## 3 Results and Discussion
### Results of Monitoring the Brake Discs' Corrosion Resistance  
Corrosion on the outer side of brake discs after their exposure to rain, as well as a 3-month exposure to atmospheric conditions away from rain and snow, is displayed in Figure 17. The first one, on the left, is a low-priced brake disc, a mid-priced brake disc is in the middle and high-priced brake disc is on the right.  
The friction surfaces of all brake discs from the outer side of the wheel were covered by a continuous layer of corrosion (Figure 17). Contrary to mid-priced and high-priced brake discs, in relation to the low-priced brake disc, the whole surface touching the wheel disc corroded as well. Thus, disassembly of the wheel would be difficult, and prior to its reassembly, it would be necessary to remove corrosion totally. The high-priced disc (Figure 17 on the right) contains corrosion even at places where a protective layer was damaged due to assembly and disassembly. In that event, the corrosion protective layer is not so effective against mechanical damages from the wheel disc.  
The extent of corrosion on the inner side of brake discs, which is in contact with a wheel naive, is displayed in Figure 18. The first one, on the left, is a low-priced brake disc, a mid-priced brake disc is in the middle and high-priced brake disc is on the right.  
Like on the outer side (Figure 17), in relation to the inner side (Figure 18), the most corrosion-covered section is on the low-priced brake disc. Both inner and outer contact areas are not resistant against corrosion at all, or in the same way as the friction areas. The brake discs with such corroded contact areas cannot be assembled without removing corrosion from the surface. There is also a presumption that if water or moisture got onto contact areas during the operation, they would adhere to the wheel disc and n  
Figure 17: Corrosion on the outer side of brake discs.  
The low-priced brake disc was totally covered by corrosion, as also evident from Figure 19 on the left.  
Corrosion on the sides of the low-priced brake disc (Figure 19, on the left) occurs very often, as the brake discs are not corrosion resistant enough and their sides are highly exposed to water as well as salt water in winter, and they are not covered in any way.  
Detail of corrosion of the low-priced and mid-priced discs' friction area is shown in Figure 20. The low-priced brake disc is on the left and the mid-priced brake disc is on the right.  
Figure 19: Corrosion on the sides of brake discs.  
Figure 18: Corrosion on the inner side of brake discs.  
Corrosion on the low-priced brake discs creates deeper damage of the material than on the mid-priced one (Figure 20). This is probably caused by an absence of alloying elements to make the production as cheap as possible.  
Detail of corrosion of the mid-priced brake disc (on the left) and the high-priced brake disc (on the right) is shown in Figure 21.  
Corrosion on the high-priced brake disc (Figure 21) is stronger than on the mid-priced brake disc. It is also seen more on the contact area with the wheel disc.  
Figure 20: Corrosion on the friction area of low-priced and mid-priced brake discs.  
Mid-priced and high-priced brake discs were corrosion resistant predominantly by using a protective coating on the surface that is in contact with the wheel disc, have and on the sides. Related to the high-priced brake discs, due to the wheel's assembly and disassembly, it led to a damaging of the protective coating followed by corrosion in those areas.