Method for coating metallic surfaces

Abstract

The invention relates to a method for treating or pre-treating parts, profiled-pieces, strips, sheet metals and/or wires having metallic surfaces, in which at least 5% of these surfaces consists of aluminum and/or of at least one aluminum alloy and, optionally, the remaining metallic surfaces can predominantly consist of iron alloys, zinc and/or zinc alloys. The treatment involves the use of an acid aqueous solution, which contains fluoride, zinc and phosphate and which has the following dissolved contents in the phosphatizing solution: sodium virtually none or in a concentration ranging from 0.04 to less than 2 g/L; potassium virtually none or in a concentration ranging from 0.025 to 2.5 g/L; sodium and potassium in a concentration ranging from 0.025 to 2.5 g/L as sodium, whereby the potassium content is converted to sodium on a molar basis; zinc in a concentration ranging from 0.2 to 4 g/L; phosphate in a concentration ranging from 4 to 65 g/L and calculated as PO 4 ; free fluoride in a concentration ranging from 0.03 to 0.5 g/L, and; total fluoride in a concentration ranging from 0.1 to 5 g/L. A zinc-containing phosphate layer is thereby deposited onto the metallic surfaces with a layer weight ranging from 0.5 to 10 g/m 2 .

1 - 19 . (canceled)  
     
     
         20 . A process comprising: 
 applying an aqueous, acidic solution having dissolved contents to a metallic surface, said metallic surface comprising at least 5% by weight of at least one of aluminum or an aluminum alloy, wherein the dissolved contents in the phosphating solution comprise:    virtually no sodium or a concentration of sodium in the range of at least 0.04 g/l,    virtually no potassium or a concentration of potassium in the range of at least 0.025 g/l,    wherein the concentrations of sodium and potassium together is in the range of 0.3 to 1.8 g/l as sodium, the potassium content being converted to sodium on a molar basis;    zinc in a concentration range of 0.2 to 4 g/l;    phosphate in a concentration range of 4 to 65 g/l, calculated as PO 4 ;    free fluoride in a concentration range of 0.03 to 0.5 gl;    total fluoride in the concentration range of 0.1 to 5 g/l;    wherein no or almost no precipitation product based on aluminium fluorocomplexes of ammonium, alkali metal or alkaline-earth metal is deposited on said metallic surface, below the phosphate film and/or between the zinc phosphate crystals in the phosphate film on the surfaces of aluminium or at least one aluminium alloy phosphated in this way and wherein a zinc-containing phosphate film is deposited on the metallic surfaces and has a coating weight in the range of 0.5 to 10 g/m 2 .    
     
     
         21 . The process according to  claim 20 , wherein the contents of dissolved aluminium in the phosphating solution are in the concentration range of 0.002 to 1 g/l.  
     
     
         22 . The process according to  claim 20 , wherein the total content of silicon complex fluoride and boron complex fluoride together in the phosphating solution is 0.01 to 8 g/l—optionally converted on a molar basis as SiF 6 , wherein the two groups of fluoride complexes may optionally both be present at the same time.  
     
     
         23 . The process according to  claim 20 , wherein the content of complex bound fluoride in the phosphating solution is from 0.01 to 8 g/l, calculated on a molar basis as SiF 6 .  
     
     
         24 . The process according to  claim 20 , wherein the contents dissolved in the phosphating solution are as follows: 
 sodium: in the concentration range of 0.050 to 2 g/l,    potassium: virtually none or in the concentration range of 0.030 to 1.5 g/l,    sodium and potassium: in the concentration range of 0.025 to 1.5 g/l as sodium, potassium being converted to sodium on a molar basis,    silicon complex fluoride: in the concentration range of 0.01 to 4 g/l and/or    boron complex fluoride: in the concentration range of 0.01 to 4 g/l, calculated as SiF 6  and BF 4  respectively.    
     
     
         25 . The process according to  claim 20 , wherein at least one of the contents in the phosphating solution are as follows: 
 sodium: virtually none or in the concentration range of 0.060 to 1.8 g/l;    potassium: in the concentration range of 0.035 to 1.4 g/l;    potassium: in the concentration range of 0.035 to 1.4 g/l;    sodium and potassium: in the concentration range of 0.05 to 2 g/l as sodium, potassium being converted to sodium on a molar basis;    silicon complex fluoride: in the concentration range of 0.02 to 1 g/l or    boron complex fluoride: in the concentration range of 0.02 to 3 g/l, calculated as SiF 6  and BF 4  respectively.    
     
     
         26 . The process according to  claim 20 , wherein the dissolved contents comprise at least one of nickel: virtually none or in the range of 0.001 to 3 g/l or manganese: virtually none or in the range of 0.002 to 5 g/l.  
     
     
         27 . The process according to  claim 20 , wherein the dissolved contents comprise at least one of 
 dissolved iron 2+  ions: virtually none or in the concentration range of 0.005 to 3 g/l or    complexed iron 3+  ions: virtually none or in the concentration range of 0.005 to 1 g/l.    
     
     
         28 . The process according to  claim 20 , wherein the dissolved contents comprises at lest one of: 
 silver: virtually none or in the concentration range of 0.001 to 0.080 g/l or    copper: virtually none or in the concentration range of 0.001 to 0.050 g/l.    
     
     
         29 . The process according to  claim 20 , wherein the dissolved contents comprises at least one of: 
 titanium: virtually none or in the concentration range of 0.001 to 0.200 g/l or    zirconium: virtually none or in the concentration range of 0.001 to 0.200 g/l.    
     
     
         30 . The process according to  claim 20 , wherein the dissolved contents comprise at least one of: 
 ammonium: virtually none or in the concentration range of 0.01 to 50 g/l or    nitrate: virtually none or in the concentration range of 0.01 to 30 g/l.    
     
     
         31 . The process according to  claim 20 , wherein the dissolved contents comprise at least one of: 
 sulfate: virtually none or in the concentration range of 0.005 to 5 g/l or    chloride: virtually none or in the concentration range of 0.020 to 0.5 g/l.    
     
     
         32 . The process according to  claim 20 , wherein the phosphating solution comprises at least one accelerator selected from the group consisting of a compounds or ions based on 
 nitrogen-containing compounds in the concentration range of 0.01 to 8 g/l;    chlorate in the concentration range of 0.01 to 6 g/l;    hydroxylamine in the concentration range of 0.01 to 3 g/l; and    peroxide, including water-soluble organic peroxide, in the concentration range of 0.001 to 0.200 g/l, calculated as H 2 O 2 .    
     
     
         33 . The process according to  claim 20 , wherein the content of magnesium in the phosphating solution is not more than 1 g/l.  
     
     
         34 . The process according to  claim 33 , wherein the contents of the magnesium is not more than 0.15 g/l.  
     
     
         35 . The process according to  claim 20 , wherein the pH is in the range of 2 to 4.  
     
     
         36 . The process according to  claim 20 , wherein the content of free acid determined with KCl is in the range of 0.3 to 6 points, the content of dilute total acid is in the range of 8 to 70 points or the content of total acid according to Fischer is in the range of 4 to 50 points.  
     
     
         37 . The process according to  claim 20 , wherein the phosphate coating is applied at a temperature of from 20 to 70° C.  
     
     
         38 . The process of  claim 20 , wherein the surface is a body part for an automobile or an aircraft, a sheet, a wire mesh, or a small plant