Hard, corrosion resistant passivate film on zinc etc. - using trivalent chromium, organic acid and another metal salt, esp. cerium

摘要

Chromate passivate film is imparted to a receptive metal surface by treating it with an aq. acidic compsn. contg. trivalent Cr ions, an org. acid of formula (OH)aR(COOH)b (where a is 0-6; b is 1-3 and R is 1-6 alkyl, alkenyl or aryl) and additional metal ions which are at least one of Fe, Co, Ni, Mo, Mn, La, Ce and lanthanide mixt. The metal surface is esp. Zn or Cd but can also be Al or Mg or alloys of any of these. The process gives improved corrosion resistance and initial hardness compared with processes using chromate. A clear bright to light blue-bright finish is obt. except when Ce is used in which case a yellow iridescent appearance results.