TECHNICAL ARTICLE—PEER-REVIEWED Effect of Friction Stir Welding Process Parameters with Interlayer Strip on Microstructural Characterization and Mechanical Properties Mohamed Abu-Okail . Ahmed Abu-Oqail . Moataz H. Ata Submitted: 13 July 2019 / in revised form: 12 October 2019 Ó ASM International 2020 Abstract Process parameters of friction stir welding (FSW) with different values of interlayer strip widths have become a very vital research area to reinforce the weak part of the nugget zone in welded joints. So, the objective of this work is to study the effect of different process parameters of FSW such as the tool rotational speed (R), travel velocity (t) and inclination angle (H) with different values of interlayer strip widths (W) of compensation material on microstructural characterization and mechani- cal properties. Optical microscope, scanning electron microscope, energy-dispersive x-ray spectroscopy and x- ray diffraction techniques were used to characterize the microstructural changes after FSW process. Microhardness and tensile tests were also used to characterize the mechanical properties of the produced joints. The results of mechanical properties of FSW process parameters with different values of interlayer strip width showed that when the tool rotational speed is increased till 2000 rpm, the tensile strength has been increased till 321 MPa, while the reduction in tool traverse speed till 20 mm/min led to an increase in the tensile strength till 239 MPa. Moreover, the best inclination angle was 2.5°. The microstructure obser- vations revealed that the use of process parameters of FSW at 2000 rpm rotational speed, 20 mm/min traverse velocity and 2.5° inclination angle with different values of inter- layer strip width showed excellent connections of reinforcement clusters of AA7075 compensation material between the matrices of AA2024 base metals. Keywords Friction stir welding (FSW) Á Interlayer strip width Á Ductility Á Strength Á Strengthening mechanisms Introduction Process parameters of friction stir welding (FSW) with different values of interlayer strip widths have become a very vital research area to reinforce the weak part of the nugget zone in welded joints, which pose challenges that limit the wide acceptance in the FSW joints in aircraft components [1]. Therefore, the huge loss of mechanical properties of the aircraft structures leads to rapid failure during the service life, especially when the quality of the joint is reduced [2]. FSW with different values of interlayer strip width is a new solid-state welding technology during which peak temperature does not exceed melting point of both the base material (BM) and interlayer strip [3, 4]. Hence, many fusion defects, such as pores and hot cracks, can be avoided. FSW was originally used to weld alu- minum alloys [1, 3], and now has been used to weld different or dissimilar alloys through adding interlayer compensation strip width [4, 5]. Several advantages of FSW with different values of interlayer strip width over fusion welding are: high joint strength, low distortion, no cracks, low power consumption and non-pollution [6, 7]. The basic concept of the FSW process with different values M. Abu-Okail (&) Manufacturing Engineering Department, Modern Academy for Engineering and Technology, P.O. Box 11571, Cairo, Egypt e-mail: MohamedAbuOkail@gmail.com A. Abu-Oqail Mechanical Department, Faculty of Industrial Education, Beni-Suef University, Beni-Suef, Egypt M. H. Ata Mechanical Department, Faculty of Industrial Education, Sohag University, Sohag, Egypt 123 J Fail. Anal. and Preven. https://doi.org/10.1007/s11668-020-00813-0