1. Grupo de Investigaciones en Corrosión GIC
Effect of zinc thickness on corrosion film breakdown of Colombian galvanized steel
Grupo de Investigaciones en Corrosión GIC
A Sandoval-Amdor1, J E Torres Ramirez2, P A Cabrales-Villamizar1, D A Laverde-Cataño1, J A Sanabria-Cala1 and D Y Peña-Ballesteros1
1 Universidad Industrial de Santander, Bucaramanga, Colombia
1 Comision Nacional de Energía Átomica, Universidad Nacional de San Martin – Argentina.  
ABSTRACT
This work presents the corrosion behavior of Colombian galvanized steel in solutions of chloride and sulfates ions. The effect of the thickness and the time of exposure on the film breakdown susceptibility and protectiveness of the corrosion products were studied using, potentiodynamic polarization curves and electrochemical impedance spectroscopy. Corrosion products were analyzed by SEM-EDS and XRD. The samples with the higher thickness in the zinc film (Z180) shown the lowest corrosion rate, the products of the chemical reactions that occurred, in this particular case, was formed Zinc hydroxide, which exhibits a passive behavior, as observed in the Pourbaix curves of the potentials obtained and the different pH of the solutions worked. The sheets with the highest thickness (Z180) presented the best performance, since at the end of the study they presented the least damage on the surface of the zinc layer. This is because the thickness of the zinc layer favors the formation of simonkolleite which is the product of corrosion that protects the material under the conditions of study.
METHODOLOGY
Figure 3. Potentiodynamic polarization curves of galvanized steel at 7 days and corrosion rates at different exposure times
RESULTS AND DISCUSSION
Figure 1. SEM images for the cross section of galvanized steel sheets. A) Z90, b) Z120 and C) Z180
Figure 4. Chemical composition maps of galvanized steel exposed at 14 days exposure
CONCLUSIONS
The exposure time of samples to chlorides and sulphates and grain size are factors that negatively affect the corrosion behavior of galvanized Steel sheets.
The thickness of the galvanizing improves the corrosion properties of galvanized steel sheets therefore; the penetration of chloride ions into the substrate will be more difficult. Although the Z90 sheet had the best performance against corrosion due to its small grain size, its coating was completely corroded with red corrosion on its surface, which is characteristic of the iron oxides, indicating that the substrate was corroded.
Figure 2. Nyquist diagrams of galvanized exposed at different times, a) 0 days, b) 7 days, c) 14 days and Equivalente cicuits used to adjustment EIS data.
Time
0 days
7 days
14 days
Sample
Z90
Z120
Z180
Z120 NaCl
Z 120 Na2SO4
Rp (kΩ/cm2)
205
52,7
---- 
5,62
1,01
1,81
0,35
7,4
1,47
0,47
 3,54
REFERENCES
[1] Ramirez-Jerez J A, et al Rev Fac Ing 24(39) 99
[2] Sandoval Amador A, et al Informador Técnico, 79, 127.
[3] Azaroual M. A., et al. 2016, Journal of Molecular Liquids, 220, 549.
Table 1. Polarization resistance obtained from the adjustment to equivalent circuits of the EIS data.
4TH INTERNATIONAL MEETING FOR RESEARCHES IN MATERIALS & PLASMA TECHNOLOGY – IMRMPT, SANTA MARTA, COLOMBIA, 2017