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Damping capacity of friction stir processed commercial pure aluminium metal
Materials Today: Proceedings xxx (xxxx) xxx
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Damping capacity of friction stir processed commercial pure aluminium metal K. Venkateswara Reddy a, R. Bheekya Naik a, G. Madhusudhan Reddy b, R. Arockia Kumar a,⇑ a b
Department of Metallurgical and Materials Engineering, National Institute of Technology, Warangal, India Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad, India
a r t i c l e
i n f o
Article history: Received 6 August 2019 Accepted 12 September 2019 Available online xxxx Keywords: Friction stir processing (FSP) Hardness Damping capacity Dynamic mechanical analyser (DMA) Pure aluminium
a b s t r a c t The metallic materials are generally poor dampers of vibration as compared to polymeric materials. However, microstructure refinement was shown to be effective in enhancing the damping properties of metallic materials. In this study, the microstructure of commercial pure (CP) aluminium has been refined using friction stir processing (FSP) further its vibration-damping properties are evaluated using the dynamic mechanical analyser. The CP-aluminium was friction stir processed at 600 rpm and 60 mm/min to achieve fine microstructure. Electron backscattered diffraction (EBSD) and XRD analysis were employed to measure grain size and dislocation density of processed samples, respectively. The stir zone of processed specimens consists of fine and fully recrystallized grains. The results showed that the average grain size is approximately 10 mm after FSP. The hardness of the Al is decreased by 27% after FSP. The damping capacity was studied by the dynamic mechanical analyser (DMA) applying three-point bending mode. The damping capacity of processed specimens at room temperature was measured to be lesser than the as-received specimen. While increasing the temperature, beyond 130 °C, the damping capacity of processed specimens was measured to be better than the as-received sample. The decrease in damping capacity of processed samples at room temperature is due to the reduction of dislocation density while an increase of damping at high temperatures due to an increase in the grain boundary area. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Damping capacity is the dissipation of energy in the material during cyclic loading [1]. Improving the damping is important in suppressing the vibrations. Most of the aluminium (Al) and its alloys exhibit low damping capacity [2]. Accordingly, researchers have done investigations on improving damping capacity of materials through techniques like equal channel angular extrusion (ECAE) [3], extrusion [4,5] and roll bonding [6]. These processes found to refine the microstructure further changes the mechanical and damping properties of materials [7]. Friction stir process (FSP) is also a kind of severe plastic deformation processes to refine grain structure. Studies showed that materials with an ultrafine grain structure could be obtained by FSP [8]. Using FSP technique, it is possible to produce high damping materials, because FSP produces fine grain structure with a lot of defects like dislocation and grain ⇑ Corresponding author. E-mail address: [email protected] (R. Arockia Kumar).
boundary area, which are responsible in improving the damping capacity [9]. The principle of FSP is a rotating tool, which plunges into a plate and produces a plastically deformed zone through the stirring action. The stirring results in heat generation, which further assist in deforming the material [10]. In this work, an attempt has been made to evaluate the damping capacity of pure aluminium after being subjected to FSP. 2. Experimentation Commercially available pure Al (99%) plate in the rolled condition is used as a base material. FSP was performed on the 5 mm plate with conical shape tool made of H13 material (shoulder / 15 mm and 4 mm pin length). The FSP process parameters are 600 rotational speed, 60 mm/min and 10 kN axial load. Microstructural observations have been carried out using optical, and Electron backscattered diffraction (EBSD). The hardness of the stir zone was measured using Vickers micro-hardness tester, applying load 200 g for about 15 s. X-Ray diffraction technique was used for dislocation
https://doi.org/10.1016/j.matpr.2019.09.059 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
2
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
density calculations. Dynamic mechanical analyzer (TA instruments, RSA G2) was used to measure the damping capacity of Al. The sample for DMA analysis (50 mm length 7 mm width 1.6 mm thickness) extracted from the stir zone using electric discharge machining (EDM). The damping capacity tests were conducted in three point bending mode. Measurements were made at frequency 1–20 Hz (constant strain amplitude 2.6 mm and room temperature) and temperatures 35–300 °C with a heating rate of 5 °C/min. 3. Results and discussions 3.1. Microstructural characterization Fig. 1a reveals that the base metal, i.e. pure Al plate, is having elongated grains of average size 45 ± 3.4 mm. Fig. 1b shows microstructure of processed Al in which three regions are distinctly seen i.e. elongated grains of base metal, stir zone in which grains are indistinguishably fine, and the third region is an interface between the aforesaid region otherwise called thermomechanically affected zone (TMAZ). The simultaneous effect of plastic deformation and dynamic recrystallization led to the refinement of microstructure in the stir zone [10]. In order to reveal the grain structure of the stir zone, EBSD maps were obtained. Fig. 2a confirms the presence of elongated grains in the base metal. At the same time, weak boundaries are also seen inside the larger
grains. Grain boundary misorientation (Table 1) analysis revealed that the fraction of boundaries having 2°–5° misorientation is about 74%. Fig. 2b confirms the equiaxed fine microstructure in the stir zone. The average grain in this region is about 6.79 mm. The fraction of low angle boundaries (2°–5°) is only 13.5%, and this is lower than the base metal, whereas the fraction of high angle boundaries is about 54.9%. The base metal was received in cold rolled condition could be the reason for having a higher fraction of low angle boundaries. The X-ray diffraction patterns of Al before and after FSP are shown in Fig. 3. The diffraction peak of FSPed sample shifted to the right which implies that lattice distortion and inter-planar spacing decreased after FSP (Fig. 3b) according to Bragg’s law (2dsinh = nk, n is the order of diffraction) with the value of h increase, the interplanar spacing, d decreases. The interplanar spacing is smaller than the base metal. The dislocation density of the base metal and FSPed sample is calculated using the following relation [11,12].
pffiffiffi
q¼2 3
e Db
ð1Þ
‘‘Where q is dislocation density, e is average lattice strain, b is Burgers vector (b = 0.286 nm for Aluminium) D is the crystallite size”. The calculated dislocation density is presented in Table 1 confirms that dislocation density significantly decreased after FSP.
Fig. 1. Optical micrograph of (a) base metal (b) friction stir processed specimen showing three regimes, i.e. base metal, the transition zone (refereed as TMAZ) and stir zone.
Fig. 2. EBSD images of (a) Base metal (b) stir zone.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
3
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Average grain size, grain boundary misorientation and dislocation density of pure Al before and after friction stir processing. Condition
Average grain size
Base metal FSP sample
45 ± 3.4 mm 6.79 mm (stir-zone)
Dislocation density (q) 1011 m2
The fraction of grain boundaries (%) 2° to 5°
5° to 15°
15° to 180°
75.4 13.5
19.7 31.6
0.05 54.9
4.24 2.57
Fig. 3. X-Ray diffraction peaks of base metal and FSPed sample.
3.2. Hardness The hardness was measured across the cross-section of the sample at a load of 200 g, and 15 s. dwell time. The hardness of the base metal is 38 Hv, whereas the stir zone has 28 Hv (Fig. 4). The percentage reduction in hardness of FSPed sample is 27% than the base metal. The X-ray measurements (Fig. 3 and Table 1) confirms that dislocation density reduced after FSP could be the reason for the observed reduction in hardness. It has been shown that the materials soften during FSP due to intense stirring caused an increase in the temperature of the stir zone. Wen-ying GAN reported that hardness mainly depends on the dislocation densities, not the grain size [13].
Fig. 4. Hardness measurements of base metal and FSPed sample.
3.3. Damping capacity The damping capacity (tan d) of the material is measured by
tan d ¼
E00 E0
where E00 is the loss modulus and E0 is storage modulus. The former refers to dissipation of energy in the material and later referred to the stiffness of the material [14]. The damping capacity of the base metal and FSPed sample with the frequency of load at constant amplitude 2.6 mm and room temperature is shown in Fig. 5. The damping of the base metal and FSPed sample is increased with fre-
Fig. 5. Damping capacity of base metal and FSPed sample against frequency at room temperature.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
4
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 6. Temperature dependence of (a) damping capacity (b) storage modulus and (c) loss modulus base metal and FSPed sample.
quency. The maximum damping capacity (tan d) 0.0094 and 0.0071 was noticed for base metal and FSPed sample respectively at 20 Hz, which indicates that the damping capacity of the FSPed sample reduced by 21%. As frequency increases, the pinned dislocations at weak points may bow and undergo further motion under high vibration amplitude. An increase in dislocation density enhances damping capacity [15]. The decrease in damping capacity is due to the reduction of dislocation density after FSP (Table. 1). Damping peak at 220 °C for FSPed Al is observed for temperature dependent damping test. H.J. Jiang et al. and Shyi-Kaan Wu associated the damping peaks observed for aluminium in the temperature range 187–250 °C with grain boundary sliding. Thus, it is believed that the observed peak at 220 °C (Fig. 6a) could be due to grain boundary sliding, particularly for FSPed specimen. Fig. 6 (a) shows the damping capacity with temperature for pure Al and FSPed Al at constant strain amplitude (2.6 mm) and frequency (1 Hz). As temperature increases, the damping increased because of the viscous behaviour of grain boundaries (GBs), which converts mechanical energy into thermal energy [9]. From Fig. 6 (a) the damping capacity of the FSPed Al shown higher than the pure Al. It is evident from Figs. 1 and 2, the stir zone grain size (6.79 mm) is much lower than the base metal (45 mm). The decrease in grain size increases the grain boundary area. As the fraction of grain boundaries is more in FSPed specimen, it damps the vibration by means of GB sliding at high temperatures [16] which is better than the base metal. 4. Conclusions 1. The grain size was refined to 6.79 mm from its initial value of 45 mm through friction stir processing.
2. The intense heat generated during friction stirring softened the stir zone by reducing the dislocation density, thereby led to a reduction in hardness. 3. At room temperature, the damping capacity of the FSPed Al was lower than the base metal owing to the reduction in dislocation density. 4. At high temperatures (>130 °C), the damping capacity of FSP-ed Al was observed to be better than the base metal, this was due to increased grain boundary area as a result of microstructure refinement.
Acknowledgments The authors would like to thank DST-SERB for funding this research work through project No. ECR/2017/00122. Authors also grateful to DRDO-DMRL for extending their facility to conduct friction stir processing. References [1] Jinmin Zhang, Robert J. Perez, Catherin R. Wong, Effect of secondary phases on damping behaviour of metals, alloys and metal matrix composites, Mater. Sci. Eng. R13 (1994) 325–390. [2] E.J. Lavernia, R.J. Perej, J. Zhang, Damping behaviour of discontinuously reinforced Al alloys metal matrix composites, Metall. Mater. Trans. A (1995) 2803–2818. [3] Z.M. Zhang, C.J. Xu, J.C. Wang, H.Z. Lid, Damping behaviour of ultrafine-grained pure aluminum l2 and the damping mechanism, Acts Metall. Sin. (Engl. Lett.) 19 (2006) 223–227. [4] Fan Gen-lian, Li Zhi-qiang, Zhang Di, Damping capacity of BaTiO3/Al composites fabricated by hot extrusion, Trans. Nonferrous Met. Soc. China 22 (2012) 2512–2516. [5] Jingfeng Wang, Zhongshan Wu, Shan Gao, Ruopeng Lu, Dezhao Qin, Wenxiang Yang, Fusheng Pan, Optimization of mechanical and damping properties of
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
[6] [7]
[8]
[9]
[10]
Mge0.6Zr alloy by different extrusion processing, J. Magnesium Alloys (2015) 79–85. E. Emadoddin, M. Tajally, M. Masoumi, Damping behavior of Al/SiCP multilayer composite manufactured by roll bonding, Mater. Des. 42 (2012). A. Azushima, R. Kopp, A. Korhonen, D.Y. Yang, F. Micari, G.D. Lahoti, P. Groche, J. Yanagimoto, N. Tsuji, A. Rosochowski, A. Yanagida, Severe plastic deformation (SPD) processes for metals, CIRP Ann. – Manuf. Technol. 57 (2008) 716–735. Devinder Yadav, Ranjit Bauri, Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite, Mater. Sci. Eng., A 528 (2011) 1326–1333. H.J. Jiang, C.Y. Liu, B. Zhang, P. Xu, Z.Y.M.K. Luo, M.Z. Ma, R.P. Liu, Simultaneously improving mechanical properties and damping capacity of Al-Mg-Si alloy through friction stir processing, Mater. Charact. 131 (2017) 425–430. Marie-Noëlle Avettand-Fènoël, Aude Simar, A review about Friction Stir Welding of metal matrix composites, Mater. Charact. 120 (2016) 1–17.
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[11] Yonggang Yang, Yutao Zhao, Xizhou Kai, Ran Tao, Superplasticity behavior and deformation mechanism of the in-situ Al3Zr/6063Al composites processed by friction stir processing, J. Alloys Compd. 710 (2017) 225–233. [12] A. Dhal, S.K. Panigrahi, M.S. Shunmugam, Insight into the microstructural evolution during cryo-severe plastic deformation and post-deformation annealing of aluminum and its alloys, J. Alloy. Compd. 726 (2017) 1205–1219. [13] G.A.N. Wen-ying, Z.H.O.U. Zheng, Hang Zhang, P.E.N.G. Tao, Evolution of microstructure and hardness of aluminum after friction stir processing, Trans. Nonferrous Met. Soc. China 24 (2014) 975–981. [14] Dora Siva Prasad, Palukuri Tualsi Radha, Chintada Shoba, Pujari Srinivasa Rao, Dynamic mechanical behavior of WC-Co coated A356.2 aluminum alloy, J. Alloys Compd. 767 (2018) 988–993. [15] Dora Siva Prasad, Chintada Shoba, Experimental evaluation onto the damping behavior of Al/SiC/RHA hybrid composites, J. Mater. Res. Technol. (2016) 123– 130. [16] Yijie Zhang, Naiheng Ma, Haowei Wang, Xianfeng Li, Study on damping behavior of A356 alloy after grain refinement, Mater. Des. 29 (2008) 706–708.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Damping capacity of friction stir processed commercial pure aluminium metal K. Venkateswara Reddy a, R. Bheekya Naik a, G. Madhusudhan Reddy b, R. Arockia Kumar a,⇑ a b
Department of Metallurgical and Materials Engineering, National Institute of Technology, Warangal, India Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad, India
a r t i c l e
i n f o
Article history: Received 6 August 2019 Accepted 12 September 2019 Available online xxxx Keywords: Friction stir processing (FSP) Hardness Damping capacity Dynamic mechanical analyser (DMA) Pure aluminium
a b s t r a c t The metallic materials are generally poor dampers of vibration as compared to polymeric materials. However, microstructure refinement was shown to be effective in enhancing the damping properties of metallic materials. In this study, the microstructure of commercial pure (CP) aluminium has been refined using friction stir processing (FSP) further its vibration-damping properties are evaluated using the dynamic mechanical analyser. The CP-aluminium was friction stir processed at 600 rpm and 60 mm/min to achieve fine microstructure. Electron backscattered diffraction (EBSD) and XRD analysis were employed to measure grain size and dislocation density of processed samples, respectively. The stir zone of processed specimens consists of fine and fully recrystallized grains. The results showed that the average grain size is approximately 10 mm after FSP. The hardness of the Al is decreased by 27% after FSP. The damping capacity was studied by the dynamic mechanical analyser (DMA) applying three-point bending mode. The damping capacity of processed specimens at room temperature was measured to be lesser than the as-received specimen. While increasing the temperature, beyond 130 °C, the damping capacity of processed specimens was measured to be better than the as-received sample. The decrease in damping capacity of processed samples at room temperature is due to the reduction of dislocation density while an increase of damping at high temperatures due to an increase in the grain boundary area. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Damping capacity is the dissipation of energy in the material during cyclic loading [1]. Improving the damping is important in suppressing the vibrations. Most of the aluminium (Al) and its alloys exhibit low damping capacity [2]. Accordingly, researchers have done investigations on improving damping capacity of materials through techniques like equal channel angular extrusion (ECAE) [3], extrusion [4,5] and roll bonding [6]. These processes found to refine the microstructure further changes the mechanical and damping properties of materials [7]. Friction stir process (FSP) is also a kind of severe plastic deformation processes to refine grain structure. Studies showed that materials with an ultrafine grain structure could be obtained by FSP [8]. Using FSP technique, it is possible to produce high damping materials, because FSP produces fine grain structure with a lot of defects like dislocation and grain ⇑ Corresponding author. E-mail address: [email protected] (R. Arockia Kumar).
boundary area, which are responsible in improving the damping capacity [9]. The principle of FSP is a rotating tool, which plunges into a plate and produces a plastically deformed zone through the stirring action. The stirring results in heat generation, which further assist in deforming the material [10]. In this work, an attempt has been made to evaluate the damping capacity of pure aluminium after being subjected to FSP. 2. Experimentation Commercially available pure Al (99%) plate in the rolled condition is used as a base material. FSP was performed on the 5 mm plate with conical shape tool made of H13 material (shoulder / 15 mm and 4 mm pin length). The FSP process parameters are 600 rotational speed, 60 mm/min and 10 kN axial load. Microstructural observations have been carried out using optical, and Electron backscattered diffraction (EBSD). The hardness of the stir zone was measured using Vickers micro-hardness tester, applying load 200 g for about 15 s. X-Ray diffraction technique was used for dislocation
https://doi.org/10.1016/j.matpr.2019.09.059 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
2
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
density calculations. Dynamic mechanical analyzer (TA instruments, RSA G2) was used to measure the damping capacity of Al. The sample for DMA analysis (50 mm length 7 mm width 1.6 mm thickness) extracted from the stir zone using electric discharge machining (EDM). The damping capacity tests were conducted in three point bending mode. Measurements were made at frequency 1–20 Hz (constant strain amplitude 2.6 mm and room temperature) and temperatures 35–300 °C with a heating rate of 5 °C/min. 3. Results and discussions 3.1. Microstructural characterization Fig. 1a reveals that the base metal, i.e. pure Al plate, is having elongated grains of average size 45 ± 3.4 mm. Fig. 1b shows microstructure of processed Al in which three regions are distinctly seen i.e. elongated grains of base metal, stir zone in which grains are indistinguishably fine, and the third region is an interface between the aforesaid region otherwise called thermomechanically affected zone (TMAZ). The simultaneous effect of plastic deformation and dynamic recrystallization led to the refinement of microstructure in the stir zone [10]. In order to reveal the grain structure of the stir zone, EBSD maps were obtained. Fig. 2a confirms the presence of elongated grains in the base metal. At the same time, weak boundaries are also seen inside the larger
grains. Grain boundary misorientation (Table 1) analysis revealed that the fraction of boundaries having 2°–5° misorientation is about 74%. Fig. 2b confirms the equiaxed fine microstructure in the stir zone. The average grain in this region is about 6.79 mm. The fraction of low angle boundaries (2°–5°) is only 13.5%, and this is lower than the base metal, whereas the fraction of high angle boundaries is about 54.9%. The base metal was received in cold rolled condition could be the reason for having a higher fraction of low angle boundaries. The X-ray diffraction patterns of Al before and after FSP are shown in Fig. 3. The diffraction peak of FSPed sample shifted to the right which implies that lattice distortion and inter-planar spacing decreased after FSP (Fig. 3b) according to Bragg’s law (2dsinh = nk, n is the order of diffraction) with the value of h increase, the interplanar spacing, d decreases. The interplanar spacing is smaller than the base metal. The dislocation density of the base metal and FSPed sample is calculated using the following relation [11,12].
pffiffiffi
q¼2 3
e Db
ð1Þ
‘‘Where q is dislocation density, e is average lattice strain, b is Burgers vector (b = 0.286 nm for Aluminium) D is the crystallite size”. The calculated dislocation density is presented in Table 1 confirms that dislocation density significantly decreased after FSP.
Fig. 1. Optical micrograph of (a) base metal (b) friction stir processed specimen showing three regimes, i.e. base metal, the transition zone (refereed as TMAZ) and stir zone.
Fig. 2. EBSD images of (a) Base metal (b) stir zone.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
3
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Average grain size, grain boundary misorientation and dislocation density of pure Al before and after friction stir processing. Condition
Average grain size
Base metal FSP sample
45 ± 3.4 mm 6.79 mm (stir-zone)
Dislocation density (q) 1011 m2
The fraction of grain boundaries (%) 2° to 5°
5° to 15°
15° to 180°
75.4 13.5
19.7 31.6
0.05 54.9
4.24 2.57
Fig. 3. X-Ray diffraction peaks of base metal and FSPed sample.
3.2. Hardness The hardness was measured across the cross-section of the sample at a load of 200 g, and 15 s. dwell time. The hardness of the base metal is 38 Hv, whereas the stir zone has 28 Hv (Fig. 4). The percentage reduction in hardness of FSPed sample is 27% than the base metal. The X-ray measurements (Fig. 3 and Table 1) confirms that dislocation density reduced after FSP could be the reason for the observed reduction in hardness. It has been shown that the materials soften during FSP due to intense stirring caused an increase in the temperature of the stir zone. Wen-ying GAN reported that hardness mainly depends on the dislocation densities, not the grain size [13].
Fig. 4. Hardness measurements of base metal and FSPed sample.
3.3. Damping capacity The damping capacity (tan d) of the material is measured by
tan d ¼
E00 E0
where E00 is the loss modulus and E0 is storage modulus. The former refers to dissipation of energy in the material and later referred to the stiffness of the material [14]. The damping capacity of the base metal and FSPed sample with the frequency of load at constant amplitude 2.6 mm and room temperature is shown in Fig. 5. The damping of the base metal and FSPed sample is increased with fre-
Fig. 5. Damping capacity of base metal and FSPed sample against frequency at room temperature.
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
4
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 6. Temperature dependence of (a) damping capacity (b) storage modulus and (c) loss modulus base metal and FSPed sample.
quency. The maximum damping capacity (tan d) 0.0094 and 0.0071 was noticed for base metal and FSPed sample respectively at 20 Hz, which indicates that the damping capacity of the FSPed sample reduced by 21%. As frequency increases, the pinned dislocations at weak points may bow and undergo further motion under high vibration amplitude. An increase in dislocation density enhances damping capacity [15]. The decrease in damping capacity is due to the reduction of dislocation density after FSP (Table. 1). Damping peak at 220 °C for FSPed Al is observed for temperature dependent damping test. H.J. Jiang et al. and Shyi-Kaan Wu associated the damping peaks observed for aluminium in the temperature range 187–250 °C with grain boundary sliding. Thus, it is believed that the observed peak at 220 °C (Fig. 6a) could be due to grain boundary sliding, particularly for FSPed specimen. Fig. 6 (a) shows the damping capacity with temperature for pure Al and FSPed Al at constant strain amplitude (2.6 mm) and frequency (1 Hz). As temperature increases, the damping increased because of the viscous behaviour of grain boundaries (GBs), which converts mechanical energy into thermal energy [9]. From Fig. 6 (a) the damping capacity of the FSPed Al shown higher than the pure Al. It is evident from Figs. 1 and 2, the stir zone grain size (6.79 mm) is much lower than the base metal (45 mm). The decrease in grain size increases the grain boundary area. As the fraction of grain boundaries is more in FSPed specimen, it damps the vibration by means of GB sliding at high temperatures [16] which is better than the base metal. 4. Conclusions 1. The grain size was refined to 6.79 mm from its initial value of 45 mm through friction stir processing.
2. The intense heat generated during friction stirring softened the stir zone by reducing the dislocation density, thereby led to a reduction in hardness. 3. At room temperature, the damping capacity of the FSPed Al was lower than the base metal owing to the reduction in dislocation density. 4. At high temperatures (>130 °C), the damping capacity of FSP-ed Al was observed to be better than the base metal, this was due to increased grain boundary area as a result of microstructure refinement.
Acknowledgments The authors would like to thank DST-SERB for funding this research work through project No. ECR/2017/00122. Authors also grateful to DRDO-DMRL for extending their facility to conduct friction stir processing. References [1] Jinmin Zhang, Robert J. Perez, Catherin R. Wong, Effect of secondary phases on damping behaviour of metals, alloys and metal matrix composites, Mater. Sci. Eng. R13 (1994) 325–390. [2] E.J. Lavernia, R.J. Perej, J. Zhang, Damping behaviour of discontinuously reinforced Al alloys metal matrix composites, Metall. Mater. Trans. A (1995) 2803–2818. [3] Z.M. Zhang, C.J. Xu, J.C. Wang, H.Z. Lid, Damping behaviour of ultrafine-grained pure aluminum l2 and the damping mechanism, Acts Metall. Sin. (Engl. Lett.) 19 (2006) 223–227. [4] Fan Gen-lian, Li Zhi-qiang, Zhang Di, Damping capacity of BaTiO3/Al composites fabricated by hot extrusion, Trans. Nonferrous Met. Soc. China 22 (2012) 2512–2516. [5] Jingfeng Wang, Zhongshan Wu, Shan Gao, Ruopeng Lu, Dezhao Qin, Wenxiang Yang, Fusheng Pan, Optimization of mechanical and damping properties of
Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059
K. Venkateswara Reddy et al. / Materials Today: Proceedings xxx (xxxx) xxx
[6] [7]
[8]
[9]
[10]
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Please cite this article as: K. Venkateswara Reddy, R. Bheekya Naik, G. Madhusudhan Reddy et al., Damping capacity of friction stir processed commercial pure aluminium metal, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.059