An Auger/SEM study of the corrosion of β-brass alloyed with tin

Abstract

Two brass samples, Cu56Zn44 and Cu56Zn43Sn1, were exposed to deaerated aqueous solution with composition 1 M NaCl+0.01 M HCl. Auger analysis of the Sn alloyed brass did not reveal any Sn surface segregation which eliminated a surface Sn passivating layer as a mechanism for the reduced corrosion rate in the Sn alloy. Auger depth profiles of the 1% Sn alloy revealed a pure copper layer separated from the bulk brass by a tin rich layer. SEM micrographs showed a porous, loosely adherent copper layer whose top surface retained the original polished finish, indicating little copper dissolution or redeposition. Our results suggest that the remaining copper is forced by the high void concentration into a porous layer whose thickness increases until a tin layer is formed, at the copper/brass interface, that separates the reactants and, thereby, retards the corrosive attack.