Citation: Klobˇ car, D.; Pušavec, F.; Braˇ cun, D.; Garaši´ c, I.; Kožuh, Z.; Vencl, A.; Trdan, U. Influence of Friction Riveting Parameters on the Dissimilar Joint Formation and Strength. Materials 2022, 15, 6812. https://doi.org/10.3390/ma15196812 Academic Editor: Bolv Xiao Received: 2 September 2022 Accepted: 27 September 2022 Published: 30 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). materials Article Influence of Friction Riveting Parameters on the Dissimilar Joint Formation and Strength Damjan Klobˇ car 1, * , Franci Pušavec 1 , Drago Braˇ cun 1 , Ivica Garaši´ c 2 , Zoran Kožuh 2 , Aleksandar Vencl 3,4 and Uroš Trdan 1, * 1 Faculty of Mechanical Engineering, University of Ljubljana, Aškerˇ ceva 6, 1000 Ljubljana, Slovenia 2 Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, 10000 Zagreb, Croatia 3 Faculty of Mechanical Engineering, University of Belgrade, 11120 Belgrade, Serbia 4 South Ural State University, 454080 Chelyabinsk, Russia * Correspondence: damjan.klobcar@fs.uni-lj.si (D.K.); uros.trdan@fs.uni-lj.si (U.T.) Abstract: Friction riveting represents a promising technology for joining similar and/or dissimilar materials of light-weight components. However, the main drawback of the technology is that it is primarily used only with special machines for friction welding that have a force control. In this study we used accessible CNC machines with a position control. A set of friction riveting experiments was performed to establish the relationship between the processing parameters, the rivet formation and its mechanical strength. During the manufacturing process, the axial force and torque were constantly measured. The fabricated joints were examined using an X-ray imaging technique, microstructural analyses, and mechanical tests. The samples were subjected to the pull-out test to analyse the joints’ strength and determine the failure mode type. In addition, a correlation between the friction riveting processing parameters, the rivet penetration depth, the rivet shape and the joint strength was established. The results depict that a higher axial force in the first production phase at the higher feeding rate increases the penetration depth, while in the second phase at lower feeding rate, an anchoring shape of a rivet forms. Keywords: friction riveting; 2024-T351 aluminium alloy; PEI polymer; X-ray imaging; pull-out force 1. Introduction In the light-weight design of the components that are used for aerospace applications, in wind power plants and in the automotive industry, for instance, an optimal combina- tion of different materials is the key requirement to obtain the desired microstructural and mechanical properties, and thereby improve the functionality of the part [1–3]. The materials are selected based on their unique properties (mechanical, electrical, physical and chemical) and their strength-to-weight ratio. Different materials are used such as advanced high strength steels (AHSS), magnesium alloys, aluminium alloys, titanium alloys, nickel based super alloys, stainless steels, fibre reinforced composites, etc. [4,5]. An important issue in the production of such multi-material components is in their manu- facturing (forming, milling and lamination) and their joining [6,7]. The joining of similar materials could present a challenge regarding the reliability of the joint, its safety and the possibilities for their certification. At the end of the product’s lifetime, an important issue is its recyclability and ability to be reused to make the value chain more sustainable. When dissimilar materials need to be joined together and the challenges of this are even more demanding [8,9]. For the adhesive bonding of dissimilar materials, rivets or bolts are frequently used in a hybrid joint in order to enhance the joint safety and to obtain the required certification [10]. The following hybrid joining techniques can be used for this purpose: (i) a combination of adhesive bonding with mechanical joining [11] (e.g., hem flange bonding, adhesive bonding in conjunction with mechanical point joints, adhesive bonding and clinching [12,13], adhesive bonding and self-piercing or riveting, adhesive Materials 2022, 15, 6812. https://doi.org/10.3390/ma15196812 https://www.mdpi.com/journal/materials