Method of treatment against corrosion and against wear

Abstract

Subjecting an aluminum or aluminum alloy substrate to anti-corrosion and anti-wear treatment that is applicable in particular in the field of aviation for protecting certain mechanical parts of airplanes or helicopters that are subjected simultaneously to corrosion and to wear, including applying to the substrate, a sol-gel treatment step forming a sol-gel layer; and after the sol-gel treatment step, a hard oxidation step forming a hard oxide layer.

Claims

1. A method of subjecting an aluminum or aluminum alloy substrate to treatment against corrosion and against wear, the method comprising: forming a first oxide layer on a surface of the substrate, the first oxide layer being porous and including pores; applying a sol-gel layer to the first oxide layer, the sol-gel filling in the pores of the first oxide layer; locally removing only the first oxide layer and the sol-gel layer at a zone of the substrate such that the surface of substrate at the zone of the substrate is free of the first oxide layer and the sol-gel layer and a geometry of the surface of the substrate at the zone of the substrate is unchanged; and forming a second oxide layer at the zone of the substrate, the second oxide layer being a hard oxide layer, wherein a thickness of the hard oxide layer is in a range of 40 μm to 100 μm, wherein the applying the sol-gel layer comprises a sol-gel deposition substep and a sol-gel baking substep, wherein the sol-gel baking substep is performed at a temperature in a range of 100° C. to 200° C. for a duration in a range of 40 minutes to 60 minutes so as to present a solidified sol-gel layer, wherein the hard oxide layer does not overlap the first oxide layer and the solidified sol-gel layer, wherein outside of the zone of the substrate, the first oxide layer presents a thickness in a range of 2 μm to 12 μm surmounted by the solidified sol-gel layer presenting a thickness in a range of 1 μm to 10 μm, the pores of the first oxide layer being filled in with the sol-gel, wherein the applying the sol-gel takes place on the first oxide layer without a prior step of filling in the first oxide layer, and wherein at least a portion of the sol-gel comprises glycidoxypropyltrimethoxysilane.

2. The method according to claim 1, wherein the second oxide layer is formed by hard anodic oxidation (HAO).

3. The method according to claim 1, wherein the first oxide layer is formed by sulfuric anodic oxidation (SAO), tartro-sulfuric anodic oxidation, or phosphoric anodic oxidation.

4. The method according to claim 1, wherein the hard oxide layer is a hard alumina layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are diagrammatic and seek above all to illustrate the principles of the invention.

(2) In the drawings, from one figure to another, elements (or portions of an element) that are identical are identified by the same reference signs. In addition, elements (or portions of an element) belonging to different implementations but presenting functions that are analogous are identified in the figures with numerical references incremented by 100, 200, etc.

(3) FIGS. 1A to 1E show various steps of a first implementation of the method.

(4) FIGS. 2A to 2F show various steps of a second implementation of the method.

DETAILED DESCRIPTION OF IMPLEMENTATIONS

(5) In order to make the invention more concrete, implementations of the method are described below in detail with reference to the accompanying drawings. It should be recalled that the invention is not limited to these implementations.

(6) FIGS. 1A to 1E show a first implementation of the method seeking to provide a substrate 10 made of aluminum or of aluminum alloy with a coating to provide protection against wear and corrosion. The substrate 10 shown in FIG. 1A may in particular be a hydromechanical part for regulating fuel in a helicopter turbine engine or it may be a flange for fastening a landing gear half-wheel, to mention but two examples. Initially, the substrate 10 may be subjected to preliminary preparation steps, such as steps of degreasing, rinsing, and/or pickling.

(7) Once the surface 10a of the substrate 10 has been made ready in this way, a liquid sol-gel layer 20 is applied to the surface 10a of the substrate 10. The sol-gel may in particular be the sol-gel commercialized by ICS under the name IC23.5 (registered trademark), in particular for applications in which the part 1 is to come into contact with kerosene; it could equally be the sol-gel sold by ICS under the name 1K-EBSil (registered trademark), in particular for applications where the part 1 is to come into contact with hydraulic fluids. Naturally, other sol-gels of equivalent composition, or having other compositions that present anti-corrosion properties, could equally well be used.

(8) The liquid sol-gel layer 20 may be applied to the surface 10a of the substrate 10 with a brush, like a paint. The liquid sol-gel may also be sprayed against the surface 10a of the substrate 10, e.g. using a paint spray gun. In another example, the sol-gel could equally well be deposited by dipping the substrate 10 in a bath of liquid sol-gel.

(9) Once this sol-gel deposition step has been finished, the part shown in FIG. 1B is subjected to a baking step in an oven during which the sol-gel is cured. This baking step may be carried out in an oven at a temperature of about 140° for a duration of 50 min. At the end of this baking step, the FIG. 1C part is obtained in which a solidified sol-gel layer 20′ covers the substrate 10, this solid sol-gel layer 20′ providing the looked-for protection against corrosion.

(10) At the end of this step, the zone U of the part for treating specifically against wear is machined so as to remove the solid sol-gel layer 20′ locally in order to uncover the substrate 10. The resulting part, as shown in FIG. 1D, can then be subjected to preparation steps such as degreasing and/or rinsing steps.

(11) The part made ready in this way is then dipped in a bath of sulfuric acid in order to be subjected to hard anodic oxidation (HAO) during which a surface layer of the substrate 1 in the zone U for treating against wear as uncovered during the machining step is oxidized in order to form an alumina layer 30. This alumina layer 30 serves to locally reinforce the ability of the part 1 to withstand wear in the zone U.

(12) The part as obtained in this way can finally be subjected to finishing steps, in particular rinsing or machining steps in order to obtain the final part as shown in FIG. 1E. Such a final part 1 can thus include in the zone U subjected to anti-wear treatment, a hard alumina layer 30 having thickness lying in the range 40 μm to 100 μm, and outside the zone U, a solidified sol-gel layer 20 having thickness lying in the range 2 μm to 10 μm. Such a sol-gel layer 20′ can withstand saline mist for longer than 500 h.

(13) FIGS. 2A to 2F show a second implementation of the method seeking to provide a substrate 110 made of aluminum or of aluminum alloy with a coating providing protection against wear and corrosion.

(14) Initially, the substrate 110 may be subjected to preparation steps such as degreasing, rinsing, and/or cleaning steps.

(15) Once the surface 110a and the substrate 110 have been made ready in this way, the part is immersed in a bath of sulfuric acid so as to subject it to sulfuric anodic oxidation (SAO) during which a surface layer of the substrate 110 is oxidized to form a porous alumina layer 140, thus obtaining the part shown in FIG. 2B. In other examples, the bath could include tartro-sulfuric acid or indeed phosphoric acid so as to perform tartro-sulfuric anodic oxidation or phosphoric anodic oxidation, respectively.

(16) The following steps of this second implementation of the method are substantially identical to those of the first implementation described above. A liquid sol-gel layer 120 is applied to the surface 140a of the porous alumina layer 140: the liquid sol-gel can then infiltrate in the pores 141 of the alumina layer 140 and fill them in. This produces the part shown in FIG. 2C.

(17) Once this sol-gel deposition step has been finished, the part is subjected to a baking step analogous to that of the first implementation, leading to the part shown in FIG. 2D in which a solidified sol-gel layer 120′ covers and fills in the pores of the porous alumina layer 140.

(18) At the end of this step, the zone U of the part that is to be treated specifically against wear is machined so as to remove locally both the solidified sol-gel layer 120′ and the porous alumina layer 140 so as to uncover the non-oxidized portion of the substrate 110. The part as obtained in this way, as shown in FIG. 2E, can then be subjected to preparation steps such as degreasing and/or rinsing steps.

(19) The part as made ready in this way is then dipped in a bath of sulfuric acid in order to obtain hard anodic oxidation (HAO) during which a surface layer of the substrate 110 in the zone U for treating against wear and uncovered during the machining step is oxidized so as to form a hard alumina layer 130.

(20) The part as obtained in this way may finally be subjected to finishing steps, in particular rinsing or machining step in order to obtain the final part 101 as shown in FIG. 2F. Such a final part 101 may thus include in the zone U that has been subjected to anti-wear treatment, a hard alumina layer 130 having thickness lying in the range 40 μm to 100 μm, and outside this zone U, an alumina layer 140 having thickness lying in the range 2 μm to 12 μm surmounted by a solidified sol-gel layer 120′ having thickness lying in the range 1 μm to 10 μm, the pores of the alumina layer 140 also being filled in with the sol-gel. Such an alumina layer 140 associated with a sol-gel layer 120′ is capable of withstanding saline mist for longer than 700 h.

(21) The implementations described in the present disclosure are given by way of non-limiting illustration, and a person skilled in the art can easily, in the light of this disclosure, modify these implementations or can envisage others, while remaining within the scope of the invention.

(22) Furthermore, the various characteristics of these implementations may be used singly or in combination with one another. When they are combined, the characteristics may be combined as described above or in other ways, the invention not being limited to the specific combinations described in the present disclosure. In particular, unless specified to the contrary, a characteristic described with reference to one particular implementation may be applied in analogous manner to any other implementation.