Abstract
Taking representative points on a zinc phosphate conversion coating is suggested as a method of preteatment in auto body painting. Conversion treatment for the dip process has been applied to improve anti-corrosion performance over the whole of the body work, and it is noted that zinc phosphate crystal converted by such treatment theoretically has an excellent quality reaction.
That is, when the dip method conversion treatment is applied a coating consisting mainly of phosphophyllite (Zn2Fe(PO4)2⋅4H2O) is found on cold-rolled steel, while on zinc coated steel, a hopeite coating (Zn3(PO4)2⋅4H2O) is found.
With a view to improve water proof ness and adhesion to zinc-coated steel, metal ions such as Mn2+ or Ni2+ were added to the treatment bath to alter the quality of the hopeite crystal. All these conversion coatings by the dip method were found to have stable properties under the paint coating, and to play an extremely important role in corrosion proofing the auto body.
It is also pointed out that the surface condition of the steel is key to phosphatability.
