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  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 5, September - October (2013), pp. 295-300 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET ©IAEME MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MILD STEELCOPPER JOINED BY FRICTION WELDING Dalip Kumar1, Antariksha Verma2, Sankalp Kulshrestha3, Prithvi Singh4 1 (Department of Mechanical Engineering, Delhi Technological University/Formerly Delhi College of Engineering, Main Bawana Road -Delhi India) 2, 3 (Department of Mechanical Engineering, Jodhpur Engineering College & Research Centre / Jodhpur National University Jodhpur – Rajasthan, India) 4 (Department of Mechanical Engineering, Shridhar University Pilani - Rajasthan, India) ABSTRACT Joining of dissimilar metals is one of the most essential needs of industries.Dissimilar metal mild steel-copper been investigated in the present work.In friction welding of two dissimilar materials, two rods are welded together by holding one of themstill while rotating the other under the influence of an axial load which creates frictional heat in theinterface. The tensilestrength of the joints was determined, using a conventional tensile test machine.Ultimate tensile strength, percentage elongation of the welded joints and hardness variations across the weld interface has been reported. The integrity of the joint has been investigated using scanning electron microscopy. Keywords: Friction welding, mechanical properties, microstructure. 1. INTRODUCTION Friction welding is a solid state process for joining materials, especially dissimilar materials, which involves generation of heat by the conversion of mechanical energy into thermal energy at the interface of the work pieces without using electrical energy or heat from other sources during rotation under pressure [1].Copper has excellent ductility, corrosion resistance, thermal and electrical conductivity, and has been widely used to produce engineering parts such as electrical component and radiator.Many ferrous and non-ferrous alloys can be friction welded. Friction welding can be used to join metals of widely differing thermal and mechanical properties. Of-ten combinations that can be friction welded cannot be joined by other welding techniques because of the formation of brittle phases which make the joint poor in mechanical properties. The sub-melting temperatures and short weld times of friction welding allow many combinations of work metals to be joined [2].Main 295
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME advantages of friction welding are high material saving, low production time and possibility of welding of dissimilar metals or alloys [3].Sahin et al. [4] joined steel and copper using friction welding process in their studies. They determined that maximum heat is away from the center, close to but not exactly at the surface during the welding process.However, due to the difference of chemical, physical and mechanical properties between the components to be welded, the welding of dissimilar materials is generally more difficult than that of homogeneous materials. High-quality Copper and mild steel dissimilar joint is hard to be produced by fusion welding techniques due to the large difference of melting points, brittle intermetallic compounds existence and crack formation [57].Mohammadet al. [8] joined alumina and mild steel using friction welding at low rotational steel. They concluded that the strength of alumina–steel bonding is much dependent on the wet ability of the alumina surface by the partially molten aluminum interlayer and the existence of mechanical interlocking between the interlayer and mild steel. Many authors have recently conducted extensive investigation into the friction welding of dissimilar materials. The main reasons for dissimilar joining are due to the combination of good mechanical properties of one material and the low specific weight, good corrosion resistance, and good electrical properties of a second material. During the friction welding of dissimilar materials, significant cost saving is possible because engineers can design bimetallic parts that use expensive materials only where needed. Expensive forgings and castings can be replaced with less expensive forgings to bar steel, tubes, plates and suchlike.Duffin and Bahrani [9] carried out a series of experiments on the friction welding of mild steel tubular specimens to study the variations in resisting torque, axial force, and axial shortening when the angular speed and axial force are varied. In this work, dissimilar friction welding of commercial pure copper and mild steel rods was carried out, and the microstructure and mechanical properties of the dissimilar joints were investigated. Based on the experimental results, the formation of the dissimilar joints was discussed. 2. EXPERIMENTAL PROCEDURE 2.1 Materials Commercially available pure copper and mild steel were used, and the chemical compositions of the experimental materials are listed in Table 1.The materials used in the experiments were mild steel and copper rods both measuring 10mm in diameter and 50mm in length. Before welding, the surfaces of the sheets were ground with grit paper to remove the oxide film and then cleaned with ethanol. Material C Si Mn Ni Cr Cu Fe Zn Mild Steel 0.175 0.118 0.394 0.016 0.02 0.022 99.1 ------- Pure Copper ----- ----- ----- 0.009 ----- 99.957 0.009 0.025 Table 1 Chemical compositions of Mild steel andpure copper 2.2 Welding set-up A friction welder capable of operating at 200kN maximum load was designed and manufactured to carry out the experiment (Figure 1). 296
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME Figure 1 Experimental Set – Up The friction welding machine operates with high precision and excellent repeatability of weld parameters. The spindle is driven by an AC motor. The axial force was applied with the help of a hydraulic group. Friction and axial forces are read by a load cell connected to machine. All relevant data of every weld is recorded. The spindle motor is of 25 HP, 3Phase AC and operating speed can be varied from 1 to 1500 RPM.During the weld the speed of rotation was kept constant at 900 RPM and up-set force of 120 KN was applied. Once the resulting welds were obtained, tests were carried out determine mechanical and metallurgicalcharacteristics of the weld joint.In first part the mechanical properties of the resulting welds, tensile testing and micro hardness of the weldcrosssection were carried out. However, on the second part the metallurgical changes during welding were examined using scanning electron microscope. 3. RESULTS & DISCUSSION 3.1 Hardness The representative section of Vickers hardness profiles of dissimilar weld were measured along the length of specimen Figure2. 250 Hardness (HV) 200 Copper Mild steel 150 100 50 0 -500 -400 -300 -200 -100 0 100 200 300 Distance (Micrometer) Figure 2 Hardness profiles of the welded mild steel-copper 297 400 500
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME It is obvious that the hardness at the mild steel side is higher than that at the copper side.The hardness of mild steel increased towards the heat affected zone. The increase in hardness towards HAZ in copper was less.This increase in the hardnessresulted in the formation of cracks at the edge of hardness indentation. Higher hardness in all the welds can be attributed to the strain hardening effect due to up-set force.It can be seen that at around the interface, the hardness of the copper increases slightly. However, slight decrease in the hardness of the steel is observed. This is due to the steel reaching the annealing temperature during the welding process, which in turn reduces hardness on the steel side. On the other hand, copper exhibits hardening due to its high thermal conductivity and fast cooling behaviour. 3.2 Tensile properties Tensile properties of parent metals and weld joints are presented inTable 2. Mild steelcopper is an insoluble system. Joints formed here were very brittle in nature and exhibited drop in strength with an increasein HAZof the weld region. Diffusivity of mild steel is higher than that of copper and hence a reaction layer is formedtowards copper side and the failure has taken place in this zone[10].Although the thermo physical properties of the two parts are quite different the tensile strengths of welds close to those of the individual parts are obtained. Mild Steel Average Tensile Strength (MPa) 390 Elongation % 22 Yield Strength (MPa) 287 Location of Failure ----- Copper 240 14 209 ----- Material Weld Joint 215 3 ----Table 2 Tensile properties of base metal and welded samples Weld 3.3 Micro-structural characterization: As the rotational phase continues, irregularities in the two faces are smoothed outby frictional contact and pressure.When the heat generated at the interface increases the materials become plastic and a condition of full-face intimate contact can be achieved. However, atless rotational speed, impurities such as surface oxides, grease or oil, can remain trapped and, hence, do not permit the close interface contact necessary to give full bonding.The small interface impurity can cause weaken the weld join. The speed of rotation affects the intermetallic layer thickness such that a low speed of rotation results in less intermetallic layer thickness. Figure 3 (A) Microstructure of weld zone of dissimilar metal at 50X (B) Microstructure of weld zone of dissimilar metal at 100X 298
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME The microstructures of the welded joints, taken at 50X and100X using the scanning electron microscope. The weld joints are seen to be continuous and the deformation zone being very different. However, there is a distinction between the microstructures developed near the interface in the two parts joined (Fig. 3a). The micrographs show diffusion at the interface of the joining.The temperature developed in the outer region close to the free surface of the sample is higher than that corresponds to the central region of the sample, during welding process. This results in relatively large melting and heat-affected zones developing in this region. Small grains in the copper side indicate hardening, whilst no significant variation is observed in the grain size on the steel side (Fig. 3b). 4. CONCLUSIONS 1. Mild steel and pure copper are jointed successfully through friction welding with pin offset technique under a rotation rate of900rpm and a set-up load of 120 KN. 2. The hardness at the mild steel side of the joint is higher than that at the copper side. The welded materials have lower hardness compared to their parent materials due to thermal effects of the friction welding. 3. The welded rods show lower tensile strength compared to their parent rods.The average tensile strength and elongation of the dissimilar joints are 215 MPa and 3%, respectively, and the dissimilar joints fail in a ductile-brittle mixed fracture mode. 4. Microstructure shows that the weld joint between mild steel-copper accompanied by the diffusion of copper into mild steel. REFERENCE 1. Sahin M. Characterization of properties in plastically deformed austenitic-stainless steels joined by friction welding. Mater Design 2009; 30:135–44. 2. Ahmet Z. Sahin, Bekir S. Yibas¸ M. Ahmed, J. Nickel, Analysis of the friction welding process in relation to the weldingof copper and steel bars, Journal of Materials Processing Technology 82 (1998) 127 – 136. 3. Sahin M. Simulation of friction welding using a developed computer program. JMater Process Technology 2004;153(4):1011–8. 4. Sahin AZ, Yibas BS, Ahmed M, Nickel J. Analysis of the friction welding processin relation to the welding of copper and steel bars. J Mater Process Technol1998;82:127–36. 5. Weigl M, Albert F, Schmidt M. Enhancing the ductility of laser-welded copper-aluminum connections by using adapted filler materials [J]. Physics Procedia, 2011, 12: 335-341. 6. Liu P, Shi Q Y, Wang W, Wang X, Zhang Z L. Microstructure and XRD analysis of FSW joints for copper T2/aluminum 5A06 dissimilar materials [J]. Materials Letters, 2008, 62: 4106-4108. 7. Ouyang J H, Yarrapareddy E, Kovacevic R. Micro structural evolution in the friction stir welded 6061 aluminum alloy (T6-temper condition) to copper [J]. Journal of Materials Processing Technology, 2006, 172: 110-122. 8. Mohamad Zaky Noha, Luay BakirHussain, ZainalArifin Ahmad, Alumina–mild steel friction welded at lowerrotational speed, Journal of materials processing technology 2 0 4 (2008) 279–283. 9. F.D. Duffin, A.S. Bahrani, The mechanics of friction welding, Metal Constr. 8 (1976) 267– 271. 299
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 10. W.B. Lee, S.B. Jung, Effect of micro structuralvariation on the Cu/CK45carbon steel friction weld joints, Z. Metallkd. 94 (2003) 1300–1306. 11. D. Kanakaraja, P. Hema and K. Ravindranath, “Comparative Study on Different Pin Geometries of Tool Profile in Friction Stir Welding using Artificial Neural Networks”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 2, 2013, pp. 245 - 253, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 12. C.Devanathan, A.Murugan and A.Suresh Babu, “Optimization of Process Parameters in Friction Stir Welding of AL 6063”, International Journal of Design and Manufacturing Technology (IJDMT), Volume 4, Issue 2, 2013, pp. 42 - 48, ISSN Print: 0976 – 6995, ISSN Online: 0976 – 7002. 13. P. Shiva Shankar, “Experimental Investigation and Stastical Analysis of the Friction Welding Parameters for the Copper Alloy – Cu Zn30 using Design of Experiment”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 5, 2013, pp. 235 - 243, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.. 14. Kannan.P, K.Balamurugan, K.Thirunavukkarasu, “Experimental Investigation on the Influence of Silver Interlayer in Particle Fracture of Dissimilar Friction Welds”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 32 - 37, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. 300