Vol.:(0123456789) 1 3 Journal of the Brazilian Society of Mechanical Sciences and Engineering (2020) 42:423 https://doi.org/10.1007/s40430-020-02509-w TECHNICAL PAPER Efect of traverse speed on microstructure and mechanical properties of friction‑stir‑welded third‑generation Al–Li alloy Sanjeev Kumar 1  · Uttam Acharya 1  · Durjyodhan Sethi 1  · Tanmoy Medhi 1  · Barnik Saha Roy 1  · Subhash Chandra Saha 1 Received: 6 December 2019 / Accepted: 16 July 2020 / Published online: 22 July 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020 Abstract The aim of the study is to investigate the consequences of tool traverse speed on force and torque distribution of friction-stir- welded third-generation Al–Cu–Li alloy joints. The microstructure and corresponding mechanical properties of the joints are investigated on force and torque perspective. Thus, the contribution of the present work lies in establishing the relation between traverse speed and mechanical properties of the AA2050-T84 joint. Four welds have been considered at varying traverse speeds from 1 to 4 mm/s at constant tool rotational speed and tool tilt angle of 1400 rpm and 2°, respectively. A tool of H13 steel having a tapered screw-threaded pin profle was used. The investigation reveals that with the increase in traverse speed, longitudinal force (X-force), vertically downward force (Z-force) and spindle torque also increase. The grain size of the nugget zone reduces from 19.84 to 14.86 µm as traverse speed increases. It has been found that the mechanical strength of the joint increases as the traverse speed increases. The Vickers microhardness value increases from 115 HV 0.1 to 131 HV 0.1 in the nugget zone as traverse speed increases from 1 to 4 mm/s. The maximum tensile strength, % elongation and joint efciency are 403.2 MPa, 7.2% and 75.5% for traverse speed of 4 mm/s. The tensile fracture samples are analyzed by scanning electron microscope and reveal ductile mode of fracture. Keywords AA2050 alloy · Friction stir welding · Traverse speed · Microstructure · Tensile strength · Microhardness · Fracture analysis 1 Introduction The third-generation Al–Cu–Li alloy, namely AA2050-T84 (heat-treated) alloy, shows remarkable properties over other aluminum alloys, with a signifcant impetus to aerospace industry (lower and upper wing cover, spars, ribs, fuselage, empennage, cryogenic tank and internal structures) [1, 2]. AA2050-T84 alloy has excellent properties as compared to other Al alloy, viz. low density, high mechanical strength, improved strength-to-weight ratio, higher damage tolerance property and excellent corrosion resistance, with low anisot- ropy [3, 4]. This notable enhancement is mainly due to the presence of Li in AA2050-T84 alloy which decreases the density of alloy by 3%, increases the modulus of elasticity by 6% and increases the fatigue crack growth resistance consid- erably [5, 6]. Fine particle of the most efcient strengthening precipitate T1 (Al 2 CuLi) phase was observed in high den- sity which yielded higher strength per volume fraction [7]. Other intermetallic strengthening precipitates, for example θ′(Al 2 Cu), δ′(Al 3 Li), T2 (Al 5 Li 3 Cu), TB (Al 7 Cu 4 Li), can be observed in a lesser amount in Al–Cu–Li alloys [8]. How- ever, the presence of intermediate Li content (< 1.4–1.5) in AA 2050 alloy limits the evolution of δ′(Al 3 Li) precipitate, which reduces the fracture toughness [9, 10]. AA2××× alloy when welded using conventional methods generates various defects including oxide layer, distortion, solidifcation cracking, porosity, etc. [11–14]. However, voids, tunnel, pinhole, wormhole, kissing bond, lack of pen- etration and joint-line remnant types of the defects are found in FSW joints due to improper material fow, insufcient consolidation of plasticized material and selection of inad- equacy process parameter in FSW [15–19]. Further, these defects may be sorted out by the selection of optimum pro- cess parameters, tool and tool geometry which has reduced the chances of the defect in the weld. Friction stir welding Technical Editor: Izabel Fernanda Machado, Dr. * Sanjeev Kumar placid.san@gmail.com 1 National Institute of Technology Agartala, Barjala, Jirania, Tripura 799046, India