Hexavalent chromium-free water-based surface treatment solution, surface-treated metal, and surface treatment method

Abstract

Provided is a hexavalent chromium-free water-based surface treatment solution used for treating metal surfaces. The hexavalent chromium-free water-based surface treatment solution comprises trivalent chromium ion, phosphate ion, sulfate ion, and colloidal silica, wherein the molar ratio of the phosphate ion to the trivalent chromium ion is 1.9-3.2 and the molar ratio of the sulfate ion to the trivalent chromium ion is 0.10-0.30.

1 . A hexavalent chromium-free water-based surface treatment solution for use in surface treatment of a metal,
 the hexavalent chromium-free water-based surface treatment solution comprising: trivalent chromium ions; phosphate ions; sulfate ions; and colloidal silica,   the hexavalent chromium-free water-based surface treatment solution having:   a molar ratio of the phosphate ions to the trivalent chromium ions of 1.9 or more and 3.2 or less; and   a molar ratio of the sulfate ions to the trivalent chromium ions of 0.10 or more and 0.30 or less.   
     
     
         2 . The hexavalent chromium-free water-based surface treatment solution according to  claim 1 , wherein the hexavalent chromium-free water-based surface treatment solution has a content of the trivalent chromium ions of 0.5 mass % or more and 10.0 mass % or less. 
     
     
         3 . The hexavalent chromium-free water-based surface treatment solution according to  claim 1 , wherein the hexavalent chromium-free water-based surface treatment solution has a molar ratio of the colloidal silica in terms of SiO 2  to the trivalent chromium ions of 0.30 or more and 2.00 or less. 
     
     
         4 . The hexavalent chromium-free water-based surface treatment solution according to  claim 1 , further comprising nickel ions,
 wherein the hexavalent chromium-free water-based surface treatment solution has a content of the nickel ions of 0.04 mass % or more and 4.00 mass % or less.   
     
     
         5 . The hexavalent chromium-free water-based surface treatment solution according to any one of  claim 1 , further comprising polyacrylic acid,
 wherein the hexavalent chromium-free water-based surface treatment solution has a content of the polyacrylic acid of 0.5 mass % or more and 30.0 mass % or less.   
     
     
         6 . The hexavalent chromium-free water-based surface treatment solution according to  claim 5 , further comprising an oxazoline group-containing polymer,
 wherein the hexavalent chromium-free water-based surface treatment solution has a content of the oxazoline group-containing polymer of 0.5 mass % or more and 5.0 mass % or less.   
     
     
         7 . The hexavalent chromium-free water-based surface treatment solution according to  claim 1 , wherein the hexavalent chromium-free water-based surface treatment solution has a pH of 1.0 or more and 4.0 or less. 
     
     
         8 . A surface-treated metal comprising: a metal; and a coating resulting from surface treatment of the metal with the hexavalent chromium-free water-based surface treatment solution according to  claim 1 . 
     
     
         9 . The surface-treated metal according to  claim 8 , further comprising a paint film on the coating. 
     
     
         10 . A surface treatment method comprising: surface-treating a metal with the hexavalent chromium-free water-based surface treatment solution according to  claim 1  to form a coating.