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Journal of Materials Processing Technology 209 (2009) 4186–4193

Contents lists available at ScienceDirect

Journal of Materials Processing Technology

journa l homepage: www.e lsev ier .com/ locate / jmatprotec

nterfacial microstructure and strength of steel/aluminum alloy joints weldedy resistance spot welding with cover plate

anfeng Qiu ∗, Chihiro Iwamoto, Shinobu Satonakaraduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan

r t i c l e i n f o

rticle history:eceived 19 June 2008eceived in revised form 28 October 2008ccepted 1 November 2008

a b s t r a c t

We joined aluminum alloy A5052 to cold-rolled steel SPCC (Steel Plate Cold Commercial) and austeniticstainless steel SUS304 using resistance spot welding with a cover plate. The interfacial microstructurewas observed using transmission electron microscopy. A thick two-layered reaction layer contains Fe2Al5and FeAl3 and a thin serration reaction layer contains Fe2Al5 and FeAl3 were observed at the A5052/SPCC

eywords:nterfaceeaction productsicrostructure

luminum alloyesistance spot welding

and A5052/SUS304 interface, respectively. Mechanical property analysis suggested that the reaction layerhas no effect on the tensile shear strength of the A5052/SUS304 joint and that the tensile shear strengthof the A5052/SPCC joint is influenced by the reaction layer formed at its interface.

© 2008 Elsevier B.V. All rights reserved.

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. Introduction

In automotive industries, weight reduction is strongly deman-ed for energy and natural resource savings. Although aluminumtructural automobile body is an attractive structure for the weighteduction, taking strength, cost and joining process into account,he multi-material structure is a practical one. In this structure, theppropriate materials to demands are selected and placed to theight components, so as to fully utilize the materials’ functional-ties. From the point of view of material supply, aluminum alloysnd steels are the most important construction materials for auto-otive structures. Therefore, the joining between aluminum alloy

nd steel is indispensable.However, the joining between the two kinds of materials accom-

anies some difficulties, because of the large difference in physicalnd thermal properties between aluminum alloy and steel, and theormation of brittle reaction products at the welding interface. In

rder to avoid the reaction between aluminum alloy and steel athe welding interface, most of the previous studies have focusedn solid-state bonding, for example, Lee et al. (2003) welded alu-inum alloy–A36 steel by friction welding, Elliott and Wallach

1981) joined aluminum alloy to steel using a method of diffusion

∗ Corresponding author. Tel.: +81 96 342 0688; fax: +81 96 342 0688.E-mail address: xdqrf@yahoo.com.cn (R. Qiu).

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924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.jmatprotec.2008.11.003

onding, Lee et al. (2007) investigated the interfacial microstruc-ure and strength of steel/aluminum alloy lap joint welded by

agnetic pressure seam welding, and Lee et al. (2006) studiedhe interfacial reaction in friction stir welded steel–aluminumoints. On the other hand, resistance spot welding (RSW) is a

idely used and important welding process in the fields of auto-otive manufacturing; nevertheless, only a few of studies have

een reported on the RSW between aluminum alloy and steel toate.

In the previous studies concerning the RSW between aluminumlloy and steel, Oikawa et al. (1999) welded 1.0 mm Al–Mg alloyheet to 0.8 mm steel sheet, and Sun et al. (2004) welded 1.4 mmAE1008 mild steel sheet and 2 mm 5182-O aluminum alloy sheet;hey introduced an aluminum clad steel sheet between aluminumlloy and steel as the transition material in order to suppress theeaction between aluminum and steel. However, the utilizationf the welding process is still restricted by the aluminum cladteel sheet’s high cost and manufacturing difficultness. Therefore,atonaka et al. (2006) developed a new method termed RSW withover plate for joining between aluminum alloy and steel, andlarified the influence of cover plate on the weld temperature dis-ribution by finite element analyses, in which 200–300 ◦C higher

emperature is obtained than in the weld without use of cover plate.n the present study, we joined aluminum alloy to steels using thisechnique, investigated the interfacial microstructure and tensilehear strength of joints, and analyzed the effect of reaction layer onhe tensile shear strength of joints.

R. Qiu et al. / Journal of Materials Processing Technology 209 (2009) 4186–4193 4187

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Fig. 2. Shape and size of specimen for welding.

Table 2Welding conditions.

Electrode Cu–Cr alloy conical electrode tip (ø6)

Welding current 6–12 kAWEP

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t1

4

4

sto

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Fig. 1. Schematic diagram of resistance spot welding with cover plate.

. RSW with cover plate

RSW is a joining process based on the heat source obtained fromoule’s effect of the resistance and electric current flow through theheets held together by the electrode force, in which the coales-ence occurs at the spot area in the faying surfaces. Therefore, inhe process of RSW between aluminum alloy and steel, enormouslyigh electric current is required because of low heat generation andigh heat conduction of aluminum alloy. In this case, the utiliza-ion of enormously high welding current would reduce electrodeip life and require adopting larger capacity RSW machine. In ordero enable the RSW between aluminum alloy and steel under rel-tively low welding current condition, we proposed a techniquef RSW with cover plate. Fig. 1 shows the schematic diagram ofhis welding process, in which a cover plate was placed on the alu-

inum alloy sheet. Here, it is required that the cover plate was aetal sheet with relatively lower electrical conductivity than alu-inum alloy, so the higher heat generated in the cover plate as to

e conducted from the cover plate to aluminum alloy sheet. Takingow cost and availability into account, we chose cold-rolled steelheet SPCC as the cover plate.

In the present study, the similar material joints of aluminumlloy sheets were also prepared to compare the strength with dis-imilar material joints between aluminum alloy and steels. In suchcase, the aluminum alloy sheets were placed between both coverlates when they are welded.

. Experimental materials and procedure

The materials used in this study were 1.0 mm thick plates ofluminum alloy A5052, SPCC and austenitic stainless steel SUS304.heir chemical compositions are listed in Table 1. The material com-inations of A5052/SPCC, A5052/SUS304 and A5052/A5052 wereelded using an AC spot welding machine. Fig. 2 shows the shape

nd size of joints, in which 30 mm × 40 mm × 1 mm cover plate wassed. Welding conditions are given in Table 2, in which the welding

urrent was changed every 1 kA between 6 and 12 kA at the fixedlectrode force and welding time.

The interfacial microstructure of dissimilar material joints werenvestigated using a scanning electron microscope (SEM, JEOL JSM-300, acceleration voltage: 20 kV) and a transmission electron

ttbwi

able 1hemical composition of materials (Mass %).

IS (ASTM) Mg Fe Cr Si Mn

5052 (5052) 2.2 0.27 0.19 0.09 0.049US304 (304) – Bal. 18.0 0.85 1.25PCC (A366/A366M-97) – Bal. – – 0.004

elding time 0.2 slectrode force 1715 Nre-treatment Degreasing with Acetone

icroscope (TEM; JEOL JEM-2000FX, acceleration voltage: 200 kV).he SEM observation was performed on the transverse cross sec-ion of the weld, which was mechanically polished using diamondastes and finished using 0.04 �m Al2O3 particle suspensions. TheEM observation was performed with thin foil, which was pre-ared with ion milling (3 keV Ar+) after mechanical polishing ofliced piece from the welded sample. Besides, the chemical com-ositions of the reaction products were examined using an energyispersive X-ray spectroscopy (EDX) with an electron beam probef approximately 10 nm in diameter.

In order to examine the mechanical properties of the joints, theensile-shear tests were performed under a cross-head velocity of.7 × 10−5 m/s at room temperature.

. Experimental results and discussions

.1. Morphology of reaction products in the welding interface

Fig. 3(a and b) shows the optical micrographs of the cross-ection of the A5052/SPCC joint and A5052/SUS304 joint, respec-ively, which were welded under the condition of welding currentf 9 kA. In either picture, a drum-shaped nugget was observed in

he A5052, the thickness of which was thinner than the originalhickness at the center. In contrast, no fusion zone was observed inoth the SPCC (SUS304) and the cover plate. Similar morphologyas also observed in the other joints welded under different weld-

ng conditions. This means that the interfacial reaction took place

Cu C P S Ni Zn Al

0.027 – – – – 0.005 Bal.– 0.06 0.04 0.02 8.0 – –– 0.05 0.01 0.01 – – –

4188 R. Qiu et al. / Journal of Materials Processin

FA

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A(fFa

eltnsrAfcArtipdA

isebtfoitcrtinrin thickness. In both the welding interfaces, moreover, the reac-

ig. 3. Optical micrograph of the weld cross-section; (a) A5052/SPCC and (b)5052/SUS304.

etween molten aluminum and solid iron. It can also be inferredrom the interfacial microstructures as mentioned below and thee–Al equilibrium phase diagram that the weld temperature waspproximately 1160 ◦C during welding (Shahverdi et al., 2002). Inddition, some blowholes were observed at the center of the nuggetn both the dissimilar material joints. In the previous study, Gean etl. (1999) claimed that excessive porosity (up to 40% of the nuggetiameter) do not affect the static performance of the welds inhear when maintaining a constant 6.3-mm weld diameter, whonvestigated the effect of discontinuities in welds on the staticnd fatigue properties of resistance spot welded aluminum alloyoint. In this study, therefore, the blowholes formed in the nuggetould not affect the shear tensile load of the joint according to their

esults.Fig. 4 shows SEM images of the interfacial region of the

5052/SPCC joint welded at the welding current of 9 kA. Imagesa to d) indicate the typical morphology of the A5052/SPCC inter-ace at the positions (A to D) in Fig. 3(a), respectively. As shown inig. 4, reaction products with different morphology were observedt the interface. The reaction products interspersed in the periph-

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Fig. 4. SEM images of the weld cross-sec

Fig. 5. SEM images of the weld cross-sect

g Technology 209 (2009) 4186–4193

ral region of the weld (Fig. 3(a)), which changed to the continuousayer as approaching to the central region (Fig. 3(d)). Otherwise,he reaction products exhibited different morphology in the thick-ess direction. In the SPCC region side, the reaction products fronthowed the tongue-like morphology, while the fine needle-likeeaction products front orientated towards the base metal in the5052 region side. Fig. 5 also shows SEM images of the inter-

acial region of the A5052/SUS304 joint welded at the weldingurrent of 9 kA. Images (a to d) indicated the morphology of the5052/SUS304 interface at the positions (A to D) in Fig. 3(b),espectively. In comparison with the A5052/SPCC interface, a serra-ion layer of reaction products was observed at the A5052/SUS304nterface, which was flat front in the SUS304 side and serrate mor-hology in the A5052 side. Moreover, as shown in Fig. 5(c and), relatively large reaction products blocks were observed in the5052 region near the welding interface.

In order to examine the thickness variation of the reaction layern the weld more precisely, the reaction layer thickness was mea-ured as the average value in 30 �m × 30 �m SEM image takenvery 100 �m along the welding interface. Fig. 6 shows the distri-ution of the reaction layer thickness at both the A5052/SPCC andhe A5052/SUS304 interfaces, respectively, which were obtainedrom the joints welded under the condition of welding currentf 7, 9 and 11 kA. Both the A5052/SPCC and the A5052/SUS304nterfaces showed that the reaction layer was thick at the cen-ral region, decreased their thickness with the distance from theenter, and finally became discontinuous layer at the peripheralegion. However, the degree of the reaction layer thickness varia-ion with the position in both the A5052/SPCC and A5052/SUS304nterfaces was different. In other words, the reaction layer thick-ess hardly varied at the A5052/SUS304 interface, while theeaction layer at the A5052/SPCC interface varied significantly

ion layer thickness increased with increasing of the weldingurrent. The maximum thickness of the reaction layer appearedt the central region and their value were approximately 7 �mt the A5052/SPCC interface and approximately 2.5 �m at the

tion at the A5052/SPCC interface.

ion at the A5052/SUS304 interface.

R. Qiu et al. / Journal of Materials Processing Technology 209 (2009) 4186–4193 4189

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Awilnc

4

watwtSttcelscaf

sar

AIAiproqoAw1isN

Fig. 6. Distribution chart of the reaction pr

5052/SUS304 interface, which were obtained from the jointselded under the condition of welding current of 11 kA. In compar-

son with the A5052/SUS304 interface, the thickness of the reactionayer formed at the A5052/SPCC interface was thick and the thick-ess variation of the reaction layer was sensitive to the weldingurrent.

.2. Microstructure of reaction products

In order to clarify the detailed structure of the reaction products,e also observed the welding interfaces using TEM. Fig. 7(a) showstypical bright field image of the A5052/SPCC interface taken from

he central region of the weld. In the image, a two-layered structureas observed, which consisted of a polycrystalline layer adjacent

o the A5052 and a large mono-crystalline layer adjacent to thePCC. The former was composed of approximately 0.2 �m fine crys-al grains. The latter were composed of approximately 3 �m largeongue-like crystals oriented towards the SPCC. These results areonsistent with the SEM images in Fig. 4. Fig. 7(b and c) shows thelectron diffraction patterns of fine crystal in the A5052 side and

arge one in the SPCC side, respectively. According to the analy-es of electron diffraction patterns, it was identified that the finerystal grains were FeAl3 and the large one was Fe2Al5. Fig. 8(and b) shows the compositions of fine and coarse crystals obtainedrom EDX analysis, respectively. These analyses showed the compo-

awFhw

s layer thickness at the welding interface.

itions of 75.09% Al and 24.91% Fe (at %) for the former and 70.93% Alnd 29.07% Fe (at %) for the latter. These correspond to the analysesesults as mentioned above.

Fig. 9(a) shows an example of bright field image of the5052/SUS304 interface taken from the central region of the weld.

n this image, the fine crystals with size of 0.5 �m were observed.ccording to the analyses of the electron diffraction patterns shown

n Fig. 9(b and c), the reaction products consisted of two majorhases, FeAl3 and Fe2Al5. These phases randomly distributed in theeaction layer. Fig. 10(a and b) shows the results of EDX analysisf FeAl3 and Fe2Al5, respectively. The results revealed that a smalluantity of Cr and Ni is contained in these phases; the compositionsf 74.11% Al, 19.84%Fe, 4.09% Cr, 1.96% Ni (at %) for FeAl3 and 71.34%l, 22.74% Fe, 4.15% Cr, 1.77% Ni (at %) for Fe2Al5. Similar resultsere obtained by Dybkov (1990), who studied the reaction between

8Cr–10Ni stainless steel and liquid aluminum (973–1123 K) in themmersion tests. He determined that the reaction products are solidolution based upon the FeAl3 and Fe2Al5, and expressed as (Fe, Cr,i) Al3 and (Fe, Cr, Ni)2Al5, respectively.

Moreover, in the reaction layer formed in both the A5052/SPCC

nd A5052/SUS304 interfaces, minor FeAl2 and unknown phaseere also found as well as major phases FeAl3 and Fe2Al5. The phase

eAl and Fe3Al were not detected; this is considered to be due to theigher free energy of these phases, which caused their formationas difficult (Richard et al., 1994).

4190 R. Qiu et al. / Journal of Materials Processing Technology 209 (2009) 4186–4193

Fp

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spioFFtnba(

a

Fw

dKaacmmrithermal phenomenon during RSW is complex, in which interactiontime depends on the position in the welding interface and the tem-perature of the point in the welding interface varies with weldingtime. As shown in Fig. 6, the reaction layer was thick at the central

ig. 7. (a) Bright field image, (b) SAED pattern of reaction product FeAl3 and (c) SAED

attern of reaction product Fe2Al5 in the welding interface of A5052/SPCC.

.3. Reason of variation of reaction layer thickness andorphology

As shown in Fig. 4, SEM observation at the A5052/SPCC interfacehowed that the reaction layer front exhibited tongue-like mor-hology in the SPCC region side and fine needle-like morphology

n the A5052 region side. According to the results through TEMbservation, it is clarified that the former is Fe2Al5 and the latter iseAl3. Although the origin of the formation of the large tongue-likee2Al5 remains unclear, anisotropic diffusion is a possible explana-ion for the production of these tongue-like Fe2Al5. There are a largeumber of aluminum vacancies along the c-axis of the orthorhom-ic structure of Fe2Al5. Along c-axis, therefore, fast diffusion of

ctive element occurred; result in the anisotropic growth of Fe2Al5Shahverdi et al., 2002).

It is well known that interfacial reaction layer thickness (X) isfunction of interaction time (t) and temperature (T) and that is

Ff

ig. 8. EDS spectra of reaction products (a) FeAl3 and (b) Fe2Al5 formed in theelding interface of the A5052/SPCC.

escribed by the equations X = (2Kt)0.5 and K = K0 exp(−Q/RT) (here:is growth constant, K0 is constant, R is the gas constant, and Q is thectivation energy for growth of reaction layer). Bouayad et al. (2003)nd Murakami et al. (2004) demonstrated the equations underonstant temperature, who investigated the interaction betweenolten aluminum and solid iron using immersion tests and alu-inization of iron and stainless steel by powder liquid coating,

espectively. We may analyze the reaction layer thickness variationn this study using the equations demonstrated by them, although

ig. 9. Bright field image and electron diffraction pattern of reaction productsormed in the welding interface of the A5052/SUS304.

R. Qiu et al. / Journal of Materials Processing Technology 209 (2009) 4186–4193 4191

Fw

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4

sebt

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atIjjcwrespectively. In the previous study, Oikawa et al. (1999) reportedthat maximum tensile shear load of 4 kN was obtained at the weld-ing current 12 kA, in which 1.0 mm Al–Mg alloy sheet and 0.8 mmsteel sheet were joined by the resistance spot welding with 0.81 mm

ig. 10. EDS spectra of reaction products (a) FeAl3 and (b) Fe2Al5 formed in theelding interface of the A5052/SUS304.

egion and decreased their thickness with the distance from theenter. This is considered to be due to the temperature distribu-ion at the welded region, high welding temperature at the centralegion of the weld and low welding temperature at the peripheralegion resulted from heat loss. Similarly, since the increase of weld-ng current results in the high welding temperature, the reactionayer thickness increased with increasing of the welding current ashown in Fig. 6.

The reaction layer formed in the A5052/SUS304 interface washinner than that formed in the A5052/SPCC interface as shownig. 6. This can be explained by the low growth rate of the reactionroducts Fe2Al5 in the A5052/SUS304 resulted from the compo-ent of Cr in this phase to reduce Al atoms activity coefficient,hich was reported by Akdeniz and Mekhrabov (1998). More-

ver, Dybkov (1990) and Eggeler et al. (1986) found the growthonstant of reaction layer K = (8 ± 2) × 10−13 m2 s−1 for the reac-ion between 18Cr–10Ni stainless steel and aluminum at 700 ◦Cnd K = 5.64 × 10−11 m2 s−1 for the reaction between low-alloyedteel and aluminum at 786 ◦C, respectively. These results revealedhat the reaction layer growth in the interface of low-alloyed steelnd aluminum is quick and sensitive to interaction time and tem-erature. For this reason, the thickness variation of reaction layerormed in the A5052/SPCC interface was sensitive to the weld-ng current and the position in the welding interface as shown inig. 6.

.4. Nugget diameter and tensile shear load of joints

The reliability of spot welding joint depends upon the tensilehear load of joint, which is usually related with the nugget diam-ter of the joint. In this section, we investigated the relationshipsetween the nugget diameter and welding current and betweenhe tensile shear load and welding current. Here, the tensile shear F

Fig. 11. Relationship between the welding current and nugget diameter.

oad and nugget diameter was the average value of 5 joints weldednder the same welding conditions, and the nugget diameter waseasured on the fractured surface after the tensile shear testing of

oints. Fig. 11 shows the relationship between the welding currentnd the nugget diameters of three types of joints; the A5052/SPCC,5052/SUS304 and A5052/A5052 joints. All three types of jointsevealed that nugget diameter increased with the increasing of theelding current. Under the same welding current, the nugget ofoth the A5052/A5052 and A5052/SPCC joints showed almost theame diameter, whereas the A5052/SUS304 joints revealed largerugget diameter. This is attributed to lower electrical conductiv-

ty and specific heat of the SUS304. As shown in Fig. 11, under theelding current of 12 kA, the maximum nugget diameter of 10 and.9 mm were obtained from the A5052/SUS304 and A5052/SPCC

oints, respectively.Fig. 12 shows the relationship between the tensile shear load

nd the welding current. As shown, the tensile shear load of threeypes of joints increased with the increasing of the welding current.n comparison with the A5052/A5052 joints, the A5052/SUS304oints exhibited higher tensile shear load, whereas the A5052/SPCCoints showed lower tensile shear load under the same weldingonditions. The maximum tensile shear load of 6.5 and 4.68 kNere obtained from the A5052/SUS304 joint and A5052/SPCC joint,

ig. 12. Relationship between the welding current and tensile shear load of joints.

4192 R. Qiu et al. / Journal of Materials Processin

F

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ig. 13. Relationship between the nugget diameter and tensile shear load of joints.

hick aluminum clad steel sheet as intermediate layer. In compar-son with their results, the joints obtained in this study revealedigher tensile shear load as shown in Fig. 12. According to Americanational Standard (1997), the nugget diameter >4t1/2 (t represents

he thickness of specimen) is required for resistance spot welded

oint; from this viewpoint, the nugget diameter of joints welded bySW with cover plate was also large enough.

For the fracture mode of joints, the A5052/A5052 and5052/SUS304 joints were shear type fracture in the welding cur-ent of 6 and 7 kA, and changes to plug type fracture in the range

Aswfw

Fig. 14. (a) A5052 side and (b) SPCC side fracture

ig. 15. (a) A5052 side, (b) SUS304 side fracture surface and (c) cross-section of shear fractoint.

g Technology 209 (2009) 4186–4193

rom 8 to 12 kA, while the fracture type of the A5052/SPCC jointsas shear type fracture through all welding current.

.5. Effect of nugget diameter and reaction layer on the tensilehear strength of joints

Generally, nugget diameter and interfacial reaction layer havenfluence on the strength of resistance spot welded dissimilar mate-ial joints. In this section, we discuss the effect of the nuggetiameter and reaction layer on the tensile shear strength of the5052/SPCC and A5052/SUS304 joints.

Compared with the A5052/A5052 joints, the A5052/SPCC jointshowed same level of nugget diameter and relatively low tensilehear load, while the A5052/SUS304 joints exhibited larger nuggetnd high tensile shear load as shown in Figs. 11 and 12. In ordero clarify the influence of the nugget diameter and reaction layern the tensile shear load of joints more precisely, the relationshipetween the tensile shear load and the nugget diameter for all jointsas shown in Fig. 13. All three types of joints, the A5052/A5052,5052/SUS304 and A5052/SPCC, revealed that the tensile shear

oad increased with the increasing of the nugget diameter. However,nder the same nugget diameter, the A5052/SUS304 joints revealedlmost the same tensile shear load, while the A5052/SPCC jointshowed relatively low tensile shear load in comparison with the

5052/A5052 joints where no reaction layer formed. These resultsuggest that the tensile shear strength of the A5052/SUS304 jointas not affected by the reaction layer formed at the welding inter-

ace, and that the tensile shear strength of the A5052/SPCC jointas influenced slightly by its interfacial reaction layer.

surface of fractured the A5052/SPCC joint.

ured the A5052/SUS304 joint; (d) cross-section of plug fractured the A5052/SUS304

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Shahverdi, H.R., Ghomashchi, M.R., Shabestari, S., Hejazi, J., 2002. Microstructuralanalysis of interfacial reaction between molten aluminum and solid iron. J.

R. Qiu et al. / Journal of Materials Pro

Fig. 14(a and b) shows the SPCC and A5052 side fracture surface,espectively, which were obtained from the tensile shear testingf the A5052/SPCC joint welded under the welding condition ofelding current 10 kA. It can be seen that both the fracture sur-

ace of the SPCC side and A5052 side were very flat. The elemente and Al of reaction products compositions were detected onoth the SPCC side and the A5052 side fracture surface using elec-ron probe microanalysis. Similar results were also observed in thether A5052/SPCC joints welded under different welding condi-ions, which were shear type fracture as mentioned above. Thus, it isdentified that the fracture occurred in the reaction layer in the casef tensile shear testing of the A5052/SPCC joints. On the other hand,lthough the A5052/SUS304 joints were also shear type fracture inhe low welding current range (6–7 kA) as mentioned above, differ-ng pattern was observed on the fracture surfaces. Fig. 15(a and c)hows an example of fracture surfaces. On the both fracture surfacesf the SUS304 and A5052 side, tear dimple features were observed.ig. 15(c) shows the cross section of the fractured A5052/SUS304oint. It was seen that the fracture crack propagated in the A5052.n the case of plug type fracture of the A5052/SUS304 joint in theigh welding current range (8–12 kA), it is obvious that the fracturerack did not propagate in the reaction layer as shown in Fig. 15(d).herefore, the results described above also reveal that the tensilehear strength of the A5052/SUS304 joint was not affected and theensile shear strength of the A5052/SPCC joint was influenced byhe reaction layer formed at their interface, respectively.

. Conclusions

In this study, we welded aluminum alloy A5052 to steel SPCCnd stainless steel SUS304 using resistance spot welding with aover plate. The joint performance was evaluated by the interfacialicrostructure and tensile shear strength of joints. The relation-

hip between the reaction layer and tensile shear strength was alsoiscussed. Main results obtained from this study are as follows:

1. It is feasible to weld aluminum alloy to steel sheets via a RSWmethod using a cover plate. Larger nugget and high tensile shearload were obtained under relatively low welding current condi-

tion.

. At the welding interface of the A5052/SPCC and A5052/SUS304joint, the reaction products were observed. From the structureand composition analyses, the reaction products contain Fe2Al5and FeAl3.

S

g Technology 209 (2009) 4186–4193 4193

. The thickness of the reaction layer varies with the welding cur-rent, which depends on the combination of materials and theposition in the welded region.

. The reaction layer has no effect on the tensile shear strength ofthe A5052/SUS304 joint and the tensile shear strength of theA5052/SPCC joint is influenced by the reaction layer formed atits interface.

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