Effect of texture on damping behaviour in ZK60 magnesium alloy

Abstract

Effect of texture on the damping capacity of ZK60 magnesium alloy is investigated through compression experiments with a deformation of 10% at room temperature. It is found that both the dislocation networks, twins and the basal texture intensity affect the damping capacity. At the low strain amplitudes, the dislocation networks and twins are dominant and the damping capacity decreases with the increase in the dislocation networks and twins. At the high strain amplitudes, the basal texture intensity is dominant and the damping capacity decreases with the increase in the basal texture intensity. Based on the anisotropy of the damping capacity of the wrought magnesium alloys, this research provides provide a direction for the study of high-strength and high-damping magnesium alloys.

Keywords

Magnesium alloy texture damping capacity dislocation

Introduction

The compelling need for the fuel-efficient high performance vehicles and the related green environment in automotive applications has attracted numerous researchers to develop the lightweight structural materials, of which magnesium is a promising candidate for the lightweight structural metallic material [1,2]. Moreover, pure Mg and some Mg alloys have excellent damping capacities. Therefore, Mg alloys can be used as damping materials for vibration and noise reduction in vehicles and instruments [3 -5]. However, their poor formability at room temperature has become an unfavourable factor limiting their wide applications, which is associated with the lack of adequate independent slip systems [6,7].

As it is known to all, polycrystals can be uniformly deformed if there are five independent slip systems according to the Taylor criterion [8]. However, Mg and Mg alloys have the hexagonal closed packed structure and only possess two dominant easy slip systems, which include the dislocations with <a > type Burgers vectors on (0001) basal plane [9]. Therefore, the number of the independent slip systems in Mg and Mg alloys at room temperature does not meet the Taylor criterion. In the early studies, some researchers discover the other slip mechanisms involving the non-basal slip of <11 0 > type dislocations and including the prismatic 10 0 and the pyramidal 10 1 planes [10 -12]. It is worth noting that the prismatic 10 0 or the first-order pyramidal 10 1 slip can only possess the extra independent slip systems, but the non-basal slip systems can be easily activated at high temperatures (>180°C) [13]. Therefore, deformation twins play a key role in the deformation of Mg alloys at room temperature [14]. In addition, twinning deformation is considered to be an effective and low-cost method to control the texture characteristics of magnesium alloys [15]. Some researchers have conducted studies on the effect of texture on the damping behaviour of magnesium alloys [3,14 -16], and they think that the basal slip is responsible for the damping behaviour of Mg and Mg alloys. They even propose that the stronger the intensity of the basal texture of magnesium and magnesium alloys, the weaker the damping capacity. However, this viewpoint is lack of the systematic in-depth analysis and discussion. Therefore, the present paper stresses on the mechanism of texture on the damping behaviour of magnesium alloys by compression deformation and thus further expands the application range of magnesium alloys.

Experimental

The ZK60 (Mg–6Zn–0.6Zr, in wt-%) Mg alloy ingots were prepared by an electric resistance furnace under an argon-shield atmosphere with pure Mg, pure Zn and Mg-30%Zr alloy as the raw materials, and the actual Zn and Zr contents are 5.90 and 0.67 wt-%, respectively. Then the as-cast alloy ingots were quenched in water after the two-stage solution treatment of 330°C × 24 h + 420°C × 4 h. The as-solutionized samples with the initial size 40 mm × 40 mm × 40 mm were pressed at room temperature with a reduction of 10%. The damping samples with the size of 30 mm × 3 mm × 1 mm were cut in three plates as shown in Figure 1 so that the normal direction of the samples was parallel to (i) the compression direction, (ii) 45° away from the compression direction and (iii) perpendicular to the compression direction of the plate. These samples were named as CD, 45 and 90 CD samples, respectively.

Microstructure analysis of the as-compressed samples etched with a mixture of 10 ml alcohol, 1.5 ml water, 1 ml glacial acetic acid and 0.3 g picric acid was carried out using an MM-6 optical microscope (OM). Macroscopic texture was conducted with an X-ray diffraction (XRD, D/MAX2500PC) using Cu Ka radiation and a scanning rate of 8° min^–1. Electron backscattered diffraction (EBSD) was examined using a FEI Quanta 200 scanning electron microscope (SEM) after electrolytic polishing with a mixture of 95% CH₃OH + 5% HClO₄ at 15 V for 180s at −20°C. The damping capacities were measured by a TA Q800 dynamic mechanical analyzer in the single cantilever vibration mode, with the vibration frequency of 1 Hz, the strain amplitude ranging from 1 × 10⁻⁵ to 1 × 10⁻³ at room temperature. Three specimens were used for damping capacities testing of the as-compressed samples in each state.

Results and discussion

OM microstructure

The optical micrographs of the three as-compressed ZK60 billets are shown in Figure 2. It is visible that there is a massive formation of shear bands in combination with many mechanical twins in the three as-compressed plates. A large number of cross twins are existent in most grains and the twin spacing is small. This is mainly due to the fact that the deformation mechanism is mainly the basal slip and mechanical twinning at room temperature [17]. Twin deformation accounts for a large part of plastic deformation of magnesium alloy [18,19]. No recrystallization is found in the three as-compressed samples.

Texture characteristics

The XRD patterns of the three compressed samples are shown in Figure 3, which exhibit the different strongest peak in (0002) and (10 1) for CD and 45CD, (10 0) and (10 1) for 90CD. In order to more clearly analyse the texture characteristics of the three samples, EBSD analysis is conducted. The inverse pole figure (IPF) maps of the three as-compressed ZK60 plates are shown in Figure 4. A large scanning area is obtained to ensure that the presented structures are statistically typical and significant. It is obvious that the three samples show different textures and a large number of twins. The CD and 45CD samples have stronger (0001) basal texture, while the 90CD samples have strong (10 1) cylindrical texture.

In order to further analyse the microscopic mechanism of three different samples in the process of compression deformation, it is necessary to analyse the as-compressed sample for dislocations. The geometrically necessary dislocation (GND) model has been widely used to calculate the GNDs of alloys, which facilitates the analysis of plastic behaviour and strengthening mechanisms of alloys [20]. The GND density (ρ^GND ) is proportional to the average local misorientation (θ) [20,21], which can be expressed as (1) where µ is the unit length (3.5 µm for the as-compressed sample in this study.) and b represents the Burgers vector (3.2 × 10⁻¹⁰ nm for magnesium). Figure 5 shows the KAM maps and local misorientation distribution histograms of the three as-compressed ZK60 plates. The different colours in the KAM maps represent the magnitude of dislocation density, where blue to green to red indicates a gradual increase in dislocation density. It can be clearly seen that the 90CD sample has the largest dislocation density, followed by the 45CD sample and the smallest CD sample. Moreover, it can be seen that the high-density dislocations are essentially scattered inside all grains in the 90CD sample. Combining the GND model and the local misorientation distribution histograms, it can be obtained the GND densities of CD, 45 and 90 CD samples are 3.8 ×10¹³ m⁻², 5.8 × 10¹³ m⁻² and 6.5 × 10¹³ m⁻².

Figure 6 presents the EBSD grain boundary maps of the three as-compressed ZK60 plates. The low angle grain boundaries (LAGBs), the high angle grain boundaries (HAGBs), 10 1 compression twins and 10 2 tensile twins are marked with different colours in Figure 6, respectively. The large number of LAGBs found in the 90CD sample is much higher than the other two. The large number of LAGBs in the 90CD sample indicates the presence of a large number of dislocations in the sample due to the rotation and distortion of grain boundaries and subgrain formation during compression [22]. It can also be seen from Figure 6 that the twins produced during the compressive deformation of the alloy are mainly tensile twins, with only a very small amount of compression twins.

Damping capacity

The variations of the room-temperature damping capacity (Q⁻¹) of the three as-pressed ZK60 plates at different strain amplitude from 1 × 10⁻⁵ to 1 × 10⁻³ are shown in Figure 7. With the increase in the strain amplitude, the damping capacity keeps relatively constant at first and then rapidly increases. Overall, the curves can be roughly divided into two stages: (1) the weakly dependent on the strain amplitude stage and (2) the strongly dependent on the strain amplitude stage. The boundary amplitude between the two stages is called the critical strain amplitude. As shown in Figure 7, the critical strain amplitudes of the three as-compressed samples are almost the same, about 6 × 10⁻⁵. When the damping capacity is weakly related to the strain amplitude, the damping capacity is basically unchanged, which is called the strain-independent damping (Q ₀⁻¹). As the strain amplitude increases to the critical strain amplitude, the damping capacity of the alloy increases rapidly with the increase in the strain amplitude.

It is reported that the alloy with the damping capacity higher than 0.01 belongs to the high-damping metal material [23]. The damping capacities of CD, 45CD and 90CD samples reach 0.01 with the strain amplitude of 2.8 × 10⁻⁴, 3.7 × 10⁻⁴ and 2.4 × 10⁻⁴, respectively. With the strain amplitude of 1 × 10⁻³, the damping capacities of CD, 45CD and 90CD alloys are as high as 0.01075 ± 0.00031, 0.01218 ± 0.00007 and 0.01703 ± 0.00100, respectively. Therefore, in the mid-to-high strain amplitude stage, the alloy studied in this paper is a high-damping metal material. Moreover, the CD and 45CD samples exhibit higher damping capacities than the 90CD alloy with the strain amplitude less than 1.8 × 10⁻⁴, while the 90CD alloy exhibits higher damping capacity than the other two alloys with the strain amplitude higher than 1.8 × 10⁻⁴. The gap in the damping capacity between the 90CD alloy and the other two alloys becomes larger with the higher strain amplitude.

Mg and its alloys have the most excellent damping capacity among the lightweight structural materials. Their damping mechanism is mainly the energy dissipation generated by the movement of dislocations, which can be expounded by the dislocation damping model put forward by Granato and Lüker [24,25], briefly stated as the G-L dislocation theory. Under the action of external force, the area swept by the dislocation moving back and forth between the weak or strong pinning points represents the vibration energy consumed by the material, and also represents the damping capacity of the material. Among them, the weak pinning points include point defects such as vacancies and solute atoms, and the strong pinning points include grain boundaries, twin grain boundaries, dislocation network nodes, precipitates, etc. According to the G-L dislocation theory, the energy consumed by the movement of the movable dislocation is relatively small and basically unchanged due to the simultaneous pinning of the weak pinning points and strong pinning points of the movable dislocation under the low strain amplitude, producing the strain-independent damping. In the low strain amplitude stage, the strain-independent damping (Q ₀⁻¹) can be a function of the average movable dislocation length (L_C ) between the weak pinning points, which can be expressed as follows: (2) where B is the damping constant for dislocation motion; Λ is the entire length of movable dislocation in per unit volume; ω is the angular frequency set in this damping test; G and b are the shear modulus and the Burgers vector, respectively. Since the three samples used in this experiment are cut from the same ingot in different plates, Q ₀⁻¹ can be expressed as (3) As the strain amplitude gradually increases to the critical strain amplitude, the damping capacity will increase rapidly. The strain-dependent damping (Q_H ⁻¹) can be generated at this stage when the dislocations break away from the weak pinning points but are still pinned by the strong pinning points. The relationship between Q_H ⁻¹ and the strain amplitude (ε) is as follows: (4) (5) where C ₁ and C ₂ are physical constants; ρ is the density of the movable dislocations which lie on the slip planes and participate in the breakaway process; F_B is the constrained force exerted on the movable dislocations between the pinning points; L_N is the average movable dislocation length between the strong pinning points; E is the Young's modulus. In this high strain amplitude stage, the damping capacity (Q⁻¹) is composed of the strain-independent damping and the strain-dependent damping as follows: (6) Equation (2) can be expressed in another form as follows: (7) That is, ln(Q_H ⁻¹ × ε) and ε are linearly related in the G-L dislocation theory. In other words, as long as ln(Q_H ⁻¹ × ε) and ε⁻¹ are linearly related, the damping capacity of the alloy can be explained by the G-L dislocation theory. The Q⁻¹ value at a particular strain amplitude can be obtained from Figure 7, and the corresponding Q_H ⁻¹ value corresponding to the same strain amplitude can be calculated in combination with Equation (6). The G-L curves (i.e. ln(Q_H ⁻¹ × ε) vs ε⁻¹) of the three as-compressed samples are shown in Figure 8. The linear relationship between ln(Q_H ⁻¹ × ε) and ε⁻¹ when the strain amplitude is less than 0.05%, which indicates that the damping behaviour of the three as-compressed samples studied in this paper can be explained by the G-L dislocation theory.

As seen from Figure 7, the 90CD sample exhibits the smaller strain-amplitude-independent damping than those of the CD and 45CD samples. Since this experiment was a compressive deformation of the as-solutionized alloy, the effect of the second phases on the damping capacity of the alloy can be neglected. Moreover, when the grain size is larger than 20 µm, the effect of grain size on the damping capacity of the Mg alloy is very small [4]. Therefore, according to G-L theory, mainly the solid solution atoms, dislocation networks and twins are used as the pinning points to pin dislocations, thus affecting the strain-amplitude-independent damping of the alloy at low strain amplitudes. That is, the large number of dislocation networks and twins in the 90CD sample severely impedes the motion of movable dislocations compared to the CD and 45CD sample, thus reducing the damping capacity of the alloy. In the previous research, it has been found that the damping capacity of the alloy decreases with the tensile deformation higher than 3% and the dislocations of the deformed alloy are intensive but relatively short when the tensile elongation is 5% [26]. When the strain amplitude exceeds the critical strain amplitude, the damping capacity of the 90CD sample increases much faster than that of the CD and 45CD samples, implying that another factor influences the damping capacity. It can be seen that the basal texture of 90CD samples is much lower than that of CD and 45CD samples from Figures 3 and 4, so the basal texture intensity plays an important role in the damping capacity of magnesium alloys. The influence of the basal texture intensity on the damping capacity of the magnesium alloys can be analysed by the aid of the force analysis of the damping sample.

The force diagram of the damping sample is shown in Figure 9. The maximum normal stress (σ _max) can be expressed by the following formula: (9) where l, w and h represent the length, width and height of the damping sample, respectively. The maximum shear stress (τ _max) can be expressed by the following formula: (10) Therefore, the ratio of σ _max to τ_max is 4 l/h. Since the length of the sample is much greater than the thickness of the sample, the maximum normal stress is much greater than the maximum shear stress. Combined with the previous analysis, the basal texture intensity of the A surface of the CD and 45CD samples are stronger, while the cylindrical texture intensity of the A surface of the 90CD sample is stronger. The initiation of the deformation modes depends on the ratio of the critical shear stress to the Schmidt factor, and the deformation mode of magnesium alloy at room temperature is mainly the basal slip [27]. Therefore, if the A surface has completely basal texture, only the shear stress acting on the A surface can cause the movable dislocation to move under the action of F_B . If the A surface has completely cylindrical texture, the C surface has completely basal texture according to the close-packed hexagonal structure of magnesium, and the normal stress acting on the A surface can cause the movable dislocation on the C surface to move. In short, the stronger the basal texture intensity on the A surface is, the more difficult it is for the movable dislocations to move under the same stress. Conversely, the stronger the cylindrical texture intensity on the A surface, the easier it is for the movable dislocations to move under the same stress. In addition, the stronger the dislocation movement is, the more elastic vibration energy will be consumed by the material, and the higher the damping capacity will be. Therefore, with the strain amplitude higher than the critical strain amplitude, the dislocations break away from the weak pinning points and the damping capacity of the 90CD sample increases rapidly until it exceeds those of the CD and 45CD samples. Therefore, there is anisotropy in the damping capacity of the wrought magnesium alloys. Since the contradiction between strength and damping capacity of magnesium alloys restricts the research and application of high-strength and high-damping magnesium alloys [28 -30], the alloy can be extended to a wide range of applications according to the specific requirements of strength and damping properties in different directions of the material in practical applications.

Conclusions

The effect of texture on the damping capacity of ZK60 magnesium alloy is confirmed by compression experiments at room temperature. At the low strain amplitude, the 90CD sample shows lower damping capacity than the CD and 45CD samples due to the large number of dislocation networks and twins. However, when the strain amplitude is higher than the critical strain amplitude, the growth rate of the damping capacity of the 90CD sample with the strain amplitude is much higher than that of the CD and 45CD samples. In addition, the 90CD alloy exhibits higher damping capacity than the other two alloys with the strain amplitude higher than 1.8 × 10⁻⁴. The stronger the basal texture intensity of the alloy surface is, the more difficult it is for the dislocations to move under the force applied to the surface. Based on the anisotropy of damping capacity of the wrought magnesium alloys, this study provides an opinion on the development of high-strength and high-damping magnesium alloys.

Footnotes

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

References

Pollock

TM.

Weight loss with magnesium alloys. Science. 2010;328:986–987.

Hirsch

Al-Samman

Superior light metals by texture engineering: optimized aluminum and magnesium alloys for automotive applications. Acta Mater. 2013;61:818–843.

Sugimoto

Matsui

Okamoto

Effect of crystal orientation on amplitude-dependent damping in magnesium. Trans JIM. 1975;16:647–655.

Sugimoto

Niiya

Okamoto

A study of damping capacity in magnesium alloys. Trans JIM. 1977;18:277–288.

Watanabe

Mukai

Sugioka

Elastic and damping properties from room temperature to 673 K in an AZ31 magnesium alloy. Scr Mater. 2004;51:291–295.

Lentz

Klaus

Beyerlein

In situ X-ray diffraction and crystal plasticity modeling of the deformation behavior of extruded Mg-Li-(Al) alloys: an uncommon tension-compression asymmetry. Acta Mater. 2015;86:254–268.

Kim

K-H

Jeon

Kim

Role of yttrium in activation of <c+a> slip in magnesium: an atomistic approach. Scr Mater. 2015;108:104–108.

Taylor

GI.

Plastic strain in metals. J Inst Met. 1938;62:307–338.

Hou

Zhang

Fan

Microstructure evolution and deformation behaviors of AZ31 Mg alloy with different grain orientation during uniaxial compression. J Alloy Compd. 2018;741:514–526.

10.

Reed-Hill

Robertson

WD.

Deformation of magnesium single crystals by nonbasal slip. JOM. 1957;220:496–502.

11.

Ward Flynn

Mote

Dorn

JE.

On the thermally activated mechanism of prismatic slip in magnesium single crystals. Trans TMS-AIME. 1961;221:1148–1154.

12.

Quimby

Mote

Dorn

JE.

Yield point phenomena in magnesium-lithium single crystals. Trans ASM. 1962;55:149–157.

13.

Wonsiewicz

Backofen

WA.

Plasticity of magnesium crystals. Trans TMS-AIME. 1967;239:1422–1431.

14.

Schwaneke

Nash

RW.

Effect of preferred orientation on the damping capacity of magnesium alloys. Metall Mater Trans B. 1971;2:3453–3457.

15.

Fan

Zheng

Internal friction and microplastic deformation behavior of pure magnesium processed by equal channel angular pressing. Mater Sci Eng A. 2013;561:100–108.

16.

Watanabe

Sawada

Sasakura

Microyielding and damping capacity in magnesium. Scr Mater. 2014;87:1–4.

17.

Koike

Kobayashi

Mukai

The activity of non-basal slip systems and dynamic recovery at room temperature in fine-grained AZ31B magnesium alloys. Acta Mater. 2003;51:2055–2065.

18.

Ghaderi

Barnett

MR.

Sensitivity of deformation twinning to grain size in titanium and magnesium. Acta Mater. 2011;59:7824–7839.

19.

Barnett

Ghaderi

Robson

JD.

Contribution of twinning to low strain deformation in a mg alloy. Metall Mater Trans A. 2013;48:3213–3221.

20.

Kubin

Mortensen

Geomrtrically necessary dislocations and strain-gradient plasticity: a few critical issues. Scr Mater. 2003;48:119–125.

21.

Calcagnotto

Ponge

Demir

Orientation gradients and geometrically necessary dislocations in ultrafine grained dual-phase steels studied by 2D and 3D EBSD. Mater Sci Eng A. 2010;527:2738–2746.

22.

Kocks

Mecking

Physics and phenomenology of strain hardening: the FCC case. Prog Mater Sci. 2003;48:171–273.

23.

Blanter

Golovin

Neuhäuser

Internal friction in metallic materials: a handbook. Berlin: Springer; 2007.

24.

Granato

Lücke

Theory of mechanical damping due to dislocations. J Appl Phys. 1956;27:583–593.

25.

Granato

Lücke

Application of dislocation theory to internal friction phenomena at high frequencies. J Appl Phys. 1956;27:789–805.

26.

Zheng

Effect of small tensile deformation on damping capacities of Mg-1%Al alloy. Trans Nonferrous Met Soc China. 2010;20:s444–s447.

27.

Liu

Tang

Microstructure and texture evolution in LZ91 magnesium alloy during cold rolling. J Magnes Alloy. 2018;6:77–82.

28.

Wang

Gao

Optimization of mechanical and damping properties of Mg-0.6Zr alloy by different extrusion processing. J Magnes Alloy. 2015;3:79–85.

29.

Wan

Wang

The damping and mechanical properties of magnesium alloys balanced by aluminum addition. J Alloy Compd. 2019;782:421–426.

30.

Niu

Yan

Duan

Effect of yttrium addition on microstructures, damping properties and mechanical properties of as-cast Mg-based ternary alloys. J Alloy. Compd. 2019;785:1270–1278.