Oxidation and diffusion in the formation of sequential-diffusion brass coatings on steel

Abstract

Sequential-diffusion brass alloy coating of steel has been investigated by using Auger electron spectroscopy (AES). In this process the coating is formed by plating pure copper and zinc films on the substrate followed by thermal diffusion of these deposits into a homogeneous alloy. AES with depth profiling has been used to investigate oxidation of the coating between 475 and 625 °C, and migration at the copper–zinc interface. Oxidation below 570 °C appeared to be controlled by bulk diffusion in zinc oxide; above this temperature a reduced activation energy was attributed to the formation of a mixed copper–zinc oxide and a coating phase transformation. Interdiffusion at the copper–zinc interface immediately after plating has been observed and attributed to electromigration during the zinc deposition. Diffusion was found to proceed via the coalescence of crystalline phases of the alloy.