Features of structure formation processes in AA2024 alloy joints formed by the friction stir welding with bobbin tool

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 2 2021 Features of structure formation processes in AA2024 alloy joints formed by the friction stir welding with bobbin tool Alexey Ivanov 1, 2, а, * , Valery Rubtsov 1, 2, b , Andrey Chumaevskii 1, с , Kseniya Osipovich 1, d , Evgeny Kolubaev 1, 2, e , Vladimir Bakshaev 3, f , Ivan Ivashkin 3, g 1 Institute of Strength Physics and Materials Science of Siberian Branch of Russian Academy of Sciences, 2/4 pr. Akademicheskii, Tomsk, 634055, Russian Federation 2 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation 3 SESPEL Cheboksary enterprise, CJSC, 36 Leningradskaya st., Cheboksary, 428021, Chuvash Republic, Russian Federation а https://orcid.org/0000-0001-8959-8499, ivan@ispms.ru , b https://orcid.org/0000-0003-0348-1869, rvy@ispms.ru, c https://orcid.org/0000-0002-1983-4385, tch7av@gmail.com, d https://orcid.org/0000-0001-9534-775X , osipovich_k@ispms.tsc.ru , e https://orcid.org/0000-0001-7288-3656, eak@ispms.ru, f https://orcid.org/0000-0001-9777-0164, bakshaevva@mail.ru , g https://orcid.org/0000-0001-8808-2183, ivashkin_in@mail.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2021 vol. 23 no. 2 pp. 98–115 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2021-23.2-98-115 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO A rticle history : Received: 15 March 2021 Revised: 25 March 2021 Accepted: 07 April 2021 Available online: 15 June 2021 Keywords : Friction stir welding Bobbin tool Structure formation Aluminum alloy Funding This work was performed within the frame of integrated project « Building of manufacturing of high-tech large-sized equipment for intelligent adaptive friction stir welding for aerospace and transport industries of the Russian Federation» (grant agreement from 22.11.2019 № 075-11-2019- 033), implemented by SESPEL Cheboksary enterprise, CJSC, NETI and ISPMS SB RAS with the financial support of the Ministry of Education and Science of Russia in the context of Russian Government decree from 09.04.2010 № 218. ABSTRACT Introduction. One of friction stir welding types is the bobbin friction stir welding (BFSW) process, which allows to obtain welded joints in various configurations without using a substrate and axial embedding force, as well as to reduce heat loss and temperature gradient across the welded material thickness. This makes the BFSW process effective for welding aluminum alloys, which properties are determined by their structural-phase state. According to research data, the temperature and strain rate of the welded material have some value intervals in which strong defect-free joints are formed. At the same time, much less attention has been paid to the mechanisms of structure formation in the BFSW process. Therefore, to solve the problem of obtaining defect-free and strong welded joints by BFSW, an extended understanding of the basic mechanisms of structure formation in the welding process is required. The aim of this work is to research the mechanisms of structure formation in welded joint of AA2024 alloy obtained by bobbin tool friction stir welding with variation of the welding speed. Results and discussion. Weld formation conditions during BFSW process are determined by heat input into a welded material, its fragmentation and plastic flow around the welding tool, which depend on the ratio of tool rotation speed and tool travel speed. Mechanisms of joint formation are based on a combination of equally important processes of adhesive interaction in “tool-material” system and extrusion of metal into the region behind the welding tool. Combined with heat dissipation conditions and the configuration of the “tool-material” system, this leads to material extrusion from a welded joint and its decompaction. This results in formation of extended defects. Increasing in tool travel speed reduce the specific heat input, but in case of extended joints welding an amount of heat released in joint increases because of specific heat removal conditions. As a result, the conditions of adhesion interaction and extrusion processes change, which leads either to the growth of existing defects or to the formation of new ones. Taking into account the complexity of mechanisms of structure formation in joint obtained by BFSW, an obtaining of defect-free joints implies a necessary usage of various nondestructive testing methods in combination with an adaptive control of technological parameters directly in course of a welding process. For citation: Ivanov A.N., Rubtsov V.E., Chumaevskii A.V., Osipovich K.S., Kolubaev E.A., Bakshaev V.A., Ivashkin I.N. Features of structure formation processes in AA2024 alloy joints formed by the friction stir welding with bobbin tool. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2021, vol. 23, no. 2, pp. 98–115. DOI: 10.17212/1994-6309-2021-23.2- 98-115. (In Russian). ______ * Corresponding author Ivanov Alexey N., Ph.D. (Engineering), Scientific associate Institute of Strength Physics and Materials, Science of Siberian Branch of Russian Academy of Sciences, 2/4 pr. Akademicheskii, 634055, Tomsk, Russian Federation Tel.: 8 (382) 228–68–63, e–mail: ivan@ispms.tsc.ru