Vol. 26 No. 2 2024 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 26 No. 2 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Gaikwad V., Chinchanikar S. Investigations on ultrasonic vibration-assisted friction stir welded AA7075 joints: Mechanical properties and fracture analysis........................................................................................................................ 6 Sirota V.V., Zaitsev S.V., Limarenko M.V., Prokhorenkov D.S., Lebedev M.S., Churikov A.S., Dan'shin A.L. Preparation of coatings with high infrared emissivity.......................................................................................................... 23 Babaev A.S., Kozlov V.N., Semenov A.R., Shevchuk A.S., Ovcharenko V.A., Sudarev E.A. Investigation of cutting forces and machinability during milling of corrosion-resistant powder steel produced by laser metal deposition............. 38 Dolgova S.V., Malikov A.G., Golyshev A.A., Nikulina A.A. The eff ect of laser surfacing modes on the geometrical characteristics of the single laser tracks............................................................................................................................... 57 Karlina Y.I., Kononenko R.V., Popov M.A., Deryugin F.F., Byankin V.E. Assessment of welding engineering properties of basic type electrode coatings of diff erent electrode manufacturers for welding of pipe parts and assemblies of heat exchange surfaces of boiler units............................................................................................................................. 71 Yanpolskiy V.V., Ivanova M.V., Nasonova A.A., Yanyushkin A.S. Determination of the rate of electrochemical dissolution of U10A steel under ECM conditions with a stationary cathode-tool............................................................... 95 EQUIPMENT. INSTRUMENTS Zakovorotny V.L., Gvindjiliya V.E. The study of vibration disturbance mapping in the geometry of the surface formed by turning............................................................................................................................................................................. 107 Gasanov B.G., Konko N.A., Baev S.S. Study of the kinetics of forming of spherical sliding bearing parts made of corrosion-resistant steels by die forging of porous blanks............................................................................................... 127 Gvindjiliya V.E., Fominov E.V., Moiseev D.V., Gamaleeva E.I. Infl uence of dynamic characteristics of the turning process on the workpiece surface roughness........................................................................................................................ 143 Lobanov D.V., Skeeba V.Yu., Golyushov I.S., Smirnov V.M., Zverev E.A. Design simulation of modular abrasive tool........................................................................................................................................................................................ 158 MATERIAL SCIENCE EroshenkoA.Yu., Legostaeva E.V., Glukhov I.A., Uvarkin P.V., TolmachevA.I., Sharkeev Yu.P. Thermal stability of extruded Mg-Y-Nd alloy structure.................................................................................................................................. 174 Bazaleeva K.O., Safarova D.E., Ponkratova Yu.Yu., Lugovoi M.E., Tsvetkova E.V., Alekseev A.V., Zhelezni M.V., Logachev I.A., Baskov F.A. The infl uence of technological parameters of the laser engineered net shaping process on the quality of the formed object from titanium alloy VT23......................................................... 186 Efi movich I.A., Zolotukhin I.S. Oxidation temperatures of WC-Co cemented tungsten carbides....................................... 199 Pribytkov G.A., Baranovskiy A.V., Firsina I.A., Akimov K.O., Krivopalov V.P. Study of Fe-matrix composites with carbide strengthening, formed by sintering of iron titanides and carbon mechanically activated mixtures................ 212 EDITORIALMATERIALS 224 FOUNDERS MATERIALS 235 CONTENTS
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Investigations on ultrasonic vibration-assisted friction stir welded AA7075 joints: Mechanical properties and fracture analysis Vaibhav Gaikwad a, *, Satish Chinchanikar b Vishwakarma Institute of Information Technology, Survey No. 3/4, Kondhwa (Budruk), Pune – 411048, Maharashtra, India a https://orcid.org/0000-0002-3818-1893, vaibhav.219p0007@viit.ac.in; b https://orcid.org/0000-0002-4175-3098, satish.chinchanikar@viit.ac.in Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 2 pp. 6–22 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.2-6-22 ART I CLE I NFO Article history: Received: 06 January 2024 Revised: 09 February 2024 Accepted: 20 March 2024 Available online: 15 June 2024 Keywords: Friction stir welding Shot peening Fracture analysis Ultrasonic vibrations AA7075 ABSTRACT Introduction. Joint efficiency and strength, particularly in aluminum alloys, are crucial in aerospace, defense, and industrial applications. Post-welding treatments like shot peening and laser shock peening significantly improve joint efficiency and strength, enhancing fatigue life, grain structure, and tensile strength. The purpose of the work. The literature reviewed shows that the ultrasonic vibration-assisted friction stir welding (UVaFSW) and post-weld treatment improved the mechanical properties and material flow. However, limited studies have been observed on the UVaFSW joints of AA7075-T651, considering the consequence of welding speed, tool rotation, and post-weld shot peeing treatment. The methods of investigation. The study investigates the ultrasonic vibration-assisted friction stir welded (UVaFSwed) AA7075-T651 joint’s tensile strength, microhardness, microstructure, and fracture behavior, considering the impact of tool rotation, welding speed, and post-weld shot peening treatment. Results andDiscussion. The post-weld treated shot-peened UVaFSWed joints demonstrated the maximum tensile strength of 373.43 MPa, the microhardness of 161 HV, and the lowest surface roughness of 15.16 µm at 40 mm/min welding speed when compared to the friction stir-welded (FSWed) joints. These results indicate that shot peening improved the mechanical properties and surface quality of the UVaFSWed joints. The high tensile strength and low surface roughness make these joints suitable for applications requiring strength and aesthetics. The fracture for the shot peened UVaFSWed joints mainly occurred in the heat-affected zone (HAZ) during the tensile test. It could be attributed to the higher temperature experienced during welding, which resulted in grain growth and decreased material strength in the HAZ. The shot-peened UVaFSWed joint has a more uniform grain distribution than the FSWed one, which contributed to the joint’s higher tensile strength. The fractured surface of the shot peened UVaFSWed joints showed larger, equiaxed, and shallow dimples, resulting in higher ultimate tensile strength (UTS) and microhardness compared to the conventional FSWed joints. The mechanical properties and microstructure observed in the welding zones of shot peened UVaFSWed joints are superior to those of conventional FSW joints. However, further investigation is required to determine the specific factors contributing to this localized failure at HAZ, considering the effects of shot peening parameters. This study also suggests the potential for optimizing shot peened UVaFSWed joints of AA7075-T651. For citation: Gaikwad V., Chinchanikar S. Investigations on ultrasonic vibration-assisted friction stir welded AA7075 joints: Mechanical properties and fracture analysis. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 2, pp. 6–22. DOI: 10.17212/1994-6309-2024-26.2-6-22. (In Russian). ______ * Corresponding author Gaikwad Vaibhav, Ph.D. (Engineering) Vishwakarma Institute of Information Technology, Survey No. 3/4, Kondhwa (Budruk), Pune – 411048, Maharashtra, India Tel.: 91-20269502401, e-mail: vaibhav.219p0007@viit.ac.in Introduction Recently, there has been a trend in various industries to find innovative and cost-effective ways to reduce the weight of its products, increase the speed of its vehicles, airplanes and missiles, as well as reduce greenhouse gas emissions produced during manufacturing. Therefore, research continues on innovative joining techniques to realize material compounds and to get closer to the goals outlined above. AA7075 aluminum alloy finds wide applications in the aerospace, defense, military, and automotive industries due to its low density and high mechanical properties. It is a precipitation hardening alloy with magnesium,
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 zinc, and copper as the main alloying elements. Due to solidification and liquation cracking in the fusion welding, Friction stir welding (FSW) is preferred to joining aluminum alloys [1]. The FSW process is preferred for joining difficult-to-weld similar and dissimilar aluminum alloys. As a solid-state joining process, FSW tends to lower distortion and residual stress in the welded joints. In comparison to the fusion welding techniques, FSW provides better joints. A specially designed rotating tool is inserted into the edges of the workpiece to be joined and moved along the interface of two plates in the FSW process. Consequently, the softened material near the tool is transported from the advancing side to the retreating side to form a joint [2]. In the FSW, a high downward force and spindle torque are required to generate a large amount of heat. The heat generated softens the material, providing the adequate plastic flow next to the tool. This leads to an increase in the volume of welding equipment and a greater welding load [3]. The FSW tool pin profile is subjected to higher stress during welding, which causes rapid tool degradation, leading to premature failure. Moreover, tool wear causes poor weld quality, resulting in higher production costs. Also, the higher welding load in the FSW limits the welding speed. These difficulties can be solved using different secondary energy sources during FSW. A group of researchers applied ultrasonic vibrations during FSW. Ultrasonic vibration-assisted friction stir welding (UVaFSW) assists in softening of the material without substantial heating [4–6]. Liu et al. [7] found that ultrasonic vibration-assisted FSW improved the joint mechanical properties, the quality of the weld, and the heat input at the localized area. According to Xu et al. [8], brazing with ultrasonic vibration assistance created a junction with a smaller grain size that improved corrosion resistance and ultimate tensile strength (UTS). Liu et al. [9], while investigating UVaFSW of AA1060 aluminum alloy, have found that ultrasonic energy enhanced the flow velocity, the volume of deformed material, and the strain rate. In aerospace, defense sectors and industrial applications, joint efficiency, and joint strength, play a key role, especially for joints made of similar and dissimilar aluminum alloys. It has been widely reported that joint efficiency and strength can be substantially improved using post-welding treatment. In the last few years, researchers have focused on post-weld treatment for aluminum joints. Shot peening and laser shock peening treatments are prominently reported in the literature as post-weld treatment, since both processes induce residual compressive stresses in the welded specimen and improve fatigue life, grain structure, and tensile strength. Fig. 1, a and b shows the schematic diagrams of laser shock peening and shot peening, respectively. a b Fig. 1. Schematics of (a) Laser shock peening process, (b) Shot peening process Amuda et al. in [10] inspected the effect of cryogenic cooling and the addition of element metal powder during the gas tungsten arc welding of the AISI 430 plate. Their study showed that both strategies refined the grain structure. However, with the accumulation of metal powder, a significant decrease in the zone of thermal influence (HAZ) is found to be up to 50 %, and cryogenic cooling reduces HAZ to 36 %. On the
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology other hand, cryogenic cooling led to an increase in the ductility of the joint by 80 % compared to the base metal (BM), whereas the addition of element metal powder led to an increase in the joint ductility by up to 60 %. Hatamleh et al. in [11] examined the effect of laser-peening, shot-peening, and cryogenic cooling on fatigue crack development and residual stresses of friction stir welded (FSWed) AA2195 aluminum alloy joints. Their study found that fatigue crack development for the specimen treated with laser peening was the same as that of shot-peening and as-welding at ambient temperature. In addition, it was difficult to distinguish crack growth from residual stresses during cryogenic treatment. Hatamleh et al. in [12] investigated the effect of laser shock peening and shot peening on the FSWed joint of the AA2195 aluminum alloy. Their study observed improved mechanical properties with laser peening compared to shot peening. They observed an increase in the yield strength in the weld nugget (WN) by about 38 % when laser welding was used as post-welding treatment, compared with an increase in the yield strength in the weld nugget (WN) by 8 % observed during shot peening. Khorrami et al. in [13] investigated the effect of cryogenic and ambient temperature on the FSW of severely deformed AA1050 aluminum alloy with SiC nanoparticles. Their work observed bimodal and finer grain sizes when using FSW joints with cryogenic cooling treatment as a measure against abnormal grain growth during the FSW. Singh et al. in [14] performed the cryogenic treatment after the FSW on a joint of AA7075 aluminum alloy. Their experimental study showed that post-weld cryogenic treatment led to a slight increase in the hardness of the joint and tensile strength. Wang et al. [15] inspected the effect of low-temperature aging and cryogenic treatment on the mechanical properties of the FSWed AA2024-T351 aluminum alloy. The elimination of softened zones near the HAZ was noted due to a single low-temperature aging. However, due to a single low-temperature aging, a decrease in the strength of the joint was noted. Wang et al. [16] performed the cryogenic treatment during FSW of the Cu joint. Their experimental work showed that grain refinement in the WN increased initially with increase in the rotational speed. However, it was observed to decrease with further increases in rotational speed. Zhemchuzhnikova et al. [17] observed extensive grain refinement and increase in the tensile strength of cryogenically treated AlMg-Sc-Zr FSW joints. Ferreira et al. [18] examined the effect of the glass and steel beads in shot peening on the welded joint. They noticed better results in fatigue and tensile strength with glass beads than with steel beads. Also, higher surface roughness was observed when using the steel beads as compared to glass beads. A group of researchers [19–21] investigated the effect of laser shock peening on the microstructural properties, fatigue properties, and corrosion resistance of FSWed aluminum alloy joints. They observed a finer grain size, better corrosion resistance, and higher fatigue strength with laser shock peening-treated joints as compared to joints without laser shock peening as a post-welding treatment. However, more studies are required in post-weld treatments to obtain better mechanical properties for the welded joint. The literature reviewed shows that the UVaFSW and post-weld treatment improved the mechanical properties and material flow. However, limited studies have been conducted on the UVaFSW joints of AA7075-T651, considering the consequence of welding speed, tool rotation, and post-weld shot peeing treatment. With this interpretation, the current work comparatively evaluates the performance of untreated and post-weld shot-peened ultrasonic vibration-assisted friction stir welded (UVaFSWed) AA7075-T651 joints, taking into account the effect of welding speed and tool rotation. The performance is evaluated in terms of microhardness in the different regions of the weld, ultimate tensile strength (UTS), surface roughness, microstructure evaluation, and fracture analysis using scanning electron microscopy (SEM) images. The experiments were performed with conical threaded tool pin-type. The results are compared with the available literature on FSW of AA7075-T651 joints produced by means of conical threaded and conical tool pin profiles. Experimental Design In the present study, the square butt joint of AA7075-T651 was produced using UVaFSW. The UVaFSW experimental setup is depicted in Fig. 2. Experiments were carried out with welding speeds of 20, 28, and 40 mm/min and tool rotations of 1,000; 1,400 and 2,000 rpm. The experiments were carried out using conical
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 threaded tool on a universal milling machine. The two plates to be welded originally had a rectangular shape and were deburred. The faying edges of the plates were machined into a smooth surface and cleaned with acetone. The ultrasonic vibrations generated by the ultrasonic transducer propagated through an amplitude transformer to expand the amplitude and focus the energy at the weld line of two plates. This energy was transmitted to the localized workpieces near and in advance of the FSW tool by a sonotrode. An output power of 1.2 kW and an ultrasonic vibration frequency of 20 kHz were used in the welding process. In the absence of a load, a vibration amplitude of 24 µm was used. The sonotrode was placed at an angle of 45° to the plane of the workpiece and at a distance of 20 mm from the FSW tool. a b Fig. 2. Schematic view (a), Actual experimental setup (b) The tool with translational and rotational motions provides thermo-mechanical action along the welding path. The conical threaded tool pin profile with flat shoulder made of tool steel type H13 is depicted in Fig. 3. The axial load on the work surface is transmitted by the tool shoulder. The plasticized material is transferred in to the weld pool by the pin. Tables 1 and 2 represent the chemical composition of the tool and the workpiece material respectively. In the present study, the shot peening process is selected as a postweld treatment. The experimental set-up and parameters of the shot peening are depicted in Fig. 4. The microstructure of the shot-peened UVaFSWed joints at different regions of the weld and the material flow in the WN were examined using SEM images. The mechanical properties of the joint, such as UTS, microhardness in WN, thermo-mechanically affected heat zone (TMAZ), HAZ, base metal, and surface roughness (SR), are inspected considering the influence of process variables. The shot peened UVaFSWed joint transverse UTS, and joint efficiency were evaluated for all the joints obtained at different process parameters. The tensile test was performed on a universal testing machine according to the ASTM E8 standard. Fig. 5, a, b shows a diagram of cutting a plate made of aluminum alloy AA7075-T651 to obtain a test specimen and a tensile test specimen, respectively. The microhardness at WN, TMAZ, HAZ, and BM was measured using Vicker’s microhardness tester in accordance with ISO6507 standard by the means of diamond indenter (136o) through a load of 100 grams and an indentation time of 20 seconds. An average SR, measured at the start, middle, and end of the weld, was obtained. Fig. 3. Conical threaded pin type tool (All dimensions are in mm)
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Fig. 4. Mounted specimen for shot peening Ta b l e 1 Chemical composition of H13 FSW tool (% weight) Elements Cr Mo Si V C Ni Cu Mn P S % weight 4.75 1.10 0.80 0.80 0.32 0.3 0.25 0.2 0.03 0.03 Ta b l e 2 Chemical composition of AA7075 alloy (% weight) Elements % weight Elements % weight Elements % weight Elements % weight Si 0.069 Mn 0.006 Ni 0.012 Ti 0.028 Fe 0.204 Mg 2.33 Pb 0.012 Cr 0.195 Cu 1.64 Zn 5.28 Sn < 0.005 Al 90.22 a b Fig. 5. AA7075 plates showing abstraction of test specimens (a), Tensile test specimen (b) (All dimensions are in mm)
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 A Field Emission Scanning Electron Microscope (FESEM) was used at several magnifications to examine the material flow in the WN and the joint microstructure at various welding zones. The specimens were cut in the perpendicular direction to the weld contour by wire electric discharge machining. Results and Discussion This section discusses the performance of shot-peened UVaFSWed AA7075-T651 joints. Tensile strength, microhardness, fracture behavior, and microstructure of welded joints are assessed considering the effect of welding speed and tool rotation. The UTS of the BM attained after the tensile test is 550 MPa. For the shot-peened UVaFSWed (Run P1 to P9) the experimental matrix and mechanical properties are presented in Table 3. Ta b l e 3 Experimental matrix with mechanical properties for shot-peened UVaFSWed AA7075 joints Run Tool rotation (rpm) Welding speed (mm/min) UTS (MPa) Joint efficiency (%) Microhardness (HV) Surface roughness (µm) WN TMAZ HAZ P1 1,000 20 301.98 54.91 148 129 119 15.350 P2 1,000 28 294.57 53.56 152 133 125 15.480 P3 1,000 40 292.32 53.15 154 143 130 16.341 P4 1,400 20 281.88 51.25 150 138 127 15.976 P5 1,400 28 304.20 55.31 158 145 129 18.277 P6 1,400 40 312.95 56.90 149 141 132 15.918 P7 2,000 20 345.73 62.86 155 145 135 17.672 P8 2,000 28 362.95 65.99 160 144 132 15.169 P9 2,000 40 373.43 67.90 161 145 136 15.651 Mechanical properties of shot peened UVaFSWed joints Stress-strain curves for AA7075-T651 shot-peened UVaFSWed joints (Run P1 to P9) are obtained. For the shot-peened UVaFSWed AA7075-T651 aluminum alloy joints, the maximum UTS of 373.43 MPa (run P9) is obtained at tool rotation of 2,000 rpm and welding speed of 40 mm/min, whereas the minimum UTS of 281.88 MPa (Run P4) is obtained at tool rotation of 1,400 rpm and welding speed of 20 mm/min. The UTS for the shot-peened UVaFSWed AA7075 joints is compared to that obtained using traditional FSW with conical and conical threaded tool pin profiles [22–25]. This study found higher UTS for joints obtained using UVaFSW, followed by the shot-peening process. In the shot peening, steel balls acted at high velocity on the UVaFSWed joint. This high velocity induces compressive residual stresses on the fabricated joint. This effect improves the UTS as well as the microhardness of the joint. Better performance, almost more than two times higher values of tensile strength, and joint efficiency can be seen for the shot-peened UVaFSWed joints compared to the FSWed joints with conical threaded tool pins [22–25]. The higher mechanical properties of the shot-peened UVaFSWed joints could be attributed to an increased strain rate leading to higher plastic deformation and better material flow around the tool pin due to the ultrasonic vibrations. A group of researchers observed better mechanical properties of the UVaFSWed joints made of similar-dissimilar aluminum alloy joints [7–9]. Higher values of UTS are obtained at a higher tool rotation speed. The higher the tool rotation speed, the greater the frictional heat between the tool shoulder and the surface of the workpiece. The increased
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology frictional heat softens the material and enhances its movement to the weld pool, resulting in uniform mixing of the material. The microhardness of joints was measured at several points from the weld center on both sides of the joint. The dynamic recrystallization of grains and higher plastic deformation causes variations in the microhardness in the welded region. The microhardness of the shot peened UVaFSWed joints showed variation in the welding zones, mostly following the distribution of a letter ‘W’-shape, and found maximum at the WN and minimum at the HAZ. A higher microhardness was obtained in all the zones of the weld: WN, TMAZ, and HAZ for the shot peened UVaFSWed joints (Run P1-P9) as compared to that obtained using traditional FSW with conical and conical threaded tool pin profiles [22–25]. This study found higher microhardness for joints obtained using UVaFSW, followed by the shot-peening process. A higher microhardness in WN is obtained for shot-peened UVaFSWed joints at higher tool rotation speeds. The shot peening process imparts compressive residual stress on the fabricated joints, resulting in higher microhardness in the WN. The maximum microhardness in WN was 161 HV and was obtained at the higher tool rotation of 2,000 rpm for the shot-peened UVaFSWed (Runs P7-P9) AA7075-T651 aluminum alloy joints. The shot-peened UVaFSWed joints showed better mechanical properties compared to FSWed joints. The shot-peened UVaFSWed joints sustained higher tensile loads, as shot-peening induces compressive stresses in the workpiece. UVaFSWed joints sustained higher tensile loads, which could be attributed to higher heat input due to the application of ultrasonic vibrations on the weld bead. Moreover, ultrasonic vibrations acting on the weld bead contributed to dynamic recrystallization and improved the material movement towards the weld bead. Further, the assistance of ultrasonic vibrations also reduced weld defects/flaws in the WN and its interfaces with TMAZ compared with the conventional FSWed joints. The joint quality was assessed by obtaining the surface roughness. An average surface roughness was 15–18 µm for shot-peened UVaFSWed AA7075-T651 aluminum alloy joints. Lower surface roughness values were obtained at a lower tool rotation speed of 1,000 rpm, regardless of the welding speed (Runs P1-P3). Fig. 6 represents the top surface appearance of the shot-peened UVaFSWed AA7075-T651 aluminum alloy joints. The surface modifications and filling of the weld bead can be seen. The “onion rings” are formed, and the tool shoulder marks can be seen. Microstructure of shot-peened UVaFSWed joints Fig. 7, a, c shows SEM images of WN, TMAZ, and HAZ of the shot-peened UVaFSWed joints obtained at Run P9, respectively. The homogeneous grain distribution in WN and the absence of tunnel defects can be Fig. 6. Weld top surface of AA7075 UVaFSWed shot-peened joints
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 seen in Fig. 7, a. These attributes resulted in a higher UTS for the shot-peened UVaFSWed joint compared to the conventional FSWed joint. Fine, equiaxed, and uniformly distributed grains of ~630 nm-5 µm in the WN of the shot-peened UVaFSWed joint can be seen in Fig. 7, a. UVaFSW improves the grain size in WN, and the material flows inside the weld bead compared to the conventional FSW. Fig. 7, b depicts the SEM image of TMAZ of the shot-peened UVaFSWed joint. Homogeneous mixing of the material with equiaxed grains can be seen. The coarser distributed grains than those in the WN differentiate this weld region. This weld region is adjacent to the WN. The grains having coarser sizes of ~ 5–7 µm can be seen in TMAZ. This could be due to lower heat distribution from the WN to TMAZ. Fig. 7, c depicts a SEM image of HAZ of a shot-peened UVaFSWed joint. Elongated grains with sizes varying in the range of ~8–11 µm can be seen. This weld zone is between TMAZ and BM and is designated as HAZ. The reduction in microhardness with an increase in grain size can be seen from the WN to HAZ. The highest microhardness observed in the WN was 161 HV, followed by 145 HV in TMAZ and 136 HV in HAZ. SEM images show that shot-peened UVaFSW improves the grain size in the WN and the material flow inside the weld bead compared to the conventional FSW [21–25]. Fine, equiaxed, and uniformly distributed grains at the WN can be seen for the shot-peened UVaFSWed joint. The higher mechanical properties obtained for the shot-peened UVaFSWed joints can be confirmed from SEM images showing higher plastic deformation, dynamic recrystallization, and better material flow toward the weld bead. Fracture behavior of UVaFSWed AA7075-T651 joints Fig. 8 depicts the fractured specimens of shot-peened UVaFSWed joints of AA7075-T651 that were obtained during Runs P1–P9. These specimens were subjected to a tensile test, and the results were compared side by side. The study found that all the test specimens had fractured in the HAZ and exhibited ductile behavior during the fracture. Fig. 9 shows SEM images of a fracture surface of specimen of the shotc Fig. 7. SEM images of the shot-peened UVaFSWed joints at WN (a), TMAZ (b), and HAZ (c) a b
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology Fig. 8. Fracture behavior of the shot-peened UVaFSWed AA7075 joints peened UVaFSWed joint that was obtained during Run P9. The large and shallow dimples in the shot-peened UVaFSWed test specimen show higher plastic deformation. The dimple sizes impact the sustainability of plastic deformation during tensile testing. The dimples observed on the shot-peened UVaFSWed specimen are larger and more equiaxed than that of the fractured conventional FSWed test specimen [22–25]. Hence, the UTS and microhardness in different weld regions are superior for shot-peened UVaFSWed joints compared to the conventional FSWed joint. Researchers have observed different fracture patterns in shot-peened UVaFSWed joints. The reason for this is due to the heat generated during the process. The dual effect of ultrasonic vibration and frictional heat produced by the tool shoulder results in the release of more heat during UVaFSW. The higher the heat Fig. 9. SEM images of the fracture surface of shot-peened UVaFSWed joint of AA7075
OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 generation, the higher the plastic deformation and material flow, which ultimately results in higher values of UTS and microhardness. Additionally, a group of researchers have observed a correlation between the large and equiaxed dimples observed on the fracture surface with the higher values of UTS and microhardness of FSWed joints [26–28]. Material flow of the shot-peened UVaFSWed AA7075-T651 joints During Friction StirWelding (FSW), the quality of the weld depends on the flow of pasty material beneath the tool. Fig. 10 illustrates the material flow at the Weld Nugget (WN) for the shot-peened UVaFSWed joint of AA7075-T651 at Run P9. At Run P9, the laminar material flow was observed. The microstructure of the shot-peened UVaFSWed AA7075-T651 joints obtained at Run P9 is free of defects and porosity compared to conventional FSW joints [22–25]. Fig. 10 shows that the material flow is unidirectional, indicating proper intermixing of the material in the WN. The proper intermixing of the material improves the mechanical properties of the joints. Due to the ultrasonic vibrations, tunnel defects and micro-voids are eliminated, and fusion between the materials is improved. This results in higher mechanical properties compared to conventional FSWed joints. Fig. 10. Material flow of the shot-peened UVaFSWed AA7075 joint In the current study, it was observed that shot-peened UVaFSWed AA7075-T651 joints exhibit superior mechanical properties, favorable microstructure, and ductile-type fracture behavior as compared to conventional FSWed joints. However, the shot peening and UVaFSW combination yielded even better results. Additional research is necessary to optimize shot-peened UVaFSW while considering various interlayers, process parameters, and tool-pin geometries. Conclusions This study aimed to evaluate the performance of AA7075-T651 joints produced through shot-peened ultrasonic vibration-assisted friction stir welding (UVaFSWed) with a conical threaded pin type tool. The study varied the tool rotation and welding speeds to assess its impact on the joints tensile strength, microhardness, microstructure, and fracture behavior. Additionally, the study examined the grain distribution, material flow at the weld nugget, and joint fracture surfaces after the tensile test using SEM images. From the investigation, the following conclusions were made: ● The joint made by UVaFSW had better tensile strength, microhardness in the WN, and minimum surface roughness in comparison to traditionally FSWed joints. The shot-peened UVaFSWed joint is characterized by a maximum value of UTS (373.43 MPa) and microhardness in the WN (161 HV) at a tool rotation of
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 technology 2,000 rpm and welding speed of 40 mm/min. However, it should be noted that when the welding speed was reduced to 28 mm/min, a lower surface roughness of 15.16 µm was obtained. ● The microhardness of the joints that underwent shot peening during the UVaFSW welding process showed variation in the welding zones, forming a letter ‘W’ shape. The maximum microhardness value was observed in the WN zone while the minimum was found in HAZ. Additionally, the microhardness values were higher in shot-peened UVaFSW joints compared to conventional FSWed joints. ● Inspection of the shot-peened UVaFSWed joint has shown that the material fusion in the weld nugget was appropriate, there was a flow of pasty material, the joint was free of tunnel defects and voids, and there was a homogeneous distribution of finer grains. This was found to be superior to the conventional FSWed joints. ● All the test specimens for the shot-peened UVaFSWed joints were fractured in the HAZ due to lower microhardness, and it exhibited ductile behavior during fracture. The fractured surface of the shot-peened UVaFSWed joints showed larger, more equiaxed, and shallow dimples, resulting in higher ultimate tensile strength (UTS) and microhardness compared to the conventional FSWed joints. ● The mechanical properties and microstructure observed in the welding zones of shot-peened UVaFSWed joints are superior to those of conventional FSW joints. This study suggests the potential for optimizing the shot-peened UVaFSWed joints of AA7075-T651. References 1. Cetkin E., Çelik Y.H., Temiz S. Microstructure and mechanical properties of AA7075/AA5182 jointed by FSW. Journal of Materials Processing Technology, 2019, vol. 268, pp. 107–116. DOI: 10.1016/j.jmatprotec.2019.01.005. 2. Chinchanikar S., Gaikwad V.S. State of the art in friction stir welding and ultrasonic vibration-assisted friction stir welding of similar/dissimilar aluminum alloys. Journal of Computational and Applied Research in Mechanical Engineering, 2021, vol. 11, pp. 67–100. DOI: 10.22061/JCARME.2021.7390.1983. 3. Arora A., De A., Debroy T. Toward optimum friction stir welding tool shoulder diameter. Scripta Materialia, 2011, vol. 64, pp. 9–12. DOI: 10.1016/j.scriptamat.2010.08.052. 4. Shi L., Wu C.S., Liu X.C. Modeling the effects of ultrasonic vibration on friction stir welding. Journal of Materials Processing Technology, 2015, vol. 222, pp. 91–102. DOI: 10.1016/j.jmatprotec.2015.03.002. 5. Yao Z., Kim G.Y., Faidley L., Zou Q., Mei D., Chen Z. Effects of superimposed high-frequency vibration on deformation of aluminum in micro/meso-scale upsetting. Journal of Materials Processing Technology, 2012, vol. 212, pp. 640–646. DOI: 10.1016/j.jmatprotec.2011.10.017. 6. Siddiq A., El Sayed T. Acoustic softening in metals during ultrasonic assisted deformation via CP-FEM. Materials Letters, 2011, vol. 65, pp. 356–359. DOI: 10.1016/j.matlet.2010.10.031. 7. Liu X.C., Wu C.S. Experimental study on ultrasonic vibration enhanced friction stir welding. Proceedings of the 1st International Joint Symposium on Joining and Welding, Osaka, Japan, 2013, pp. 151–154. DOI: 10.1533/9781-78242-164-1.151. 8. Xu C., Sheng G., Cao X., Yuan X. Evolution of microstructure, mechanical properties and corrosion resistance of ultrasonic assisted welded-brazed Mg/Ti joint. Journal of Materials Science and Technology, 2016, vol. 32, pp. 1253–1259. DOI: 10.1016/j.jmst.2016.08.029. 9. Liu X., Wu C., Padhy G.K. Characterization of plastic deformation and material flow in ultrasonic vibration enhanced friction stir welding. Scripta Materialia, 2015, vol. 102, pp. 95–98. DOI: 10.1016/j.scriptamat.2015.02.022. 10. Amuda M.O.H., Mridha S. Comparative evaluation of grain refinement in AISI 430 FSS welds by elemental metal powder addition and cryogenic cooling. Materials and Design, 2012, vol. 35, pp. 609–618. DOI: 10.1016/j. matdes.2011.09.066. 11. Hatamleh O., Hill M., Forth S., Garcia D. Fatigue crack growth performance of peened friction stir welded 2195 aluminum alloy joints at elevated and cryogenic temperatures. Materials Science and Engineering A, 2009, vol. 519, pp. 61–69. DOI: 10.1016/j.msea.2009.04.049. 12. Hatamleh O., Mishra R.S., Oliveras O. Peening effects on mechanical properties in friction stir welded AA2195 at elevated and cryogenic temperatures. Materials and Design, 2009, vol. 30, pp. 3165–3173. DOI: 10.1016/j. matdes.2008.11.010. 13. Khorrami M.S., Kazeminezhad M., Miyashita Y., Saito N., Kokabi A.H. Influence of ambient and cryogenic temperature on friction stir processing of severely deformed aluminum with SiC nanoparticles. Journal of Alloys and Compounds, 2017, vol. 718, pp. 361–372. DOI: 10.1016/j.jallcom.2017.05.234.
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