Method for anodizing aluminum
First Claim
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1. An improved method of anodizing an aluminum alloy workpiece comprising the steps of:
- providing an aqueous anodizing solution consisting essentially by weight of about 3 to 5 percent sulfuric acid, from about 0.5 to 1 percent boric acid and not more than about 3.7 percent aluminum ion and 0.2 percent chloride ion;
maintaining said bath at a temperature from about 70 to about 90 degrees F;
immersing said workpiece in said bath;
ramping the voltage applied across said workpiece in said bath from about 5 to about 20 volts;
such that the current density is substantially uniform across the workpiece and the average current density does not exceed about 10 amperes per square foot; and
maintaining said workpiece in said bath for a time such that an adherent coating of aluminum oxide is applied thereto having a coating weight between about 200 and 600 milligrams per square foot.
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Abstract
A controlled method of anodizing aluminum comprises formation of an aqueous solution of sulfuric and boric acids, immersion of a workpiece in the solution maintained at about room temperature and controlled application of voltage to achieve a current density not greater than about 10 Amperes per square foot. Aluminum oxide coatings in the weight range of from about 200 to 600 milligrams per square foot applied in this manner have properties as good as or superior to coatings applied in traditional hexavalent chromium anodizing solutions.
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4 Claims
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1. An improved method of anodizing an aluminum alloy workpiece comprising the steps of:
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providing an aqueous anodizing solution consisting essentially by weight of about 3 to 5 percent sulfuric acid, from about 0.5 to 1 percent boric acid and not more than about 3.7 percent aluminum ion and 0.2 percent chloride ion; maintaining said bath at a temperature from about 70 to about 90 degrees F; immersing said workpiece in said bath; ramping the voltage applied across said workpiece in said bath from about 5 to about 20 volts;
such that the current density is substantially uniform across the workpiece and the average current density does not exceed about 10 amperes per square foot; andmaintaining said workpiece in said bath for a time such that an adherent coating of aluminum oxide is applied thereto having a coating weight between about 200 and 600 milligrams per square foot. - View Dependent Claims (2, 3)
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4. An improved method of anodizing an aluminum alloy comprising the steps of immersing a workpiece into an anodizing solution consisting essentially by weight of about 3 to 5 percent sulfuric acid, from about 0.5 to 1 percent boric acid and not more than about 3.7 percent aluminum ion and 0.2 percent chloride ion;
- maintaining said bath at a temperature from about 70 to about 90 degrees F;
applying from about 5 to 15 Volts across the workpiece such that average current density does not exceed about 10 amperes per square foot; and
maintaining said workpiece in said bath for a time such that an adherent coating of aluminum oxide is applied thereto having a coating weight between about 200 and 600 milligrams per square foot, which coating does not substantially reduce the fatigue resistance of the workpiece.
- maintaining said bath at a temperature from about 70 to about 90 degrees F;
Specification