Low temperature electrogalvanization: Texture and corrosion behavior

Electrogalvanization at room temperature using aqueous bath is extensively used for protection of steel in highly corrosive environments. Here, it is shown that low temperature galvanization conducted at -2 degrees C using aqueous electrolyte bath produces Zn coating which exhibits significantly lower corrosion current density (icorr) value when compared to the icorr values of coatings deposited at room temperature (-28 degrees C) and high temperature (-60 degrees C) when these coatings are exposed to a corrosive environment (3.5 wt% NaCl solution). The icorr values for coatings deposited at 2 degrees C, 28 degrees C and 60 degrees C were 8.94 mu A/cm2, 24 mu A/cm2 and 182 mu A/cm2 respectively. Micro-texture analysis revealed that the texture (grain orientation and grain boundary constitution) of the coatings is also highly sensitive to the deposition temperature. Higher corrosion resistance observed in case of 2 degrees C deposited coatings was due to factors such as growth of grains oriented with relatively inert basal plane on the coating surface which retards the transgranular corrosion and presence of higher fraction of low energy special boundaries (such as low angle grain boundaries, coincidence site lattices and symmetrical tilt grain boundaries) which retards the intergranular corrosion significantly.

Automated summary

Electrogalvanization at room temperature using aqueous bath is widely used to protect steel in highly corrosive environments. However, low temperature galvanization at -2 degrees C produces Zn coating with significantly lower corrosion current density, leading to higher corrosion resistance compared to coatings deposited at higher temperatures. The texture of the coatings is highly sensitive to the deposition temperature, with coatings deposited at 2 degrees C showing the highest corrosion resistance due to specific grain orientation and grain boundary constitution.