Electrochemical and AFM/SEM studies of Ni-Cr electroplated and sol-gel coated samples

Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to study the surface characteristics and corrosion mechanisms of Ni/Cr electrocoats and Al2O3 sol-gel coats before and after accelerated corrosion tests in a 0.5% NaCl solution at 18degreesC. The results of electrochemical tests show that the corrosion resistance of substrates has been much improved by the application of both coats, and the Al2O3 coated sample exhibits the better anti-corrosion performance. Surface morphology observations revealed the presence of highly homogeneous and adherent films formed on the metal substrate during the sol-gel process. These films act as a barrier to prevent the substrate from corrosion in the aggressive environment. This sol-gel coating is therefore seen as a promising replacement for that of Cr6+ electroplating.