- Email: [email protected]
SiCP multilayer composite manufactured by roll bonding
Materials and Design 42 (2012) 334–338
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Damping behavior of Al/SiCP multilayer composite manufactured by roll bonding E. Emadoddin ⇑, M. Tajally, M. Masoumi Dept. of Materials, Faculty of Engineering, Semnan University, Semnan, Iran
a r t i c l e
i n f o
Article history: Received 24 April 2012 Accepted 6 June 2012 Available online 19 June 2012 Keywords: Damping Multilayer composite Roll bonding
a b s t r a c t High damping materials comprising good mechanical properties as structural materials and high damping capacity for vibration loading are the best solutions for vibration problem. In current study, functionally graded material from composite sheets with different percentages of reinforcement was manufactured by hot rolling process. The damping behavior of base alloy composite including different percentages of SiC particles and Al/SiCP multilayer composite sheets was studied at room temperature conditions. The Al/SiCP composites were found to exhibit higher damping capacity compared to Al alloy. The damping capacity increased by increase in the percentage of reinforcement. Furthermore, Al/SiCP multilayer composite sheet provided higher damping capacity in comparison to Al alloy. Therefore, damping capacity enhanced by increasing the number of layers. The main source for damping behavior in composite materials is dislocation damping whereas in stepwise multilayer composite sheets, it comes from boundary conditions between layers. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Progress in technology and industry is based on developments in materials. New high efficient materials are able to increase service life, reduce energy consumption (light vehicles) and production costs. The damping capacity of a material is determined by evaluating the energy dissipated in the material during mechanical vibration. High damping materials, which have the ability to dissipate mechanical vibration energy, are valuable to be applied in the fields of noise control and in stabilizing structures in order to suppress mechanical vibrations and attenuate wave propagation [1–4]. Practical applications need low density materials that simultaneously exhibit high damping capacity and good ductility. However, in metals these properties are usually incompatible because of the dependence on microscopic mechanisms involved in strengthening and damping. Therefore, it would be interesting to develop new materials that simultaneously exhibit good mechanical properties and high damping [5]. This is possible only when the main mechanisms responsible for the dissipation of the vibration energy are independent of the mechanisms that control the hardening and strengthening. This new idea can be achieved by developing two reinforcement composites in which each phase plays a specific role; one in damping and the other in providing mechanical strength. The mechanical damping energy is usually dissipated as heat within the material under the vibration loading, loosing energy at interfaces or connections between two coupled members under relative motion, but it excludes energy dissipation ⇑ Corresponding author. Tel./fax: +98 231 3354 119. E-mail address: [email protected] (E. Emadoddin). 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.06.009
due to absorbents and various mechanical interactions among parts in the materials [6]. Aluminum alloys are widely used in structural applications because of their light weight, easy fabrication and high strength by alloying and heat treatment. Aluminum metal matrix composites (MMCs) are unique class of materials involving a reinforcing phase embedded in an aluminum alloy matrix [7–9]. Functionally gradient aluminum matrix composite reinforced by SiC particles exhibits good mechanical properties at high temperature and abrasive resistance [10,11]. Damping capacity, which is related to the internal friction of the material, is an essential mechanical property of MMCs which should be considered in the development of the MMCs microstructure. The energy dissipation in particle reinforcement composites essentially takes place as a result of different mechanisms such as thermal mismatch-induced dislocation, particle/matrix interface mechanism and damping due to the damage. Damping in laminated composite materials has recently been considered as a popular research area. Damping depends on the individual layer properties, inter-lamellar effect, stacking sequence and boundary conditions [12]. Although numerous investigations have been carried out on damping behavior of uniform and homogeneous bulk materials which are widely used in structural applications, there are few reports on multilayer composite sheets. In this study, having different percentages of reinforcement phase, Al/SiCP multilayer composite sheets were manufactured by hot rolling process as a new method in stepwise variation of functionally graded materials (FGMs). The effects of SiC particles of the MMCS, number of layers and stacking sequence on damping characteristics of laminated composite plates in five different setup layers were examined and reported.
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
2. Materials and methods 2.1. Samples manufacturing A roll bonding process was performed to produce multilayer composite and induce gradient of particle reinforcement along thickness as well as stepwise FGM composite. Commercial Al6061, Al6061/3%SiC, Al6061/7%SiC and Al6061/11% SiC sheets, with 1.0 mm thickness were annealed for 40 min at 420 °C to obtain recrystallized structure sheets used as an initial material in roll bonding process. The annealed sheets were cut to 60 mm width and 100 mm length, and were degreased and wire-brushed in order to obtain good bonding. The roll-bonding interfaces were also cleaned by acetone and scratched by stainless steel wire brush. After the surface treatment, certain pieces of sheet were stacked so that the brushed surfaces were in contact with each other and fixed tightly by copper wires. Stacks were kept in an electrical furnace at 300 °C for 300 s and then hot rolled by 50% reduction in thickness at one pass. Roll-bonding was carried out without any lubricant by using a two-high mill with a roll diameter of 310 mm. The roll peripheral speed was 17.5 m/min, so that the mean strain rate during the roll-bonding was 19 s1. Stacks manufactured by this methods were: Al–Al/7%SiC, Al–Al/11%SiC, Al–Al/ 3%SiC–Al/7%SiC, Al–Al/3%SiC–Al/3%SiC–Al/7%SiC and Al–Al/3%SiC– Al/7%SiC–Al/3%SiC–Al. Fig. 1 shows the successful bonding of five-layers stack specimen. In order to measure and compare the damping capacity of all sheets, they were tested at constant moment of inertia. For this purpose, all stacks were reduced to final thickness of 1 mm by cold rolling. To remove the effects of subsequent cold rolling, all stacks were annealed at 300 °C for 300 s. 2.2. Damping measurements The damping characteristics of the materials were obtained by subjecting the beam sample of the material to flexural vibrations [13]. The equipments used in this study are shown in Fig. 2. The test specimens were supported vertically as a cantilever beam in a clamping block. The vibration capacity of all samples was measured with a fixed clamping force at the same condition. An impulse hammer was also used to induce the excitation of the flexural vibrations of the beam, and the beam response was detected using a laser vibro-meter. The excitation and the response signals were digitalized and processed by a dynamic signal analyzer. This analyzer linked to a computer which performed the acquisition of signals, controlled the acquisition conditions and analyzed the signals acquired. The output of the test is represented by the frequency function and FRF graphs. An example for the FRF graphs on four-layer sheet
is shown in Fig. 3. As it can be seen, graphs are free from disturbance and two peaks in the graph represent two modes in the first movement of vibration which are easily detectable from each other. 3. Results and discussion 3.1. Damping capacity of composite sheets Frequency results for the first two modes for samples of different percent of reinforcing particles are given in Table 1. The results show that by increasing the percentage of reinforcing particles, the natural frequency increases. Since natural frequency is directly related to the material strength, by increasing the reinforcement particles and strengthening the material, this frequency increases. Damping capacity of the samples caused depreciation kinetic energy in the vibration loading by different mechanisms. Determination of damping capacity is not easily possible, since the basic mechanism of energy loss in the most real systems is not completely understood. Therefore determination of damping capacity by modal test is considered as the active mechanism. Values of damping capacity in the first mode for different percentages of reinforcing particles in constant thickness are presented in Fig. 4. The results indicate that by increasing the percentage of reinforcing phase, the damping capacity increases. It is obvious that the damping capacity of the composite is higher than that of Al6061 alloy. Results show that the increase of damping by internal friction is due to the presence of SiC particles. Wei et al. [14] also pointed out that the damping capacity of the pure aluminum reinforced by macroscopic graphite particles was increased by the enhancement in the amount of reinforcement particles. Improving the damping capacity of MMCs could be the results of contribution of addition of SiC reinforcement and the accompanying modification of the microstructure of the Al matrix. The intrinsic damping of SiC is low because of strength properties. Values of damping for as-cast Al2519 and SiC at room temperature are 0.008 and 0.0016–0.003, respectively [15]. Thus, the enhancement of damping behavior of composite cannot be attributed to SiC itself, and should be resulted from effect of SiC on aluminum matrix. The main modifications of the microstructure in the metal matrix Al/ SiC composite are reinforcement/matrix interfaces and thermal mismatch induced dislocation in the adjacent matrix. When the composite is cooled from elevated temperature of annealing or other processes, mismatch strains occur as a result of differential thermal contraction at the reinforcement/matrix interface, which generated dislocations sufficiently. The residual strain or accumulative strain produced as a consequence of the thermal mismatch may be calculated from the following equation [16]:
e ¼ Da DT
Fig. 1. SEM micrograph of five-layer bonded as-manufactured using roll bonding.
335
ð1Þ
where DT is the temperature change and Da is the difference between the coefficient of thermal expansion of reinforcement and metal matrix. Plastic deformation will be taken place by thermal mismatch strains, and subsequent processes create high dislocation density especially in the region adjacent to the matrix/reinforcement interface. The dislocation damping theory of Koehler, Granato, and Lücke was modified for metals with high stacking fault energy. It is assumed that the most abundant impurity of atom species interact only with the edge component of each dislocation. Granato–Lücke theory can offer the main factor for increasing the internal friction under cyclic loading. It is concluded that the dislocation damping is the primary damping mechanism especially at low temperature and that the damping peaks may be related to the dislocation motion. According to Zhang et al. [17], the dislocation structure is considered as a set of segments of length Ln which
336
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
Fig. 2. Schematic of damping measurement test equipments.
Fig. 3. Diagram showing the frequency function of Al–Al/3%SiC–Al/3%SiC–Al/7%SiC.
Table 1 Frequencies of the first two modes for sheets having different percent of reinforcing phase. Sheets
Al
Al/3%SiC
Al/7%SiC
Al/ 11%SiC
Frequency of first mode (HZ) Frequency of second mode (HZ)
98.8609 607.478
99.1409 602.0251
100.271 619.5935
105.9785 595.296
along them weak pinning points are distributed randomly, as shown in Fig. 5, which show that the dislocations are pinned by fine precipitation. At lower temperature, the dislocation can just drag swing weak pinning points (such as some solute atoms and vacancies) moving and thus dissipating energies by increasing the temperature. The stress for break-away from weak pinning points is decreased when the process is thermally activated. At a certain temperature, the dislocation can move faster and then break-away, in a snow-slide like mode, from the weak pinning point which can result in a long and comparatively free dislocation in the condition
Fig. 4. Damping capacity of first mode for sheets having different percent of reinforcing phase.
of hard pinning (such as network node of dislocation and the second phase). Therefore, the energy dissipated by dislocation movement will not increase but the damping value may decrease slightly
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
337
matrix and reinforcement particles are not strong enough and there are a lot of holes around the aluminum matrix as a result of detaching of SiC particles during preparation that can be observed in Fig. 6, due to weak bonded in particles/matrix interface which enhances damping capacity in Al/SiCP Composites.
3.2. Damping capacity of multilayer composite sheets
Fig. 5. The damping mechanism according to dislocation movement.
Fig. 6. Presence and absence of SiC particulate in aluminum matrix.
Table 2 Damping capacity of first two mode for multilayer composite sheets. Sheet
Al–Al/ 7%SiC
Al–Al/ 11%SiC
Al–Al/3%SiC– Al–Al/3%SiC– Al–Al/ 3%SiC–Al/ Al/3%SiC–Al/ Al/7%SiC–Al/ 3%SiC–Al 7%SiC 7%SiC
97.7371 98.049 93.4204 97.1153 Frequency for first mode (HZ) Frequency for 663.6603 596.6999 612.0807 628.6523 second mode (HZ)
94.6831
580.733
inducing damping peak. Later the damping may increase again as a consequence of the contribution of interface damping. It is found that the dislocation motion is the main course of damping generation at low temperature [18]. Moreover, the interface between the reinforcement and matrix also plays an important role in the damping behavior of the composite materials [19]. It seems that the bond between metal
Frequency results of the first two modes for samples are given in Table 2. The results show that by increasing the number of layers in constant thickness of sheets, the natural frequencies are decreased; in the other words, its period is increased. Since the natural frequency is directly related to the material strength, the reduction in natural frequency by increasing the number of layers of stack due to the bond strength is confirmed (Fig. 7). Values of damping capacity in the first mode for stepwise multilayer composite sheets are shown in Fig. 8. The results show that by increasing the number of layers in constant thickness of sheets, the damping capacity increases. In the case of stepwise laminated composite, the main source for mechanical damping in laminated composite sheets comes from boundary conditions between layers and intrinsic damping capacity of each layer. To obtain well bonding between layers, heavy deformation (r = 50%) was applied into the sheets by rolling that is a source of dislocation generation. Thus, internal friction and damping capacity were increased. During deforming dissimilar sheets, softer layer tolerated more strain than the harder one. Hence, the dislocation density would be increased. Dislocations produced a regular direction for reducing the energy of internal system which induced shear bands around interfaces. Stress concentration caused by the accumulated dislocation finally led to interfaces rupture, until the two adjacent layers were fully integrated in some zone. This process caused the damping capacity to be increased during manufacturing multilayer sheets. Moreover, following brushing, preparation and induction of deformation at relatively high temperature, the dislocation density increased. By occurrence of recrystallization in the interfaces and formation of finer grain by increasing the grain boundary density lead to more energy absorption. Then, the internal friction and damping capacity in manufactured sheets increased consequently. Also, residual shear strain resulting from roll bonding process in thickness direction enhanced the damping capacity. In general, by increasing the number of layers, the damping capacity of multilayer materials would increase. By increasing the temperature, the damping capacity increased [20]. Zhang et al. [21] have pointed out that in 6061Al/SiCp MMC, at relatively low temperatures the possible dominant damping mechanisms are intrinsic damping of reinforcing particulate, matrix dislocation damping, and particulate/matrix interface damping, while at high temperatures, grain boundary sliding and interface sliding are likely to be responsible for a large portion of the observed damping. The interface damping resulted from the mobility of
Fig. 7. Shear strength for multilayer composite sheet, two-layer stack: Al–Al/11%SiC, three-layer stack: Al–Al/3%SiC–Al/7%SiC, four-layer stack: Al–Al/3%SiC–Al/3%SiC–Al/ 7%SiC and five-layer stack: Al–Al/3%SiC–Al/7%SiC–Al/3%SiC–Al.
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Fig. 8. Damping capacity of first mode for multilayer composite sheets.
the incoherent microstructure at the interface and interface slip. When the temperature is elevated, the interface effect may become more significant because the metal matrix becomes soft relative to the ceramic reinforcement; hence, irreversible movement at the interface is likely to occur. Therefore, the interface damping may be dominant for Al/SiC at high temperature. Accordingly at high temperature, the high background damping of the MMCs can be attributed to the interface damping. 4. Conclusion Practically, applied materials having high damping capacity provide an effective alternative method for manufacturing MMC materials. The evaluation of the mechanical properties and damping of multilayer composites containing different percentages of reinforcement particles led to the following conclusions: The results show that by increasing the percentage of reinforcing particles, the natural frequency and damping capacity increases. The results indicate that by increasing the number of layers in constant thickness of sheets, the natural frequencies decrease, but the damping capacity increases. The higher percentages of reduction in the area and increasing the number of layers lead to higher damping capacity. The higher damping capacity was achieved at high temperature of hot roll bonding which was in agreement with Zhang et al. [21].
References [1] Zhang JM, Perez RJ, Wong CR, Lavernia EJ. Effects of secondary phases on the damping behavior of metals, alloys and metal–matrix composites. Mater Sci Eng R 1994;13:325–89. [2] Zhang J, Perez RJ, Lavernia EJ. Documentation of damping capacity of metallic, ceramic and metal–matrix composite materials. J Mater Sci 1993;28(9): 2395–2404. [3] Lavernia EJ, Perez RJ, Zhang J. Damping behavior of discontinuously reinforced al-alloy metal–matrix composites. Metall Mater Trans A 1995;26(11): 2803–2818.
[4] Sugita IKG, Soekrisno R, Suyitno IMM. Mechanical and damping properties of silicon bronze alloys for music applications. Int J Eng & Technol IJET-IJENS 2011;11(6):98–105. [5] Schaller R. Metal matrix composites, a smart choice for high damping materials. J Alloy Compd 2003;355:131–5. [6] Lu H, Wang X, Zhang T, Cheng Z, Fang Q. Design, fabrication, and properties of high damping metal matrix composite. Materials 2009;2(3):958–77. [7] Rohatgi PK, Nath D, Singh SS. Factors affecting the damping capacity of cast aluminum matrix composites. J Mater Sci 1994;29(22):5975–84. [8] Chen MC, Hsieh CC, Wu W. Microstructural characterization of Al/Mg alloy interdiffusion mechanism during accumulative roll bonding. Met Mater Int 2007;13(3):201–5. [9] Nasiri Dehsorkhi R, Qods F, Tajally M. Investigation on microstructure and mechanical properties of Al–Zn composite during accumulative roll bonding (ARB) process. Mater Sci Eng A 2011;530:63–72. [10] Chunlei J. Study on damping behavior of FeAl3 reinforced commercial purity aluminum. Mater Des 2007;28:1711–3. [11] Freund LB. Some elementary connections between curvature and mismatch strain in compositionally graded thin films. J Mech Phys Solids 1996;44(5): 723–736. [12] Zabaras N, Pervez T. Viscous damping approximation of laminated anisotropic composite plates using finite element method. Comput Methods Appl Mech Eng 1990;81:291–316. [13] Green MF, modal test methods for bridges: a review. In: Proceedings of the 14th international modal analysis conference, Nashville, TN, vol. 1; 1995. p.552–558. [14] Wei JN, Cheng HF, Zhang YF, Han FS, Zhou ZC, Shui JP. Effects of macroscopic graphite particulates on the damping behavior of commercially pure aluminum. Mater Sci Eng A 2002;325:444–53. [15] Nishiyama K, Yamanaka M, Omori M, Umekawa S. High-temperature dependence of the internal friction and modulus change of tetragonal ZrO2, Si3N4 and SiC. J Mater Sci Lett 1990;9:526–8. [16] San Marchi C, Kouzeli M, Rao R, Lewis JA, Dunand DC. Alumina–aluminum interpenetrating-phase composites with three-dimensional periodic architecture. Scripta Mater. 2003;49:861–6. [17] Zhang J, Perez RJ, Lavernia EJ. Dislocation-induced damping in metal matrix composites. J Mater Sci 1993;28(3):835–46. [18] Gu J, Zhang X, Gu M, Gu M, Wang X. Internal friction peak and damping mechanism in high damping 6061Al/Sicp/Gr hybrid metal matrix composite. J Alloy Compd 2004;372:304–8. [19] Zhang Y, Ma N, Wang H. Effect of ti on the damping behavior of aluminum composite reinforced with in-situ TiB2 particulate. Scripta Mater 2005;53: 1171–1174. [20] Tam KF, Tjong SC. Internal friction and dynamic Young’s modulus of aluminum composites reinforced in-situ with TiB2 and Al2O3 particulates. Mater Sci Technol 2004;20(8):1055–8. [21] Zhang H, Gu M. Internal friction behavior in sic particulate reinforced aluminum metal matrix composite in thermal cycling. J Alloy Compd 2006; 426:247–52.
Contents lists available at SciVerse ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Damping behavior of Al/SiCP multilayer composite manufactured by roll bonding E. Emadoddin ⇑, M. Tajally, M. Masoumi Dept. of Materials, Faculty of Engineering, Semnan University, Semnan, Iran
a r t i c l e
i n f o
Article history: Received 24 April 2012 Accepted 6 June 2012 Available online 19 June 2012 Keywords: Damping Multilayer composite Roll bonding
a b s t r a c t High damping materials comprising good mechanical properties as structural materials and high damping capacity for vibration loading are the best solutions for vibration problem. In current study, functionally graded material from composite sheets with different percentages of reinforcement was manufactured by hot rolling process. The damping behavior of base alloy composite including different percentages of SiC particles and Al/SiCP multilayer composite sheets was studied at room temperature conditions. The Al/SiCP composites were found to exhibit higher damping capacity compared to Al alloy. The damping capacity increased by increase in the percentage of reinforcement. Furthermore, Al/SiCP multilayer composite sheet provided higher damping capacity in comparison to Al alloy. Therefore, damping capacity enhanced by increasing the number of layers. The main source for damping behavior in composite materials is dislocation damping whereas in stepwise multilayer composite sheets, it comes from boundary conditions between layers. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Progress in technology and industry is based on developments in materials. New high efficient materials are able to increase service life, reduce energy consumption (light vehicles) and production costs. The damping capacity of a material is determined by evaluating the energy dissipated in the material during mechanical vibration. High damping materials, which have the ability to dissipate mechanical vibration energy, are valuable to be applied in the fields of noise control and in stabilizing structures in order to suppress mechanical vibrations and attenuate wave propagation [1–4]. Practical applications need low density materials that simultaneously exhibit high damping capacity and good ductility. However, in metals these properties are usually incompatible because of the dependence on microscopic mechanisms involved in strengthening and damping. Therefore, it would be interesting to develop new materials that simultaneously exhibit good mechanical properties and high damping [5]. This is possible only when the main mechanisms responsible for the dissipation of the vibration energy are independent of the mechanisms that control the hardening and strengthening. This new idea can be achieved by developing two reinforcement composites in which each phase plays a specific role; one in damping and the other in providing mechanical strength. The mechanical damping energy is usually dissipated as heat within the material under the vibration loading, loosing energy at interfaces or connections between two coupled members under relative motion, but it excludes energy dissipation ⇑ Corresponding author. Tel./fax: +98 231 3354 119. E-mail address: [email protected] (E. Emadoddin). 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.06.009
due to absorbents and various mechanical interactions among parts in the materials [6]. Aluminum alloys are widely used in structural applications because of their light weight, easy fabrication and high strength by alloying and heat treatment. Aluminum metal matrix composites (MMCs) are unique class of materials involving a reinforcing phase embedded in an aluminum alloy matrix [7–9]. Functionally gradient aluminum matrix composite reinforced by SiC particles exhibits good mechanical properties at high temperature and abrasive resistance [10,11]. Damping capacity, which is related to the internal friction of the material, is an essential mechanical property of MMCs which should be considered in the development of the MMCs microstructure. The energy dissipation in particle reinforcement composites essentially takes place as a result of different mechanisms such as thermal mismatch-induced dislocation, particle/matrix interface mechanism and damping due to the damage. Damping in laminated composite materials has recently been considered as a popular research area. Damping depends on the individual layer properties, inter-lamellar effect, stacking sequence and boundary conditions [12]. Although numerous investigations have been carried out on damping behavior of uniform and homogeneous bulk materials which are widely used in structural applications, there are few reports on multilayer composite sheets. In this study, having different percentages of reinforcement phase, Al/SiCP multilayer composite sheets were manufactured by hot rolling process as a new method in stepwise variation of functionally graded materials (FGMs). The effects of SiC particles of the MMCS, number of layers and stacking sequence on damping characteristics of laminated composite plates in five different setup layers were examined and reported.
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
2. Materials and methods 2.1. Samples manufacturing A roll bonding process was performed to produce multilayer composite and induce gradient of particle reinforcement along thickness as well as stepwise FGM composite. Commercial Al6061, Al6061/3%SiC, Al6061/7%SiC and Al6061/11% SiC sheets, with 1.0 mm thickness were annealed for 40 min at 420 °C to obtain recrystallized structure sheets used as an initial material in roll bonding process. The annealed sheets were cut to 60 mm width and 100 mm length, and were degreased and wire-brushed in order to obtain good bonding. The roll-bonding interfaces were also cleaned by acetone and scratched by stainless steel wire brush. After the surface treatment, certain pieces of sheet were stacked so that the brushed surfaces were in contact with each other and fixed tightly by copper wires. Stacks were kept in an electrical furnace at 300 °C for 300 s and then hot rolled by 50% reduction in thickness at one pass. Roll-bonding was carried out without any lubricant by using a two-high mill with a roll diameter of 310 mm. The roll peripheral speed was 17.5 m/min, so that the mean strain rate during the roll-bonding was 19 s1. Stacks manufactured by this methods were: Al–Al/7%SiC, Al–Al/11%SiC, Al–Al/ 3%SiC–Al/7%SiC, Al–Al/3%SiC–Al/3%SiC–Al/7%SiC and Al–Al/3%SiC– Al/7%SiC–Al/3%SiC–Al. Fig. 1 shows the successful bonding of five-layers stack specimen. In order to measure and compare the damping capacity of all sheets, they were tested at constant moment of inertia. For this purpose, all stacks were reduced to final thickness of 1 mm by cold rolling. To remove the effects of subsequent cold rolling, all stacks were annealed at 300 °C for 300 s. 2.2. Damping measurements The damping characteristics of the materials were obtained by subjecting the beam sample of the material to flexural vibrations [13]. The equipments used in this study are shown in Fig. 2. The test specimens were supported vertically as a cantilever beam in a clamping block. The vibration capacity of all samples was measured with a fixed clamping force at the same condition. An impulse hammer was also used to induce the excitation of the flexural vibrations of the beam, and the beam response was detected using a laser vibro-meter. The excitation and the response signals were digitalized and processed by a dynamic signal analyzer. This analyzer linked to a computer which performed the acquisition of signals, controlled the acquisition conditions and analyzed the signals acquired. The output of the test is represented by the frequency function and FRF graphs. An example for the FRF graphs on four-layer sheet
is shown in Fig. 3. As it can be seen, graphs are free from disturbance and two peaks in the graph represent two modes in the first movement of vibration which are easily detectable from each other. 3. Results and discussion 3.1. Damping capacity of composite sheets Frequency results for the first two modes for samples of different percent of reinforcing particles are given in Table 1. The results show that by increasing the percentage of reinforcing particles, the natural frequency increases. Since natural frequency is directly related to the material strength, by increasing the reinforcement particles and strengthening the material, this frequency increases. Damping capacity of the samples caused depreciation kinetic energy in the vibration loading by different mechanisms. Determination of damping capacity is not easily possible, since the basic mechanism of energy loss in the most real systems is not completely understood. Therefore determination of damping capacity by modal test is considered as the active mechanism. Values of damping capacity in the first mode for different percentages of reinforcing particles in constant thickness are presented in Fig. 4. The results indicate that by increasing the percentage of reinforcing phase, the damping capacity increases. It is obvious that the damping capacity of the composite is higher than that of Al6061 alloy. Results show that the increase of damping by internal friction is due to the presence of SiC particles. Wei et al. [14] also pointed out that the damping capacity of the pure aluminum reinforced by macroscopic graphite particles was increased by the enhancement in the amount of reinforcement particles. Improving the damping capacity of MMCs could be the results of contribution of addition of SiC reinforcement and the accompanying modification of the microstructure of the Al matrix. The intrinsic damping of SiC is low because of strength properties. Values of damping for as-cast Al2519 and SiC at room temperature are 0.008 and 0.0016–0.003, respectively [15]. Thus, the enhancement of damping behavior of composite cannot be attributed to SiC itself, and should be resulted from effect of SiC on aluminum matrix. The main modifications of the microstructure in the metal matrix Al/ SiC composite are reinforcement/matrix interfaces and thermal mismatch induced dislocation in the adjacent matrix. When the composite is cooled from elevated temperature of annealing or other processes, mismatch strains occur as a result of differential thermal contraction at the reinforcement/matrix interface, which generated dislocations sufficiently. The residual strain or accumulative strain produced as a consequence of the thermal mismatch may be calculated from the following equation [16]:
e ¼ Da DT
Fig. 1. SEM micrograph of five-layer bonded as-manufactured using roll bonding.
335
ð1Þ
where DT is the temperature change and Da is the difference between the coefficient of thermal expansion of reinforcement and metal matrix. Plastic deformation will be taken place by thermal mismatch strains, and subsequent processes create high dislocation density especially in the region adjacent to the matrix/reinforcement interface. The dislocation damping theory of Koehler, Granato, and Lücke was modified for metals with high stacking fault energy. It is assumed that the most abundant impurity of atom species interact only with the edge component of each dislocation. Granato–Lücke theory can offer the main factor for increasing the internal friction under cyclic loading. It is concluded that the dislocation damping is the primary damping mechanism especially at low temperature and that the damping peaks may be related to the dislocation motion. According to Zhang et al. [17], the dislocation structure is considered as a set of segments of length Ln which
336
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
Fig. 2. Schematic of damping measurement test equipments.
Fig. 3. Diagram showing the frequency function of Al–Al/3%SiC–Al/3%SiC–Al/7%SiC.
Table 1 Frequencies of the first two modes for sheets having different percent of reinforcing phase. Sheets
Al
Al/3%SiC
Al/7%SiC
Al/ 11%SiC
Frequency of first mode (HZ) Frequency of second mode (HZ)
98.8609 607.478
99.1409 602.0251
100.271 619.5935
105.9785 595.296
along them weak pinning points are distributed randomly, as shown in Fig. 5, which show that the dislocations are pinned by fine precipitation. At lower temperature, the dislocation can just drag swing weak pinning points (such as some solute atoms and vacancies) moving and thus dissipating energies by increasing the temperature. The stress for break-away from weak pinning points is decreased when the process is thermally activated. At a certain temperature, the dislocation can move faster and then break-away, in a snow-slide like mode, from the weak pinning point which can result in a long and comparatively free dislocation in the condition
Fig. 4. Damping capacity of first mode for sheets having different percent of reinforcing phase.
of hard pinning (such as network node of dislocation and the second phase). Therefore, the energy dissipated by dislocation movement will not increase but the damping value may decrease slightly
E. Emadoddin et al. / Materials and Design 42 (2012) 334–338
337
matrix and reinforcement particles are not strong enough and there are a lot of holes around the aluminum matrix as a result of detaching of SiC particles during preparation that can be observed in Fig. 6, due to weak bonded in particles/matrix interface which enhances damping capacity in Al/SiCP Composites.
3.2. Damping capacity of multilayer composite sheets
Fig. 5. The damping mechanism according to dislocation movement.
Fig. 6. Presence and absence of SiC particulate in aluminum matrix.
Table 2 Damping capacity of first two mode for multilayer composite sheets. Sheet
Al–Al/ 7%SiC
Al–Al/ 11%SiC
Al–Al/3%SiC– Al–Al/3%SiC– Al–Al/ 3%SiC–Al/ Al/3%SiC–Al/ Al/7%SiC–Al/ 3%SiC–Al 7%SiC 7%SiC
97.7371 98.049 93.4204 97.1153 Frequency for first mode (HZ) Frequency for 663.6603 596.6999 612.0807 628.6523 second mode (HZ)
94.6831
580.733
inducing damping peak. Later the damping may increase again as a consequence of the contribution of interface damping. It is found that the dislocation motion is the main course of damping generation at low temperature [18]. Moreover, the interface between the reinforcement and matrix also plays an important role in the damping behavior of the composite materials [19]. It seems that the bond between metal
Frequency results of the first two modes for samples are given in Table 2. The results show that by increasing the number of layers in constant thickness of sheets, the natural frequencies are decreased; in the other words, its period is increased. Since the natural frequency is directly related to the material strength, the reduction in natural frequency by increasing the number of layers of stack due to the bond strength is confirmed (Fig. 7). Values of damping capacity in the first mode for stepwise multilayer composite sheets are shown in Fig. 8. The results show that by increasing the number of layers in constant thickness of sheets, the damping capacity increases. In the case of stepwise laminated composite, the main source for mechanical damping in laminated composite sheets comes from boundary conditions between layers and intrinsic damping capacity of each layer. To obtain well bonding between layers, heavy deformation (r = 50%) was applied into the sheets by rolling that is a source of dislocation generation. Thus, internal friction and damping capacity were increased. During deforming dissimilar sheets, softer layer tolerated more strain than the harder one. Hence, the dislocation density would be increased. Dislocations produced a regular direction for reducing the energy of internal system which induced shear bands around interfaces. Stress concentration caused by the accumulated dislocation finally led to interfaces rupture, until the two adjacent layers were fully integrated in some zone. This process caused the damping capacity to be increased during manufacturing multilayer sheets. Moreover, following brushing, preparation and induction of deformation at relatively high temperature, the dislocation density increased. By occurrence of recrystallization in the interfaces and formation of finer grain by increasing the grain boundary density lead to more energy absorption. Then, the internal friction and damping capacity in manufactured sheets increased consequently. Also, residual shear strain resulting from roll bonding process in thickness direction enhanced the damping capacity. In general, by increasing the number of layers, the damping capacity of multilayer materials would increase. By increasing the temperature, the damping capacity increased [20]. Zhang et al. [21] have pointed out that in 6061Al/SiCp MMC, at relatively low temperatures the possible dominant damping mechanisms are intrinsic damping of reinforcing particulate, matrix dislocation damping, and particulate/matrix interface damping, while at high temperatures, grain boundary sliding and interface sliding are likely to be responsible for a large portion of the observed damping. The interface damping resulted from the mobility of
Fig. 7. Shear strength for multilayer composite sheet, two-layer stack: Al–Al/11%SiC, three-layer stack: Al–Al/3%SiC–Al/7%SiC, four-layer stack: Al–Al/3%SiC–Al/3%SiC–Al/ 7%SiC and five-layer stack: Al–Al/3%SiC–Al/7%SiC–Al/3%SiC–Al.
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Fig. 8. Damping capacity of first mode for multilayer composite sheets.
the incoherent microstructure at the interface and interface slip. When the temperature is elevated, the interface effect may become more significant because the metal matrix becomes soft relative to the ceramic reinforcement; hence, irreversible movement at the interface is likely to occur. Therefore, the interface damping may be dominant for Al/SiC at high temperature. Accordingly at high temperature, the high background damping of the MMCs can be attributed to the interface damping. 4. Conclusion Practically, applied materials having high damping capacity provide an effective alternative method for manufacturing MMC materials. The evaluation of the mechanical properties and damping of multilayer composites containing different percentages of reinforcement particles led to the following conclusions: The results show that by increasing the percentage of reinforcing particles, the natural frequency and damping capacity increases. The results indicate that by increasing the number of layers in constant thickness of sheets, the natural frequencies decrease, but the damping capacity increases. The higher percentages of reduction in the area and increasing the number of layers lead to higher damping capacity. The higher damping capacity was achieved at high temperature of hot roll bonding which was in agreement with Zhang et al. [21].
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