Electrolyte solution and electrochemical surface modification methods
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. A method of treating the surface of a nonferrous metal workpiece, comprising
exposing the surface to a bath of an aqueous electrolyte solution including a concentration of citric acid from about 1 g/L to about 982 g/L and a concentration of ammonium bitluoride from about 1 gL to about 360 g/L, and having no more than about 3.35 g/L of a strong acid;
controlling the temperature of the bath between about 2° C. and about 98° 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.
2. The method of claim 1 , wherein the temperature of the bath is controlled from about 21° C. to about 85° C.
3. The method of claim 1 , wherein the current applied across the bath is less than or equal to about 255,000 amperes per square meter.
4. The method of claim 3 , wherein the current applied across the bath is less than or equal to about 5,000 amperes per square meter.
5. The method of claim 1 , wherein the concentration of citric acid is less than about 780 g/L.
6. The method of claim 1 , wherein the concentration of ammonium bifluoride is less than or equal to about 120 g/L.
7. 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 from about 1 g/L to about 982 g/L and a concentration of ammonium bifluoride from about 1 g/L to about 360 g/L, and having no more than about 3.35 g/L, of a strong acid;
connecting the workpiece to the anode of a DC power supply and immersing a cathode of the DC power supply in the bath;
applying a current across the bath of less than about 255,000 amperes per square meter;
maintaining the current for a time sufficient to round the bottoms of the cracks; and
discontinuing the current and removing the workpiece from the bath before the surface of the workpiece is removed to the level of the bottom of the cracks.
8. A method of metal oxide removal from the substrate 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 from about 1 g/L to about 180 g/L and a concentration of ammonium bifluoride from about 1 g/L, to about 120 g/L, and having no more than about 135 g/L of a strong acid;
controlling the temperature of the bath to be less than or equal to about 85° 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 255,000 amperes per square meter.
9. A method of alpha case removal from the substrate 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 from about 1 g/L to about 180 g/L and a concentration of ammonium bifluoride from about 1 g/L to about 120 g/L and having no more than about 3.35 g/L of a strong acid;
controlling the temperature of the bath to be less than or equal to about 85° 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 5,000 amperes per square meter.