U.S. patent application number 14/006915 was filed with the patent office on 2014-05-08 for method for repairing an aluminium alloy component.
This patent application is currently assigned to GE AVIO S.r.L.. The applicant listed for this patent is Simone Vezzu, Giovanni Paolo Zanon. Invention is credited to Simone Vezzu, Giovanni Paolo Zanon.
Application Number | 20140127400 14/006915 |
Document ID | / |
Family ID | 43977491 |
Filed Date | 2014-05-08 |
United States Patent
Application |
20140127400 |
Kind Code |
A1 |
Zanon; Giovanni Paolo ; et
al. |
May 8, 2014 |
Method For Repairing An Aluminium Alloy Component
Abstract
The invention refers to a method for the repair of an aluminium
alloy component, in particular a precipitation-hardened aluminium
alloy component, comprising the steps of: a) depositing by cold
spray on said component to be repaired a portion of supplied
material, thus obtaining a partially repaired component; b)
subjecting said partially repaired component to a thermal
treatment, thus obtaining a repaired component, the conditions of
performance of said thermal treatment being selected according to
the composition and dimensional tolerances of said component.
Inventors: |
Zanon; Giovanni Paolo;
(Rivalta Di Torino, IT) ; Vezzu; Simone; (Padova,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zanon; Giovanni Paolo
Vezzu; Simone |
Rivalta Di Torino
Padova |
|
IT
IT |
|
|
Assignee: |
GE AVIO S.r.L.
Rivalta Di Torino
IT
|
Family ID: |
43977491 |
Appl. No.: |
14/006915 |
Filed: |
March 26, 2012 |
PCT Filed: |
March 26, 2012 |
PCT NO: |
PCT/IB2012/051434 |
371 Date: |
January 15, 2014 |
Current U.S.
Class: |
427/140 |
Current CPC
Class: |
C23C 24/04 20130101;
C23C 26/00 20130101 |
Class at
Publication: |
427/140 |
International
Class: |
C23C 26/00 20060101
C23C026/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 24, 2011 |
IT |
TO2011A000257 |
Claims
1-12. (canceled)
13. A method for repairing an aluminum alloy component comprising
the steps of: a) cold spray depositing on said component to be
repaired a portion of supplied material having a composition
identical to that of said component to be repaired, thus obtaining
a partially repaired component; b) subjecting said partially
repaired component to a thermal treatment, thus obtaining a
repaired component, the conditions for performing said thermal
treatment being selected as a function of the composition and of
the dimension tolerances of said component, wherein step b) thermal
treatment comprises: c) a first step of solubilisation followed by
cooling in water; and d) a second step, following the first step
c), of precipitation.
14. The method according to claim 13, wherein, if said component to
be repaired is obtained from type 355, 356 or 357 Al--Si alloys,
said first step c) of solubilisation is performed at a temperature
from 500.degree. C. to 580.degree. C. for a time in the range
between 6 and 20 hours, and said second step d) of precipitation is
performed at a temperature from 100.degree. C. to 300.degree. C.
for a time in the range between 3 and 12 hours.
15. The method according to claim 14, wherein, if said component to
be repaired is obtained from type 355, 356 or 357 Al--Si alloys,
said first step c) of solubilisation is performed at a temperature
from 530.degree. C. to 550.degree. C. for a time in the range
between 6 and 20 hours, and said second step d) of precipitation is
performed at a temperature from 150.degree. C. to 230.degree. C.
for a time in the range between 3 and 12 hours.
16. The method according to claim 13, wherein, if said component to
be repaired is obtained from type 2014, 2618 or 2024 Al--Si alloys,
said first step c) of solubilisation is performed at a temperature
from 400.degree. C. to 600.degree. C. for a time in the range
between 1 and 3 hours; said second step of precipitation is
performed at a temperature from 150.degree. C. to 250.degree. C.
for a time in the range between 8 and 20 hours.
17. The method according to claim 16, wherein, if said component to
be repaired is obtained from type 2014, 2618 or 2024 Al--Si alloys,
said first step c) of solubilisation is performed at a temperature
from 460.degree. C. to 535.degree. C. for a time in the range
between 1 and 3 hours; said second step of precipitation is
performed at a temperature from 160.degree. C. to 200.degree. C.
for a time in the range between 8 and 20 hours.
18. A method for repairing an aluminium alloy component obtained
from an alloy selected from the group consisting of 355, 356, 357,
2014, 2618 and 2024 Al--Si alloys, comprising the steps of: a) cold
spray depositing on said component to be repaired a portion of
supplied material having a composition identical to that of said
component to be repaired, thus obtaining a partially repaired
component; b) subjecting said partially repaired component to a
thermal treatment, thus obtaining a repaired component, the
conditions for performing said thermal treatment being selected as
a function of the composition and of the dimension tolerances of
said component, wherein step b) of thermal treatment comprises a
step e) of stress-relieving, wherein: if said component to be
repaired is obtained from type 355, 356 or 357 Al--Si alloys, said
step e) of stress-relieving is performed at a temperature from
80.degree. C. to 250.degree. C. for a time from 3 to 10 hours,
or;--if said component to be repaired is obtained from type 2014,
2618 or 2024 Al--Si alloys, said step e) of stress-relieving is
performed at a temperature from 80.degree. C. to 200.degree. C. for
a time from 3 to 20 hours.
19. The method according to claim 18, wherein, if said component to
be repaired is obtained from type 355, 356 or 357 Al--Si alloys,
said step e) of stress-relieving is performed at a temperature from
100.degree. C. to 200.degree. C.
20. The method according to claim 18, wherein, if said component to
be repaired is obtained from type 2014, 2618 or 2024 Al--Si alloys,
said step e) of stress-relieving is performed at a temperature from
100.degree. C. to 180.degree. C. for a time from 3 to 20 hours.
Description
TECHNICAL FIELD
[0001] The present invention concerns a method for repairing an
aluminium alloy component, in particular a precipitation-hardened
aluminium alloy component.
BACKGROUND ART
[0002] As is known, aeronautical components, in general, are
subjected during use to high levels of mechanical stress and must
therefore have specific mechanical properties, in particular in
terms of mechanical resistance at high temperature, hardness and
wear resistance.
[0003] In particular, this need is felt for components such as
accessory or power transmission housings for aeronautical and
helicopter engines. Said components are typically made of
precipitation-hardened lightweight aluminium alloys.
[0004] Frequently, said components need repairs. This can occur in
the various manufacturing phases of new components, for example at
the level of production of the 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, cracks or inclusions.
Moreover, finished components frequently have to be repaired after
a period of operation due to problems of wear, corrosion, undesired
impacts or other.
[0005] Traditionally, repair of aluminium alloy components is
carried out using various technologies including: repair by deposit
of weld material (TIG welding, laser cladding, etc.); application
of high resistance resins; interference fit (for recovery of
oversized internal diameters by means of bushing); depositing
techniques by thermal spraying.
[0006] Said technologies have various drawbacks, as will be
illustrated below.
[0007] Repair techniques based on welding are widely used for the
repair of rough components prior to heat treatment. They have the
undoubted advantage of producing a metallurgical link with the
material of the substrate, but they are difficult to apply to the
repair of components that have already been machined, due to the
deformations produced by the welding. Furthermore, in particular
for precipitation-hardened aluminium alloys, the weld material has
a very different microstructure and significantly inferior
mechanical properties with respect to the substrate.
[0008] The repair techniques by application of high resistance
polymeric resins have limited applicability due to the evident
dissimilarity between the metallic base material and the supplied
material, which consists substantially of an organic resin. The
high polymerisation temperatures of some epoxy type resins, which
can be in the order of 200.degree. C., moreover, can cause an
undesirable deterioration in the mechanical characteristics of some
precipitation-hardened lightweight alloys.
[0009] The repair techniques based on interference fit are usually
used for recovering worn or oversized internal diameters, but this
type of application is evidently limited by geometric and
structural factors.
[0010] Repair of components made of aluminium or relative alloys by
means of thermal spraying techniques entails depositing of supplied
material in which the particles of the material to be deposited are
brought to a high temperature which causes them to melt. This
technology consequently has the disadvantage, as regards the
depositing of aluminium powder, of favouring oxidisation of the
melted particles in contact with the atmospheric oxygen.
[0011] Furthermore, the mechanical properties of the portion of
supplied material are decidedly inferior to those of the substrate,
and also the quality of the relative adhesion is generally
unsatisfactory.
[0012] To remedy this drawback, thermal spraying for repair of
aluminium alloys is often performed by depositing materials
different from the base material. Bronze powders or Ni--Al alloys
are often used. However, the application of materials different
from the base material entails other problems connected with the
different behaviour of dissimilar materials during the component
manufacturing completion processes (for example in the case of
application of the anode oxidisation process of the aluminium
component) or during operation (for example due to effects of
accelerated galvanic corrosion, differential thermal expansion
coefficients, etc.).
[0013] A further disadvantage of the repair techniques by
traditional thermal spraying processes (plasma spray, HVOF,
thermo-spray, D-gun, etc.) derives from the fact that the substrate
temperature must be very carefully monitored to avoid excessive
temperatures being reached with consequent possible deterioration
of the mechanical properties. It is known, in fact, that aluminium
alloys, in particular those hardened by precipitation of hardening
phases, can rapidly lose their characteristics of tensile strength
and yield strength following heating to temperatures higher than
the precipitation temperatures.
[0014] The need is therefore felt in the sector to provide a method
for the repair of aluminium alloy components, in particular
precipitation-hardened aluminium alloy components, which overcomes
at least one of the drawbacks described previously.
[0015] More specifically the need is felt, especially in the
aeronautical sector, to provide a method for the repair of
aluminium alloy components which gives the repaired components
mechanical characteristics that meet the requirements of the
particular conditions of use, with particular reference to the
uniformity of the properties between the material forming the
support (or the component to be repaired) and the portion of
supplied material, and their relative adhesion.
[0016] Furthermore, the need is felt in the sector to provide a
method for the repair of aluminium alloy components, in particular
precipitation-hardened aluminium alloy components, which requires
low plant investment and reduced management and maintenance costs
and which can guarantee high productivity.
DISCLOSURE OF INVENTION
[0017] The object of the present invention is therefore to provide
a method for the repair of aluminium alloy components, in
particular precipitation-hardened aluminium alloy components, said
method meeting simply and economically at least one of the
above-mentioned needs.
[0018] The above-mentioned object is achieved by the present
invention, as it relates to a method as defined in claim 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0019] For a better understanding of the present invention, a
preferred embodiment thereof is described below, purely by way of
non-limiting example.
[0020] Advantageously, an aluminium alloy component and, in
particular, a precipitation-hardened aluminium alloy component, is
repaired by depositing by cold spray a portion of supplied material
on the component to be repaired, thus obtaining a partially
repaired component.
[0021] In the context of the invention, "component to be repaired"
indicates an aluminium alloy component which requires repair,
regardless of the machining state of said component.
[0022] "Regardless of the machining state of said component"
indicates that the component to be repaired can be, with reference
to the relative manufacturing process: in the rough state; in the
state of a semi-finished product; finished; or even a finished
component which has already been operating and which requires
repair to remedy damage sustained during operation in situ.
[0023] The "component to be repaired" constitutes the substrate of
the cold spray depositing phase, which will be described in greater
detail below.
[0024] Following the step of depositing the portion of supplied
material on the component to be repaired, a "partially repaired
component" is obtained.
[0025] Cold spray depositing is a relatively recent technique which
entails the depositing of metallic materials in the form of powder.
Unlike the thermal spraying processes, however, in cold spray
depositing the supplied material remains in the solid state without
ever reaching the melting conditions.
[0026] Typically, according to this technique, a metallic powder or
a mixture of metallic powders having a pre-defined composition is
injected via a nozzle and applied to a substrate, undergoing
acceleration in the non-melted state, at speeds in the order of
300/1,200 m/s by means of a flow of carrier gas which crosses the
nozzle. Impacting with the substrate with sufficient kinetic
energy, the particles of the powder locally deform the substrate
and are themselves deformed.
[0027] In the context of the invention, the component to be
repaired forms the "substrate" on which the metallic powder is
deposited constituting a "portion of supplied material".
[0028] Preferably, the metallic powder or mixture of metallic
powders used for depositing the portion of supplied material has a
composition substantially identical to that of the substrate (i.e.
the component to be repaired). The use of supplied material with
composition substantially identical to that of the substrate has
the advantage of minimising the differences in behaviour between
the substrate and the supplied material, restoring as far as
possible the conditions of the repaired component with respect to
the new component.
[0029] For physical and chemical-physical reasons, the technique of
cold spray depositing favours the formation of a portion of
supplied material which is compact and securely adhering to the
substrate. In particular, this advantageous result is promoted by
the reciprocal interpenetration of supplied material and substrate
and the breakage, at the moment of impact, of the fine surface
layers of oxide which, in practice, are always present in the
materials exposed to the external atmosphere.
[0030] This aspect is particularly 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.
[0031] Typically, in the cold spray depositing technique, a
compressed gas flow at a pressure of approximately 5/50 bars is
used. This gas flow envelops the particles of metallic powder and
entrains them, expelling them through the nozzle at high speed.
Optionally, at least a part of the gas flow is heated before
arriving at the application nozzle.
[0032] Preferably, a monatomic inert gas such as helium is used as
the carrier gas. Helium has the twin advantage of allowing, as a
monatomic gas, acceleration of the particles at the highest speeds
and simultaneously, due to its inertia, excluding the possibility
of oxidisation of the metallic powder. However, since the contact
times between the components of the mixture of metallic powders 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 can be reached by the particles are
inferior to those that can be reached with helium.
[0033] The depositing temperature is typically the lowest possible,
compatibly with the need to obtain a minimum level of deformation
of the sprayed powder particles.
[0034] The mean dimension of the metallic particles forming the
powder to be deposited can be advantageously chosen in the range
between 1 and 200 .mu.m.
[0035] This technique therefore favours by nature the formation of
a portion of supplied material having a low porosity level and good
adhesion characteristics vis-a-vis the material constituting the
support.
[0036] In the case of aluminium alloy components and, more
specifically, precipitation-hardened aluminium alloy components,
the portion of supplied material deposited by cold spray typically
has a high fragility and high internal tensions which are not
wholly satisfactory in view of the use in the aeronautical
sector.
[0037] 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 spray. This lack of uniformity is
undesirable in view of the intended use of the components.
[0038] Furthermore, the adhesion quality between the portion of
supplied material deposited and the substrate, although generally
better than other depositing techniques by thermal spraying, is
generally limited.
[0039] Advantageously, according to the invention, the method for
the repair of aluminium alloy components furthermore comprises the
step of subjecting the partially repaired component obtained from
the cold spray depositing phase to a thermal treatment, thus
obtaining a repaired component.
[0040] Said thermal treatment has the purpose of improving the
mechanical characteristics of the portion of supplied material,
with the objective of reducing the lack of uniformity between
portion of supplied material and substrate. Furthermore, said
thermal treatment is conceived to improve the quality of the
adhesion between the portion of supplied material and the
substrate.
[0041] Advantageously, according to the invention, a repaired
component is subjected to a specific thermal treatment, the
performance conditions of which have been selected according to the
composition and dimensional tolerances of said component to be
repaired. Furthermore, it will also be possible to take account of
the final use of the component, once repaired.
[0042] If the component to be repaired has sufficiently broad
dimensional tolerances to allow for any deformations produced by
the thermal treatment, the partially repaired component is
advantageously subjected to the specific thermal treatment of the
alloy, comprising: [0043] a first step of solubilisation followed
by rapid cooling; and [0044] a second step, following the first
one, of precipitation.
[0045] If the component to be repaired is obtained from Al--Si
alloys, type 355, 356 or 357, the first phase of solubilisation is
preferably performed at a temperature from 500 to 580.degree. C.,
more preferably from 530.degree. C. to 550.degree. C., for a time
in the range between 6 and 20 hours, while the precipitation phase
is preferably performed at a temperature from 100 to 300.degree.
C., more preferably from 150.degree. C. to 230.degree. C., for a
time in the range between 3 and 12 hours.
[0046] If the component to be repaired is obtained from Al--Cu
alloys, type 2014, 2618, 2024, the first step of solubilisation is
preferably performed at a temperature from 400 to 600.degree. C.,
more preferably from 460.degree. C. to 535.degree. C., for a time
in the range between 1 and 3 hours, while the step of precipitation
is preferably performed at a temperature from 150 to 250.degree.
C., more preferably from 160.degree. C. to 200.degree. C., for a
time in the range between 8 and 20 hours.
[0047] Some examples are given below of the advantages that can be
obtained with application of the complete thermal treatment of
solubilisation and ageing on test pieces made of 357
aluminium-silicon alloy repaired by means of cold spray using 357
aluminium-silicon alloy powder as the supplied material:
EXAMPLE 1a
[0048] Repair of rough components in 357 aluminium-silicon alloy
already subjected to complete thermal treatment of solubilisation
and precipitation (ageing).
[0049] The mechanical strength of the 357 aluminium-silicon alloy
with complete thermal treatment, measured on cylindrical test
pieces with diameter 9.0 mm according to ASTM B557, is on average
307 MPa.
[0050] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
of depth such as to reduce the resistant area to 49% of the
original area. The mean mechanical resistance measured on these
test pieces was 179 MPa.
[0051] The test pieces with simulated defect were repaired by means
of cold spray by depositing a layer of 357 aluminium alloy powder
of thickness sufficient to completely fill the circumferential
groove. After removal of the excess layer from the working section
of the test pieces, in order to restore the original diameter of
9.0 mm, the mechanical resistance measured on the repaired test
pieces was on average 226 MPa.
[0052] Analogous test pieces repaired by cold spray and subjected,
after repair, to thermal solubilisation treatment at 540.degree. C.
for 17.5 hours with cooling in water, followed by thermal treatment
of precipitation (ageing) at 200.degree. C. for 7 hours, showed a
mean mechanical resistance of 250 MPa, with an improvement of
approximately 11% compared to the components that were not
thermally treated.
EXAMPLE 1b
[0053] Repair of rough components in 357 aluminium-silicon alloy
already subjected to complete thermal treatment of solubilisation
and precipitation (ageing).
[0054] The mechanical resistance of the 357 aluminium-silicon alloy
completely thermally treated, measured on cylindrical test pieces
with diameter of 9.0 mm according to ASTM B557, is on average 307
MPa.
[0055] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
with depth such as to reduce the resistant area to 33% of the
original area. The mean mechanical resistance measured on these
test pieces was 122 MPa.
[0056] The test pieces with simulated defect were repaired by means
of cold spray depositing a layer of 357 aluminium alloy powder with
thickness sufficient to completely fill the circumferential groove.
After removal of the excess layer from the working section of the
test pieces, in order to restore the original diameter of 9.0 mm,
the mechanical resistance measured on the repaired test pieces was
on average 197 MPa. After repair by cold spray, a thermal treatment
of solubilisation was performed at 540.degree. C. for 17.5 hours
with cooling in water, followed by thermal treatment of
precipitation (ageing) at 200.degree. C. for 7 hours; these
treatments increased the mechanical characteristics of the repaired
test pieces to mean values of 216 MPa, with an improvement also in
this case of approximately 10% with respect to the components that
did not undergo the thermal treatment.
EXAMPLE 2a
[0057] Repair of rough non-treated (as-cast) components in 357
aluminium-silicon alloy.
[0058] The mechanical resistance of the non thermally treated
(as-cast) 357 aluminium-silicon alloy, measured on cylindrical test
pieces with diameter 9.0 mm according to ASTM B557, is on average
199 MPa.
[0059] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
with depth such as to reduce the resistant area to 49% of the
original area. The mean mechanical resistance measured on these
test pieces was 116 MPa.
[0060] The test pieces with simulated defect were repaired by cold
spray depositing a layer of 357 aluminium alloy powder with
thickness sufficient to completely fill the circumferential groove.
After removal of the excess layer from the working section of the
test pieces, in order to restore the original diameter of 9.0 mm,
the mechanical resistance measured on the repaired test pieces was
on average 127 MPa. Analogous test pieces repaired by cold spray
and subjected, after repair, to a thermal solubilisation treatment
at 540.degree. C. for 17.5 hours with cooling in water, followed by
a thermal precipitation (ageing) treatment at 200.degree. C. for 7
hours, showed a mean mechanical resistance of 271 MPa, with an
improvement of approximately 113% compared to the components that
did not undergo the thermal treatment.
EXAMPLE 2b
[0061] Repair of rough non-treated (as-cast) components in 357
aluminium-silicon alloy.
[0062] The mechanical resistance of the non thermally treated
(as-cast) 357 aluminium-silicon alloy, measured on cylindrical test
pieces with diameter 9.0 mm according to ASTM B557, is on average
199 MPa.
[0063] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
with depth such as to reduce the resistant area to 33% of the
original area. The mean mechanical resistance measured on these
test pieces was 75 MPa.
[0064] The test pieces with simulated defect were repaired by cold
spray depositing a layer of 357 aluminium alloy powder with
thickness sufficient to completely fill the circumferential groove.
After removal of the excess layer from the working section of the
test pieces, in order to restore the original diameter of 9.0 mm,
the mechanical resistance measured on the repaired test pieces was
on average 78 MPa. Analogous test pieces repaired by cold spray and
subjected, after repair, to thermal treatment of solubilisation at
540.degree. C. for 17.5 hours with cooling in water, followed by
thermal treatment of precipitation (ageing) at 200.degree. C. for 7
hours, showed a mean mechanical resistance of 191 MPa, with an
improvement of approximately 145% compared to the components that
did not undergo the thermal treatment.
[0065] The examples given above highlight the benefits of complete
thermal treatment on rough components made of 357 aluminium alloy
repaired by cold-spray depositing.
[0066] As mentioned previously, the complete thermal treatment of
solubilisation and ageing can entail deformations of the component,
and it is therefore generally applied to rough components (e.g.
castings or semi-finished products) where the dimensional
tolerances allow for the deformations induced by the thermal
treatment.
[0067] If, on the other hand, the component to be repaired has
limited dimensional tolerances which do not allow for potential
deformations by the thermal treatment, the partially repaired
component is advantageously subjected to a thermal treatment
comprising a single stress-relieving phase.
[0068] If the component to be repaired is obtained from Al--Si
alloys, type 355, 356 or 357, the stress-relieving phase is
preferably performed at a temperature from 80.degree. C. to
250.degree. C., more preferably from 100.degree. C. to 200.degree.
C., for a time in the range between 3 and 10 hours.
[0069] If the component to be repaired is obtained from Al--Cu
alloys, type 2014, 2618, 2024, the stress-relieving phase is
preferably performed at a temperature from 80.degree. C. to
200.degree. C., more preferably from 100.degree. C. to 180.degree.
C., for a time in the range between 3 and 20 hours.
[0070] Some examples are given below of the advantages that can be
obtained with application of only stress-relieving thermal
treatment on test pieces made of 357 aluminium-silicon alloy
repaired by cold spray using 357 aluminium-silicon alloy powder as
supplied material:
EXAMPLE 3a
[0071] Repair of semi-finished or finished components in 357
aluminium-silicon alloy already subjected to complete thermal
treatment of solubilisation and precipitation (ageing).
[0072] The mechanical resistance of the 357 aluminium-silicon alloy
completely thermally treated, measured on cylindrical test pieces
with diameter 9.0 mm according to ASTM B557, is on average 307
MPa.
[0073] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
of depth such as to reduce the resistant area to 49% of the
original area. The mean mechanical resistance measured on these
test pieces was 179 MPa.
[0074] The test pieces with simulated defect were repaired by cold
spray depositing a layer of 357 aluminium alloy powder of thickness
sufficient to completely fill the circumferential groove. After
removal of the excess layer from the working section of the test
pieces, in order to restore the original diameter of 9.0 mm, the
mechanical resistance measured on the repaired test pieces was on
average 226 MPa. Analogous test pieces repaired by cold spray and
subjected, after repair, to thermal stress-relieving treatment at
125.degree. C. for 7 hours highlighted a mean mechanical resistance
of 245 MPa, with an improvement of approximately 8% compared to the
components that did not undergo the stress-relieving treatment.
EXAMPLE 3b
[0075] Repair of semi-finished or finished components in 357
aluminium-silicon alloy already subjected to complete thermal
treatment of solubilisation and precipitation (ageing).
[0076] The mechanical resistance of the 357 aluminium-silicon alloy
completely thermally treated, measured on cylindrical test pieces
with diameter 9.0 mm according to ASTM B557, is on average 307
MPa.
[0077] To simulate a defect to be repaired, the working section of
some test pieces was re-machined, creating a circumferential groove
with depth such as to reduce the resistant area to 33% of the
original area. The mean mechanical resistance measured on these
test pieces was 122 MPa.
[0078] The test pieces with simulated defect were repaired by cold
spray depositing a layer of 357 aluminium alloy with thickness
sufficient to completely fill the circumferential groove. After
removal of the excess layer from the working section of the test
pieces, in order to restore the original diameter of 9.0 mm, the
mechanical resistance measured on the repaired test pieces was on
average 197 MPa. After repair by cold spray, the performance of
subsequent thermal stress-relieving treatment at 125.degree. C. for
7 hours increased the mechanical characteristics of the repaired
test pieces to mean values of 263 MPa, with an improvement of 33%
compared to the components that did not undergo the
stress-relieving treatment.
[0079] The method of the invention has particularly positive
effects on the repaired components in terms of both improvement of
the mechanical properties of the portion of supplied material and
in terms of adhesion of the portion of supplied material to the
substrate.
[0080] In particular, with the method of the invention the internal
tensions in the portion of supplied material and at the interface
with the substrate are reduced. Furthermore, the hardening phases
are precipitated, improving and stabilising the structure of the
portion of supplied material which is thus made as far as possible
uniform and similar to that of the substrate. At the same time, the
method promotes the interdiffusion of lightweight elements at the
interface, consequently improving adhesion between the portion of
supplied material and the substrate.
[0081] In the condition in which the component to be repaired has
sufficiently broad dimensional tolerances to allow for any
deformations introduced by the complete thermal treatment, the
method of the invention has the particularly desirable effect, from
the mechanical point of view and in terms of performance, of making
the behaviour of the portion of supplied material very similar to
that of the substrate. In fact, the tensions due to the
deformations inside the portion of supplied material are completely
annulled and the material substantially re-precipitates in the
precipitation (ageing) phase, thus obtaining the maximum benefit in
terms of mechanical characteristics and adhesion between the
parts.
[0082] In any case, even when the component to be repaired has
limited dimensional tolerances which do not allow for potential
deformations caused by thermal treatment, or because it has already
been thermally treated before the repair, the method of the
invention produces a significant benefit. In fact, the thermal
stress-relieving treatment is performed at temperatures and for
times such as to favour a sort of ageing of the material, but not
such as to cause phenomena of over-precipitation, which would
result in unacceptable deterioration in the characteristics of the
substrate base material.
[0083] With the treatment of the invention, in fact, the tensions
inside the portion of supplied material are reduced and a
precipitation of hardening phases is provoked in the same, thus
minimising the differences with respect to the substrate base
material (or the component to be repaired).
[0084] It should be noted that, on the basis of the previous
studies performed on depositing of aluminium alloys by cold spray,
such as those reported in the patent U.S. 2009/0148622, it would
appear not necessary to carry out thermal treatments after the
depositing to obtain the required mechanical properties.
Nevertheless, the method proposed in the present invention provides
an undoubted improvement in the mechanical properties of the
components.
[0085] The patent U.S. Pat. No. 6,905,728 cites the performance,
after repair of high pressure turbine components by cold spray, of
a process of vacuum sintering, followed by a process of hot
isostatic pressing and then thermal treatment. It is evident that
said thermal treatment has the main objective of restoring the
properties of the material after the sintering and hot isostatic
pressing processes rather than that of improving the
characteristics of the material deposited by cold spray.
[0086] Lastly, the publication "Characterization of low pressure
type cold spray aluminium coatings" by K. Ogawa, K. Ito, K.
Ichimura, Y. Ichikawa and T. Shoji, Sendai/J explicitly cites the
beneficial effect of an annealing treatment at 270.degree. C. for 9
hours on the ductility of the aluminium deposit applied by cold
spray. However, although this thermal treatment improves the
ductility of the material, it has the drawback of drastically
reducing the mechanical properties of the substrate and therefore
cannot be conveniently used in practice in the sector of interest
taken into consideration for the present invention.
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