PURPOSE: To form an under coat for coating with superior corrosion resistance and superior adhesion to a film on the surface of Al, Mg or their alloy by treating the surface with a warm aqueous soln. contg. a specified metallic salt, imidazole, etc.
CONSTITUTION: In order to form each under coat for coating with superior corrosion resistance and superior adhesion of coating, the surfaces of parts made of Al, Mg or their alloy are treated with a treating soln. at 40W90°C for 3W120min. The treating soln. is an aqueous soln. contg. 1 or ≥2 kinds of Ti salts such as titanium fluoride or Zr salts such as zirconium fluoride by 0.01W20g/l as metal and imidazole or 1 or ≥2 kinds of imidazole derivs. such as 2-methylimidazole by 0.01W50g/l or further contg. an oxidizing agent such as nitric acid, hydrogen peroxide or potassium permanganate by 0.01W100g/l. Thus, each under coat comparable with a chromate coat in characteristics can be formed without causing environmental pollution.
ENDOU RIYOUJI
KOSAKA TAISUKE
