Controlled trivalent chromium pretreatment

Patent metadata

Field	Value
Publication number	US-9695523-B2
Application number	US-201314052719-A
Country	US
Kind code	B2
Filing date	Oct 12, 2013
Priority date	Oct 12, 2013
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

A method for forming a trivalent chromium coating on an aluminum alloy substrate includes adding a chromium-containing solution to a vessel, immersing the aluminum alloy substrate in the chromium-containing solution, immersing a counter electrode in the chromium-containing solution, and applying an electrical potential bias to the aluminum alloy substrate with respect to its equilibrium potential to form a trivalent chromium coating on an outer surface of the aluminum alloy substrate. A method for forming a trivalent chromium coating on a metal substrate includes adding a chromium-containing solution to a vessel, immersing the metal substrate in the chromium-containing solution, immersing a counter electrode in the chromium-containing solution, and modulating an electrical potential difference between the metal substrate and the counter electrode to form a trivalent chromium coating on an outer surface of the metal substrate.

First claim

The invention claimed is:

1. A method for forming a trivalent chromium coating on an aluminum alloy substrate, the method comprising:
adding a chromium-containing solution to a vessel;
immersing the aluminum alloy substrate in the chromium-containing solution;
immersing a counter electrode in the chromium-containing solution; and
applying an electrical potential bias to the aluminum alloy substrate with respect to its equilibrium potential to form a trivalent chromium coating on an outer surface of the aluminum alloy substrate, wherein the electrical potential bias is modulated between a positive value and a negative value relative to the equilibrium potential of the aluminum alloy substrate.

2. The method of claim 1 , wherein the chromium-containing solution comprises ZrO 2 or TiO 2 and wherein the electrical potential bias is at the positive value for a period of time longer than the negative value to promote dissolution of Al 3+ ions from the outer surface of the aluminum alloy substrate and promote deposition of ZrO 2 or TiO 2 on the outer surface of the aluminum alloy substrate.

3. The method of claim 2 , wherein the electrical potential bias is between about 0 V and about 0.6 V with respect to a SHE at the positive value.

4. The method of claim 1 , wherein the electrical potential bias is at the negative value for a period of time longer than the positive value to promote deposition of Cr(OH) 3 on the outer surface of the aluminum alloy substrate.

5. The method of claim 4 , wherein the electrical potential bias is between about −0.8 V and about −1.8 V with respect to a SHE at the negative value.

6. The method of claim 1 , wherein a difference between the positive value and the negative value is less than about 1.5 V with respect to a SHE.

7. The method of claim 1 , wherein the chromium-containing solution is maintained at a pH between about 3.6 and about 3.9 while the electrical potential bias is maintained.

8. The method of claim 1 , further comprising:
monitoring formation of the trivalent chromium coating using in situ spectroscopic ellipsometry; and
modulating the electrical potential bias between the positive value and the negative value depending on results obtained from the spectroscopic ellipsometry.

9. A method for forming a trivalent chromium coating on a metal substrate, the method comprising:
adding a chromium-containing solution to a vessel;
immersing the metal substrate in the chromium-containing solution;
immersing a counter electrode in the chromium-containing solution; and
modulating an electrical potential difference between the metal substrate and the counter electrode to form a trivalent chromium coating on an outer surface of the metal substrate, wherein the electrical potential difference varies between a positive value and a negative value.

10. The method of claim 9 , wherein the metal substrate comprises aluminum, wherein the chromium-containing solution comprises ZrO 2 or TiO 2 and wherein the electrical potential difference with respect to the metal substrate is at the positive value for a period of time longer than the negative value to promote dissolution of Al 3+ ions from the outer surface of the metal substrate and promote deposition of ZrO 2 or TiO 2 on the outer surface of the metal substrate.

11. The method of claim 9 , wherein the electrical potential difference with respect to the metal substrate is at the negative value for a period of time longer than the positive value to promote deposition of Cr(OH) 3 on the outer surface of the metal substrate.

12. A method for forming a trivalent chromium coating on an aluminum alloy substrate, the method comprising:
adding a chromium-containing solution to a vessel, the chromium-containing solution comprising ZrO 2 or TiO 2 ;
immersing the aluminum alloy substrate in the chromium-containing solution;
immersing a counter electrode in the chromium-containing solution; and
applying an electrical potential bias to the aluminum alloy substrate with respect to its equilibrium potential to form a trivalent chromium coating on an outer surface of the aluminum alloy substrate, wherein the electrical potential bias is between about −0.1 V and about −1.6 V with respect to a standard hydrogen electrode (SHE).

13. The method of claim 12 , wherein the electrical potential bias is between about −0.1 V and about −1.3 V with respect to a standard hydrogen electrode (SHE) to promote dissolution of Al 3+ ions from the outer surface of the aluminum alloy substrate and promote deposition of ZrO 2 or TiO 2 on the outer surface of the aluminum alloy substrate.

14. The method of claim 12 , wherein the electrical potential bias is between about −1.3 V and about −1.6 V with respect to a SHE to promote deposition of Cr(OH) 3 on the outer surface of the aluminum alloy substrate.

Assignees

• Hamilton Sundstrand Corp

Inventors

• Dardona Sameh
• Jaworowski Mark R
• Burlatsky Sergei F
• Novikov Dmitri
• Chen Lei

Classifications

• C25D9/06

  by anodic processes · CPC title

• C25D3/06 Primary

  from solutions of trivalent chromium · CPC title

• C25D9/04

  with inorganic materials · CPC title

• C25D21/12

  Process control or regulation (controlling or regulating in general G05) · CPC title

• C25D5/18

  Electroplating using modulated, pulsed or reversing current · CPC title