modification of electrical conductivity by friction stir processing of aluminum alloys

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The International Journal ofAdvanced Manufacturing Technology ISSN 0268-3768Volume 57Combined 5-8 Int J Adv Manuf Technol (2011)57:511-519DOI 10.1007/s00170-011-3308-4

Modification of electrical conductivity byfriction stir processing of aluminum alloys

Telmo G. Santos, R. M. Miranda, PedroVilaça & J. Pamies Teixeira

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ORIGINAL ARTICLE

Modification of electrical conductivity by friction stirprocessing of aluminum alloys

Telmo G. Santos & R. M. Miranda & Pedro Vilaça &

J. Pamies Teixeira

Received: 6 January 2011 /Accepted: 28 March 2011 /Published online: 20 April 2011# Springer-Verlag London Limited 2011

Abstract A wide range of solid-state manufacturing tech-nologies for joining and modification of material originalproperties are assuming increasing importance in industrialapplications. Among these, friction stir-based technologiesare the most significant, namely, friction stir processing(FSP) and friction stir surfacing. The electrical conductivityis a significant property undergoing modification, but thisproperty has not been characterized and fully exploitedfrom the technological point of view. The present workaims to study the electrical conductivity behavior in FSP ofaluminum alloys in order to identify the major factorsgoverning this property. FSP was applied on AA1100,AA6061-T6, and AA5083-H111 alloys with differentparameters. Electrical conductivity profiles were measuredat different depths and compared with hardness profiles andmicrostructures. It was found that solid-state friction stirprocessing of aluminum alloys lead to electrical conductivitychanges of about 4%IACS (International Annealed CopperStandard). These changes are more intense in heat-treatablealloys than in work-hardenable ones. Higher rotating versustravel speed ratios (Ω/V) induce higher variations in theelectrical conductivity. In FSP, the factors governing the

electrical conductivity variations are mostly the grain sizeand the presence of precipitates. It was shown that, for someFSP applications, electrical conductivity may be a processcharacterization method more precise and meaningful thanhardness to assess local material condition.

Keywords Friction stir processing . Aluminum alloys .

Electrical conductivity . Process characterization

1 Introduction

Solid-state materials processing technologies involve mech-anisms that lead to chemical and physical propertiesmodifications [1]. This fact triggered the development ofseveral mechanical technological processes dedicated tomodify these properties to improve materials and compo-nent performance. Examples of these processes are thefriction stir processing (FSP) [2] that aims to improve basematerial properties. Friction hydro pillar processing [3] andfriction stir surfacing (FSS) [4] aim to improve wearresistance and surface hardness.

Other mechanical technological processes do not have amain purpose of material modification, but this is aninevitable consequence of solid-state processing as infriction stir welding [5], ultrasonic welding, or friction spotwelding [6].

As a consequence of any solid-state manufacturingtechnology, the electrical conductivity is more or lessmodified. Nevertheless, this significant property has notbeen fully exploited from a technological point of view. Infact, limited work exists to characterize the electricalconductivity variation in solid-state processed materialsand its correlation with inherent physical and metallurgicalphenomena [7, 8]. There is insufficient knowledge on the

T. G. Santos (*) :R. M. Miranda : J. P. TeixeiraUNIDEMI, Departamento de Engenharia Mecânica e Industrial,Faculdade de Ciências e Tecnologia,Universidade Nova de Lisboa,2829-516, Caparica, Portugale-mail: [email protected]

P. VilaçaIDMEC, Instituto de Engenharia Mecânica—Pólo IST,Lisbon, Portugal

P. VilaçaIST, Instituto Superior Técnico, Universidade Técnica de Lisboa,Lisbon, Portugal

Int J Adv Manuf Technol (2011) 57:511–519DOI 10.1007/s00170-011-3308-4

Author's personal copy

variation of electrical conductivity fields and the materialbehavior that influences the former.

This scientific knowledge can be useful to predict anddevelop solid-state processing parameters enabling betteroverall performance of the components. Another field ofapplication of the electrical conductivity is the possibility touse this property to characterize processed materials andwelded joints complementing, or even substituting, otherexisting techniques as hardness measurements and metal-lographic analysis [7]. Additionally, this information iscrucial when non-destructive testing based on electricalmethods is to be applied, as eddy currents [9, 10]. In fact, inthese methods, defects are detected based on a local changeof the electrical conductivity in the material. A previousknowledge of the electrical conductivity field variation dueto processing is required, in order to distinguish back-ground material from eventual discontinuities [11].

The aim of this study was to characterize and understandthe variation of electrical conductivity fields in severalaluminum alloys processed in solid state and to correlatethis property with the hardness variation and the micro-structures observed in the various regions. Friction stirprocessing was performed on AA1100, AA6061-T6, andAA5083-H111 alloys with different parameters. Electricalconductivity profiles were measured at different depths andcompared with hardness profiles and microstructuresobserved under optical microscopy.

Since electrical conductivity behavior depends on theelectrons mobility, it is affected by both mechanical andthermal effects (Eq. 1). The mechanical effects include thestress and strain levels applied on the material and thepresence of preexisting or induced macro defects (Eq. 2). Thethermal effects include diffusion-controlled processes as grainsize, precipitates dispersion, and their morphology (Eq. 3).

s ¼ f ðM ; TÞ ð1Þ

M ¼ f ð"; S;DÞ ð2Þ

T ¼ f ðP; GÞ ð3ÞWhere:

σ Electrical conductivity [%IACS]M Mechanical effectsT Thermal effectsε Strain [m/m]S Stress [MPa]D Macro defectsP Precipitates (quantity and morphology)G Grain (shape and size)

From these equations, it can be seen that some of thefactors have contributions in opposite senses, that is, some

have a direct contribution to improve electrical conductivity,while others have an inverse contribution. Additionally, somefactors are coupled, that is, not independent. For instance, acold rolled plate that is subjected to a raise in temperatureundergoes recrystallization with grain refining.

2 Methodology

In order to understand the predominance and the individualcontribution of each factor to the electrical conductivityvariation, an experimental plan was established.

A first set of experiments was conducted under uniaxialtensile testing to evaluate the individual effect of the stress(S). According to Eq. 4:

s ¼ f ðSÞ j "; D; P; G¼Const: ð4ÞThe following group of experiments aimed to assess the

effect of induced strain (ε) under compression (Eq. 5).

s ¼ f ð"Þ j S; D; P; G¼Const: ð5ÞA third set of experiments was performed by FSP on

AA1100 plates. In these experiments the additional factorstudied was the grain size (G). This was assessedperforming the process under ratios of rotating speed (Ω)versus travel speed (V) of 6.2 and 1.0 rev/mm, whichcorrespond to the so called “hot” and “cold” friction stirprocessing conditions, respectively (Eq. 6). All FSP trialswere performed as bead on plate in order to avoid macroroot defects (D). Additionally, an adequate vertical forcewas applied to each alloy to avoid volume defects.

s ¼ f ð"; S; GÞ j D; P¼Const: ð6ÞA fourth set consisted of processing AA6061-T6 and

AA5083-H111, a heat-treatable and a non-heat-treatablealloy, respectively, also in cold and hot processingconditions. The objective was to evaluate the previousfactors plus the influence of precipitates (Eq. 7), since thesealloys have a significative amount of alloying elements.

s ¼ f ð"; S; G; PÞ j D¼Const: ð7Þ

3 Experimental procedure

4 Materials

The materials under study were plates of extruded AA1100,10 mm thick; rolled AA6061-T6, 10 mm thick; and rolledAA5083-H111, 8 mm thick with the chemical compositionpresented in Table 1.

512 Int J Adv Manuf Technol (2011) 57:511–519


4.1 Tensile and compression tests

Prismatic specimens with 20 mm width and 200 mm lengthwere tested in AA1100, AA6061-T6, and AA5083-H111 with5, 7, and 8 mm thickness, respectively. Specimens weremachined in order to verify the existence of any differencebetween the outer surface and inner machined surface of thespecimens, since the materials were obtained by extrusion androlling. Tensile tests were performed in a universal tensiletesting machine ZWICK Z050 equipped with a 50-kN loadcell, with a load application speed of 0.2 kN/s. AA1100 wastested from 0 to 40 MPa with increments of 10 MPa while inAA6061-T6 these increments were of 75 MPa from 0 to224 MPa (81% yield strength), and AA5083-H111 wastensiled from 0 to 188 MPa (82% yield strength) withincrements of 31 MPa. At each step, the test was stopped for60 s keeping the stress constant to perform electricalconductivity measurements.

Uniaxial compression tests between two flat plates wereperformed in a conventional hydraulic press at a very slowspeed. The specimens were lubricated between each smallcompression stages in order to ensure good homogeneityplasticity, and minimize barreling. Specimens with a squaretransversal section of 20×20 mm were compressed until amaximum true strain (ε) of 1.77, 1.20, and 0.98 (m/m) inAA1100, AA6061-T6, and AA5083-H111, respectively.

4.2 Friction stir processing

Friction stir processing was performed with a conicalthreaded probe and a shoulder with a spiral scrolled profile,as depicted in Fig. 1 and described in Table 2. Table 3summarizes the parameters used in the hot and coldprocessed conditions.

4.3 Electrical conductivity measurements

The electrical conductivity measurements were performedusing an absolute helicoidally shielded eddy current (EC)probe Olympus Nortec p/100–500 kHz/90.5/6. A perma-nent lift-off of thin polymer of 50 μm thickness was used.

The electrical conductivity was calculated from the realand imaginary part of the electrical impedance of the probe.Calibration tests were made in conductivity standardsamples and the results were compared with other com-mercial EC equipments, namely Sigmatests® D 2.0068 andNortec 500 d with an accuracy within ±0.5%IACS from 0.9to 65%IACS and ±1.0% of values over 65%IACS.

Preliminary conductivity measurements were performedat different frequencies, in the range of 10 kHz to 2 MHzand the final tests were performed at 150 kHz. For thisfrequency the penetration depths of the eddy currents were0.29, 0.34, and 0.41 mm for AA1100, AA6061-T6, andAA5083-H111, respectively. This is due to the skin effectof the eddy currents, that is, the current density is maximumat the material surface and decreases exponentially withdepth. According to the non-destructive testing practice, thestandard penetration depth is defined as the depth at whicheddy current density decreases down to 1/e, where “e” isthe nepper number [10].

Conductivity measurements were made along a sweep inthe x-axis perpendicular to the processed bead, at halfthickness. The starting point was set at 30 mm before thecenter of the nugget and 60-mm long segments werecharacterized with 200-μm distance between each valueacquisition. In order to assure repeatability of results,measurements were taken in samples extracted from thestarting and ending zones of the processed beads.

Material Al Cr Cu Fe Mg Mn Si Ti Zn

AA1100 99 – 0.05 – – 0.05 – – 0.1

AA6061-T6 98.8–98.6 0.04–0.35 0.15–0.4 0.7 0.8–1.2 0.15 0.4–0.8 0.15 0.25

AA5083-H111 92.4–95.6 0.05–0.25 0.1 – 4–4.9 0.4–1 0.4 0.15 0.25

Table 1 Chemical compositionof base materials (wt.%)

a) b)Fig. 1 Friction stir weldingtool. a Probe of the tool, bassembled tool (probe andshoulder)

Int J Adv Manuf Technol (2011) 57:511–519 513


4.4 Microstructural analysis and hardness measurements

Processed samples were prepared for microstructuralanalysis and hardness measurements. Samples were cut,polished, and chemically etched with Keller reagent toreveal the metallurgical structure of the different zonesobserved under optical microscopy. Vickers hardness testswere made on transversal section of the processed beads,according to ISO 6507-1, using a Mitutoyo HM-112Vickers hardness tester under a load of 1.96 N.

5 Results and discussion

5.1 Effect of stress and strain on the electrical conductivity

From Fig. 2 it is possible to see that the electricalconductivity does not depend on the stress within the testedrange that was 80% above the yield strength of the alloysunder study. No differences were found between the outerand inner surfaces of the machined specimens. This is animportant information when comparing the fields of electricconductivity due to FSP between different plates, and atdifferent depths. It must be noticed that electrical conduc-tivity measurements were performed with a circular eddycurrent probe which does not evaluate the eventual effectsof anisotropy of this property. In fact, the electricalconductivity depends on the electrical field direction ofapplication and during a uniaxial tensile test, the materialundergoes extensions of opposite signs in longitudinal andtransversal directions, so that an increase in electricalconductivity in one direction and reduction in the othercould occur, which is not detectable with a circular probe.The use of directional probes could detect this phenome-non. However, other researchers [12] showed that this

variation is insignificant and within the error range of theequipment.

The variation of electrical conductivity with strain isdepicted in Fig. 3. A small decrease is observed for allalloys due to the plastic deformation as observed by [13].

Though the strain induced during these experiments isbelow the one observed in FSP, it must be noticed that itproduces significant variations in hardness, as shown inFig. 4. These variations are of the same order of magnitudeas the one observed in friction-stir-processed materials.Thus, it can be said that the conductivity is independent ofthe strain. For AA1100 an increase of 2%IACS is observedfor true strains of 0.4 to 0.5, eventually due to ametallurgical hardening process, that is also responsiblefor the increase in hardness. This phenomenon is out of thescope of this investigation and thus it will not be addressed.

Table 2 Geometric parameters of the FSP probe

Geometric shoulder features Geometric probe features

Morphology Outerdiameter[mm]

Morphology Length[mm]

Meandiameter[mm]

Plan with 2scrolledprofiles

18 Conic withtrapezoidalscrew

5 7

Table 3 FSP parameters for hot and cold conditions

FSWcondition

Travel speed V[mm/min]

Rotation speed Ω[rev/min]

Ratio Ω/V[rev/mm]

Hot 180 1,120 6.22

Cold 355 355 1.00

Fig. 2 Effect of the stress in electrical conductivity of AA1100,AA6061-T6, and AA5083-H111

Fig. 3 Effect of the strain in electrical conductivity of AA1100,AA6061-T6, and AA5083-H111



5.2 Effect of stress and strain on hardness

Opposite to the electrical conductivity, for the aluminumalloys under study, hardness was always seen to increasewith the strain, that is, with plastic deformation. Figure 4shows the micro hardness variation with strain measured oncompressed specimens as described in the experimentalprocedure. In fact, work hardening of aluminum alloys is acommon process for improving mechanical strength.

Comparing Figs. 3 and 4 it can be observed thatincreasing the strain does not affect the electrical conduc-tivity, but significantly increases hardness. In fact, theplastic deformation, or strain imposed, generate defects asdislocations, which oppose a mechanical resistance to thehardness tester indenter. This results in an increase inhardness. However, the quantity of dislocations does notaffect the electronic mobility that is responsible for the

electrical conductivity. So, in summary, the mechanicalfactors highlighted before, stress and strain do not affectsignificantly the electrical conductivity, thus, Eq. 1 can besimplified according to Eq. 8.

s ¼ f ð"; S; G; PÞ �! s � f ðG; PÞ ð8Þ

5.3 Friction stir processing on AA1100 plates

As shown before, since the residual stress and straininvolved in FSP beads do not contribute to the electricalconductivity variations, the factors governing this propertyare the grain size (G) and the presence of precipitates (P).So, the following tests will be analyzed regarding G and P.

Considering the processed beads produced under coldand hot conditions, Fig. 5 and 6, respectively, it can be seenthat the latter are wider than the former due to the higherheat input. This is clearly noticed in AA1100 and AA6061-T6 alloys that are both heat treatable.

For AA1100, the electrical conductivity is almost constantalong the processed bead produced in cold conditions, while adrop in hardness is observed, from the base material to thenugget. Non-homogeneities in the nugget are observed due tothe resulting visco-plastic material flow, as a consequence oflow rotation speed versus travel speed ratio. The low plasticdeformation and heat input in this condition are insufficientfor homogeneous dynamic recrystallization and grain refine-ment in the nugget.

The electric conductivity is sensitive to processing con-ditions as revealed in processed beads performed under hotconditions. In this case, hardness shows a profile along theprocessed bead similar to the electrical conductivity, that is,they both decrease in the nugget. The very fine grain observedin this region can make the electron mobility responsible forthe electrical conductivity difficult, while the high deform-

Fig. 4 Effect of the strain in micro Vickers hardness of AA1100,AA6061-T6, and AA5083-H111

Fig. 5 Transversal macrograph,electrical conductivity, andVickers hardness profiles of thecold FSP on AA1100



ability of AA1100 alloy and the low content of residualelements explain the decrease in hardness since there is aninsufficient amount of precipitates to affect hardness.

Figure 7 shows the microstructures of the differentregions of the processed bead produced in hot conditionsthat is under high rotation speeds and low transversespeeds, which induce higher plastic deformation and heatgeneration, thus dynamic recrystallization of the grains is

more intense, together with the solubilization of the existingresidual elements. This behavior was also observed in theother heat-treatable alloy: AA6061-T6.

5.4 Friction stir processing on AA6061-T6

Figure 8 shows the macrograph of a transverse section of acold processed bead in AA6061-T6, as well as the hardness

Fig. 6 Transversal macrograph,electrical conductivity, andVickers hardness profiles of thehot FSP on AA1100

Fig. 7 Macrograph of a trans-versal section of a hot FSP onAA1100 and micrographs ofidentified regions



and electrical conductivity profiles. It can be observed thatthe electrical conductivity is almost constant along theprocessed bead as shown by the green square dotted line fora depth z=−2 mm. At half thickness, however, it largelyincreases in the nugget from 43.3 to 47%IACS, due to thepresence of heterogeneities in the nugget as a result of coldFSP condition with insufficient visco-plastic material flowand an apparent low forging force. Thus, it is possible thatunder these conditions the grain refinement was limited,especially in the heterogeneous zones, placed exactly at halfthickness where this abnormal increase in conductivity wasmeasured.

Hardness has a significant drop from the base material tothe nugget since this is more sensible to structuralmodifications, mainly due to the presence of precipitatesfrom alloying elements in this heat-treatable alloy. The twoadjacent hardness peaks can be due to overaging of thisalloy that is annealed and artificially aged.

For high rotation and low travel speeds, that is, under hotconditions, the variation of electrical conductivity is verysmall, about 1.5%IACS. It decreases to a minimum of42.5%IACS in the nugget. The decrease in the heat-affectedzone is due to precipitate solubilization and grain coales-cence that occurs as a consequence of the heat generated inthe process. A slight increase of electrical conductivity isobserved in the nugget that is attributed to the coalescenceof dynamic recrystallized grain due to total heat generated.This reduces hardness in the nugget as observed in Fig. 9.The two adjacent peaks can be due to overaging of thisalloy that is annealed and artificially aged.

5.5 Friction stir processing on AA5083-H111

Observing the electrical conductivity and hardness profilesfor the work-hardenable AA5083-H111 alloy processed incold and hot conditions, Fig. 10 and Fig. 11, respectively,

Fig. 8 Transversal macrograph,electrical conductivity, andVickers hardness profiles of thecold FSP on AA6061-T6

Fig. 9 Transversal macrograph,electrical conductivity, andVickers hardness profiles of thehot FSP on AA6061-T6



no significant variations were noticed. In cold processedsample, the electrical conductivity was constant along thebead, while a slight increase in hardness occurred due to thegrain refinement in the nugget. In the hot processed samplethe electrical conductivity had very minor variations, from28%IACS in the base material to 28.5%IACS in the TAMZregion to 27%IACS in the nugget. Hardness was also seento be constant along the processed bead. This is a typicalbehavior of non-heat-treatable alloys which are hardened bycold plastic deformation. The small decrease of theelectrical conductivity in the nugget is essentially due tothe slight grain refinement in the stirred zone, increasing thegrain boundary density. The increase of electrical conduc-tivity in the thermo-mechanical affected zone (TMAZ) isdue to the grain coalescence, since this is not a stirred zone;it was subjected to an increase in temperature by conduc-tion, promoting the grain coalescence.

So, in this alloy, electrical conductivity variations arereduced, while a small increase in hardness is seen due tograin refinement. The main factor governing the electricalconductivity is, thus, the grain size, while the precipitatescan be neglected since electrons can easily find alternativeflowing paths in a highly conductive aluminum matrix.

Figure 11 evidences the intrinsic different physicalphenomenon inherent to each characterization method,providing complementary information. Hardness profile ismore irregular affected mainly by the presence of existingprecipitates, size, and distribution, while electrical conduc-tivity clearly identifies major structural modificationsdelimiting the different zones as base material, TMAZ,and nugget.

The tests in this alloy permit to conclude that electricalconductivity may be a process characterization methodmore useful than hardness to assess the material condition.

Fig. 10 Transversal macro-graph, electrical conductivity,and Vickers hardness profiles ofthe cold FSP on AA5083-H111

Fig. 11 Transversal macro-graph, electrical conductivity,and Vickers hardness profiles ofthe hot FSP on AA5083-H111



6 Conclusions

From the present study the following conclusions can bedrawn:

1. Solid-state friction stir processing of aluminum alloyslead to electrical conductivity changes of about 4%IACS. These changes are more intense in heat-treatablealloys as AA1100 and AA6061-T6 than in work-hardenable alloys as AA5083-H111.

2. Friction stir processing conditions with high rotatingversus travel speed ratios (Ω/V) induce higher varia-tions in the electrical conductivity. These processparameters showed to be determinant for governingthe electrical conductivity variation.

3. It was seen that stress and strain do not affectsignificantly the electrical conductivity, while strainlargely increases hardness. In FSP, the factors govern-ing the electrical conductivity variations are mostly thegrain size and the presence of precipitates (bothquantity and morphology).

4. Grain size is the major responsible factor for theelectrical conductivity level since grain boundariesconstitute an inevitable obstacle to electron mobility.So, an increase of electrical conductivity reflects a graincoalescence phenomena, or alternatively, a decrease ofelectrical conductivity is observed in grain-refinedprocessed zones.

5. Precipitates mostly affect hardness but not theelectrical conductivity, since electrons can easily findalternative flowing paths in a highly conductivealuminum matrix.

6. It was shown that, for some FSP applications, electricalconductivity may be a process characterization methodmore useful than hardness to assess material condition,since it identifies more precisely different zones as basematerial, TMAZ, and nugget.

Acknowledgment The authors would like to acknowledge thePortuguese Foundation for Science and Technology (FCT/MCTES)for its financial support of FSW conditions development via the

project PTDC/EME-TME/69999/2006 and FSP conditions via projectPTDC/EME-TME/103543/2008-FRISURF.

References

1. Ma ZY (2008) Friction stir processing technology: a review. Metaland Mat Trans A 39A:642–658

2. Nascimento F, Santos T, Vilaça P, Miranda RM, Quintino L(2009) Microstructural modification and ductility enhancement ofsurfaces modified by FSP in aluminium alloys. Mater Sci Eng A506:16–22. doi:10.1016/j.msea.2009.01.008

3. Pinheiro G (2008) Local Reinforcement of Magnesium Compo-nents by Friction Processing: Determination of Bonding Mecha-nisms and Assessment of Joint Properties. Dissertation,Technischen Universität Hamburg-Harburg. http://www.gkss.de/imperia/md/content/gkss/zentrale_einrichtungen/bibliothek/berichte/gkss_berichte_2008/gkss_2008_12.pdf. Accessed 9December 2010

4. Rafi H et al (2011) Microstructural evolution during frictionsurfacing of tool steel H13. Mater Des 32:82–87. doi:10.1016/j.matdes.2010.06.031

5. International Patent no. PCT/GB92/02203 and GB Patent no.9125978.8, 6 December 1991; Thomas, Wayne M.

6. Rosendo T, et al. (2009) Friction Spot Processes: FSSW and FSpW.Helmholtz Zentrum Geesthacht Centre website.http://www.gkss.de/imperia/md/content/gkss/institut_fuer_werkstoffforschung/wmp/poster-apresentacao-gkss2.pdf. Accessed 9 December 2010

7. Santos T, Vilaça P, Miranda RM (2011) Electrical conductivityfield analysis for evaluation of FSW joints in AA6013 andAA7075 alloys. J Mater Process Technol 211:174–180.doi:10.1016/j.jmatprotec.2010.08.030

8. Ari M et al (2008) Microstructure and thermo-electrical transportproperties of Cd–Sn alloys. Mater Charact 59:624–630.doi:10.1016/j.matchar.2007.05.014

9. ASM Handbook Committee (1992) Nondestructive Evaluationand Quality Control, Volume 17, ASM Handbook. Ed. ASM, NY

10. Hellier CJ (2001) Handbook of nondestructive evaluation.McGraw-Hill, New York

11. Rosado L et al (2010) Advanced technique for non-destructivetesting of friction stir welding of metals. Measurement 43:1021–1013. doi:10.1016/j.measurement.2010.02.006

12. Blodgett M, Nagy P (2004) Eddy current assessment of near-surface residual stress in shot-peened nickel-base superalloys. JNon destruct Eval 23:107–123

13. Çetinarslan C (2009) Effect of cold plastic deformation onelectrical conductivity of various materials. Mater Des 30:671–673. doi:10.1016/j.matdes.2008.05.035



http://dx.doi.org/10.1016/j.msea.2009.01.008

http://www.gkss.de/imperia/md/content/gkss/zentrale_einrichtungen/bibliothek/berichte/gkss_berichte_2008/gkss_2008_12.pdf



http://dx.doi.org/10.1016/j.matdes.2010.06.031


http://www.gkss.de/imperia/md/content/gkss/institut_fuer_werkstoffforschung/wmp/poster-apresentacao-gkss2.pdf



http://dx.doi.org/10.1016/j.jmatprotec.2010.08.030

http://dx.doi.org/10.1016/j.matchar.2007.05.014

http://dx.doi.org/10.1016/j.measurement.2010.02.006


modification of electrical conductivity by friction stir processing of aluminum alloys

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