Original Article

Microstructure and static immersioncorrosion behavior of AA7020-O Al platesjoined by friction stir welding

AO Mosleh, FH Mahmoud, TS Mahmoud and TA Khalifa

Abstract

In the present investigation, the influence of tool pin profile and postweld heat treatment on microstructure, hardness,

and static immersion corrosion behavior of AA7020-O Al plates joined by friction stir welding was investigated. Friction

stir welding was conducted using two tools having different pin profiles, typically, a tool with tapered cylindrical pin and a

tool with two flat-sided cylindrical pin. Postweld heat treatment was carried out using a solution heat treatment tem-

perature of 540� 1�C for 12 h followed by aging at 155� 1�C for 6 h. Corrosion tests were carried out by immersing

the welds in an aqueous solution containing NaCl and H2O2 for 6 h according to ASTM-G110. The results revealed that

the two flat-sided cylindrical pin tool produces finer a-Al grains, at the center of dynamically recrystallized zones, than

the tapered cylindrical pin tool. The postweld heat treatment slightly increases the size of the a-Al grains at the center of

dynamically recrystallized zones. In the as-welded conditions, the friction stir welded regions exhibited lower hardness

values than the base alloy. However, the regions friction stir welded using two flat-sided cylindrical pin tool showed

relatively higher hardness values than those regions friction stir welded using the tapered cylindrical pin tool. The

postweld heat treatment slightly increases the hardness of the welded regions to values that are still lower than the

base alloy. Generally, the dynamically recrystallized zones are more susceptible to corrosion than the base alloy. In both

AW and postweld heat treatment conditions, the thermomechanically affected zones showed the lowest corrosion

resistance when compared with dynamically recrystallized zones and heat affected zone regions. In the as-welded

conditions, regions friction stir welded using tapered cylindrical pin tool exhibited better corrosion resistance than

those friction stir welded using two flat-sided cylindrical pin. The postweld heat treatment improves the corrosion

resistance of the dynamically recrystallized zones friction stir welded using two flat-sided cylindrical pin tool.

Keywords

Friction stir welding, aluminum alloys, postweld heat treatment, corrosion

Date received: 15 March 2015; accepted: 14 June 2015

Introduction

The corrosion behavior of friction stir (FS) weldedaluminum alloys has been investigated in recentyears.1–6 Generally, it has been found that the weldzones are more susceptible to corrosion than theparent metal. FS welds of aluminum alloys such as2219, 2195, 2024, 7075, and 6013 did not exhibitenhanced corrosion of the weld zones. FS welds ofAl alloys exhibit intergranular corrosion mainlylocated along the nugget’s heat affected zone (HAZ)and enhanced by the coarsening of the grain bound-ary precipitates. The effect of friction stir welding(FSW) parameters on corrosion behavior of FSwelded joints was reported by many workers.5,7 Forexample, Surekha et al.7 studied the effect of tool rota-tion and traverse speeds on corrosion behavior ofAA2219-T87 Al alloy. The results indicated that therotation speed has the major influence in determining

the rate of corrosion, which is attributed to the break-ing down and dissolution of the intermetallic par-ticles. Jariyaboon et al.5 studied the effect of the toolrotation and travel speeds on the corrosion behaviorof FS welded joints of AA2024–T351 Al alloy. Again,they confirmed that the rotation speed plays the majorrole in controlling the location of corrosion attack.Localized intergranular attack was observed in thenugget region for low rotation speed welds, whereasfor higher rotation speed welds, attack occurred pre-dominantly in the HAZ.

Mechanical Engineering Department, Shoubra Faculty of Engineering,

Benha University, Cairo, Egypt

Corresponding author:

TS Mahmoud, 108 Shoubra St., B.O. 11629, Cairo, Egypt.

Emails: Tamer.AbdelMagid@feng.bu.edu.eg; Tsamir@benha-univ.edu.eg

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Generally, the joints are used in the as-welded(AW) condition, but there may be some advantagesin carrying out the welding with base material in a softcondition and improving properties by post-weld heattreatment (PWHT). For the base metal (BM) in theO-condition, the welding tool forces were found to below as compared to when it is in the T6 condition.8

Accordingly, FSW may be easier for the O-conditionand the welding system need not be very expensive.PWHT can restore the required properties. Severalinvestigations studied the effect of PWHT on themicrostructural and mechanical characteristics of Alalloys.8–12 For instance, Krishnan8 examined theeffect of PWHT on the microstructure and mechanicalproperties of FSW 6061 Al alloys. PWHT was carriedout using solution treatment temperatures of 520, 540,and 560�C followed by aging at 175 or 200�C. It wasfound that the welded regions exhibited very coarsegrains after PWHT. The hardness was found to beuniform across the welded regions after PWHT.Sullivan and Robson9 studied the microstructuralproperties of FS welded and postweld heat-treated(PWHTed) AA7449 Al alloy plates. The resultsshowed that applying the PWHT to a FS weld has adramatic effect on the hardness within the weldedregion. A reduction in the hardness was noticed inthe nugget and the thermomechanically affectedzone (TMAZ). The microstructure and hardness ofthe HAZ were relatively unaffected by PWHT.PWHT has the effect of reducing the sharp transitionin hardness at the boundary between the HAZexhibiting low hardness and the nugget with a rela-tively high hardness. Recently, Prisco et al.10 studiedthe tensile properties and fracture location ofAA2139-T351 FS welded joints in the AW and post-weld aged conditions. The results showed that whenthe joints are free of welding defects, they fail on theadvancing side (AS) of the HAZ exhibiting a largeamount of plastic deformation. When the revolutionarypitch (welding speed/rotational speed ratio) exceeds athreshold value, some micro-defects are formed in theweld nugget and the joints fail near the weld center.Postweld aged joints are less defect tolerant and theyfracture closer to the weld center, showing a reducedelongation at fracture and a ultimate tensile strength(UTS) within the order of magnitude of the AW joints.

The aim of the present work is to study the effect ofthe tool pin profile and PWHT on the corrosionbehavior of AA7020-O Al alloy plates joined byFSW. During FSW, the tool rotational and weldingspeeds were kept constant at 1800 r/min and 40 mm/min, respectively.

Experimental procedures

The base material used in the current study is AA7020Al alloy. The AA7020 aluminum alloy has a nominalchemical composition of (in wt%) 4.9% Zn, 1.15%Mg, 0.085% Si, 0.3% Mn, 0.12% Fe, 0.3% Cr,

0.001% Cu, 0.12% Ti, 0.12% Zr, and 92.904% Al.The alloy was received in the form of rolled plateswith 10 mm thickness. The base material was sub-jected to O-temper heat treatment, i.e. it was in theannealed condition before welding.

Two plates of AA7020-O Al alloy, each havedimensions of 250 mm (length)� 50 mm (width)� 10mm (thickness), were joined using FSW. Figure 1shows a schematic illustration of the FSW processwhich was conducted normal to the rolling directionto simulate a more drastic mechanical condition withrespect to the joints FS welded parallel to rolling dir-ection. Previous investigations showed superior mech-anical properties for the weldments with welddirection parallel to the rolling direction as comparedwith the joints with weld direction perpendicular tothe rolling direction.13,14

Two different tools having two different pin pro-files were used to weld the plates. The tools were madefrom H13 tool steel. A schematic illustration of theused tools is shown in Figure 2. FSW was conductedusing a vertical CNC milling machine at constant toolrotational and welding speeds of 1800 r/min and 40mm/min, respectively. In all experiments, the toolangle (angle between the tool axis and BM surface)was fixed to 2� and the friction pressure was held con-stant. The PWHT of welds was carried out using asolution heat treatment temperature of 540þ 1�C for12 h followed by aging at 155� 1�C for 6 h. Hardnessprofiles of the welded regions were measured for bothas-weld (AW) and PWHTed samples on the cross-sec-tion perpendicular to the welding direction using aVickers indenter with a 15 kg (&150 N) load.

Both macro- and microstructural characteristics ofthe FS welded plates were investigated using an opti-cal metallurgical microscope. Specimens were groundunder water on a rotating disc using SiC abrasivediscs of increasing finesse up to 1200 grit. Then theywere polished using 10 mm alumina paste and 3 mmdiamond paste. Micro-etching was carried out using achemical solution (0.5 ml HF 40%� 100 ml of H2O)for 5–60 s at ambient temperature. The macro-etchingwas carried out using a chemical solution consisting of100 ml of H2O, 50 ml of HNO3, 20 ml of HF, and 30ml of HCl for 1–3 min at ambient temperature. Thesize of the primary a-Al grains was measured usingstandard quantitative methods via a metallurgicalimage analyzer software. The chemical compositionof the elements and second phases in the DRZswere analyzed using a scanning electron microscope(SEM) equipped with an energy dispersive X-ray spec-troscopy analysis system.

Static immersion corrosion tests were performedon both AW and PWHTed samples according toASTM-G110 standard.15 This standard practiceevaluates the intergranular corrosion resistance ofheat-treatable aluminum alloys by immersion insodium chloride (NaCl)�hydrogen peroxide solution(H2O2). The corrosion tests were performed as

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Figure 2. A schematic illustration of the tools used for FSW AA7020 Al plates: (a) tapered cylindrical pin (TCP) tool and (b) two flat

sides cylindrical pin (TFSCP) tool (dimensions in mm).

Figure 1. A schematic illustration of the four stages of the FSW process: (A) start, (B) penetrations, (C) welding, and (D) finishing.

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follows: (1) The FS welded joints were cleaned withacetone to remove organic materials such as oils andother residuals; (2) prior to immersion in the test solu-tion, specimens were immersed in etching cleaner (945ml of reagent water� 50 ml of nitric acid (70%)� 5ml of hydrofluoric acid (48%)) for 1 min, followed bywashing in reagent water; (3) samples were thenimmersed in a solution of 57 g/l (0.98 M) NaCl and10 ml/l H2O2 (0.09 M) for 6 h; (4) after that, speci-mens were immersed in concentrated nitric acid (70%)for 1 min followed by washing in reagent water anddry air. The corroded samples were examined usingboth optical and SEMs to determine the corrosionbehavior of the FS welded joints.

Results and discussion

Macro- and microstructural characteristics

Figure 3 shows macrographs of the cross-sections ofthe as-weld AA7020-O joints. The welded region isclearly seen in the macrographs. At the center of thewelded region, the dynamically recrystallized zone(DRZ) is located. The HAZ is not clearly seen inthe macrographs. The macrographs show that thejoints FS welded using either a TCP (Figure 3(a)) ora TFSCP (Figure 3(b)) are free from cavities. Thecombination of tool rotational and welding speedsas well as the tool shape plays an important role inobtaining welded joints free of cavities.

The microstructure of the AA7020-O Al alloy BMconsists of large elongated grains typical of a rolledstructure, with an average grain size of 200 mm andaspect ratio of �6.9. The grains in the BM have anorientation along the rolling direction, whereas thegrains in the weld region are equiaxed. Figure 4shows a typical microstructure of a welded region.The micrograph shown in Figure 4 is located at theretreating side (RS) of a sample FS welded using TCPtool. The microstructure of the FS welded joints con-sists mainly of three distinct zones, typically, (i) finegrained DRZ, (ii) TMAZ, and (iii) HAZ. The TMAZexperiences both temperature and deformation during

FSW and characterized by a highly deformed struc-ture. The HAZ is the zone that is believed to be unaf-fected by any mechanical effects but only the thermaleffects caused by the frictional heat generated by theshoulder and tool pin rotation. Figure 5(a) and (b)shows the optical micrograph of the microstructure,at the central portion of the DRZs, of joints FSwelded using TCP and TFSCP tools, respectively. Itis clear that the dynamic recrystallization during FSWresults in generation of fine and equiaxed grains of thea-Al primary phase in the DRZ.

It is clear from Figure 5 that, joints FS weldedusing the TFSCP tool exhibited smaller size of a-Algrains, at the center of DRZ, as compared to thegrains resulting from the TCP tool (compareFigure 5(a) and (b)). The DRZs of samples FSwelded using the TCP and TFSCP tools exhibitedaverage grain sizes of �12.5 and �7 mm, respectively.These results may attribute to the pulsating action ofthe TFSCP that produces a high number of pulses/s.There is no such pulsating action produced by theTCP. Pin profile plays an important role in materialflow and in turn regulates the welding speed of theFSW process.8,9 The relationship between the static

Figure 3. The macrostructure of the as-weld AA7020-O joints FS welded using (a) TCP tool and (b) TFSCP tool.

Figure 4. Typical microstructure of FS welded zone located

at the retreating side of a sample FS welded using TCP tool.

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volume and dynamic volume decides the path for theflow of plasticized material from the leading edge tothe trailing edge of the rotating tool.8 The dynamic-to-static volume ratio for the different pin profilesused in the current investigation was calculated andlisted in Table 1. The ratios for TCP and TFSCP areequal to 1 and 1.23, respectively. Table 2 shows theeffect of tool profile on the pulsating stirring action inthe flowing material at a tool rotational speed of 1800r/min (i.e. 30 rev/s). It is clear that TFSCP producespulsating stirring action in the flowing material due tothe flat faces. The TFSCP produces 60 pulses/s whilethere is no such pulsating action exhibited by TCP asshown in Table 2.

Figure 6 shows typical optical micrographs of themicrostructure, at the center of DRZs, after PWHT ofsamples FS welded using both TCP and TFSCP tools.The microstructure of PWHT joints FS welded usingTCP tool showed uniformly distributed hardeningprecipitates. In contrast, nonuniform distribution ofthe hardening precipitates was observed at the weldedregions when using TFSCP tool (see Figure 6(b)).Moreover, the DRZs of samples FS welded usingTFSCP tool exhibited coarser precipitates than

those exhibited by the DRZs of samples FS weldedusing TCP tool. Microstructural examinationsshowed also that, after PWHT precipitates such as(AlZn4.5Mg1) were produced (see Figure 6(c)).Figure 7 shows a comparison between the mean sizeof a-Al grains, at the center of DRZs, for samples inboth AW and PWHT conditions. Both samples FSwelded using TCP and TFSCP tools exhibited graincoarsening, at the center of DRZs, after PWHT. Forexample, AW and PWHT samples FS welded using aTFSCP tool exhibited mean grain sizes, at the centerof the DRZs, of 7� 0.35 and 9.7� 0.65mm, respect-ively. The grain coarsening after PWHT observed inthe present investigation was also noticed by manyinvestigators.8,16–19

Hardness measurements

Figure 8 shows the effect of PWHT on hardness ofregions FS welded using TCP and TFSCP tools. Thewelded regions of the AW samples exhibited lowerhardness values than the BM. It has been reportedthat precipitate-strengthened alloys show a deterior-ation of mechanical properties in the weld zone

Figure 5. Optical micrographs of the microstructure, at the central portion of the DRZs, of joints FS welded using TCP (a) and

TFSCP (b) tools.

Table 1. Effect of pin profile on dynamic-to-static volume

ratio.

Pin profile

Area occupied

by pin in

static condition

Static

area

(mm2)

Dynamic

area

(mm2)

Dynamic

volume/

static

volume

Tapered

cylindrical

pin (TCP)

19.63 19.63 1.00

Two flat side

cylindrical

pin (TFSCP)

15.94 19.63 1.23

Note: The static and dynamic volume is calculated for the pin height of

7 mm.

Table 2. Effect of pin profile on the number of pulses/s at tool

rotational speed of 1800r/min.

Pin profile

Portion of

dynamic orbit

No. of

pulses/s

Tapered cylindrical

pin (TCP)

Nil

Two flat side cylindrical

pin (TFSCP)

60

Note: Pulses/s ¼ rotational speed � number of flat faces¼ 30� 2¼

60 pulses/s.

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because of the dissolution and growth of strengthen-ing precipitates during the welding thermal cycle.16

The PWHT samples exhibited higher hardnessvalues than that of the AW samples but still lowerthan that of the BM. The hardness values of theTMAZ, HAZ, and BM of the AW joint were alsoincreased after PWHT. This may attribute to the for-mation of precipitates during PWHT. The precipitateshave no glide planes in common with the matrix andact as dislocation barriers. This is the main reason forthe enhancement of the hardness observed in the pre-sent investigation. For the AW conditions, samples

FS welded using the TFSCP tool exhibited higherhardness values than those FS welded using theTCP tool. This may attribute to the finer grain struc-ture exhibited by the welded zones when using theTFSCP tool. In contrast, for the PWHT conditions,samples FS welded using the TCP tool exhibitedslightly higher hardness values than those FS weldedusing the TFSCP tool. This may attribute to the non-uniform distribution of the precipitates inside thewelded region after PWHT for zones FS weldedusing TFSCP tool as compared to those FS weldedusing TCP tool (compare Figure 6(a) and (b)). It iswell known that the hardness in the precipitation-hardening aluminum alloys greatly depends on thea-Al grain size as well as the size and distribution ofprecipitates.20 The finer size and distribution of the a-Al grains and precipitates, the higher hardness of thealloy. In the PWHT condition, regions FS weldedusing TFSCP tool exhibited finer grain size of a-Algrains (see Figure 7) but in the same time exhibitedcoarser and nonuniform distribution of the precipi-tates in comparison with regions FS welded usingTCP tool. The above results suggest that the sizeand distribution of the precipitates play a predomin-ant role in determining the hardness of the weldedregion.

The increase of the hardness of the welded regionafter PWHT observed in the present work was alsoreported by many workers.8,16 For example,Krishnan8 reported that the hardness values of thePWHT samples depend on the temperature of solu-tion treatment and aging. Increasing the solutionizedtemperature of the AA6061 Al alloy increases the

Figure 6. Optical micrographs of the microstructure after PWHT, at the center of DRZs, for samples FS welded using (a) TCP tool,

(b) TFSCP tool, (c) SEM micrograph of the precipitates shown in (b); (d) EDX analysis of precipitates shown in (c).

Figure 7. The mean size of the primary a-Al grains, at the

center of DRZs, for the AW and PWHT samples FS welded

using TCP and TFSCP tools.

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hardness of the welded regions. This is because theamount of quenched-in vacancies would be higher athigher temperatures thus increasing the number ofnucleation sites. Among all solutionized temperatures(520, 540, and 560�C), samples solutionized at 560�Cshowed the maximum hardness while those whichwere solutionized at 520�C showed the lowest hard-ness values. The samples aged at 200�C resulted insomewhat lower hardness values as compared to thesamples aged at 175�C.

Corrosion behavior

Figure 9 shows typical optical macrographs of cross-sections perpendicular to the welding direction for theAW and PWHT joints after immersion in a solutioncontaining sodium chloride (NaCl) and hydrogen per-oxide (H2O2) for 6 h. It is clear that surface degrad-ation has occurred and corrosion products (blackdark regions) cover the surfaces of the specimens.For the AW conditions, the surfaces of the specimensat the DRZs were less covered with the corrosionproducts when compared with the HAZ. ForPWHT samples, corrosion products appear to coverheavily the entire surface of the specimen weldedusing a TCP (Figure 9(c)) without a clear differenti-ation between the weld micro-zones. In the case of

joints welded using a TFSCP, less corrosion productswere observed in the DRZ as compared to the HAZ.

Micrographs of the BM regions after corrosiontests in both AW and PWHT conditions are shownin Figure 10. Examinations of the micrographsrevealed that the pitting corrosion is the main corro-sion mechanism. Few sites with intergranular corro-sion attack at the grain boundaries were observed. Inthe AW conditions, relatively few number of pits wereobserved on the corroded surfaces of BM (seeFigure 10(a)) while in the PWHT conditions, largenumber of small size pits are observed on the cor-roded surface of BM (see Figure 10(b)). Such resultsindicate the higher corrosion severity of BM inPWHT condition than in the AW condition.The reduction of the corrosion resistance of BM inPWHT condition may attribute to the formation ofcoarse and nonuniformly distributed precipitates afterPWHT. Such precipitates may interact electrochem-ically with the a-Al matrix leading to accelerated cor-rosion.21 In addition, galvanic interactions betweenthe precipitates and matrix can also accelerate corro-sion. Preferential corrosion along the precipitates/matrix interface can lead to rapid penetration alongthe interfacial areas. This can result in enhanced cor-rosion of the BM in the PWHT condition in compari-son to the corrosion of the BM in the AW condition.

Figure 8. The effect of PWHT on hardness of regions FS welded using TCP (a) and TFSCP (b) tools.

Figure 9. Macrostructure of cross-sections perpendicular to the welding direction of the AW (a,b) and PWHT (c,d) joints after

immersion in a solution containing sodium chloride (NaCl)þ hydrogen peroxide (H2O2) for 6 h. (a,c) TCP tool, (b, d) TFSCP tool.

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It has been observed22–24 that coarse equiaxed grainstend to improve the corrosion resistance when com-pared with fine equiaxed grains.

Examination of the corroded surfaces indicatesthat the AS showed relatively less corrosion than theRS. Figure 11 shows optical micrographs of typicallocalized corrosion at the RS of AW and PWHT FSwelded joints after immersion in NaCl�H2O2 solu-tion for 6 h. Examination of the micrographs indi-cates that, in both AW and PWHT conditions, theTMAZ regions showed lower corrosion resistancethan both the DRZ and HAZ regions. During FSW,the TMAZ heats up to a temperature just below thesolutionizing temperature of the alloy. This results ina coarsening of second phase particles, which make

the TMAZ region more highly susceptible to corro-sion and severe pitting corrosion may have occurred.

Figure 12 shows optical micrographs of the typicallocalized corrosion, at the center of DRZs, for AWand PWHT samples. It is clear that intergranular cor-rosion has taken place at the boundaries of a-Algrains. In addition, a considerable number of pits(dark points) were observed on the corroded surfacesof the DRZs indicating that pitting corrosion has alsooccurred. It has been observed also that the DRZs ofjoints FS welded using TCP tool exhibited a largerquantity and size of pits in the PWHT conditionthan in the AW condition (compare Figure 12(a)and (c)). In contrast, the DRZs of joints FS weldedusing TFSCP tool exhibited a smaller quantity and

Figure 10. Optical micrographs of the BM region after corrosion tests in (a) the AW condition and (b) PWHT condition.

Figure 11. Optical micrographs of the typical localized corrosion at retreating side of AW and PWHT friction stir welded joints

after immersion in NaClþH2O2 solution for 6 h. (a,c) TCP, (b,d) TFSCP.

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size of the pits in the PWHT condition than in theAW condition (compare Figure 12(b) and (d)).

Examination of the micrographs of the AW cor-roded surfaces revealed that the corrosion resistancein DRZs is higher when using TCP tool than TFSCPtool. This may attribute to the smaller grain size ofDRZs achieved with TFSCP tool as mentioned ear-lier. The smaller grain size provides a larger area ofgrain boundaries, which accelerates corrosion.Generally, for AW condition, the corrosion attack isless in BM compared to the weld metal (see Figures 10and 12). The AA7020-O Al base alloy has corrodedmainly by pitting corrosion whereas the DRZs werecorroded by both intergranular and pitting corrosionmechanisms. Comparing Figure 12(b) and (d), it canbe concluded that the DRZs FS welded using TFSCPtool exhibited better corrosion resistant in the PWHTcondition than in the AW condition.

Corrosion potential of the precipitates is not thesame as the Al matrix. This difference creates the for-mation of a galvanic cell. The potential differencebetween the precipitates and the matrix causes theformation of corrosion cells. Higher quantities ofthe precipitates cause more cathodic reactions tooccur. Figure 13 shows SEM micrograph of the pre-cipitates found on the corroded surface of DRZregion of sample FS welded using TCP tool in thePWHT condition. It is obvious that corrosion hasmostly occurred on the neighborhood of the precipi-tates. This indicates formation of corrosion cellbetween Al matrix and the precipitates. Bousquet

et al.25 investigated the corrosion behavior of FSwelded AA2024-T3 aluminum alloy using both nor-malized intergranular corrosion test (ASTM-G110)and local electrochemical open circuit potential meas-urements. The results showed that corrosion severitydepends on size and density of intermetallics and onintergranular precipitation. The HAZ close to theTMAZ is the most sensitive to intergranular corrosionbecause of the presence of continuous lines of S?(S)intergranular precipitates at grain boundaries. Pitting

Figure 12. Optical micrographs of the typical localized corrosion, at the center of DRZs, of AW (a,b) and PWHT (c,d) joints after

immersion in a solution containing sodium chloride (NaCl)þ hydrogen peroxide (H2O2) for 6 h. (a, c) TCP, (b, d) TFSCP tool.

Figure 13. SEM micrograph of the precipitates found on the

corroded surface of DRZs of sample FS welded using TCP tool

in the PWHT condition.

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corrosion is due to the intermetallic particles. Theirfragmentation produced by stirring effect modifies thepitting corrosion behavior.

Conclusions

The following conclusions are drawn based on thepresent investigation:

1. The AW joints FS welded using TFSCP toolexhibited finer a-Al grain size, at the center ofDRZs, than those joints FS welded using TCPtool. The DRZs of samples FS welded using theTCP and TFSCP tools exhibited average a-Algrain sizes of �12.5 and �7 mm, respectively.After the PWHT, a slight coarsening of the a-Algrains was observed.

2. For the AW conditions, regions FS welded usingTFSCP and TCP tools exhibited lower hardnessvalues than the base alloy. However, using theTFSCP tool resulted in a slightly higher hardnessvalues in the welded regions than those observedwhen using the TCP tool. The PWHT increasesthe hardness of the welded regions but still lowerthan the base alloy.

3. The BM exhibited better corrosion resistance com-pared to the FS welded regions. For the AW con-ditions, the DRZs regions of samples FS weldedusing TCP tool showed better corrosion resistancethan those regions FS welded using TFSCP tool.The PWHT improved the corrosion resistance ofthe DRZs regions FS welded using the TFSCP.For both AW and PWHT conditions, theTMAZ region showed poor corrosion resistanceas compared to DRZs and the HAZ regions.

Funding

The authors are thankful to Benha University—ShoubraFaculty of Engineering for providing financial support

and facilities for carrying out this work.

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