Methods for treating the surfaces of aluminium alloys by means of formulations containing alkane sulfonic acid

Abstract

Aluminum or aluminum alloys are surface-treated by anodic oxidation (anodization) in an electrolyte containing from 3 to 30% by weight of an alkanesulfonic acid. Workpieces based on aluminum or aluminum alloys and produced by this process can be used in building and construction, in automobile or aircraft construction and in the packaging industry. An electrolyte composition containing from 3 to 30% by weight of an alkanesulfonic acid can be used in the anodic oxidation of aluminum or aluminum alloys (anodization) to increase the rate of anodic oxidation and to reduce the energy consumption.

We claim:  
     
         1 . A process for the surface treatment of aluminum or aluminum alloys by anodic oxidation of the aluminum or the aluminum alloys (anodization) using direct current in an electrolyte containing from 3 to 30% by weight of an alkanesulfonic acid.  
     
     
         2 . A process as claimed in  claim 1 , wherein the electrolyte comprises from 20 to 100 parts by weight of an alkanesulfonic acid and from 80 to 0 parts by weight of a further acid selected from among sulfuric acid, phosphoric acid and oxalic acid, where the sum of alkanesulfonic acid and the further acid is 100 parts by weight and the concentration of the alkanesulfonic acid is from 3 to 30% by weight of the electrolyte.  
     
     
         3 . A process as claimed in  claim 1  or  2 , wherein the alkanesulfonic acid is methanesulfonic acid.  
     
     
         4 . A process as claimed in any of  claims 1  to  3 , wherein the anodic oxidation is carried out at from 0 to 30° C.  
     
     
         5 . A process as claimed in any of  claims 1  to  4 , wherein the anodic oxidation is carried out in two stages, comprising: 
 preanodization of the aluminum or the aluminum alloy in an electrolyte comprising sulfuric acid as sole acid or a mixture of sulfuric acid and oxalic acid,  
 oxidation in an electrolyte comprising an alkanesulfonic acid as claimed in any of  claims 1  to  3 .  
 
     
     
         6 . A process for the surface treatment of aluminum or aluminum alloys, comprising the following steps: 
 a) pretreatment of the aluminum or the aluminum alloy;    b) anodic oxidation by a process as claimed in  claims 1  to  5  (anodization);    c) if desired, coloration of the oxidized surface of the aluminum or the aluminum alloys;    d) after-treatment of the workpiece obtained after steps a), b) and, if employed, c);    e) if desired, recovery of the alkanesulfonic acid used and/or its salts, where step e) can follow or be carried out in parallel with any step in which an alkanesulfonic acid can be used, in particular the steps b) and/or, if employed, c).    
     
     
         7 . A process as claimed in  claim 6 , wherein solutions comprising alkanesulfonic acids are also used in the pretreatment of the aluminum or the aluminum alloys in step a).  
     
     
         8 . A process as claimed in  claim 6  or  7 , wherein the coloration of the oxidized surface of the aluminum or the aluminum alloys in step c) is carried out by an electrolytic process in an electrolyte comprising metal salts.  
     
     
         9 . A process as claimed in  claim 8 , wherein a gold color of the oxidized surface of the aluminum or the aluminum alloys is achieved in an electrolyte comprising silver salts, if desired in admixture with tin salts and/or copper salts.  
     
     
         10 . A process as claimed in  claim 8  or  9 , wherein the electrolyte comprising metal salts comprises from 20 to 100 parts by weight of an alkanesulfonic acid and from 80 to 0 parts by weight of sulfuric acid, where the sum of alkanesulfonic acid and sulfuric acid is 100% by weight and makes up from 0.1 to 20% by weight of the electrolyte.  
     
     
         11 . The use of an alkanesulfonic acid in a process for the anodic oxidation of aluminum or aluminum alloys (anodization) using direct current to increase the rate of anodic oxidation and to reduce the energy consumption  
     
     
         12 . An electrolyte composition consisting of from 20 to 100 parts by weight of an alkanesulfonic acid and from 80 to 0 parts by weight of a further acid selected from among sulfuric acid, phosphoric acid and oxalic acid, where the sum of alkanesulfonic acid and further acid is 100 parts by weight and the concentration of the alkanesulfonic acid is from 3 to 30% by weight of the electrolyte, water and optionally further additives such as aluminum sulfate.  
     
     
         13 . An electrolyte composition as claimed in  claim 12 , wherein the alkanesulfonic acid is methanesulfonic acid.  
     
     
         14 . The use of workpieces with a surface based on aluminum or aluminum alloys, wherein the surface was treated by a process as claimed in any of  claims 1  to  10 , in building and construction, in particular for producing window profiles or components of exterior walls, in automobile or aircraft construction and in the packaging industry, in particular for producing cans.