The manuscript presents the results of butt joining of 3-millimeter-thick AlCu4Mg1 alloy sheets using the FSW (friction stir welding) and UWFSW (underwater friction stir welding) methods. The aim of the research is to verify the influence of the water environment on the FSW friction welding process. The article checked three sets of joint parameters. The parameters differed in tool rotation speed and feed rate. The same sets of parameters were used for the FSW and UWFSW fusion techniques. With the supplied devices, metallographic sections are cross-sectioned, and the power supplies are subjected to a light microscope. Microhardness tests and the influence of the heat-affected zone were carried out. A monotonic test was performed. A monotonic test is available, extended with a visual correlation test. The obtained cracked fracture surfaces were examined using a scanning microscope. An analysis of the microfractographic cracking process was carried out. The obtained results did not show any improvement in the strength properties of the obtained joints made using the UWFSW technique when using a scanning microscope.

Nowadays, industries are increasingly developing advanced materials that combine high durability, sustainability, and ease of fabrication. Aramid fibers, particularly Kevlar, are widely used in engineering applications due to their excellent mechanical properties, such as high tensile strength, impact resistance, and thermal stability. At the same time, growing concerns over environmental impacts have led to increased interest in the reuse of waste materials and the development of sustainable composite systems. In this paper, we review experimental studies on Kevlar-based composites, with particular emphasis placed on composites manufactured from waste Kevlar fibers. Particular attention is given to the influence of fiber fragmentation and surface modification performed using polyvinyl butyral (PVB) on mechanical properties. We also cover material characteristics, manufacturing techniques, and the mechanical behavior of various composite systems. We primarily focus on analyzing the methodologies and research results of studies in the literature to enable future researchers to verify the quality of existing research.