Electrolyte solution and electrochemical surface modification methods

Abstract

An aqueous electrolyte solution including a concentration of citric acid in the range of about 1.6 g/L to about 982 g/L and an effective concentration of ammonium bifluoride (ABF), and being substantially free of a strong acid. Methods of treating the surface of a non-ferrous metal workpiece include exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid less than or equal to about 300 g/L and a concentration of ammonium bifluoride greater than or equal to about 10 g/L, and having no more than about 3.35 g/L of a strong acid, controlling the temperature of the bath to be greater than or equal to about 54° C., connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath, and applying a current across the bath.

1 . An aqueous electrolyte solution comprising:
 about 0.1% by weight to about 59% by weight of a carboxylic acid; and   about 0.1% by weight to about 25% by weight of a fluoride salt; and   being substantially free of a strong acid.   
     
     
         2 . The electrolyte solution of  claim 1 , wherein the fluoride salt is selected from the group consisting of alkali metal fluorides, alkali earth metal fluorides, silicate etching compounds, and combinations thereof. 
     
     
         3 . The electrolyte solution of  claim 2 , wherein the fluoride salt is ammonium bifluoride. 
     
     
         4 . The electrolyte solution of  claim 1 , wherein the carboxylic acid is citric acid. 
     
     
         5 . An aqueous electrolyte solution comprising:
 about 1.665 g/L citric acid to about 982 g/L citric acid; and   about 2 g/L ammonium bifluoride to about 360 g/L ammonium bifluoride of a fluoride salt; and   being substantially free of a strong acid.   
     
     
         6 . A method of treating the surface of a non-ferrous metal workpiece, comprising:
 exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid less than or equal to about 300 g/L and a concentration of ammonium bifluoride greater than or equal to about 10 g/L, and having no more than about 3.35 g/L of a strong acid;   controlling the temperature of the bath to be greater than or equal to about 54° C.;   connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath; and   applying a current across the bath.   
     
     
         7 . The method of  claim 6 , wherein the temperature of the bath is controlled to be greater than or equal to about 71° C. 
     
     
         8 . The method of  claim 6 , wherein the current applied across the bath is less than or equal to about 538 amperes per square meter. 
     
     
         9 . The method of  claim 8 , wherein the current applied across the bath is less than or equal to about 53.8 amperes per square meter. 
     
     
         10 . The method of  claim 6 , wherein the concentration of citric acid is less than about 60 g/L. 
     
     
         11 . The method of  claim 6 , wherein the concentration of ammonium bifluoride is greater than or equal to about 60 g/L. 
     
     
         12 . A method of modulating cracks in the surface of a non-ferrous metal workpiece, comprising:
 exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid less than or equal to about 600 g/L and a concentration of ammonium bifluoride greater than or equal to about 60 g/L, and having no more than about 3.35 g/L of a strong acid;   controlling the temperature of the bath to be greater than or equal to about 54° C.;   connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath; and   applying a current across the bath of less than about 53.8 amperes per square meter.   
     
     
         13 . A method of metal oxide removal from the surface of a non-ferrous metal workpiece, comprising:
 exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid less than or equal to about 60 g/L and a concentration of ammonium bifluoride greater than or equal to about 60 g/L, and having no more than about 3.35 g/L of a strong acid;   controlling the temperature of the bath to be greater than or equal to about 54° C.;   connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath; and   applying a current across the bath of less than about 53.8 amperes per square meter.   
     
     
         14 . A method of alpha case removal from the surface of a titanium or titanium alloy workpiece, comprising:
 exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid less than or equal to about 60 g/L and a concentration of ammonium bifluoride greater than or equal to about 60 g/L, and having no more than about 3.35 g/L of a strong acid;   controlling the temperature of the bath to be greater than or equal to about 54° C.;   connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath; and   applying a current across the bath of less than about 53.8 amperes per square meter.