Methods of Characterizing Phosphate Coatings on Automotive Sheet Steels

A review is made of some of the existing methodologies for assessing phosphate characteristics on automotive sheet steels. Data obtained from on-line processing of zinc and zinc-iron substrates are presented comparing phosphate attributes to performance in the Chipping Corrosion Test. Phosphate characteristics measured were: crystal size; nickel content; coating weight; porosity; alkali solubility. A definitive relationship between these characteristics and chipping corrosion performance was not found.