Processes and compositions for improving corrosion performance of zirconium oxide pretreated zinc surfaces

Abstract

A method of improving corrosion resistance of a metal substrate comprising a zinc surface coated with zirconium oxide conversion coating by, prior to conversion coating, contacting the zinc surface with a composition comprising: a) iron(III) ions, b) a source of hydroxide ion; c) at least one complexing agent selected from organic compounds which have at least one functional group —COOX, wherein X represents either a H or an alkali and/or alkaline earth metal; d) 0.0 to about 4 g/l cobalt (II) ions; and optionally e) a source of silicate: wherein the composition has a pH of at least 10.

What is claimed is: 
     
         1 . A coated metal article coated according to a method comprising steps of:
 1.) providing a metal substrate comprising at least one zinc or zinc alloy surface;   2.) contacting said one at least one zinc or zinc alloy surface with an alkaline pre-rinse composition comprising:
 a) iron(III) ions, 
 b) a source of hydroxide ion; 
 c) at least one complexing agent selected from organic compounds which have at least one functional group —COOX, wherein X represents either a H or an alkali and/or alkaline earth metal; 
 d) 0.0 to about 4 g/l cobalt (II) ions; and 
 optionally 
 e) a source of silicate: 
 wherein the composition has a pH of at least 10; 
   3.) optionally rinsing said surface;   4.) applying to the metal substrate a zirconium-based metal pretreatment coating composition comprising zirconium, thereby forming a zirconium oxide coating on all surfaces of the metal substrate including said at least one zinc or zinc alloy surface resulting in a zirconium oxide conversion coated substrate; and   5.) optionally applying a paint to the metal pretreatment coated metal substrate.   
     
     
         2 . The coated metal article of  claim 1  wherein contact time of step 2.) is from 2 to 60 seconds and the alkaline pre-rinse composition has a temperature of 85 to 125 degrees F. 
     
     
         3 . The coated metal article of  claim 1  wherein the iron(III) ions are present in the alkaline pre-rinse composition in an amount of about 5 ppm to about 400 ppm; and the source of hydroxide ion is present in an amount of about 0.5 g/l to about 4.0 g/l. 
     
     
         4 . The coated metal article of  claim 1  wherein the metal pretreatment coated metal substrate comprises iron on the at least one zinc or zinc alloy surface and/or in the zirconium oxide coating. 
     
     
         5 . The coated metal article of  claim 1  wherein the cobalt (II) ions are present in the alkaline pre-rinse composition in an amount of 1 ppm up to the solubility limit of the cobalt (II) ions. 
     
     
         6 . The coated metal article of  claim 5  wherein the metal pretreatment coated metal substrate comprises cobalt and iron on the at least one zinc or zinc alloy surface and/or in the zirconium oxide coating. 
     
     
         7 . The coated metal article of  claim 1  wherein the alkaline pre-rinse composition is phosphate-free. 
     
     
         8 . The coated metal article of  claim 1  wherein the zirconium-based metal pretreatment coating composition further comprises fluoride and a chelating agent. 
     
     
         9 . The coated metal article of  claim 1  wherein the zirconium-based metal pretreatment coating composition comprises 50 to 300 ppm of dissolved Zr, 0 to 50 ppm of dissolved Cu, 0 to 100 ppm of SiO 2 , 150 to 2000 ppm of total Fluoride, 10 to 100 ppm of free Fluoride and optionally a chelating agent. 
     
     
         10 . A coated metal article comprising:
 A) a steel substrate;   B) a first layer comprising a zinc or zinc alloy metal surface deposited on the steel substrate;   C) a phosphate-free second layer comprising iron, and optionally cobalt, deposited on said zinc or zinc alloy metal surface;   D) a third layer comprising a zirconium oxide conversion coating; and   E) a fourth layer comprising at least one paint applied to the zirconium oxide conversion coating;
 wherein said coated metal article having a coating of the first, second, third and fourth layers has better resistance to cyclic corrosion than a comparative metal article coated with the first layer, the third layer and the paint in the absence of the second layer. 
   
     
     
         11 . The coated metal article of  claim 10  wherein the fourth layer is an electrodeposition paint. 
     
     
         12 . The coated metal article of  claim 10  further comprising at least one of a primer and a basecoat paint layer applied to the fourth layer. 
     
     
         13 . The coated metal article of  claim 12  further comprising a clearcoat paint layer applied to the primer or basecoat paint layer. 
     
     
         14 . The coated metal article of  claim 10  wherein said coating comprises iron on the at least one zinc or zinc alloy surface and/or in the zirconium oxide coating. 
     
     
         15 . The coated metal article of  claim 10  wherein the coating comprises cobalt and iron on the at least one zinc or zinc alloy surface and/or in the zirconium oxide coating. 
     
     
         16 . The coated metal article of  claim 10  wherein the first and second layers are phosphate-free. 
     
     
         17 . A coated metal article comprising:
 A) a metal substrate comprising at least one zinc or zinc alloy surface;   B) a phosphate-free layer comprising iron, and optionally cobalt, deposited on said zinc or zinc alloy metal surface;   C) a zirconium oxide conversion coating layer deposited on B); and   D) a paint applied to the zirconium oxide conversion coating layer;   
       wherein said coated metal article has better resistance to cyclic corrosion than a comparative metal article coated similarly coated in the absence of B). 
     
     
         18 . The coated metal article of  claim 17  wherein the paint comprises one or more paint layers selected from an electrodeposition paint layer, a primer layer, a basecoat paint layer and a clearcoat paint layer. 
     
     
         19 . The coated metal article of  claim 17  wherein the metal substrate further comprises at least one cold rolled steel surface. 
     
     
         20 . The coated metal article of  claim 17  wherein the metal substrate is a hot dip galvanized or electro galvanized steel substrate.