Relationship between texture and corrosion resistance in hot-dip galvanized steel sheets

The addition of lead or antimony to the zinc bath promotes both excessive g rowth of the zinc crystals and a dendritic solidification in the form of sp angles. This phenomenon affects not only the zinc coating texture but also its surface appearance and corrosion resistance. Therefore, the effects of the zinc bath chemical composition (changed by the addition of lead or anti mony) on the texture and corrosion behaviour of hot-dip galvanized steel sh eets were evaluated. Standardized salt spray tests as well as exposure to a 0.5 M NaClO4 solution test were employed. The surface texture was analyzed using X-ray diffraction (XRD). In order to study the corrosion performance , electrochemical impedance spectroscopy (EIS) and scanning electron micros copy (SEM) techniques were employed. From the experimental results it was c oncluded that the characteristic texture of zinc coatings was not modified by an increase in the antimony content, but an increment in the lead conten t produced a crystallographic preferential orientation with the pyramidal f amily planes parallel to the coating surface. This last effect deteriorates not only the surface appearance but also the corrosion resistance of the g alvanized steel sheets. (C) 1999 Elsevier Science S.A. All rights reserved.