## 3 Results
### Evaluation of Casting Porosity  
The porosity of casting was evaluated using an optical microscope, and the resulting images were analyzed using Stream Motion software (Figure 6). The software uses graphic filters with defined sensitivity to detect and evaluate pores in the images. Before measurement, the filters are set to an appropriate sensitivity level to ensure that only pores are detected. The objects in the images that meet all required conditions and differ in color from their environment are analyzed, and the program saves the results of all specimen values in tables, which are then used to generate graphical representations of the data.  
Figure 7 displays photographs that were used for the casting porosity analysis, and, for each specimen, three independent spots were selected to measure and evaluate porosity. It was necessary to select spots that were perfectly polished to avoid any scratches, dents, or cracks in the specimens that could be mistakenly evaluated as pores by the software. If such imperfections were included in the analysis, the porosity measurement results would be misrepresented, and the software could potentially overestimate the occurrence of porosity. Therefore, it was important to ensure that the selected spots were free of any such imperfections to obtain accurate measurements of the porosity of the casting.  
Figure 5: Sampling scheme for the evaluation of the porosity of the test rod.  
Figure 6: Evaluation of casting porosity in the Stream Motion.  
According to the graphical representation shown in Figure 8, there is a decrease in porosity when the pressure or holding pressure in the mold cavity increases. The decrease in porosity with increasing pressure or holding pressure indicates that higher pressures exerted during the die casting process led to a denser and more compact internal structure of the castings. The measured values of the porosity in the examined samples support this conclusion. It is important to note that the decrease in porosity may not continue indefinitely with increasing pressure or holding pressure. At some point, the porosity may reach a minimum value, and further pressure increases may not result in a significant decrease in porosity. It is also possible that excessive pressure or holding pressure could lead to other defects in the casting, such as cracking or distortion, and, therefore, the optimal pressure or holding pressure must be determined based on a careful evaluation of the casting quality.  
Figure 7: Metallographic photographs of specimens obtained by optical microscopy.  
As shown in Figure 8, there is a clear correlation between the change in pressure or holding pressure in the mold cavity and the porosity values of the casting. As the pressure or holding pressure increases, the porosity values decrease, which is generally considered desirable for castings. This is because a lower porosity typically results in higher mechanical properties and better overall quality of the casting. However, it is important to note that the relationship between pressure and porosity is not linear, and, at some point, further pressure increases may not result in significant improvements in porosity or other mechanical properties. Therefore, it is important to determine the optimal pressure or holding pressure based on careful evaluation of the casting quality and other relevant factors.