Effect of Al₂O₃ content on properties of copper-based powder metallurgy friction materials

【Objective】 The development of the wind power industry has placed higher demands on the wear resistance and stability of the friction coefficient of friction materials under low-speed and high-load conditions. In this paper, Al₂O₃, which has high hardness, good thermal conductivity and low cost, is used as the friction component to study the effect of its content on the performance of friction materials.
【Method】 In this study, friction materials with Cu-Fe-Ni-graphite composition and Al₂O₃ content of 1%, 2% and 3% respectively were prepared by powder metallurgy process under a forming pressure of 400 MPa and a hot-pressing sintering process at 990 ℃ for 3 hours. The microstructure and composition uniformity of the friction materials were observed and analyzed by scanning electron microscopy. The mechanical properties of the friction materials were tested by an electronic universal testing machine and a Brinell hardness tester. The friction and wear properties of the friction materials were characterized by a friction material testing machine.
【Result】 SEM and EDS analysis of the friction material indicated that the components are uniformly distributed in the matrix, which effectively enhances the friction and wear performance of the material. Tests reveal that when the mass fraction of Al₂O₃ in the friction material is 1% and 2%, the hardness and strength of the material are similar. However, when the mass fraction of Al₂O₃ increases to 3%, the hardness of the material increases while the density and strength decrease significantly. The friction material with a 2% mass fraction of Al₂O₃ has the best comprehensive mechanical properties, with a hardness of 32.67 HBW, a shear strength of 33.74 MPa, and a bonding strength of 29.70 MPa. The friction and wear tests show that the wear mechanism of the friction material is abrasive wear. As the content of Al₂O₃ increases, the wear of the friction material increases. The friction material with a 2% mass fraction of Al₂O₃ is more readily to achieve a stable coefficient of friction and has the highest coefficient of friction of 0.58 and a wear of 0.88 g.
【Conclusion】 When the loss Al₂O₃ increases to an excessive content, it will reduce the density and strength of the friction material. The wear mechanism of the friction material is abrasive wear. With the increase of Al₂O₃ content, the number of friction cycles required before the friction coefficient stabilizes is reduced, and the friction coefficient first increases and then decreases, resulting in increased wear. When the mass fraction of Al₂O₃ in the friction material is 2%, the material has the best comprehensive performance.