FR2663250A1 - METHOD FOR MANUFACTURING ALUMINUM COLOR ALLOY PARTS COMPRISING AN INSERT AND CULASSE OF AN INTERNAL COMBUSTION ENGINE OBTAINED BY THIS PROCESS. - Google Patents

Abstract

The present invention relates to a method of manufacturing cast aluminum alloy parts comprising an insert. This insert is composed of a composite material with a metal matrix, which is constituted by a reinforcement based on ceramic fibers such as alumina or alumina fibers - silica forming felt, impregnated under high pressure with an aluminum alloy different from or identical to the casting alloy. The invention finds application in the automotive industry for the manufacture of aluminum alloy cylinder heads.

Description

The invention generally relates to a method for manufacturing parts in

cast aluminum alloy

having an insert.

  The present invention finds particular application in the manufacture of a motor cylinder head to

  internal combustion, equipped with an insert.

  In the metallurgy of foundry alloys, a method of manufacturing a casting having a ceramic insert is known It consists in depositing on the insert, a flexible mat of ceramic fibers, and then placing the insert in a mold

  and finally to sink the metal into the mold.

  However, the parts thus obtained, are often subject in their use, to thermal cycles and under the effect of high temperatures, these parts quickly reach their limit of rupture, their limit to thermal fatigue and their elastic limit to

  temperature of the material considered.

  In the particular case of engine cylinder heads, the alloy part forming the cylinder head undergoes large temperature variations during the operation of the engine, the maximum temperature being up to 3500 C. The part of the cylinder head forming the inter-valve seat zones is deteriorates by cracking, deforms when hot

  and its service life decreases accordingly.

  The object of the present invention is to overcome the drawbacks mentioned above by proposing a method for manufacturing cast aluminum alloy parts comprising an insert, where the insert is composed of a composite material with a metal matrix, which consists of by a reinforcement based on alumina fibers or alumina-silica felt, impregnated under high pressure by an aluminum alloy different from or

identical to the casting alloy.

  Furthermore, in this process, the fixing, in particular chemical, between the insert and the cast alloy piece must be perfect Indeed, an impermeable and non-fusible alumina layer covers the entire surface of the insert and presents an obstacle the creation of a chemical bond between the insert and the casting alloy piece. The invention therefore also aims to create

  a chemical bond to the coin insert interface.

  For this purpose, the invention proposes a process for manufacturing cast aluminum alloy parts comprising an insert, which more precisely consists of subjecting a matrix alloy surface of at least one face of the insert to a treatment. Zincate chemical followed by at least one electrolytic treatment

such as a nickel coating.

  According to one characteristic of the invention, the zincate chemical treatment forms on the aforementioned surface a layer of zinc or iron zinc alloy

containing about 15% iron.

  According to another characteristic of the invention, the electrolytic treatment is carried out from a nickel sulphate or sulphamate solution. According to a variant of the invention, the abovementioned surface of the insert undergoes a second treatment

  electrolytic such as a silver coating.

  The invention also relates to an internal combustion engine cylinder head, provided with at least one insert, the cast aluminum alloy cylinder head being

  manufactured by the method according to the invention.

  Other features and advantages of the invention will appear better on reading the

  detailed description that follows and which refers to

  accompanying drawings, given by way of example, in which: Figure 1 shows a schematic section of the insert formed of a composite material before the treatment of its surface; Figure 2 shows a schematic section of the same insert after the treatment of its surface; Figure 3 shows a plan view of the insert after impregnation and before introduction into the mold; Figure 4 is a sectional view of the insert along line IV-IV; FIG. 5 represents a partial view from below of an internal combustion engine cylinder head; FIG. 6 represents a partial section of the cylinder head shown in FIG. 5, along the line VI-VI; and FIG. 7 is a partial perspective view of the cylinder head shown in FIG. 5

following direction VII.

  According to the process for manufacturing cast alloy parts according to the invention, an insert is disposed at

within the room.

  This insert is manufactured beforehand from composite material which consists on the one hand of a reinforcing material based on ceramic fibers such as

  that for example alumina or alumina fibers -

  silica, which are entangled in the manner of a felt whose cohesion is provided by a mineral binder, such as for example a silica binder, and on the other hand an aluminum-based matrix and more specifically of an aluminum alloy different from or identical to the aluminum alloy of the casting This aluminum alloy

  forming the matrix is still called matrix alloy.

  This composite material is manufactured by impregnating under high pressure the reinforcing material with the alloy

  aluminum or matrix alloy in the liquid state.

  A method of manufacturing this composite material is described in particular in the patent application

  French Patent No 88 15113.

  An example of a material of this type comprises a reinforcement of short fibers of alumina, a matrix A 55 U 4 G 2

according to AFNOR standards.

  Referring to Figure 1, the insert 1 comprises: a central portion a, which is formed of composite material reinforced with ceramic fibers impregnated with an aluminum alloy; a face b of composite material where the ceramic fibers are flush, it is the useful face of the insert that allows the optimal exploitation of the properties of the composite material, this face will not come into contact with the casting alloy; a face c and a face d which are constituted by an extra thickness of aluminum alloy or alloy matrix, the aluminum alloy without fibers

so outcrops the faces c and d.

  The face c by its undercut, will serve only for the mechanical attachment between the insert and the

casting piece.

  As for the face d, it will be used as described below to create a chemical bond to the insert part interface, which allows the fixation

  between the room and the insert.

  The insert thus manufactured is then subjected to

chemical treatments.

  More specifically, the surface of the face d of the insert will undergo a chemical treatment and at least one

electrolytic treatment.

  Indeed, the face d described above has on its surface an impermeable and non-fusible alumina layer which hampers the subsequent chemical fixation between

the insert and the piece.

  To do this, it is necessary to eliminate

this layer of alumina.

  For this purpose, the surface d is subjected to a chemical treatment of the zincate type and preferably of the zinc iron type. This treatment is carried out using a solution containing zinc oxide, sodium hydroxide, potassium and sodium double tartrate and ferric chloride. The mechanisms used in the reaction

  are for the principals as follows.

  The reactions of the anodic type Al + H) Al (OH) 3 + 3 e Al (OH) A 10 + H + 20 allow to destroy the alumina layer, and the cathodic type reactions H + + e) 4 1 / 2 H 2 Zn (OH) 4 - Zn + 40H

2 + -

  Zn + 2 e Zn then form a layer of zinc, or zinc iron alloy

which replaces the alumina layer.

  In the case of the zinc iron alloy, this

  layer has an iron content of about 15%.

  With reference to FIG. 2, this layer represented at f is very thin, having a thickness

less than 1 micron.

  This layer f has the role of preventing the alumina layer from reforming on the surface of the face d of the insert, it thus avoids the superficial reoxidation of

the face d of the insert.

  But this thin layer is fragile and must be protected to facilitate handling and

  the preservation of the state of the surface of the insert.

  As a result, the surface of the insert, i.e., this face f, undergoes a treatment

  electrolytic to form a coating.

  A conventional coating is for example a

electrolytic deposition of nickel.

  The treatment is carried out in a bath containing nickel sulphate or sulphamate, nickel chloride,

and boric acid.

  A layer g of a few microns thick is formed, thus protecting the layer f and limiting the surface reoxidation of the insert before the casting of the piece Moreover, this layer f allows the diffusion of nickel in the aluminum alloy casting thus creating

  the chemical bond to the casting step of the part.

  Finally, under difficult casting conditions, it is possible to place on the layer g, an additional coating by electrolytic deposition

money.

  This coating is made from a bath typically containing: cyanide double silver and potassium, potassium cyanide and carbonate

of potassium.

  The silver layer thus obtained, with a thickness of a few microns, protects the surface of the insert better than nickel by more effectively limiting the reoxidation of the surface of the insert before casting. silver enhances the chemical bond at the insert coin interface because the diffusion coefficient of silver in aluminum is higher than that of nickel in aluminum. The faces of the insert thus prepared and treated ensure both mechanical attachment and

  a chemical bond to the coin insert interface.

  All forms of insert can be considered. The insert that will be placed in the mold for pouring the piece, may be in a temporary form, sometimes necessary to keep it immobile during the casting In this case, it will be machined after

  the casting step, in order to reach its final form.

  Then, the actual insertion step is

considered.

  All room configurations are

  possible, the molds being prepared accordingly.

  The insert comprising all of the coating layers f and g and possibly h on its face d is positioned inside the mold The latter is then

  closed and the casting of the piece can begin.

  All techniques of casting alloys

  current and future light weight can be applied here.

  The aluminum alloy of the part is cast according to specific parameters such as the temperature of the insert in the mold, the casting temperature of the liquid alloy and the amount of alloy which, in contact with the insert The combination of these parameters taken in combination acts on the creation of a chemical bond at the coin insert interface. An optimal combination of the

  parameters gives rise to a very good chemical bond.

  The casting thus comprising an insert, is

then demolded.

  The method of manufacturing an alloy part comprising an insert according to the invention, finds

  application in the automotive industry.

  In particular, cylinder heads of internal combustion engine, made of aluminum alloy, are thus produced. An example of insert intended to be introduced into a cylinder head, is shown in Figure 3 It has side faces 2 and 3 of concave shape, where will be housed the valves in the inter-seating areas 4 and 5 The insert in cross section according to Figure 4, has a trapezoidal section The undercuts 6 and 7 are used for the mechanical fixing of the insert, and the face 8 which will undergo the chemical and electrolytic treatments according to the invention, is used for the

  chemical fixation between the insert and the workpiece.

  The aluminum alloy of the cylinder head is then cast for example by gravity on this composite material insert which has undergone the chemical treatments and

  electrolytes mentioned above.

  In the case of the yokes, one or more inserts are, for example, disposed at the level of the zones

between the valve seats.

  Referring to Figure 5, the insert 1 is housed between two inter-valve seats areas 4 and 5 inside the cylinder head 9 Valves will come to

stay in spaces 10 and 11.

  FIG. 6 being a partial section of the cylinder head shown in FIG. 5, clearly shows the insert 1 fastened in particular by its face 8 to the cylinder head 9 by the chemical bond generated by the manufacturing process.

of the breech.

  The insert 1 is positioned between the spaces 10 and 11 or else the valve ducts, one duct

  intake, the other exhaust duct.

  The valve heads respectively 12 and 13 are housed against the insert 1 in the ducts 10 and 11, coming into contact with the insert 1 in the

zones 4 and 5.

  Similarly, the perspective view of FIG. 7 illustrates the positioning of the insert fixed in the cylinder head. The valve heads 12 and 13 can

  move on both sides of the insert 1.

  The aluminum alloy yoke thus manufactured, comprising an insert in at least one of its inter-seat valve zones, extends the life of the cylinder head by significantly improving the thermal fatigue life and the temperature yield stress.

  of these areas inter-valve seats.

  The cylinder head is therefore much more resistant to temperature variations during engine cycles,

compared to classic breeches.

  The invention is also applicable in the manufacture of other aluminum alloy parts

sank.

Claims (1)

1 A method of manufacturing cast aluminum alloy parts comprising an insert, characterized in that the insert is composed of a composite metal matrix material, which is constituted by a reinforcement based on ceramic fibers such as fibers alumina or alumina silica-felt, impregnated under high pressure by an aluminum alloy different from or identical to the casting alloy. 2 Process according to claim 1, characterized in that it involves subjecting a matrix alloy surface of at least one face (d) of the aforementioned insert (1), a chemical treatment of zincate type, followed by at least one electrolytic treatment such as a nickel coating to create a chemical bond at the insert-part interface. 3. Process according to claim 2, characterized in that the zincate treatment forms on the aforementioned surface a layer (f) of zinc or iron-zinc alloy containing approximately 15% iron. Process according to Claim 3, characterized in that the zincate chemical treatment is preferably a zinc iron treatment in a solution comprising zinc oxide, sodium hydroxide, ferric chloride and potassium double tartrate and sodium. Process according to claim 2, 3 or 4, characterized in that the electrolytic treatment is carried out from a solution of sulphate or nickel sulphamate, forming a layer (g) of nickel. Process according to claim 5, characterized in that the nickel sulfate or sulfamate solution further comprises nickel chloride and boric acid. Process according to one of Claims 2 to 6, characterized in that the abovementioned surface of the insert undergoes a second electrolytic treatment such as a coating of silver to form a layer (h) of silver. 8 Process according to one of claims 2 to 7, characterized in that the insert thus treated is introduced into a mold where the part is cast and in that the part comprising the insert is then removed from the mold. 9 cylinder head (9) of an internal combustion engine, provided with at least one insert (1), characterized in that said cylinder head (9) cast aluminum alloy, is manufactured by the process according to one of the claims 1 to 8.   Cylinder head according to claim 9, characterized in that said insert (1) is provided in   zones (4,5) between the valve seats.