METHOD FOR FORMING MOLYBDATE-BASED ALTERNATIVES AS A PASSIVATION TREATMENT FOR ZINC GALVANIZING STEEL

摘要

PURPOSE: A method for forming molyphosphate coating on a zinc plated steel plate is provided, which can form molyphosphate film that shows the same coating film characteristics as the existing chromate coating film on a zinc plated steel plate, by shortening treatment time greatly by improving reactivity that is increased by enlarged etching force of fluorine ion. CONSTITUTION: The method is as follows: (i) impregnate zinc plated steel plate into coating treatment solution of molyphosphate composition consists of sodium molybdate and phosphoric acid to form molyphosphate coating on the steel plate; (ii) the treatment solution is made by adding one selected from 2-8ml per liter of H2SiF6 or 2-20ml per liter of Na2SiF6-6H2O to 10-40g per liter of sodium molybdate and 5-10ml per liter of phosphoric acid as a base material at 55-65deg.C.