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EFFECT OF PULSING ON MECHANICAL PROPERTIES

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EFFECT OF PULSING ON MECHANICAL PROPERTIES Powered By Docstoc
					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
                                                                        IJMET
Issue 2, May – July (2011), pp. 52-62                            ©IAEME
© IAEME, http://www.iaeme.com/ijmet.html



 EFFECT OF PULSING ON MECHANICAL PROPERTIES OF 90/10
             AND 70/30 CUNI ALLOY WELDS

                                     1
                                      M. P. Chakravarthy
                            1
                             PhD Scholar, , Mechanical Engg.Dept.
                         Andhra University Visakhapatnam, A.P., India
                           E-mail: chakravarthymp@rediffmail.com
                                             2
                                       N. Ramanaiah
 2
     Associate Professor, Andhra University, Mechanical Engg.Dept.Visakhapatnam, A.P.,
                           India, E-mail: n_rchetty1@yahoo.com
                                         3
                                        B.S.K.Sundara Siva Rao.
     3
         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 (90Cu-
10Ni 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


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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

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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
                  29.31   0.40    0.65   0.015      -          -    -     0.001   0.058   0.28    0.1     REST
   (70/30 CuNi)




           Fig.1. Schematic view of the Tungsten inert gas (TIG) welding process




                           Fig: 2. Tensile test specimen cut from weld


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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                                   Pulsed current welds
Arc voltage           18 V                                 Arc voltage                   18V
Welding current     105A                                   Peak current                  210A
Welding speed     manually operated                        Base current                  105A
                                                           Pulse frequency        1Hz, 3Hz, 5Hz
                                                           Pulse on time                 50%
                                                           Welding speed          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          Elongation               Vickers Hardness
                                      Strength (N/mm2)              (%)                    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)




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN
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                              (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.




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN
0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME

                                  Microhardness-
Table 4 90/10 CuNi and 70/30 CuNi Microhardness center of the weld
                   Pulse    90/10 CuNi Alloy  70/30 CuNi Alloy
                 Frequency        welds             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
                             shown
    Tensile test results are shown in Table 5 and Fig 7(a) & 7(b). Table 5 shows that the
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

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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN
0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME

                               Hz
acquired for pulse frequency 1 Hz shown in Fig: 7(a) but in 70/30 CuNi alloy welds, the
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.

                                    specimens
   The fractured surface of tensile specimens of welded joints was analyzed using SEM
                                                        a-d
to reveal the fracture surface morphology. Figures 8 a d shows that the fractographs of
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.        Base/Puls           90/10 CuNi Alloy welds             70/30 CuNi Alloy welds
      No.           e            Ultimate          % Elong.            Ultimate       % Elong.
                frequency         Tensile                               Tensile
                 (Hz)/CC         strength                              strength
                                (N/mm2 )                              (N/mm2 )
       1          Base             311.6              15.2               412.3           13.3
                 material
       2          1 Hz            302.4               13.7               405.1            10.9
       3          3 Hz            299.8               13.3               406.0            11.0
       4          5 Hz            301.1               13.1               402.2            12.8
       5           CC             297.8               13.0               378.6            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.



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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.




                          CC,105A,
         5(a) 90/10 CuNi -CC,105A, 200X Fusion Zone                         CC,105A,
                                                           5(e) 70/30 CuNi -CC,105A, 200X Fusion Zone




                         1Hz,105A,
         5(b) 90/10 CuNi-1Hz,105A, 200X Fusion Zone               5(f)70/30 CuNi- 1Hz,105A, 200X Fusion Zone




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International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN
0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME

                            3Hz,105A,
            5(c) 90/10 CuNi-3Hz,105A, 200X Fusion Zone                              CuNi-3Hz,105A,
                                                                         5(g) 70/30 CuNi 3Hz,105A, 200X Fusion Zone




           5(d) 90/10 CuNi- 5Hz,105A, 200X Fusion Zone                     5(h)70/30 CuNi- 5Hz,105A, 200X Fusion Zone
                                                                           5


           Fig. 5. Microstructures of 90/10 alloy weld
                   5(a) CC; 5(b) PC, 1Hz; 5(c)PC, 3Hz ;    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



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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]   Structural integrity of Cu-Ni to steel using metal inert gas welding .T. S.
        SUDARSHAN, J.(1986).
  [2]   Copper-nickel Fabrication, Nickel Institute Publication 12014, CDA Publication
        139, 1999N
  [3]   Flux Cored Arc Welding of CuNi 90/10 Piping with CuNi 70/30 Filler Metal by
        Jack H. (2006)
  [4]   Structural integrity of copper-nickel to steel using MIG welding .T. S.
        SUDARSHAN, J. 1986.

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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”.




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