HIGHLY CORROSION-RESISTANT CHROMATE TREATMENT OF ALUMINIZED STEEL SHEET

摘要

PURPOSE:To form a chromate film improved in the elution of Cr6+ and the peeling of film by using an aqueous solution of chromic acid containing Cr6+, total Cr, Si, and P in specific ratios and successively carrying out the plating treatment and drying by heating of a steel sheet under respectively specified conditions. CONSTITUTION:An aqueous solution of chromic acid containing silica sol and phosphoric acid and satisfying Cr3+/(total Cr)=0.4-0.6, Si/Cr3+=0.5-5.0, and further P/(total Cr)=0.02-0.50 is prepared. Subsequently, this aqueous solution is applied to an alminized steel sheet so that coating weight is regulated to 20-250mg/m2, which is dried by heating to 150-250 deg.C sheet temp. By this method, highly corrosion-resistant chromate treatment improve in the elution of Cr6+ and the peeling of film can be applied to the Al-plated steel sheet.