THE EFFECT OF Mg ADDITION TO THE PHOSPHATE FILM ON THE PROPERTIES OF PREPHOSPHATED ELECTROGALVANIZED STEEL SHEETS

摘要

The effect of Mg addition to the phosphate film on the properties of prephosphated EG was investigated. The morphologies of the phosphate film have changed from needle shape crystals to fine granular crystals by Mg addition. Friction properties and corrosion resistance of prephosphated EG were remarkably improved by the change of the phosphate film as above mentioned. No influence was observed on the other properties such as paint adhesion. Fine granular crystals could be less damaged than needle shape crystals under high pressure press forming conditions, so that friction properties of prephosphated EG were improved. Mg containing prephosphated EG also showed excellent corrosion resistance due to improvement of the coverage of zinc surface, and Mg in phosphate film could stabilize the initial zinc corrosion products, resulted in restraint of consumption of zinc coating layer. Although Mg containing prephosphated EG exhibited excellent corrosion resistance without any additional sealing treatment such as chromate passivation treatment, further excellent corrosion resistance was obtained by applying additional sealing treatment with aqueous solution of magnesium phosphate