Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/024—Anodisation under pulsed or modulated current or potential
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/005—Apparatus specially adapted for electrolytic conversion coating
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/10—Electrodes, e.g. composition, counter electrode
  • C25D17/12—Shape or form
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
  • F02F1/00—Cylinders; Cylinder heads 
  • F02F1/004—Cylinder liners
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
  • F02F1/00—Cylinders; Cylinder heads 
  • F02F1/24—Cylinder heads
  • F02F1/42—Shape or arrangement of intake or exhaust channels in cylinder heads
  • F02F1/4264—Shape or arrangement of intake or exhaust channels in cylinder heads of exhaust channels
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
  • F05C2203/00—Non-metallic inorganic materials
  • F05C2203/08—Ceramics; Oxides
  • F05C2203/0865—Oxide ceramics
  • F05C2203/0869—Aluminium oxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
  • F05C2253/00—Other material characteristics; Treatment of material
  • F05C2253/12—Coating

Definitions

• the invention relates to a process for forming an aluminum oxide coating on the walls of an aluminum alloy automobile head, and an automobile cylinder head obtained by such a method.
• the cylinder heads are made of aluminum alloy mainly for reasons of weight gain.
• the increase in the specific power of recently developed engines imposes on the cylinder head increasingly high thermal loads.
• the good cooling of the cylinder head is obtained by the integration of cooling circuits inside it, more and more complex, made during the molding of the cylinder head by sand cores.
• document WO 2013/38249 describes such a process for anodic oxidation of the walls of exhaust ducts of a cylinder head.
• this method has the disadvantage that the coating thus obtained is porous because of the dissolution of the aluminum during the electrolysis.
• the presence of these porosities can generate crack primers in particular when the cylinder head is exposed to the usual operating temperatures of the engine, which can reach 250 ° C or more.
• JP3944788 a process for coating internal conduit cylinder revolution.
• the treatment disclosed by this document is presented as allowing to confer on the inner surface of the cylinder good abrasion resistance while ensuring good lubrication.
• the oxide layer thus formed does not limit the heat exchange between the inside of the duct and the walls.
• teaching of this document is limited to the processing of a cylinder of extremely simple geometry, and the processing of complex geometries is not considered.
• a unit volume is defined as a volume in which any segment linking in a straight line two points M and N of the volume fully belongs to this volume (in other words: for any pair of points (M, N) of the volume, any point of the segment linking these two points in a straight line also belongs to said volume).
• a complex volume with ramifications is thus not unitary.
• the object of the invention is to propose a process for forming an oxide coating in internal cylinder head ducts that do not have the drawbacks of the prior art.
• an object of the invention is to allow the formation of an oxide coating that does not require post-treatment clogging.
• Another object of the invention is to provide a method of forming an oxide coating to obtain an improved quality of oxide relative to the prior art.
• Another object of the invention is to provide a process for forming an oxide coating faster implementation compared to the prior art, compatible with mass production.
• the subject of the invention is a process for forming an oxide coating on walls of an inner duct of an aluminum alloy casting, comprising the insertion of a cathode into the duct. , circulating an electrolytic solution in said conduit between the cathode and the walls of the anode conduit, and applying a potential difference between the anode and the cathode,
• the method being characterized in that the application of the potential difference between the anode and the cathode comprises applying a series of DC voltage pulses to the anode.
• the method according to the invention may further comprise at least one of the following characteristics:
• each pulse of the series has a duration between 0.01 and 0.02 s and two successive pulses are separated from 0.001 to 0.01 s.
• the voltage applied to the anode varies during the series of pulses and is between 0 and 150 V to maintain a current density of between 10 and 50 A dm 2 of surface to be treated.
• the total duration of the series of pulses is between 30 and 300 s depending on the type of alloy to be treated and the desired oxide thickness
• the electrolyte comprises 10 to 20% of sulfuric acid and 1 to 5% ferrous sulphate.
• the flow of electrolyte in a conduit is between 0.5 and 2.0 m 3 / h per dm 2 of surface to be treated.
• the temperature of the electrolyte in a conduit is between -10 ° C and 0 ° C.
• the cathode is shaped to conform to the shape of the internal duct or ducts of the casting, leaving a mean gap between 3 and 15 mm between the cathode and the duct wall.
• the subject of the invention is also an aluminum alloy automobile cylinder head, characterized in that it comprises, on the walls of at least one internal duct, an aluminum oxide coating having a thickness of between 50 and 200 ⁇ , adapted to ensure the sealing and thermal insulation of the wall of the internal duct of the cylinder head during the flow, in said duct, exhaust gas at a temperature above 900 ° C.
• the breech is obtained by implementing the method according to the foregoing description.
• the internal conduits of the cylinder head provided with an oxide coating are exhaust pipes of combustion products.
• the pulsed streams also provide a coating of increased quality and non-porous. This coating thus makes it possible to seal the ducts of the cylinder head, which eliminates the need for a post-treatment clogging.
• composition of the electrolyte contributes to the reduction of the porous character of the coating and thus contributes to its sealing character.
• the modulation of the electrolyte flow also makes it possible to evacuate at best the calories generated (Joule losses) during the electrolysis in order to limit the phenomenon of dissolution of the oxide layer occurring during the generation of this layer. Maintaining the electrolyte temperature in the desired range improves the quality of the resulting coating layer.
• Figure 1 schematically a system for implementing a method of forming a coating on a cylinder head according to an embodiment of the invention.
• Figure 2a shows internal ducts of a cylinder head
• Figure 2b shows an integrated exhaust manifold cylinder head
• Figure 3 shows a cathode shaped to correspond to the shape of the internal ducts of a cylinder head.
• FIG. 4 represents the evolution of the voltage applied to the cylinder head and the current density between the anode and the cathode during the implementation of the insulating coating formation process.
• FIG. 5 represents an EDS analysis spectrum of the aluminum oxide deposited by the process.
• FIG. 6 is a sectional illustration of the geometry of an internal automobile cylinder head for which the method of forming a coating according to the invention is suitable.
• FIG. 7a illustrates a section of thickness observation of the anodizing layer
• Figure 7b illustrates another thickness observation section of the anodizing layer.
• FIG. 1 there is shown schematically a casting part 10 of aluminum alloy.
• This casting piece is of complex geometry and includes internal conduits 1 1 embedded.
• the constituent alloy of this casting is based on aluminum-silicon hypo-eutectic type, comprising less than 12.5% silicon by mass, and may contain alloying elements such as copper and magnesium .
• the constituent alloy of this part 10 may be AA319 or an AA356 type alloy.
• the casting is advantageously a motor yoke 10.
• the internal ducts 1 1 considered are advantageously exhaust ducts of combustion products.
• the cylinder head 10 is advantageously a cylinder head comprising an integrated exhaust gas manifold, as is the case, for example, of the cylinder head of FIG. 2b.
• Figure 2b are also shown the combustion chambers 19 of the cylinder head.
• FIG. 1 The system 1 used to implement this method is shown in FIG. 1
• Electrolytic solution circulation system It comprises a cathode 3 disposed inside the cylinder head, a circuit 2 for circulating an electrolytic solution between the cathode and the walls of the ducts of the anode cylinder head, and a control circuit 4 for controlling the potential difference imposed. between the anode and the cathode, said potential difference generating the oxidation reaction at the anode forming the oxide coating.
• Electrolytic solution circulation system
• the circulation system 2 of the electrolytic solution in the ducts 1 1 of the cylinder head is shown in FIG. It advantageously comprises an electrolytic solution tank 20, a pump 21, and a closed circuit 22 for circulating the solution between the reservoir and the ducts 1 1 of the cylinder head.
• the electrolyte solution preferably comprises between 10 and 20% sulfuric acid and 1 to 5% ferrous sulfate.
• the solution is advantageously maintained at a temperature between -10 ° C and 0 ° C.
• the circuit 2 advantageously comprises a cooling member 23 of the electrolytic solution.
• the pump is advantageously variable flow to modulate the flow of electrolyte as a function of temperature.
• the pump 21 is sized according to the surface to be coated and the thickness of the oxide layer to be grown, and is advantageously adapted to circulate a flow of electrolytic solution in the cylinder head between 0.5 and 2 m 3 per hour and per square decimeter (/ hr dm 2 ) of surface to be treated.
• a cathode 3 is positioned inside the exhaust ducts 1 1 of the cylinder head.
• This cathode is made of a material allowing oxidation-reduction reactions to occur in the electrolytic solution.
• the cathode is advantageously made of stainless steel type 316L for example.
• the cathode 3 is advantageously shaped so as to match the shape of the ducts 1 1 leaving a gap, preferably constant, between the cathode and the ducts, allowing the circulation of the electrolyte. This makes it possible to establish, when applying a potential difference between the anode and the cathode, current lines homogeneous over an entire surface to be coated, and thus to obtain a growth rate of the identical layer on the surface. This makes it possible to obtain at the end of the process a homogeneous layer thickness on all the treated surfaces.
• the average gap between the cathode and the wall of a duct is advantageously between 3 and 15 mm. This is a good compromise on the thickness to be maintained between the cathode and the wall of the duct 1 1, firstly to promote the circulation of the electrolyte and the entrainment of the gases generated during the electrolysis, including when the oxide layer has begun to form, and secondly to maintain a current density sufficient to not slow down the growth of the oxide layer.
• the system for implementing the process for forming a coating layer on the ducts of the cylinder head 10 further comprises a circuit 4 for controlling the potential difference between the anode and the cathode.
• the circuit 4 comprises a voltage source 40, adapted to deliver a voltage to the anode forming head 10, a control unit 41 of the voltage source, and one or more sensors (not shown) adapted to detect the voltages between the voltage source. anode and the cathode, as well as the current between the anode and the cathode to obtain the defined current.
• control unit 41 drives the voltage source 40 to deliver a series of DC voltage pulses to the anode.
• the frequency of the voltage pulses is advantageously greater than 10 Hz, preferably between 10 and 50 Hz.
• each voltage pulse has a duration of less than 0.1 seconds, and preferably between 0.01 and 0.02 seconds, during which the value of the voltage applied to the anode is constant.
• Each pulse is further separated from the next pulse by a non-zero time interval of less than 0.1 second, preferably less than 0.01 second, and advantageously between 0.001 and 0.01 second. During this time interval, the voltage applied to the anode is zero.
• the values of the voltage of each pulse gradually change as the formation of the oxide layer. Indeed, because of its insulating nature, the oxide layer opposes establishing a current between the anode and the cathode.
• control of the voltage source 40 by the control unit 41 is slaved to the value of the current density between the anode and the cathode.
• the measurement of the current by the sensors enables the control unit 41 to calculate the current density and, depending on the result, to control the value of the voltage delivered by the voltage source 40.
• the voltage is generally increasing on the series of pulses.
• the desired current density is advantageously between 5 and 50 A dm 2 of surface to be treated.
• the pulses occurring in the first seconds, for example the first 5 or 10 seconds, of the process having a voltage of between 0 and 50 V, and the following pulses advantageously having an increasing voltage up to to reach a voltage sufficient to maintain a current density advantageously greater than 5 A / dm 2 , preferably greater than 10 A / dm 2 .
• This maximum voltage is advantageously between 70 and 150 V, and preferably between 70 and 120 V.
• This series of continuous voltage pulses at the anode is implemented for a period of between 30 and 300 s depending on the type of alloy to be treated and the thickness of the oxide layer that is desired get.
• the formed oxide layer each inner duct advantageously has a thickness advantageously between 50 and 200 ⁇ " ⁇ This thickness varies mainly as a function of the silicon and copper concentration of the treated aluminum alloy, but it remains fine enough not to modify the dimensional characteristics of the product within a tolerance range of ⁇ 0.5 mm.
• FIGS. 7a and 7b show a sectional view of an oxide coating on a cylinder head obtained as a result of a treatment according to a method according to the invention.
• the oxide layer is between 34.92 ⁇ and 70.32 ⁇ and has a maximum porosity of 15%. Porosity is understood to mean a global void ratio within the oxide layer.
• the proposed method thus makes it possible to obtain, in a reduced time, an insulating coating of uniform thickness on internal ducts of aluminum alloy parts such as automobile heads.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Exhaust Silencers (AREA)

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• 2015
  • 2015-09-03 FR FR1558180A patent/FR3040712B1/fr not_active Expired - Fee Related
• 2016
  • 2016-09-05 KR KR1020187009047A patent/KR20180081039A/ko not_active Withdrawn
  • 2016-09-05 US US15/756,976 patent/US20180252180A1/en not_active Abandoned
  • 2016-09-05 JP JP2018530963A patent/JP2018527516A/ja active Pending
  • 2016-09-05 WO PCT/EP2016/070897 patent/WO2017037303A1/fr not_active Ceased
  • 2016-09-05 CA CA2997386A patent/CA2997386A1/fr not_active Abandoned
  • 2016-09-05 CN CN201680063920.5A patent/CN108368633A/zh active Pending
  • 2016-09-05 EP EP16762776.9A patent/EP3344801A1/de not_active Withdrawn
  • 2016-09-05 MX MX2018002736A patent/MX2018002736A/es unknown

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