Trivalent chromium chemical conversion treatment liquid for zinc or zinc alloy base and chemical conversion treatment method using the same

Abstract

An object is to provide a trivalent chromium chemical conversion treatment liquid for a zinc or zinc alloy base capable of forming an environmentally-friendly chemical conversion coating with high corrosion resistance. The present invention provides a hexavalent chromium-free trivalent chromium chemical conversion treatment liquid for zinc or zinc alloy, the liquid comprising trivalent chromium ions, zirconium ions, nitrate ions, and chain colloidal silica, in which the pH of the treatment liquid is 2.5 to 5.0.

1 . A hexavalent chromium-free trivalent chromium chemical conversion treatment liquid for zinc or zinc alloy comprising trivalent chromium ions, zirconium ions, nitrate ions, and chain colloidal silica, wherein
 the pH of the treatment liquid is 2.5 to 5.0.   
     
     
         2 . The chemical conversion treatment liquid according to  claim 1 , wherein the treatment liquid has a trivalent chromium ion concentration in a range of 2 to 200 mmol/L and a zirconium ion concentration in a range of 1 to 300 mmol/L. 
     
     
         3 . The chemical conversion treatment liquid according to  claim 1 , wherein the treatment liquid has a chain colloidal silica concentration in a range of 25 to 600 mmol/L. 
     
     
         4 . The chemical conversion treatment liquid according to  claim 1 , wherein the treatment liquid has a nitrate ion concentration in a range of 30 to 400 mmol/L. 
     
     
         5 . The chemical conversion treatment liquid according to  claim 1 , wherein a molar ratio of trivalent chromium ions to zirconium ions (trivalent chromium ions/zirconium ions) is 0.1 to 4. 
     
     
         6 . The chemical conversion treatment liquid according to  claim 1 , wherein the treatment liquid does not contain cobalt ions. 
     
     
         7 . A chemical conversion treatment method comprising bringing the chemical conversion treatment liquid according to  claim 1  into contact with a zinc or zinc alloy surface. 
     
     
         8 . The chemical conversion treatment liquid according to  claim 1 , wherein the content of trivalent chromium ions in the treatment liquid is 2 to 200 mmol/L. 
     
     
         9 . The chemical conversion treatment liquid according to  claim 1 , wherein the content of zirconium ions in the treatment liquid is 1 to 300 mmol/L. 
     
     
         10 . The chemical conversion treatment liquid according to  claim 1 , wherein the average particle size of the primary particles of the chain colloidal silica is 5 to 20 nm. 
     
     
         11 . The chemical conversion treatment liquid according to  claim 1 , wherein the primary particles of the chain colloidal silica are bound in a link having a length of 20 to 200 nm. 
     
     
         12 . The chemical conversion treatment liquid according to  claim 1 , further comprising cobalt ions in the content of 300 mmol/L or less. 
     
     
         13 . The chemical conversion treatment liquid according to  claim 1 , further comprising fluoride ions in the content of 6 to 1800 mmol/L. 
     
     
         14 . The chemical conversion treatment liquid according to  claim 1 , further comprising one or more water-soluble carboxylic acids or salts thereof in the content of 0.1 g/L to 10 g/L. 
     
     
         15 . The chemical conversion treatment liquid according to  claim 1 , further comprising one or more water-soluble metal salts containing a metal selected from the group consisting of Zn, Al, Ti, Mo, V, Ce, and W in the content of 0.1 g/L to 10 g/L. 
     
     
         16 . The chemical conversion treatment liquid according to  claim 1 , further comprising one or more phosphorus compounds in the content of 0.01 g/L to 1.0 g/L. 
     
     
         17 . The chemical conversion treatment liquid according to  claim 1 , further comprising cobalt ions in the content of 300 mmol/L or less; fluoride ions in the content of 6 to 1800 mmol/L; one or more water-soluble carboxylic acids or salts thereof in the content of 0.1 g/L to 10 g/L; one or more water-soluble metal salts containing a metal selected from the group consisting of Zn, Al, Ti, Mo, V, Ce, and W in the content of 0.1 g/L to 10 g/L; and one or more phosphorus compounds in the content of 0.01 g/L to 1.0 g/L, wherein the residue is water.