Method for cleaning and passivating a metal surface

Abstract

A surface of a light-metal alloy is anodically polarized in a cleaning process. The surface is cleaned with a solution containing phosphoric acid, alcohol, and optionally fluoride. Additionally, the surface is passivated in an oxidizing process using, for example, fluoride ions or an aqueous oxidizing agent. Preferably, the light-metal alloy has a relatively high Al or Mg content. This method is suitable for preparing the surface for a subsequent coating operation.

What is claimed is:  
     
         1 . A method for cleaning and passivating a metallic surface comprising the steps of: 
 cleaning a surface of a light-metal alloy with a solution comprising phosphoric acid and an alcohol, wherein the alloy is anodically polarized; and    passivating the surface in an oxidizing step.    
     
     
         2 . The method according to  claim 1  wherein the cleaning solution has a phosphoric acid content which ranges from about 30 to about 90 percent by volume.  
     
     
         3 . The method according to  claim 2  wherein the phosphoric acid comprises H 3 PO 4  in a concentration ranging from about 50 to about 95 percent by weight.  
     
     
         4 . The method according to  claim 3  wherein the cleaning solution consists essentially of phosphoric acid and alcohol.  
     
     
         5 . The method according to  claim 1  further wherein the surface is passivated by contacting the surface with fluoride ions.  
     
     
         6 . The method according to  claim 5  wherein the light-metal alloy has a Si content of at least about 0.1 percent by weight.  
     
     
         7 . The method according to  claim 5  wherein the light-metal alloy has an Mg content of at least 50 percent by weight.  
     
     
         8 . The method according to  claim 5  wherein the cleaning solution further comprises fluoride ions.  
     
     
         9 . The method according to  claim 8  wherein the cleaning solution has a fluoride content which ranges from about 0.1 to about 10 percent by weight.  
     
     
         10 . The method according to  claim 5  wherein the cleaning solution has a phosphoric acid content which ranges from about 30 to about 90 percent by volume.  
     
     
         11 . The method according to  claim 10  wherein the phosphoric acid comprises H 3 PO 4  in a concentration ranging from about 50 to about 95 percent by weight.  
     
     
         12 . The method according to  claim 11  wherein the cleaning solution consists essentially of phosphoric acid, alcohol, and fluoride.  
     
     
         13 . The method according to  claim 2  wherein the surface is contacted with a second solution comprising phosphoric acid and fluoride ions subsequent to the cleaning step.  
     
     
         14 . The method according to  claim 13  wherein the second solution further comprises an alcohol.  
     
     
         15 . The method according to  claim 13  wherein the solution has a fluoride content which ranges from about 0.1 to about 10 percent by weight.  
     
     
         16 . The method according to  claim 13  wherein the solution has a phosphoric acid content which ranges from about 30 to about 90 percent by volume.  
     
     
         17 . The method according to  claim 13  wherein the phosphoric acid comprises H 3 PO 4  in a concentration ranging from about 50 to about 95 percent by weight.  
     
     
         18 . The method according to  claim 1  wherein the light-metal alloy has an Al content of at least about 60 percent by weight and wherein the surface is passivated by oxidizing the surface with an aqueous oxidizing agent subsequent to the cleaning step.  
     
     
         19 . The method according to  claim 1  further comprising a final alkaline rinsing step.  
     
     
         20 . The method according to  claim 1  wherein the alloy is anodically polarized with a current density which ranges from about 10 to about 500 A/m 2 .  
     
     
         21 . The method according to  claim 1  wherein the solution has a temperature which ranges from about 10° C. to about 40° C.  
     
     
         22 . The method according  claim 1  wherein the cleaning and passivating steps are performed in a time period ranging from about 10 seconds to about 5 minutes.  
     
     
         23 . The method according  claim 1  wherein the light-metal alloy surface has not undergone a preliminary chemical treatment prior to the cleaning and passivating steps.  
     
     
         24 . The method according  claim 1  wherein the light-metal alloy is a regenerated material.  
     
     
         25 . A method for coating a metallic surface comprising the steps of: 
 cleaning a surface of a light-metal alloy with a solution comprising phosphoric acid and an alcohol, wherein the alloy is anodically polarized;    passivating the surface in an oxidizing step; and    coating the surface after the cleaning and passivating steps.    
     
     
         26 . The method according to  claim 25  in which the coating is carried out by means of electroless metal plating.