Investigation of dissimilar metal joints with nanoparticle fillers

Accepted Manuscript Investigation of dissimilar metal joints with nanoparticle fillers E. Jasiūnienė, E. Žukauskas, D.A. Dragatogiannis, E.P. Koumoulos, C.A. Charitidis PII:

S0963-8695(17)30002-6

DOI:

10.1016/j.ndteint.2017.08.005

Reference:

JNDT 1901

To appear in:

NDT and E International

Received Date: 2 January 2017 Revised Date:

2 August 2017

Accepted Date: 14 August 2017

Please cite this article as: Jasiūnienė E, Žukauskas E, Dragatogiannis DA, Koumoulos EP, Charitidis CA, Investigation of dissimilar metal joints with nanoparticle fillers, NDT and E International (2017), doi: 10.1016/j.ndteint.2017.08.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Investigation of dissimilar metal joints joints with nanoparticle fillers E. Jasiūnienė1, E. Žukauskas1, D.A. Dragatogiannis2, E.P. Koumoulos2, C.A. Charitidis2 1

RI PT

Ultrasound Institute, Kaunas University of Technology, Kaunas, Lithuania Research Unit of Advanced, Composite, Nano Materials & Nanotechnology, School of Chemical Engineering, National Technical University of Athens, Athens, Greece

2

SC

ABSTRACT

There is high demand for lightweight but strong materials, which has brought about hybrid structures that

M AN U

are made from dissimilar light materials such as aluminium alloys. Friction stir welding (FSW) can be used not only for the joining of dissimilar materials but to produce structures with enhanced properties by incorporating reinforcing fillers (e.g., SiC) into the weld. The quality of welds produced using FSW can be affected by imperfect welding process parameters or uncontrollable variables. The objective of this work was the application and verification of a high-frequency ultrasonic technique for the investigation of

TE D

dissimilar metal joint quality. Four welds with different numbers of friction stir processing passes were investigated using macroscopic study, acoustic microscopy (AM), and X-ray computed tomography (CT) techniques. Image fusion of the AM and CT results are presented, and these confirm the images obtained

EP

with the acoustic microscope correlate well with the X-ray CT. Investigations demonstrate that scanning

AC C

acoustic microscopy can show even the smallest voids, their position, and their size in the weld. It was shown that number and the direction of passes influence the quality of the weld considerably. The presented results prove that the macrostructural study is not sufficient to evaluate the quality of the friction stir weld.

KEYWORDS Dissimilar friction stir welding, aluminium alloys, SiC, non-destructive testing, high-frequency acoustic microscopy, X-ray tomography, image fusion

ACCEPTED MANUSCRIPT

1

INTRODUCTION

There is high demand for lightweight but strong materials in the transport industry [1,2] in order for the weight of the structures to be reduced and to save energy [3]. Hence, the hybrid structures that are made

RI PT

from dissimilar lightweight materials were introduced [2]. Therefore, suitable dissimilar material joining methods are needed for reliable joints to be produced [2]. Various technologies for the joining of dissimilar materials exist depending on the materials used in the joint, application, and service requirements [2].

SC

Dissimilar materials are joined using adhesive bonding, mechanical fastening, and welding [2]. Aluminium alloys are widely used in the aerospace industry due to their unique characteristics, such as a

M AN U

high strength-to-weight ratio, good corrosion and wear resistance [2,4], but the main drawback is that they present low weldability when conventional welding methods are applied [5]. Friction stir welding (FSW) has emerged as an alternative welding method for aluminium alloys [5,2,4,6]. FSW is a solid-state welding process patented by the Welding institute [7]. The advantage of FSW is that it does not alter chemical

TE D

composition and mechanical properties due to localized heating and does not create brittle bonds [8]. FSW produces a very fine microstructure with better mechanical properties, higher tensile strength, and lower residual stress [4,9]. Friction stir welds, due to the solid-state nature of joining, are usually defect free [4],

EP

but if the welding process parameters are imperfect or are affected by uncontrollable variables (slight thickness variation, material inhomogeneity, uncertainty in welding parameters) or unforeseen

AC C

circumstances, the quality of the weld may be affected [10–13]. The quality of welds produced using FSW can also be affected by rotational speed (RPM), feed rate, lack of penetration of the tool pin, tilt angle, among other factors [4,8,14–18]. Typically, the quality of the FSW is assessed using macrographs and micrographs obtained by optical and electron microscopes but only in a cut section [4,16,19]. Non-destructive testing can assess quality of the whole weld, even being performed on-line, and the weld parameters can be adjusted [16,19]. However, FSW has some unique features, which limit the application of non-destructive testing techniques; defects in FSW can occur at random orientation and at any angle [9,20]. Typical defects in FSW are lack of

ACCEPTED MANUSCRIPT penetration (LOP), cavities, voids, wormholes, and root flaws [4,11,20–22]. For non-destructive testing of friction stir welds, ultrasonic inspection, X-ray radiography, infrared thermography, eddy current, and fluorescent penetrating fluid inspection can be used. However, all techniques have their limitations [8–

RI PT

10,16,17,19]. Ultrasonic immersion testing technique using high frequency focussed transducers is good for determining porosity and voids, and ultrasonic phased arrays are effective for finding tiny void defects at unusual orientations. X-ray radiography is suitable for detecting large-sized voids [9,16,19], fluorescent penetrating fluid inspection and eddy current are best for revealing superficial crack-like root flaws

SC

[9,16,19], and laser ultrasonics can be used to measure residual stresses [20]. Charitidis et al. applied

M AN U

nanoindentation on FSWed Al-alloys for residual stress investigations [23]. However, localization and microstructural characterization of small defects in friction stir welds is still challenging for conventional NDT techniques [19], but even small defects can have impact on the joint performance [11,13,19]. For the localization of small defects, high-frequency acoustic microscopy could be used [4]. Sagar et al. [4] have used acoustic microscopy for excitation of leaky surface waves.

TE D

Friction stir welding can be used not only for joining of dissimilar materials but also to produce structures with enhanced properties, e.g., by incorporating reinforcing fillers such as SiC [5,24], TiC [25] or CNTs [26– 29] into the weld. By incorporating nanoparticles, enhanced properties such as higher strength, stiffness,

EP

etc. are achieved [5,27]. Therefore, there is a great interest to use different nanopowders to strengthen the

AC C

dissimilar joints. The effect of SiC nanopowders on the microstructure and mechanical properties have been studied by Tebyani et al. [24], however, the parent material, steel, has been used. More widely, the effect of CNTs on the properties of the joints has been studied [26–29]. Recently, Kartsonakis et al. [30] studied the effect of nanoreinforcements on the corrosion behaviour of dissimilar friction stir welded aluminium joints. However, to the authors’ knowledge, there are no studies of the inner structure of the joints with the nanoparticles using non-destructive testing techniques. The objective of this work was to non-destructively evaluate the quality of the friction stir welds of different aluminium alloys with SiC nanoparticle fillers obtained using different numbers and directions of

ACCEPTED MANUSCRIPT passes. Non-destructive evaluation was performed using high-frequency acoustic microscopy and X-ray computed tomography.

EXPERIMENTAL PROCEDURE PROCEDURE

RI PT

2

2.1 Materials used

The nominal mass composition of the alloys AA6082-T6 and AA5083-H111 used as parent material plates

SC

are demonstrated in Table 1. The aluminium plates that were used for the FSW had dimensions of 200 mm × 100 mm × 3 mm. Both aluminium alloys have many industrial applications, mainly in the marine

M AN U

and automotive industry.

The SiC nanoparticles used as reinforcing material had an average particle size of 20 – 30 nm (crystalline, surface area 109 m2/gr, β-SiC main phase). The morphology of the SiC nanoparticles (spheres), which were produced by Chemical Vapor Deposition (CVD), was determined by scanning electron microscopy (SEM)

TE D

using a PHILIPS Quanta Inspect (FEI Company) microscope with a 25 KV tungsten filament equipped with energy dispersive X-ray analysis EDAX Genesis (Ametex Process & Analytical Instruments), as shown in Fig. 1. In Fig. 1(a), the SEM image of SiC nanoparticles is presented and in Fig. 1(b), the EDAX analysis of the

Table 1

EP

SiC nanopowder.

AC C

Chemical composition of AA5083-H111 and AA6082-T6 and alloys (wt%). Si

Fe

Cu

Mn

Mg

Cr

Zn

Ti

Ni

Ga

V

Al

0.37

0.32

0.072

0.53

4.5

0.093

0.044

0.03

0.005

0.011

0.013

bal.

1.07

0.28

0.04

0.7

1.15

0.024

0.04

0.015

0.005

0.013

0.016

bal.

AA5083H111

AA6082T6

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

(b)

Fig. 1. (a) SEM image of SiC nanoparticles and (b) EDAX analysis of SiC nanopowder.

2.2 Friction Stir Welding When the plates were rigidly clamped on the backplate, a groove with dimensions of 180 mm length, 1 mm width and 2.5 mm depth was created to incorporate the SiC nanoparticles, as shown in Fig. 2. The optimum

ACCEPTED MANUSCRIPT operating conditions of FSW of AA6082-T6 to AA5083-H111 in the absence of nanoparticles were as follows: rotation speed at 750 rpm, traverse speed at 85 mm/min, and application of one pass. The welding direction was parallel to the rolling direction of the plates. The nanoparticles, which were

RI PT

mixed with ethanol (13.8 % slurry concentration), were deposited into the grooves and pressed tightly. The groove was aligned along with the central line of the rotating pin. The optimization procedure and mechanical characterization of dissimilar joints (microhardness, nanoindentation, and tensile tests) are

M AN U

SC

presented in detail in our previous work [5].

Fig. 2. Geometric characteristics of the machined grooves [5].

TE D

According to a Avettand-Fenoel et al. [31], increasing the number of friction stir processing passes results in a more uniform nanoparticle distribution in the weld nugget. Based on this previous result, various FSW

AC C

EP

tests were conducted using the welding conditions as presented in Table 2.

Table 2 FSW parameters.

ACCEPTED MANUSCRIPT

FSW specimen

Rotational

Traverse

speed (RPM)

speed

Tilt angle

Passes (mm)

(mm/min) 750

85

3o

2

750

85

3o

2 of the same direction

3

750

85

3o

3 of the same direction

4

750

85

3o

2 of the opposite direction

5 (without SiC)

750

85

RI PT

SC

Metallographic preparation

1

3o

1

M AN U

2.3

1

After the welding procedure, all specimens were cut at the transverse section with respect to the welding direction and the appropriate metallographic preparation was conducted. For the metallographic observation, all the specimens were etched with “modified Poulton’s reagent” and the macroscopic

TE D

observation was made using an optical stereoscope (Leica MZ6).

EP

2.4 Scanning acoustic microscopy

The scanning acoustic microscopy technique was used for non-destructive investigation of the friction stir

AC C

welds of different aluminium alloys with SiC nanoparticle fillers. Scanning acoustic microscopy allows the capture of high resolution images as a result of the high frequency transducers and small wavelength, respectively. The experimental set-up of the system used is presented in Fig. 3. Investigations of the welds were performed using pulse echo technique. An acoustic microscope was used for excitation of longitudinal waves for inspection of the friction stir welds. For investigation of the samples, an acoustic microscope KSI V8 [32] was used with a 50 MHz focused ultrasonic transducer PT-50-3-10. Aperture of ultrasonic transducer is 3 mm, focal distance in water – 10 mm. Scanning step for C-scan imaging was 100 µm and for B-scan imaging - 50µm. Ultrasonic field was focused at the defect depth.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 3. The experimental set-up for scanning acoustic microscopy

2.5 X-ray computed tomography

TE D

Investigations were performed using an X-ray 3D Computer tomograph RayScan 250E (RayScan Technologies GmbH, Meersburg, Germany). The measurements were carried out using a 10-230 kV micro

EP

focus X-ray source. During measurements, the X-ray source irradiates the test object with the cone beam and a 2D image at the detector is recorded (Fig. 4). A flat panel detector with 2048x2048 pixels was used.

AC C

Overall, 2430 projections were acquired during each measurement, when the object was rotated. To achieve the highest resolution possible, the projections were acquired with the 5 s integration time at a 100 kV voltage and 100 µA current, with a resulting voxel size of 12 µm. The dimensional analysis was carried out with VGStudio MAX 3.0 software.

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

3

EP

Fig. 4. The experimental set-up for X-ray computed tomography

EXPERIMENTAL INVESTIGATIONS

AC C

In the presented investigation, four welds with a different number of friction stir processing passes were investigated using macroscopic study, acoustic microscopy, and X-ray computed tomography techniques.

3.1 Macrostructural study In Fig. 5, the macrostructure of the weld nugget is observed after the application of one (Fig. 5(a)), two (Fig. 5(b)), and three passes of the same direction (Fig. 5(c)), as well as after two passes of the opposite direction (Fig. 5(d)).

ACCEPTED MANUSCRIPT In Fig. 5(a), agglomeration of SiC nanoparticles, mainly at the lower area of the weld nugget, can be observed. Additionally, micro-voids were observed near the agglomeration at the edges of the weld nugget. In Fig. 5(b), it is observed that the application of the second pass of the same direction (Fig. 5(b)) reduced

RI PT

the formation of agglomerations around the stir zone. The formed agglomerates near the heat affected zone, after the application of one and two passes of the same direction, are primarily owed to the lefthanded screw pin, which directed the material downwards at the centre and upwards near the heat affected zone [33]. The improvement of particle distribution after the application of two FSW passes was

SC

also observed by Sun at al. [34], as the application of a second FSW pass with pure copper alloys creates a

M AN U

homogeneous distribution of SiC.

In Fig. 5(c), it can be observed that a region of agglomerated particles is present in the upper area of the retreating side after the application of the 3rd pass of the same direction. In contrast, as depicted in Fig. 5(d), after the application of 2 passes of the opposite direction, no agglomeration is observed, and no defects were detected. The weld nugget of specimen no. 4 (two passes of the opposite direction were

TE D

applied) presents the most uniform macrostructural morphology, with the absence of defects and is

AC C

EP

characterized by an onion ring structure.

Fig. 5. Macrostructure of welds (a) specimen no. 1: after 1 pass, (b) specimen no. 2: after 2 passes of the same direction, (c) specimen no. 3: after 3 passes of the same direction, (d) specimen no. 4: after 2 passes of the opposite direction (RS – retreating side, AS – advancing side)

ACCEPTED MANUSCRIPT

In Fig. 6(a), the macrostructure of the weld nugget for specimen no. 5 (without reinforcement) is presented for comparison purposes. Absence of defects, a large flow arm, and an onion ring structure can be

RI PT

observed. The microstructure of the weld nugget is presented in Fig. 6(b). The reduction of the grain size of the weld without reinforcement in the WN compared to that of the untreated base metals (AA5083-H111: 26 μm and AA6082-T6: 40 μm) is a result of the dynamic

TE D

M AN U

SC

recrystallization, which according to previous reports [35,36] took place during FSW.

AC C

EP

Fig. 6. (a) Optical macrograph of specimen no. 5, (b) Optical micrograph of the weld nugget.

ACCEPTED MANUSCRIPT

3.2 NonNon-destructive evaluation To visualize the inner structure of the welded samples using acoustic microscopy, a signal detection window was selected in such a way that the surface and back wall reflection signals were eliminated and

RI PT

the inner structure of the weld in 3D is presented in Fig. 7(a). For verification, the CT 3D results are shown in Fig. 7 (b). In CT, the resulting surface and bottom non-homogeneities and unevenness were removed in order for the defects in the weld to be visualized better. Analysing the results presented in Fig.7, it can be

SC

observed that defects were present in all samples and can be detected using both, acoustic microscopy and X-ray computed tomography. When passes are performed in the same direction (Specimens no. 1, no. 2,

M AN U

no. 3) defects have their major dimension parallel to the welding direction because the friction weld process is performed by moving in a linear fashion [21]. Application of passes in the opposite direction improves the weld structure; however, voids are formed nevertheless, only they don’t have their major direction parallel to the welding direction and most of them are parallel to the surface of the weld.

TE D

Most nonhomogeneous structure in the weld zone is in the case of 1 and 2 passes in the same direction (Specimens no. 1 and no. 2). After the 1st FSW pass, voids were observed near the agglomeration at the edges (both at the advancing as well as the retreating side) of the weld nugget. On the advancing side,

EP

micro voids are observed, whereas on the retreating side C-shaped voids are formed along the weld zone, which can be noticed in the X-ray CT images. Although the application of the 2nd pass of the same direction

AC C

resulted in a lower number of agglomerated particles as can be seen in Fig. 5(b), but defects along the weld zone on both sides of the weld nugget were observed, with a channel defect propagating along the advancing side and C-shaped void on the retreating side (Fig. 7). Analysis of the macroscopic image presented in Fig. 5(c) suggests that application of the 3rd pass in the same direction improves the distribution but analysis of NDE results shows that the weld structure differs a lot along the weld line; voids with different form along the welding direction can be observed in Fig. 7. Analysis of the macroscopic image presented in Fig. 5(d) suggests that the application of 2 passes of the opposite direction resulted in the best formed weld nugget compared to all the other specimens and is characterized by an onion ring structure.

ACCEPTED MANUSCRIPT However, analysis of the acoustic microscopy and X-ray CT results shows that micro-voids are formed in the weld but are not propagating along all of the weld line such as in other cases. To see the position of the non-homogeneities in depth direction, B-scans at different positions of the

RI PT

samples were acquired using acoustic microscope and presented in Fig. 9(a). In Fig. 8, the C-scans of the samples, showing the positions of the B-scans, are presented. In Fig. 9(a), B-scans at different planes are presented. Representative slices at the same positions from the CT data were extracted as well for the

SC

comparison. In Fig. 9(c), image fusion of AM and CT results is presented. It can be observed that, using the acoustic microscopy, the depth and position of voids can be determined accurately, however, some voids,

M AN U

which are deeper, can be shadowed by the upper ones (sample 2/slice 2, sample 4/slice 1, etc.). A bent surface reflection line in B-scans of Samples No1 and No2 is observed due to the curved surface line in the weld zone. Due to different ultrasonic wave propagation velocities and distance in water and the aluminium surface, reflection cannot be directly aligned to the surface in the CT image. The smallest voids,

Fig. 9(a).

TE D

detected using acoustic microscopy were 25µm (sample 1/slice 1 and slice 2) in the top right in the image in

Investigations show, that scanning acoustic microscopy can give a 3D view of the inner structure of the

AC C

EP

welds and can show non-homogeneities, their position, and size in the weld in 3D with 25µm resolution.

ACCEPTED MANUSCRIPT Acoustic microscopy C-scan (a) AS

no. 2

RS

AS

no. 3

RS

AS

RS

AS

RI PT

RS

RS

AS

RS

AS

RS

AS

RS

AC C

no. 4

EP

TE D

M AN U

no. 1

X-ray CT (b)

SC

Specimen

AS

Fig. 7. Experimental results – (a) – Acoustic microscopy C-scan, (b) –X-ray CT (RS – retreating side, AS – advancing side)

ACCEPTED MANUSCRIPT Acoustic microscopy C-scan RS AS

RS

AS

no. 3

RS

AS

EP

TE D

M AN U

SC

no. 2

RI PT

Specimen no. 1

RS

AS

AC C

no. 4

Fig. 8. Acoustic microscopy C-scans with shown positions of the B-scans in Fig. 9 (RS – retreating side, AS – advancing side)

ACCEPTED MANUSCRIPT Sample / slice no.

Acoustic microscopy B-scan

x-ray CT

UT and CT image fusion

(a)

(b)

(c)

no. 1

RS

AS

RS

AS

RS

AS

RS

AS

RS

RS

AS

RS

Slice 2

Slice 1

Slice 2

AS

AC C

Slice 1

RS

AS

RS

RS

AS

RS

AS

AS

RS

AS

EP

no. 4

M AN U

Slice 1

no. 3

AS

SC

no. 2

TE D

Slice 2

RI PT

Slice 1

Slice 2

Fig. 9. Experimental results – a – B-scans, b – CT slices, c – UT and CT image fusion (RS – retreating side, AS – advancing side)

ACCEPTED MANUSCRIPT

4

CONCLUSIONS

The non-destructive evaluation of the quality of friction stir welds is challenging because the welded plates are thin and because defects that form in the weld are small. However, these defects must be detected

RI PT

because even small defects can have a significant impact on joint performance. Localization and characterisation of small defects is still challenging for conventional NDT techniques. It was determined that, for the inspection of dissimilar metal joints, high-frequency ultrasonic focused transducers are

SC

required.

In the presented study, four welds with different numbers of FSW passes were investigated using

M AN U

macroscopic study, acoustic microscopy, and X-ray computed tomography techniques. Investigations show that higher frequency (50 MHz) inspections using scanning acoustic microscopy give detailed view of inner structure of the welds, showing the smallest voids and their position and size in the weld with 25µm resolution. The images obtained with the acoustic microscope correlated well with the X-

TE D

ray computed tomography results.

It was shown, that number and direction of passes influence the quality of the weld considerably. The

EP

presented results prove that just the macroscopic view of the weld at one cross-section could give the impression that the weld is without defect; however, investigation of the whole weld line is required to

AC C

make a conclusion about the quality of the weld.

ACKNOWLEDGEMENTS The authors acknowledge the financial support of the FP7 Collaborative project “SAFEJOINT”. The abbreviation “SAFEJOINT” stands for “Enhancing structural efficiency through novel dissimilar material joining techniques” (Grant agreement no.: 310498). Authors would like to thank D.I. Pantelis and P. Karakizis for providing the FSW aluminium alloys.

ACCEPTED MANUSCRIPT

[1]

REFERENCES Pantelis DI, Karakizis PN, Daniolos NM, Charitidis CA, Koumoulos EP, Dragatogiannis DA.

RI PT

5

Microstructural Study and Mechanical Properties of Dissimilar Friction Stir Welded AA5083-H111 and AA6082-T6 Reinforced with SiC Nanoparticles. Mater Manuf Process 2016;31:264–74. doi:10.1080/10426914.2015.1019095.

Kah P, Suoranta R, Martikainen J, Magnus C. Techniques for Joining Dissimilar Materials : Metals and Polymers. Rev Adv Mater Sci 2014;36:152–64.

Dong H, Hu W, Duan Y, Wang X, Dong C. Dissimilar metal joining of aluminum alloy to galvanized

M AN U

[3]

SC

[2]

steel with Al-Si, Al-Cu, Al-Si-Cu and Zn-Al filler wires. J Mater Process Technol 2012;212:458–64. doi:10.1016/j.jmatprotec.2011.10.009. [4]

Sagar SP, Miyasaka C, Ghosh M, Tittmann BR. NDE of friction stir welds of Al alloys using highacoustic

microscopy.

Nondestruct

Test

Eval

2012;27:375–89.

TE D

frequency

doi:10.1080/10589759.2012.656638. [5]

Pantelis DI, Karakizis PN, Daniolos NM, Charitidis CA, Koumoulos EP, Dragatogiannis DA.

EP

Microstructural Study and Mechanical Properties of Dissimilar Friction Stir Welded AA5083-H111 and AA6082-T6 Reinforced with SiC Nanoparticles. Mater Manuf Process 2015;in press:1–41.

[6]

AC C

doi:10.1080/10426914.2015.1019095. Li D, Yang X, Cui L, He F, Zhang X. Investigation of stationary shoulder friction stir welding of

aluminum

alloy

7075-T651.

J

Mater

Process

Technol

2015;222:391–8.

doi:10.1016/j.jmatprotec.2015.03.036. [7]

Thomas W., Nicholas E. Friction stir welding for the transportation industries. Mater Des 1997;18:269–73. doi:10.1016/S0261-3069(97)00062-9.

[8]

Akinlabi E, Levy A, Akinlabi S. Non-Destructive Testing of Dissimilar Friction Stir Welds. Proc World Congr … 2012;III:4–8.

ACCEPTED MANUSCRIPT [9]

Lamarre A, Dupuis O, Moles M. Complete inspection of friction stir welds in aluminum using ultrasonic and eddy current arrays. 16th WCNDT , Monteral, Canada, 2004.

[10]

Bird CR. Ultrasonic phased array inspection technology for the evaluation of friction stir welds.

[11]

RI PT

Insight Non-Destructive Test Cond Monit 2004;46:31–6. doi:10.1784/insi.46.1.31.52658. Tabatabaeipour M, Hettler J, Delrue S, Van Den Abeele K. Non-destructive ultrasonic examination of root

defects

in

friction

stir

welded

butt-joints.

doi:10.1016/j.ndteint.2016.02.007.

Int

2016;80:23–34.

Pietras A, Węglowski MS. Imperfections in FSW joints and NDT methods of their detection. Biul Inst

M AN U

Spaw 2014:23–32. [13]

E

SC

[12]

NDT

Tabatabaeipour M, Hettler J, Delrue S, Van Den Abeele K. Nondestructive ultrasonic inspection of friction stir welds. Phys Procedia 2015;70:660–3. doi:10.1016/j.phpro.2015.08.071.

[14]

Mishra RS, Ma ZY. Friction stir welding and processing. Mater Sci Eng R Reports 2005;50. doi:10.1016/j.mser.2005.07.001.

Su JQ, Nelson TW, Mishra R, Mahoney M. Microstructural investigation of friction stir welded 7050-

TE D

[15]

T651 aluminium. Acta Mater 2003;51:713–29. doi:10.1016/S1359-6454(02)00449-4. [16]

Li B, Shen Y, Hu W. The study on defects in aluminum 2219-T6 thick butt friction stir welds with the

EP

application of multiple non-destructive testing methods. Mater Des 2011;32:2073–84. doi:10.1016/j.matdes.2010.11.054. Saravanan T., Lahiri BB., Arunmuthu K., Bagavathiappan S., Sekhar AS., Pillai VPM., et al. Non-

AC C

[17]

destructive evaluation of friction stir welded joints by X-ray radiography and infrared thermography. Procedia Eng 2014;86:469–75. doi:10.1016/j.proeng.2014.11.060.

[18]

Doude H, Schneider J, Patton B, Stafford S, Waters T, Varner C. Optimizing weld quality of a friction stir

welded

aluminum

alloy.

J

Mater

Process

Technol

2015;222:188–96.

doi:10.1016/j.jmatprotec.2015.01.019. [19]

Rosado LS, Santos TG, Piedade M, Ramos PM, Vila??a P. Advanced technique for non-destructive testing of friction stir welding of metals. Meas J Int Meas Confed 2010;43:1021–30.

ACCEPTED MANUSCRIPT doi:10.1016/j.measurement.2010.02.006. [20]

Lévesque D, Dubourg L, Blouin A. Laser ultrasonics for defect detection and residual stress measurement

of

friction

stir

welds.

Nondestruct

Test

Eval

2011;26:319–33.

[21]

Gibson BT, Lammlein DH, Prater TJ, Longhurst WR, Cox CD, Ballun MC, et al. Friction stir welding: Process,

automation,

and

control.

J

doi:10.1016/j.jmapro.2013.04.002.

Manuf

Process

2014;16:56–73.

Chen H-B, Yan K, Lin T, Chen S-B, Jiang C-Y, Zhao Y. The investigation of typical welding defects for aluminum

alloy

friction

stir

welds.

Mater

Sci

Eng

A

2006;433:64–9.

M AN U

5456

SC

[22]

RI PT

doi:10.1080/10589759.2011.573551.

doi:10.1016/j.msea.2006.06.056. [23]

Charitidis CA, Dragatogiannis DA, Koumoulos EP, Kartsonakis IA. Residual stress and deformation mechanism of friction stir welded aluminum alloys by nanoindentation. Mater Sci Eng A 2012;540:226–34. doi:10.1016/j.msea.2012.01.129.

Tebyani SF, Dehghani K. Effects of SiC nanopowders on the mechanical properties and

TE D

[24]

microstructure of interstitial free steel joined via friction stir spot welding. JMADE 2016;90:660–8. doi:10.1016/j.matdes.2015.11.016.

Dragatogiannis DA, Koumoulos EP, Kartsonakis IA, Pantelis DI, Karakizis PN, Charitidis CA. Dissimilar

EP

[25]

Friction Stir Welding Between 5083 and 6082 Al Alloys Reinforced With TiC Nanoparticles. Mater

AC C

Manuf Process 2016;31:2101–14. doi:10.1080/10426914.2015.1103856.

[26]

Pantelis DII, Karakizis PNN, Dragatogiannis DAA, Charitidis CAA, Dragatogiannis DAA. Dissimilar

friction stir welding of aluminum alloys reinforced with carbon nanotubes. Phys. Sci. Rev., vol. 1. doi:10.1515/psr-2015-0010.

[27]

Liu Q, Ke L, Liu F, Huang C, Xing L. Microstructure and mechanical property of multi-walled carbon nanotubes reinforced aluminum matrix composites fabricated by friction stir processing. Mater Des 2013;45:343–8. doi:10.1016/j.matdes.2012.08.036.

[28]

Lim DK, Shibayanagi T, Gerlich AP. Synthesis of multi-walled CNT reinforced aluminium alloy

ACCEPTED MANUSCRIPT composite

via

friction

stir

processing.

Mater

Sci

Eng

A

2009;507:194–9.

doi:10.1016/j.msea.2008.11.067. Izadi H, Gerlich AP. Distribution and stability of carbon nanotubes during multi-pass friction stir processing

of

carbon

nanotube/aluminum

composites.

doi:10.1016/j.carbon.2012.06.012. [30]

Carbon

N

Y

2012;50:4744–9.

RI PT

[29]

Kartsonakis IA, Dragatogiannis DA, Koumoulos EP, Karantonis A, Charitidis CA. Corrosion behaviour of dissimilar friction stir welded aluminium alloys reinforced with nanoadditives. Mater Des

Avettand-Fènoël M-N, Simar A, Shabadi R, Taillard R, De Meester B. Characterization of oxide

M AN U

[31]

SC

2016;102:59–67. doi:10.1016/j.matdes.2016.04.027.

dispersion strengthened copper based materials developed by friction stir processing 2014. doi:10.1016/j.matdes.2014.04.012. [32]

Tamulevičius T, Šimatonis L, Ulčinas O, Tamulevičius S, Žukauskas E, Rekuvienė R, et al. Micromachining and validation of the scanning acoustic microscope spatial resolution and sensitivity block

for

20–230

MHz

TE D

calibration

frequency

range.

Microscopy

2016;65:429–37.

doi:10.1093/jmicro/dfw027. [33]

Ji SD, Shi QY, Zhang LG, Zou AL, Gao SS, Zan LV. Numerical simulation of material flow behavior of

EP

friction stir welding influenced by rotational tool geometry. Comput Mater Sci 2012;63:218–26. doi:10.1016/j.commatsci.2012.06.001. Sun YF, Fujii H. The effect of SiC particles on the microstructure and mechanical properties of friction

AC C

[34]

stir welded pure copper joints. Mater Sci Eng A 2011;528:5470–5. doi:10.1016/j.msea.2011.03.077.

[35]

McNelley TR, Swaminathan S, Su JQ. Recrystallization mechanisms during friction stir

welding/processing

of

aluminum

alloys.

Scr

Mater

2008;58:349–54.

doi:10.1016/j.scriptamat.2007.09.064. [36]

Humphreys FJ, Hatherly M. Recrystallization and related annealing phenomena. Elsevier; 2004.

ACCEPTED MANUSCRIPT

HIGHLIGHTS • •

AC C

EP

TE D

M AN U

SC

•

number and direction of passes influence the quality of the friction stir weld with SiC nano particles considerably; macrostructural study is not sufficient to evaluate the friction stir weld quality; high frequency acoustic microscopy investigations give detailed view of inner structure of the welds and show the defects, their position and size in the weld. ultrasonic and x-ray tomography image fusion gives complete information about the inner structure of the friction stir weld.

RI PT

•