On the function of lead (Pb) in machining brass alloys

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Lead has traditionally been added to brass alloys to achieve high machinability, but the exact mechanisms at work are still debated. Lead-free brass alternatives could be developed if these mechanisms were better understood. Accordingly, machinability characteristics were investigated for two brass alloys with similar mechanical properties and phase composition, but with very different machining characteristics because one has 3 wt.% lead (CuZn38Pb3) while the other has only 0.1 wt.% (CuZn42). The effect of the lead was investigated using infrared temperature measurement, electron microscopy, secondary ion mass spectroscopy, quick-stop methods, and high-speed filming. Neither melting of lead nor its deposition on the tool rake surface takes place during machining thus confirming its limited lubrication and tribological effects. Instead, the main role of lead is to promote discontinuous chip formation. Lead deforms to flake-like shapes that act as crack initiation points when the workpiece material passes through the primary deformation zone. This effect prevents the development of stable tool–chip contact, thus lowering cutting forces, friction, and process temperature.

Bibliografisk information

Funding Information:
Open access funding provided by Lund University. This work was funded by the national strategic innovation program — national action for Metallic Materials, organized by Vinnova and Jernkontoret (Sweden) under the Optibrass project (ID 2019–02933) and the Sustainable Production Initiative (SPI), a collaboration between Lund University and Chalmers Institute of Technology.

Funding Information:
This work was funded by Vinnova (Sweden) as a part of the OPTIBRASS project (ID 2019-02933). The project is a part of the national strategic innovation program — Metallic Materials under committee 10766. The work is also a part of the Sustainable Production Initiative, a collaboration between Lund University and Chalmers Institute of Technology. ToF-SIMS analysis was carried out at the Infrastructure for Chemical Imaging at Chalmers University of Technology and University of Gothenburg.

Publisher Copyright:
© 2022, The Author(s).

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