The hybrid metal extrusion and bonding (HYB) process is a new solid-state joining technique developed for aluminum alloys. By the use of filler material addition and plastic deformation sound joints can be produced at operating temperatures below 400 °C. The HYB process has the potential to compete with commonplace welding technologies, but its comparative advantages have not yet been fully explored. Here, we present for the first time the results from an exploratory investigation of the mechanical integrity of a 4-mm AA6082-T6 HYB joint, covering both hardness, tensile and Charpy V-notch testing. The joint is found to be free from defects like pores, internal cavities and kissing bonds, yet a soft heat-affected zone (HAZ) is still present. The joint yield strength is 54% of that of the base material, while the corresponding joint efficiency is 66%. The indications are that the HYB process may compete or even outperform conventional welding techniques for aluminum in the future after it has been fully developed and optimized. . . . Keywords Hybrid metal extrusion and bonding (HYB) Solid state joining Al-Mg-Si alloys Mechanical properties 1 Introduction formation, hot cracking, liquation cracking, and bonding de- fects causing additional degradation of the joint [1, 2]. Aluminum alloys, as the Al–Mg–Si alloys, exhibit unique Solid-state processes offer several advantages for joining of physical and mechanical properties making them attractive aluminum as material melting does not occur. Instead, metallic for a wide range of structural applications and welded assem- bonding is achieved through plastic deformation and diffusion blies [1, 2]. Although the Al–Mg–Si alloys are readily weld- taking place across the mating interface. Over the years a vari- able, the excessive heat generation associated with the tradi- ety of solid-state joining processes have been developed, but tional welding processes makes them vulnerable to HAZ soft- most of them are limited to joining of certain materials with ening due to reversion of the hardening precipitates which simple geometries [5, 6]. Among the more recent technologies, form during artificial aging . Despite that some strength friction stir welding (FSW) is perhaps the most successful one. recovery may be achieved by natural aging or by applying Since its entry in 1991 the process has continuously evolved an appropriate post-weld heat treatment, the mechanical integ- thanks to successful parameter optimization and new tool de- rity of the welded component is always poorer than that of the sign. Also modified versions of the process exist, as self- base material [1, 4]. Moreover, the material melting occurring reacting friction stir welding (SR-FSW)  and filling friction during fusion welding makes the weld susceptible to pore stir welding (FFSW) [8, 9], aiming to increase the initial bond strength in different regions of the weld. The comprehensive research and technical development of the FSW process have The original version of this article was revised due to a retrospective Open Access order. brought it to the leading edge of aluminum welding technology [10, 11]. Still, FSW has some fundamental limitations. For * Lise Sandnes instance, the frictional heat generated through the process is still Lise.Sandnes@ntnu.no large enough to cause HAZ softening. In addition, strict base plate and profile tolerances are required, as lack of filler mate- Department of Mechanical and Industrial Engineering, Norwegian rial addition may result in insufficient material feeding and University of Science and Technology, 7491 Trondheim, Norway consequently to undercuts and internal defects in the joint [6, HyBond AS, Alfred Getz vei 2, 7491 Trondheim, Norway 12]. These limitations need to be overcome in the future. 1060 Int J Adv Manuf Technol (2018) 98:1059–1065 Although the hybrid metal extrusion & bonding (HYB) process is still technologically immature compared to FSW, it is deemed to have a great potential. By the use of filler material addition and plastic deformation the HYB process can produce sound joints in the solid state [13–15]. At the same time, the filler material addition makes the process more flexible and less vulnerable to undercuts and weld defects compared to conventional solid state joining processes. Fig. 2 Illustration of the rotating pin and its location in the groove during Moreover, except from cold pressure welding the operational HYB butt welding of plates temperature is lower than that reported for other solid state joining techniques, including FSW. forced to flow against the abutment blocking the extrusion In order to illuminate the potential of the HYB process, we chamber and subsequently (owing to the pressure build-up) aim to put it to the test in its current development stage. This continuously extruded through the moving dies in the extruder will be done by characterizing a 4-mm AA6082-T6 butt weld head. They are, in turn, helicoid-shaped, which allow them to based on hardness measurements, tensile testing and Charpy act as small “Archimedes screws” during the pin rotation, thus V-notch testing of different regions across the weld zone. The preventing the pressure from dropping on further extrusion in results will then be compared with corresponding test data the axial direction of the pin. Furthermore, if the stationary reported in the scientific literature for gas metal arc (GMA) housing is provided with a separate die at the rear, a weld face and FS welds. can be formed by controlling the flow of aluminum in the radial direction. In this case both the width and height of the weld reinforcement can be varied within wide limits, depend- 2 Current status of the HYB technology ing on the die geometry, ranging from essentially flat to a fully reinforced weld face. It is this flexibility that makes the HYB 2.1 Characteristic features of the HYB PinPoint PinPoint extruder suitable for a number of other applications extruder as well, including fillet joining, bead-on-plate deposition, plate surfacing, additive manufacturing , and welding of The HYB PinPoint extruder is based on the principles of con- aluminum to steel . tinuous extrusion . The current version of the extruder is built around a 10-mm diameter rotating pin, provided with an 2.2 Working principle during butt welding extrusion head with a set of moving dies through which the aluminum is allowed to flow. This is shown by the drawing in In a real joining situation, the extruder head is clamped against Fig. 1. When the pin is rotating, the inner extrusion chamber the two aluminum plates to be joined. The plates are separated with three moving walls will drag the filler wire both into and through the extruder due to the imposed friction grip. At the same time it is kept in place inside the chamber by the station- ary housing constituting the fourth wall. The aluminum is then Fig. 3 Cross-sectional view of a HYB butt joint. Metallic bonding is Fig. 1 The HYB PinPoint extruder is built around a rotating pin provided mainly achieved by oxide dispersion and shear deformation along the with an extrusion head with a set of moving dies through which the groove side walls, whereas in the root region where the metal flows aluminum is allowed to flow meet surface expansion and pressure contribute most to bonding Int J Adv Manuf Technol (2018) 98:1059–1065 1061 Table 1 Chemical composition Si Mg Cu Fe Mn Cr Zn Ti Zr B Other Al (wt.%) of base and filler materials (BM and FM) BM 0.9 0.8 0.06 0.45 0.42 0.02 0.05 0.02 –– 0.03 Balance FM 1.11 0.61 0.002 0.20 0.51 0.14 – 0.043 0.13 0.006 0.029 Balance from each other so that an I-groove forms in-between. The pin down to the final dimension. The chemical compositions of diameter is slightly larger than the groove width to ensure the base and filler materials (BM and FM) are summarized in contact between the sidewalls of the groove and the pin (see Table 1. From the table it can be seen that the FM contains Zr Fig. 2). Analogous to that in FSW, the side of the joint where and larger amounts of Cr compared to the BM. These alloying the tool rotation is the same as the welding direction is referred elements have been added on purpose to the FM in order to to as the advancing side (AS), whereas the opposite side is increase its work hardening capacity by allowing dispersoids referred to as the retreating side (RS). Hence, the process is by to form during homogenization. The HYB single-pass butt definition asymmetrical, as the force transferred from the ex- joining of the plates was carried out by HyBond AS, using truder head to the base plates during processing will be differ- an I-groove with 3 mm root opening and the welding param- ent on the AS compared to the RS. During pin rotation some eters listed in Table 2. Note that these parameters are not of the base material along with the oxide layer on the groove considered to be optimal from a mechanical strength point of sidewalls will be dragged around by the motion of the pin. view, but represent rather a sensible compromise between a Because of that they tend to mix with the filler material as it number of conflicting requirements to achieve a defect-free flows downwards into the groove and consolidates behind the butt joint under the prevailing circumstances. pin. Typically, the temperature in the groove between the two base plates to be joined is between 350 and 400 °C, which is 3.2 Mechanical testing below the operating temperature reported for FSW . In the HYB case, metallic bonding is achieved through a Transverse samples were cut from the HYB welded plates. combination of oxide dispersion, shear deformation, surface The tensile and Charpy V-notch (CVN) specimens were lo- expansion and pressure, as shown in Fig. 3. This creates fa- cated in different regions of the weld relative to the center-line. vorable conditions for metallic bonding between the filler They were subsequently flush-machined to remove the con- metal and the base material when the new oxide-free inter- tribution from the weld reinforcement. Details of the specimen faces (being formed following the re-shaping of the groove locations and the number of specimens being tested can be by the rotating pin) immediately become sealed-off by the found in Fig. 4 and Table 3,respectively. Theflat specimens filler metal under high pressure. used for tensile testing had a reduced section length and width of 32 and 6 mm, respectively, a thickness of 4 mm (corre- sponding to the plate thickness), and a total length of 100 mm. The grip section width was 10 mm. Tensile testing 3 Experimental was carried out at room temperature using an Instron hydrau- lic test machine (50 kN load cell) with a fixed cross-head 3.1 Materials and welding conditions speed of 1.5 mm/min. The applied gauge length was 25 mm. Similarly, the CVN specimens had a total length of 55 mm, a In the present welding trial, 4-mm rolled plates of AA6082-T6 width of 10 mm and a thickness of 4 mm (corresponding to the were used as base material. These were obtained from an external supplier. The dimensions of the base plates prior to welding were 120 mm × 60 mm. The filler material was a Ø1.2 mm wire of the AA6082-T4 type, produced by HyBond AS. The wire was made from a DC cast billet, which then was homogenized, hot extruded, cold drawn and shaved Table 2 Summary of welding parameters used in the HYB butt joining trial Pin rotation Travel speed Wire feed rate Gross heat input (RPM) (mm/s) (mm/s) (kJ/mm) Fig. 4 Schematic illustration of different weld zones in the HYB butt joint. Also the welding and plate rolling directions are indicated in the sketch. EZ: Extrusion zone (consists of a mix of FM and BM), HAZ: 400 6 142 0.34 (pure BM) 1062 Int J Adv Manuf Technol (2018) 98:1059–1065 Table 3 Number of specimens tested and their location Finally, selected fracture surfaces of broken tensile and CVN specimens were examined in a Quanta FEG 450 scan- Base plate HAZ Bond line EZ Total ning electron microscope (SEM). The fracture surface exam- Tensile testing 4 3 – 310 ination was performed at an acceleration voltage of 20 kVand Charpy testing 3 3 3 3 12 a fixed working distance of 10 mm. 4 Results plate thickness). The depth of the V-notch being oriented in 4.1 Weld macrostructure and hardness distribution weld length direction was 2 mm and the flank angle was 45°. CVN testing was carried out at room temperature, using a The measured hardness profile along the horizontal mid- Zwick impact testing machine with a total impact energy ab- section of the HYB joint is presented graphically in sorption capacity of 450 J. Fig. 5a. Moreover, Fig. 5b shows an overview of the Specimens used for microstructural analyses and hard- different weld zones, from which the FM and the BM ness measurements were prepared according to standard flow patterns in the groove also can be seen. Note that sample preparation procedures. To reveal the micro- and each hardness point represents the arithmetic mean of macrostructure of the joint, the specimen was immersed in three individual measurements. The vertical dotted line an alkaline sodium hydroxide solution (1 g NaOH + 100 ml in Fig. 5a represents the hardness of the unaffected BM, H O) for 3 to 4 min. The macro- and microstructure of the measured to be 111 HV with a standard deviation of 2.2. weld were analyzed using a Leca DMLB light microscope The minimum hardness is found on the advancing side of and an Alicona Confocal Microscope. Transverse hardness the joint, yielding a value of 66 HV approximately 3 mm measurements were performed along the horizontal and from the center-line. The total width of the HAZ is seen to vertical mid-sections of the joint, see Fig. 4. The hardness be 25 mm, whereas the observed asymmetry in the hard- measurements were made using a Mitutoyo Micro (HM- ness profile and FM and BM flow patterns is probably a 200 series) Vickers hardness testing machine at a constant reflection of the pertinent difference in the force acting on load of 1 kg. The distance between each indentation was the AS and RS, respectively during pin rotation. The 0.45 mm. In total, three test series were carried out for each hardness measurements along the vertical mid-section re- of the two mid-sections. The base material hardness was vealed that the hardness was highest in the top region, established from ten individual measurements being ran- where it reached a value of 93 HV. The harness then domly taken on one separate base plate specimen. dropped monotonically with increasing depths below the Fig. 5 a Measured hardness profile along the horizontal mid- section of the HYB joint. The graph represents the mean value of three individual measurements. b Optical micrograph showing the transverse macrostructure of the HYB joint Int J Adv Manuf Technol (2018) 98:1059–1065 1063 plate surface, finally approaching its lowest value of the dispersoid-forming elements Zr and Cr, which are known 51 HV at the weld toe. to influence the work hardening behavior of Al–Mg–Si alloys. The fracture strain of the different weld zones is presented in Fig. 6b. Owing to the necking effect caused by the HAZ 4.2 Tensile properties softening the measured fracture strain of the welded speci- mens is seen to be significantly lower than that of the base The measured tensile properties of the HYB joint are graphi- material. Another consequence of the HAZ softening is also cally presented in Fig. 6. It is evident that both the EZ and the that fracture always occurs in the HAZ on the advancing side HAZ have significantly lower tensile properties compared to of the joint regardless of the sample location (i.e. whether it is the base material. However, there is apparently no significant located on the advancing side or not). This is in good agree- difference in the properties between the EZ and the HAZ. The ment with the results found from the transverse hardness mea- weld yield strength, as presented in Fig. 6a, amounts to 54% of surements, where the minimum HAZ hardness appears on the the BM yield strength, while the corresponding joint efficien- AS. cy (i.e. the σ /σ ratio) is higher reaching a value UTS, HAZ UTS, BM of 66%. This means that the EZ has a higher work hardening 4.3 Impact properties capacity compared to the base plate. The latter observation is not surprising, considering the fact that the FM also contains 3 −1 The joint response to very high strain rates (> 10 s )was determined by the use of CVN testing. The measured energy absorption (per unit area) for the different weld regions is shown in Fig. 7. The base material displays a relatively low initial base material toughness, whereas all of the welded specimens show an increase in impact toughens relative to the base material. The highest energy absorption is found for the EZ specimens, which is almost three times larger than that of the base material. No difference is observed between the bond line (BL) and the HAZ when it comes to energy absorption. 4.4 Microscopic analysis The microstructure of the HYB joint is shown in Fig. 8a. Obviously, the microstructure changes across the bond line, and the filler material reveals much finer grains compared to the HAZ. Close to the bond line, strongly elongated and heavily deformed grains are visible. Figure 8bshows arepre- sentative image of the fracture surface of a broken weld tensile Fig. 6 Average tensile properties for specimens sampling different weld Fig. 7 Measured energy absorption for CVN specimens sampling zones. a Offset yield strength and ultimate tensile strength. b Fracture different weld zones: base material (BM), extrusion zone (EZ), bond strain. Note that the error bars in the graphs represent the standard line (BL), and heat-affected zone (HAZ). The error bars in the graph deviation of the measurements represent the standard deviation of the measurements 1064 Int J Adv Manuf Technol (2018) 98:1059–1065 width of the HAZ varied between 35 and 50 mm. For the FS welds these values are significantly lower, varying between 20 and 25 mm, depending on the applied welding speed. The corresponding value for the HYB joint is 25 mm (revisit Fig. 5). To completely eliminate problems related to HAZ softening in Al–Mg–Si weldments, the operational tempera- ture needs to be kept below about 250 °C . This is phys- ically feasible and within the reach of what is possible using the HYB process as demonstrated previously by Aakenes  and Aakenes et al. . Moving on to the tensile properties, the GMAwelds have a yield strength corresponding to about 50% of the base material and a joint efficiency of 70%. On the other hand, the FS welds reach a yield strength of 52% with a joint efficiency of about 80%. In comparison, the HYB joint yield strength is 54%, while the joint efficiency is 66%. This indicates that the me- chanical strength of the HYB joint is within the range of that reported for conventional welding technologies such as GMAW and FSW. In practice, a variety of factors may influence the properties of welded Al–Mg–Si components. The total width of the HAZ and subsequentstrengthlossinthisregiondependbothonthe base metal chemistry and the initial temper condition, as well as on the applied welding parameters which determine the HAZ T-t pattern [1, 4]. Thus, following further optimization the HYB process needs to be benchmarked against GMAW and FSW under otherwise comparable conditions using exact- Fig. 8 a Optical micrograph showing changes in microstructure across ly the same base material and plate thickness. This work is the bond line between the base material and filler material. b now in progress. Representative SEM fractograph of a selected broken tensile specimen sampling the EZ 6 Conclusions specimen. Extensive dimple formation is observed being char- acteristic of a ductile fracture. As a matter of fact, all tensile For the first time the successful HYB joining of 4-mm and CVN specimens examined in the SEM revealed the same AA6082-T6 rolled plates is presented. The joint is found to fracture mode, thereby excluding possible kissing bond for- be free from internal defects like pores, cavities, and kissing mation. This means that full metallic bonding is achieved in bond. Full metallic bonding is achieved between the filler the groove between the FM and the BM under the prevailing material and the base material in the groove, as documented circumstances. both by tensile testing and Charpy V-notch (CVN) testing. Transverse hardness testing of the HYB joint disclosed evi- dence of significant HAZ softening, reaching a total HAZ 5 Discussion width of 25 mm. This reduces both the yield strength and the joint efficiency to values well below those of the base In order to evaluate the HYB joint mechanical performance, material (54 and 66%, respectively). In contrast, the HAZ the propertiesachievedmustbe comparedwith corresponding softening appears to have a positive effect on the CVN impact results reported for conventional welding technologies such as toughness, which is about three times larger for the welded gas metal arc welding (GMAW) and FSW. Among others, the specimens. transverse hardness profile and tensile properties of AA6082- Moreover, to get an indication of the HYB joint mechanical T6 GMA and FS welded plates have been determined by performance a comparison with corresponding results report- Moreira et al. [19, 20] and by Ericsson and Sandström . ed for GMA and FS welds has also been made. This shows In the work of Moreira et al. 3-mm-thick rolled plates were that the HYB joint mechanical properties are slightly better used, whereas in the work of Ericsson and Sandström 4-mm- than the properties reported for similar GMAwelds, but do not thick extruded profiles were used. In the GMA welds the total fully match those of sound FS welds. Therefore, there is still a Int J Adv Manuf Technol (2018) 98:1059–1065 1065 8. Huang Y, Han B, Lv S, Feng J, Liu H, Leng J, Li Y (2012) Interface potential for further optimization of the HYB process in order behaviours and mechanical properties of filling friction stir weld to bring the method to the forefront of aluminum welding joining AA 2219. Sci Technol Weld Join 17(3):225–230 technology. This work is now in progress. 9. Huang YX, Han B, Tian Y, Liu HJ, Lv SX, Feng JC, Leng JS, Li Y (2011) New technique of filling friction stir welding. Sci Technol Acknowledgements The authors are indebted to Ulf Roar Aakenes and Weld Join 16(6):497–501 Tor Austigard of HyBond AS for valuable assistance in producing the 4- 10. Threadgill P, Leonard A, Shercliff H, Withers P (2009) Friction stir mm AA6082-T6 HYB joint being examined in the present investigation. welding of aluminium alloys. Int Mater Rev 54(2):49–93 11. Nandan R, DebRoy T, Bhadeshia HKDH (2008) Recent advances in friction-stir welding—process, weldment structure and proper- Funding information The authors acknowledge the financial support ties. Prog Mater Sci 53(6):980–1023 from HyBond AS, NTNU, and NAPIC (NTNU Aluminum Product 12. Frigaard Ø, Grong Ø, Midling OT (2001) A process model for Innovation Center). friction stir welding of age hardening aluminum alloys. Metall Mater Trans A 32(5):1189–1200 Compliance with ethical standards 13. Aakenes UR (2013) Industrialising of the hybrid metal extrusion & bonding (HYB) method—from prototype towards commercial pro- Conflict of interest The authors declare that they have no conflict of cess. PhD Thesis, Norwegian University of Science and interest. Technology, Trondheim, Norway 14. Sandnes L (2017) Preliminary benchmarking of the HYB (hybrid Open Access This article is distributed under the terms of the Creative metal extrusion & bonding) process for butt welding of AA6082-T6 Commons Attribution 4.0 International License (http:// plates against FSW and GMAW. Norweigan University of Science creativecommons.org/licenses/by/4.0/), which permits use, duplication, and Technology, Trondheim, Norway, Master Thesis adaptation, distribution and reproduction in any medium or format, as 15. Grong Ø (2012) Recent advances in solid-state joining of alumi- long as you give appropriate credit to the original author(s) and the num. Weld J 91(1):26–33 source, provide a link to the Creative Commons license, and indicate if 16. Grong Ø (2006) Method and device for joining of metal compo- changes were made. nents, particularly light metal components. United States Patent US 7131567 B2 Published: Nov 7, 2006v 17. Blindheim J, Grong Ø, Aakenes UR, Welo T, Steinert M (2018 in Publisher’sNote Springer Nature remains neutral with regard to jurisdic- press) Hybrid metal extrusion & bonding (HYB)—anewtechnol- tional claims in published maps and institutional affiliations. ogy for solid-state additive manufacturing of aluminium compo- nents. In: Procedia Manufacturing, 46th North American Manufacturing Research Conference (NAMRC46), Texas, United States, 2018 References 18. Abbatinali F (2017) Characterization of AA6082 aluminium alloy and S355 steel welding achieved witht the hybrid metal extrusion & bonding (HYB) process. University of Padua, Italy, Master Thesis 1. Grong Ø (1997) Metallurgical modelling of welding, 2nd edn. 19. Moreira PMGP, de Figueiredo MAV, de Castro PMST (2007) Institute of Materials, Cambridge, UK Fatigue behaviour of FSW and MIG weldments for two aluminium 2. Davis JR (1993) Aluminum and aluminum alloys. ASM interna- alloys. 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The International Journal of Advanced Manufacturing Technology – Springer Journals
Published: Jun 2, 2018
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