Aluminum alloy cylinder head with valve seat formed integrally by copper alloy cladding layer and underlying alloy layer

This internal combustion engine cylinder head includes a main portion made substantially from aluminum alloy and having a valve port which has a circumferential valve seat surface for cooperation with a poppet valve to open and close communication through the valve port. A cladding layer is formed of copper alloy claddingly laid upon this valve seat surface, and an intermediate alloy layer is present between the copper alloy cladding layer and the main cylinder head portion, this intermediate alloy layer being composed essentially of an alloy between the aluminum alloy of the main cylinder head portion and the copper alloy of the cladding layer. Thereby, the anti-wear properties of the valve seat are desirably improved without making the fabrication process unduly troublesome or costly. The proportion of aluminum diffused into the copper alloy cladding layer from the main portion of the cylinder head should preferably be not more than about 15%. The thickness of the intermediate alloy layer should preferably be between about 5 microns and about 300 microns, and the thickness of the copper alloy cladding layer should preferably be at least about 50 microns. If "x" denotes the thickness of the intermediate alloy layer in microns, this thickness value being between about 5 and about 300, and if "y" denotes the thickness of the copper alloy cladding layer in mm, then preferably the relationship y=1.5254x+42.373 should at least approximately hold.

BACKGROUND OF THE INVENTION 
The present invention relates to a cylinder head for an internal combustion 
engine, and more particularly relates to such a cylinder head for an 
internal combustion engine for a vehicle such as an automobile, 
particularly which has a valve seat maunfactured integrally therein and 
endowed with exceptional wear resistance. 
The present invention has been described in Japanese Patent Application 
Ser. No. Showa 60-296191 (1985), filed by an applicant the same as the 
applicant or the entity assigned or owed duty of assignment of the present 
patent application; and the present patent application hereby incorporates 
into itself by reference the text of said Japanese Patent Application and 
the claims and the drawings thereof; a copy is appended to the present 
application. 
In the prior art, internal combustion engine cylinder heads have been often 
formed of aluminum alloys of various types, because of the advantages 
conferred upon such a material in view of its low weight and easy 
formability. However, the valve seat portions of such a cylinder head are 
very liable to wear, because they are repeatedly impacted by the intake or 
the exhaust poppet valves while the internal combustion engine is in 
operation, while simultaneously being exposed to extreme conditions of 
temperature and shock and gas abrasion and the like caused by the 
explosion of air-fuel mixture in the combustion chambers of the engine. As 
a result of this, in order to prevent excessive wear of and/or braking up 
and away of the valve seat portions of such a cylinder head made of 
aluminum alloy, due to friction and heat damage from frictional contact 
with the intake and the exhaust valves and with the products of combustion 
such as flaming gases, and also in order to limit dimensional changes of 
the valve seat portions due to thermal expansion caused by said hot 
combustion products, it has been in the past practiced to form a recess in 
the valve seat portion of the cylinder head by valve seat grinding or the 
like, and to insert, for example by cold pressing, into this recess a ring 
shaped valve seat insert made of cast iron or iron based sintered 
material. 
However, in such a conventional type of cylinder head with pressed in 
insert valve seat, there is the problem that it is quite common for a 
thermal air insulation layer to be formed between the pressed in valve 
seat and the material of the cylinder head, and as a result of this, when 
under the operating conditions of the internal combustion engine the 
cylinder head and the valve seat are exposed to extremely high 
temperature, the transmission of heat from the valve seat to the cylinder 
head can be substantially obstructed by this thermal air insulation layer. 
As a result of this, the valve seat is liable to become unduly hot, 
particularly at particular portions thereof corresponding to points at 
which said thermal air insulation layer is thicker than at other points 
thereof--for the thermal air insulation layer is typically not of the same 
thickness all around the valve seat. In such a case, deterioration of 
various operational characteristics, including deterioration of the wear 
resistance of the valve seat, are liable to occur. 
Furthermore, since the coefficent of thermal expansion and the coefficient 
of thermal conduction of such cast iron or sintered iron based material of 
which the valve seat is typically made are very different from the 
corresponding coefficients relating to the aluminum alloy of which the 
main body of the cylinder head is made, thereby, when the valve seat is 
pressed into the cylinder head itself, in view of these differences in 
thermal conductivity and thermal expansion, very high dimensional accuracy 
of the valve seat and of the recess in the cylinder head for receiving it 
become crucially important, and thus complicated and painstaking machining 
processes come to be required. This inevitably entails high cost. 
A further problem that is encountered is that it is necessary to determine 
the strength and the dimensions of the portion of the cylinder head itself 
which receives the valve seat to be sufficient to reliably hold the valve 
seat when said valve seat is pressed into said cylinder head portion, and 
therefore the diameter of the valve seat and the diameters of the intake 
and the exhaust poppet valves come to be restricted, and it is in such a 
case difficult to increase the cooling efficiency of the cooling system 
for the cylinder head by making the coolant passages within said cylinder 
head very closely approach the valve seats and the combustion chambers. 
Thus, it becomes difficult to provide high performance of the internal 
combustion engine. 
In order to resolve the above outlined problems with regard to forming the 
valve seat portions in a conventional cylinder head, methods of alloying 
which may be considered applicable to the formation of a valve seat 
portion of a cylinder head have been described in Japanese Patent Laying 
Open Publications Ser. Nos. 55-8497 (1980) and 57-171572 (1982), neither 
of which is it intended hereby to admit as prior art to the present patent 
application except to the extent in any case required by applicable law. 
In these methods, there is disclosed the concept whereby the surface 
portion of a metal sample made of a base metal material is melted by the 
use of a high energy source, an alloying material is added to this melted 
base metal surface portion, and then the melted and alloy portion is 
rapidly cooled down by absorption of heat by the other portions of the 
sample, whereby an alloy layer is formed on the surface of the base metal 
portion, comprising the base metal material and the alloy material alloyed 
therewith. Furthermore, in SAE Technical Paper Series 850406 there is 
described an internal combustion engine cylinder head in which a valve 
seat surface is defined by using such a local surface alloying method. 
When the above type of alloying method is applied to the formation of a 
valve seat portion of a cylinder head which is made of aluminum alloy, all 
of the alloying material is melted into the aluminum alloy base material, 
and therefore a layer of substantially only the alloying material is 
definitely not formed on the surface of the alloy layer which is formed. 
Thus, the surface layer of the valve seat is in fact an aluminum alloy of 
a different composition from the aluminum alloy which makes up the main 
body of the cylinder head, but which is manufactured therefrom by alloying 
thereto the added alloying material. As a result of this, it is difficult 
satisfactorily to improve the wear resistance characteristics and so on of 
the valve seat. Again, when elements such as silicon and nickel and so on 
are added as alloying materials in order to improve the wear resistance 
and the heat resistance and so on of the valve seat, primary crystalline 
silicon and metallic compounds such as nickel-aluminum are formed, and 
these come to be distributed finely throughout the alloy layer. Such 
primary crystalline silicon and metallic compounds such as nickel-aluminum 
have good heat resistance, but, since the basic composition of the surface 
of the valve seat is inevitably that of an aluminum alloy material, if 
such a valve seat is exposed to a relatively high temperature such as 
about 150.degree. C. for at least about 100 hours continuously, then the 
strength, the heat resistance, and the like of the valve seat surface will 
inevitably be severely deteriorated and in the worst case the valve seat 
will completely fail. Thus, such an aluminum alloy layer type valve seat 
surface is not durable enough for practical use in an internal combustion 
engine. If, in order to improve the heat resistance, the amount of the 
above described primary crystalline silicon and metallic compound such as 
nickel-aluminum is increased, then although such distributed materials 
have good heat resistance, since their toughness is extremely small and is 
in fact close to zero, a hard but extremely brittle alloy layer is formed 
as the valve seat surface. In an alloy layer thus formed, the problem 
arises that cracks may have already occurred after the formation thereof 
and even before the use thereof, and therefore such an alloy layer, 
although it can be described and conceived of from a theoretical 
standpoint, is not a practically useful material. 
Also, with an alloying type surface preparation method such as described 
above for a valve seat surface for a cylinder head of an internal 
combustion engine, the rate of cooling of the alloy layer decreases in 
order from the interface with the main body portion of the cylinder head, 
the interior of the alloy layer, and the surface of the alloy layer, and 
it is not possible to ensure a uniform rate of cooling for all portions of 
the alloy layer, as a result of which it is difficult to obtain a uniform 
composition of the alloy layer, and in particular it is difficult to make 
the wear resistance of the surface of the alloy layer high, and therefore 
in the formation of the valve seat portion of the cylinder head a thick 
alloy layer is formed, and it is necessary in practice to apply a 
machining process with a relatively high process cost to the surface of 
the alloy layer. 
SUMMARY OF THE INVENTION 
The inventors of the present invention have considered the various problems 
detailed above in the conventional case of a pressed in valve seat insert 
portion being utilized for a cylinder head, and also in the case of 
applying a surface alloying method to the portion of such a cylinder head 
which is to constitute a valve seat portion thereof, from the point of 
view of the desirability of improving the working effectiveness and the 
quality and durability of the resulting cylinder head. 
Accordingly, it is the primary object of the present invention to provide 
an internal combustion engine cylinder head, which avoids the problems 
detailed above. 
It is a further object of the present invention to provide such an internal 
combustion engine cylinder head, which, in order to provide a good quality 
valve seat portion for an intake or an exhaust poppet valve, does not 
require any insert portions to be manufactured or inserted into any 
recesses thereof. 
It is a further object of the present invention to provide such an internal 
combustion engine cylinder head, which provides good heat transmission 
characteristics for a valve seat portion thereof. 
It is a further object of the present invention to provide such an internal 
combustion engine cylinder head, which keeps the equilibrium or operating 
temperature of a valve seat portion thereof relatively low. 
It is a further object of the present invention to provide such an internal 
combustion engine cylinder head, a valve seat portion of which has 
relatively superior heat resistance characteristics. 
It is a further object of the present invention to provide such an internal 
combustion engine cylinder head, a valve seat portion of which has 
relatively superior wear resistance characteristics. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which minimizes cost. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which minimizes the amount of 
accurate machining required during manufacture. 
It is yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which allows for the valves 
fitted therein to be made as large as practicable. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which allows for the cooling of 
the valves fitted therein to be as good as practicable. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which allows for the cooling of 
the combustion chamber defined therein to be as good as practicable. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which is compact and light in 
weight. 
It is a yet further object of the present invention to provide such an 
internal combustion engine cylinder head, which provides good performance 
for the internal combustion engine incorporating it. 
According to the most general aspect of the present invention, these and 
other objects are attained by a cylinder head for an internal combustion 
engine including a poppet valve, comprising: a main portion made 
substantially from aluminum alloy and generally formed with a valve port 
which has a circumferential valve seat surface for cooperation with said 
poppet valve to open and close communication through said valve port; a 
cladding layer formed of copper alloy claddingly laid upon said 
circumferential valve seat surface; and an intermediate alloy layer 
between said copper alloy cladding layer and said main portion of said 
cylinder head, composed essentially of an alloy of said alluminum alloy of 
said main portion of said cylinder head and said copper alloy of said 
copper alloy cladding layer. 
According to such an internal combustion engine cylinder head as specified 
above, since the valve seat surface is defined by a cladding layer of 
copper alloy which is cladded on the aluminum alloy base material of the 
cylinder head, since the thermal conduction rate of copper alloy is high 
compared with that of cast iron or the like and moreover the cladded layer 
is continuous with the base cylinder head material via the alloy larger, 
as a result heat received by the valve seat portion is conducted 
effectively to the base cylinder head material, and thereby, when the 
internal combustion engine is operating, the final or equilibrium 
operating temperature of the valve seat portion is reduced, as compared 
with a conventional pressed in type of valve seat for a cylinder head. 
Therefore, by choosing as the copper alloy to form the cladding layer an 
alloy whose composition has superior wear resistance characteristics, the 
wear resistance characteristics of the valve seat surface can be improved. 
Since, moreover, the valve seat surface is defined by the cladding layer, 
and is not defined by any alloy layer in which is present a large quantity 
of aluminium from the base cylinder head material as in the case where the 
valve seat portion is formed by an alloying method, thereby the basic 
composition of the cladding layer is the composition of a copper alloy 
having the desired characteristics of wear resistance and so forth or in a 
composition close thereto, and therefore, by comparison with the 
previously described case in which the cylinder head valve seat portion is 
formed by an alloying method, the durability of the cylinder head can be 
greatly improved. 
Since furthermore an alloy layer is present between the cladding layer and 
the base cylinder head material, and the cladding layer and the base 
cylinder head material are integrated through this alloy layer, therefore, 
as compared with the case of a conventional pressed in valve seat type 
cylinder head or with the case in which the valve seat portion is formed 
as an alloy layer without any cladding layer being provided, the 
integrated nature of the valve seat portion with respect to other portions 
of the cylinder head is remarkably improved. 
Since furthermore the total thickness of the cladding layer and of the 
alloy layer may be less than that of a valve seat which is pressed in, and 
since there is no requirement to provide any recessed portion around the 
valve seat for receiving any separate valve seat member, the diameter of 
the intake or the exhaust valve for the internal combustion engine can be 
increased, and it is possible for the coolant passages in the cylinder 
head to be made as passing closer to the valve seat portions of the 
cylinder head and to the combustion chambers thereof, whereby relatively 
higher performance of the internal combustion engine can be obtained. 
Since furthermore it is not necessary, as in the contrasting case of a 
pressed in valve seat type cylinder head, to manufacture a valve seat 
member in a material other than aluminium alloy with high accuracy, nor is 
it necessary to form any recess in the cylinder head itself to accept such 
a valve seat member with high accuracy, nor it is required to fix any such 
valve seat member to the cylinder head itself by any complicated pressing 
operation, thereby the cost of the cylinder head can be beneficially 
reduced. 
It has been discovered, according to various experimental researches 
conducted by the present inventors as will be particularly described 
later, that, as the dilution amount from the base aluminum alloy material 
of the cylinder head into the cladding layer material which is the copper 
alloy material increases, various characteristics of the cladding layer, 
and particularly the wear resistance thereof, are deteriorated, and 
further the number of blow holes therein increases. Therefore, according 
to a particular specialization of the present invention, the above and 
other objects may more particularly be accomplished by such an internal 
combustion engine cylinder head as first specified above, wherein the 
percentage proportion of aluminum diffused into said copper alloy cladding 
layer from said main portion of said cylinder head is not more than about 
15%. Now, according to the results of the experimental researches carried 
out by the present inventors as will be described hereinafter, as the 
thickness of the alloy layer increases, the percentage dilution of 
aluminium from the base cylinder head material into the cladding layer 
increases; while, on the other hand, if the thickness of said alloy layer 
is too little, the cladding layer tends to become detached from the base 
cylinder head material, and durability is deteriorated. Also, further 
according to the result of experimental research carried out by the 
inventors of the present application, a substantially linear relationship 
holds between the percentage dilution of aluminium from the base cylinder 
head material into the cladding layer and the thickness of the alloy 
layer, and it has been confirmed that if the thickness of the alloy layer 
exceeds 300 microns then the dilution amount of the aluminium alloy base 
metal into the cladding layer will be higher than about 15%. Therefore, 
according to another detailed characteristic of the present invention, the 
thickness of the alloy layer is preferably set to be between about 5 and 
about 300 microns, and even more preferably is set to be between about 10 
and about 260 microns. In this case, whereas with regard to the cladding 
process itself it is relatively difficult to set and control the cladding 
conditions so that a priori the aluminium dilution amount is definitely 
not more than 15%, it is on the other hand relatively easy to control the 
thickness of the alloy layer to be within the above ranges. 
Furthermore, according to results of experimental research carried out by 
the inventors of the present application, as also described in more detail 
below, if the thickness of the cladding layer is too small, when the 
internal combustion engine has been operating for a long time, the 
cladding layer is liable to become worn away, and in such a case the alloy 
layer will be exposed to the valve seat surface, and as a result the wear 
resistance of the valve seat surface will be drastically reduced and early 
failure of the internal combustion engine as a whole will likely ensure. 
Therefore, according to yet another detailed characteristic of the present 
invention, the thickness of the cladding layer is set to be as least about 
50 microns, and preferably is set to be at least about 200 microns. 
Furthermore, according to results of the experimental researches carried 
out by the inventors of the present application as described in more 
detail below, the thickness of the required cladding layer depends on the 
thickness of the alloy layer, and increases as the thickness of the alloy 
layer increases. Therefore according to yet another detailed 
characteristic of the present invention, denoting by "x" the thickness of 
said intermediate alloy layer in microns, said thickness x in microns 
being between about 5 and about 300, and denoting by "y" the thickness of 
said copper alloy cladding layer in mm, the following relationship holds 
at least approximately: y=1.5254x+42.373. 
If the thickness of the cladding layer is excessive, there will be no 
problems with the characteristics thereof, but some of the relatively 
expensive copper alloy will have been wasted, and the energy required for 
the clading process will have been increased. Therefore, according to yet 
another detailed characteristic of the present invention, the thickness of 
the copper alloy cladding layer is set to be not more than about 700 
microns, and even more preferably is set to be not more than about 500 
microns. 
The copper alloy for forming the cladding layer may be any copper alloy 
which is capable of cladding on an aluminium alloy matrix material and 
which has good resistance to wear, good resistance to heat, and good 
resistance to corrosion, and this copper alloy cladding material is 
preferably an alloy of copper, nickel and iron, such as: a copper alloy 
with a composition of about 15.0% nickel, and about 3.0% iron, about 1.0% 
phosphorus, and remainder substantially copper; a copper alloy with a 
composition of about 20.0% nickel, about 4.5% iron, about 1.0% phosphorus, 
and remainder substantailly copper; or a copper alloy with a composition 
of about 25.0% nickel, about 2.5% iron, about 1.0% phosphorus, and 
remainder substantially copper. Further, as a method of cladding the 
copper alloy on the aluminium alloy matrix material, any cladding method 
may be performed, such as one using a high intensity energy source such as 
a laser, a TIG arc, or an electron beam, but particularly the cladding 
method disclosed in Japanese Patent Application Sho 60-157622 (1985), 
being an application by an applicant the same as the applicant of or the 
entity assigned or owed duty of assignment of the present patent 
application, is considered to be suitable; however, it is not intended 
hereby to admit this document as prior art to the present patent 
application, except to the extent in any case required by applicable law. 
It should be noted that in this specification all percentages are 
percentages by weight, and all measurements are given in units of the 
metric system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to various 
preferred embodiments thereof, and with reference to the figures. 
In the first preferred embodiment of the internal combustion engine 
cylinder head of the present invention, an intake side portion of which is 
shown in partial longitudinal cross sectional view in FIG. 1, the 
reference numeral 11 denotes the cylinder head as a whole, while 12 
denotes an intake port formed in this cylinder head 11 and 13 is a 
combustion chamber depression defined on a surface of said cylinder head 
11 which is adapted for being mated with a cylinder block, not 
particularly shown in any of the figures, so as to define a combustion 
chamber to which said intake port 12 opens. In fact, of course, typically 
this cylinder head 11 is formed with several such combustion chamber 
depressions 13 and so on, and defines several such combustion chambers; 
however, only one set of such arrangements is shown in the figures. And 
each said combustion chamber is formed with an exhaust side portion which 
is formed with an exhaust port; again, none of these arrangements are 
particularly shown. Through an upper portion of the defining wall surface 
of the intake port 12 there is fitted a valve guide 14, and in this valve 
guide 14 there is slidably fitted an intake valve 15 which is a poppet 
valve having a valve head 16 which is generally disk shaped and has a 
conical frustum shaped valve head mating surface formed on its annular 
peripheral edge portion. Corresponding to this, the cylinder head 11 is 
formed at its portion where the intake port 12 opens into the combustion 
chamber depression 13 with a valve seat portion 18 which is shaped with a 
conical frustum shaped valve seat surface 17. Thus, when the intake valve 
15 is displaced downwards with respect to the valve guide 14 as shown in 
FIG. 1, its valve head mating surface is displaced away from the valve 
seat surface 17 of the cylinder head 11, thus leaving an ample gap for the 
passage of intake gases from the intake port 12 into the engine combustion 
chamber defined by the combustion chamber depression 13; but, when on the 
other hand said intake valve 15 is displaced downwards with respect to 
said valve guide 14 as shown in FIG. 1, its said valve head mating surface 
is pressed against said valve seat surface 17 of said cylinder head 11 and 
closely cooperates therewith, thus completely closing said gap 
therebetween and positively preventing any passage of intake gases from 
said intake port 12 into said engine combustion chamber or in the reverse 
direction, thereby sealing said combustion chamber for the combustive 
explosion of combustion gases therein. So far the construction is per se 
conventional. 
In FIG. 2 there is shown an enlarged view of a portion of the sectional 
view of FIG. 1, particularly showing a cross section of the valve seat 
portion 18 of this preferred embodiment internal combustion engine 
cylinder head, and of its valve seat surface 17. In detail, the main body 
19 of the cylinder head is made of aluminum alloy of a per se known type, 
and the valve seat surface 17 is defined by being formed on a copper alloy 
cladding layer 20 of copper alloy material which is claddingly laid, as 
will be described shortly hereinafter, on an appropriate part of the 
portion of said cylinder head 11 where the intake port 12 opens into the 
combustion chamber depression 13. And, between the main aluminum alloy 
body portion 19 of the cylinder head 11 and the copper alloy cladding 
layer 20, there is also formed, as also will be defined shortly, an 
intermediate layer 21 of alloy material produced by alloyingly mixing the 
elements of the aluminum alloy which composes the cylinder head 11 and the 
copper alloy which composes the copper alloy cladding layer 20. And the 
main aluminum alloy body portion 19 of the cylinder head, the intermediate 
alloy layer 21, and the copper alloy cladding layer 20 are in fact 
integral and continuous with one another, actually blending into one 
another without any such discontinuous boundaries being defined as are 
shown in FIG. 2 for the purposes of illustrative explanation only. 
For reasons which will be described in detail hereinafter, the dilution 
amount of aluminum alloy from the main aluminum alloy body portion 19 of 
the cylinder head into the copper alloy cladding layer 20 is restricted to 
be not more than about 15%, the thickness of the intermediate alloy layer 
21 is required to be in the range of from about 5 to about 300 microns, 
and the thickness of the copper alloy cladding layer 20 is required to be 
at least 50 microns. 
WORKING EXAMPLE 
Now, a particular working example of the preferred invention, which 
constitutes a preferred embodiment thereof, will be explained. 
First, a cylinder head rough casting denoted as 22 was formed from an 
aluminum alloy material of JIS standard AC2C, having nominal composition 
of from about 2.0% to about 4.0% copper, from about 5.0% to about 7.0% 
silicon, from about 0.2% to about 0.4% magnesium, not more than about 0.5% 
zinc, not more than about 0.5% iron, from about 0.2% to about 0.4% 
manganese, not more than about 0.35% nickel, not more than about 0.2% 
titanium, not more than about 0.2% lead, not more than about 0.1% tin, not 
more than about 0.2% chromium, and remainder substantially aluminum. Next, 
as shown in FIG. 3 in schematic sectional view, the cylinder head rough 
casting work piece 22 was rotated as a unit around the central axis of the 
portion 23 thereof which was to constitute the valve seat portion 18 in 
the finished product (i.e. was rotated around the central axis of the hole 
formed for the valve guide 14), and while this was being done the surface 
24 thereof which corresonded to the valve seat surface 17 of the finished 
product was steadily supplied from a powder supply nozzle 25 with a layer 
26 of powder of a copper alloy, composition about 15.0% nickel, from about 
3.0% iron, from about 1.0% phosphorus, and remained substantially copper, 
with the assistance of an assist gas flow, and this laid down copper alloy 
powder layer 26 was carried into the path of and was irradiated by the 
beam 27 of a CO.sub.2 laser which followed behind said powder supply 
nozzle 25 and was oscillated rapidly to and fro in a direction 
perpendicular to the drawing paper in FIG. 3 (i.e. transverse to the 
direction of advancement of the process), so that said copper alloy powder 
layer 26 was thereby melted along with a portion of the substrate aluminum 
alloy material of the cylinder head rough casting work piece 22 on which 
said copper alloy powder layer 26 rested, to subsequently congeal in the 
wake of the CO.sub.2 laser beam 27 as a cladding layer 28 (which 
corresponds to the copper alloy cladding layer 20 of FIG. 2) with an 
intermediate alloy layer 21 lying underneath it which is not shown in FIG. 
3, said intermediate alloy layer 21 being composed of a mixture of the 
copper alloy material of said copper alloy cladding layer 20 and the 
aluminum alloy material of which the cylinder head rough casting work 
piece 22 was made. In this exemplary implementation: the laser output was 
about 2.0 Kw; the output mode was multi mode; the laser beam diameter was 
about 1.0 mm; the assist gas was argon gas and had a flow rate of about 
0.5 kg/cm.sup.2 by 10 liters/minute; the thickness of the copper alloy 
powder layer 26 was about 1.0 mm; the rate of advancement of the process 
(i.e. the peripheral speed of the valve seat rough surface 24) was about 
300 mm/minute; the oscillation frequency of the laser beam 27 was about 
150 Hz; and the width of said laser beam 27 was about 5 mm. Lastly, 
machine processing such as grinding was applied to the resultant work 
piece, to finally form a cylinder head with valve seat integrally formed 
therein such as shown in FIGS. 1 and 2. 
FIG. 4 is a sectional photo micrograph taken at an enlargement of 10.times. 
in a longitudinal sectional plane which includes the central axis of the 
valve guide 14, showing the thus produced valve seat portion 18 of the 
cylinder head 11 along with an adjoining portion of the substrate aluminum 
alloy material of said cylinder head 11. The central horizontally 
extending line portion in FIG. 4 is the valve seat surface 17, and the 
white colored portion directly below that line is the copper alloy 
cladding layer 20; the black colored portion directly below said copper 
alloy 20 is the intermediate alloy layer 21 which is of relatively large 
crystalline structure, and below said intermediate alloy layer 21 there is 
the main aluminum alloy body portion 19 of the cylinder head which is 
speckled in color. As will be clear from this photo micrograph, 
substantially no blow holes or cracks or other defects are produced in the 
copper alloy cladding layer 20 or in the intermediate alloy layer 21. 
By measurement, it was established that the thickness of the copper alloy 
cladding layer 20 was from about 100 microns to about 300 microns, the 
thickness of the intermediate alloy layer 21 was from about 50 microns to 
about 250 microns, and the average dilution amount of aluminum in said 
copper alloy cladding layer 20 was not more than about 10%. 
In order to form an estimate of the characteristics of the cylinder head 
11, hereinafter designated as "A", formed as described above, a bench 
durability test was carried out by using said cylinder head A in a test 
engine and running said test engine for about 200 hours at substantially 
full load at a rotational speed of approximately 6,500 rpm. The depression 
amount of the valve seat surface 17 of the valve seat portion 18, i.e. the 
change in the axial position of the intake valve 15 when in its closed 
position, was then measured, and was taken as being the amount of wear on 
said valve seat surface 17. Further, for the purpose of comparison, four 
similar tests were run using four comparison cylinder heads which were not 
embodiments of the present invention: a cylinder head hereinafter 
designated as "B", made of aluminum alloy of type ASTM standard A390 with 
nominal composition from about 16.0% to about 18.0% silicon, from about 
4.0% to about 5.0% copper, not more than about 1.3% iron, from about 0.45% 
to about 0.65% magnesium, and remainder substantially aluminum, of which 
the valve seat portions were not specially prepared by any cladding or the 
like process and accordingly were not particularly differentiated from the 
main body of said cylinder head B; a cylinder head hereinafter designated 
as "C", made by pressing a valve seat formed of aluminum alloy of said 
type ASTM standard A390 into a cylinder head formed of another aluminum 
alloy of the type JIS standard AC2C described above; a cylinder head 
hereinafter designated as "D", made of aluminum alloy of said type ASTM 
standard A390, of which the valve seat portions were prepared by alloying, 
so that said valve seat portions were defined in an alloy layer of 
composition about 16.0% to about 18.0% silicon, not more than about 10% 
copper, not more than about 5.0% nickel, not more than about 1.3% iron, 
from about 0.45% to about 0.65% magnesium, and remainder substantially 
aluminum; and a cylinder head hereinafter designated as "E", made by 
pressing a valve seat formed of a sintered iron type material of 
composition about 10.0% to about 16.0% copper, from about 3.5% to about 
8.0% lead, from about 3.0% to about 5.0% molybdenum, from about 0.05% to 
about 0.30% carbon, and remainder substantially iron, into a cylinder head 
formed of aluminum alloy of the type JIS standard AC2C described above. 
The results of these tests are shown in the graph of FIG. 5, in which 
elapsed test time in hours is shown along the horizontal axis and wear 
amount of the valve seats of the various above detailed cylinder heads is 
shown in mm along the vertical axis. 
From this FIG. 5 graph it will be understood that for all of the three 
comparison cylinder heads B through D the wear amount of the valve seat 
surface was extremely high within the short time after the start of the 
test. Furthermore, it will be seen that, in the case of the comparison 
cylinder head E which had a conventional type of pressed in valve seat 
made of a sintered iron type material, even after the full 200 hours of 
testing the wear amount on the valve seat was less than 0.4 mm, which is a 
typical amount that can be actually allowed for an internal combustion 
engine, but the wear amount of the cylinder head A which is a preferred 
embodiment of the present invention was substantially less even than said 
relatively acceptable wear amount of said comparison cylinder head E. 
Therefore, it is seen that the cylinder head A, being a preferred 
embodiment of the present invention, had overall superior characteristics 
as regarded wear performance, when compared with cylinder heads generally 
used conventionally. 
Next, a discussion will be made of the appropriate range for the thickness 
of the intermediate alloy layer 21 and of how it is related to the 
dilution of aluminum alloy into the copper alloy cladding layer 20. By 
varying the processing conditions of the laser cladding process described 
above in various other tests which will not be described in detail herein 
in view of the desirability of conciseness of disclosure, various other 
test cylinder heads were produced, the thickness of the intermediate alloy 
layer 21 of the valve seat portions thereof being of various different 
values. In each case, the percentage of dilution of aluminum alloy into 
the material of the copper alloy cladding layer 20 was measured, along 
with the amount of blow holes in said copper alloy cladding layer 20 and 
said intermediate alloy layer 21 (measured as the number of blow holes per 
cm.sup.2). Then, for each of these cylinder heads, a bench durability test 
carried out under substantially the same or similar conditions as in the 
case of the tests outlined above; and in each case the amount of wear 
(depression) on the valve seat portion was measured, substantially as 
before. The results of these tests are shown in FIG. 6, in which the 
thickness of the intermediate alloy layer 21 is shown along the horizontal 
axis and the valve seat portion wear amount, the blow hole count, and the 
percentage aluminum dilution into the cladding layer 20 are all shown 
along their own vertical axes. 
Further, another battery of tests was run, substantially the same as the 
FIG. 6 tests, except in that as the copper alloy used for forming the 
copper alloy cladding layer 20 there was utilized a quantity of copper 
alloy having composition of about 25.0% nickel, about 2.5% iron, about 
1.0% phosphorous, and balance substantially copper. The results of these 
tests are shown in FIG. 7, which is similar to FIG. 6 for the first 
battery of tests. 
From FIGS. 6 and 7, it will be clear that there is a close relation between 
the percentage of dilution of aluminum alloy into the material of the 
copper alloy cladding layer 20 and the thickness of the intermediate alloy 
21. When the thickness of the intermediate alloy layer 21 is relatively 
low, for instance in the case when said thickness is about 5 microns, the 
aluminum dilution amount into the copper alloy cladding layer 20 is 
approximately zero (i.e., is 0.5% or less), while as the thickness of said 
intermediate alloy layer 21 increases the aluminum dilution amount into 
the cladding layer increases substantially linearly in such a manner that, 
when the thickness of the intermediate alloy layer 21 is approximately 300 
microns the aluminum dilution amount is approximately 15% or greater. It 
will also be seen that the amount of wear on the valve seat surface 
increases as the thickness of said intermediate alloy layer 21 increases, 
although the relationship is not linear in this case. Additionally, it 
will be seen that the number of blow holes is relatively small when the 
thickness of the alloy layer 21 is less than about 300 microns, and 
particularly is very reasonably small when said thickness of said alloy 
layer 21 is less than about 250 microns, but on the other hand increases 
rapidly when the thickness of said intermediate alloy layer 21 increases 
above about 300 microns. It will further be understood that, when the 
thickness of the alloy layer 21 is too small, the copper alloy cladding 
layer 20 tends to become detached from the main aluminum alloy body 
portion 19 of the cylinder head; and thus, in order to restrict the amount 
of depression of the valve seat portions of the cylinder head to a value 
of about 0.4 mm or less, which as explained above is a typical actually 
acceptable value in the case of such a bench durability test as described 
above, and for stable results of the valve seats during operation, it is 
desired that the thickness of the intermediate alloy layer 21 should be 
from about 5 microns to about 300 microns, and more preferably should be 
from about 10 microns to about 260 microns. 
The reason for the amounts of depression of the valve seat portions of the 
cylinder heads in the FIG. 7 tests being substantially less than the 
corresponding amounts of depression of the valve seat portions of the 
cylinder heads of the FIG. 6 tests is surmised to be that, because the 
amount of nickel included in the copper alloy used to form the copper 
alloy cladding layer 20 is greater in the case of the FIG. 7 tests than in 
the FIG. 6 tests, the heat resistance of the copper alloy cladding layer 
20 is thereby improved by this additional nickel. 
Next, a discussion will be made of the minimum required thickness for the 
copper alloy cladding layer 20. FIG. 8 is a schematic enlarged sectional 
diagram of the valve seat portion shown in FIGS. 1 and 2, and illustrates 
the relationship between the thickness reduction amount denoted as 
"delta-t" of the copper alloy cladding layer 20 and the amount of wear 
(depression) on the valve seat portion, denoted as "h"; further, "y" 
denotes the thickness of the copper alloy cladding layer 20. And FIG. 9 is 
based upon the data of FIG. 6, and shows the thickness of the intermediate 
alloy layer 21 along the horizontal axis and the valve seat portion wear 
amount and the minimum required thickness for the cladding layer 20 along 
their own vertical axes. 
Referring to FIG. 8, it will be seen that in this typical case the angle 
between the valve seat surface 17 and the axis of to and fro motion of the 
intake valve 15 is 45.degree., i.e. the semi angle of the cone defined by 
said valve seat surface 17 is 45.degree.. Therefore, the relation between 
the amount of wear h on the valve seat surface 17 as defined above (the 
change in the closed axial position of the intake valve 15) and the 
reduction delta-t in the thickness of the copper alloy cladding layer 20 
is that h is equal to delta-t multiplied by 21/2. Therefore, in the case 
of the FIG. 9 configuration, if it is for example the case that the 
thickness of the intermediate alloy layer 21 is 5 microns, the amount of 
wear h on the valve seat surface 17 is about 0.02 mm, and then in this 
case the minimum required thickness t for the copper alloy cladding layer 
20 is given, approximately, by: 
EQU t=0.02/21/2 mm=0.0141 mm=14.1 microns 
It will therefore be seen that, in this first exemplary case that the 
thickness of the intermediate alloy layer 21 is about 5 microns, it may be 
adequate for the copper alloy cladding layer 20 to have thickness y equal 
to about 15 microns; but, in order to provide stability, said thickness y 
of said copper alloy cladding layer 20 should preferably be set to be at 
least about 50 microns. On the other hand, in the case that the thickness 
of the intermediate alloy layer 21 is about 300 microns, the amount of 
wear h on the valve seat surface 17 is about 0.35 mm, and then in this 
case the minimum required thickness t for the copper alloy cladding layer 
20 is given, again approximately, by: 
EQU t=0.35/21/2 mm=0.245 mm=245 microns 
It will therefore be seen that, in this second exemplary case that the 
thickness of the intermediate alloy layer 21 is about 300 microns, it may 
be adequate for the copper alloy cladding layer 20 to have thickness y 
equal to about 250 microns; but, in order to provide stability, said 
thickness y of said copper alloy cladding layer 20 should preferably be 
set to be at least about 500 microns. 
When, on the other hand, the thickness y of the intermediate alloy layer 21 
is between about 5 microns and about 300 microns, then a proportionality 
equation may be applied to the cases above for which the thickness of said 
intermediate alloy layer 21 was about 5 microns and was about 300 microns, 
and thereby it can be determined that it is adequate and satisfactory, in 
other words is preferable, for the thickness y of the copper alloy 
cladding layer 20, in microns, to be approximately determined by the 
following equation, where "x" represents the thickness of the intermediate 
alloy layer 21: 
EQU y=1.5254x+42.373 
CONCLUSION 
Although the present invention has been shown and described in terms of the 
preferred embodiments thereof, and with reference to the appended 
drawings, it should not be considered as being particularly limited 
thereby, since the details of any particular embodiment or of the 
drawings, could be varied without, in many cases, departing from the ambit 
of the present invention. Accordingly, the scope of the present invention 
is to be considered as being delimited, not by any particular perhaps 
entirely fortuitous details of the disclosed preferred embodiments, or of 
the drawings, but solely by the scope of the accompanying claims, which 
follow.