Hot dip galvanised steels with thermal treatment or galvannealed steels are used in automotive industries because of their properties of weldability, workability and corrosion resistance. The galvannealed steels show three iron-zinc phases: zeta, delta and gamma. The distribution and concentration of iron-zinc phases affect the quality of the zinc layer and can produce stamping and welding problems. In the present work, the optimisation study of the electrochemical stripping process of industrial galvannealed steel was performed. The effect of electrolyte, pH, current density and scan rate was evaluated. The best resolution of the potential levels in the electrochemical dissolution curves was obtained for the zinc sulphate heptahydrate and sodium chloride aqueous solution, with a current density of 2 mA cm 22 and pH 4?5. Each sample surface obtained by using electrochemical stripping was analysed using X-ray diffraction and scanning electron microscopy.

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Low alloyed carbon steels are used in several applications as in automotive, home appliances and civil industries. Sb-bearing steels have been developed to withstand acid condensation, mainly to exhibit corrosion resistance to sulphuric acid aqueous solutions. This work is aimed at studying the corrosion resistance of three experimental low alloyed carbon steels with additions of copper, antimony and molybdenum using the electrochemical impedance spectroscopy (EIS) in a sulphuric acid aqueous solution, and field tests in industrial and marine atmospheres. The field tests showed the mass loss of antimony-molybdenum carbon steels was higher compared to that of other steels. The alloyed carbon steels with copper and antimony additions showed the highest atmospheric corrosion resistance evaluated by using field tests in industrial and marine environments. The molybdenumbearing steels showed the highest corrosion resistance in a sulphuric acid solution, measured by using the EIS.

The corrosion resistance of phosphated and painted steels is associated with the integrity of phosphate and paint layers. In this work, a methodology to measure the porosity of phosphated coatings based on cathodic polarization technique with an electrolyte of a sodium sulfate aqueous solution was developed. The morphology and mass of phosphate layers were determined. Phosphating was performed using the spraying and immersion techniques, varying the refiner content of bath in the immersion operation. The phosphate coatings obtained by immersion with a refiner showed the lowest values of porosities among the samples studied. The phosphate layers, obtained by spraying, immersion without a refiner, and immersion with a half content of refiner, showed the lowest porosity on electrogalvanized steel. The phosphate layer obtained by immersion with a refiner displayed the lowest porosity on the substrate of ungalvanized steel.