06 effect of pulsing on mechanical properties of pulsing o… · refinement in weld fusion zones...

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

0976 – 6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME

52

EFFECT OF PULSING ON MECHANICAL PROPERTIES OF 90/10

AND 70/30 CUNI ALLOY WELDS

1M. P. Chakravarthy

1 PhD Scholar, , Mechanical Engg.Dept.

Andhra University Visakhapatnam, A.P., India

E-mail: [email protected]

2N. Ramanaiah

2 Associate Professor, Andhra University, Mechanical Engg.Dept.Visakhapatnam, A.P.,

India, E-mail: [email protected]

3B.S.K.Sundara Siva Rao.

3Professor, Andhra University, Mechanical Engg.Dept.Visakhapatnam, A.P., India,

E-mail : [email protected]

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

International Journal of Mechanical Engineering

and Technology (IJMET), ISSN 0976 – 6340(Print)

ISSN 0976 – 6359(Online) Volume 2

Issue 2, May – July (2011), pp. 52-62

© IAEME, http://www.iaeme.com/ijmet.html

IJMET © I A E M E



53

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



54

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)

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

Fig: 2. Tensile test specimen cut from weld

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



55

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)

Continuous current welds Pulsed current welds

Arc voltage 18 V

Welding current 105A

Welding speed manually operated

Arc voltage 18V

Peak current 210A

Base current 105A

Pulse frequency 1Hz, 3Hz, 5Hz

Pulse on time 50%

Welding speed manually operated



56

(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.

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976

0976 – 6359(Online) Volume 2, Issue

Table 4 90/10 CuNi and 70/30 CuNi Microhardness

Pulse

Frequency

/ CC

1 Hz

3 Hz

5 Hz

CC

BM

Fig: 6(a). Micro hardness profiles on top surface of the weld with different pulse

frequencies (1Hz,3Hz,5Hz) and CC of 90/10

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 show

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


6359(Online) Volume 2, Issue 2, May- July (2011), © IAEME

57

Table 4 90/10 CuNi and 70/30 CuNi Microhardness- center of the weld

90/10 CuNi Alloy

welds

Microhardness VHN

70/30 CuNi Alloy

welds

Microhardness VHN

109.0 110.1

103.7 114.3

103.4 109.5

101.4 108.3

130.0 140.0





Tensile test results are shown in Table 5 and Fig 7(a) & 7(b). Table 5 shows that the



6340(Print), ISSN


CuNi alloy TIG welds.


n in Table 5 and Fig 7(a) & 7(b). Table 5 shows that the





acquired for pulse frequency 1 H

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 sp

to reveal the fracture surface morphology. Figures 8 a

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

S.

No.

Base/Puls

e

frequency

(Hz)/CC

(N/mm2 )

1 Base

material

2 1 Hz

3 3 Hz

4 5 Hz

5 CC

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

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



the dominant microstructure in the fusion zone. Compared to


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

to reveal the fracture surface morphology. Figures 8 a-d shows that the fractographs of


. An appreciable difference exists in the Base metal fracture ,



weld metal region and a higher amount of precipitate formation at the



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.


and 70/30 CuNi)

90/10 CuNi Alloy welds 70/30 CuNi Alloy welds

Ultimate

Tensile

strength

(N/mm2 )

% Elong. Ultimate

Tensile

strength

(N/mm2 )

311.6 15.2 412.3

302.4 13.7 405.1

299.8 13.3 406.0

301.1 13.1 402.2

297.8 13.0 378.6


freq’s (1Hz, 3Hz, 5Hz) and CC of 90/10 CuNi alloy TIG welds.

6340(Print), ISSN

z shown in Fig: 7(a) but in 70/30 CuNi alloy welds, the



the dominant microstructure in the fusion zone. Compared to


ecimens of welded joints was analyzed using SEM

d shows that the fractographs of


. An appreciable difference exists in the Base metal fracture ,



weld metal region and a higher amount of precipitate formation at the



PC condition. of 90/10 CuNi welds and 3 Hz ,PC condition. of 70/30


70/30 CuNi Alloy welds

% Elong.

13.3

10.9

11.0

12.8

8.4




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

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



59

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

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

6340(Print), ISSN

Transverse tensile properties to welding direction of the joints at different pulse

CC,105A, 200X Fusion Zone

1Hz,105A, 200X Fusion Zone



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

5(d) 90/10 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 ;



60

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

5Hz,105A, 200X Fusion Zone 5(h)70/30 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 ; 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

6340(Print), ISSN



5(a) CC; 5(b) PC, 1Hz;



61

(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.



62

[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


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”.


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”.

06 effect of pulsing on mechanical properties of pulsing o… · refinement in weld fusion zones...

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