## 1 Introduction
The most popular solution is the groove method [25; 26; 27; 28; 29], but the chamber method [30; 31; 32] or, for example, the DFSP (direct friction stir processing) method [33; 34] is also becoming progressively more popular. Each of these methods allows the introduction of the reinforcing material into the plasticized matrix material and the creation of a composite microstructure in it. Composite layers are also successfully produced in aluminum alloys in this way. SiC, Al\({}_{2}\)O\({}_{3}\), and ZrO\({}_{2}\) particles, but also, e.g., carbon nanotubes, are most often used as the reinforcing phase. The research results presented in the world literature, including the results of the authors' own research, prove that in this way beneficial changes can be induced in the microstructure and properties of aluminum alloys [35; 36; 37; 38]. In analyzing the literature data, it can also be noticed that attempts are being made to use waste materials as a reinforcing phase in the design of composites. Replacing typical reinforcing materials with waste materials not only allows effective waste management, but also contributes to reducing the total costs of composite production, and is also a pro-ecological activity, consistent with global trends in replacing materials and natural raw materials with waste. Therefore, such action is justified not only economically, but also ecologically. The literature data indicate that attempts have already been made to use industrial waste or by-products generated in production processes to produce composites [39; 40; 41; 42; 43; 44; 45; 46; 47]. For this purpose, e.g., dust from power plants, rice husks rich in silicon, particles from snail shells, walnut powder, and ash obtained from peanut shells have been used. [PERSON] et al. [40] found, for example, that the use of fly ash for the production of metal matrix composites results in a significant increase in the hardness of the alloy, although this effect depends on the final share of this phase in the composite. The authors observed the greatest increase in hardness was with a 4% share of the reinforcing phase, while the introduction of a larger amount of the reinforcing phase (6 and 8%) was not as effective in increasing the hardness value due to the agglomeration of the micropowder and weak interfacial bonding. [PERSON] et al. [44] used eggshell to produce a surface composite based on AZ31B magnesium alloy. They used two types of reinforcement in the composite, namely, Si\({}_{3}\)N\({}_{4}\) particles, which constituted the primary reinforcement, and chicken eggshell powder (ESP), which constituted the secondary reinforcement. In this way, an AZ31B/Si\({}_{3}\)N\({}_{4}\)/ESP composite was produced. The authors concluded that waste chicken eggshells provide a useful reinforcement to improve the mechanical and tribological properties of the magnesium alloy. [PERSON] and [PERSON] [39] also obtained promising results. The authors used fly ash to produce composites based on the AA6061 aluminum alloy, AZ31 magnesium alloy, and copper. The composites were synthesized by means of friction stir processing. A uniform distribution of fly ash particles in the metal matrix was observed, which, according to the authors, is a result of the effective stirring action of the rotating tool. FSP treatment also caused refinement of the reinforcement phase particles, but it should be emphasized that the crushed remains of these particles also mixed well with the plasticized matrix material and formed a composite. A consequence of introducing the reinforcing phase into the composite matrix was an increase in the hardness of the material. An improvement in hardness was observed in all the composite samples. The authors of work [45] produced a composite layer in the 7075-T651 aluminum alloy by means of the FSP method. They used fly ash from industrial waste mixed with silicon carbide particles. The main goal of the work was to improve the hardness and wear resistance of the alloy's surface layer.