PRODUCTION OF ELECTROLYTICALLY CHROMATED GALVANIZED STEEL SHEET EXCELLENT IN RESISTANCE TO CORROSION, FINGERPRINTING AND CHROMATE ELUTION AND IN CONTINUOUS PRODUCTIVITY AND TO PROVIDE ELECTROLYTIC CHROMATING BATH USED IN THAT CASE

摘要

PURPOSE: To propose a method for producing electrolytically chromated galvanized steel sheet excellent in resistance to corrosion, fingerprinting and chromium elution and in continuous productivity and to provide an electrolytic chromating bath used in that case. ;CONSTITUTION: A zinc or galvanized steel sheet with at least one side plated with zinc is used as a cathode and electrolytically chromated in an electrolytic chromate bath contg. hexavalent chromium ion, trivalent chromium ion, bivalent Ni ion and silica sol, further added with phosphate ion and sulfate ion and then with the trivalent chromium ion concn./total chromium concn. controlled to 0.1 and the silica concn. in the bath/trivalent chromium ion concn. to 70 at pH2.5-3.8 and 30-70°C bath temp. to form an electrolytic chromate film on the zinc or galvanized layer.;COPYRIGHT: (C)1996,JPO