Effect of anodized coating on friction noise in aluminum

This study looks at the frictional noise and vibration generated by the relative motion of steel with an uncoated Al pin and an anodized Al pin in a reciprocating system. Frictional noise occurred with both the uncoated and anodized Al pins near 2 kHz and 7.2 kHz. However, the onset of the frictional noise with the uncoated Al pin was generated relatively quickly. The sound pressure level of the two specimens was similar at the moment when the friction coefficient became similar. The results of the surface characteristics using scanning electron microscope (SEM)/energy dispersive spectroscopy (EDS) analysis shows that the uncoated Al pin sharply generated wear from the beginning of the test. And, adhesive wear occurred at the edge of the contact surface. When the friction continued, there were increases in the debris due to material transfer on the worn surface, as well as oxygen and Fe on the surface. This result suggests that the friction surface was further damaged. In contrast, the coating on the anodized Al pin protected the friction surface at the beginning of the test and delayed the damage of the surface due to friction. However, as the friction continued, the coating surface was damaged because the nickel and sulfur added in the post-processing of the coating were reduced, and the debris was increased by the material transfer. Thus, the friction coefficient gradually increased at the anodized Al pin. And, frictional noise was generated. Frictional noise at the anodized Al pin was generated by the gradual increase in the friction coefficient.