Friction Welding of AA6061 to AISI 4340 Using Silver Interlayer

Home , Friction welding

+ MODEL

HOSTED BY Available online at www.sciencedirect.com ScienceDirect

Defence Technology xx (2015) 1e7 www.elsevier.com/locate/dt

Friction welding of AA6061 to AISI 4340 using silver interlayer

SURESH D. MESHRAM*, G. MADHUSUDHAN REDDY

Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India

Received 27 March 2015; revised 17 May 2015; accepted 19 May 2015 Available online ▪▪▪

Abstract

The present work pertains to the study on joining of AA6061 and AISI 4340 through continuous drive friction welding. The welds were evaluated by metallographic examination, X-ray diffraction, electron probe microanalysis, tensile test and microhardness. The study reveals that the presence of an intermetallic compound layer at the bonded interface exhibits poor tensile strength and elongation. Mg in AA6061 near to the interface is found to be favourable for the formation and growth of Fe2Al5 intermetallics. Introduction of silver as an interlayer through electroplating on AISI 4340 resulted in accumulation of Si at weld interface, replacing Mg at AA6061 side, thereby reducing the width of intermetallic compound layer and correspondingly increasing the tensile strength. Presence of silver at the interface results in partial replacement of FeeAl based intermetallic compounds with AgeAl based compounds. The presence of these intermetallics was conﬁrmed by X-ray diffraction technique. Since AgeAl phases are ductile in nature, tensile strength is not deteriorated and the silicon segregation at weld interface on AA6061 in the joints with silver interlayer acts as diffusion barrier for Fe and further avoids formation of FeeAl based intermetallics. A maximum tensile strength of 240 MPa along with 4.9% elongation was obtained for the silver interlayer dissimilar metal welds. The observed trends in tensile properties and hardness were explained in relation to the microstructure. Copyright © 2015, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: Dissimilar metal weld; Interlayer; Friction welding; Intermetallics; Microstructure; Tensile strength

1. Introduction be extremely brittle. In the case of two metals having different melting temperatures or thermal conductivities, the process of Several situations arise in industrial practices which call for welding is complicated because one metal is molten before the joining of dissimilar metals. The joining of dissimilar metals is other. There is a continuing demand for reliable methods of commonly done to satisfy different requirements for effective joining dissimilar metals and alloys. For example, welding is and economic utilization of the special properties of each ma- irreplaceable in the manufacture of vacuum system made of terial for enhanced performance. Dissimilar metal joints can be dissimilar metals for cryogenic engineering. Recently, the made successfully if there is a mutual solubility between the range of combinations of the dissimilar metals, used in welded two metals. Otherwise, using interlayer/layers that is/are structures, has greatly increased and is continuous to increase. compatible with each other is required to produce joint. For Joining of aluminium with steel finds its application in the fields dissimilar metals having widely different coefficients of ther- of cryogenic engine, space craft and automobile. However, the mal expansion, the joint may fail due to thermal fatigue either fusion welding of aluminium to steel is difficult due to the during solidification or soon thereafter. This is because the in- formation of brittle intermetallic compounds at the interface ternal stresses are setup in the intermetallic zone, which tends to [1e4]. The solid state joining of steel directly to aluminium also gives an unsatisfactory product because of incompatibility of physico-chemical properties of the two metals to be bonded * þ þ Corresponding author. Tel.: 91 4024586433; fax: 91 4024342697. [5]. The interdifussion of Al and Fe often yields a series of E-mail addresses: [email protected] (S.D. MESHRAM), gmreddy_ [email protected] (G. MADHUSUDHAN REDDY). brittle intermetallic compounds at the interface. Such brittle Peer review under responsibility of China Ordnance Society. layers cannot sustain the strain of subsequent metal working http://dx.doi.org/10.1016/j.dt.2015.05.007 2214-9147/Copyright © 2015, China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Aluminium alloy AA6061 in T6 condition and low alloy 3.1. Optical microscopy steel AISI 4340 in quenched and tempered condition in the form of 16 mm diameter rods were used for friction welding. Optical macrograph of a longitudinal section of welds made Friction welding was carried out on a continuous drive friction without interlayer is shown in Fig. 3. From the macrograph it welding machine with friction force of 3 kN, upsetting force of may be observed that aluminium alloy (AA6061) is deformed 6 kN, rotational speed of 2400 RPM, and burn-off length of extensively while no deformation could be noticed on the low 2 mm. Friction welding parameters were selected based on the alloy steel side during welding. The microstructure near the optimization studies carried out earlier on joining of dissimilar interface does not show any refinement of grains in steel. metal combinations [19]. It was recommended that the However, the aluminium resulted in fine grain structure near incompatible materials should be welded at low burn-off interface. The microstructures of the welds without and with length (length loss during friction stage of welding). Low interlayer are presented in Fig. 4. The weld interface is burn-off length results in lower heat input and consequently straight, a wide dark region is noted on the aluminium alloy less time availability for formation of intermetallics. Silver beside the weld interface. The joints with silver as interlayer was electroplated on the faying surface of AISI 4340 using show the replacement of dark region with a bright region. standard commercial technique by subcontracted plating firm. The detailed electroplating procedures are not given because 3.2. Scanning electron probe microanalysis (SEPMA) they are confidential to the various electroplating firms. A m 20 m-thick silver was electroplated on AISI 4340 since it The elemental X-ray mappings and quantitative analysis does not undergo deformation as compared to AA6061. Fig. 1 across the weld interface in the central region of weld without shows the friction welded joints obtained with AA6061 and AISI 4340 without interlayer and with silver interlayer. The weld specimens were sectioned and metallographically polished. The specimens were etched with Keller's reagent for AA6061 side and with Nital solution for AISI 4340. Tensile testing was performed employing standard specimen config- uration confirming to ASTM standard E8-04, having gauge Fig. 2. Tensile test specimen with dimensions (all dimensions in mm).

Fig. 3. Optical macrograph and micrograph of friction welded AA6061-AISI 4340 joint. interlayer are presented in Fig. 5 and Fig. 6, respectively. Uni- (without interlayer). Mg is intermittently replaced by Si when form distribution of Mg at weld interface towards Al base metal silver interlayer is used (Fig. 7). Fig. 8 shows an accumulation of side of the joint could be observed (Fig. 5). Diffusion of Si from Si at the joint interface toward aluminium base metal with silver Al to steel could be noticed for direct dissimilar metal weld interlayer, indicating impediment of Si migration towards steel.

Fig. 4. Micrograph of the cross-section of (a) joint without interlayer and(b) joint with silver interlayer.

Fig. 5. Elemental X-ray mapping at the weld interface for a joint without Fig. 7. Elemental X-ray mapping at the weld interface for a joint with silver interlayer. interlayer.

3.3. Microhardness to be noted that the highest hardness is observed at the weld Microhardness distribution across the interface of welds interface for direct and interlayer weldments. It is observed made without and with silver interlayer is shown in Fig. 9.Itis that the direct weld gives the maximum hardness compared to silver interlayer weld.

3.4. Tensile properties

The tensile properties of parent metal and joints made with and without silver interlayer are detailed in Table 1. Improve- ment in tensile strength was observed for silver interlayer weld compared to the weld made without interlayer. Failure during tensile testing occurred through the weld interface.

3.5. X-ray diffraction analysis

X-ray diffraction analysis of fractured surface of tensile specimen for welds with and without interlayer is shown in Fig. 10. Examination of the joint made without interlayer revealed an interfacial layer of FeeAl intermetallics (Fe2Al5 and FeAl3). However, introducing silver as an interlayer results in the formation of Ag3Fe2,Ag2Al and Ag3Al in addition Fig. 6. Quantitative analysis across the weld interface for joint without to Fe Al and FeAl . interlayer. 2 5 3

flows either axially away from the interface or radially along the interface as material is upset from the joint forming the characteristic flash. The different thermal and physical properties of the materials welded in dissimilar metal welding, including heat capacity, thermal conductivity, relation between hardness and temperature, generally results in asymmetrical deformation. The formation of flash on aluminium side and no flash on low alloy steel (Fig. 3) can be attributed to lower thermal conductivity and higher hardness of low alloy steel at elevated temperatures compared to aluminium alloys. The same phenomenon has been reported during friction welding of dissimilar welds namely Al to Cu [20], Al to stainless steel [21] and titanium to steel [22]. From the metallographic study it is observed that direct welding of AISI 4340 to AA6061 is not feasible due to the presence of continuous intermetallic Fig. 8. Quantitative analysis across the weld interface for joint with silver layer across the weld width (Fig. 4). interlayer. A correlation of strength data of welds with microstructure at the interface suggests that the direct welding of AISI 4340 3.6. Fractography to AA6061 aluminium alloy results in the formation of continuous intermetallic zone, and therefore exhibits very poor The fractograph features of tensile samples of welds with and strength and almost nil ductility (Table 1). without interlayer are shown in Fig. 11. The fracture is pre- X-ray diffraction data of fractured tensile samples of direct dominantly by cleavage. However, in the case of joints without weld contains highly brittle intermetallics such as Fe2Al5 and silver interlayer, a weak bonding can be observed as indicated FeAl3 (Fig. 10). Incorporation of silver interlayer in the form of by arrows where the steel surface is exposed, indicating either electroplating has been observed to be a solution to realize the no bonding has occurred or the bond is so weak that it has left no welding of low alloy steel to aluminium alloy. Silver interlayer mark of aluminium on steel surface. In the case of joint with is found to be most useful as it implants good ductility as well as silver as an interlayer, no such unbounded/weak zone is strength. Silver as an interlayer results in the formation of observed. This gives an indication of good joint integrity. Ag3Fe2,Ag2Al and Ag3Al in addition to Fe2Al5 and FeAl3 (Fig. 10). Silver, presenting in the form of interlayer, acts as a 4. Discussion barrier for the direct interaction between aluminium and steel, resulting in partial replacement of FeeAl based intermetallic The friction welding process can be used to produce a compound with AleAg based intermetallic compound. metallurgical bond through the interaction of frictional heating Mg and Si are the major alloying elements in AA6061. Mg and simultaneous deformation along the interface separating is reported to be favourable for increasing the width of FeeAl the material to be joined. Heat generated along the interface based intermetallic compound layer [23], particularly Fe2Al5.

Fig. 9. Microhardness distribution across the weld interface (a) without interlayer and (b) with silver interlayer.

Table 1 Tensile strength of parent metal and welds. Material Ultimate tensile strength/MPa 0.2% yield strength/MPa Elongation/% AA6061 305 270 12 AISI 4340 1100 710 12.8 AA6061 e AISI 4340 weld without Ag interlayer 162 147 0.5 AA6061 e AISI 4340 weld with Ag interlayer 240 140 4.9

Fig. 10. X-ray diffraction analysis of fractured tensile samples (a) without interlayer and (b) with silver interlayer.

Fig. 11. Fractograph of tensile samples at weld interface (a) (b) without interlayer and (c) (d) with silver interlayer.

Uniform distribution of Mg at weld interface towards Al base diffusion of Si across the silver interlayer is restricted, resulting metal side of the joint can be observed in the joint without in higher concentration of Si at interface of aluminium base silver interlayer (Fig. 5), which is a favourable condition for metal and silver (Fig. 7). This observation is supported by the formation of FeeAl based intermetallics. However the quantitative analysis of Si across the weld interface for joints joints with silver interlayer show that Mg is intermittently with silver interlayer (Fig. 8). Higher concentration of Si retards replaced by Si at the weld interface (Fig. 7). The absence of the formation of Fe2Al5 at weld interface by acting as a barrier Mg near interface for joint with silver interlayer results in less to Fe diffusion [6,18,26,27]. Silicon segregation at the weld favourable condition for the formation of Fe2Al5, and the interface is not observed in a joint without silver interlayer, situation is more favorable for the silver/aluminium interme- which allows more Fe to diffuse towards Al, resulting in Fe2Al5 tallic formation at the interface. This intermetallic compound formation and poor tensile property. is reported to be signiﬁcantly softer than that formed between Higher value of microhardness in a joint without silver iron and aluminium and hence much greater thickness can be interlayer can be attributed to the formation of Fe2Al5 and FeAl3 tolerated in the attainment of good quality welds between [28]. Slight reduction in hardness with silver interlayer can be aluminium and its alloy to low alloy steel [24]. observed due to the presence of silver/aluminium intermetallic Heating of aluminium alloy at high temperature results in compounds which are soft in nature. Low tensile strength and diffusing Si out of the lattice [25]. Since SieAg is an eutectic elongation of joints without silver interlayer can be attributed to system which is practically immiscible in solid state, the the formation of Fe2Al5 and FeAl3 intermetallics which are

Please cite this article in press as: MESHRAM SD, MADHUSUDHAN REDDY G, Friction welding of AA6061 to AISI 4340 using silver interlayer, Defence Technology (2015), http://dx.doi.org/10.1016/j.dt.2015.05.007 + MODEL S.D. MESHRAM, G. MADHUSUDHAN REDDY / Defence Technology xx (2015) 1e7 7 brittle in nature. Introduction of silver interlayer results in [9] Madhusudhan Reddy G, Sambasiva Rao A, Mohandas T. Role of elec- improvement in tensile strength and elongation since, and troplated interlayer in continuous drive friction welding of AA6061 to e FeeAl based intermetallic compound are partially replaced by AISI 304 dissimilar metals. Sci Technol Weld Join 2008;13(7):619 28. e [10] Sun X, Stephens EV, Khaleel MA, Shao H, Kimchi M. Resistance spot Al Ag based compounds which are ductile in nature. welding of aluminum alloy to steel with transition material-from process to performance-part I: experimental study. Weld J 2004;83(7):188e95. 5. Conclusions [11] Date H, Kobayakawa S, Naka M. Microstructure and bonding strength of impact-welded aluminum-stainless steel joints. J Mater Process Technol e e A friction welding technique has been developed for 1999;85(1 3):166 70. [12] Shubhavardhan RN, Surendran S. Friction welding to join stainless steel joining aluminium (AA6061) to low alloy steel (AISI 4340) and aluminium materials. Int J Metall Mater Sci Eng (IJMMSE) using an interlayer of silver. Silver as an interlayer partially 2012;2(3):53e73. reduces the formation of FeeAl based intermetallic and re- [13] Tsujino J, Hidai K, Hasegawa A, Kanai R, Matsuura H, Matsushima K, places it with AleAg based intermetallic, such as Ag Fe , et al. Ultrasonic butt welding of aluminum, aluminum alloy and stainless 3 2 e e Ag Al and Ag Al, resulting in better tensile strength and steel plate specimens. Ultrasonics 2002;40(1 8):371 4. 2 3 [14] He P, Yue X, Zhang JH. Hot pressing diffusion bonding of a titanium ductility of welds. Presence of silver as an interlayer reduces alloy to a stainless steel with an aluminum alloy interlayer. Mater Sci Mg concentration at the weld interface by intermittently Eng A 2008;486(1e2):171e6. replacing it with Si on AA6061 side, which restricts the [15] Acarer M, Demir B. An investigation of mechanical and metallurgical interaction of Fe with aluminium. The higher strength and properties of explosive welded aluminum-dual phase steel. Mater Lett e ductility of aluminium to low alloy steel dissimilar metal 2008;62(25):4158 60. [16] Dehghani M, Amadeh A, Akbari Mousavi SAA. Investigations on the welds with silver as an interlayer was attributed to the for- effects of friction stir welding parameters on intermetallic and defect mation of ductile phases like Ag3Fe2,Ag2Al and Ag3Al. formation in joining aluminum alloy to mild steel. Mater Des 2013;49(1):433e41. Acknowledgement [17] Patel VK, Bhole SD, Chen DL. Ultrasonic spot welding of aluminum to high-strength low-alloy steel: microstructure, tensile and fatigue properties. Metall Mater Trans A 2014;45A(1):2055e66. The authors express their gratitude to Defence Research [18] Fuji A. Friction welding of AleMgeSi alloy to NieCreMo low alloy and Development Organization for the financial support to steel. Sci Technol Weld Join 2004;9(1):83e9. carry out this program and are thankful to Dr. Amol A. [19] Meshram SD, Mohandas T, Madhusudhan Reddy G. Friction welding of Gokhale, Distinguished scientist, Director, Defence Metallur- dissimilar pure metals. J Mater Process Technol 2007;184(1e3):330e7. gical Research Laboratory, India for his continued encour- [20] Yilbas BS, Sahin AZ, Kahraman N, Al-Garni AZ. Friction welding of SteAl and AleCu materials. J Mater Process Technol agement and support. 1995;49(3e4):431e43. [21] Kimura M, Ishii H, Kusaka M, Kaizu K, Fuji A. Joining phenomena and References joint strength of friction welded joint between aluminium magnesium alloy (AA5052) and low carbon steel. Sci Technol Weld Join 2009;14(7):655e61. [1] Agudo L, Eyidi D, Schmaranzer CH, Arenholz E, Jank N, Bruckner J, [22] Dey HC, Ashfaq M, Bhaduri AK, Rao KP. Joining of titanium to 304L et al. Intermetallic FexAly-phases in a steel/Al-alloy fusion weld. J Mater stainless steel by friction welding. J Mater Process Technol e Sci 2007;42(24):4205 14. 2009;209(18e19):5862e70. [2] Zhang H, Liu J. Microstructure characteristics and mechanical property of [23] Hwang IH, Watanabe T, Doi Y. Dissimilar metal welding of steel to Al- aluminum alloy/stainless steel lap joints fabricated by MIG welding- Mg Alloy by spot resistance welding. Adv Mater Res e e brazing process. Mater Sci Eng A 2011;528(19 20):6179 85. 2007;15(17):381e6. [3] Zhang HT, Feng JC, He P, Hackl H. Interfacial microstructure and me- [24] Rosalie JM, Bourgeois L, Muddle BC. Precipitate assemblies formed on chanical properties of aluminium-zinc-coated steel joints made by a dislocation loops in aluminium-silver alloys. Philos Mag modified metal inert gas welding brazing process. Mater Charact 2009;89(15):1267e78. e 2007;58(7):588 92. [25] Fujikawa SI, Hirano KI, Yoshiaki Fukushima Y. Diffusion of silicon in [4] Donga H, Yanga L, Dong C, Kou S. Improving arc joining of Al to steel aluminum. Metall Mater Trans A 1978;9(12):1811e5. e and Al to stainless steel. Mater Sci Eng A 2012;534(1 Feb):424 35. [26] Yin FC, Zhao MX, Liu YX, Han W, Li Z. Effect of Si on growth ki- [5] Dieter GE. ASM handbook, materials selection and design. 1st ed. Ma- netics of intermetallic compounds during reaction between solid iron terials Park, OH: ASM International; 1997. and molten aluminum. Trans Nonferr Met Soc China [6] Kobayashi S, Yakou T. Control of intermetallic compound layers at 2013;23(2):556e61. interface between steel and aluminum by diffusion-treatment. Mater Sci [27] Springer H, Kostka A, Payton EJ, Raabe D, Kaysser-Pyzalla A, e e Eng A 2002;338(1 2):44 53. Eggeler G. On the formation and growth of intermetallic phases during [7] Cao R, Yu G, Chen JH, Wang PC. Cold metal transfer joining aluminum interdiffusion between low carbon steel and aluminum alloys. Acta Mater alloys-to galvanized mild steel. J Mater Process Technol 2011;59(4):1586e600. e 2013;213(10):1753 63. [28] Rathod MJ, Kutsuna M. Joining of aluminum alloy 5052 and low-carbon [8] Borrisutthekul R, Yachi T, Miyashita Y, Mutoh Y. Suppression of interme- steel by laser roll welding. Weld J 2004;83(1):16se26s. tallic reaction layer formation by controlling heat flow in dissimilar joining of steel and aluminum alloy. Mater Sci Eng A 2007;467(1e2):108e13.