Investment casting of leaded brass: Microstructure micro-hardness and corrosion protection by epoxy coating

Abstract

The objective of this work is to examine thermally induced microstructure of duplex brass specimens containing 2wt% Pb, which were previously cooled in five different molds (iron, steel, sand,marble and clay mold) having decreasing thermal conductivity when going from iron mold to clay mold, microscopic observations revealed that the α phase formation is predominant when the specimen is casted in mold having low thermal conductivity, this finding was assessed by images analyzing software giving phases quantification, it was found that β phase is precipitated in the grains boundaries and α phase appears in the shape of thin Widmanstätten array when the casting is performed in molds with high thermal conductivity.The microhardness results have confirmed that the formation of β phase give maximum of hardness to the studied material whereas α phase give arise to ductility. We aimed to study the investigation of the influence of epoxy coating on the inhibition of brass corrosion in 0.5 M HNO3 solution. Electrochemical techniques such as potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were coupled to scanning electron microscopy (SEM) to evaluate protection efficiency. The obtained results indicate the used coating has a good anticorrosion efficiency, the protection efficiency (IE%) was found to be significant. Polarization studies showed that the coating acts as a mixed type protector, while electrochemical impedance spectroscopic technique (EIS) indicated the presence of one capacitive loop revealing that the charge transfer process controls the corrosion reaction.