Electrolyte composition, electrochemical process and anodized component

Abstract

The disclosure relates to an electrolyte composition for eloxation of a component, for example, a component for a vehicle braking system, wherein the electrolyte composition comprises an aqueous solution of the following components: (A) potassium titanium oxide oxalate; (B) oxalic acid; and (C) at least one buffer. The disclosure further relates to an electrochemical method of eloxation using the electrolyte and to an eloxed component.

1 . An electrolyte composition for eloxation of a component, wherein the electrolyte composition comprises an aqueous solution of the following components:
 (A) potassium titanium oxide oxalate;   (B) oxalic acid; and   (C) at least one buffer.   
     
     
         2 . The electrolyte composition according to  claim 1 , wherein the potassium titanium oxide oxalate is present in a concentration of 30-50 g/L in the aqueous solution. 
     
     
         3 . The electrolyte composition according to  claim 1 , wherein the oxalic acid is present in a concentration of 5-85 g/L in the aqueous solution. 
     
     
         4 . The electrolyte composition according to  claim 1 , wherein the buffer is selected from the group consisting of citric acid and boric acid and a combination thereof. 
     
     
         5 . The electrolyte composition according to  claim 1 , wherein the buffer is present in a concentration of 1-30 g/L in the aqueous solution. 
     
     
         6 . The electrolyte composition according to  claim 1 , wherein the aqueous solution has a pH within a range of 0.1-5. 
     
     
         7 . The electrolyte composition according to  claim 1 , wherein that the aqueous solution further comprises aluminium oxalate as a component present in a concentration of 1-15 g/L in the aqueous solution. 
     
     
         8 . The electrochemical method for eloxation of a component, especially a component for a vehicle braking system, using an electrolyte composition according to, wherein the method comprises the following steps:
 a) applying a voltage with a first voltage value U 1  between a component immersed an the electrolyte composition and an electrode, wherein the electrolyte composition comprises an aqueous solution of the following components: potassium titanium oxide oxalate; oxalic acid; and at least one buffer;   b) optionally maintaining the first voltage value for a first time interval,   c) increasing the first voltage value within a second time interval to a second voltage value, and   d) holding the second voltage value for a third time interval.   
     
     
         9 . The electrochemical method according to  claim 8 , wherein the method has at least one of the following features:
 the first voltage value is within a range of 60-140 V,   the second voltage value is within a range of 100-220 V,   the first time interval in step b) has a duration within a range of 2 to 120 s,   the second time interval in step c) has a duration within a range of 40 to 400 s,   the third time interval in step d) has a duration within a range of 400-1200 s,   the increase in the first voltage value within the second time interval to the second voltage value is essentially linear, and   a temperature of the electrolyte composition during the method is within a range of 1-45° C.   
     
     
         10 . The electrochemical method according to  claim 8  wherein, during the method, at least one control sequence comprising the following steps is conducted:
 a) detecting at least one actual current value, 
 b) comparing the actual current value with a range of values predetermined for the actual current value in which an eloxal layer with predetermined properties is formed on the component, and 
 c) if the comparison shows that the actual current value is outside the range of values: adjusting a method-relevant parameter such that the actual current value drops into the predetermined range of values. 
 
     
     
         11 . The electrochemical method according to  claim 10 , wherein the method-relevant parameter is selected from the group consisting of voltage value between component and electrode, current between component and electrode, electrolyte temperature, electrolyte flow rate, electrolyte backpressure, pressure in the pressure chamber. 
     
     
         12 . The electrochemical method according to  claim 10 , wherein the control sequence is conducted at periodic time intervals during the method. 
     
     
         13 . An eloxed component, wherein characterized in that the component has been provided with an eloxal layer obtainable by a method according to  claim 9 . 
     
     
         14 . The eloxed component according to  claim 13 , wherein the eloxal layer has at least one of the following features:
 the eloxal layer has a Vickers hardness within a range of 375-650 HV,   the eloxal layer has a roughness of R pk =0.05-0.2, R a =0.1-0.3 and R max =1.5-2.0, where the roughness parameters R pk , R a  and R max  have been measured according to ISO 13565,   the eloxal layer has a layer thickness within a range of 5-30 μm, and   the eloxal layer has a homogeneous coral structure, where the coral structure is defined by a multitude of hexagonal, tubular rod structures that are aligned essentially orthogonally to the substrate and have an average length within a range of 0.1 to 2.5 μm.   
     
     
         15 . The eloxed component according to  claim 13  wherein the eloxal layer is provided in at least one bore of the component. 
     
     
         16 . The electrolyte composition according to  claim 2 , wherein the oxalic acid is present in a concentration of 5-85 g/L in the aqueous solution. 
     
     
         17 . The electrolyte composition according to  claim 16 , wherein the buffer is selected from the group consisting of citric acid and boric acid and a combination thereof. 
     
     
         18 . The electrolyte composition according to  claim 17 , wherein the buffer is selected from the group consisting of citric acid and boric acid and a combination thereof. 
     
     
         19 . The electrolyte composition according to  claim 17 , wherein the aqueous solution has a pH within a range of 0.1-5. 
     
     
         20 . The electrolyte composition according to  claim 1 , wherein that the aqueous solution further comprises aluminium oxalate as a component present in a concentration of 1-15 g/L in the aqueous solution.