Continuous surface treatment for coils made of aluminum alloys sheets

Abstract

The invention relates to a continuous coil surface treatment process suitable for both a coil of a 5XXX aluminum alloy sheet and of a 6XXX aluminum alloy sheet. The process comprises the successive steps of etching the surface with a fluorine-free acidic solution; rinsing with deionized water; applying a conversion solution comprising titanium and zirconium, and drying. The invention surface treatment method is environmentally friendly and enables the production of the treated surfaces in an efficient and reliable manner for both 5XXX and 6XXX alloys. It is particularly adapted for the production of aluminum alloy sheets for the automotive industry.

1 . A continuous coil surface treatment process suitable for both a coil of a 5XXX aluminum alloy sheet and of a 6XXX aluminum alloy sheet having a surface, said process successively comprising:
 a) optionally cleaning the surface of the aluminum alloy sheet;   b) etching the surface of the optionally cleaned aluminum alloy sheet with a fluorine-free acidic solution;   c) rinsing the surface of the etched aluminum alloy sheet with deionized water;   d) applying to the surface of the etched aluminum alloy sheet a conversion solution comprising titanium and zirconium, with a zirconium to titanium weight ratio of from about 3.0 to about 5.0 optionally from 3.2 to 4.0;   e) optionally rinsing the surface of the converted aluminum alloy sheet with deionized water; and,   f) drying the surface of the aluminum alloy sheet.   
     
     
         2 . The process of  claim 1 , wherein the conversion solution comprises titanium and zirconium, with a titanium content of from about 20 to about 200 mg/l and optionally of from 60 to 140 mg/l. 
     
     
         3 . The process of  claim 1  wherein the conversion solution comprises hexafluotitanic acid, hexafluozirconic acid, hydrofluoric acid and optionally ammonium hydrogendifluoride. 
     
     
         4 . The process of  claim 1 , wherein the fluorine-free acidic solution comprises sulfuric acid, nitric acid, phosphoric acid, or mixtures thereof. 
     
     
         5 . The process of  claim 1 , wherein the concentration of sulfuric acid of the fluorine-free acidic solution is from about 2 g/l to about 60 g/l, optionally from 15 g/l to 50 g/l. 
     
     
         6 . The process of  claim 1 , wherein the aluminum alloy sheet is made from an aluminum alloy selected from the group consisting of AA5754, AA5182, AA6451, AA6005, AA6605, AA6005A, AA6016, AA6116, AA6022, AA6013, AA6056, AA6156, AA6111 and AA6014. 
     
     
         7 . The process of  claim 1 , wherein the applying in (d) is performed by immersing the aluminum alloy sheet in the conversion solution. 
     
     
         8 . The process of  claim 1 , wherein the applying in (d) is performed by spraying the aluminum alloy sheet with the conversion solution. 
     
     
         9 . The process of  claim 1 , wherein the etching in (b) is performed by spraying the aluminum alloy sheet with the fluorine-free acidic solution. 
     
     
         10 . The process of  claim 1 , wherein the fluorine-free acidic solution in (b) comprises less than about 2 g/l of aluminum ions and magnesium ions. 
     
     
         11 . The process of  claim 1 , wherein the fluorine-free acidic solution, comprises one or more surfactant additives or accelerators and is used at a temperature of from about 55° C. to about 85° C. for a period of about 5 to about 30 seconds.