Effects of Zinc Borate and Fly Ash on the Mechanical and Tribological Characteristics of Brake Friction Materials

Friction materials based on several combinations of zinc borate (ZB) and fly ash (FA) were fabricated and characterized for their mechanical and tribological performance. The triboperformance of the friction materials was evaluated on a Chase friction testing machine according to the brake lining quality test procedure as per SAE J661. The composites were manufactured based on a nonasbestos organic-based friction material for an automotive brake system and contained typical ingredients for commercial brake friction materials. The composites had a fixed composition of 15 wt% resin, 15 wt% fibers, and 5 wt% friction additives. ZB and FA as fillers were added to the the raw materials mixture at a total fraction of 65 wt%. The results showed that ZB and FA contents have a significant influence on the mechanical and tribological properties of the friction composites. In particular, the composites containing 0–5 wt% ZB and 65–60 wt% FA showed better friction stability and improved fade resistance compared to those containing 10–35 wt% ZB and 55–30 wt% FA, whereas the composite with 5 wt% ZB and 60 wt% FA showed a maximum friction coefficient. On the other hand, the specific wear rate of the composites decreased with increasing ZB and decreasing FA contents. The morphologies of the worn surfaces as well as wear debris were analyzed by means of scanning electron microscopy.