of yttrium addition on damping and mechanical properties for Mgbased alloys, the damping and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been experimentally measured and theoretically explained through combining the observed microstructures with related theoretical models or mechanisms. The experimental results indicate that added [Y] in the ternary alloys has clear effect on grain refinement. Changing [Y] from 1.0 to 5.0 mass % can effectively decrease the average size of formed equiaxed aMg grains from 70.15 to 33.62 mm. The bulk-shaped yttrium-rich phase in aMg matrix is mainly composed of Mg24Y5 phase. Increasing [Y] from 1.0 to 5.0 mass % can significantly affect damping properties described by tan 4 under the condition of ε > εcr ¼ 2.0 102, while no visible effect of increasing [Y] on tan 4 at ε < εcr ¼ 2.0 102 can be obtained. Furthermore, the influence of changing strain ε from 1.0 104 to 1.0 101 on tan 4 complies with dislocation pinning theory or the GL model. Meanwhile, increasing [Y] in the ternary alloys shows the similar variation tendency for relationship between tan 4 and temperature T from ambient temperature Tam to 673 K (400 C). The effect of varying temperature T from Tam to 673 K (400 C) on tan 4 for the ternary alloys can be well explained by the grain boundary damping mechanism. In addition, increasing [Y] from 1.0 to 4.0 mass % can effectively promote both yield strength Rp0:2 and ultimate tensile strength Rm , however further increasing [Y] from 4.0 to 5.0 mass % cannot result in an obviously increasing tendency for Rp0:2 and Rm . The similar results of adding [Y] on elongation A can also be obtained with [Y] ¼ 3.0% as a criterion. Meanwhile, the measured results of adding [Y] on Rp0:2 and Rm for the ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms. Therefore, the optimal chemical composition for as-cast MgZrY ternary alloys with higher damping properties and greater tensile properties is recommended to be Mg0.6Zr4.0Y. © 2019 Elsevier B.V. All rights reserved.
Keywords: Effect of yttrium Damping properties Mechanical properties Damping mechanism As-cast MgZrY ternary alloys Microstructures
1. Introduction Mechanical vibration can cause many harmful effects such as causing brittle cracks, reducing precision of equipments and so on [1e3]. Decreasing mechanical vibration involved in many industry
* Corresponding author. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China. ** Corresponding author. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China. E-mail addresses: [email protected] (D.P. Duan), [email protected] (X.M. Yang). https://doi.org/10.1016/j.jallcom.2019.01.287 0925-8388/© 2019 Elsevier B.V. All rights reserved.
processes and production practices is a challengeable task over a long period of time. Beside the wide application in automobile, aerospace and other industries [4e6], the Mgbased alloys with light weight and high specific strength are considered to be one of prospective damping materials [6e12]. It has been verified [13e16] that among various Mgbased alloys, MgeZr binary alloys, especially Mge0.6 %Zr alloys, show better damping properties and can meet the principal requirements of damping alloys. Evidently, not only better damping properties but also ideal mechanical properties can pave the foundation for wide applications of Mge0.6 %Zr alloys. Based on the previous publication [3] of Mge0.6 %Zr alloys having wonderful damping properties, adding yttrium into Mge0.6 %Zr alloys has been investigated in this work because yttrium has potential to improve mechanical properties of Mge0.6 %Zr alloys
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due to the verified effect as a strong grain refiner [17,18] in Mgebased alloys. In the present work, the microstructures of refined as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been characterized. The damping properties of as-cast Mg0.6ZrxY ternary alloys described by tangent phase angle 4 [3], i.e., tan 4, have also been measured under conditions of changing temperature T from ambient temperature Tam to 673 K (400 C), varying vibration frequencies f from 0.5 to 20.0 Hz, and altering strain ε from 1.0 104 to 1.0 101. Furthermore, the mechanical properties at ambient temperature Tam for the as-cast Mg0.6ZrxY ternary alloys have been measured. The influence of adding [Y] from 1.0 to 5.0 mass % on damping properties and mechanical properties of as-cast Mg0.6ZrxY ternary alloys have also been probed and explained by the dislocation damping model [19,20] and grain boundary damping mechanism [21e23] based on the obtained microstructures, εtan 4 plots, and Ttan 4 plots, and related ε¡s curves. The ultimate aims of this work are to provide valuable information to design the optimal composition of MgZrY ternary alloys with wonderful damping performances and ideal mechanical properties. It should be specially mentioned that the similar investigation of studying the effects of element yttrium on the damping properties and mechanical properties of Mge0.6 %ZreY ternary alloys was also carried out and recently reported by Wan and co-workers [15]. Both the present authors and Wan et al. [15] studied the influences of adding element yttrium into Mge0.6 %Zr alloys on straindamping properties, i.e., εtan 4, and mechanical properties. However, this work investigated a larger Y content range as [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %, while Wan et al. [15] reported a smaller Y content range as [Y] ¼ 0.5, 1.0 and 1.5 mass %. Moreover, this work considered the influence of temperature T from ambient temperature Tam to 673 K (400 C) on damping properties tan 4 for the prepared as-cast MgZrY ternary alloys, while no temperature changing effect was reported by Wan et al. [15]. 2. Experimental The refining process of Mg0.6ZrxY ternary alloys including pretreatment of raw materials, applied techniques for characterizing microstructures, measuring both damping properties and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys are briefly introduced in the following sub-sections. 2.1. Preparation of as-cast Mg0.6ZrxY ternary alloys 2.1.1. Pretreatment of three raw materials Three kinds of raw materials of pure magnesium ingot with 99.9 mass % purity, Mg30.0Zr, and Mg30.0Y binary alloys were applied to the refining of the aimed chemical composition of Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %. All three raw materials were supplied by Changchun Seemay Magnesium Company Limited, P. R. China. Three applied raw materials were pretreated by preheating them individually in other heating furnaces under air atmosphere to eliminate the absorbed moisture and other volatile impurities on surface of three raw materials before charging into the refining furnace. The pretreatment of three raw materials was carried out in an electric resistance heating furnace by silicon carbide bars as heating elements with a hearth in 250 mm of inner diameter and in 400 mm of depth. The weighted pure magnesium ingots were pretreated at a temperature of 573 K (300 C) for 30.0 min to eliminate absorbed moisture and volatile impurities on surface, while the weighted Mg30.0Y alloys and Mg30.0Zr alloys were pretreated at a temperature of 623 K (350 C) for 30.0 min for the same aims.
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2.1.2. Refining process of as-cast Mg0.6ZrxY ternary alloys The refining process for preparing the aimed chemical composition of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % as listed in Table 1 was carried out in an electric resistance heating furnace with silicon carbide bars as the heating elements using 99.0 vol % CO21.0 vol % SF6 mixing gas as protective gas. The flow rate of protective gas was controlled by the mass flow controller (MFC) in a flow rate of 0.02 Nl/min in order to avoid oxidization of molten Mgbased melts. The refining furnace containing a steel crucible with inner diameter (ID) as 240 mm and outer diameter (OD) as 250 mm was switched on electricity and heated from ambient temperature Tam to a temperature of 573 K (300 C). Then, the weighted pre-heated pure magnesium ingots were charged into the steel crucible under protection of 99.0 vol % CO21.0 vol % SF6 mixing gas at a fixed flow rate during the whole refining process. After that, the charged pure magnesium ingots in the steel crucible was heated to a temperature of 983 K (680 C) at a heating rate n of 10 K/min and maintained for at least 20.0 min. Next, an agitator was inserted into the molten Mg melts and agitated by hands for at least 5.0 min to ensure fully melting of magnesium melts. The molten Mg melts were further heated to a temperature range of 993e1003 K (720e730 C) at a heating rate n of 5.0 K/min. The weighted pre-treated Mg30.0Y alloys were charged into the molten Mg melts and agitated by hands for at least 5.0 min simultaneously. The formed molten MgY binary melts were successively heated to a temperature range of 1033e1053 K (760e780 C) at the same heating rate n as 5.0 K/min, the weighted pre-treated Mg30.0Zr alloys were charged into MgY binary melts and agitated by hands for at least 5.0 min simultaneously. The formed MgZrY ternary melts were maintained at the elevated temperature around 1033e1053 K (760e780 C) for 30.0 min to ensure homogeneity by self-diffusion of alloying elements. After that, the molten ternary melts were cooled down to a temperature range of 968e978 K (695e705 C) and poured from the steel crucible into a pre-heated steel mould at 373 K (100 C) in atmosphere of 99 vol % CO21 vol % SF6 mixing gas as protective gas. The steel mould was designed with inner diameter as 95 mm and inner length as 800 mm. The ingot of as-cast MgZrY ternary alloys in steel mould was cooled to ambient temperature Tam in air atmosphere. 2.2. Characterization of microstructures, damping and mechanical properties of as-cast Mg0.6ZrxY ternary alloys 2.2.1. Determination of chemical composition of as-cast Mg0.6ZrxY ternary alloys To verify the fluctuation of chemical composition between aimed and prepared as-cast Mg0.6ZrxY ternary alloys, the actual chemical compositions of five specimens of prepared ternary alloys were determined by the inductivity coupled plasma atomic emission spectroscopy (ICPAES, Thermo Scientific iCAP 6300, USA).
Table 1 Comparison between designed and measured chemical compositions of five prepared specimens of as-cast MgZrY ternary alloys by ICPAES analysis. No. of specimen
Designed composition (mass %)
Measured content of three elements (mass %) [Y]
[Zr]
[Mg]
1 2 3 4 5
Mg0.6Zr1.0Y Mg0.6Zr2.0Y Mg0.6Zr3.0Y Mg0.6Zr4.0Y Mg0.6Zr5.0Y
0.88 1.87 2.86 3.95 4.88
0.51 0.62 0.55 0.50 0.51
margin margin margin margin margin
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The obtained actual chemical compositions of five refined ternary alloys are also summarized in Table 1. Obviously, the measured contents of [Y] and [Zr] in Table 1 fluctuate in a smaller range compared with the aimed ones. In order to describe simply, the aimed contents of [Y] and [Zr] are applied to the description of chemical composition of five specimens of ternary alloys in the following text.
under the condition of constant vibration frequency f ¼ 1.0 Hz, respectively; 2) The second category of testing experiments was designed to test the damping properties tan 4 by increasing temperature T from ambient temperature Tam to 673 K (400 C) at a heating rates n of 5.0 K/min under conditions of six vibration frequencies f ¼ 0.5, 1.0, 2.0, 5.0, 10.0 and 20.0 Hz, and constant strain ε ¼ 1.0 104, respectively.
2.2.2. Characterization of microstructures of as-cast Mg0.6ZrxY ternary alloys The morphological characteristics of prepared as-cast Mg0.6ZrxY ternary alloys were observed by the optical microscopy (OM, OlympusBX51M, Japan) and the thermal field emission scanning electron microscope (SEM, JSM7001F, Japan) equipped with energy-dispersive Xray spectroscopy under an accelerating voltage of 15 kV. The chemical composition of intermetallic phases in the ternary alloys was detected by Xray diffractometer (XRD, Bruker D8 FOCUS, USA) at 40 kV and 40 mA with Cu Ka radiation (l¼0.15406 nm) and further confirmed by the transmission electron microscopy in the bright field (BF) mode (BFTEM, JEM2100F, Japan) operating at 200 kV. The specimens for OM and SEM characterizations were cut into a cuboid shape in size of 10 mm 10 mm 2 mm from ingots of ascast Mg0.6ZrxY ternary alloys, and polished by silicon carbide abrasive paper in size of 800, 1600, 2000, 3000, and 4000 grits for successively polishing the surface of specimens, subsequently slightly etched by a mixture solution of 5 ml acetic acid, 5 g picric acid, 10 ml H2O, and 100 ml ethanol [24]. The thin foils for TEM observations were prepared by mechanical polishing, and then punched discs with a diameter of 3 mm and ion-milled using a precision ion polishing system (PIPS, Gatan 691, USA).
2.2.4. Measurement of mechanical properties of as-cast Mg0.6ZrxY ternary alloys The mechanical properties of five specimens of the ternary alloys were measured by the tensile tests for obtaining ε s curves using the universal testing machine (Instron 5869, USA) at ambient temperature Tam with an initial strain rate ε_ ¼ 1.0 103 s1. The tested tensile specimens are made in the standard size for traditional tensile tests as illustrated in Fig. 1. Average values from three measurements for each tested specimen were used to plot the ε s curves in this study in order to eliminate experimental errors.
2.2.3. Measurement of damping properties of as-cast Mg0.6ZrxY ternary alloys The damping properties expressed by tangent phase angle 4[3], i.e., tan 4, for as-cast Mg0.6ZrxY ternary alloys were measured by a dynamic mechanical analyzer (DMA) produced by TA Instruments company in a type of Q800 (Q800DMA, USA). The forced vibration in a test mode of single cantilever beam was applied in this study to the measurement of tan 4 from loss and storage modulus. Five measured specimens of as-cast Mg0.6ZrxY ternary alloys were cut into cuboid shape in a size of 30 mm 10 mm 2 mm using the electric spark line cutting technique, and then polished by silicon carbide abrasive papers in size of 800, 1600, and 2000 grits for successively polishing the surface of specimens before testing damping properties. Two categories of testing experiments were conducted to measure the damping properties of five as-cast Mg0.6ZrxY ternary alloys: 1) The first category of testing experiments was carried out to measure the damping properties tan 4 by changing strain ε from 1.0 104 to 1.0 101 at ambient temperature Tam
3. Experimental results and discussion Based on obtained information from microstructures for prepared as-cast Mg0.6ZrxY ternary alloys, the experimental results of damping properties at ambient temperature Tam and in a temperature range from ambient temperature Tam to 673 K (400 C) as well as mechanical properties from measured tensile stressstrain curves, i.e., ε¡s curves, are provided in the following subsections. 3.1. Microstructures of as-cast Mg0.6ZrxY ternary alloys 3.1.1. Micrographs of as-cast Mg0.6ZrxY ternary alloys by optical microscopy The influence of changing [Y] ¼ 1.0e5.0 mass % on micrographs of prepared as-cast Mg0.6ZrxY ternary alloys by optical microscopy is illustrated in Fig. 2, respectively. Five sub-figures of Fig. 2 for specimens with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % evidently indicate that the main microstructure is composed of the equiaxed aMg grains in uniform sizes. Meanwhile, the calculated average sizes of aMg grains by a Nano Measurer software based on micrographs in Fig. 2 for five specimens are shown in Fig. 3. The average size of equiaxed aMg grains shows a clearly decreasing tendency from 70.15 to 33.62 mm with an increase of [Y] from 1.0 to 5.0 mass %. The obtained refinement effect of aMg grain size by adding yttrium in Mgbased ternary alloys in this study is in a good agreement with that recently reported by Wan et al. [15] for the same Mgbased ternary alloys with different Y contents. 3.1.2. Primary determination of intermetallic phases compositions in as-cast Mg0.6ZrxY ternary alloys by XRD patterns The Xray diffraction (XRD) patterns of five specimens of the ternary alloys are shown in Fig. 4. No clear diffraction peaks caused
Fig. 1. Schematic illustration of round specimens from as-cast Mg0.6ZrxY ternary alloys for tensile test.
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Fig. 2. Micrographs by optical microscope for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0 (a), 2.0 (b), 3.0 (c), 4.0 (d) and 5.0 mass % (e), respectively.
Fig. 3. Grain diameter distribution for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0 (a), 2.0 (b), 3.0 (c), 4.0 (d) and 5.0 mass % (e), respectively.
by intermetallic phases was detected by the XRD pattern except those from aMg matrix. This finding indicates that the intermetallic phases in the ternary alloys cannot be examined by the XRD analysis in this study. The possible reasons can be ascribed to the measurement limitation of XRD [24e26]. 3.1.3. Further determination of intermetallic phases in as-cast Mg0.6ZrxY ternary alloys by SEM and TEM In order to reveal the morphological characteristics and chemical composition of intermetallic phases in the ternary alloys, five specimens were first characterized by means of SEM and EDS. To describe simply, the determined SEM micrographs by taking specimen of Mg0.6Zr4.0Y ternary alloys as an example, the
bulk-shaped yttrium-rich phases can be observed from the determined SEM micrographs as displayed in Fig. 5(a). However, no useful information can be obtained from the corresponding EDS spectra. In order to further identify chemical compositions of the bulkshaped yttrium-rich phases presented in Fig. 5(a), the BFTEM micrograph and corresponding selected area electron diffraction (SAED) pattern, and EDS spectrum with area scanning of the specimen of Mg0.6Zr4.0Y ternary alloys is shown in Fig. 5(b) Fig. 5(f), respectively. The SAED pattern in Fig. 5(c) indicates that the bulk-shaped yttrium-rich phase in Fig. 5(b) is mainly composed of Mg24Y5 phase. It can be clearly observed in Fig. 5(d)Fig. 5(f) that the bulk-shaped phases have more Y than aMg matrix.
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Fig. 4. X-ray diffraction patterns by XRD for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %, respectively.
3.2. Damping properties of as-cast Mg0.6ZrxY ternary alloys 3.2.1. Plots of εtan 4 at Ambient temperature Tam The effect of changing strain ε from 1.0 104 to 1.0 101 on damping properties tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0, and 5.0 mass % at ambient temperature Tam under the condition of vibration frequency f ¼ 1.0 Hz is shown in Fig. 6, respectively. The twosegment characteristics of εtan 4 curves can be observed in Fig. 6 for prepared ternary alloys, which is similar with that for MgZr binary alloys reported in previous publication [3] by the present authors. Obviously, damping properties tan 4 of five specimens only show a slightly increasing tendency with an increase of strain ε under the condition of strain ε less than a certain value as the critical strain εcr ¼ 2.0 102, i.e., ε < εcr ¼ 2.0 102, however damping properties tan 4 display a sharply increasing trend with an increase of strain ε under the condition of strain ε>εcr ¼2.0 102. Moreover, increasing [Y] from 1.0 to 5.0 mass %
Fig. 6. Effect of strain ε on internal friction tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam under the condition of frequency f ¼ 1.0 Hz, respectively.
can lead to a negative influence on damping properties tan 4 under the condition of strain ε>εcr ¼2.0 102 at ambient temperature Tam . According to the compiled Mg-rich part of the equilibrium MgZrY phase diagram at 773 K (500 C) [27] and results in Fig. 5(c), the added [Y] in the ternary alloys can promote the formation of solid solution as Mg24Y5 phase in aMg matrix. The dissolved [Y] in aMg matrix can effectively cause lattice distortion, furthermore generate larger distortion energy. Hence, the formed distortion by added [Y] in the ternary alloys can promote the generation of stress field. In addition, the dislocation can also induce more or less formation of elastic stress field. Under those circumstances, the interaction between stress field from added [Y] and elastic stress field around the dislocation will impede the motion of dislocation [28]. This implies that increasing addition of [Y] can lead to more distortion, furthermore impede the motion of dislocation, and result in a deteriorating trend of damping properties of prepared as-cast Mg0.6ZrxY ternary alloys. Thus, damping properties of as-cast Mg0.6ZrxY ternary alloys with
Fig. 5. SEM micrograph (a) and BFTEM micrograph for specimen of as-cast Mg0.6Zr4.0Y ternary alloys (b), corresponding SAED pattern (c), and EDS mapping of Mg, Y, and Zr elements (def), respectively.
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[Y] ¼ 1.0e5.0 mass % are less than those reported by the present authors [3] for Mg0.6Zr binary alloys without Y addition due to impeding the motion of dislocation by Y addition. Additionally, the added alloying elements [Y] or/and [Zr] can be easily assembled in the vicinity of dislocation to form the so-called Cottrell atmosphere [29]. The formed Cottrell atmosphere by alloying elements [Y] or/and [Zr] in aMg matrix can also hinder the dislocation motion [30]. Therefore, increasing addition of [Y] in the ternary alloys can lead to generating much more lattice distortion and enhancing the difficulty of dislocation motion, i.e., reducing the damping properties of as-cast Mg0.6ZrxY ternary alloys. It is widely accepted that the damping characteristics of metalbased alloys can be well explained by the dislocation pinning model [19,20] proposed by Granat and Lücke, i.e., GL model. Under the condition of stress s is greater than the breakaway stress, damping capacity expressed by dH caused by strong pinning points for metalbased alloys is related with strain ε, rather than vibration frequency f . According to GL model [19,20], the defined damping capacity dH can be calculated by Refs. [3,5]:
dH ¼
C1 C exp 2 ε ε
(1)
where C1 and C2 are dimensionless coefficients, (). It can be evidently derived from Eq. (1) that greater coefficient C1 and smaller coefficient C2 can lead to larger value of dH . Because Eq. (1) can be rewritten by taking the logarithm for two sides as Refs. [3,5]:
lnðdH εÞ ¼ lnC1
C2 ε
(2)
the linear relationship of lnðdH εÞ against 1=ε can be evidently used as a criterion to verify whether or not the metal-based damping materials complies with the GL model [19,20,31]. The defined damping capacity dH can be calculated from measured tangent phase angle tan 4 for the ternary alloys under the condition of tan 4<0.06 by Ref. [3]:
dH ¼ p tan 4 ðtan 4 < 0:06Þ
(3)
According to plotted εtan 4 curves at ambient temperature Tam in Fig. 6, the correlated relationship between lnðdH εÞ and 1=ε for the ternary alloys is illustrated in Fig. 7. The better linear relationships of lnðdH εÞ against 1=ε at ambient temperature Tam for five specimens of the ternary alloys with changing [Y] from 1.0 to 5.0 mass %
Fig. 7. Relationship between lnðdH εÞ ¼ lnðεp tan 4Þ and 1=ε for five specimens of ascast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam based on data in Fig. 6 through GeL model, respectively.
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in Fig. 7 indicate that the damping properties of five specimens obey the GL model. The specimen of [Y] ¼ 1.0 mass %, i.e., No. 1 specimen, displays the greatest intercept lnC1 . This means that the prepared Mg0.6Zr1.0Y specimen has better damping properties than other four specimens at ambient temperature Tam . 3.2.2. Plots of Ttan 4 at constant strain ε The influence of increasing temperature T from ambient temperature Tam to 673 K (400 C) on damping properties tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0e5.0 mass % at a heating rate n as 5 K/min under conditions of vibration frequency f ¼ 0.5, 1.0, 2.0, 5.0, 10.0 and 20.0 Hz and strain ε ¼ 1.0 104 is illustrated in Fig. 8, respectively. The obtained two-segment characteristics of Ttan 4 plots in Fig. 8 for the ternary alloys is similar with the previously reported results for ascast Mg-Zr binary alloys [3] by the present authors. This means that damping properties tan 4 of five specimens with different addition of [Y] display a slightly increasing tendency under the condition of temperature T less than a certain value as the critical temperature Tcr ¼ 552 K (279 C), i.e., T < Tcr ¼ 552 K (279 C), however the damping properties tan 4 show a significantly increasing trend at T > Tcr ¼ 552 K (279 C) and reach the maximal values of tan 4 at T ¼ 650e670 K (377e397 C). At temperatures T < Tcr ¼ 552 K (279 C), increasing vibration frequency f can result into an obviously increasing tendency of damping properties tan 4 except for results at f ¼ 0.5 Hz. Moreover, plots of Ttan 4 at vibration frequencies f ¼ 1.0 Hz are similar with those at f ¼ 2.0 Hz in Fig. 8. This result is attributed to unknown reason(s), which should be investigated in the future. However, at temperatures T > Tcr ¼ 552 K (279 C), increasing vibration frequency f from 0.5 to 20.0 Hz can lead to an obviously decreasing tendency of damping properties tan 4 with an increase of temperature T from 552 to 673 K (279e400 C). The decaying effect of damping properties tan 4 at vibration frequencies f < 5.0 Hz is clearly larger than that at vibration frequencies f >5.0 Hz. Further increasing vibration frequency f from 5.0 to 20.0 Hz cannot cause a visible effect on damping properties tan 4, i.e., increasing vibration frequency f from 5.0 to 20.0 Hz cannot result in an obvious change of damping properties tan 4 at temperatures T>Tcr ¼552 K (279 C). It can be deduced that damping properties tan 4 for prepared as-cast Mg0.6ZrxY ternary alloys cannot be easily improved by increasing vibration frequency f under the condition of f >5.0 Hz at temperatures T>Tcr ¼552 K (279 C). The influence of changing [Y] from 1.0 to 5.0 mass % on Ttan 4 plots for five specimens of as-cast Mg0.6ZrxY ternary alloys in a temperature range of Tam < T < 673 K (400 C) at a heating rate n as 5 K/min under conditions of strain ε ¼ 1.0 104 and vibration frequency f ¼ 1.0 Hz is shown in Fig. 9, respectively. Increasing [Y] from 1.0 to 5.0 mass % cannot dramatically change the two-segment characteristics of Ttan 4 plots in Fig. 9. Obviously, specimen with [Y] ¼ 4.0 mass %, i.e., No. 4 specimen, displays the greatest value of maximal damping properties tan 4 in five specimens, while specimen with [Y] ¼ 1.0 mass %, i.e., No. 1 specimen, exhibits the smallest value of maximal damping properties tan 4. This finding implies that increasing [Y] can easily improve the maximal damping properties tan 4 at temperatures T>Tcr ¼552 K (279 C). It can be easily understood that parts of aMg grain boundary might be soften at temperatures T>Tcr ¼552 K (279 C) and become main reason for decreasing mechanical vibration based on grain boundary damping mechanism [21e23]. As described in Section 3.1.1, increasing [Y] in the ternary alloys can result in smaller size and more boundaries of aMg grain. Thus, further increasing [Y] in the ternary alloys can lead to generating more softening microzones/points to enhance damping properties at temperatures
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Fig. 8. Effect of vibration frequency f from 0.5 to 20.0 Hz on Ttan 4 plot for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % (aef) at heating rate as 5 K/min under the condition of strain ε ¼ 1.0 104, respectively.
Fig. 9. Influence of [Y] from 1.0 to 5.0 mass % on Ttan 4 plot for five specimens of ascast Mg0.6ZrxY ternary alloys at heating rate as 5 K/min under conditions of strain ε ¼ 1.0 104 and vibration frequency f ¼ 1.0 Hz, respectively.
T>Tcr ¼552 K (279 C). However, too much aMg grain boundaries by more adding [Y]>4.0 mass % can impede the sliding of aMg grain boundaries and then deteriorate the damping properties. This is the main reason that the maximal value of damping properties tan 4 of specimen with [Y] ¼ 4.0 mass % is greater than those of other four specimens. In summary, the specimen of Mg0.6Zr1.0Y ternary alloys shows better damping properties at ambient temperature Tam , while the specimen of Mg0.6Zr4.0Y ternary alloys exhibits ideal damping properties at T>Tcr ¼552 K (279 C).
3.3. Mechanical properties of as-cast Mg0.6ZrxY ternary alloys The measured tensile stress-strain curves, i.e., ε¡s curves, at ambient temperature Tam for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0e5.0 mass % are shown in Fig. 10(a). By taking specimen of Mg0.6Zr5.0Y ternary alloys
as an example, three parameters for representing the tensile properties as yield strength Rp0:2 , ultimate tensile strength Rm , and elongation A can be obtained from ε¡s curves in Fig. 10(a). The influence of changing [Y] from 1.0 to 5.0 mass % on measured yield strength Rp0:2 , ultimate tensile strength Rm , and elongation A for five specimens of the ternary alloys is illustrated in Fig. 10(b). It can be evidently observed in Fig. 10(b) that increasing [Y] from 1.0 to 4.0 mass % can effectively promote two mechanical properties of both yield strength Rp0:2 and ultimate tensile strength Rm . However, no obvious increase of both yield strength Rp0:2 and ultimate tensile strength Rm can be obtained under the condition of further increasing [Y] from 4.0 to 5.0 mass %. The obtained variation tendency of yield strength Rp0:2 and ultimate tensile strength Rm against [Y] for the ternary alloys is in good agreement with result by Wan et al. [15] for the same ternary alloys. The variation relationship of both yield strength Rp0:2 and ultimate tensile strength Rm against [Y] in Fig. 10(b) can be explained from the obtained microstructures of as-cast Mg0.6ZrxY ternary alloys. Adding [Y] in Mgebased alloys can stimulate the formation of smaller aMg grains, and result in obvious refinement effect of aMg grains. The smaller aMg grains correspond to much more grain boundaries per volume and lead to more obstacles for dislocation motion. According to the famous HallePetch equation [32e35] between mechanical properties and grain size, i.e., mechanical properties is inversely proportional to grain size, greater [Y] in the ternary alloys can effectively increase the mechanical properties [36,37] of both yield strength Rp0:2 and ultimate tensile strength Rm . In addition, the added [Y] in the ternary alloys is mainly dissolved into aMg matrix, which is confirmed by the XRD patterns in Fig. 4. The interaction between added [Y] as alloying element and dislocation can cause local lattice distortion, which can improve both of yield strength Rp0:2 and ultimate tensile strength Rm by solid solution strengthening [33,38]. To mechanical property of elongation A, increasing [Y] from 1.0 to 3.0 mass % in the ternary alloys can result in an increasing tendency, however further increasing [Y] from 3.0 to 5.0 mass % can lead to a great decreasing trend. The specimen with [Y] ¼ 4.0 mass % indicates the ideal results of three mechanical properties as yield
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Fig. 10. Tensile stress-strain curves (a) and the influence of [Y] on measured ultimate tensile strength Rm , yield strength Rp0:2 , and elongation A (b) of five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam , respectively.
strength Rp0:2 , ultimate tensile strength Rm , and elongation A as shown in Fig. 10(b). It is interesting to reveal that the specimen of Mg0.6Zr1.0Y ternary alloys, i.e., No. 1 specimen, shows better damping properties at ambient temperature Tam and worse tensile properties. However, the specimen of Mg0.6Zr4.0Y ternary alloys, i.e., No. 4 specimen, has both ideal damping properties and tensile properties at T>Tcr ¼552 K (279 C). Therefore, prepared as-cast Mg0.6Zr4.0Y ternary alloys, i.e., No. 4 specimen, are recommended to apply under the condition of requiring high damping properties and greater tensile properties.
[Y] ¼ 3.0% as a criterion. The measured results of yield strength Rp0:2 and tensile strength Rm for the as-cast Mg0.6ZrxY ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms. 5) The optimal chemical composition for as-cast MgZrY ternary alloys with higher damping properties and greater tensile properties is recommended to be Mg0.6Zr4.0Y.
Notes The authors declare no competing financial interest.
4. Conclusions Acknowledgement The functions of yttrium addition on damping and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been experimentally measured and explained through combining the observed microstructures with related theoretical models or mechanisms. The main summary remarks can be obtained as follows: 1) The bulk-shaped yttrium-rich phase in aMg matrix is mainly composed of Mg24Y5 phase. Changing [Y] from 1.0 to 5.0 mass % can effectively decrease the average size of formed equiaxed aMg grains from 70.15 to 33.62 mm. Thus, the added [Y] in Mg0.6ZrxY ternary alloys has clear effect on grain refinement. 2) Increasing [Y] from 1.0 to 5.0 mass % can greatly affect damping properties described by tan 4 under the condition of ε>εcr ¼2.0 102, while no visible effect of increasing [Y] on damping properties tan 4 under the condition of ε<εcr ¼2.0 102 can be obtained. The influence of changing strain ε from 1.0 104 to 1.0 101 on damping properties tan 4 complies with dislocation pinning theory or the GL model. 3) Increasing [Y] in Mg0.6ZrxY ternary alloys shows the similar variation tendency for relationship between damping properties tan 4 and temperature T from ambient temperature Tam to 673 K (400 C). The effect of varying temperature T from ambient temperature Tam to 673 K (400 C) on damping properties for prepared as-cast Mg0.6ZrxY ternary alloys can be well explained by the grain boundary damping mechanism. 4) Increasing [Y] from 1.0 to 4.0 mass % can obviously promote both yield strength Rp0:2 and ultimate tensile strength Rm , however further increasing [Y] from 4.0 to 5.0 mass % cannot result in an evidently increasing tendency for Rp0:2 and Rm . The similar results of adding [Y] on elongation A can also be obtained with
This work is supported by the Beijing Natural Science Foundation under Grant No. 2182069 and the National Natural Science Foundation of China under Grant No. 51174186. References [1] S.A. Stansfeld, C. Clarka, R.M. Cameron, T. Alfred, J. Head, M.M. Haines, I. van Kamp, E. van Kempen, I. Lopez-Barrioc, Aircraft and road traffic noise exposure and children's mental health, J. Environ. Psychol. 29 (2009) 203e207. [2] Y.S. Shih, G.Y. Wu, Effect of vibration on fatigue crack growth of an edge crack for A rectangular plate, Int. J. Fatig. 24 (2002) 557e566. [3] R.L. Niu, F.J. Yan, Y.S. Wang, D.P. Duan, X.M. Yang, Effect of Zr content on damping property of MgZr binary alloys, Mater. Sci. Eng. A 718 (2018) 418e426. [4] L.H. Wen, Z.S. Ji, M.L. Hu, H.Y. Ning, Microstructure and mechanical properties of Mge3.0Nde0.4Zne0.4Zr magnesium alloy, J. Magnes. Alloys 2 (2014) 85e91. [5] J.H. Jun, Damping behaviors of as-cast and solution-treated AZ91eCa magnesium alloys, J. Alloys Compd. 610 (2014) 169e172. [6] T. Li, Y. He, H.L. Zhang, X.T. Wang, Microstructure, mechanical property and in vitro biocorrosion behavior of single-phase biodegradable Mge1.5Zne0.6Zr alloy, J. Magnes. Alloys 2 (2014) 181e189. [7] Q. Yang, K. Guan, B.S. Li, F.Z. Meng, S.H. Lv, Z.J. Yu, X.H. Zhang, J.Q. Zhang, J. Meng, Coexistence of 14H and 18R-type long-period stacking ordered (LPSO) phases following a novel orientation relationship in A cast MgAlREZn alloy, J. Alloys Compd. 766 (2018) 902e907. [8] Q. Chen, Z.X. Zhao, D.Y. Shu, Z.D. Zhao, Microstructure and mechanical properties of AZ91D magnesium alloy prepared by compound extrusion, Mater. Sci. Eng. A 528 (2011) 3930e3934. [9] X.S. Xia, Q. Chen, S.H. Huang, J. Lin, C.K. Hu, Z.D. Zhao, Hot deformation behavior of extruded MgeZneYeZr alloy, J. Alloys Compd. 644 (2015) 308e316. [10] L. Gao, R.S. Chen, E.H. Han, Effects of rare-earth elements Gd and Y on the solid solution strengthening of Mg alloys, J. Alloys Compd. 481 (2009) 379e384. [11] H.T. Zhou, Z.D. Zhang, C.M. Liu, Q.W. Wang, Effect of Nd and Y on the microstructure and mechanical properties of ZK60 alloy, Mater. Sci. Eng. A 445e446 (2007) 1e6. [12] Q. Li, Q.D. Wang, Y.X. Wang, X.Q. Zeng, W.J. Ding, Effect of Nd and element Y addition on microstructure and mechanical properties of as-cast MgeZneZr alloy, J. Alloys. Compd. 427 (2007) 115e123.
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Effect of yttrium addition on microstructures, damping properties and mechanical properties of as-cast Mgbased ternary alloys Rui-long Niu a, b, Fang-jia Yan a, b, Dong-ping Duan a, b, *, Xue-min Yang a, b, ** a b
CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China University of Chinese Academy of Sciences, Beijing, 100049, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 29 October 2018 Received in revised form 22 January 2019 Accepted 24 January 2019 Available online 25 January 2019
In order to reveal the functions of yttrium addition on damping and mechanical properties for Mgbased alloys, the damping and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been experimentally measured and theoretically explained through combining the observed microstructures with related theoretical models or mechanisms. The experimental results indicate that added [Y] in the ternary alloys has clear effect on grain refinement. Changing [Y] from 1.0 to 5.0 mass % can effectively decrease the average size of formed equiaxed aMg grains from 70.15 to 33.62 mm. The bulk-shaped yttrium-rich phase in aMg matrix is mainly composed of Mg24Y5 phase. Increasing [Y] from 1.0 to 5.0 mass % can significantly affect damping properties described by tan 4 under the condition of ε > εcr ¼ 2.0 102, while no visible effect of increasing [Y] on tan 4 at ε < εcr ¼ 2.0 102 can be obtained. Furthermore, the influence of changing strain ε from 1.0 104 to 1.0 101 on tan 4 complies with dislocation pinning theory or the GL model. Meanwhile, increasing [Y] in the ternary alloys shows the similar variation tendency for relationship between tan 4 and temperature T from ambient temperature Tam to 673 K (400 C). The effect of varying temperature T from Tam to 673 K (400 C) on tan 4 for the ternary alloys can be well explained by the grain boundary damping mechanism. In addition, increasing [Y] from 1.0 to 4.0 mass % can effectively promote both yield strength Rp0:2 and ultimate tensile strength Rm , however further increasing [Y] from 4.0 to 5.0 mass % cannot result in an obviously increasing tendency for Rp0:2 and Rm . The similar results of adding [Y] on elongation A can also be obtained with [Y] ¼ 3.0% as a criterion. Meanwhile, the measured results of adding [Y] on Rp0:2 and Rm for the ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms. Therefore, the optimal chemical composition for as-cast MgZrY ternary alloys with higher damping properties and greater tensile properties is recommended to be Mg0.6Zr4.0Y. © 2019 Elsevier B.V. All rights reserved.
Keywords: Effect of yttrium Damping properties Mechanical properties Damping mechanism As-cast MgZrY ternary alloys Microstructures
1. Introduction Mechanical vibration can cause many harmful effects such as causing brittle cracks, reducing precision of equipments and so on [1e3]. Decreasing mechanical vibration involved in many industry
* Corresponding author. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China. ** Corresponding author. CAS Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, PR China. E-mail addresses: [email protected] (D.P. Duan), [email protected] (X.M. Yang). https://doi.org/10.1016/j.jallcom.2019.01.287 0925-8388/© 2019 Elsevier B.V. All rights reserved.
processes and production practices is a challengeable task over a long period of time. Beside the wide application in automobile, aerospace and other industries [4e6], the Mgbased alloys with light weight and high specific strength are considered to be one of prospective damping materials [6e12]. It has been verified [13e16] that among various Mgbased alloys, MgeZr binary alloys, especially Mge0.6 %Zr alloys, show better damping properties and can meet the principal requirements of damping alloys. Evidently, not only better damping properties but also ideal mechanical properties can pave the foundation for wide applications of Mge0.6 %Zr alloys. Based on the previous publication [3] of Mge0.6 %Zr alloys having wonderful damping properties, adding yttrium into Mge0.6 %Zr alloys has been investigated in this work because yttrium has potential to improve mechanical properties of Mge0.6 %Zr alloys
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due to the verified effect as a strong grain refiner [17,18] in Mgebased alloys. In the present work, the microstructures of refined as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been characterized. The damping properties of as-cast Mg0.6ZrxY ternary alloys described by tangent phase angle 4 [3], i.e., tan 4, have also been measured under conditions of changing temperature T from ambient temperature Tam to 673 K (400 C), varying vibration frequencies f from 0.5 to 20.0 Hz, and altering strain ε from 1.0 104 to 1.0 101. Furthermore, the mechanical properties at ambient temperature Tam for the as-cast Mg0.6ZrxY ternary alloys have been measured. The influence of adding [Y] from 1.0 to 5.0 mass % on damping properties and mechanical properties of as-cast Mg0.6ZrxY ternary alloys have also been probed and explained by the dislocation damping model [19,20] and grain boundary damping mechanism [21e23] based on the obtained microstructures, εtan 4 plots, and Ttan 4 plots, and related ε¡s curves. The ultimate aims of this work are to provide valuable information to design the optimal composition of MgZrY ternary alloys with wonderful damping performances and ideal mechanical properties. It should be specially mentioned that the similar investigation of studying the effects of element yttrium on the damping properties and mechanical properties of Mge0.6 %ZreY ternary alloys was also carried out and recently reported by Wan and co-workers [15]. Both the present authors and Wan et al. [15] studied the influences of adding element yttrium into Mge0.6 %Zr alloys on straindamping properties, i.e., εtan 4, and mechanical properties. However, this work investigated a larger Y content range as [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %, while Wan et al. [15] reported a smaller Y content range as [Y] ¼ 0.5, 1.0 and 1.5 mass %. Moreover, this work considered the influence of temperature T from ambient temperature Tam to 673 K (400 C) on damping properties tan 4 for the prepared as-cast MgZrY ternary alloys, while no temperature changing effect was reported by Wan et al. [15]. 2. Experimental The refining process of Mg0.6ZrxY ternary alloys including pretreatment of raw materials, applied techniques for characterizing microstructures, measuring both damping properties and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys are briefly introduced in the following sub-sections. 2.1. Preparation of as-cast Mg0.6ZrxY ternary alloys 2.1.1. Pretreatment of three raw materials Three kinds of raw materials of pure magnesium ingot with 99.9 mass % purity, Mg30.0Zr, and Mg30.0Y binary alloys were applied to the refining of the aimed chemical composition of Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %. All three raw materials were supplied by Changchun Seemay Magnesium Company Limited, P. R. China. Three applied raw materials were pretreated by preheating them individually in other heating furnaces under air atmosphere to eliminate the absorbed moisture and other volatile impurities on surface of three raw materials before charging into the refining furnace. The pretreatment of three raw materials was carried out in an electric resistance heating furnace by silicon carbide bars as heating elements with a hearth in 250 mm of inner diameter and in 400 mm of depth. The weighted pure magnesium ingots were pretreated at a temperature of 573 K (300 C) for 30.0 min to eliminate absorbed moisture and volatile impurities on surface, while the weighted Mg30.0Y alloys and Mg30.0Zr alloys were pretreated at a temperature of 623 K (350 C) for 30.0 min for the same aims.
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2.1.2. Refining process of as-cast Mg0.6ZrxY ternary alloys The refining process for preparing the aimed chemical composition of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % as listed in Table 1 was carried out in an electric resistance heating furnace with silicon carbide bars as the heating elements using 99.0 vol % CO21.0 vol % SF6 mixing gas as protective gas. The flow rate of protective gas was controlled by the mass flow controller (MFC) in a flow rate of 0.02 Nl/min in order to avoid oxidization of molten Mgbased melts. The refining furnace containing a steel crucible with inner diameter (ID) as 240 mm and outer diameter (OD) as 250 mm was switched on electricity and heated from ambient temperature Tam to a temperature of 573 K (300 C). Then, the weighted pre-heated pure magnesium ingots were charged into the steel crucible under protection of 99.0 vol % CO21.0 vol % SF6 mixing gas at a fixed flow rate during the whole refining process. After that, the charged pure magnesium ingots in the steel crucible was heated to a temperature of 983 K (680 C) at a heating rate n of 10 K/min and maintained for at least 20.0 min. Next, an agitator was inserted into the molten Mg melts and agitated by hands for at least 5.0 min to ensure fully melting of magnesium melts. The molten Mg melts were further heated to a temperature range of 993e1003 K (720e730 C) at a heating rate n of 5.0 K/min. The weighted pre-treated Mg30.0Y alloys were charged into the molten Mg melts and agitated by hands for at least 5.0 min simultaneously. The formed molten MgY binary melts were successively heated to a temperature range of 1033e1053 K (760e780 C) at the same heating rate n as 5.0 K/min, the weighted pre-treated Mg30.0Zr alloys were charged into MgY binary melts and agitated by hands for at least 5.0 min simultaneously. The formed MgZrY ternary melts were maintained at the elevated temperature around 1033e1053 K (760e780 C) for 30.0 min to ensure homogeneity by self-diffusion of alloying elements. After that, the molten ternary melts were cooled down to a temperature range of 968e978 K (695e705 C) and poured from the steel crucible into a pre-heated steel mould at 373 K (100 C) in atmosphere of 99 vol % CO21 vol % SF6 mixing gas as protective gas. The steel mould was designed with inner diameter as 95 mm and inner length as 800 mm. The ingot of as-cast MgZrY ternary alloys in steel mould was cooled to ambient temperature Tam in air atmosphere. 2.2. Characterization of microstructures, damping and mechanical properties of as-cast Mg0.6ZrxY ternary alloys 2.2.1. Determination of chemical composition of as-cast Mg0.6ZrxY ternary alloys To verify the fluctuation of chemical composition between aimed and prepared as-cast Mg0.6ZrxY ternary alloys, the actual chemical compositions of five specimens of prepared ternary alloys were determined by the inductivity coupled plasma atomic emission spectroscopy (ICPAES, Thermo Scientific iCAP 6300, USA).
Table 1 Comparison between designed and measured chemical compositions of five prepared specimens of as-cast MgZrY ternary alloys by ICPAES analysis. No. of specimen
Designed composition (mass %)
Measured content of three elements (mass %) [Y]
[Zr]
[Mg]
1 2 3 4 5
Mg0.6Zr1.0Y Mg0.6Zr2.0Y Mg0.6Zr3.0Y Mg0.6Zr4.0Y Mg0.6Zr5.0Y
0.88 1.87 2.86 3.95 4.88
0.51 0.62 0.55 0.50 0.51
margin margin margin margin margin
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The obtained actual chemical compositions of five refined ternary alloys are also summarized in Table 1. Obviously, the measured contents of [Y] and [Zr] in Table 1 fluctuate in a smaller range compared with the aimed ones. In order to describe simply, the aimed contents of [Y] and [Zr] are applied to the description of chemical composition of five specimens of ternary alloys in the following text.
under the condition of constant vibration frequency f ¼ 1.0 Hz, respectively; 2) The second category of testing experiments was designed to test the damping properties tan 4 by increasing temperature T from ambient temperature Tam to 673 K (400 C) at a heating rates n of 5.0 K/min under conditions of six vibration frequencies f ¼ 0.5, 1.0, 2.0, 5.0, 10.0 and 20.0 Hz, and constant strain ε ¼ 1.0 104, respectively.
2.2.2. Characterization of microstructures of as-cast Mg0.6ZrxY ternary alloys The morphological characteristics of prepared as-cast Mg0.6ZrxY ternary alloys were observed by the optical microscopy (OM, OlympusBX51M, Japan) and the thermal field emission scanning electron microscope (SEM, JSM7001F, Japan) equipped with energy-dispersive Xray spectroscopy under an accelerating voltage of 15 kV. The chemical composition of intermetallic phases in the ternary alloys was detected by Xray diffractometer (XRD, Bruker D8 FOCUS, USA) at 40 kV and 40 mA with Cu Ka radiation (l¼0.15406 nm) and further confirmed by the transmission electron microscopy in the bright field (BF) mode (BFTEM, JEM2100F, Japan) operating at 200 kV. The specimens for OM and SEM characterizations were cut into a cuboid shape in size of 10 mm 10 mm 2 mm from ingots of ascast Mg0.6ZrxY ternary alloys, and polished by silicon carbide abrasive paper in size of 800, 1600, 2000, 3000, and 4000 grits for successively polishing the surface of specimens, subsequently slightly etched by a mixture solution of 5 ml acetic acid, 5 g picric acid, 10 ml H2O, and 100 ml ethanol [24]. The thin foils for TEM observations were prepared by mechanical polishing, and then punched discs with a diameter of 3 mm and ion-milled using a precision ion polishing system (PIPS, Gatan 691, USA).
2.2.4. Measurement of mechanical properties of as-cast Mg0.6ZrxY ternary alloys The mechanical properties of five specimens of the ternary alloys were measured by the tensile tests for obtaining ε s curves using the universal testing machine (Instron 5869, USA) at ambient temperature Tam with an initial strain rate ε_ ¼ 1.0 103 s1. The tested tensile specimens are made in the standard size for traditional tensile tests as illustrated in Fig. 1. Average values from three measurements for each tested specimen were used to plot the ε s curves in this study in order to eliminate experimental errors.
2.2.3. Measurement of damping properties of as-cast Mg0.6ZrxY ternary alloys The damping properties expressed by tangent phase angle 4[3], i.e., tan 4, for as-cast Mg0.6ZrxY ternary alloys were measured by a dynamic mechanical analyzer (DMA) produced by TA Instruments company in a type of Q800 (Q800DMA, USA). The forced vibration in a test mode of single cantilever beam was applied in this study to the measurement of tan 4 from loss and storage modulus. Five measured specimens of as-cast Mg0.6ZrxY ternary alloys were cut into cuboid shape in a size of 30 mm 10 mm 2 mm using the electric spark line cutting technique, and then polished by silicon carbide abrasive papers in size of 800, 1600, and 2000 grits for successively polishing the surface of specimens before testing damping properties. Two categories of testing experiments were conducted to measure the damping properties of five as-cast Mg0.6ZrxY ternary alloys: 1) The first category of testing experiments was carried out to measure the damping properties tan 4 by changing strain ε from 1.0 104 to 1.0 101 at ambient temperature Tam
3. Experimental results and discussion Based on obtained information from microstructures for prepared as-cast Mg0.6ZrxY ternary alloys, the experimental results of damping properties at ambient temperature Tam and in a temperature range from ambient temperature Tam to 673 K (400 C) as well as mechanical properties from measured tensile stressstrain curves, i.e., ε¡s curves, are provided in the following subsections. 3.1. Microstructures of as-cast Mg0.6ZrxY ternary alloys 3.1.1. Micrographs of as-cast Mg0.6ZrxY ternary alloys by optical microscopy The influence of changing [Y] ¼ 1.0e5.0 mass % on micrographs of prepared as-cast Mg0.6ZrxY ternary alloys by optical microscopy is illustrated in Fig. 2, respectively. Five sub-figures of Fig. 2 for specimens with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % evidently indicate that the main microstructure is composed of the equiaxed aMg grains in uniform sizes. Meanwhile, the calculated average sizes of aMg grains by a Nano Measurer software based on micrographs in Fig. 2 for five specimens are shown in Fig. 3. The average size of equiaxed aMg grains shows a clearly decreasing tendency from 70.15 to 33.62 mm with an increase of [Y] from 1.0 to 5.0 mass %. The obtained refinement effect of aMg grain size by adding yttrium in Mgbased ternary alloys in this study is in a good agreement with that recently reported by Wan et al. [15] for the same Mgbased ternary alloys with different Y contents. 3.1.2. Primary determination of intermetallic phases compositions in as-cast Mg0.6ZrxY ternary alloys by XRD patterns The Xray diffraction (XRD) patterns of five specimens of the ternary alloys are shown in Fig. 4. No clear diffraction peaks caused
Fig. 1. Schematic illustration of round specimens from as-cast Mg0.6ZrxY ternary alloys for tensile test.
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Fig. 2. Micrographs by optical microscope for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0 (a), 2.0 (b), 3.0 (c), 4.0 (d) and 5.0 mass % (e), respectively.
Fig. 3. Grain diameter distribution for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0 (a), 2.0 (b), 3.0 (c), 4.0 (d) and 5.0 mass % (e), respectively.
by intermetallic phases was detected by the XRD pattern except those from aMg matrix. This finding indicates that the intermetallic phases in the ternary alloys cannot be examined by the XRD analysis in this study. The possible reasons can be ascribed to the measurement limitation of XRD [24e26]. 3.1.3. Further determination of intermetallic phases in as-cast Mg0.6ZrxY ternary alloys by SEM and TEM In order to reveal the morphological characteristics and chemical composition of intermetallic phases in the ternary alloys, five specimens were first characterized by means of SEM and EDS. To describe simply, the determined SEM micrographs by taking specimen of Mg0.6Zr4.0Y ternary alloys as an example, the
bulk-shaped yttrium-rich phases can be observed from the determined SEM micrographs as displayed in Fig. 5(a). However, no useful information can be obtained from the corresponding EDS spectra. In order to further identify chemical compositions of the bulkshaped yttrium-rich phases presented in Fig. 5(a), the BFTEM micrograph and corresponding selected area electron diffraction (SAED) pattern, and EDS spectrum with area scanning of the specimen of Mg0.6Zr4.0Y ternary alloys is shown in Fig. 5(b) Fig. 5(f), respectively. The SAED pattern in Fig. 5(c) indicates that the bulk-shaped yttrium-rich phase in Fig. 5(b) is mainly composed of Mg24Y5 phase. It can be clearly observed in Fig. 5(d)Fig. 5(f) that the bulk-shaped phases have more Y than aMg matrix.
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Fig. 4. X-ray diffraction patterns by XRD for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass %, respectively.
3.2. Damping properties of as-cast Mg0.6ZrxY ternary alloys 3.2.1. Plots of εtan 4 at Ambient temperature Tam The effect of changing strain ε from 1.0 104 to 1.0 101 on damping properties tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0, and 5.0 mass % at ambient temperature Tam under the condition of vibration frequency f ¼ 1.0 Hz is shown in Fig. 6, respectively. The twosegment characteristics of εtan 4 curves can be observed in Fig. 6 for prepared ternary alloys, which is similar with that for MgZr binary alloys reported in previous publication [3] by the present authors. Obviously, damping properties tan 4 of five specimens only show a slightly increasing tendency with an increase of strain ε under the condition of strain ε less than a certain value as the critical strain εcr ¼ 2.0 102, i.e., ε < εcr ¼ 2.0 102, however damping properties tan 4 display a sharply increasing trend with an increase of strain ε under the condition of strain ε>εcr ¼2.0 102. Moreover, increasing [Y] from 1.0 to 5.0 mass %
Fig. 6. Effect of strain ε on internal friction tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam under the condition of frequency f ¼ 1.0 Hz, respectively.
can lead to a negative influence on damping properties tan 4 under the condition of strain ε>εcr ¼2.0 102 at ambient temperature Tam . According to the compiled Mg-rich part of the equilibrium MgZrY phase diagram at 773 K (500 C) [27] and results in Fig. 5(c), the added [Y] in the ternary alloys can promote the formation of solid solution as Mg24Y5 phase in aMg matrix. The dissolved [Y] in aMg matrix can effectively cause lattice distortion, furthermore generate larger distortion energy. Hence, the formed distortion by added [Y] in the ternary alloys can promote the generation of stress field. In addition, the dislocation can also induce more or less formation of elastic stress field. Under those circumstances, the interaction between stress field from added [Y] and elastic stress field around the dislocation will impede the motion of dislocation [28]. This implies that increasing addition of [Y] can lead to more distortion, furthermore impede the motion of dislocation, and result in a deteriorating trend of damping properties of prepared as-cast Mg0.6ZrxY ternary alloys. Thus, damping properties of as-cast Mg0.6ZrxY ternary alloys with
Fig. 5. SEM micrograph (a) and BFTEM micrograph for specimen of as-cast Mg0.6Zr4.0Y ternary alloys (b), corresponding SAED pattern (c), and EDS mapping of Mg, Y, and Zr elements (def), respectively.
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[Y] ¼ 1.0e5.0 mass % are less than those reported by the present authors [3] for Mg0.6Zr binary alloys without Y addition due to impeding the motion of dislocation by Y addition. Additionally, the added alloying elements [Y] or/and [Zr] can be easily assembled in the vicinity of dislocation to form the so-called Cottrell atmosphere [29]. The formed Cottrell atmosphere by alloying elements [Y] or/and [Zr] in aMg matrix can also hinder the dislocation motion [30]. Therefore, increasing addition of [Y] in the ternary alloys can lead to generating much more lattice distortion and enhancing the difficulty of dislocation motion, i.e., reducing the damping properties of as-cast Mg0.6ZrxY ternary alloys. It is widely accepted that the damping characteristics of metalbased alloys can be well explained by the dislocation pinning model [19,20] proposed by Granat and Lücke, i.e., GL model. Under the condition of stress s is greater than the breakaway stress, damping capacity expressed by dH caused by strong pinning points for metalbased alloys is related with strain ε, rather than vibration frequency f . According to GL model [19,20], the defined damping capacity dH can be calculated by Refs. [3,5]:
dH ¼
C1 C exp 2 ε ε
(1)
where C1 and C2 are dimensionless coefficients, (). It can be evidently derived from Eq. (1) that greater coefficient C1 and smaller coefficient C2 can lead to larger value of dH . Because Eq. (1) can be rewritten by taking the logarithm for two sides as Refs. [3,5]:
lnðdH εÞ ¼ lnC1
C2 ε
(2)
the linear relationship of lnðdH εÞ against 1=ε can be evidently used as a criterion to verify whether or not the metal-based damping materials complies with the GL model [19,20,31]. The defined damping capacity dH can be calculated from measured tangent phase angle tan 4 for the ternary alloys under the condition of tan 4<0.06 by Ref. [3]:
dH ¼ p tan 4 ðtan 4 < 0:06Þ
(3)
According to plotted εtan 4 curves at ambient temperature Tam in Fig. 6, the correlated relationship between lnðdH εÞ and 1=ε for the ternary alloys is illustrated in Fig. 7. The better linear relationships of lnðdH εÞ against 1=ε at ambient temperature Tam for five specimens of the ternary alloys with changing [Y] from 1.0 to 5.0 mass %
Fig. 7. Relationship between lnðdH εÞ ¼ lnðεp tan 4Þ and 1=ε for five specimens of ascast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam based on data in Fig. 6 through GeL model, respectively.
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in Fig. 7 indicate that the damping properties of five specimens obey the GL model. The specimen of [Y] ¼ 1.0 mass %, i.e., No. 1 specimen, displays the greatest intercept lnC1 . This means that the prepared Mg0.6Zr1.0Y specimen has better damping properties than other four specimens at ambient temperature Tam . 3.2.2. Plots of Ttan 4 at constant strain ε The influence of increasing temperature T from ambient temperature Tam to 673 K (400 C) on damping properties tan 4 for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0e5.0 mass % at a heating rate n as 5 K/min under conditions of vibration frequency f ¼ 0.5, 1.0, 2.0, 5.0, 10.0 and 20.0 Hz and strain ε ¼ 1.0 104 is illustrated in Fig. 8, respectively. The obtained two-segment characteristics of Ttan 4 plots in Fig. 8 for the ternary alloys is similar with the previously reported results for ascast Mg-Zr binary alloys [3] by the present authors. This means that damping properties tan 4 of five specimens with different addition of [Y] display a slightly increasing tendency under the condition of temperature T less than a certain value as the critical temperature Tcr ¼ 552 K (279 C), i.e., T < Tcr ¼ 552 K (279 C), however the damping properties tan 4 show a significantly increasing trend at T > Tcr ¼ 552 K (279 C) and reach the maximal values of tan 4 at T ¼ 650e670 K (377e397 C). At temperatures T < Tcr ¼ 552 K (279 C), increasing vibration frequency f can result into an obviously increasing tendency of damping properties tan 4 except for results at f ¼ 0.5 Hz. Moreover, plots of Ttan 4 at vibration frequencies f ¼ 1.0 Hz are similar with those at f ¼ 2.0 Hz in Fig. 8. This result is attributed to unknown reason(s), which should be investigated in the future. However, at temperatures T > Tcr ¼ 552 K (279 C), increasing vibration frequency f from 0.5 to 20.0 Hz can lead to an obviously decreasing tendency of damping properties tan 4 with an increase of temperature T from 552 to 673 K (279e400 C). The decaying effect of damping properties tan 4 at vibration frequencies f < 5.0 Hz is clearly larger than that at vibration frequencies f >5.0 Hz. Further increasing vibration frequency f from 5.0 to 20.0 Hz cannot cause a visible effect on damping properties tan 4, i.e., increasing vibration frequency f from 5.0 to 20.0 Hz cannot result in an obvious change of damping properties tan 4 at temperatures T>Tcr ¼552 K (279 C). It can be deduced that damping properties tan 4 for prepared as-cast Mg0.6ZrxY ternary alloys cannot be easily improved by increasing vibration frequency f under the condition of f >5.0 Hz at temperatures T>Tcr ¼552 K (279 C). The influence of changing [Y] from 1.0 to 5.0 mass % on Ttan 4 plots for five specimens of as-cast Mg0.6ZrxY ternary alloys in a temperature range of Tam < T < 673 K (400 C) at a heating rate n as 5 K/min under conditions of strain ε ¼ 1.0 104 and vibration frequency f ¼ 1.0 Hz is shown in Fig. 9, respectively. Increasing [Y] from 1.0 to 5.0 mass % cannot dramatically change the two-segment characteristics of Ttan 4 plots in Fig. 9. Obviously, specimen with [Y] ¼ 4.0 mass %, i.e., No. 4 specimen, displays the greatest value of maximal damping properties tan 4 in five specimens, while specimen with [Y] ¼ 1.0 mass %, i.e., No. 1 specimen, exhibits the smallest value of maximal damping properties tan 4. This finding implies that increasing [Y] can easily improve the maximal damping properties tan 4 at temperatures T>Tcr ¼552 K (279 C). It can be easily understood that parts of aMg grain boundary might be soften at temperatures T>Tcr ¼552 K (279 C) and become main reason for decreasing mechanical vibration based on grain boundary damping mechanism [21e23]. As described in Section 3.1.1, increasing [Y] in the ternary alloys can result in smaller size and more boundaries of aMg grain. Thus, further increasing [Y] in the ternary alloys can lead to generating more softening microzones/points to enhance damping properties at temperatures
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Fig. 8. Effect of vibration frequency f from 0.5 to 20.0 Hz on Ttan 4 plot for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % (aef) at heating rate as 5 K/min under the condition of strain ε ¼ 1.0 104, respectively.
Fig. 9. Influence of [Y] from 1.0 to 5.0 mass % on Ttan 4 plot for five specimens of ascast Mg0.6ZrxY ternary alloys at heating rate as 5 K/min under conditions of strain ε ¼ 1.0 104 and vibration frequency f ¼ 1.0 Hz, respectively.
T>Tcr ¼552 K (279 C). However, too much aMg grain boundaries by more adding [Y]>4.0 mass % can impede the sliding of aMg grain boundaries and then deteriorate the damping properties. This is the main reason that the maximal value of damping properties tan 4 of specimen with [Y] ¼ 4.0 mass % is greater than those of other four specimens. In summary, the specimen of Mg0.6Zr1.0Y ternary alloys shows better damping properties at ambient temperature Tam , while the specimen of Mg0.6Zr4.0Y ternary alloys exhibits ideal damping properties at T>Tcr ¼552 K (279 C).
3.3. Mechanical properties of as-cast Mg0.6ZrxY ternary alloys The measured tensile stress-strain curves, i.e., ε¡s curves, at ambient temperature Tam for five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0e5.0 mass % are shown in Fig. 10(a). By taking specimen of Mg0.6Zr5.0Y ternary alloys
as an example, three parameters for representing the tensile properties as yield strength Rp0:2 , ultimate tensile strength Rm , and elongation A can be obtained from ε¡s curves in Fig. 10(a). The influence of changing [Y] from 1.0 to 5.0 mass % on measured yield strength Rp0:2 , ultimate tensile strength Rm , and elongation A for five specimens of the ternary alloys is illustrated in Fig. 10(b). It can be evidently observed in Fig. 10(b) that increasing [Y] from 1.0 to 4.0 mass % can effectively promote two mechanical properties of both yield strength Rp0:2 and ultimate tensile strength Rm . However, no obvious increase of both yield strength Rp0:2 and ultimate tensile strength Rm can be obtained under the condition of further increasing [Y] from 4.0 to 5.0 mass %. The obtained variation tendency of yield strength Rp0:2 and ultimate tensile strength Rm against [Y] for the ternary alloys is in good agreement with result by Wan et al. [15] for the same ternary alloys. The variation relationship of both yield strength Rp0:2 and ultimate tensile strength Rm against [Y] in Fig. 10(b) can be explained from the obtained microstructures of as-cast Mg0.6ZrxY ternary alloys. Adding [Y] in Mgebased alloys can stimulate the formation of smaller aMg grains, and result in obvious refinement effect of aMg grains. The smaller aMg grains correspond to much more grain boundaries per volume and lead to more obstacles for dislocation motion. According to the famous HallePetch equation [32e35] between mechanical properties and grain size, i.e., mechanical properties is inversely proportional to grain size, greater [Y] in the ternary alloys can effectively increase the mechanical properties [36,37] of both yield strength Rp0:2 and ultimate tensile strength Rm . In addition, the added [Y] in the ternary alloys is mainly dissolved into aMg matrix, which is confirmed by the XRD patterns in Fig. 4. The interaction between added [Y] as alloying element and dislocation can cause local lattice distortion, which can improve both of yield strength Rp0:2 and ultimate tensile strength Rm by solid solution strengthening [33,38]. To mechanical property of elongation A, increasing [Y] from 1.0 to 3.0 mass % in the ternary alloys can result in an increasing tendency, however further increasing [Y] from 3.0 to 5.0 mass % can lead to a great decreasing trend. The specimen with [Y] ¼ 4.0 mass % indicates the ideal results of three mechanical properties as yield
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Fig. 10. Tensile stress-strain curves (a) and the influence of [Y] on measured ultimate tensile strength Rm , yield strength Rp0:2 , and elongation A (b) of five specimens of as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % at ambient temperature Tam , respectively.
strength Rp0:2 , ultimate tensile strength Rm , and elongation A as shown in Fig. 10(b). It is interesting to reveal that the specimen of Mg0.6Zr1.0Y ternary alloys, i.e., No. 1 specimen, shows better damping properties at ambient temperature Tam and worse tensile properties. However, the specimen of Mg0.6Zr4.0Y ternary alloys, i.e., No. 4 specimen, has both ideal damping properties and tensile properties at T>Tcr ¼552 K (279 C). Therefore, prepared as-cast Mg0.6Zr4.0Y ternary alloys, i.e., No. 4 specimen, are recommended to apply under the condition of requiring high damping properties and greater tensile properties.
[Y] ¼ 3.0% as a criterion. The measured results of yield strength Rp0:2 and tensile strength Rm for the as-cast Mg0.6ZrxY ternary alloys can be well explained by the grain boundary strengthening and solid solution strengthening mechanisms. 5) The optimal chemical composition for as-cast MgZrY ternary alloys with higher damping properties and greater tensile properties is recommended to be Mg0.6Zr4.0Y.
Notes The authors declare no competing financial interest.
4. Conclusions Acknowledgement The functions of yttrium addition on damping and mechanical properties of prepared as-cast Mg0.6ZrxY ternary alloys with [Y] ¼ 1.0, 2.0, 3.0, 4.0 and 5.0 mass % have been experimentally measured and explained through combining the observed microstructures with related theoretical models or mechanisms. The main summary remarks can be obtained as follows: 1) The bulk-shaped yttrium-rich phase in aMg matrix is mainly composed of Mg24Y5 phase. Changing [Y] from 1.0 to 5.0 mass % can effectively decrease the average size of formed equiaxed aMg grains from 70.15 to 33.62 mm. Thus, the added [Y] in Mg0.6ZrxY ternary alloys has clear effect on grain refinement. 2) Increasing [Y] from 1.0 to 5.0 mass % can greatly affect damping properties described by tan 4 under the condition of ε>εcr ¼2.0 102, while no visible effect of increasing [Y] on damping properties tan 4 under the condition of ε<εcr ¼2.0 102 can be obtained. The influence of changing strain ε from 1.0 104 to 1.0 101 on damping properties tan 4 complies with dislocation pinning theory or the GL model. 3) Increasing [Y] in Mg0.6ZrxY ternary alloys shows the similar variation tendency for relationship between damping properties tan 4 and temperature T from ambient temperature Tam to 673 K (400 C). The effect of varying temperature T from ambient temperature Tam to 673 K (400 C) on damping properties for prepared as-cast Mg0.6ZrxY ternary alloys can be well explained by the grain boundary damping mechanism. 4) Increasing [Y] from 1.0 to 4.0 mass % can obviously promote both yield strength Rp0:2 and ultimate tensile strength Rm , however further increasing [Y] from 4.0 to 5.0 mass % cannot result in an evidently increasing tendency for Rp0:2 and Rm . The similar results of adding [Y] on elongation A can also be obtained with
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