Effect of lead content on the dezincification behaviour of leaded brass in neutral and acidified 3.5% NaCl solution

Abstract

The corrosion behaviour of leaded brasses with 2, 2.4, 2.8, and 4.85 wt.% of lead in both neutral (pH 6.5) and acidified (pH 3.0) 3.5% NaCl solution was studied. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), current–time transient, and accelerated leaching studies were employed to assess the corrosion behaviour. The study reveals that the lead content of the alloy has a pronounced influence on the extent of corrosion attack in neutral and acidified 3.5% NaCl solutions at potentials closer to and anodic to Ecorr. Scanning electron micrographs (SEM) show the existence of lead as a separate phase in leaded brass before subjecting it to corrosion and the formation of hexagonal platelets or flower shaped crystals on selected areas after corrosion. The structural separation of lead from the rest of the alloy forms galvanic cells and decreases the corrosion resistance of leaded brasses in neutral 3.5% NaCl solution at potentials closer to Ecorr. In contrast, at potentials anodic to Ecorr in neutral 3.5% NaCl solution and in acidified 3.5% NaCl solution, precipitation of lead based compounds on the surface of leaded brass decreases the extent of corrosion attack and causes a deviation from the typical dezincification behaviour. The precipitation of lead based compounds induces passivity of the leaded brasses, which is evident in the anodic segments of the polarization curves obtained for acidified 3.5% NaCl solution. This study concludes that increase in lead content of leaded brass alloys could provide an improvement in their corrosion resistance only under conditions where compounds of lead gets precipitated on the surface and induces passivity.