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Effects of Y content and temperature on the damping capacity of extruded Mg-Y sheets
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Journal of Magnesium and Alloys 7 (2019) 522–528 www.elsevier.com/locate/jma
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Effects of Y content and temperature on the damping capacity of extruded Mg-Y sheets Y.T. Tang a, C. Zhang a, L.B. Ren a, W. Yang a, D.D. Yin a,∗, G.H. Huang a, H. Zhou b, Y.B. Zhang a,∗ a Key
Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, PR China b Nano and Heterogeneous Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China Received 10 January 2019; received in revised form 7 May 2019; accepted 10 May 2019 Available online 5 June 2019
Abstract The damping behavior of extruded Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets were investigated in detail concerning the effects of Y addition and temperature, and the relationship between damping capacity and yield strength was discussed. At room temperature (RT), with Y content increasing from 0.5% to 3.0%, the damping capacity (Q−1 ) significantly decreased from 0.037 to 0.015. For all the studied sheets, the relationship between strain amplitude and Q−1 fitted well with the Granato and Lücke (G-L) dislocation damping model. With temperature increased, the G-L plots deviated from linearity indicating that the dislocation damping was not the only dominate mechanism, and the grain boundary sliding (GBS) could contribute to damping capacity. Consequently, the Q−1 increased remarkably above the critical temperature, and the critical temperature increased significantly from 50 °C to 290 °C with increasing Y contents from 0 to 3.0 wt.%. This result implied that the segregation of Y solutes at grain boundary could depress the GBS, which was consistent with the recent finding of segregation tendency for rare-earth solutes. The extruded Mg-1Y sheet exhibited slightly higher yield strength (Rp0.2 ) and Q−1 comparing with high-damping Mg-0.6Zr at RT. At an elevated temperature of 325 °C, the Mg-1Y sheet had similar Q−1 but over 3 times larger Rp0.2 than that of the pure Mg. The present study indicated that the extruded Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys, especially for the elevated-temperature application. © 2019 Published by Elsevier B.V. on behalf of Chongqing University. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University Keywords: Extruded sheets; Mg-Y alloys; Damping capacity; Granato and Lücke model; Elevated temperature.
1. Introduction With the increasing demands of high-damping and lightweight performance for transportation, magnesium (Mg) and its alloys have attracted more and more attention [1–3]. Thus, it has become a continuous subject to develop highperformance Mg alloys with an excellent combination property of damping capacity, strength and ductility [4,5]. Alloying is one of the most important ways to achieve such goal. The effects of some alloying elements (Si, Mn, Cu, Ni, Ca, ∗
Corresponding authors. E-mail addresses: [email protected] (D.D. Yin), yingbozhang@ 163.com (Y.B. Zhang).
Zr, Sc, Er, and Ce) on the damping capacity of Mg alloys have been studied. And some high-performance damping Mg alloys such as Mg-Zr alloys and Mg-Cu-Mn alloys have been successfully developed [6–14]. It has been reported that Yttrium (Y) can markedly improve the strength and ductility of Mg alloys simultaneously. As we all know, Y is a rare earth element [15–17]. At the same time, Y can improve the corrosion resistance as well [18]. Besides, the high-temperature tensile, compressive strength and creep resistance can be improved significantly by adding Y to Mg [19–23]. Wang et al. [24] found that the addition of trace Y (0.05–0.15 wt.%) in Mg-Zr alloys can significantly improve the mechanical properties at the same time improve the damping capacity. Another group
https://doi.org/10.1016/j.jma.2019.05.003 2213-9567/© 2019 Published by Elsevier B.V. on behalf of Chongqing University. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University
Y.T. Tang, C. Zhang and L.B. Ren et al. / Journal of Magnesium and Alloys 7 (2019) 522–528 Table 1 Actual chemical compositions of the studied alloys (in weight%). Alloys
Actual chemical compositions
Mg-0.5Y Mg-1Y Mg-3Y
Mg-0.28Y Mg-0.86Y Mg-2.70Y
[25] studied the effects of Y and Zn on the damping capacity of the Mg-Cu-Mn alloy, and they found the damping capacity of Mg-3Cu-1Mn-1Y-2 Zn was close to that of pure Mg at strain amplitudes over 5 × 10−4 . Our previous work [5] have investigated the effects of heat treatment and pre-deformation on the damping capacity of the cast Mg-xY (x = 1, 3, 7 wt.%) binary alloys at room temperature (RT). The results indicated that compared with several Mg-based damping alloys, the cast Mg-Y alloys has the great potential of development of high-performance damping alloys with adequate strength. Compared with cast Mg alloys, wrought (such as rolling, extruding and forging) Mg alloys generally exhibit better mechanical properties [26,27]. However, comprehensive effects of Y on damping property and mechanical strength of extruded Mg-Y based alloys, especially at sub-zero temperatures and elevated temperatures, are yet to be completely clear. The purpose of the present work is to investigate the effects of Y addition and temperature on the damping behavior of extruded Mg-xY (x = 0.5, 1, 3 wt.%) sheets. The temperature dependence of damping mechanism was discussed and revealed. The comprehensive properties in terms of Q − 1 and Rp0.2 of the extruded Mg-Y sheets were evaluated by comparing with extruded pure Mg and several Mg-based damping alloys at temperatures between RT and 325 °C. 2. Materials and experimental procedures Pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%, hereafter, all alloy compositions are in weight percent unless otherwise state) alloys were prepared by melting high purity Mg (99.99%) and Mg-30Y master alloy in an electric resistance furnace at 720 °C. And it is then cast into a steel mold with diameter of 95 mm. The protection atmosphere is a mixture of CO2 and SF6 , which is 100:1 (It is the volume ratio). The inductively coupled plasma (ICP) is the equipment that we used to analyze the actual chemical composition of the studied alloys. And table 1 lists the actual chemical compositions. The as-cast ingots were homogenized at 560 °C for 8 h followed by air cooling, and then processed into an extrusion processing of the billet with a diameter of 90 mm. The billets were preheated at 300 °C for 2 h before extrusion and then extruded into sheets with a cross section of 80 × 5 mm2 . The setting temperature of the extrusion die and the extrusion container was 300 °C and 300–330 °C, respectively. And the extrusion ratio was 16. The ram speed was approximately 0.5–1.0 mm/s. We test the yield strength, Rp0.2 , of the alloys by MTS (CMT5105) universal testing machine. And the initial strain rate was 10−3 /s. The Zeiss A1 optical microscope was applied
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to observe the microstructure. The microscopically observed samples were mechanically ground on 2000 coarse SiC sandpaper, polished with diamond mortar to a mirror finish, then etched in mixed acid. Used to measure the damping of the rectangular beam bending specimen size 40 mm × 5 mm × 1.5 mm were cut from the sheets along the extrusion direction (ED) using an electric discharge machine (EDM). The TA-Q800 dynamic mechanical analyzer (DMA), which is the equipment that used to measure the damping capacity of the alloys with a single cantilever vibration mode. The damping capacity (Q−1 ) in this study is defined as the loss tangent (tanψ), where ψ is the lag angle between applied strain and the responding stress. Strain-dependent damping tests were made at maximum strain amplitudes ranging between 10−6 to 10−3 at RT. The temperature range for the temperature-dependent damping tests was from −50 °C to 390 °C, with 5 °C/min. And the strain amplitude was selected as 3 × 10−4 . It is important to note that the vibration frequency (f) was 1 Hz for all the damping tests. [41]. 3. Results and discussions 3.1. Microstructure The representative optical micrographs of the extruded pure Mg and the Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets in extrusion direction (ED)-transverse direction (TD) plane are shown in Fig. 1. It can be seen that the as-extruded microstructure consisted of uniform and fine equiaxed grains, and a small amount of secondary phases particles distributing homogeneously both in the grains and at grain boundaries. The average grain sizes of pure Mg, Mg-0.5Y, Mg1Y, and Mg-3Y sheets were approximately 120 ± 27 μm, 8.7 ± 0.9 μm, 5.5 ± 0.6 μm, 7.4 ± 0.7 μm, respectively, which means the addition of Y can remarkably decrease grain size of the extruded Mg alloys. With the addition of Y, the volume fraction of the second phase particles increased slightly, reaching 0.5%. 3.2. Damping capacity at room temperature (RT) The Strain amplitude dependence of damping capacity at RT for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets is shown in Fig. 2. All the measured Q−1 curves can be divided into two parts: the strain-amplitude independent damping (Q0−1 ) and the strain-amplitude dependent damping (Qa−1 ). The critical strain amplitude (εc ) refers to the strain amplitude when break-away pinned dislocation line [28]. In the curve, the εc is the transition point which represents the beginning of the second part or the end of the first part. Small Y addition, as low as 0.5%, to pure Mg decreased Q−1 , and the decrement was larger at higher strain amplitudes. However, further increasing of Y content up to 3% did not change the Q−1 of the extruded Mg-Y sheets in the strain-amplitude independent region. While in the strainamplitude dependent part, with the Y content increasing to
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Fig. 1. Optical micrographs of the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets: (a) Pure Mg, (b) Mg-0.5Y, (c) Mg-1Y, and (d) Mg-3Y. The average grain size of each samples is labelled in the pictures.
Q0−1 and the strain-dependent damping Qa−1 . Q−1 = Q0−1 + Qa−1
(1)
The end of the dislocation lines are strongly pinned by some strong point defects, such as dislocation net, precipitates or intermetallic compounds, etc. And the middle part of the dislocation lines is nailed by relatively weak pinning points, such as solute atoms or vacancy. At low strain amplitude, the strain-independent damping is affected by the vibration of the dislocation segment nailed by the weak pinning points. While the strain-dependent damping is affected by the vibration of the dislocation nailed by the strong pinning points.
Fig. 2. Strain amplitude dependence of damping capacity at room temperature for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets with f = 1 Hz.
−1
0.5%, 1.0% and 3.0%, the Q obviously decreased from 0.080 of pure Mg to 0.040, 0.020 and 0.016 at the strain amplitude (ε) of 1 × 10−3 , respectively. The εc of extruded Mg-Y sheets (∼4 × 10−5 ) is much higher than that of pure Mg (∼4 × 10−6 ). We know that dislocation damping is the dominant damping mechanism at RT, and the classical theory to illustrate the dislocation damping is the theory of Granato and Lücke (G-L) model. [28]. According to the G-L model, the total damping capacity (Q−1 ) is the sum of the strain-independent damping
Q0−1 ∼ ρLC4
(2)
Qa−1 = (C1 /ε ) exp(−C2 /ε )
(3)
C1 = (ρFB LN3 )/(6bE LC2 )
(4)
C2 = FB /(bE LC )
(5)
Where LC and LN are the average distance between weak pinning points and the average distance between strong pinning points, respectively; ρ is the dislocation density and b is the Burgers vector; FB is the binding force between dislocations and the weak pinning points; E is the elastic modulus. Eq. (6) is a modification of Eq. (3). ln (Qa−1 · ε) = −C2 /ε + ln C1
(6)
Fig. 3 illustrates the G-L plots for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets at RT with f = 1 Hz.
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Fig. 3. G-L plots for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets at room temperature with f = 1 Hz. Table 2 Values of C1 and C2 parameters obtained from the G-L plots. Composition
C1 (×10−5)
C2 (×10−4)
Ref.
Extruded pure Mg Extruded Mg-0.5Y Extruded Mg-1Y Extruded Mg-3Y As-cast Mg-1Y As-cast Mg-3Y
2.7 2.2 1.4 1.0 209.5 41.5
2.2 2.7 2.6 2.7 16.3 16.0
This This This This [5] [5]
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Fig. 4. Temperature-dependent damping capacity at the strain amplitude of 3 × 10−4 with f = 1 Hz.
the more second phase particles observed in the Mg-Y sheets than that of pure Mg. work work work work
A linear relationship between ln (Qa−1 × ε) and 1/ε demonstrated that the damping behavior at RT of pure Mg and Mg-Y sheets were closely related to the dislocation damping mechanism. From Eq. (3), it can be seen that in G-L plots the C2 was related to the value of the slope, and ln (C1 ) was related to the intercept. The calculated C1 and C2 values are listed in Table 2. Considering the C2 value is controlled by LC and Q0−1 is dependent on C2 , the larger C2 values of Mg-Y than that of pure Mg indicated that the addition of Y decreased the LC and Q0−1 which was consistent with that Y solutes acted as the weak pinning points. In the case of C1 , the value of C1 decreased with increasing Y content. This result indicated that with the increase of Y content, the strong pinning points of dislocations increases. It was correspond to what observed in the microstructure of Fig. 1. Due to more second phase particles by Y addition could act as strong pinning points and reduce LN . Similar changing trend of C1 and C2 with Y increasing was found in our previous study on the as-cast Mg-Y alloys [5]. However, the as-cast Mg-Y alloys exhibited larger C1 than that of the extruded Mg-Y sheets, which indicated that after the extrusion the LN was significantly reduced. As demonstrated before, dislocation damping was the predominant damping mechanism in the present Mg-Y sheets at RT. It was reported that the more second phase particles spread among the dislocation, the higher stress to break away from the constraint of second phase particles was required, and thus increased εc [28]. In this work, the εc increased with the addition of Y (Fig. 2), which was consistent with
3.3. Temperature-dependent damping capacity Fig. 4 illustrates the temperature-dependent damping capacity at the strain amplitude of 3 × 10−4 . The overall trends were that the Y addition to Mg decreased the Q−1 at temperatures between −50 °C to 300 °C, and the discrepancy was pronounced above 100 °C. However, it is interesting to note that increasing Y content did not worsen Q−1 of the extruded Mg-Y sheets at temperatures higher than 100 °C, and Q−1 of Mg-1Y and Mg-3Y were even larger than that of the pure Mg at 325 °C and above. The detailed analysis and discussion for this interesting phenomenon will be provided later. For the extruded pure Mg, Q−1 firstly increased gradually from −50 °C to 50 °C, and then increased remarkably at temperatures range of 50–180 °C, finally Q−1 continuously decreased with increasing temperature until test ended at 390 °C. As shown in Fig. 4, a damping peak P1 , appeared at around 180 °C for the extruded pure Mg, and its value was 0.11. Kê [29] reported similar damping peak at about 225 °C with a value of 0.06 in extruded and annealed polycrystalline pure Mg rod. However, the peak disappeared in single crystal pure Mg, and Kê [29] found that the grain boundaries behaved in a viscous manner at elevated temperatures and the damping peak corresponded to viscous slide of the grain boundary. Experimental evidence proved that the damping peak value was determined by the resistance to the grain boundary sliding and the sliding distance [29]. The average grain size of the extruded pure Mg sheet in the present study is ∼120 μm which is much smaller than that of pure Mg (∼200 μm) studied by Kê [29]. Therefore, the large amount of grain boundaries provides for a higher damping peak value than that of the pure Mg investigated by Kê. For the extruded Mg-Y sheets, between −50 °C to 50 °C Q−1 firstly increased gradually. The damping peak P2 which
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Fig. 5. G-L plots of the extruded Mg-0.5Y sheet at the temperatures of 100 °C and 300 °C with f = 1 Hz.
we found appeared at ∼50 °C, and it became less obvious as the Y content increases further. Similar peak of P2 has been reported in some other Mg alloys such as Mg-Ni alloys, Mg-Si alloys and Mg-Cu-Mn alloys [12,24,30]. G. Fantozzi et al. studied the internal friction of high purity Mg, they reported the peak is due to the interaction of the dislocations with interstitials defects. Thus, the P2 peak was believed to be caused by the interaction between dislocations and interstitials defects such as solute atoms [31]. The Q−1 was almost constant after P2 until it reached the critical temperature, and then it increased remarkably as the temperature rising. The critical temperatures for Mg-0.5Y, Mg-1Y and Mg-5Y were about 230 °C, 250 °C, and 290 °C, respectively. It should be noted that the Q−1 of Mg-1Y and Mg-3Y became even larger than that of pure Mg at temperatures of ∼340 °C and above. For example, the Q−1 of extruded Mg-3Y sheet (0.137) was 1.6 times of the extruded pure Mg (0.085) at the temperature of 385 °C. The Q−1 of the Mg-Y sheets increased significantly at high temperatures. To better understand the elevated-temperature damping mechanism, we investigated the G-L plots of Mg0.5Y at temperatures of 100 °C and 300 °C (Fig. 5). As Fig. 5 shows, the data for 100 °C slightly deviated from a linear fitting, while the data for 300 °C could hardly fit by a straight line. Thus, it is reasonable to believe that dislocation damping was not the only dominate damping mechanism at elevated temperatures for the present Mg-Y sheets. Among the internal friction mechanism, energy dissipation by dislocation movements is evident at RT. We know that at elevated temperatures grain boundary can behave in a viscous manner [29]. So it is realized that an existence of grain boundaries will affect the elastic and damping properties. Accordingly, it is reasonable to believe the grain boundaries sliding (GBS) could contribute to damping capacity of Mg-Y sheets at elevated temperatures. From Fig. 4, it can be seen that beyond the critical temperature which is 230 °C, 250 °C and 290 °C for Mg-0.5Y, Mg-1Y and Mg-3Y, respectively, the Q−1 increases signifi-
Fig. 6. The mechanical and damping properties of the present studied sheets in comparison with several typical commercial and experimental alloys [35–39] at room temperature. The strain amplitude was 1 × 10−3 and the forced frequency was 1 Hz.
cantly with the increases of the temperature. With the addition of Y, the critical temperature goes up. The impurity atoms segregate easily at grain boundary, in other words, the more concentrated alloys should have more segregation tendency in the grain boundaries [29]. Basu et al. [32,41] found that Gd exhibits strong grain boundary segregation trends. Both Y and Gd belong to the same subgroup of the rare-earth metals with a similar atomic structure which may result in a similar segregation tendency [33,34]. Christopher D. Barrett et al. [40] studied the effect of Y on grain boundaries, they found Y exhibits grain boundary segregation trends and Y segregation curtailed conventional recrystallization. The Y segregation at the grain boundary inhibits the grain boundary diffusion of Mg-Y sheets. The required activation energy of grain boundary is larger, and the required temperature for the GBS is higher. 3.4. Damping and mechanical properties Fig. 6 summarizes the Q−1 and Rp0.2 at RT of the present studied sheets and some other typical Mg alloys including commercial ZK60 [35] and AZ61 [36] alloys, high-damping Mg alloys (Mg-0.6Zr [37] and Mg-0.6Zr-0.5Y [38]), and high-strength experimental Mg-Zn-Y-Zr [39] alloys. Generally speaking, there was a damping capacity-yield strength trade-off. As expected, the extruded pure Mg exhibited the highest Q−1 value of 0.08 but extremely low Rp0.2 . The Q−1 of Mg-1Y was almost 2 times of ZK60 [35], AZ61 [36], and high-strength Mg-Zn-Y-Zr [39] alloys. However, the Rp0.2 of Mg-1Y was much lower than that of ZK60 [35] and Mg-ZnY-Zr [39] alloys but comparable with that of AZ61 [36].The values of Q−1 and Rp0.2 of Mg-1Y were higher than that of Mg-0.6Zr [37], but lower than that of Mg-0.6Zr-0.5Y [38] as compared with the high-damping Mg alloys. Thus, the present studied Mg-Y sheets and Mg-Y based alloys exhibited good damping performance with acceptable yield strength at RT.
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tribute to damping capacity. This result implied that the segregation of Y solutes at grain boundary could depress the GBS which led to the increase of critical temperature. (3) Considering the balance of damping properties and yield strength at both RT and elevated temperature, it implied that the Mg-Y and Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys with good comprehensive properties, especially for elevated-temperature application. Acknowledgment
Fig. 7. The yield strength and damping capacities of the extruded pure Mg and Mg-xY (x = 1.0, 3.0 wt.%) sheets at temperatures between 25 °C and 325 °C. The strain amplitude was 1 × 10−3 and the forced frequency was 1 Hz.
Due to the limited elevated-temperature data available in literature, we here took extruded pure Mg as baseline for comparing. The Rp0.2 and Q−1 of the extruded pure Mg and Mg-Y sheets at different temperatures show in the Fig. 7. As the temperature increases, the Rp0.2 significantly decreases while the Q−1 increases gradually. At 25 °C, the Rp0.2 and Q−1 of Mg-1Y was 2.5 and 0.39 times than that of pure Mg, respectively. At high temperature of 325 °C, the extruded Mg1Y and pure Mg exhibited the same Q−1 (0.09) but Rp0.2 of Mg-1Y (51 MPa) was 3.4 times of pure Mg (15 MPa). For Mg-3Y sheet, although the Q−1 (0.07) was slightly lower than that of pure Mg (0.09), the Rp0.2 (79 MPa) was 5.3 times of pure Mg (15 MPa). According to the comparison and discussion above, it is reasonable to conclude that the extruded MgY sheets and Mg-Y based alloys exhibit promising potential for developing high-performance damping alloys with good comprehensive properties, especially for elevated-temperature application. 4. Conclusion The primary results of this study are outlined as follows: (1) With Y content increasing from 0.5% to 3.0%, the Q−1 significantly decreased from 0.037 to 0.015 at the strain amplitude of 1 × 10−3 , the εc of extruded Mg-Y sheets is much higher than that of pure Mg. The relationship between strain amplitude and Q−1 fitted well with GL dislocation damping model for all the studied Mg-Y sheets and pure Mg at RT. (2) The Q−1 increased remarkably above the critical temperature, and the critical temperature increased significantly from 50 °C to 290 °C with increasing Y contents from 0 to 3.0wt.%. The dislocation damping was not the only dominate damping mechanism at elevated temperatures for the extruded pure Mg and Mg-Y sheets, and the grain boundary sliding (GBS) could con-
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Journal of Magnesium and Alloys 7 (2019) 522–528 www.elsevier.com/locate/jma
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Effects of Y content and temperature on the damping capacity of extruded Mg-Y sheets Y.T. Tang a, C. Zhang a, L.B. Ren a, W. Yang a, D.D. Yin a,∗, G.H. Huang a, H. Zhou b, Y.B. Zhang a,∗ a Key
Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, PR China b Nano and Heterogeneous Materials Center, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China Received 10 January 2019; received in revised form 7 May 2019; accepted 10 May 2019 Available online 5 June 2019
Abstract The damping behavior of extruded Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets were investigated in detail concerning the effects of Y addition and temperature, and the relationship between damping capacity and yield strength was discussed. At room temperature (RT), with Y content increasing from 0.5% to 3.0%, the damping capacity (Q−1 ) significantly decreased from 0.037 to 0.015. For all the studied sheets, the relationship between strain amplitude and Q−1 fitted well with the Granato and Lücke (G-L) dislocation damping model. With temperature increased, the G-L plots deviated from linearity indicating that the dislocation damping was not the only dominate mechanism, and the grain boundary sliding (GBS) could contribute to damping capacity. Consequently, the Q−1 increased remarkably above the critical temperature, and the critical temperature increased significantly from 50 °C to 290 °C with increasing Y contents from 0 to 3.0 wt.%. This result implied that the segregation of Y solutes at grain boundary could depress the GBS, which was consistent with the recent finding of segregation tendency for rare-earth solutes. The extruded Mg-1Y sheet exhibited slightly higher yield strength (Rp0.2 ) and Q−1 comparing with high-damping Mg-0.6Zr at RT. At an elevated temperature of 325 °C, the Mg-1Y sheet had similar Q−1 but over 3 times larger Rp0.2 than that of the pure Mg. The present study indicated that the extruded Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys, especially for the elevated-temperature application. © 2019 Published by Elsevier B.V. on behalf of Chongqing University. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University Keywords: Extruded sheets; Mg-Y alloys; Damping capacity; Granato and Lücke model; Elevated temperature.
1. Introduction With the increasing demands of high-damping and lightweight performance for transportation, magnesium (Mg) and its alloys have attracted more and more attention [1–3]. Thus, it has become a continuous subject to develop highperformance Mg alloys with an excellent combination property of damping capacity, strength and ductility [4,5]. Alloying is one of the most important ways to achieve such goal. The effects of some alloying elements (Si, Mn, Cu, Ni, Ca, ∗
Corresponding authors. E-mail addresses: [email protected] (D.D. Yin), yingbozhang@ 163.com (Y.B. Zhang).
Zr, Sc, Er, and Ce) on the damping capacity of Mg alloys have been studied. And some high-performance damping Mg alloys such as Mg-Zr alloys and Mg-Cu-Mn alloys have been successfully developed [6–14]. It has been reported that Yttrium (Y) can markedly improve the strength and ductility of Mg alloys simultaneously. As we all know, Y is a rare earth element [15–17]. At the same time, Y can improve the corrosion resistance as well [18]. Besides, the high-temperature tensile, compressive strength and creep resistance can be improved significantly by adding Y to Mg [19–23]. Wang et al. [24] found that the addition of trace Y (0.05–0.15 wt.%) in Mg-Zr alloys can significantly improve the mechanical properties at the same time improve the damping capacity. Another group
https://doi.org/10.1016/j.jma.2019.05.003 2213-9567/© 2019 Published by Elsevier B.V. on behalf of Chongqing University. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University
Y.T. Tang, C. Zhang and L.B. Ren et al. / Journal of Magnesium and Alloys 7 (2019) 522–528 Table 1 Actual chemical compositions of the studied alloys (in weight%). Alloys
Actual chemical compositions
Mg-0.5Y Mg-1Y Mg-3Y
Mg-0.28Y Mg-0.86Y Mg-2.70Y
[25] studied the effects of Y and Zn on the damping capacity of the Mg-Cu-Mn alloy, and they found the damping capacity of Mg-3Cu-1Mn-1Y-2 Zn was close to that of pure Mg at strain amplitudes over 5 × 10−4 . Our previous work [5] have investigated the effects of heat treatment and pre-deformation on the damping capacity of the cast Mg-xY (x = 1, 3, 7 wt.%) binary alloys at room temperature (RT). The results indicated that compared with several Mg-based damping alloys, the cast Mg-Y alloys has the great potential of development of high-performance damping alloys with adequate strength. Compared with cast Mg alloys, wrought (such as rolling, extruding and forging) Mg alloys generally exhibit better mechanical properties [26,27]. However, comprehensive effects of Y on damping property and mechanical strength of extruded Mg-Y based alloys, especially at sub-zero temperatures and elevated temperatures, are yet to be completely clear. The purpose of the present work is to investigate the effects of Y addition and temperature on the damping behavior of extruded Mg-xY (x = 0.5, 1, 3 wt.%) sheets. The temperature dependence of damping mechanism was discussed and revealed. The comprehensive properties in terms of Q − 1 and Rp0.2 of the extruded Mg-Y sheets were evaluated by comparing with extruded pure Mg and several Mg-based damping alloys at temperatures between RT and 325 °C. 2. Materials and experimental procedures Pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%, hereafter, all alloy compositions are in weight percent unless otherwise state) alloys were prepared by melting high purity Mg (99.99%) and Mg-30Y master alloy in an electric resistance furnace at 720 °C. And it is then cast into a steel mold with diameter of 95 mm. The protection atmosphere is a mixture of CO2 and SF6 , which is 100:1 (It is the volume ratio). The inductively coupled plasma (ICP) is the equipment that we used to analyze the actual chemical composition of the studied alloys. And table 1 lists the actual chemical compositions. The as-cast ingots were homogenized at 560 °C for 8 h followed by air cooling, and then processed into an extrusion processing of the billet with a diameter of 90 mm. The billets were preheated at 300 °C for 2 h before extrusion and then extruded into sheets with a cross section of 80 × 5 mm2 . The setting temperature of the extrusion die and the extrusion container was 300 °C and 300–330 °C, respectively. And the extrusion ratio was 16. The ram speed was approximately 0.5–1.0 mm/s. We test the yield strength, Rp0.2 , of the alloys by MTS (CMT5105) universal testing machine. And the initial strain rate was 10−3 /s. The Zeiss A1 optical microscope was applied
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to observe the microstructure. The microscopically observed samples were mechanically ground on 2000 coarse SiC sandpaper, polished with diamond mortar to a mirror finish, then etched in mixed acid. Used to measure the damping of the rectangular beam bending specimen size 40 mm × 5 mm × 1.5 mm were cut from the sheets along the extrusion direction (ED) using an electric discharge machine (EDM). The TA-Q800 dynamic mechanical analyzer (DMA), which is the equipment that used to measure the damping capacity of the alloys with a single cantilever vibration mode. The damping capacity (Q−1 ) in this study is defined as the loss tangent (tanψ), where ψ is the lag angle between applied strain and the responding stress. Strain-dependent damping tests were made at maximum strain amplitudes ranging between 10−6 to 10−3 at RT. The temperature range for the temperature-dependent damping tests was from −50 °C to 390 °C, with 5 °C/min. And the strain amplitude was selected as 3 × 10−4 . It is important to note that the vibration frequency (f) was 1 Hz for all the damping tests. [41]. 3. Results and discussions 3.1. Microstructure The representative optical micrographs of the extruded pure Mg and the Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets in extrusion direction (ED)-transverse direction (TD) plane are shown in Fig. 1. It can be seen that the as-extruded microstructure consisted of uniform and fine equiaxed grains, and a small amount of secondary phases particles distributing homogeneously both in the grains and at grain boundaries. The average grain sizes of pure Mg, Mg-0.5Y, Mg1Y, and Mg-3Y sheets were approximately 120 ± 27 μm, 8.7 ± 0.9 μm, 5.5 ± 0.6 μm, 7.4 ± 0.7 μm, respectively, which means the addition of Y can remarkably decrease grain size of the extruded Mg alloys. With the addition of Y, the volume fraction of the second phase particles increased slightly, reaching 0.5%. 3.2. Damping capacity at room temperature (RT) The Strain amplitude dependence of damping capacity at RT for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets is shown in Fig. 2. All the measured Q−1 curves can be divided into two parts: the strain-amplitude independent damping (Q0−1 ) and the strain-amplitude dependent damping (Qa−1 ). The critical strain amplitude (εc ) refers to the strain amplitude when break-away pinned dislocation line [28]. In the curve, the εc is the transition point which represents the beginning of the second part or the end of the first part. Small Y addition, as low as 0.5%, to pure Mg decreased Q−1 , and the decrement was larger at higher strain amplitudes. However, further increasing of Y content up to 3% did not change the Q−1 of the extruded Mg-Y sheets in the strain-amplitude independent region. While in the strainamplitude dependent part, with the Y content increasing to
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Fig. 1. Optical micrographs of the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets: (a) Pure Mg, (b) Mg-0.5Y, (c) Mg-1Y, and (d) Mg-3Y. The average grain size of each samples is labelled in the pictures.
Q0−1 and the strain-dependent damping Qa−1 . Q−1 = Q0−1 + Qa−1
(1)
The end of the dislocation lines are strongly pinned by some strong point defects, such as dislocation net, precipitates or intermetallic compounds, etc. And the middle part of the dislocation lines is nailed by relatively weak pinning points, such as solute atoms or vacancy. At low strain amplitude, the strain-independent damping is affected by the vibration of the dislocation segment nailed by the weak pinning points. While the strain-dependent damping is affected by the vibration of the dislocation nailed by the strong pinning points.
Fig. 2. Strain amplitude dependence of damping capacity at room temperature for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets with f = 1 Hz.
−1
0.5%, 1.0% and 3.0%, the Q obviously decreased from 0.080 of pure Mg to 0.040, 0.020 and 0.016 at the strain amplitude (ε) of 1 × 10−3 , respectively. The εc of extruded Mg-Y sheets (∼4 × 10−5 ) is much higher than that of pure Mg (∼4 × 10−6 ). We know that dislocation damping is the dominant damping mechanism at RT, and the classical theory to illustrate the dislocation damping is the theory of Granato and Lücke (G-L) model. [28]. According to the G-L model, the total damping capacity (Q−1 ) is the sum of the strain-independent damping
Q0−1 ∼ ρLC4
(2)
Qa−1 = (C1 /ε ) exp(−C2 /ε )
(3)
C1 = (ρFB LN3 )/(6bE LC2 )
(4)
C2 = FB /(bE LC )
(5)
Where LC and LN are the average distance between weak pinning points and the average distance between strong pinning points, respectively; ρ is the dislocation density and b is the Burgers vector; FB is the binding force between dislocations and the weak pinning points; E is the elastic modulus. Eq. (6) is a modification of Eq. (3). ln (Qa−1 · ε) = −C2 /ε + ln C1
(6)
Fig. 3 illustrates the G-L plots for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets at RT with f = 1 Hz.
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Fig. 3. G-L plots for the extruded pure Mg and Mg-xY (x = 0.5, 1.0, 3.0 wt.%) sheets at room temperature with f = 1 Hz. Table 2 Values of C1 and C2 parameters obtained from the G-L plots. Composition
C1 (×10−5)
C2 (×10−4)
Ref.
Extruded pure Mg Extruded Mg-0.5Y Extruded Mg-1Y Extruded Mg-3Y As-cast Mg-1Y As-cast Mg-3Y
2.7 2.2 1.4 1.0 209.5 41.5
2.2 2.7 2.6 2.7 16.3 16.0
This This This This [5] [5]
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Fig. 4. Temperature-dependent damping capacity at the strain amplitude of 3 × 10−4 with f = 1 Hz.
the more second phase particles observed in the Mg-Y sheets than that of pure Mg. work work work work
A linear relationship between ln (Qa−1 × ε) and 1/ε demonstrated that the damping behavior at RT of pure Mg and Mg-Y sheets were closely related to the dislocation damping mechanism. From Eq. (3), it can be seen that in G-L plots the C2 was related to the value of the slope, and ln (C1 ) was related to the intercept. The calculated C1 and C2 values are listed in Table 2. Considering the C2 value is controlled by LC and Q0−1 is dependent on C2 , the larger C2 values of Mg-Y than that of pure Mg indicated that the addition of Y decreased the LC and Q0−1 which was consistent with that Y solutes acted as the weak pinning points. In the case of C1 , the value of C1 decreased with increasing Y content. This result indicated that with the increase of Y content, the strong pinning points of dislocations increases. It was correspond to what observed in the microstructure of Fig. 1. Due to more second phase particles by Y addition could act as strong pinning points and reduce LN . Similar changing trend of C1 and C2 with Y increasing was found in our previous study on the as-cast Mg-Y alloys [5]. However, the as-cast Mg-Y alloys exhibited larger C1 than that of the extruded Mg-Y sheets, which indicated that after the extrusion the LN was significantly reduced. As demonstrated before, dislocation damping was the predominant damping mechanism in the present Mg-Y sheets at RT. It was reported that the more second phase particles spread among the dislocation, the higher stress to break away from the constraint of second phase particles was required, and thus increased εc [28]. In this work, the εc increased with the addition of Y (Fig. 2), which was consistent with
3.3. Temperature-dependent damping capacity Fig. 4 illustrates the temperature-dependent damping capacity at the strain amplitude of 3 × 10−4 . The overall trends were that the Y addition to Mg decreased the Q−1 at temperatures between −50 °C to 300 °C, and the discrepancy was pronounced above 100 °C. However, it is interesting to note that increasing Y content did not worsen Q−1 of the extruded Mg-Y sheets at temperatures higher than 100 °C, and Q−1 of Mg-1Y and Mg-3Y were even larger than that of the pure Mg at 325 °C and above. The detailed analysis and discussion for this interesting phenomenon will be provided later. For the extruded pure Mg, Q−1 firstly increased gradually from −50 °C to 50 °C, and then increased remarkably at temperatures range of 50–180 °C, finally Q−1 continuously decreased with increasing temperature until test ended at 390 °C. As shown in Fig. 4, a damping peak P1 , appeared at around 180 °C for the extruded pure Mg, and its value was 0.11. Kê [29] reported similar damping peak at about 225 °C with a value of 0.06 in extruded and annealed polycrystalline pure Mg rod. However, the peak disappeared in single crystal pure Mg, and Kê [29] found that the grain boundaries behaved in a viscous manner at elevated temperatures and the damping peak corresponded to viscous slide of the grain boundary. Experimental evidence proved that the damping peak value was determined by the resistance to the grain boundary sliding and the sliding distance [29]. The average grain size of the extruded pure Mg sheet in the present study is ∼120 μm which is much smaller than that of pure Mg (∼200 μm) studied by Kê [29]. Therefore, the large amount of grain boundaries provides for a higher damping peak value than that of the pure Mg investigated by Kê. For the extruded Mg-Y sheets, between −50 °C to 50 °C Q−1 firstly increased gradually. The damping peak P2 which
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Fig. 5. G-L plots of the extruded Mg-0.5Y sheet at the temperatures of 100 °C and 300 °C with f = 1 Hz.
we found appeared at ∼50 °C, and it became less obvious as the Y content increases further. Similar peak of P2 has been reported in some other Mg alloys such as Mg-Ni alloys, Mg-Si alloys and Mg-Cu-Mn alloys [12,24,30]. G. Fantozzi et al. studied the internal friction of high purity Mg, they reported the peak is due to the interaction of the dislocations with interstitials defects. Thus, the P2 peak was believed to be caused by the interaction between dislocations and interstitials defects such as solute atoms [31]. The Q−1 was almost constant after P2 until it reached the critical temperature, and then it increased remarkably as the temperature rising. The critical temperatures for Mg-0.5Y, Mg-1Y and Mg-5Y were about 230 °C, 250 °C, and 290 °C, respectively. It should be noted that the Q−1 of Mg-1Y and Mg-3Y became even larger than that of pure Mg at temperatures of ∼340 °C and above. For example, the Q−1 of extruded Mg-3Y sheet (0.137) was 1.6 times of the extruded pure Mg (0.085) at the temperature of 385 °C. The Q−1 of the Mg-Y sheets increased significantly at high temperatures. To better understand the elevated-temperature damping mechanism, we investigated the G-L plots of Mg0.5Y at temperatures of 100 °C and 300 °C (Fig. 5). As Fig. 5 shows, the data for 100 °C slightly deviated from a linear fitting, while the data for 300 °C could hardly fit by a straight line. Thus, it is reasonable to believe that dislocation damping was not the only dominate damping mechanism at elevated temperatures for the present Mg-Y sheets. Among the internal friction mechanism, energy dissipation by dislocation movements is evident at RT. We know that at elevated temperatures grain boundary can behave in a viscous manner [29]. So it is realized that an existence of grain boundaries will affect the elastic and damping properties. Accordingly, it is reasonable to believe the grain boundaries sliding (GBS) could contribute to damping capacity of Mg-Y sheets at elevated temperatures. From Fig. 4, it can be seen that beyond the critical temperature which is 230 °C, 250 °C and 290 °C for Mg-0.5Y, Mg-1Y and Mg-3Y, respectively, the Q−1 increases signifi-
Fig. 6. The mechanical and damping properties of the present studied sheets in comparison with several typical commercial and experimental alloys [35–39] at room temperature. The strain amplitude was 1 × 10−3 and the forced frequency was 1 Hz.
cantly with the increases of the temperature. With the addition of Y, the critical temperature goes up. The impurity atoms segregate easily at grain boundary, in other words, the more concentrated alloys should have more segregation tendency in the grain boundaries [29]. Basu et al. [32,41] found that Gd exhibits strong grain boundary segregation trends. Both Y and Gd belong to the same subgroup of the rare-earth metals with a similar atomic structure which may result in a similar segregation tendency [33,34]. Christopher D. Barrett et al. [40] studied the effect of Y on grain boundaries, they found Y exhibits grain boundary segregation trends and Y segregation curtailed conventional recrystallization. The Y segregation at the grain boundary inhibits the grain boundary diffusion of Mg-Y sheets. The required activation energy of grain boundary is larger, and the required temperature for the GBS is higher. 3.4. Damping and mechanical properties Fig. 6 summarizes the Q−1 and Rp0.2 at RT of the present studied sheets and some other typical Mg alloys including commercial ZK60 [35] and AZ61 [36] alloys, high-damping Mg alloys (Mg-0.6Zr [37] and Mg-0.6Zr-0.5Y [38]), and high-strength experimental Mg-Zn-Y-Zr [39] alloys. Generally speaking, there was a damping capacity-yield strength trade-off. As expected, the extruded pure Mg exhibited the highest Q−1 value of 0.08 but extremely low Rp0.2 . The Q−1 of Mg-1Y was almost 2 times of ZK60 [35], AZ61 [36], and high-strength Mg-Zn-Y-Zr [39] alloys. However, the Rp0.2 of Mg-1Y was much lower than that of ZK60 [35] and Mg-ZnY-Zr [39] alloys but comparable with that of AZ61 [36].The values of Q−1 and Rp0.2 of Mg-1Y were higher than that of Mg-0.6Zr [37], but lower than that of Mg-0.6Zr-0.5Y [38] as compared with the high-damping Mg alloys. Thus, the present studied Mg-Y sheets and Mg-Y based alloys exhibited good damping performance with acceptable yield strength at RT.
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tribute to damping capacity. This result implied that the segregation of Y solutes at grain boundary could depress the GBS which led to the increase of critical temperature. (3) Considering the balance of damping properties and yield strength at both RT and elevated temperature, it implied that the Mg-Y and Mg-Y based alloys exhibited promising potential for developing high-performance damping alloys with good comprehensive properties, especially for elevated-temperature application. Acknowledgment
Fig. 7. The yield strength and damping capacities of the extruded pure Mg and Mg-xY (x = 1.0, 3.0 wt.%) sheets at temperatures between 25 °C and 325 °C. The strain amplitude was 1 × 10−3 and the forced frequency was 1 Hz.
Due to the limited elevated-temperature data available in literature, we here took extruded pure Mg as baseline for comparing. The Rp0.2 and Q−1 of the extruded pure Mg and Mg-Y sheets at different temperatures show in the Fig. 7. As the temperature increases, the Rp0.2 significantly decreases while the Q−1 increases gradually. At 25 °C, the Rp0.2 and Q−1 of Mg-1Y was 2.5 and 0.39 times than that of pure Mg, respectively. At high temperature of 325 °C, the extruded Mg1Y and pure Mg exhibited the same Q−1 (0.09) but Rp0.2 of Mg-1Y (51 MPa) was 3.4 times of pure Mg (15 MPa). For Mg-3Y sheet, although the Q−1 (0.07) was slightly lower than that of pure Mg (0.09), the Rp0.2 (79 MPa) was 5.3 times of pure Mg (15 MPa). According to the comparison and discussion above, it is reasonable to conclude that the extruded MgY sheets and Mg-Y based alloys exhibit promising potential for developing high-performance damping alloys with good comprehensive properties, especially for elevated-temperature application. 4. Conclusion The primary results of this study are outlined as follows: (1) With Y content increasing from 0.5% to 3.0%, the Q−1 significantly decreased from 0.037 to 0.015 at the strain amplitude of 1 × 10−3 , the εc of extruded Mg-Y sheets is much higher than that of pure Mg. The relationship between strain amplitude and Q−1 fitted well with GL dislocation damping model for all the studied Mg-Y sheets and pure Mg at RT. (2) The Q−1 increased remarkably above the critical temperature, and the critical temperature increased significantly from 50 °C to 290 °C with increasing Y contents from 0 to 3.0wt.%. The dislocation damping was not the only dominate damping mechanism at elevated temperatures for the extruded pure Mg and Mg-Y sheets, and the grain boundary sliding (GBS) could con-
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