Influence of copper on automotive brake performance

Previous studies have shown that the copper originated from the wear of automotive brake friction materials (BFM) is one of the main sources of the deposit of this metal in rivers and lakes, leading to environmental impacts. As a result, recent US legislations have forced a drastic reduction of the copper used in BFM's in the next years, which will be likely followed by other governments around the world. Although the copper is widely used in BFM's, the understanding of the action mechanisms of this metal is quite limited. This work aims to contribute to a better understanding of the role of copper in automotive brake pads in terms of friction coefficient and wear. Tests were carried out in a laboratory-scale tribometer, where three kinds of specimens of brake pads (with 0%, 10% and 30% of copper each, in % wt) were subjected to different temperatures (100 degrees C, 200 degrees C and 300 degrees C). Friction coefficient, as well as the wear of the brake pad and disc was measured. Morphological parameters of contact plateaus (area fraction, size and amount) were also described. An inverse behavior was observed between friction and copper content, where an increase in the copper content led to a decrease in friction coefficient. The absence or excess of copper negatively affect the BFM's wear rate. Strong inverse correlation between BFM's and disc was observed in terms of wear resistance. Among the morphological parameters studied, the amount of contact plateaus showed the highest correlation with friction coefficient.