Dezincification Test for Brass based on Potentiostatic Polarisation

The corrosion rate for a series of copper-zinc alloys has been determined under potentiostatic conditions by measuring the corrosion current and by analytical determination of dissolved copper and zinc. The measurements were made in a chloride-containing acetic acid solution with pH = 4·2, in the temperature range 20°–80°c.The dissolution rate for copper can be described by a normal Tafel expression, in which the constants are independent of the alloy composition and the same as for pure copper.Under dezincification conditions, the dissolution rate for zinc can be described by an expression for the polarisation curve taking in account both activation polarisation and resistance polarisation. If no dezincification is observed, the dissolution rate of zinc is equivalent to that of copper. The dezincification factor, Z, shows a maximum around the corrosion potential of pure copper owing to resistance polarisation.The polarisation current is shown to be equivalent to the dissolution rate for zinc by polarising brass to the corrosion potential of copper. On this basis a method has been developed for estimating the dezincification rate of various brasses. This rate is strongly dependent on the copper and arsenic contents as well as on temperature.