Method for coating metal surfaces

Abstract

A method for coating a light metal alloy component to form a protective layer comprising Sn. First, a surface of the light metal alloy component is cleaned and passivated. A layer comprising Zn is formed on the surface, and a layer comprising Sn is deposited. An intermediate layer is preferably deposited between the Zn-containing layer and the Sn containing layer. The Sn-containing layer may additionally be varnished.

What is claimed is:  
     
         1 . A method for coating a metallic surface comprising: 
 cleaning and passivating a surface of a light metal alloy component;    forming a first layer on the cleaned and passivated surface wherein the first layer comprises Zn; and    forming a second layer which comprises Sn such that the first layer is located between the surface of the light metal alloy component and the second layer.    
     
     
         2 . The method according to  claim 1  wherein the cleaning and passivating step comprises: 
 alkaline degreasing the surface of the light metal alloy component; and  
 performing an acid treatment of the surface to oxidatively produce a passivation layer on the surface, the acid treatment comprising contacting the surface with a solution which is selected from a group consisting of an acidic solution, a solution comprising the salt of an acid, and combinations thereof.  
 
     
     
         3 . The method according to  claim 2  wherein the light metal alloy comprises Mg.  
     
     
         4 . The method according to  claim 3  wherein the acid treatment step comprises: 
 contacting the surface of the light metal alloy component with a weak acidic solution; and  
 contacting the surface with a strong acidic solution which comprises fluoride ions.  
 
     
     
         5 . The method according to  claim 4  wherein the light metal alloy has a Mg composition of at least about 50 weight %.  
     
     
         6 . The method according to  claim 5  wherein the weak acidic solution has a pH of from about 3 to about 5.  
     
     
         7 . The method according to  claim 5  wherein the weak acidic solution comprises a carboxylic acid and a pyrophosphate.  
     
     
         8 . The method according to  claim 5  wherein the strong acidic acid solution has a pH of from about 0.5 to about 2.  
     
     
         9 . The method according to  claim 5  wherein the strong acidic acid solution comprises phosphoric acid and ammonium bifluoride.  
     
     
         10 . The method according to  claim 5  wherein the weak acidic solution has a pH of from about 3 to about 5 and the strong acidic acid solution has a pH of from about 0.5 to about 2.  
     
     
         11 . The method according to  claim 5  wherein the weak acidic solution comprises a carboxylic acid and a pyrophosphate and wherein the strong acidic acid solution comprises phosphoric acid and ammonium bifluoride.  
     
     
         12 . The method according to  claim 5  wherein the weak acidic solution has a pH of from about 3 to about 5 and comprises a carboxylic acid and a pyrophosphate and wherein the strong acidic acid solution has a pH of from about 0.5 to about 2 and comprises phosphoric acid and ammonium bifluoride.  
     
     
         13 . The method according to  claim 2  wherein the light metal alloy comprises Al.  
     
     
         14 . The method according to  claim 13  wherein the acid treatment step comprises contacting the surface of the light metal alloy component with a strong oxidizing solution.  
     
     
         15 . The method according to  claim 14  wherein the light metal alloy has an Al composition of at least about 60 weight %.  
     
     
         16 . The method according to  claim 15  wherein the strong oxidizing solution comprises an oxidizer selected from the group consisting of nitric acid, peroxomonosulfuric acid, and a persulfate solution.  
     
     
         17 . The method according to  claim 1  wherein the cleaning and passivating of the surface of the light metal alloy component comprises: 
 anodically connecting the surface to an electrical source; and  
 contacting the surface with a solution which comprises phosphoric acid and an alcohol.  
 
     
     
         18 . The method according to  claim 17  wherein the light metal alloy comprises a metal selected from the group consisting of Mg, Si, and combinations thereof.  
     
     
         19 . The method according to  claim 18  wherein the light metal alloy has a Mg composition of at least about 50 weight %.  
     
     
         20 . The method according to  claim 18  wherein the light metal alloy has a Si composition of at least about 0.1 weight %.  
     
     
         21 . The method according to  claim 18  wherein the cleaning and passivating step comprises contacting the anodically connected surface with a solution that comprises phosphoric acid and fluoride ions.  
     
     
         22 . The method according to  claim 17  wherein the light metal alloy comprises Al.  
     
     
         23 . The method according to  claim 22  wherein the light metal alloy has an Al composition of at least about 60 weight %.  
     
     
         24 . The method according to  claim 22  wherein the cleaning and passivating step comprises contacting the surface of the light metal alloy component with an aqueous oxidation agent.  
     
     
         25 . The method according to  claim 1  wherein the first layer is formed by chemical metal plating.  
     
     
         26 . The method according to  claim 1  wherein the first layer further comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         27 . The method according to  claim 1  wherein the second layer is formed by electrolytic deposition.  
     
     
         28 . The method according to  claim 1  wherein the second layer further comprises a metal selected from the group consisting of Zn, Bi, Pb, and combinations thereof.  
     
     
         29 . The method according to  claim 1  further comprising forming an intermediate layer such that the intermediate layer is located between the first layer and the second layer.  
     
     
         30 . The method according to  claim 29  wherein the intermediate layer is formed by electrolytic deposition.  
     
     
         31 . The method according to  claim 29  wherein the intermediate layer comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         32 . The method according to  claim 1  further comprising depositing varnish layer on the second layer wherein the varnish layer comprises a varnish.  
     
     
         33 . The method according to  claim 32  wherein the varnish is a two-component varnish.  
     
     
         34 . The method according to  claim 32  further comprising performing a passivating treatment on the second layer prior to depositing the varnish layer.  
     
     
         35 . The method according to  claim 34  wherein the passivating treatment comprises an alkaline anodic oxidation.  
     
     
         36 . The method according to  claim 35  wherein the passivating treatment comprises contacting the second layer with a solution comprising a compounds selected from the group consisting of phosphates, carbonates, and combinations thereof.  
     
     
         37 . The method according to  claim 35  wherein the passivating treatment further comprises a cathodic treatment wherein the second layer is contacted with a solution comprising hexavalent chromium ions.  
     
     
         38 . The method according to  claim 32  further comprising removing a portion of the varnish layer to expose a portion of the second layer.  
     
     
         39 . The method according to  claim 38  wherein the portion of the varnish layer is removed by bombarding the varnish layer with a laser beam.  
     
     
         40 . The method according to  claim 39  wherein the varnish layer is bombarded by the laser beam at least twice to remove the portion of the varnish layer.  
     
     
         41 . A method for coating a metallic surface comprising: 
 alkaline degreasing the surface of a light metal alloy component, wherein the light metal alloy component has a Mg composition of at least about 50 weight %;    performing an acid treatment of the surface to oxidatively produce a passivation layer on the surface, the acid treatment comprising: 
 contacting the surface of the light metal alloy component with a weak acidic solution having a pH of from about 3 to about 5; and  
 contacting the surface with a strong acidic solution which has a pH of from about 0.5 to about 2 which comprises fluoride ions;  
   forming a first layer on the cleaned and passivated surface wherein the first layer comprises Zn; and    forming a second layer which comprises Sn such that the first layer is located between the surface of the light metal alloy component and the second layer.    
     
     
         42 . The method according to  claim 41  further comprising forming an intermediate layer such that the intermediate layer is located between the first layer and the second layer.  
     
     
         43 . The method according to  claim 42  wherein the intermediate layer is formed by electrolytic deposition.  
     
     
         44 . The method according to  claim 42  wherein the intermediate layer comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         45 . A method for coating a metallic surface comprising: 
 contacting a surface of a light metal alloy component with an aqueous oxidation agent, wherein the light metal alloy component has an Al composition of at least about 60 weight %;    forming a first layer on the surface wherein the first layer comprises Zn; and    forming a second layer which comprises Sn such that the first layer is located between the surface of the light metal alloy component and the second layer.    
     
     
         46 . The method according to  claim 45  further comprising forming an intermediate layer such that the intermediate layer is located between the first layer and the second layer.  
     
     
         47 . The method according to  claim 46  wherein the intermediate layer is formed by electrolytic deposition.  
     
     
         48 . The method according to  claim 46  wherein the intermediate layer comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         49 . A coating for a light metal alloy comprising: 
 a first layer comprising Zn wherein the first layer is deposited on a surface of the light metal alloy component; and    a second layer comprising Sn,    wherein the first layer is located between the surface of the light metal alloy component and the second layer.    
     
     
         50 . The coating according to  claim 49  wherein the light metal alloy comprises Mg.  
     
     
         51 . The coating according to  claim 49  wherein the light metal alloy comprises Al.  
     
     
         52 . The coating according to  claim 49  wherein the first layer is formed by is formed by chemical metal plating.  
     
     
         53 . The coating according to  claim 49  wherein the first layer further comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         54 . The coating according to  claim 49  wherein the second layer is formed by electrolytic deposition.  
     
     
         55 . The coating according to  claim 49  wherein the second layer further comprises a metal selected from the group consisting of Zn, Bi, Pb, and combinations thereof.  
     
     
         56 . The coating according to  claim 49  further comprising an intermediate layer wherein the intermediate layer is located between the first layer and the second layer.  
     
     
         57 . The coating according to  claim 56  wherein the intermediate layer is formed by electrolytic deposition.  
     
     
         58 . The coating according to  claim 56  wherein the intermediate layer comprises a metal selected from the group consisting of Cu, Ni, and combinations thereof.  
     
     
         59 . The coating according to  claim 49  further comprising a varnish layer which comprises a varnish wherein the second layer is located between the first layer and the varnish layer.