Friction and Wear Properties of Zn-25Al-Based Bearing Alloys

Abstract

A series of Zn-25Al-based ternary and quaternary alloys was prepared by permanent mold casting and their dry sliding friction and wear properties were investigated using a block-on-disc machine. The hardness and strength of the alloys increased with increasing copper and silicon contents, but when the copper and silicon contents exceeded certain levels the trend reversed. However, their impact energy and ductility showed completely opposite changes with copper and silicon contents. T6 heat treatment increased the hardness and strength of Zn-25Al-3Cu-1Si alloy but reduced its impact energy, ductility, and wear resistance. The working temperature and wear volume of the alloys increased almost linearly with increasing sliding distance and contact pressure, but the latter had no considerable effect on their friction coefficient. Microstructural changes that resulted in the formation of different regions were observed below the wear surface of the alloys. The formation of these regions was discussed in terms of deformation of surface material, oxidation, and smearing of wear particles. The Zn-25Al-based ternary and quaternary alloys were found to be much stronger and more wear resistant than SAE 660 bronze.

KEY WORDS:

• Unlubricated Friction
• Unlubricated Wear
• Equipment Wear Tests
• Wear Mechanisms
• Non-Ferrous Alloys
• Hardness

ACKNOWLEDGEMENTS

The authors thank Professor S. Timur in the Metallurgy and Materials Engineering Department of Istanbul Technical University for chemical analysis of the alloys. The authors also thank technicians H. F. Demirci, M. Kıraslan, H. Ekşi, and L. Demir in the Mechanical Engineering Department of Karadeniz Technical University for their assistance.