International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06 81 Mechanical and Damping Properties of Silicon Bronze Alloys for Music Applications I Ketut Gede Sugita, R. Soekrisno, I Made Miasa, Suyitno Mechanical and Industrial Engineering Department, Gadjah Mada University, Jl. Grafika no 2, 5528 Yogyakarta, Indonesia. E-mail: sgita_03@yahoo.com Abstract-- An alloy for musical instruments should have high enough strength, hardness, specific elastic properties and low damping capacity. The high tin bronze alloys with composition 20-22 wt.% Sn has good acoustical properties, which is capable of producing long-lasting slowly damping vibrations but there is brittle materials. Cracks and fracture may appear on these materials. The study on mechanical and acoustic characteristic becomes the primary consideration in determining the new material as a musical instrument. The aim of this study is to investigate the effect of silicon fraction of Cu-(2.5-7.5) wt. % Si on mechanical and acoustical properties of bronze alloys for music instruments. As-cast Cu- (2.5-7.5) wt. % Si were cut from 250 x 55 x 15 mm of billet and manufactured for tensile, hardness, impact, and damping test specimen. Simply supported beam model was used for measuring damping capacity. Mechanical and damping properties of silicon bronze (Cu-Si) were studied. Investigation of bronze 20 wt. % Sn alloys was conducted as comparison. The results show that the mechanical properties and damping capacity of Cu-xSi is higher than Cu-20 wt. % Sn bronze alloys. The ductility and impact strength of silicon bronze also higher than this of tin Cu-20 wt.% Sn. It is recommended that Cu (5-7.5) wt. % Si are suitable to substitute tin bronze (Cu-20 wt.% Sn) for music instrument applications. I. INTRODUCTION Tin bronze alloys are one of the importance materials in industry for a long time, because of their good properties such as; high strength, thermal conductivity, machine ability, corrosion resistance and wear resistance [1]. It has a good formability. Its crystal structure is hexagonal closed packed (HCP), which is quite easy to shape in hot conditions [2] The high tin bronze alloys with composition 20-22 wt.% Sn has good acoustical properties, which is capable of producing long-lasting slowly damping vibrations [3-5]. It is commonly used for music materials such as bell, or Javanese and Balinese gamelan. This is a double phase alloy containing brittle particles of Cu 31 Sn 8 intermetallic (δphase), so that it becomes harder, more brittle than brass [6-7]. Also, tin bronze at low suffer from climate factor. It has a low frost resistance at temperature t = ( (20-25 o C), the metal becomes brittle and cracks may appear. Likewise, the sound that is produced becomes poor and short (5-6). The brittleness of bronze is a very important concern because cracked or broken often found in bell as well as gamelan as shown in Figure 1. Index Term-- Tin bronze, silicon bronze, mechanical properties and damping capacity crack Fig. 1. Crack on Balinese Gong Tin as the main alloying tin bronze have a great price and scarred element [3, 5], so that the resulting product becomes too expensive. Research on the weakness prevention efforts of high tin bronze and bronze acoustic as musical material has limited information The investigations of new materials need to be done to overcome the weaknesses of tin bronze. This research was carried out to investigate the mechanical properties and damping capacity of silicon bronze for music instruments. It is feasible to produce new alloys that have good mechanical properties, good acoustic and lower-priced, that is expected to as substitute for tin bronze
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06 82 2. EXPERIMENTAL DETAILS 2.1. Materials and process Bronze alloys TABLE I CHEMICAL COMPOSITION OF ALLOYS Content of elements wt% Cu Sn Si Pb Zn Mn S As Cu-20%Sn 79.18 19.1-1.18 0.505 0.001 0.014 0.055 Cu-2.5%Si 97.0 0.396 2.12 0.010 0.015 0.002-0.005 Cu-5%Si 93.83 0.276 5.16 0.16 0.427 0.002 0.042 0.074 Cu-5%Si 93.7 0.001 6.10 0.01 0.015 0.002-0.009 The studied bronze alloys in this research were Cu- (2.5-7.5) wt. %Si and Cu-20 wt. % Sn. Investigation of Cu- 20%Sn bronze alloy was conducted as comparison Table 1 shows the composition of the alloys. The commercial pure copper (99.99 wt. %) and commercial pure silicon (99.99 wt. %) were melted in crucible furnace at temperature of 1100 o C. The molten metal was poured into the preheated permanent mold at 200 o C, 300 o C, and 400 o C. Tensile test specimens were cut from as-cast materials 250 x 55 x 15 mm. They were made based on JIS Z2201. No.7 standard. Tensile test are conducted on Universal testing machine with a digital 20 KN capacity. Hardness test was carried out on Vickers type hardness-test. The notched specimens were used for impact toughness measurement, using a Charpy hammer impact testing machine. damping capacity measurement refers to the standard ASTM E 1876-01, it can be shown in Fig. 2. The logarithmic decrement method is used to calculate damping capacity. The logarithmic decrement δ, derived from the amplitude decay of specimen under free vibration, is given by [8]. 1 n ln Ai A Where A i and A i+n are the amplitudes of the i th cycle and the (i + n) th cycle, by n periods of oscillation. For the case of relatively small damping capacity, the relationship between δ and ζ is simple and it is given by [8]. in 2.2. Damping test ( ) The damping capacity was determined under simply supported free vibration bending model. The set up of 2.3 Microstructure observation The specimens for the metallographic investigation were prepared by cutting, mounting, grinding and polishing of the small (30 mm diameter, 15 mm long) specimens. Having cut them off, they were polished using silicon carbide abrasive paper of: 240, 400, 600, 800, 1000, 2000, grits, respectively, and then were polished perfectly using diamond pasta and etched using 10% HNO3+90% alcohol. These procedures were applied in accordance with standard metallographic techniques 3. RESULTS 3.1 Mechanical Properties The solidification rate was influenced by variations in the temperature gradient between the molten metal with the mold temperature. The greater the temperature difference between liquid metal with the mold temperature, Fig. 2. Set up of damping measurement the solidification rate will increase by lowering the solidification time. The solidification time and heat transfer affect the morphology of microstructure forms, such as grain size and dendrite arm spacing. The effect of silicon contents on mechanical properties such as the tensile strength, hardness, and impact strength of bronze silicon on the variation of mold temperature shows in Fig. 3-5 respectively. It can be seen from Fig. 2, that the ultimate tensile strength (UTS) increase on addition of 2.5% wt Si and 5% wt silicon, but there is a decrease on addition of 7.5% wt. Si. Also, the raising the molds temperature (200 o C to 400 o C) decreasing tensile strength. It indicated that the higher mould temperature on casting process, the lower the tensile strength in which the highest ultimate strength was 231.4 MPa at the temperature of 200 o C. Meanwhile the lowest ultimate strength was about.218.7 MPa at the temperature of 400 o C.
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06 83 Fig. 3 Tensile strength of tensile strength Fig 4 shows that the hardness of bronze increased along with the increase of the silicon percentage within the alloys. Besides, it was also affected by the variation of mold temperature. The lower of the mold temperature, the harder the bronze gained. The highest hardness materials were obtained from cast in mold temperature of 200 o C, 300 o C, and then 400 o C. In contrast, the impact strength decreased by the increase of silicon within the alloy. The strength impact as the result of the casting increased along with the temperature. It can be best shown in Fig 5. Fig. 5. Impact strength of bronze alloys 3.2 Damping Capacity The damping capacity of materials (internal damping) is the measure of a material s ability to dissipate elastic energy during mechanical vibration or wave propagation. Internal damping of materials is characterized by the energy dissipation associated with microstructure defect, such as grain boundaries, thermo elastic effect, dislocation motion in metals, and non uniform stresses. Fig. 5 shows the effect of wt % Si on the damping capacity of silicon bronze alloys. The damping capacity of materials decreased along with the increase of Si content. On the other hand, the increase of the mold temperature on casting resulted in the decrease of damping capacity. Figure 5 also shows that the damping capacity of 20 wt. % Sn tin bronze is relatively lower compared with 5 wt. % Si bronze alloy. It means that when the blades are made of tin bronze is vibrated; the blades will vibrate longer than the blades are made from silicon bronze. Fig. 4. Hardness strength of bronze alloys Fig. 6. Damping capacity of bronze alloys
3.3 Microstructure Examination International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06 84 a b Figs. 7a-c show that the microstructures of tin bronze 20 wt %. Sn and silicon bronze by containing varied of silicon content i.e.; 2.5 wt.% Si, 5 wt.% Si, and 7.5 wt.% Si, respectively. The microstructure of as-cast silicon bronze containing 2.5% Si is the largest structure of Cu primary α- phase. Only α phase was formed in this alloy. On the other hand, microstructure of silicon bronze containing 5 wt % Si is dendrite structures. The dendrite structural of silicon bronze 7.5 wt. % Si was finer than dendrite structure of silicon bronze 5 wt. % Si. (Fig.7c and d). The changes in the microstructures are associated with the addition of wt% Si. 4. DISCUSSIONS Mechanical properties and damping capacity are influenced by the variation of silicon composition in alloys and solidification process. The raising mold temperature affected the solidification process and increased the solidification time. High gradient temperature on liquid cooling region was affected by different temperature between pouring temperature and the mold temperature. When the thermal gradient between the mold and the molten metal is high, the cooling rate increases and solidification time decreases. The solidification rate affects the microstructure forms, such as grain size and dendrite arm spacing [10-13]. The microstructure that results from solidification directly affects on the mechanical properties of alloys [12, 13]. The ultimate strength (UTS) and hardness c d Fig. 7 Microstructure of bronze alloys a) Tin bronze 20 wt.% Sn, b) Silicon bronze 2.5 wt.% Si, c) Silicon bronze 5 wt.% Si, d) Silicon bronze 7.5 wt.% Si strength (VHN) increases as the solidification rate increases but impact strength decreases. In the metals and alloys, internal damping results from mechanical-energy dissipation within the material due to various microscopic and macroscopic processes. Material damping is extremely sensitive to the presence of defects. The defects in metals and alloys include point defects, dislocation, surface defect and bulk defect. point defects give rise to damping in the range of low to intermediate levels, line defects give rise to damping levels in the intermediate to high range, and surface defects give rise to damping levels in the high range [16]. The addition of silicon alloy produced finer dendrite structure, hence increases in the amount of grain boundaries. The greater grain boundary surface area more effectively block or movement of dislocation and the strength increased. The microstructure of the silicon bronze 7.5%wt Si consists of coarse δ phase in the microstructure. The area of grain boundary is small, so the damping capacity is low. 5. CONCLUSION The mechanical and damping properties of silicon bronze with the variation of wt% Si content were evaluated and compared with high tin bronze 20% Sn. It was found out that the variation content of Si and solidification rate affected the mechanical properties and damping capacity. The ultimate tensile strength (UTS) and hardness of material
International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06 85 increase as cooling rate increases but impact strength and damping capacity decreases. The properties of silicon bronze with containing 5% wt Si and 7% wt Si showed better mechanical properties and high ductility, when it is compared with high tin bronze. The damping capacity of silicon bronze is relatively the same with high tin bronze 20% Sn, therefore, it is suitable to substitute high tin bronze especially for music instrument applications. REFERENCES [1] Schmidt, R.F., Schmidt D.G., Selection and Application of Copper Alloy Castings, ASM Handbook, Metals Handbook, vol. 2, pp. 346, 1993. [2] Callister, W., Fundamental of Materials Science and Engineering. John Wiley and Son Inc. p. 179, 2001. [3] Gupta, R.B., Materials Science, Tech India Publication, p.239, 2001. [4] Hosford, F. W., Mechanical Behaviour of Materials, Cambridge University Press, 2005. [5] Lisovskii, V.A., Lisovskaya, O.B., Kochetkova, L.P, Favstov, Y..K., Sparingly Alloyed Bell Bronze with Elevated Parameters of Mechanical Properties Journal Metal Science and Heat treatment, vol. 49, 232-235, 2007. [6] Jang-Sik, P., Robert, B., Gordon, Traditions and Transitions in Korean Bronze Technology, Journal of Archaeological Science, pp. 1-12, 2007. [7] Favstov, Y. K., Zhravel, L.V., Kochetkova, L.P., Structure and Damping Capacity of Br022 Bell Bronze, Journal Metal science and Heat treatment, vol.45, pp. 449-451, 2003. [8] De Silva, C., Vibration Fundamental and Practice, Boca Raton London, CRC Press, 2000. [9] ASTM, E 1876-01, Standard Test Method for Dynamic Young, Shear Modulus, and Poisson s Ratio, by Impulse Excitation of vibration, ASTM International, 2002. [10] Campbell, J., The New Metallurgy of Cast Metals, Second Edition, Butterworth Heinemann, 2003. [11] Stefanescu, D.M., Science and Engineering of Casting Solidification, Kluwer Academic/Plenum Publisher, 2002. [12] Hemanth, J., Effect of cooling rate on dendrite arm spacing (DAS),eutectic cell count (ECC) and ultimate tensile strength (UTS) of austempered chilled ductile iron, Materials and Design 21, pp. 1-8, 2000. [13] Talamantes-Silva, M.A., Rodri, G, A. Talamantes-Silva, J.S., Valtierra, S., and Cola, L., Effect of Solidification Rate and Heat Treating on the Microstructure and Tensile Behavior of an Aluminum-Copper Alloy, The Minerals, Metals & Materials Society and ASM International, 2008. [14] Huang, S.K., Lia, N., Wen, Y.H., Tenga, Y.G., Xub S. Ding, Temperature Dependence of The Damping Capacity in Fe 19.35Mn Alloy, Journal of Alloys and Compounds vol.455,pp. 225 230, 2008. [15] Zhang, L,Y, Jiang, Y,H, Ma, Z, Shan, S.F., Jia, Y.Z., Fan, C.Z, Wang, W.K., Microstructural evolution of the supersaturated ZA27 alloy and its damping capacities, Journal of Materials Processing Technology, vol. 207, pp. 107 111, 2008.