Abstract
As zinc rich paint coated steel sheet, such as Zincrometal, affords excellent corrosion resistance even without finish painting, it is employed extensively as corrosion resistant precoated steel sheet for automobile bodies as well as zinc and zinc alloy plated sheet. However, when zinc rich paint coated steel sheet is pressformed, many problems arise. The coating film tends to peel and corrosion resistance of the formed areas deteriorates. Another problem is poor weldability.
In order to improve these unsatisfactory performances of the product, we have developed Ni-Zn plated sheet coated with a new organic-silicate composite entirely different from zinc rich paint film.
The new coating consists of two layers on Ni-Zn alloy plated steel sheets. The lower layer is an inorganic chromate film and the upper layer is an organic-silicate composite film of colloidal silica which is chemically combined with organic materials. The new product is superior to zinc rich paint coated steel sheets in corrosion resistance, powdering and weldability due to excellent performances of thin (about 1μm) organic-silicate composite film.
