## 4 Results and Discussion
### Wear Resistance Tests  
Abrasive wear resistance, next to hardness measurement, is one of the basic parameters verifying the effectiveness of the conducted surface treatment. As part of this work, wear resistance tests were performed by means of a T01-M tester (ITEE, Radom, Poland) employing the pin-on-disc method. The tests were carried out under dry friction conditions at the temperature of 23 \({}^{\circ}\)C. All the samples after FSP friction modification, as well as the aluminum alloy in its initial state, were subjected to tribological tests. The research was of a comparative nature to illustrate both the differences in the wear resistance of the composites depending on the reinforcing phase used and also the changes in the tribological properties of the material caused by FSP treatment. During the tests, the linear wear of the tested sample was recorded. The test samples had the form of a cylinder with a diameter of 4 mm and a height of 15 mm and were cut from the central part of the band, perpendicular to its surface. The counter sample was made of bearing steel EN 100 Cr6 [56] (E52100 according to AISI). The rotational speed of the counter sample was 150 rpm, and the test duration was 90 min. The load during the test was constant and amounted to 20 N. The selection of the tribological test parameters was based on previous experiments conducted with the AA/075 aluminum alloy and composites manufactured using the FSP method. The samples for the tribological tests were subjected to preparatory processing consisting of grinding a thin surface layer with a thickness of approximately 20 \(\upmu\)m. Initial microscopic examinations showed that the geometric structure of individual samples differs, which could affect the accuracy of the tribological tests. During the microscopic examinations, it was found that the maximum depth of furrows and grooves formed on the surface of the samples as a result of FSP treatment does not exceed approximately 20 \(\upmu\)m; therefore, it was decided to remove the surface layer of this thickness before the tribological tests. The tribological tester was utilized to remove the surface layer. The abrasion process was completed when the tester's measurement system registered a linear loss of the assumed value, i.e., 20 \(\upmu\)m. In this way, uniform starting conditions were achieved and potential measurement errors resulting from differences in the surface geometry of individual samples were eliminated. The results of the tribological test are presented in the figures in the form of the \"linear sample loss-test duration\" characteristic (Figure 9). Taking into account the previous hardness measurement results, improvement in the wear resistance of the aluminum alloy was expected after the introduction of the reinforcing phase. This was also the obtained effect. All the analyzed samples were characterized by higher wear resistance than the starting material. The improvement in wear resistance was primarily a consequence of the presence of the hard reinforcing phase in the composite matrix, but also of strong grain refinement in the stirring zone. As follows from the Archard wear model [57], the rate of material wear is inversely proportional to the hardness of the material, and the hardness, in turn, depends on the microstructure, including the degree of grain refinement. The analysis of the influence of the type of reinforcing phase on the wear resistance revealed that the sample reinforced with SiC particles had the lowest linear loss, while the sample reinforced with the A-1 particles also exhibited only slightly lower resistance, while the highest linear loss was recorded in the case of the sample reinforced with the A-2 particles. Nonetheless, it should be emphasized that the wear resistance of the sample reinforced with the A-2 particles was still much higher than that of the AA/7075 aluminum alloy, which proves the advisability of using this material as a reinforcing phase in composites.