Effect of Friction Welding Parameters on Mechanical and Microstructural Properties of Dissimilar AISI 1010-ASTM B22 Joints

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In this study, the characteristic of structures, tensile properties, hardness values, and microstructural changes of friction joints were investigated

BY A. KURT, I. UYGUR, AND U. PAYLASAN

ABSTRACT it is necessary to produce high-quality joints between them. Typical solid-state Rotary friction welding is one of the most economical and efficient production meth- joining applications of diffusion welding ods for joining similar and dissimilar materials. It is widely used with metals and thermo- for various content of the aluminum metal matrix composites (Refs. 5–7) and friction

WELDING RESEARCH plastics in a wide variety of aviation, transport, and aerospace industrial component de- signs. Individually, mild steel to mild steel and copper to copper are normally easy to weld stir welding (Ref. 8) have been studied in by fusion welding methods, but the joint of mild steel to copper can be extremely difficult detail. Welding copper alloys is usually dif- due to the differences in the two materials’ melting temperature, density, strength, and ficult using a conventional fusion welding thermal conductivity. Thus, these kinds of problems can be eliminated by a solid-state fric- process because copper has high thermal tion welding technique. Hence, the current study attempts to understand the friction weld- diffusivity, which is about 10 to 100 times ing characteristics of mild steel-bronze dissimilar parts. This study looks into the influence higher than in many steels and nickel al- of process parameters, which includes friction pressure, upsetting pressure, and upset time loys. The effects of diffusion welding pa- on the axial shortening, hardness, microstructure, and tensile properties of the welds. The rameters on the mechanical response of optimum parameters for upset time, upset pressure, and friction pressure necessary for low carbon steel and commercially pure welding were obtained. Finally, the obtained mechanical properties results were com- copper were studied in detail by Kurt et al. mented on the light of optical microscopy. (Ref. 5). Welding time, applied load, welding temperature, and chemical composi- Introduction good mechanical and physical properties. tion of the steel are some of the key pa- It is an easy process to weld these materi- rameters to controlling the solid-state diffusion welding process. Welding of machinery components is als by themselves. Unfortunately, most Rotary friction welding is one of the compulsory in most engineering applica- engineering materials have to join with solid-state techniques that is applied to tions. Just a few decades ago, materials dissimilar counterparts. Thus, it is difficult the joining of similar and dissimilar coun- were classified as weldable and nonweld- to obtain good-quality weld joints using terparts. In this technique, machinery able, but innovations in technology al- molten welding methods. Some defects components are brought into contact. lowed joining of most materials by fusion and intermetallic phases can occur during While one of them remains stationary, the and solid-state welding techniques. Typi- the process because of the great differ- other is rotated with the applied pressure. cal fusion welding techniques include gas ences between Fe and Cu in physical, me- When the temperature of the interfaces welding (oxyacetylene), arc welding chanical, and chemical properties. Table 1 has reached an optimum value for the ex- (shielded metal, gas tungsten, and sub- shows some physical and mechanical tensive plastic deformation, the rotation is merged), and high-energy beam welding properties of AISI 1010 mild steel and stopped, while the forging pressure re- (electron and laser). Heat sources for ASTM B22 copper bronze (Ref. 4). These mains unchanged or increased. The appli- these techniques are a gas flame, an elec- metals have good electrical and heat con- cation of an axial force maintains intimate tric arc, and a high beam, respectively. ductivity and have a good ability for cast- contact between the parts and causes plas- However, in the nature of these tech- ing and machining. In order to take ad- tic deformation of the material near the niques, excessive heating can cause dam- vantage of the dissimilar metals involved, weld interface. If sufficient frictional heat age to the workpiece, including weakening has been produced during softening, and distortion. Some of the fusion tech- larger wear particles begin to expel from niques are applied for various materials the interfaces and axial shortening of the (Refs. 1–3). Low carbon (mild) steel and KEYWORDS components begin as a result of the ex- copper alloys are widely applied prospects pelled upsetting. In general, heat is con- because of their economic value, plus Friction Welding Mild Steel-Bronze ducted away from the interfaces, and a Welding Parameters plastic zone develops. The plasticized A. KURT is with Gazi University, Faculty of Tech- Mechanical Properties layer is formed on the interfaces and the nology, Ankara-Turkey. I. UYGUR (ilya- local stress system with the assistance of [email protected]) is with Duzce University, the rotary movement extrudes material Faculty of Engineering, Duzce, Turkey. U. PAY- from the interface into the flash. It has LASAN is with Korfez Vocational and Technical been shown that weld integrity is strongly High School, Kocaeli, Turkey. affected by the rate of flash expelled under

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A B

Fig. 1 — Microstructure of A — AISI 1010 steel (× 500); B — ASTM B22 copper bronze (× 50).

appropriate conditions (Ref. 9). Friction yield strength of the welded welding has a lot of advantages over other specimens were determined. welding processes, such as no melting, Hardness values (VH0.5) were high reproducibility, short production determined by using a Zwick time, low energy input, limited heat-af- 3212 device. Measurements fected zone (HAZ), avoidance of porosity were taken in the welding cen- formation and grain growth, and the use of ter through base metals. For nonshielding gases during the welding tensile strength and hardness process. Also, the technique is not only ap- test values, at least three speci- plied to round specimens but used for rec- mens were carried out for each tangular components. It is called linear parameter. The axial shorten- friction welding and has recently been ap- ing was estimated by measuring plied to steel (Ref. 10). the length of the specimens be- Although a large amount of previous fore and after welding. The mi- studies (Refs. 7–11) in similar and dissimi- crostructure was investigated Fig. 2 — The effect of upset time and friction pressure on the axial lar materials have been studied, mechanical by optical microscopy. The steel shortening with 22 MPa upset pressure. properties of the mild steel to copper specimens were polished and bronze joint by friction welding method etched with a solution consist- have never been reported up-to-date. Thus, ing of 70% HCl and 30% upset time and pressure on axial shortening the aim of this study is to examine the me- HNO3. The grains have equaxied shapes are also shown in Fig. 3. It is clearly seen that chanical properties and optimal welding ranging from 30 to 150 μm in dimension. axial shortening significantly increased with conditions of friction welded joints of The bronze specimens were also polished increasing friction, upset pressures, and ASTM B22 Tin bronze and AISI 1010. and etched with a solution consisting of times. To ensure good metallurgical in- 40% NH4OH, 60% H2O. Typical mi- tegrity, it is necessary to break up and expel Materials and Methods crostructures of materials can be seen in the contaminated surface layers. In rotary Fig. 1A, B. friction welding, this is achieved with WELDING RESEARCH Chemical composition of the copper- greater pressure and upset times. Also, in based bronze and mild steel employed is Results and Discussions light of these figures, the axial shortening given in Table 2. Cylindrical test specimens exponentially increased by increasing these of 20 mm in diameter and 100 mm in length Effects of Welding Parameters on Axial welding parameters. The fit of the results were prepared for friction welding. Before Shortening yields the following simple formula: friction welding, the surfaces facing each 0.22 other were machined using a lathe. Before The effect of upset time and friction As = 0.4 – 0.8 t (1) welding, the surface of the workpieces were pressure on the axial shortening is pre- cleaned with a stainless steel brush and ace- sented in Fig. 2. Similarly, the effects of where As is the axial shortening (mm) and tone to remove the oxide layer and stains. Joining of these two dissimilar alloys was performed on a continuous drive friction Table 1 — Some Physical and Mechanical Properties of Mild Steel and Copper Bronze welding machine of 250 kN capacity at a constant rotation speed of 2500 rev/min, Properties Unit AISI 1010 ASTM B22 and constant friction time of 3 s. Friction Density g/cc 7.87 8.72 and upset pressures can be observed on the Themal Conductivity W/m-K 51.9 74 screen, and the welding sequence stages are CTE μm/m-°C 12.2 20 controlled by a solenoid valve. The welding Ultimate Tensile Strength MPa 425 310 parameters were as follows: friction pres- Yield Strength MPa 180 150 sures (P1): 10, 15, 20 MPa; upset pressures Elongation % 28 25 (P2): 22, 25, 30 MPa; and upset (forging) Elastic Modulus GPa 200 105 time (t1) of 1, 5, 7, 8 s. Tensile test specimens Melting Temperature °C 1535 1000 were prepared according to ASTM E8M- Hardness Hv 100 83 00b. Ultimate tensile strength (UTS) and

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Fig. 3 — The effect of upset time and pressure on the axial shortening Fig. 4 — Typical axial shortening against upset time graph with 15 MPa friction with 10 MPa friction pressure. pressure and 22 MPa upset pressure. A B C WELDING RESEARCH

Fig. 5 — The microhardness distribution of materials. A — The effect of friction pressure (P2 = 22 MPa, t1 = 5 s); B — the effect of upset pressure (P1 = 10 MPa, t1 = 5); C — the effect of upset time (P1 = 10 MPa, P2 = 30 MPa).

physical and some mechanical properties. the axial shortening rate, which can also be At the low friction and upset pressures, a factor indicative of joint quality. the friction heat is not enough to soften Figure 4 shows the effect of the materi- the interfacial materials; and the interface als on axial shortening. The different ther- temperature is relatively low due to low mal and physical properties of the materials heat input. As time increases, the friction to be welded in dissimilar metal welding and contact area also significantly in- (heat capacity, thermal conductivity, rela- creases the heat generation on the inter- tionship between hardness and tempera- faces, and in return flash is formed. ture) generally result in asymmetrical de- Hence, axial shortening increases remark- formation. In this study, during the friction ably with the interface temperature rise welding of steel to bronze, a flash forms and softening of materials following the mostly on the bronze side. While the axial extruding process under the rotary mo- shortening increased exponentially for the tion. Therefore, upset friction pressures bronze materials, the steel showed a linear and times are key parameters in control- increase in axial shortening. Although both Fig. 6 — The effect of friction pressure on the tensile ling the formation of a perfect joint. materials were axially shortened with in- response of the 22 MPa upset pressure at 5 s upset time. Sathiya et al. (Ref. 11) found that in the creasing upset times, shortening of the case of stainless steel, a combination of bronze material was more pronounced high friction, upset pressure, friction time, compared with steel. It is well known that t is the upset time (s). This formula can and upset time produced more axial short- bronze melting temperature and yield clearly explain the change of axial shortening (melt-off) that played an important strength are significantly low, and thermal ening with the upset time under the weld- role in the mechanical properties. They conductivity and coefficient of thermal ex- ing conditions in this study. However, this observed that increased axial shortening pansion are quite high, compared to steel. basic equation is primitive, and further ex- resulted in better mechanical properties of Thus, more bronze materials will be soft- perimental study should be done to incor- joints. In general, the mechanical proper- ened during the welding process due to the porate the factors related to material ties of a weld are more closely related to extensive plastic deformation, and relatively high temperature occurs on the joint sur- Table 2 — Chemical Compositions of Copper Bronze and Mild Steel face. Hence, more bronze materials deformed plastically due to the decreased Material Sn Zn Pb Ni Fe Cu yield strength (effect of the high tempera- ASTM B22 10 1.14 0.5 0.16 0.04 remain ture) compared to the steel. The heat gen- Elements wt-% eration in the joint surface is significantly Material C Mn Ni Cr Si Fe different from center to outer shell. This AISI 1010 0.1 0.3 0.22 0.1 0.04 remain fact suggests that the extrusion rates of ma-

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A ASISI 1010

B Bronze 500 μm

Fig. 8 — Microstructural changes inside the welding region.

Hardness Distribution Tensile Strength

Figure 5A shows the effect of fric- The influence of friction pressure on the tion pressures, B shows the effect of tensile test result is shown in Fig. 6. From upset pressures, and C shows the effect the data, it may be noted that UTS and yield of upset time on the hardness distribu- strength increased with an increase in friction in the direction perpendicular to tion pressure and axial shortening. The the weld interface of the as-welded UTS strength corresponds to about 70% specimen. As can be seen from these that of the bronze part and 50% that of the figures, almost the same trend was ob- steel. Nearly full performance can be ob- C Bronze served in the microhardness profiles of tained for the yield strength of the bronze all samples. The maximum hardness material that was tested on the highest fric- values of joints were obtained on the tion pressure and the highest axial shorten- steel side next to the welding center- ing. In general, tensile strength increased up line. The hardness values generally in- to a certain value with increasing friction creased with increasing friction pres- pressure and then decreased slightly after sure and upset pressures, but hardness reaching the optimum value. This reduction values decreased with increasing upset is probably due to flashing of the heated soft time. Increasing hardness in the weld- material from the interface on upset pres- ing interface can be related to the mi- sure. Flashing increases with increasing fric- crostructure formed in the weld inter- tion pressure (Ref. 17). Joints performed Fig. 7 — The effect of friction pressure on the microstruc- face as a result of the heat input and here were quite brittle in nature and either ture. A — P = 10 MPa, P = 22 MPa, t = 5 s. B — P 1 2 1 1 plastic deformation. As can be seen in the HAZ region of the bronze or joint in- WELDING RESEARCH = 15 MPa, P2 = 22 MPa, t1 = 5 s. C — P1 = 20 MPa, P2 = 22 MPa, t = 5 s. from Table 1, the hardness of bronze is terface. This can be attributed to the diffu- 1 83–96 Hv, but, the weld interface hard- sivity of Fe that is higher than that of Cu and ness is measured around 147 Hv. Sim- hence a reaction layer can be formed to- terials in the middle and edges will have dif- ilarly, the hardness value of mild steel ward the bronze side and the failure has ferent microstructures in both specimens is 100–118 Hv, but the welding interface is taken place in this zone. owing to the nonuniform temperature dis- measured around 200 Hv. It can be said tribution. In friction welding, the tempera- that microstructural evaluations around Microstructure ture would be minimum at the center and the interface, diffusion of elements on the maximum at the periphery because more in- sides, work hardening, dislocation density, Figure 7A–C shows the microstruc- termixing takes place at the peripheral re- grain refinement, and formation of pre- tural features of interfaces with increasing gion of the weld. Thus, the maximum heat cipitations may have caused this increase. friction pressure. It is clearly seen that in- generation point occurred somewhere close Although work hardening is also effective sufficient friction pressure on the joining to the periphery beneath the surface of dis- on the hardening in the bronze side, hard- surface resulted in an inadequate locking similar metals (Ref. 12). In addition, the ening in steel is mostly a direct result of of the surfaces (Fig. 7A) where limited flash was found to increase not only with the fine grains, rapid cooling from the welding plastic deformation and microstructural increase in friction welding parameters but temperature, and formation of precipi- changes occurred, and these facts caused also with the density of bronze. Similar re- tates. A similar hardness profile was also poor tensile response of the joint. An in- sults were also reported by Jayabharath et observed for dissimilar material couples crease in the friction pressure caused bet- al. (Ref. 13). Furthermore, for a dissimilar (Refs. 11, 15, 16). It can be said that the ter joining surfaces (Fig. 7B, C) where re- weld in rheology and geometry, computer hardness properties are influenced by an crystallization occurs on the bronze side, simulation demonstrates that the weaker interactive effect of friction, upset pres- and grain refinement and strain hardening material is thicker than the stronger part, sures, and upset times, which are combi- occurs on the steel side. The width of the which leads to different flash shapes and rel- nations of heat input and a degree of strain recrystallized region is mainly affected by ative upset (Ref. 14). hardening. the friction pressure. An increase in the

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friction pressure resulted in a wider fine grains were evident along the rolling di- dustrial Lubrication and Tribology 58(6): grain region. A change in microstructure rection. The intensity of orientation was 303–311. and axial shortening also notably occurred found to be dependent on the welding pa- 3. Uygur, I., and Dogan, I. 2005. The effect in the bronze side. The same phenomenon rameters (Ref. 17). of TIG welding on microstructure and mechanical properties of a butt-joined unalloyed tita- has been reported during friction welding nium. Metalurgija 44(2): 119–123. of dissimilar welds, namely Fe-Ti, Cu-Ti, Conclusions 4. www.matweb.com Fe-Cu, Fe-Ni (Ref. 12). The recrystallized 5. Uygur, I. 2007. Microstructure and per- region of Fig. 7C decreases compared to To clarify the feasibility of friction weld- formance in diffusion welded joints of Al 5-10- that of Fig. 7A, and fracture occurred in ing to AISI 1010-ASTM B22 copper bronze, 15% WCp composites. Materials Science Forum the faying surface. However, tensile frac- the characteristic of structures, tensile prop- 546–549: 671–674. ture of the joint (Fig. 7C) did not occur in erties, hardness values, and microstructural 6. Kurt, A., Uygur, I., and Ates, H. 2007. Ef- fects of temperature on the weldability of pow- the faying surface but in the bronze side of changes of friction joints were investigated der metal parts joined by diffusion welding. Ma- the HAZ. This means that the decrease in with various welding parameters. The main terials Science Forum 546–549: 667–670. recrystallized region was caused by high conclusions are summarized as follows: 7. Kurt, A., Uygur, I., and Mutlu, E. 2006. friction pressure that contributes to better 1. Friction welding can be used suc- The effect of allotropic transformation temper- tensile strength. Heat flow occurs prefer- cessfully to join mild steel to bronze. The ature in diffusion-welded low carbon steel and entially in the material with the greatest processed joints exhibited better mechan- copper. Metallofiz., Noveishie Tekhnol. 28(1): thermal conductivity. Due to the different ical and metallurgical characteristics as 39–52. thermal conductivities between bronze compared to those made with fusion weld- 8. Kurt, A., Uygur, I., and Ates, H. 2007. Ef- and steel, the specific heat is so large, and ing techniques. fect of porosity content on the weldability of hence, most of the frictional heat was gen- 2. The tensile strength of the obtained powder metal parts produced by friction stir welding. Materials Science Forum 534–536: erated in bronze. The difference in ther- weld joints can reach a base metal strength of 70% if suitable welding parameters are 789–792. mal conductivity explains the microstruc- 9. Vairis, A., and Frost, M. 1999. On the ex- tural changes that occur preferentially in determined. Fracture usually occurs ei- trusion stage of linear friction welding of ther in the HAZ of soft material or in the the bronze side. Similar microstructural Ti6Al4V. Mater. Sci. Eng. A 271: 477–484. WELDING RESEARCH observations for the Cu-Ti couples were joint surface. 10. Li, W. Y., Ma, T. J., Yang, S. Q., Xu, Q. also reported in Ref. 18. Most of the 3. The axial shortening exponentially Z., Zhang, Y., Li, J. L., and Liao, H. L. 2008. Ef- changes occurred preferentially in the increased by increasing the upset time. fect of friction time on flash shape and axial shortening of linear friction welded 45 steel. copper, no evidence of microstructural The best fit of data yields a formula: As = 0.4 – 0.8 t0.22. Materials Letters 62: 293–296. variation was seen in the vicinity of the in- 11. Sathiya, P., Aravidan, S., and Noorul terface, neither grain growth nor grain 4. Upset time, friction time, and axial Haq, A. 2007. Effect of friction welding param- boundary precipitation was observed. shortening play important roles in the eters on mechanical and metallurgical proper- They attributed this behavior to the dif- metallographic structure and mechanical ties of ferritic stainless steel. Int. J. Adv. Technol. ference in thermal conductivity (Ref. 18). response of the weld. 31: 1076–1082. It can be said that for the perfect interfa- 5. Extensive deformation is confined 12. Meshram, S. D., Mohandas, T., and cial bonding, sufficient upset time and mostly to the bronze side due to their low Reddy, G. M. 2007. Friction welding of dissim- J. Mater. Proces. Techn. friction pressures are necessary to reach flow stress and high thermal conductivity. ilar pure metals. 184: 330–337. the optimal temperature and severe plas- 6. Higher hardness values are observed 13. Jayabharath, K., Ashfaq, M., Veugopal, tic deformation to bring these materials next to the interface, but they dramatically P., and Achar, D. R. G. 2007. Investigations on within the attraction range. Sathiya et al. decreased with increasing distance and the continuous drive friction welding of sin- (Ref. 11) found that in the case of stainless upset time. tered powder metallurgical (P/M) steel and steel, a combination of high friction, upset 7. An increase in the friction and upset wrought copper parts. Materials Sci. & Eng. A pressure, and high upset time produced pressure result in slightly higher hardness 454: 114–123. high tensile strength and high impact val- values. 14. D`Alvise, L., Massoni, E., and Walloe, S. J. 2002. Finite element modelling of the inertia ues. A bond quality classification system 8. Typical microstructural features friction welding process. J. Mater. Process. was developed using a novel, noncontact, were observed in the welding region. Re- Techn. 125–126: 387–391. acoustic emission sensing technique. An crystallized fine and elongated grains were 15. Ozdemir, N., Sarsilmaz, F., and Hasca- efficient, inexpensive, and fast production evident adjacent to the joint surface. lik, A. 2007. Effect of rotational speed on the in- benefit can be achieved by using process 9. For this study, the optimal joint per- terface properties of friction-welded AISI 304L monitoring systems (Refs. 19, 20). formance was attained at a friction pressure to 4340 steel. Mater. & Design 28: 301–307. Figure 8 shows the microstructural of 20 MPa, upset pressure of 22 MPa, and 16. Sahin, M. 2009. Joining of stainless-steel and aluminum materials by friction welding. changes of the bronze and steel sides of upset time of 5 s. Int. J. Adv. Manuf. Techn. 41(5–6): 487–497. the weld. During the friction weld process, 17. Ates, H., Turker, M., and Kurt, A. 2007. the temperature near the weld interface Acknowledgments Effect of friction pressure on the properties of would reach just below A1 temperature, friction welded MA956 iron-based superalloy. which is about the recrystallization tem- The authors wish to thank Prof. Dr. G. Mater. & Design 28: 948–953. perature for the mild steel. Therefore, Said and H. Ozden for their valuable con- 18. Kim, S. Y., Jung, S. B., and Shur, C. C. 2003. Mechanical properties of copper to tita- very fine equaxied grains formed from fer- tributions. Also, special thanks to Turkish Track Factory for its support and guidance nium joined by friction welding. J. Mater. Scien. rite and pearlite. A martensitic structure 38: 1281–1287. can even be seen in this region when the during the experimental stage. 19. www.boulder.nist.gov/div853/Events weld interface reaches above the A3 tem- %20%20Welding%20Conference/Weld_Papers/ perature with the occurrence of rapid References 1-1%20Hartman-paper.pdf cooling (Ref. 21). Beyond this region, 20. library.lanl.gov/cgi-bin/getfile?0081 elongated and severely compressed grains 1. Uygur, I., and Gulenc, B. 2004. The effect 8853.pdf of shielding gas composition for MIG welding 21. Sahin, M., Akata, H. E., and Ozel, K. can be seen in the HAZ region of the steel. process on mechanical behaviour of low carbon 2008. An experimental study on joining of se- However, for the bronze side, there was no steel. Metalurgija 43(1): 35–40. vere plastic deformed aluminum materials with fine grain next to the interface, but par- 2. Uygur, I. 2006. Microstructure and wear friction welding method. Mater. & Design 29(1): tially melted zones and fibrous elongated properties of AISI 1038H steel weldments. In- 265–274.

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