METHOD FOR CHROMATING ZINC PLATED STEEL SHEET

• Main Authors: SHINDO YOSHIO, KABEYA MOTOO, SUDA ARATA, AOKI TAKAYUKI, OGINO RIKUO, FUJII SHIRO, YOSHIDA MAKOTO, ISAKI TERUAKI
• Format: Patent
• Language: English
• Published: 18.05.1992
• Subjects: CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION

PURPOSE:To render superior corrosion and alkali resistance, etc., even in the case of drying for a short time by forming a specified amt. of a chromate film on the surface of a Zn plated steel sheet with an aq. chromating soln. contg. Cr<6+>, Cr<3+>, hydrofluoric acid, phosphoric acid and a silane coupling agent and prepd. under specified conditions. CONSTITUTION:An aq. chromating soln. contg. 1-30g/l Cr<6+> and 1-30g/l Cr<3+> in 0.1-2.0 weight ratio of Cr<6+> to Cr<3+> and further contg. 1-59g/l hydrofluoric acid and 1-59g/l phosphoric acid in 0.5-3.5 weight ratio of all of acid ions to Cr<3+> is prepd. and a silane coupling agent is added to the soln. in 0.05-0.3 molar ratio to Cr<6+>. The resulting chromating soln. is applied to the surface of a Zn or Zn alloy plated steel sheet and dried to form a chromate film by 10-150mg/m (expressed in terms of Cr). Even in the case of drying at a low temp. for a short time, the chromate film has superior welding resistance and coatability.