Effect of porosity of phosphate coating on corrosion resistance of galvanized and phosphated steels Part II: Evaluation of corrosion resistance

摘要

The effect of porosity of phosphate coatings on the corrosion resistance of ungalvanized (UG), electrogalvanized, and hot dip galvanized steels is evaluated in this study. The corrosion resistance of phosphatized and painted steel is related to the integrity and continuity of phosphate and paint layers, and pores in the phosphate layer affect the corrosion resistance of material. The porosity of the phosphate coating was evaluated by using the cathodic polarization electrochemical test. To evaluate the corrosion resistance of the phosphatized and painted steels, they were submitted to accelerated corrosion tests. As was expected, the creep back from the scribe increased with the increase in porosity. This behavior was evident for UG steel, but less evident for galvanized steels due to cathodic protection and/or barrier effect of the zinc coating.