A Note on the Dezincification of Brass and the Inhibiting Effect of Elemental Additions

The dezincification of brasses has been the subject of substantial conjecture and investigation over the past century and the technical press is littered with papers on the problem. Very broadly the technical literature can be subdivided into five main groups as follows: (a) Observations of dezincification phenomena including mechanically induced dezincification and in-service experience in various solutions; (b) Development of tests to assess the propensity of particular brasses to dezincify; (c) Mechanistic theories and kinetics of dezincification; (d) Inhibition of dezincification by alloying additions to the brass; and (e) Inhibition of dezincification by chemical treatment of the brass. This note is concerned only with the inhibition of dezincification by alloying additions, although some notice is taken of operating conditions such as water temperature and composition and the effect that alloying additions may have on other important properties of the brass, e.g., susceptibility to stress corrosion cracking. A few notes on the effect of cold work on dezincification together with a short bibliography on dezincification tests are presented in the Appendix. The intensity of dezincification of brass is very closely related to the structure of the alloy which is controlled by composition. As might be expected the resistance to dezincification increases with copper content of the brass, but the relationship is not linear. Major improvements in performance occur when the structure changes from all-beta to alpha+beta (duplex) and from duplex to all-alpha phase. Alloys containing less than 15% Zn rarely dezincify. Some alloying additions have a large effect on the structure of brass, e.g., by altering the proportion of alpha, beta or gamma phase present. Many years ago Guillet and Portevin 1 established the concept of designating a "zinc equivalent value" for each commonly used alloying addition. Some zinc equivalents are listed in Table 1. However it is well to remember that these values were developed for dilute solutions of the alloying additions and it is not surprising that they sometimes generate inaccurate estimates. Consequently other values, based on experience of particular alloy systems, are sometimes used to provide a more realistic estimate of the likely structure that will be generated in practice. Thus, the value for aluminum is often reduced to 4, whereas that for lead probably approaches zero as the lead content exceeds about 0.5%. Brunhuber, 2 who made a study of Guillet and Portevin's work, dismissed the whole concept of zinc equivalents as being too unreliable for practical …