ES2551080T3 - Method to repair an aluminum alloy component - Google Patents

Abstract

A method for repairing a precipitation hardened aluminum alloy component, including the steps of: a) cold spray depositing on said component to be repaired a portion of supplied material having an identical composition to that of said component to be repaired, obtaining thus a partially repaired component; b) subjecting said partially repaired component to a heat treatment, thus obtaining a repaired component, selecting the conditions to carry out said heat treatment based on the composition and dimensional tolerances of said component, characterized in that said heat treatment step b) includes : c) a first solubilization step followed by cooling in water; and d) a second precipitation step, after the first step c).

Description

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DESCRIPTION

Method to repair an aluminum alloy component

The present invention relates to a method for repairing an aluminum alloy component, in particular a precipitation hardened aluminum alloy component.

As is known, aeronautical components, in general, are subjected to high levels of mechanical stress during use and therefore must have specific mechanical properties, in particular in terms of high temperature mechanical strength, hardness and wear resistance.

In particular, this need is felt with components such as power transmission boxes or accessories for aeronautical and helicopter engines. Such components are typically made of lightweight aluminum alloys hardened by precipitation.

Frequently, these components need to be repaired. This can take place in the various manufacturing phases of new components, for example at the level of production of castings, semi-finished products or after a machining phase, for dimensional reasons or due to local damage resulting from handling or transport, or due to metallurgical defects such as porosity, fissures or inclusions. In addition, the finished components have to be repaired frequently after a period of operation due to wear, corrosion, unwanted or other problems.

The repair of aluminum alloy components is traditionally carried out using various technologies including: repair by deposition of welding material (TIG welding, laser coating, etc); application of high strength resins; interference adjustment (for recovery of oversized internal diameters by means of bushing); thermal spray deposition techniques.

These technologies have several drawbacks, as will be illustrated below.

Welding-based repair techniques are widely used for the repair of coarse components before heat treatment. They have the undoubted advantage of producing a metallurgical bond with the substrate material, but they are difficult to apply to the repair of components that have already been machined, due to the deformations produced by welding. Furthermore, in particular for precipitation hardened aluminum alloys, the welding material has a very different microstructure and significantly lower mechanical properties with respect to the substrate.

Repair techniques by application of high strength polymer resins have limited applicability due to the apparent dissimilarity between the base metal material and the material supplied, which consists substantially of an organic resin. In addition, the high polymerization temperatures of some epoxy-type resins, which may be of the order of 200 ° C, may cause undesirable deterioration of the mechanical characteristics of some light precipitation hardened alloys.

Repair techniques based on interference adjustment are generally used to recover worn or oversized internal diameters, but this type of application is obviously limited by geometric and structural factors.

The repair of components made of aluminum or relative alloys by means of thermal spray techniques involves the deposition of material supplied in which the particles of the material to be deposited are placed at a high temperature that causes them to melt. Consequently, this technology has the disadvantage, with respect to the deposition of aluminum powder, of favoring the oxidation of molten particles in contact with atmospheric oxygen.

In addition, the mechanical properties of the portion of material supplied are clearly inferior to those of the substrate, and also the quality of the relative adhesion is generally unsatisfactory.

To remedy this problem, thermal spraying for the repair of aluminum alloys is often carried out by depositing different materials from the base material. Bronze powders or Ni-Al alloys are often used. However, the application of materials other than the base material involves other problems connected with the different behavior of dissimilar materials during the process of termination of component manufacturing (for example, in the case of application of the anode oxidation process of the component aluminum) or during operation (for example, due to accelerated galvanic corrosion effects, differential thermal expansion coefficients, etc.).

Another disadvantage of repair techniques by traditional thermal spraying processes (plasma spraying, HVOF, thermal spraying, gun D, etc.) derives from the fact that the substrate temperature must be carefully supervised in order to avoid reaching them excessive temperatures with the consequent

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Possible deterioration of mechanical properties. In fact, it is known that aluminum alloys, in particular those hardened by precipitation of hardening phases, can quickly lose their tensile strength and deformation resistance characteristics after heating at temperatures higher than precipitation temperatures.

EP1674595 describes a method for repairing components including the steps of providing a component that has a defect to be repaired and depositing a repair material containing aluminum on an affected area on a surface of component 10 so that the repair material is plastically deformed and join the area affected by the impact with the affected area and therefore cover the affected area.

EP2204473 describes a process for repairing components that includes the steps of providing a component that has an affected area on a surface of a component to be repaired; depositing a repair material on the affected area on the surface of the component so that the repair material is plastically deformed without fusion and joins the affected area to the impact with the affected area and thus covers the affected area; provide an anodizing solution based on sulfuric acid; anodize a repair material deposited on the surface of the component in the anodizing solution based on sulfuric acid; consume only a portion of the deposited repair material to form a hard anodized coating layer on the deposited repair material to form a hard anodized coated component; provide a corrosion resistant sealant solution; and placing a hard anodized coated component in contact with the corrosion resistant sealant solution to form a corrosion resistant sealant coating on the hard anodized coated component.

Therefore, the need to provide a method for the repair of aluminum alloy components, in particular precipitation hardened aluminum alloy components, which overcomes at least one of the previously described drawbacks is observed in the sector.

More specifically, it is felt, especially in the aeronautical sector, the need to provide a method for the repair of aluminum alloy components that gives the repaired components mechanical characteristics that meet the requirements of the specific conditions of use, with special reference to the uniformity of properties between the material that forms the support (or the component to be repaired) and the portion of material supplied, and its relative adhesion.

In addition, the sector feels the need to provide a method for the repair of aluminum alloy components, in particular precipitation hardened aluminum alloy components, which requires a low investment in plant and reduced management and maintenance costs and that Can guarantee high productivity.

Therefore, the object of the present invention is to provide a method for the repair of precipitation hardened aluminum alloy components, said method satisfying in a simple and economical way at least one of said needs.

Said object is achieved with the present invention, insofar as it refers to a method defined in the claim.

one.

For a better understanding of the present invention, its preferred embodiment is described below, purely by way of non-limiting example.

Advantageously, an aluminum alloy component and, in particular, a precipitation hardened aluminum alloy component, is repaired by cold depositing a portion of material supplied on the component to be repaired, thereby obtaining a partially repaired component.

In the context of the invention, "component to be repaired" indicates an aluminum alloy component that requires repair, regardless of the machining state of said component.

“Regardless of the state of machining of said component” it indicates that the component to be repaired may be, with reference to the relative manufacturing process: in the rough state; in the state of a semi-finished product; finish; or even a finished component that has already been operating and that requires repair to remedy the damage produced during the on-site operation.

The "component to be repaired" constitutes the substrate of the cold spray deposition phase, which will be described in more detail below.

After the step of depositing the portion of material supplied on the component to be repaired, a "partially repaired component" is obtained.

Cold spray deposition is a relatively recent technique that involves the deposition of materials

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Metal in powder form. However, unlike thermal spray processes, in the cold spray deposition the material supplied remains in the solid state without reaching the melting conditions.

Typically, according to this technique, a metal powder or a mixture of metal powders is injected which has a predefined composition by means of a nozzle and is applied to a substrate, which undergoes acceleration in the unmelted state, at speeds of the order of 300  1,200 m / s by means of a flow of carrier gas that crosses the nozzle. Upon impact with the substrate with sufficient kinetic energy, the dust particles deform the substrate locally and deform.

In the context of the invention, the component to be repaired forms the "substrate" on which the metallic powder that constitutes a "portion of material supplied" is deposited.

Preferably, the metal powder or the mixture of metal powders used to deposit the portion of material supplied has a composition substantially identical to that of the substrate (ie, the component to be repaired). The use of material supplied with a composition substantially identical to that of the substrate has the advantage of minimizing differences in behavior between the substrate and the material supplied, restoring as much as possible the conditions of the repaired component with respect to the new component.

For physical and chemical physical reasons, the cold spray deposition technique favors the formation of a portion of supplied material that is compact and fixedly adheres to the substrate. In particular, this advantageous result is promoted by the reciprocal interpenetration of material supplied and substrate and the breakage, at the time of impact, of the thin surface layers of oxide which, in practice, are always present in the materials exposed to the atmosphere Exterior.

This aspect is especially advantageous in the case of repair of components damaged during operation, or when they have been exposed for a prolonged period to aggressive atmospheric conditions.

Typically, in the cold spray deposition technique, a flow of compressed gas at a pressure of about 5 aproximadamente50 bar is used. This flow of gas envelops the metal dust particles and drags them, expelling them through the nozzle at high speed. Optionally, at least a part of the gas flow is heated before reaching the application nozzle.

A monoatomic inert gas such as helium is preferably used as the carrier gas. Helium has the double advantage of allowing, as a monoatomic gas, the acceleration of the particles at the highest speeds and simultaneously, due to their inertia, exclude the possibility of oxidation of the metal dust. However, since the contact times between the components of the metal powder mixture and the carrier gas are very limited, it is also possible to use cheaper carrier gases, such as nitrogen or air, although, at the same pressure, the speeds that They can reach the particles are inferior to those that can be reached with helium.

The deposition temperature is typically as low as possible, compatible with the need to obtain a minimum level of deformation of the powdered powder particles.

The average size of the metallic particles that form the deposit powder can be advantageously chosen in the range of between 1 and 200 μm.

Therefore, this technique naturally favors the formation of a portion of material supplied that has a low porosity level and good adhesion characteristics against the material constituting the support.

In the case of aluminum alloy components and, more specifically, precipitation hardened aluminum alloy components, the portion of cold spray deposited material typically has high fragility and high internal stresses that are not completely satisfactory in view of the use in the aeronautical sector.

In general, a significant lack of uniformity in terms of mechanical properties and microstructural characteristics is typically found between the substrate and the portion of supplied material deposited by cold spraying. This lack of uniformity is undesirable in view of the intended use of the components.

In addition, the quality of adhesion between the portion of material supplied deposited and the substrate, although generally better than other thermal spray deposition techniques, is generally limited.

Advantageously, according to the invention, the method for repairing aluminum alloy components further includes the step of subjecting the partially repaired component obtained from the cold spray deposition phase to a heat treatment, thus obtaining a repaired component.

Said heat treatment is intended to improve the mechanical characteristics of the material portion

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supplied, with the aim of reducing the lack of uniformity between the portion of material supplied and the substrate. Furthermore, said heat treatment has been conceived in order to improve the quality of adhesion between the portion of material supplied and the substrate.

Advantageously, according to the invention, a repaired component is subjected to a specific heat treatment, whose operating conditions have been selected according to the composition and dimensional tolerances of said component to be repaired. In addition, it will also be possible to consider the final use of the component, once repaired.

If the component to be repaired has sufficiently large dimensional tolerances to allow any deformations caused by the heat treatment, the partially repaired component is advantageously subjected to the specific heat treatment of the alloy, including:

-a first solubilization step followed by rapid cooling; Y

-a second step of precipitation, which follows the first.

If the component to be repaired is obtained from Al-Si alloys, type 355, 356 or 357, the first solubilization phase is preferably carried out at a temperature of 500 to 580 ° C, more preferably 530 ° C to 550 ° C, for a time in the range of 6 to 20 hours, while the precipitation phase is preferably performed at a temperature of 100 to 300 ° C, more preferably 150 ° C to 230 ° C, for a time in the range between 3 and 12 hours.

If the component to be repaired is obtained from Al-Cu alloys, type 2014, 2618, 2024, the first solubilization step is preferably carried out at a temperature of 400 to 600 ° C, more preferably 460 ° C to 535 ° C, for a time in the range of 1 to 3 hours, while the precipitation step is preferably performed at a temperature of 150 to 250 ° C, more preferably 160 ° C to 200 ° C, for a time in the range between 8 and 20 hours.

Below are some examples of the advantages that can be obtained with the application of all the heat treatment of solubilization and aging in test pieces made of 357 aluminum-silicon alloy repaired by means of cold spraying using aluminum alloy powder -silicon 357 as the material supplied:

Example 1a: Repair of coarse components in aluminum-silicon alloy 357 already subjected to complete heat treatment of solubilization and precipitation (aging).

The mechanical strength of the 357 aluminum-silicon alloy with the complete heat treatment, measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is on average 307 MPa.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove of depth such that it reduced the resistant zone to 49% of the original zone. The average mechanical resistance measured in these test pieces was 179 MPa.

Test pieces with simulated defect were repaired by cold spraying by depositing a layer of 357 aluminum alloy powder of sufficient thickness to completely fill the circumferential groove. After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 226 MPa. Analog test pieces repaired by cold spraying and subjected, after repair, to thermal solubilization treatment at 540 ° C for 17.5 hours with water cooling, followed by heat precipitation treatment (aging) at 200 ° C during 7 hours, they presented an average mechanical resistance of 250 MPa, with an improvement of approximately 11% compared to components that were not heat treated.

Example 1b: Repair of coarse components in aluminum-silicon alloy 357 already subjected to complete heat treatment of solubilization and precipitation (aging).

The mechanical strength of the fully heat-treated 357 aluminum-silicon alloy, measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is on average 307 MPa.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove with a depth such that it reduced the resistant zone to 33% of the original zone. The average mechanical resistance measured in these test pieces was 122 MPa.

The test pieces with simulated defect were repaired by cold-depositing a layer of 357 aluminum alloy powder thick enough to completely fill the circumferential groove.

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After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 197 MPa. After cold spray repair, a solubilization heat treatment was performed at 540 ° C for 17.5 hours with water cooling, followed by heat precipitation treatment (aging) at 200 ° C for 7 hours; These treatments increased the mechanical characteristics of the test pieces repaired at average values of 216 MPa, with an improvement in this case also of approximately 10% with respect to the components that did not undergo the heat treatment.

Example 2a: Repair of rough untreated components (in the casting state) of aluminum-silicon alloy

357

The mechanical strength of the 357 non-heat-treated aluminum-silicon alloy (in the casting state), measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is 199 MPa on average.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove with a depth such that it reduced the resistant zone to 49% of the original zone. The average mechanical resistance measured in these test pieces was 116 MPa.

The test pieces with simulated defect were repaired by cold spraying a layer of 357 aluminum alloy powder thick enough to completely fill the circumferential groove. After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 127 MPa. Analog test pieces repaired by cold spraying and subjected, after repair, to a thermal solubilization treatment at 540 ° C for 17.5 hours with water cooling, followed by a thermal precipitation treatment (aging) at 200 ° C for 7 hours, they presented an average mechanical resistance of 271 MPa, with an improvement of approximately 113% compared to components that were not subjected to heat treatment.

Example 2b: Repair of rough untreated components (in the casting state) of aluminum-silicon alloy

357

The mechanical strength of the 357 non-heat-treated aluminum-silicon alloy (in the casting state), measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is 199 MPa on average.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove with a depth such that it reduced the resistant zone to 33% of the original zone. The average mechanical resistance measured in these test pieces was 75 MPa.

The test pieces with simulated defect were repaired by cold-depositing a layer of 357 aluminum alloy powder thick enough to completely fill the circumferential groove. After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 78 MPa. Analog test pieces repaired by cold spraying and subjected, after repair, to solubilization heat treatment at 540 ° C for 17.5 hours with water cooling, followed by heat precipitation treatment (aging) at 200 ° C during 7 hours, they presented an average mechanical resistance of 191 MPa, with an improvement of approximately 145% compared to components that were not subjected to heat treatment.

The examples set forth above highlight the benefits of complete heat treatment in coarse components made of 357 aluminum alloy repaired by cold spray deposition.

As previously mentioned, the complete heat treatment of solubilization and aging can lead to deformations of the component, and therefore it is usually applied to coarse components (for example, castings or semi-finished products) where dimensional tolerances allow induced deformations by heat treatment.

On the other hand, if the component to be repaired has limited dimensional tolerances that do not allow potential deformations caused by the heat treatment, the partially repaired component is advantageously subjected to a heat treatment including a single stress release phase.

If the component to be repaired is obtained from Al-Si alloys, type 355, 356 or 357, the stress release phase is preferably carried out at a temperature of 80 to 250 ° C, more preferably 100 ° C to 200 ° C, for a time in the range of 3 to 10 hours.

If the component to be repaired is obtained from Al-Cu alloys, type 2014, 2618, 2024, the stress release phase is preferably carried out at a temperature of 80 to 200 ° C, more preferably from 100 ° C to 180 ° C,

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for a time in the range of 3 to 20 hours.

The following are some examples of the advantages that can be obtained with the application only of stress release heat treatment in test pieces made of 357 aluminum-silicon alloy repaired by cold spraying using 357 aluminum-silicon alloy powder as supplied material:

Example 3a: Repair of finished or semi-finished components of 357 aluminum-silicon alloy already subjected to complete heat treatment of solubilization and precipitation (aging).

The mechanical strength of the fully heat-treated 357 aluminum-silicon alloy, measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is on average 307 MPa.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove of a depth that reduced the resistant zone to 49% of the original zone. The average mechanical resistance measured in these test pieces was 179 MPa.

The test pieces with simulated defect were repaired by cold spraying a layer of 357 aluminum alloy powder of sufficient thickness to completely fill the circumferential groove. After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 226 MPa. Analogous test pieces repaired by cold spraying and subjected, after repair, to heat stress release treatment at 125 ° C for 7 hours showed an average mechanical resistance of 245 MPa, with an improvement of approximately 8% compared to components that did not undergo stress release treatment.

Example 3b: Repair of semi-finished or finished aluminum-silicon alloy 357 components already undergoing complete heat treatment of solubilization and precipitation (aging).

The mechanical strength of the fully heat-treated 357 aluminum-silicon alloy, measured on cylindrical test pieces with a diameter of 9.0 mm according to ASTM B557, is on average 307 MPa.

To simulate a defect to be repaired, the working section of some test pieces was reworked, creating a circumferential groove with a depth such that it reduced the resistant zone to 33% of the original zone. The average mechanical resistance measured in these test pieces was 122 MPa.

The test pieces with simulated defect were repaired by cold-depositing a layer of 357 aluminum alloy thick enough to completely fill the circumferential groove. After removing the excess layer from the working section of the test pieces, in order to restore the original 9.0 mm diameter, the mechanical strength measured on the repaired test pieces was on average 197 MPa. After cold spray repair, the subsequent heat-stress treatment at 125 ° C for 7 hours increased the mechanical characteristics of the test pieces repaired to average values of 263 MPa, with a 33% improvement in comparison with components that did not undergo stress release treatment.

The method of the invention has especially positive effects on the repaired components both in terms of the improvement of the mechanical properties of the portion of material supplied and in terms of the adhesion of the portion of material supplied to the substrate.

In particular, with the method of the invention the internal stresses in the portion of material supplied and in the interface with the substrate are reduced. In addition, the hardening phases precipitate, improving and stabilizing the structure of the portion of material supplied that is thus made as uniform as possible and similar to that of the substrate. At the same time, the method promotes the interdiffusion of light elements in the interface, thereby improving the adhesion between the portion of material supplied and the substrate.

In the condition in which the component to be repaired has sufficiently large dimensional tolerances to allow any deformations introduced by the complete heat treatment, the method of the invention has the especially desirable effect, from the mechanical point of view and in terms of performance, of make the behavior of the portion of material supplied very similar to that of the substrate. In fact, the stresses due to deformations within the portion of material supplied are completely canceled out and the material precipitates substantially again in the precipitation (aging) phase, thus obtaining the maximum benefit in terms of mechanical characteristics and adhesion between the parts. .

In any case, even when the component to be repaired has limited dimensional tolerances that do not allow potential deformations caused by heat treatment, or because it has already been heat treated before repair, the method of the invention produces a significant benefit. In fact, heat stress release treatment is carried out at temperatures and during times that favor

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kind of aging of the material, but that does not produce phenomena of excessive precipitation, which would lead to an unacceptable deterioration of the characteristics of the base material of the substrate.

In fact, with the treatment of the invention, the stresses within the portion of material supplied 5 are reduced and precipitation of the hardening phases thereof is caused, thus minimizing differences with respect to the base material of the substrate (or the component to repair).

It should be noted that, based on previous studies on the deposition of aluminum alloys by cold spraying, such as those referred to in US patent 2009/0148622, it would not seem necessary to put into practice

10 heat treatments after deposition to obtain the required mechanical properties. However, the method proposed in the present invention provides an undoubted improvement of the mechanical properties of the components.

US 6,905,728 indicates the realization, after the repair of high pressure turbine components

15 by cold spraying of a vacuum sintering process, followed by a hot isostatic pressure process and then heat treatment. It is evident that said heat treatment has the main objective of restoring the properties of the material after sintering and the hot isostatic pressure processes rather than improving the characteristics of the material deposited by cold spraying.

20 Finally, the publication “Characterization of low pressure type cold spray aluminum coatings” by K. Ogawa, K. Ito,

K. Ichimura, Y. Ichikawa and T. Shoji, Sendai / J explicitly indicates the beneficial effect of an annealing treatment at 270 ° C for 9 hours on the ductility of cold deposition aluminum deposition. However, although this heat treatment improves the ductility of the material, it has the disadvantage of drastically reducing the mechanical properties of the substrate and therefore cannot be conveniently used in the

25 practice in the sector of interest taking into account the present invention.

Claims (1)

1. A method to repair a precipitation hardened aluminum alloy component, including the steps of: 5 a) depositing a portion of supplied material by cold spraying on said component to be repaired having a composition identical to that of said component to be repaired, thereby obtaining a partially repaired component; 10 b) subjecting said partially repaired component to a heat treatment, thereby obtaining a repaired component, selecting the conditions for performing said heat treatment based on the composition and dimensional tolerances of said component, characterized in that said heat treatment step b) includes: 15 c) a first solubilization step followed by cooling in water; Y d) a second precipitation step, after the first step c).

The method according to claim 1, wherein, if said component to be repaired is obtained from Al-Si alloys of type 355, 356 or 357, said first solubilization step c) is performed at a temperature of 500 ° C at 580 ° C for a time in the range of 6 to 20 hours, and said second precipitation step d) is performed at a temperature of 100 ° C to 300 ° C for a time in the range of 3 to 12 hours.

The method according to claim 2, wherein, if said component to be repaired is obtained from Al-Si alloys of type 355, 356 or 357, said first solubilization step c) is performed at a temperature of 530 ° C at 550 ° C for a time in the range of 6 to 20 hours, and said second precipitation step d) is performed at a temperature of 150 ° C to 230 ° C for a time in the range of 3 to 12 hours.

The method according to claim 1, wherein, if said component to be repaired is obtained from Al-Si alloys of type 2014, 2618 or 2024, said first solubilization step c) is carried out at a temperature of 400 ° C at 600 ° C for a time in the range of 1 to 3 hours; said second precipitation step is carried out at a temperature of 150 ° C to 250 ° C for a time in the range of between 8 and 20 hours.

The method according to claim 4, wherein, if said component to be repaired is obtained from Al-Si alloys of type 2014, 2618 or 2024, said first solubilization step c) is carried out at a temperature of 460 ° C at 535 ° C for a time in the range of 1 to 3 hours; said second precipitation step is carried out at a temperature of 160 ° C to 200 ° C for a time in the range of between 8 and 20 hours.

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