Low-Cost Surface Alloying of Brass to Improve Corrosion Resistance in Chloramine-Rich Aqueous Environments

A cost-effective method of surface alloying brasses (CuZn40 and Bi-alloy C89836) during sand casting was investigated to improve their corrosion resistance. The process involved coating the mold surfaces with slurries containing suspended metal powders before pouring the melt into the sand molds. This casting process allows the internal and external surfaces of a component to be enriched with selected alloying elements, including nickel, leaving the bulk unmodified. Surface-alloyed castings were made both in a laboratory and an industrial setting. The surface-alloyed castings were analyzed using optical and electron microscopy following the casting process. Distinct surface-alloyed layers of average thickness ranging from 100 to 1000 µm were observed on the surfaces of the castings in contact with the molds treated with the slurry containing metal powders. An SEM-EDS analysis confirmed that the surface-alloyed layer was enriched with nickel, ranging from 21 to 62 wt%. Potentiodynamic testing demonstrated that the cast surface-alloyed samples had a higher corrosion resistance than those without surface alloying.