Effect of pulsing on mechanical properties

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Effect of pulsing on mechanical properties

  1. 1. International Journal of Mechanical Engineering International Journal of Mechanical Engineering and Technology and Technology (IJMET), ISSN 0976 – 6340(Print) (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME ISSN 0976 – 6359(Online) Volume 2 Issue 2, May – July (2011), pp. 52-62 ©IAEME © IAEME, http://www.iaeme.com/ijmet.html IJMET EFFECT OF PULSING ON MECHANICAL PROPERTIES OF 90/10 AND 70/30 CUNI ALLOY WELDS 1 M. P. Chakravarthy PhD Scholar, , Mechanical Engg.Dept. Andhra University Visakhapatnam, A.P., India E-mail: chakravarthymp@rediffmail.com 1 2 2 N. Ramanaiah Associate Professor, Andhra University, Mechanical Engg.Dept.Visakhapatnam, A.P., India, E-mail: n_rchetty1@yahoo.com 3 3 B.S.K.Sundara Siva Rao. Professor, Andhra University, Mechanical Engg.Dept.Visakhapatnam, A.P., India, E-mail : bsk_sundara@yahoo.co.in ABSTRACT This paper describes the effect of pulsing on the microstructural, mechanical properties (hardness and tensile strength) of 90Cu-10Ni alloy and 70Cu-30Ni alloy welds produced by Tungsten Inert Gas (TIG) welding. The pulsed current (PC) has been found beneficial due to its advantages over the conventional continuous current (CC) process. It was observed that the PC is used for effective improvement in the mechanical properties (hardness and tensile strength) of the welds compared to those of CC welds in both the 90Cu-10Ni alloy and 70Cu-30Ni alloy welds. In cases of PC Weld metal and Fusion Zone (FZ) were found stronger than the CC in both the 90Cu-10Ni alloy and 70Cu-30Ni alloy welds.. It was observed that pulse TIG welding produced finer grain structure of weld metal than conventional TIG welding in both the 90Cu-10Ni alloy and 70Cu-30Ni alloy welds. Keywords- Pulsed current; Tungsten Inert Gas (TIG) Welding; Cupronickel alloy (90Cu10Ni and 70Cu-30Ni), Mechanical properties 1. INTRODUCTION The increasing need to minimize the use of high-priced energy has forced the shipbuilding industry to explore more efficient forms of design and construction to minimize fuel consumption. Practically all ships that are in use employ painting schemes to provide protection against corrosion and biofouling. However, this type of protection is short-lived and requires frequent maintenance during the operating life of the ship. The 52
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME maritime industry is therefore exploring the possibility of either sheathing or cladding ships with copper alloys to provide the required protection without the necessity for frequent maintenance. Copper-nickel alloys possess excellent corrosion resistance in sea water and the constant low-level discharge of copper ions provides protection against biofouling. The copper-clad ship hull thus remains slick during service and surface induced drag is minimized. Therefore, fuel or energy efficiency is maximized and the need to drydock for surface cleaning is reduced, resulting in lower maintenance and service costs [1, 2]. Earlier investigation shows that CuNi (70/30) has been welded by Flux Cored filler using GTAW and GMAW-p [3]. Structural integrity of copper-nickel to steel using metal inert gas welding [4]. Temperature field and flow field during tungsten inert gas bead welding of copper alloy onto steel [5].There were no evidence observed that using of Pulsed TIG welding for joining of Cu-Ni alloys from the earlier investigations. Pulsed current tungsten inert gas (PCTIG) welding, developed in 1950s, is a variation of tungsten inert gas (TIG) welding which involves cycling of the welding current from a high level to a low level at a selected regular frequency. The high level of the peak current is generally selected to give adequate penetration and bead contour, while the low level of the background current is set at a level sufficient to maintain a stable arc. This permits arc energy to be used efficiently to fuse a spot of controlled dimensions in a short time producing the weld as a series of overlapping nuggets and limits the wastage of heat by conduction into the adjacent parent material as in normal constant current welding. In contrast to constant current welding, the fact that heat energy required to melt the base material is supplied only during peak current pulses for brief intervals of time allows the heat to dissipate into the base material leading to a narrower heat affected zone (HAZ). The technique has secured a niche for itself in specific applications such as in welding of root passes of tubes, and in welding thin sheets, where precise control over penetration and heat input are required to avoid burn through. Extensive research has been performed in this process and reported advantages include improved bead contour, greater tolerance to heat sink variations, lower heat input requirements, reduced residual stresses and distortion. Metallurgical advantages of pulsed current welding frequently reported in literature include refinement of fusion zone grain size and substructure, reduced width of HAZ, control of segregation, etc. [6]. All these factors will help in improving mechanical properties. Current pulsing has been used by several investigators to obtain grain refinement in weld fusion zones and improvement in weld mechanical properties [7,8]. Hence, in this investigation an attempt has been made to study the effect of pulsing on mechanical properties (hardness and tensile strength) and microstructure of Copper Nickel alloy (70% Cu 30-% Ni ) TIG welds and therefore assumes special significance since such detailed studies are not hitherto reported. 2. EXPERIMENTAL DETAILS The investigations were carried out on 90/10 CuNi and 70/30 CuNi (5 mm thick) plates. The composition of the Base metals and filler wire was given in Table 1. Autogenous, full penetration welds were produced by alternate current (AC) GTAW process. The weld bead was made perpendicular to the sheet rolling direction (Fig.1 and Fig.2). Prior to welding, the base material coupons, ER CuNi fillers were wire brushed 53
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME and thoroughly cleaned with acetone. Details of the welding parameters are presented in Table 2. Two types of current modes were used: Continuous Current (CC) and Pulsed Current (PC). The microstructural characterization of the fusion zones (FZ) were carried out by means of optical microscope (OM). Samples for microstructural investigations were cut from the base material (BM) and fusion zone(FZ). The metallographic samples were polished on Emery papers and disc cloth to remove the very fine scratches. Polished surfaces were etched in a solution of Glacial acitic acid and Nitric acid (1:1). The microstructures were recorded with an image analyzer attached to the metallurgical microscope. Microhardness was carried out using LECO’s LV700 Vickers hardness testing machine with 2Kg load. Tensile testing was performed on a computer controlled Universal Testing Machine using transverse-weld specimens, cut from the fusion zones and base metal, prepared according to ASTM E-8 (Fig.3) Table 1: Chemical Composition of 90/10 CuNi , 70/30 CuNi and Filler ERCuNi(70/30 CuNi) Material Ni Fe Mn Pb Zn C Ag P Si Ti others Cu 90/10 CuNi 11.50 0.30 0.65 0.0025 0.025 0.04 0.15 - - - 0.1 REST 70/30 CuNi 32.50 0.010 0.75 0.0025 0.025 0.04 0.15 - - - 0.1 REST Filler ERCuNi (70/30 CuNi) 29.31 0.40 0.65 0.015 - - - 0.001 0.058 0.28 0.1 REST Fig.1. Schematic view of the Tungsten inert gas (TIG) welding process Fig: 2. Tensile test specimen cut from weld 54
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME Continuous current welds Arc voltage 18 V Welding current 105A Welding speed manually operated Pulsed current welds Arc voltage Peak current Base current Pulse frequency Pulse on time Welding speed 18V 210A 105A 1Hz, 3Hz, 5Hz 50% manually operated Table 2 Welding Parameters Fig: 3 Tensile test specimen as per ASTM- E8 Table 3 Mechanical properties of the base materials of 90/10 CuNi and 70/30 CuNi Sl.No. Material Ultimate Tensile Strength (N/mm2) Elongation (%) Vickers Hardness Number (HN) 1 90/10CuNi 311 15.2 130 2 70/30CuNi 412 39 140 3. RESULTS AND DISCUSSION 3.1. MICROSTRUCTURE (a) Base material (90/10 CuNi alloy) 55
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME (b) Base material (70/30 CuNi alloy) Fig. 4 Optical microstructures of (a) Base material (90/10 CuNi alloy) (b) Base material (70/30 CuNi alloy) The optical microstructure of the base metals (90/10 CuNi and 70/30 CuNi ) as shown in Fig.4. This shows coarse grains throughout the base metal. Optical micrographs of both CC and PC welds regions of FZ was shown in Fig. 5 . All fusion zone has equiaxed grains except FZ made with CC. Out of all PC technique,1Hz frequency of PC TIG 90/10 CuNi alloy welds (Fig:5b) and 3 Hz frequency of PC TIG 70/30 CuNi alloy welds (Fig:5g) shows improved equiaxed grains compared to all other welds. 3.2. MICROHARDNESS The microhardness of FZ made with CC and PC was tabulated (Table.4). All FZ shows lower microhardness than the BM. In a precipitation hardened Cu alloy, the mechanical properties of the weld zone mainly depended on the precipitates behavior during the welding thermal cycles. This result could be attributed to the reason why lower hardness than that of base metals. Hardness of the fusion zone showed high values at 1Hz frequency of PC TIG 90/10 CuNi alloy welds and 3Hz frequency of PC TIG 70/30 CuNi alloy welds. A lower pulse frequency welding resulted in homogeneously dispersed Cu and Ni particles through out the weld region. Therefore, larger difference of hardness with hardness measured location was represented compared to other PC and CC welding conditions. Out of all frequencies (1 Hz,, 3Hz and 5Hz) and CC welds, 1Hz frequency of PC TIG 90/10 CuNi alloy welds and 3Hz frequency of PC TIG 70/30 CuNi alloy welds shows highest hardness value .This was mainly due to the different thermal effects with welding conditions. The thermal effect of TIG depends on the welding condition [9].More thermal effects were added when the Pulse frequency with 1Hz frequency of PC TIG 90/10 CuNi alloy welds and 3Hz frequency of PC TIG 70/30 CuNi alloy welds. Therefore the grain size and precipitates might grow at the lower welding condition. The Hardness profiles are shown in Fig.6(a) & 6(b),the fluctuations were more in CC welds than PC welds .this is due to more amount of heat is transferred to the base metal in CC than PC. Out of all, the fluctuations are minimum with 3 Hz frequency. 56
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME Table 4 90/10 CuNi and 70/30 CuNi Microhardness center of the weld Microhardness70/30 CuNi Alloy Pulse 90/10 CuNi Alloy welds Frequency welds / CC Microhardness VHN Microhardness VHN 1 Hz 109.0 110.1 3 Hz 103.7 114.3 5 Hz 103.4 109.5 CC 101.4 108.3 BM 130.0 140.0 Fig: 6(a). Micro hardness profiles on top surface of the weld with different pulse frequencies (1Hz,3Hz,5Hz) and CC of 90/10 CuNi alloy TIG welds. Fig: 6(b). Microhardness profiles on top surface of the weld with different pulse frequencies (1Hz,3Hz,5Hz) and CC of 70/30 CuNi alloy TIG welds. 3.3 TENSILE STRENGTH Tensile test results are shown in Table 5 and Fig 7(a) & 7(b). Table 5 shows that the shown all PC welds of 90/10CuNi and 70/30 CuNi have better strength than CC welds. This is because of pulsing effect in PC welds. The highest strength of the weld zone was 57
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME acquired for pulse frequency 1 Hz shown in Fig: 7(a) but in 70/30 CuNi alloy welds, the Hz highest strength of the weld zone was acquired for welding pulse frequency 3 Hz shown in Fig: 7(b). The reason of the different strength according to the arc stability of each pulsing was explained by the dominant microstructure in the fusion zone. Compared to 90/10 CuNi alloy welds , 70/30 CuNi alloy C.C welds shows lower strength value than P.C welds and strength of the P.C welds are closed to base metal strength. The fractured surface of tensile specimens of welded joints was analyzed using SEM specimens to reveal the fracture surface morphology. Figures 8 a d shows that the fractographs of a-d tensile specimens which are all of the tensile specimens failed in a ductile manner under the action of tensile loading. An appreciable difference exists in the Base metal fracture , . pulse frequencies and continuous current of TIG welding processes. An intergranular fracture feature has been observed joints and this may be due to the combined influence of a coarse grained weld metal region and a higher amount of precipitate formation at the grain boundaries are seen in Pulse TIG fracture welds compared to Base metals fractured (Figs. 8) .This result confirms that, although high strengths were obtained in BM compared to 1Hz, PC condition. of 90/10 CuNi welds and 3 Hz ,PC condition. of 70/30 CuNi welds failure occurred at the FZ in all samples. Table 5. Transverse tensile test: mechanical properties of the studied joints (90/10 CuNi and 70/30 CuNi) S. No. Base/Puls e frequency (Hz)/CC 1 Base material 1 Hz 3 Hz 5 Hz CC 2 3 4 5 90/10 CuNi Alloy welds Ultimate % Elong. Tensile strength (N/mm2 ) 311.6 15.2 302.4 299.8 301.1 297.8 13.7 13.3 13.1 13.0 70/30 CuNi Alloy welds Ultimate % Elong. Tensile strength (N/mm2 ) 412.3 13.3 405.1 406.0 402.2 378.6 10.9 11.0 12.8 8.4 Fig.7 (a) Transverse tensile properties to welding direction of the joints at different pulse freq’s (1Hz, 3Hz, 5Hz) and CC of 90/10 CuNi alloy TIG welds. 58
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME Fig.7 (b) Transverse tensile properties to welding direction of the joints at different pulse freq’s (1Hz,3Hz,5Hz) and CC of 70/30 CuNi alloy TIG welds. 5(a) 90/10 CuNi -CC,105A, 200X Fusion Zone CC,105A, 5(e) 70/30 CuNi -CC,105A, 200X Fusion Zone CC,105A, 5(b) 90/10 CuNi-1Hz,105A, 200X Fusion Zone 1Hz,105A, 5(f)70/30 CuNi- 1Hz,105A, 200X Fusion Zone 59
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME 5(c) 90/10 CuNi-3Hz,105A, 200X Fusion Zone 3Hz,105A, 5(g) 70/30 CuNi 3Hz,105A, 200X Fusion Zone CuNi-3Hz,105A, 5(d) 90/10 CuNi- 5Hz,105A, 200X Fusion Zone Fig. 5. Microstructures of 90/10 alloy weld 5(a) CC; 5(b) PC, 1Hz; 5(c)PC, 3Hz ; 5 5(h)70/30 CuNi- 5Hz,105A, 200X Fusion Zone Microstructures of 70/30 alloy weld 5(a) CC; 5(b) PC, 1Hz; 5(c)PC, 3Hz ; 5(d)PC, 5Hz (a) 90/10 CuNi SEM- Fractured surface BM (b) 90/10 CuNi SEM- Fractured surface FZ, 1Hz, PC (c) 70/30CuNi SEM- Fractured surface BM 60
  10. 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME (d) 70/30 CuNi SEM- Fractured surface FZ, 3Hz, PC Fig.8 90/10 CuNi SEM - Fractured surface (a) BM (b) FZ, 1Hz, PC ; 70/30 CuNi SEM - Fractured surface (c) BM (d) FZ, 3Hz, PC 4. CONCLUSION The effect of pulsing on mechanical properties and microstructure of 90/10CuNi and 70/30 CuNi (Cupro-nickel) alloy welds are investigated and the following conclusions are drawn. 1. 90/10CuNi and 70/30 CuNi alloy similar plates were joined successfully by TIG welding Techniques (PC and CC). 2. Of All welds, 1Hz frequency of PC TIG 90/10 CuNi alloy welds and and 3Hz frequency of PC TIG 70/30 CuNi alloy welds shows better hardness and CC shows lowest respectively. 3. Microhardness of welds shows distribution near the weld zone was related to the microstructure of each region. 4. The Hardness profiles are shown in Fig.6, the fluctuations were more in CC welds than PC Welds. 1Hz frequency of PC TIG 90/10 CuNi alloy welds and and 3Hz frequency of PC TIG 70/30 CuNi alloy welds shows less fluctuation compare to all other welds. 5. Transverse tensile strength of 1Hz frequency of PC TIG 90/10 CuNi alloy welds and 3Hz frequency of PC TIG 70/30 CuNi alloy welds showed the highest value with 105A . 6 The formation of equiaxed grains and uniformly distributed, fine strengthening precipitates in the weld region are the reasons for superior tensile properties of Pulse TIG weld joints compared to Continuous Current TIG weld joints of 90/10 CuNi and 70/30 CuNi welds. 5. REFERENCES [1] [2] [3] [4] Structural integrity of Cu-Ni to steel using metal inert gas welding .T. S. SUDARSHAN, J.(1986). Copper-nickel Fabrication, Nickel Institute Publication 12014, CDA Publication 139, 1999N Flux Cored Arc Welding of CuNi 90/10 Piping with CuNi 70/30 Filler Metal by Jack H. (2006) Structural integrity of copper-nickel to steel using MIG welding .T. S. SUDARSHAN, J. 1986. 61
  11. 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME [5] Temperature field and flow field during tungsten inert gas bead welding of copper alloy onto Steel, Shixiong Lv∗, Jianling Song, HaitaoWang, Shiqin Yang, A 499 (2009) 347–351 [6] Ravi Vishnu P. Weld World 1995; 35(4):214–20. [7] Gokhale AA, Ecer GM. In: Proceedings of conference on grain refinement in casting and welds. [8] Madhusudhan Reddy G, Gokhale AA, Prasad Rao K. J Mater Sci 1997; 32(1993):4117–26. [9] Yamamoto H. Weld Int 1993; 7(6):456–62. [10] Effect of Pulsing on Mechanical Properties of 90/10 CuNi Alloy Welds, M. P. Chakravarthy .,N. Ramanaiah., B.S.K.Sundara Siva Rao. 3RD International & 24th AIMTDR Conference Dec 2010,Page no. 493-498 [11] Effect of Pulsing on Mechanical Properties of 90/10 CuNi Alloy Welds, M. P. Chakravarthy ., N. Ramanaiah., B.S.K.Sundara Siva Rao. Paper accepted for Journal “International Journal of Material Sciences and Technology(IJMST) and issue of journal “Jan-June 2011”. [12] Effect of Pulsing on Mechanical Properties of 70/30 CuNi Alloy Welds, M. P. Chakravarthy .,N. Ramanaiah., B.S.K.Sundara Siva Rao. Paper accepted for Journal “International Journal of Mechanical Engineering and Material Sciences and issue of journal “Jan-June 2011”. 62

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