Comparison of Wear and Mechanical Properties of Copper Alloys Used as Welding Electrodes and Plunger Tips

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1 Comparison of Wear and Mechanical Properties of Copper Alloys Used as Welding Electrodes and Plunger Tips Tuba Özeren, Taner Yenigün, Nebi Akgün, Erkan Artut, Feriha Birol Sağlam Metal A.Ş., Department of R&D, Kocaeli, Turkey Abstract CuCoNiBe and CuNiSi copper alloys are widely used as welding electrodes and molding applications due to their high wear resistance and good electrical conductivity properties. In this study, wear properties of two CuNiSi alloys and a CuCoNiBe alloy were compared at room and Additionally, mechanical properties, hardness and electrical conductivity values of the alloys were determined and evaluated. 1. Introduction High copper alloys are widely used for resistance welding electrodes and molding tool applications due to their properties such as high strength and wear properties, good electrical and thermal conductivity. Among high copper alloys, Cu-Be alloys have attracted much attention for such applications. However, their higher cost due to expensive Be content have always led to searching cheaper alternative copper alloys. Cu-Ni-Si alloys are considered as a promising copper alloy group alternative to Cu-Be alloys for such applications. CuNiSi alloys, also called Corson alloys, are age hardening alloys. They are used either without addition of alloying element or their various properties can be improved adding alloying elements such as Cr, Zr, Mg. [1-7]. Higher wear resistance and mechanical properties are important properties for resistance welding electrode and molding tool applications. The alloys could be classified by measuring mechanical properties and wear resistance. In this study, wear properties of a Be containing CuCoNiBe (CCNB) and two Ni, Si containing CuNiSiCr (NSH) and CuNiSiCrZr (NSS) alloys prepared in acco alternative alloy to Be containing copper alloy. Wear tests and under a load of 10 N. Weight loss and friction coefficients of the alloys were compared in order to specifies alternatives. Additionally microstructure and mechanical properties of the alloys were determined and evaluated with their wear test results. 2. Experimental 2.1. Materials Three alloys were cast in permanent mould. Their chemical analysis after casting are given Table 1-2. The samples taken from the ingots were submitted to heat treatments of solutionizing and ageing following hot onditions were applied. The specimens were prepared in the dimensions of 46*46mm cutting from the forged rods. Table 1. Chemical Composition of NSH and NSS Alloys. Materia l Cu Ni Si Cr Fe Zr NSH 95,3 3,15 0,79 0,47 0, NSS 95,9 2,49 0,74 8 0,39 4 0, ,3 Table 2. Chemical Composition of CCNB Alloy. Material Cu Ni Co Be Fe CCNB 97,3 1,05 1,06 0,459 0, Metallography Microstructure of the aged samples after heat treatments were examined using a Nikon Eclipse MA 100 model light microscope after metallographic preparation. The samples were grounded with first coarse and then fine sand papers and final surfaces were polis diamond solution. The samples were etched with a chemical solution of 50 ml HCl + 10 ml + 10 g ml to determine the phases. 248 IMMC th International Metallurgy & Materials Congress

2 Bildiriler Kitabı TMMOB Metalurji ve Malzeme Mühendisleri Odası Eğitim Merkezi 2.3. Mechanical tests and conductivity measurements Mechanical tests and conductivity measurements were made on the prepared samples. Hardness measurements were made by using Vickers hardness tester of Struers Duramin under 0,5 kgf load at room temparature and after wear tests at. Hardness values were determined by taking average of multiple measurements. Tensile tests were performed according to ASTM E8/E8M using MTS C universal test machine. Dimensions of the tensile test samples are shown in Figure 1. Electrical conductivity was measured using a GE Inspection Tech Auto Sigma 3000 instrument. a Figure 1. Dimension of the tensile test samples Wear tests b Wear tests were conducted under the load of 10N at room T30M-HT (Figure 2). Aluminium oxide balls were forced against copper alloy disc samples. Wear samples were of friction coefficient for both temperatures were determined to evaluate wear resistance of the alloys. c Figure 3. Optical light microscope images of the aged alloys NSH, NSS, c) CCNB. Figure 2. Pin on disc wear test parameters. 3. Results and Discussion 3.1. Microstructural characterization of aged condition Microstructure of three alloys NSH (CuNiSiCr), NSS (CuNiSiCrZr), and CCNB (CuCoNiBe) are given in Figure 3a, b and c respectively.. CuNiSi alloys, also called Corson alloys, are age hardening alloys. They can be used without any alloying element or their various properties can be improved adding alloying elements such as Cr, Zr, Mg. The resulting precipitates and their formation mechanism are reported in various studies [4]. The precipitation reaction can not only improve strength but also enhance the electrical conductivity of the alloy by depletion of the solute elements from the matrix. Age hardening in this system was first investigated by Corson and the precipitating - -binary section of the Cu-Ni-Si 19. Uluslararası Metalurji ve Malzeme Kongresi IMMC

3 ternary diagram [5]. In Cr containing Cu-Ni-Si alloys, Cr 2Si 3 - -Cu matrix [2]. Optical micrographs of the NSS and NSH alloys show that very small partical distribution at aged conditions, whi - In the solidification of Cu- -Cu and resembling Chinese scripts primary beryllides are crystallized from the liquid phase. T -phase peritectic reaction occurs with decrease in temperature. This phase transforms into beryllides phase that occurs during solidification is best observed as a blue-gray color in the polished state. The secondary beryllium phase is seen in a certain crystallographic orientation and in plaques morphology. precipitates with aging [8]. The microstructure images of the CCNB alloy, it is observed that the (Ni,Co) beryllides reprecipitate in the copper phase by aging (Figure 3c) Wear resistance and friction coefficient Mass loses (mg) of there alloys after wear tests at room temperature and are shown in Figure 4 and Table 5. Mass loss results of room temperatures experiments reveal that CCNB has the highest wear loss (27,5 mg) while NSS has the lowest one (9,1 mg) (Table 5). On the other hand, all of the alloys have lower mass loss (NSS, NSH and CCNB 7; 8,8 and 8,6 mg respectively) at 400 compared to room temperature and their mass loss values were close to each other. It is expected that the harder the alloy is the higher wear resistance according to Archard wear equation [9,10]. However, the hardest alloy CCNB shows the higher mass loss at room temperature indicating lower wear resistance. Explanation of this result needs to more examination of the worn surfaces by using SEM and 3D profilometer Hardness, conductivity and mechanical properties of alloys Table 3. shows hardness and electrical conductivity of the aged alloys. The alloy of CCNB has the highest hardness, tensile and yield strength and electrical conductivity while NSS has the lowest ones as expected. hardness of the alloys increases likely due to progression of aging at higher temperatures. Table 3.Hardness values of the alloys after wear tests at room and 400 C and electrical conductivity measurements. Material Hardness (HV-0.5 kgf) Temperatur 400 Electrical Conductivity (MS/m) NSS 21,5 NSH 23,7 CCNB 26,4 Table 4. Mechanical properties of the alloys. Material Tensile Strength (MP Yield Strength (MP Elongation NSS 589,6 498,7 12,3 NSH 764,1 662,7 7,8 CCNB 809,7 668,3 14,9 Figure 4. Mass loss in specimens as a result of wear tests. Table 5. Values of mass losses (mg). Temperature (22) Mass Loss (mg) NSS NSH CCNB 9,1 17,3 27, ,8 8,6 The behavior of the friction coefficient of three alloys was similar at both test temperatures (Fig 5, 6 and 7 and Table 250 IMMC th International Metallurgy & Materials Congress

4 Bildiriler Kitabı TMMOB Metalurji ve Malzeme Mühendisleri Odası Eğitim Merkezi 6). All the alloys have lower friction coefficient values at the beginning of the wear test at room temperature. Then, it reached to higher values with large scatterings after from a distance changing depending on alloy (300 m for NSS and NSH, 100 m for CCNB). At high test temperature stable and lower along all wear test. Table 6. Approximate values of friction coefficient of the Temperature Temperature Coefficient of Friction NSS NSH CCNB 0.5 to (after 300 m) 0.5 to (after 300 m) 0.5 to (after 100 m) Figure 6. Friction coefficient graphs of NSS samples obtained during wear test room temperature and at Although mass loss results and hardness values of the alloys at room temperature wear test are contradictory and require further investigation, high temperature results appears to be more meaningful and consistent. Furthermore, since both applications are high temperature application, high temperature wear results appear to be more suitable in terms of determining alternative alloy for electrode and mold application. Figure 5. Friction coefficient graphs of NSH sample obtained during wear test room temperature and at. 19. Uluslararası Metalurji ve Malzeme Kongresi IMMC

5 Figure 7. Friction coefficient graphs of CCNB sample obtained during wear test room temperature and at 1. Conclusions Among investigated three alloys NSS (CuNiSiCrZr), NSH (CuNiSiCr), and CCNB (CuCoNiBe), Be containing CCNB alloy has the highest hardness, electrical conductivity and mechanical properties. NSS and NSH alloys revealed lower mass loss while the CCNB had the highest mass loss at room temperature alloys was similiar. It was low at the beginning of wear test, then increased with large scattering. at room temperature wear tests. Friction coefficient values were small and stable along all wear test. conductivity of Cu-Ni-Si alloys by aging and cold rolling, Journal of Alloys, and Compounds, 417 (2006) [7] S. Lee, H. Matsunaga, X. Sauvage, Z. Horita, Strengthening of Cu-Ni-Si alloy using high-pressure torsion and aging, Material Characterization 90(2014) M.Sc. Thesis, Kocaeli University, 2014, Kocaeli, Turkey. Behaviour of Nickel-Aluminum Bronzes Produced With -. [10] ASM Handbook, Vol. 18, Friction, Lubrication and Wear Technology, ASM International Publications, Altough mass loss results and hardness values of the alloys at room temperature wear test are contradictory and require further investigation, high temperature results appears to be more meaningful and consistent. Furthermore, since both applications are high temperature application, high temperature wear results appear to be more suitable in terms of determining alternative alloy for electrode and mold application. As a result, both NSS and NSH alloy could be offered as electrode and mold materials alternative to CCNB alloy. References -step increase in hardness of precipitation hardened CuCoNiBe alloys and characterization of precipitates, Journal of Alloys and Compounds 701 (2017) [2] W. Wang, H. Kang, Z. Chen, Z. Chen, C. Zou, R. Li, G. Yin, T. Wang, Effects of Cr and Zr additions on microstructure and properties of Cu-Ni-Si alloys, Material Science& Engineering A 673 (2016) [3] D. Zhao, Q.M. Dong, P. Liu, B.X. Kang, J.L. Huang, Z.H. Jin, Aging behavior of Cu Ni Si alloy, Materials Science and Engineering A361 (2003) [4] M. Gholami, J. Vesely, I. Altenberger, H.-A. Kuhn, M. Janecek, M. Wollmann, L. Wagner, Effects of microstructure on mechanical properties of CuNiSi alloys, Journal of Alloys and Compounds 696 (2017) 201e212. [5] X.P. Xiao, B.Q. Xiong, Q.S. Wang, G.L. Xie, L.J. Peng,G.X.Huang, Microstructure and properties of Cu Ni Si Zr alloy after thermomechanical treatments, Rare Met. (2013) 32(2): [6] S. Suzuki, N. Shibutani, K. Mimura, M. Isshiki, Y. Waseda, Improvement in strength and electrical 252 IMMC th International Metallurgy & Materials Congress