Effect of Post Weld Heat Treatment and Welding Parameters Welded … · 2019-03-14 · Draft Effect of Post Weld Heat Treatment and Welding Parameters on Mechanical and Corrosion

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Effect of Post Weld Heat Treatment and Welding Parameters on Mechanical and Corrosion Characteristics of Friction Stir

Welded Aluminium Alloy AA2014-T6

Journal: Transactions of the Canadian Society for Mechanical Engineering

Manuscript ID TCSME-2018-0185

Manuscript Type: Article

Date Submitted by the Author: 31-Aug-2018

Complete List of Authors: KANNUSAMY, ASHOK; Dr.Mahalingam college of engineering and technology, Automobile EngineeringR, Ravindran; Dr.Mahalingam college of engineering and technology

Keywords: Friction Stir Welding, Aluminum Alloy AA2014-T6, Post weld heat treatment, Corrosion

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Transactions of the Canadian Society for Mechanical Engineering

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Effect of Post Weld Heat Treatment and Welding Parameters on Mechanical and Corrosion Characteristics of Friction Stir Welded Aluminium Alloy AA2014-T6

Ashok S.Kannusamy1*, Ravindran Ramasamy2

1 Assistant Professor, Dr.Mahalingam College of engineering & Technology, Pollachi, Tamilnadu, India.2 Professor, Dr.Mahalingam College of engineering & Technology, Pollachi, Tamilnadu, India.

*E-mail: [email protected]

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Abstract

This paper addresses the effect of post weld heat treatment methods on the mechanical and corrosion

characteristics of friction stir welded Aluminum alloy AA2014-T6. Aluminum alloy AA2014 is mainly

used in application where there is a greater demand for high strength to weight ratio like aerospace, marine

and industrial applications. In this work, AA2014-T6 plates of 6 mm thick were butt welded using a tool

with a square profile. The tensile strength, hardness and corrosion characteristics were compared between

the as welded and post weld heat treated samples. It was found that the welded samples heat treated with the

low ageing period (8hrs) show improved tensile strength irrespective of the welding process parameters

compared to the as-welded samples. Whereas the samples heat treated with high ageing period (9hrs) show

a decline in tensile strength for low tool rotation speed. The hardness of the samples has increased in

welded samples heat treated with low ageing period. The welded samples heat treated with high ageing

period show high passivity in the corrosion media.

Keywords: Friction Stir Welding, Aluminum Alloy AA2014-T6, Post weld heat treatment, Corrosion

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1. Introduction

Friction stir welding (FSW) is a solid state joining process used widely for joining Aluminum alloys which

are difficult to weld using conventional methods as the joints are free from defects like distortion and

porosity. The alloy AA2014-T6 is used widely in aerospace, naval and defence industry due to its high

strength to weight ratio. Various researchers have studied the mechanical and corrosion characteristics of

friction stir welded high strength Aluminum alloys.

Gürel Çam and Güven İpekoğlu have reviwed the recent developments in the joining of aluminum alloys.

They have presented that the joint performance of FSWed age-hardened Aluminum alloys can be increased

by keeping the heat input sufficiently low and also by conducting post weld heat treatment (Çam and

İpekoğlu 2017). Mosleh et al. have studied the microstructure and corrosion behavior of friction stir welded

AA7020-O plates. They have observed that the corrosion resistance of thermomechanically affected zone is

lower when compared with heat affected zone regions and dynamically recrystallized zones. They also

observed that the corrosion resistance of the samples welded using tapered cylindrical pin tool is better than

those welded using two flat-sided cylindrical pin (Mosleh et al. 2016). Ghorbanzade et al. have investigated

the microstructural evolutions and mechanical charcteristics of friction stir welded AA2024. They have

presented that the rotational speed of the tool highly inflence the mechanical parameters of the welded

samples (Ghorbanzade et al. 2016).

The effect of post weld heat treatment methods on mechanical properties of Aluminum alloys was

analysed by different researchers in the recent past. El-Danaf and El-Rayes have studied the effect of post

weld heat treatments on the microstructure and mechanical properties of friction stir welded alloy AA6082.

They have observed that the samples welded at lower welding speeds responded more to PWHT than that

welded at higher speeds. They also have observed that the strength and hardness can be partially recovered

by the suitable post weld heat treatment (El-Danaf and El-Rayes 2013). Sivaraj et al. have examined the

effect of PWHT on the tensile properties of the FSW joints of AA7075 alloy. It was observed that the

tensile strength of the FSW specimens subjected to Solutionizing and artificial aging (STA) treatment was

higher than that subjected to artificial aging (AA) treatment (Sivaraj et al. 2014). Aydın et al. have studied

the effect of post weld heat treatment on the mechanical properties of friction stir welded joints of AA2024-

T4 alloy. They have reported that the T6 ageing treatment is beneficial in increasinng the mechanical

properties of the 2024-T4 joints (Aydın et al. 2010). The post weld heat treatment T6 condition results in

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joints with higher strength compred to other treatments and the T6 treated welds are prone to corrosion

(Kumar et al. 2015).

This paper addresses the combined effect of friction stir welding parameters and the post weld heat

treatment methods on the mechanical as well as corrosion characteristics of friction stir welded Aluminum

alloy AA2014-T6.

2. Materials and Methods

The AA2014-T6 Aluminum alloy plates purchased were tested for its composition before being welded.

The chemical composition of the Aluminum alloy plates used in the experiments is shown in table 1. The

Aluminum alloy AA2014-T6 plates of 6 mm thick were friction stir welded using a vertical machining

centre (LMW Make – KODI 40 Model). The plates were welded in the direction perpendicular to the

direction of rolling of the plate. Radiography was done to check the quality of the welded joints. The welds

with defects were discarded and the ones with good quality are used in tests and experiments.Table 1. Chemical composition of AA2014-T6 plates.

2.1. Welding Parameters

The Aluminum alloy plates were welded with two different tool rotation speeds (1000 rpm, 1400 rpm) and

weld speeds (20mm/min, 35mm/min). The tool was tilted to an angle of 2o during welding. The tool used

for friction stir welding was made up of H13 tool steel with a square profile. The length of the pin was 5.5

mm and the tool shoulder diameter was 18mm (Kadaganchi et al. 2015). The profile of the tool is shown in

figure1. The figure 2 shows the friction stir welded sample.Figure 1. Friction stir welding Tool

Figure 2. Friction stir welded sample

2.2. Heat treatment method

The Aluminum alloy AA2014-T6 plates were successfully friction stir welded using a tool with square

profile. Part of the welded samples was subjected to Solution Treatment followed by Artificial ageing

(STA) (Ahmad and Asmael 2015). The solutionizing was carried out by heating the samples at 5020C for a

soaking period of 1 hour and quenched in water followed by artificial ageing at 1770C for two different

soaking periods of 8 hours (STA-I) and 9 hours (STA-II) (Elangovan and Balasubramanian 2008). Table 2

shows the sample ID for as welded and heat treated specimens welded with different process parameters.

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Table 2. Sample ID for different process parameters

2.3. Testing procedure

2.3.1. Tensile test

The tensile strength for the friction stir welded work pieces was determined as per the ASTM E8M standard

testing procedure. Figure 3 shows the dimensions of the standard tensile specimen. The figure 4 shows the

sample tensile test specimen.

Figure 3. Specifications of the tensile specimen

Figure 4. Sample tensile test specimen

2.3.2. Hardness test

The hardness of the friction stir welded plates was measured using the Vickers hardness tester (Mitutoyo–

HM113). The welded specimens were cut perpendicularly to the weld direction and hardness was measured

along the transverse cross section at the mid thickness (Hejazi and Mirsalehi 2016). Hardness measurements

were taken at every 1mm from the center of the weld region up to the parent metal on either side. The load

employed was 300 gf with the dwell time of 15 seconds.

2.3.3. Corrosion test

Specimens for electrochemical test were cut along the weld zone. Different zones (advancing, retreating and

nugget) were exposed to the electrolyte in all the experiments. The remaining unaffected areas of the

specimen were painted to protect it from the corrosion environment. Electrochemical experiments were

performed using CHI660C electrochemical work station controlled through a personal computer. The setup

of electrochemical experiment is shown in figure 5.

Figure 5. Electrochemical cell and electrochemical work station

Surfaces of the specimens were mechanically polished using silicon carbide sheets (grade starting from 100

to 1200, ANSI) and then they were rinsed in distilled water before being used for each electrochemical

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experiment. Corrosion test was carried out in 3.5% of NaCl solution. The reference electrode employed in

this experiment was Ag/AgCl electrode. All the potential data taken were referred to this Ag/AgCl reference

electrode potential. The counter electrode used here was platinum wire loop and work piece was working

electrode (Sato et al. 2011).

3. Results and Discussion

3.1. Tensile strength

The as welded and heat treated plates were subjected to tensile test as per ASTM-E8 standards and the

tensile strength values of as-welded and heat treated samples are shown in figure 6. All the tests were

replicated thrice and the average values were taken for comparison.

Figure 6. Tensile strength of as-welded and heat treated samples

The as-welded samples show an average tensile strength of 349 MPa which is 31% lower than the tensile

strength of the unwelded parent metal. (Sabari et al. 2015). The heat treated samples show an average

tensile strength of 363 MPa for STA-I and 366 MPa for STA-II which is lower than the tensile strength of

the unwelded parent metal by 27% and 16% respectively (Chu et al. 2017). The results indicate that the

welded samples heat treated with the low ageing period (8hrs) (A1,B1,C1 and D1) show improved tensile

strength irrespective of the welding process parameters compared to the as-welded samples (Muruganandam

et al. 2015). Whereas the samples heat treated with high ageing period (9hrs) show a decline in tensile

strength for low tool rotation speed and show improved tensile strength for high tool rotation speed.

The decline in the tensile strength for heat treated samples welded with low tool rotation speed may be due

to the high heat input during welding and the coarsening of precipitates. It is also evident that for the

samples welded with high tool rotation speed along with high welding speed the tensile strength has

declined.

3.2. Hardness

The hardness profiles of all the samples are shown in figure 7 (a)-(d). The hardness plots of as welded and

heat treated samples are plotted together for samples welded with same process parameters to compare the

effect of heat treatment on the hardness of samples.

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Figure 7. Hardness profiles of as welded and heat treated samples

Figure 7. (a) shows the hardness profile of the samples A, A1 & A2. The heat treatment STA-I shows very

marginal improvement on the hardness value, whereas heat treatment STA-II show higher improvement in

the hardness of the samples. (Krishnan 2002). The hardness profiles of samples welded with the parameters

(1000rpm, 30mm/min) are shown in figure 7(b). From the plot it is inferred that the samples aged for 9 hrs.

has resulted in a drop in the hardness values compared to the ones aged for 8 hrs. (Hu et al. 2011).

Comparing the two plots 7(a) and 7(b), for the same tool rotational speed (1000 rpm) the lower ageing time

(8 hr.) shows a marginal improvement on the hardness profile at almost all regions of the weld compared to

the as-welded specimens.

The hardness profiles of samples welded with a tool rotational speed of 1400 rpm are shown in figure 7(c)

and (d) with weld speeds of 20 mm/min and 30 mm/min respectively. The hardness in the nugget region of

these samples has increased considerably. The hardness of the welded samples has increased considerably

irrespective of the aging period compared to the as welded samples. The samples with higher aging period

show increased hardness than the samples with low aging period (Essa et al. 2016).

3.3. Corrosion rate

Electrochemical measurement methods can be used to determine corrosion rates of welded specimens.

Polarization resistance is one of these methods, in which the specimens are polarized a few millivolts above

and below the open-circuit potential and the current response is measured.

3.3.1. Open Circuit Potential

The open circuit potential (OCP) is the potential of the working electrode when no potential or current is

being applied to the cell relative to the reference electrode. The figure 8. shows the open circuit potential

plot for the sample B (1000rpm, 30mm/min, non-heat treated) in the nugget zone.

Figure 8. OCP plot for sample B (1000 rpm, 30mm/min)

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The OCP fluctuates during the initial period of immersion and after a period it gets stabilized. It is evident

from the plot that the open circuit potential gets stabilized around -0.58 V. In general the open circuit

potential of the specimens range between -0.54v to -0.58v.

3.3.2. Polarization curve - TAFEL plot

The polarization plots are the curves drawn between the electrode current and the potential. The potential of

the welded sample is scanned in set increments over a range as determined from the open circuit potential.

All the samples are subjected to potentiodynamic polarization to obtain the Tafel plot and hence the

corrosion rate.

Figure 9. Tafel Plot for as welded and heat treated samples

The figure 9(a) shows the Tafel plot of the samples A, A1 and A2. The plot indicates that the potential drop

of all the specimens lies between -0.46V and -0.52V. The corrosion current of the sample A is 1.812

mA/cm2, which is lesser than the remaining samples. The corrosion rate of the sample A is 1.546e+003

mils/year which is comparatively less than the sample A1 and sample A2.

The figure 9(b). shows the Tafel plot of the samples B, B1 and B2. The plot indicates that the potential drop

of all the specimens lies between -0.38V and -0.50V. The corrosion current of the sample B2 is 2.298

mA/cm2, which is lesser than the remaining samples. The corrosion rate of the sample B2 is 1.96e+003

mils/year which is comparatively less than the sample B and sample B1.

Tafel plot of the samples C, C1 and C2 are shown in figure 9(c). The plot indicates that the potential drop of

all the specimens lies between -0.38V and -0.48V. The corrosion current of the sample C2 is 1.564 mA/cm2,

which is lesser than the remaining samples. The corrosion rate of the sample C2 is 1.334e+003 mils/year

which is comparatively less than the sample C and sample C1.

The figure 9(d). shows the Tafel plot of the samples D, D1 and D2. The plot indicates that the potential drop

of all the specimens lies between -0.44V and -0.50V. The corrosion current of the sample D2 is 4.614

mA/cm2, which is lesser than the remaining samples. The corrosion rate of the sample D2 is 3.936e+003

mils/year which is comparatively less than the sample D and sample D1. It is observed that the post welded

heat treated samples are more stable in the selected corrosion media (Oladele et al. 2017).

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4. Conclusion

The Aluminum alloy AA2014-T6 was friction stir welded and subjected to heat treatment involving solution

treatment and artificial ageing. The as welded and heat treated samples were tested for their mechanical and

corrosion characteristics.

The tensile strength of the heat treated samples is higher when compared to the as welded samples for

higher tool rotation speed. For samples with lower tool rotation speed the heat treatment method has a

marginal negative effect on the tensile strength.

The hardness profile indicates that the increase in soaking time during ageing within limits has increased the

hardness values of the samples irrespective of the process parameters.

The corrosion rate of the samples are analysed by conducting polarization test. The Tafel polarization plots

are obtained using a three electrode electrochemical cell and an electrochemical analyser (potentiostat). The

Tafel plots indicate that the samples subjected to ageing treatment have higher passivity than the as welded

samples.

Acknowledgements

The authors would like to thank the management, secretary and Principal of the institution for providing

necessary facilities and support to carry out the research. The authors also like to thank the support staff at

the chemistry laboratory of the institution for the support provided in conducting the electrochemical tests.

ReferencesAhmad, R. and Asmael, M.B.A., 2015. Effect of aging time on microstructure and mechanical properties of AA6061 friction stir welding joints.

International Journal of Automotive and Mechanical Engineering, 11, p.2364.

Aydın, H., Bayram, A. and Durgun, I., 2010. The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-

welded joints. Materials & Design (1980-2015), 31(5), pp.2568-2577.

Çam, G. and İpekoğlu, G., 2017. Recent developments in joining of aluminum alloys. The International Journal of Advanced Manufacturing

Technology, 91(5-8), pp.1851-1866.

Chu, G., Sun, L., Lin, C. and Lin, Y., 2017. Effect of Local Post Weld Heat Treatment on Tensile Properties in Friction Stir Welded 2219-O Al

Alloy. Journal of Materials Engineering and Performance, 26(11), pp.5425-5431.

Elangovan, K. and Balasubramanian, V., 2008. Influences of post-weld heat treatment on tensile properties of friction stir-welded AA6061

aluminum alloy joints. Materials characterization, 59(9), pp.1168-1177.

El-Danaf, E.A. and El-Rayes, M.M., 2013. Microstructure and mechanical properties of friction stir welded 6082 AA in as welded and post

weld heat treated conditions. Materials & Design, 46, pp.561-572.

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Essa, G.M., Zakria, H.M., Mahmoud, T.S. and Khalifa, T.A., 2016. Microstructure examination and microhardness of friction stir welded joint

of (AA7020-O) after PWHT. HBRC Journal.

Ghorbanzade, T., Soltanipour, A., Dehghani, K. and Chabok, A., 2016. Microstructural evolutions and mechanical properties of friction stir

welded AA2024-3. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, 230(1),

pp.75-87.

Hejazi, I. and Mirsalehi, S.E., 2016. Mechanical and metallurgical characterization of AA6061 friction stir welded joints using microhardness

map. Transactions of Nonferrous Metals Society of China, 26(9), pp.2313-2319.

Hu, Z., Yuan, S., Wang, X., Liu, G. and Huang, Y., 2011. Effect of post-weld heat treatment on the microstructure and plastic deformation

behavior of friction stir welded 2024. Materials & Design, 32(10), pp.5055-5060.

Kadaganchi, R., Gankidi, M.R. and Gokhale, H., 2015. Optimization of process parameters of aluminum alloy AA 2014-T6 friction stir welds

by response surface methodology. Defence Technology, 11(3), pp.209-219..

Krishnan, K.N., 2002. The effect of post weld heat treatment on the properties of 6061 friction stir welded joints. Journal of Materials Science,

37(3), pp.473-480.

Kumar, P.V., Reddy, G.M. and Rao, K.S., 2015. Microstructure, mechanical and corrosion behavior of high strength AA7075 aluminium alloy

friction stir welds–Effect of post weld heat treatment. Defence Technology, 11(4), pp.362-369.

Mosleh, A.O., Mahmoud, F.H., Mahmoud, T.S. and Khalifa, T.A., 2016. Microstructure and static immersion corrosion behavior of AA7020-O

Al plates joined by friction stir welding. Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and

Applications, 230(6), pp.1030-1040.

Muruganandam, D., Raguraman, D. and Kumaraswamidhas, L.A., 2015. Effect of post-welding heat treatment on mechanical properties of butt

FSW joints in high strength aluminium alloys. (22): pp. 381-388

Oladele, I.O., Betiku, O.T. and Fakoya, M.B., 2017. Effect of post weld heat treatment on the mechanical and corrosion behaviour of welded

Al-Fe-Si alloy joints. Leonardo Electronic Journal of Practice and Technologies,(30), pp.75-86.

Sabari, S.S., Balasubramanian, V., Malarvizhi, S. and Reddy, G.M., 2015. Influences of post weld heat treatment on tensile properties of friction

stir welded AA2519-T87 aluminium alloy joints. Journal of the Mechanical Behavior of Materials, 24(5-6), pp.195-205.

Sato, Y.S., Kokawa, H. and Kurihara, S., 2011. Systematic Examination of Precipitation Phenomena Associated With Hardness and Corrosion

Properties in Friction Stir Welded Aluminium Alloy 2024. Welding in the World, 55(11-12), pp.39-47.

Sivaraj P., Kanagarajan D. and Balasubramanian V., 2014. Effect of post weld heat treatment on tensile properties and microstructure

characteristics of friction stir welded armour grade AA7075-T651 aluminium alloy. Defence Technology, 10(1), pp.1-8.

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List of Tables

Table 1. Chemical composition of AA2014-T6 plates.

Element Al Cr Cu Mg Mn Si Ti Fe Zn

wt. % 93.80 0.008 3.96 0.56 0.48 0.67 0.066 0.16 0.057

Table 2. Sample ID for different process parameters

Sample ID Tool rotational Speed (rpm)

Weld Speed (mm/min)

As welded STA -I STA -II

1000 20 A A1 A2

1000 35 B B1 B2

1400 20 C C1 C2

1400 35 D D1 D2

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Figure 1. Friction stir welding Tool

21x14mm (300 x 300 DPI)

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Figure 2. Friction stir welded sample

60x10mm (300 x 300 DPI)

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Figure 3. Specifications of the tensile specimen

57x15mm (300 x 300 DPI)

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Figure 4. Sample tensile test specimen

55x10mm (300 x 300 DPI)

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Figure 5. Electrochemical cell and electrochemical work station

99x64mm (300 x 300 DPI)

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Figure 6. Tensile strength of as-welded and heat treated samples

26x18mm (300 x 300 DPI)

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Figure 7. Hardness profiles of as welded and heat treated samples

36x39mm (300 x 300 DPI)

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Figure 8. OCP plot for sample B (1000 rpm, 30mm/min)

86x52mm (300 x 300 DPI)

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Figure 9. Tafel Plot for as welded and heat treated samples

41x51mm (300 x 300 DPI)

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Effect of Post Weld Heat Treatment and Welding Parameters Welded … · 2019-03-14 · Draft Effect of Post Weld Heat Treatment and Welding Parameters on Mechanical and Corrosion

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