Generation and Preconditioning of Aluminium Matrix Composite Friction Surfaces of Braking Discs

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In the industrialised countries, transport plays a significant role in the generation of emissions, which result in addition to the combustion of the fuel from the abrasion of tires and brake system components. A hitherto comparatively little considered tribological system are the braking systems of passenger cars, contributing significantly to brake dust emissions into the environment. Currently, brake discs made of cast iron are used in the vast majority of cars. However, in addition to the brake pads they are subject to significant wear.The application of particle-reinforced aluminium matrix composites (AMCs) is intended in particular to considerably reduce the wear of both the brake disc and the brake pad. A large-scale use of such a braking system in motor vehicles is still not possible, since on the one hand, basic tribological relationships are poorly understood. On the other hand, suitable finishing processes for the generation of functional surfaces (friction surfaces) at the AMCs are missing. The primary goal of the project is therefore to gain a deeper understanding of the interactions in the tribological system consisting of the brake disc and the brake pad. In this case, the surface properties resulting from the specific finishing of the brake discs as well as a preconditioning of the brake discs are to be taken into account. In the end, the wear mechanisms occurring in relevant loading regimes shall be understood. This can only be achieved through an interdisciplinary research approach, uniting material and production engineering work.An important research goal is the creation of knowledge for a largely damage-free and appropriate surface generation of AMCs for the application as a brake disc friction surface. The focus of the tribological investigations lies on fundamental mechanisms of action between the surface properties, a preconditioning (controlled production of tribological films), as well as its running-in and wear behaviour. For preconditioning, micro-edges that are perpendicular to the direction of the braking motion are considered favourable. One approach is to remove the matrix alloy by just a few microns so that the sharp-edged particles protrude slightly out of the matrix. By superimposing an ultrasonic vibration in turning as a second approach, corresponding micro-edges are to be produced directly during finish machining without a subsequent process step. The respective surfaces are characterised in detail by optical and tactile methods as well as the surface layers by means of microstructure resolving methods. The results obtained on a laboratory scale at Chemnitz University of Technology are to be transferred to the industrial partner on the component brake disc and tested there comprehensively according to the test procedures prescribed for the braking system.