As a reinforcement in composites with an aluminium matrix, it is possible to incorporate particles of Fly Ash (FA), which is appearing as a side-product during the combustion of coal in thermal power plants. Small particles of fly ash can affect people's health, and its disposal represents a serious ecological and economic problem, which can be solved by finding opportunities for its useful application. The properties of the composite material can be further improved by intensive plastic deformation, such as that of Equal Channel Angular Pressing (ECAP). The main goal of the research was to produce a composite based on aluminium alloy reinforced with as much FA as possible, suitable for ECAP, and to improve its properties by applying this process. The scientific research is presented through six chapters. In Chapter 1 of the doctoral dissertation, the motivation and main goals are given, as well as an explanation of the methods and research phases. The hypothesis was defined and given in this chapter also. In the Chapter 2, an overview of the literature related to ALuminium + Fly Ash (ALFA) composites are given. The basic characteristics of the materials used for production of the composites are described: aluminium and its alloys (AlCu4Mg1 and AlSi7Mg0.3), as well as fly ash. Various methods for the preparation and characterization of ALFA composites are also described. Chapter 3 describes the influence of plastic deformation on the change in the microstructure of the material. According to the available literature, the principle, and dynamics of the ECAP, as well as the influencing parameters of this process, are described in detail. The fourth chapter provides theoretical considerations on tribology, a multidisciplinary scientific discipline that studies phenomena and processes on the surfaces of elements that are in direct or indirect contact and in relative motion. The basic principles of wear, especially solid particle erosion wear, are explained. Chapters 5 and 6 are related to the experimental part of the work. Materials and methods used in the research are described in Chapter 5. In this research, FA from the thermal power plant "Kolubara", Republic of Serbia, was used for the preparation of composites. FA was sieved (w = 45 µm, d = 63 µm) and only this fraction was characterized. The phase composition was determined by X-ray diffraction analysis (XRD), chemical composition by Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES), particle size by laser diffraction, and morphological analysis by Scanning Electron Microscope (SEM). This chapter also describes the casting of composites in the semi-solid state and the ECAP of the samples. Composite samples with aluminium alloy matrices reinforced with 4 % FA and 6 % FA were cast. The composite AlCu4Mg1 + 4 % FA was not suitable for ECAP and was abandoned. The samples of AlSi7Mg0.3 alloy and composites with 4 % FA and 6 % FA were subjected to multiple passes of ECAP with rotation around the longitudinal axis by 90° after each pass (route BC). They have been successfully pressed a maximum of three times. In the final phase, the samples were characterized. The microstructure, hardness and solid particle erosion resistance were analysed. The microstructure was analysed on an optical and scanning electron microscope, and when necessary, Energy Dispersive Spectroscopy (EDS analyse) and Computer Tomography (CT) were also used. The micro and macro hardness of the samples were tested using the Vickers method, from HV0.02 to HV1. Meyer's model was used to interpret the results of microhardness measurements. When solid particle erosion resistance was tested the impact angle of the particles was varied (30° and 90°), and silicon carbide (SiC) particles were used as erodent. Erosion resistance was determined based on volume loss ΔV. The obtained results are given and discussed in Chapter 6. The results of the FA characterization show that a used FA fraction consists of metal oxides such as SiO2, Al2O3, Fe2O3 and others in the amount of 95.8 %. Morphologically FA particles are mostly spheric and precipitator type. Approximately 90 % of all used FA particles are smaller than 68.3 µm. The microstructure of the cast alloy consists of primary (α-Al) crystals and eutectic (Al-Si). Due to the applied casting process, dendritic formations of α-crystals take the form of primary and mature rosettes, and spheroidal forms are also visible. Larger or smaller agglomerations of fly ash are present in the microstructure of the cast composite. About 1 % of pores were observed by CT analysis in the cast composite. Applying the ECAP procedure causes the collapse of the rosettes, and FA is additionally distributed in the matrix. The material becomes homogenized and the pores disappear. After one ECAP pass CT scans show a certain orientation of the microstructure in the direction of the shear planes, while after the second pass, there is no difference in the CT scans in the horizontal and vertical planes. The addition of fly ash particles reduces the hardness and resistance to erosion compared to the cast, rheologically treated alloy. ECAP increases the hardness of the alloy, and especially the hardness of the composite. After the second extrusion, the hardness of the alloy and composite is equal. Whit very high coefficients of determination (R 2 ≈ 1), a significant influence of load on the measured values of microhardness of the samples was confirmed.The hardness of the alloy and composite with 6 % FA in the as-cast condition, decreases with the increase of the test load, which is defined as the normal Indentation Size Effect (ISE). Angularly extruded specimens have a Reverse Indentation Size Effect (RISE). Applying ECAP generally increases solid particle erosion resistance. On the SEM images, signs of wear characteristic of certain impact erodent angles were observed. For an angle of 90°, cavities were observed due to the "falling out" of particles and slight indentations caused by plastic deformation, which indicates surface fatigue. For an angle of 30°, micro-ploughing, and volume displacement were observed in the direction of the erodent movement, which indicates an abrasive wear mechanism. Linear regression analyses showed that there was a very strong negative linear relationship between hardness and volume loss at the solid particle erosion wear at an impact angle of 30°, where the dominant wear mechanism is abrasion. In the case of composites with 6 % FA, the mutual dependence of hardness and resistance to impact erosion was also established (impact 90°), while in the case of non-reinforced alloy and composites with 4 % FA, the observed values are not correlated. Considering all the results, it can be concluded that the main goals of the work have been achieved and the hypothesis was confirmed. It is possible to prepare a composite with an aluminium matrix reinforced with FA and to improve its properties by multiple ECAP passes.