In car body, the pre-phosphate treated electrogalvanized steel sheets were applied in many parts. The pre-phosphate layer was formed on electroplated zinc layer in EGL and consists of zinc-phosphate "Hopeite" crystals which contain Ni and Mn. The pre-phosphate layer improved the formability of electrogalvanized steel sheets. The Ni and Mn in Hopeite crystals improve the paint adhesion in wet condition. The Mg was contained in Hopeite crystals by addition of Mg ions in pre-phosphate solution. The formability and corrosion resistance of the pre-phosphate treated steel sheets are improved by Mg in Hopeite crystals. The shape of Hopeite crystals became granular and the corrosion products become stable by Mg in Hopeite crystals. The Mg contained pre-phosphate treated electrogalvanized steel sheets have good performance for car body.
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