On the tool wear reducing mechanism of Zn in brass alloys

Cemented carbide (WC-Co) tools are used in the zipper manufacturing industry to shear a pre-formed Cu-Zn alloy wire (15 wt.% Zn) into zipper elements. Somewhat, surprisingly, the much softer Cu-Zn alloy is capable of wearing down the cemented carbide. Moreover, the carbide and the binder phase are worn to an even level, which is generally not expected if abrasive wear was dominant, due to their vast difference in hardness. Instead, tribochemical wear is thought to be the primary wear mechanism behind these phenomena. Tribological tests, mimicking the wear of the tools used in zipper manufacturing, have shown that the wear rate of the cemented carbide increases drastically when Zn is omitted from the work-material. In the present study, the tool wear when sliding against Cu-Zn alloys containing 0.6 and 3.0 wt.% Zn, respectively, is investigated to gain a deeper understanding of the effect that small amounts of Zn have on the wear of cemented carbide. Tests are performed in a sliding test rig and the wear is analysed using scanning electron microscopy, energy dispersive X-ray spectroscopy and optical surface profilometry. The cemented carbide is gradually worn when sliding against both Cu-Zn alloys, and the wear is primarily concentrated to the periphery of the contact. Large amounts of oxidized Zn are found on the cemented carbide in regions of low wear, indicating that Zn can protect the cemented carbide. The wear rate of the cemented carbide is lower with more Zn in the work-material. Interestingly, as little as 0.6 wt.% Zn is enough to more than half the wear rate compared to when sliding against pure Cu. • Crossed cylinder sliding tests with WC-15Co and Cu-Zn, where Zn content is varied. • Wear surfaces of WC-Co are studied, and the wear is shallow, gradual and even. • Both Cu and Zn adhere to cemented carbide, and any transferred Zn is oxidized. • The wear rate of WC-Co decreases with increasing Zn content in the alloy. • The addition of as little as 0.6 wt.% Zn to Cu more than halves the wear rate.