The effect of phase fraction, size and shape on the dezincification of duplex brasses

Abstract

Duplex brass (α + β’) can be susceptible to dezincification in potable water environments. The use of dezincification inhibitors is a common approach to protect the α phase, and heat treatments are usually applied to reduce the volume fraction of the susceptible β’ phase. In this work, we explore an alternative ‘microstructural engineering’ approach to improve the dezincification resistance. A systematic study of the dezincification behaviour has been conducted on low-Pb duplex brass as a function of β’ phase fraction, and α grain size and shape. Microstructures have been designed that allow deconvolution of the phase fraction, size and shape effects on dezincification. The classic expectation that less β’ phase fraction improves dezincification resistance is reproduced, but it is also shown that a small α grain size with high aspect ratio (Widmanstätten α) can be just as important as the β’ phase fraction for dezincification control. The dezincification behaviour has been rationalised using percolation simulations, where the β’ phase interconnectivity and geometric arrangements are highlighted. These observations provide new degrees of freedom for the brass metallurgist to design microstructures that balance the required dezincification performance with the other important properties such as strength, formability, machinability and thermo-mechanical processing schedules.