U.S. patent application number 11/435399 was filed with the patent office on 2006-11-30 for forged piston.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Hidenori Fujii, Tomoo Oka.
Application Number | 20060266443 11/435399 |
Document ID | / |
Family ID | 37461931 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266443 |
Kind Code |
A1 |
Oka; Tomoo ; et al. |
November 30, 2006 |
Forged piston
Abstract
To provide a forged piston made of an aluminum alloy which is
excellent in heat resistance and abrasion resistance and the
lightening of which is enabled. A forged piston made of an aluminum
alloy is provided including 8 to 18 wt % of Si, 0.5 to 3 wt % of Cu
and 1 to 5 wt % of Ni, further including Al and unavoidable
impurities, in which more Ni is included than Cu and the maximum
length of an intermetallic compound generated by Al and Ni is 3 to
100 .mu.m.
Inventors: |
Oka; Tomoo; (Wako-shi,
JP) ; Fujii; Hidenori; (Wako-shi, JP) |
Correspondence
Address: |
HAMRE, SCHUMANN, MUELLER & LARSON, P.C.
P.O. BOX 2902
MINNEAPOLIS
MN
55402-0902
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Minato-ku
JP
|
Family ID: |
37461931 |
Appl. No.: |
11/435399 |
Filed: |
May 16, 2006 |
Current U.S.
Class: |
148/438 ;
420/534; 420/537 |
Current CPC
Class: |
C22C 21/02 20130101 |
Class at
Publication: |
148/438 ;
420/534; 420/537 |
International
Class: |
C22C 21/04 20060101
C22C021/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2005 |
JP |
2005-153740 |
Claims
1. A forged piston made of an aluminum alloy, comprising: 8 to 18
wt % of Si; 0.5 to 3 wt % of Cu; and 1 to 5 wt % of Ni, further
comprising: Al; and unavoidable impurities, wherein: more Ni is
included than Cu; and the maximum length of an intermetallic
compound generated by Al and Ni is 3 to 100 .mu.m.
2. A forged piston made of an aluminum alloy, comprising: 8 to 18
wt % of Si; 0.5 to 3 wt % of Cu; 1 to 5 wt % of Ni; and 2.0 wt % or
less of Fe, further comprising: Al; and unavoidable impurities,
wherein: the total of Ni and Fe is more than Cu and is equivalent
to 5 wt % or less; and the maximum length of an intermetallic
compound generated by Al, Ni and Fe is 3 to 100 .mu.m.
3. A forged piston according to claim 1, wherein: the aluminum
alloy further includes 2.0 wt % or less of Mg.
4. A forged piston according to claim 1, wherein: the aluminum
alloy further includes at least either of 0.25 wt % or less of Zr,
or 0.25 wt % or less of Ti; and the total of Zr and Ti in the case
where Zr and Ti are both included is equivalent to 0.3 wt % or
less.
5. A forged piston according to any of claim 1, wherein: the
aluminum alloy further includes at least either of 2.0 wt % or less
of the total of Fe and Mn, or 2.0 wt % or less of the total of Fe
and Cr.times.5.
6. A forged piston according to any of claim 1, wherein: the
particle size of eutectic Si and pro-eutectic Si in metallographic
structure of the aluminum alloy is 10 to 100 .mu.m.
7. A forged piston according to claim 2, wherein: the aluminum
alloy further includes 2.0 wt % or less of Mg.
8. A forged piston according to claim 2, wherein: the aluminum
alloy further includes at least either of 0.25 wt % or less of Zr,
or 0.25 wt % or less of Ti; and the total of Zr and Ti in the case
where Zr and Ti are both included is equivalent to 0.3 wt % or
less.
9. A forged piston according to any of claim 2, wherein: the
aluminum alloy further includes at least either of 2.0 wt % or less
of the total of Fe and Mn, or 2.0 wt % or less of the total of Fe
and Cr.times.5.
10. A forged piston according to any of claim 2, wherein: the
particle size of eutectic Si and pro-eutectic Si in metallographic
structure of the aluminum alloy is 10 to 100 .mu.m.
Description
TECHNICAL FIELD
[0001] The present invention relates to a forged piston made of an
aluminum alloy.
BACKGROUND
[0002] Typically, a piston is used in an internal combustion engine
designed for converting energy produced by combustion to motive
power. Improvements may yet be made in such pistons to provide a
piston that is lighter and has more excellent properties in heat
resistance and abrasion resistance. A piston that can meet such
properties are in demand. Particularly, forged pistons made of an
aluminum alloy attract attention. Past piston designs have been
proposed in attempt to achieve such desirable characteristics.
[0003] For example, JP-A No. 216487/1995 proposes an aluminum alloy
on which abrasion resistance is conferred by Si, which includes a
precipitation hardening element of Cu and Mg and further includes
Fe and Ni, elements that contribute to the enhancement in strength,
and includes Mn, Ti, Zr and V provided for the effect of recovery
at high temperature and the effect of inhibiting recrystallization
coexist. However, as the effect of the enhancement of the strength
in this case is acquired only approximately at 250.degree. C. at
the highest, sufficient strength at the top of a piston at high
temperature cannot be acquired in the case where the piston is made
of such an aluminum alloy.
[0004] In the meantime, JP-A No. 54053/2000 proposes an aluminum
alloy in which the maximum length of a crystallized substance by
casting is controlled to be 200 .mu.m and proposes that the
strength of which at further higher temperature is enhanced by
strengthening the dispersion of the crystallized substances.
However, in this reference, as a transition element for
crystallizing an intermetallic compound is added in a large
quantity, the specific gravity increases and the enhancement of
engine performance by lightening is hindered. Besides, as a bulky
crystallized substance causes an internal defect and a crack in
forging, difficulties arise for enhancing the quality of material
by forging becomes difficult.
[0005] In the meantime, JP-A No. 260089/1996 proposes that the
strength at high temperature equal to or exceeding 250.degree. C.
is enhanced by setting the percentage content of Ni, out of the
elements of an Al--Si aluminum alloy used in a piston, to 2 to 6 wt
%. However, in this reference, as Cu and Ni are included in a large
quantity, the specific gravity increases and as the weight
increases, a merit that the strength is enhanced is conversely
lost. Besides, a bulky crystallized substance causes a defect in
forging and remarkably deteriorates the strength.
[0006] Further, other examples of an aluminum alloy for a forged
piston may be employed, such as A4032 and A2618 according to JIS.
However, as A4032 is material depending upon precipitation
hardening, the strength of the piston is deteriorated when the
material is exposed to high temperature. In the meantime, as only a
small quantity of Si is included in A2618, the coefficient of
thermal expansion increases and the sliding performance of the
piston is deteriorated.
SUMMARY
[0007] In view of the above conventional designs, it is an object
of the following disclosure to provide a forged piston with
excellent properties in heat resistance and abrasion resistance and
made of a light aluminum alloy.
[0008] In one embodiment, a forged piston comprises an aluminum
alloy which includes 8 to 18 wt % of Si (wt %: percentage by
weight), 0.5 to 3 wt % of Cu and 1 to 5 wt % of Ni, which further
includes Al and unavoidable impurities, in which more Ni is
included than Cu and in which the maximum length of an
intermetallic compound generated by Al and Ni is 3 to 100
.mu.m.
[0009] In another embodiment, a forged piston comprises an aluminum
alloy which includes 8 to 18 wt % of Si, 0.5 to 3 wt % of Cu, 1 to
5 wt % of Ni and 2.0 wt % or less of Fe, which further includes Al
and unavoidable impurities, in which the total in wt % of Ni and Fe
is more than Cu and is equivalent to 5 wt % or less and in which
the maximum length of an intermetallic compound generated by Al, Ni
and Fe is 3 to 100 .mu.m.
[0010] In yet another embodiment, the aluminum alloy further
includes 2.0 wt % or less of Mg.
[0011] In another embodiment, the aluminum alloy further includes
at least either of 0.25 wt % or less of Zr, or 0.25 wt % or less of
Ti, and the total of Zr and Ti in the case where Zr and Ti are
included is 0.3 wt % or less.
[0012] In another embodiment, the aluminum alloy further includes
2.0 wt % or less of at least one type of the total of Fe and Mn,
and 2.0 wt % or less of the total of Fe and Cr.times.5.
[0013] In yet another embodiment, comprises a mean particle
diameter of eutectic Si and pro-eutectic Si in the metallographic
structure of the aluminum alloy is 10 to 100 .mu.m.
[0014] As described above, a forged piston can be provided with
excellent properties in heat resistance and abrasion resistance and
made of the light aluminum alloy can be acquired by the aluminum
alloy the strength at high temperature of which is enhanced,
securing toughness and productivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a perspective view of one embodiment of a
forged piston according to the inventive principles.
[0016] FIG. 2 illustrates a graph showing the results of
measurement in which each fatigue strength of a forged piston
according to the principles of the invention and conventional type
forged pistons is measured.
[0017] FIG. 3 illustrates a photograph showing metallographic
structure in the forged piston according to the principles of the
invention.
[0018] FIG. 4 shows a photograph showing metallographic structure
in a forged piston in a comparative example.
DETAILED DESCRIPTION
[0019] Referring to the drawings, a forged piston to which the
inventive principles are applied will be described in detail
below.
[0020] The forged piston for example, as shown in FIG. 1, has a
structure provided with a piston head 1 for receiving an explosion
load in a cylinder of an internal combustion engine, a skirt 2 for
smoothly reciprocating the piston in the cylinder, a plurality of
piston-ring grooves 3 for incorporating a piston ring which
slidingly contacts an inner wall of the cylinder in the piston and
a pin hole 4 for inserting a piston pin to connect the piston to a
connecting rod.
[0021] The forged piston to which the inventive concepts may be
applied is characterized in that it is made of an aluminum alloy
which includes 8 to 18 wt % of Si, 0.5 to 3 wt % of Cu and 1 to 5
wt % of Ni, which further includes Al and unavoidable impurities,
in which more Ni is included than Cu and in which the maximum
length of an intermetallic compound generated by Al and Ni is 3 to
100 .mu.m.
[0022] Further, the forged piston to which the inventive concepts
may be applied is characterized in that it is made of an aluminum
alloy which includes 8 to 18 wt % of Si, 0.5 to 3 wt % of Cu, 1 to
5 wt % of Ni and 2.0 wt % or less of Fe, which further includes Al
and unavoidable impurities, in which the total in wt % of Ni and Fe
is more than Cu and is equivalent to 5 wt % or less and in which
the maximum length of an intermetallic compound generated by Al, Ni
and Fe is 3 to 100 .mu.m.
[0023] In the forged piston to which the inventive concepts may be
applied, a coefficient of linear expansion of the piston
reciprocated in the high-temperature cylinder is inhibited by Si
and its dimensional change can be minimized. In addition, sliding
resistance at high speed can be enhanced.
[0024] Moreover, in the forged piston to which the inventive
concepts may be applied, the material strength at room temperature
to 200.degree. C. can be enhanced by Cu.
[0025] Further, in the forged piston to which the inventive
concepts may be applied, the aluminum alloy crystallizes an
Al--Cu--Ni ternary compound and enhances material strength up to
250.degree. C.
[0026] Furthermore, in the forged piston to which the inventive
concepts may be applied, an Al--Ni compound in the aluminum alloy
enhances strength up to high temperature of 250.degree. C. or
higher, inhibits the generation of a bulky crystallized substance,
and prevents an internal defect and a crack in forging.
[0027] Besides, in the forged piston to which the inventive
concepts may be applied, the Al--Ni compound in the aluminum alloy
can enhance the strength even when exposed to high temperatures of
250.degree. C. or higher, can inhibit the generation of a bulky
crystallized substance, and can prevent an internal defect and an
occurrence of a crack caused by forging.
[0028] Therefore, the forged piston to which the inventive concepts
may be applied can be made into a forged piston of light aluminum
alloy with excellent properties in heat resistance and abrasion
resistance by the aluminum alloy, the strength of which at high
temperatures can be enhanced, while securing toughness and
productivity.
[0029] In another embodiment, in the forged piston to which the
inventive concepts may be applied, Mg can be further included in
the aluminum alloy. In this case, the percentage content of Mg
shall be 2.0 wt % or less. Hereby, the strength of the material can
be enhanced by the strengthening of solid solution.
[0030] Further, in the forged piston to which the inventive
concepts may be applied, at least either of Zr or Ti can be
included in the aluminum alloy. In this case, the percentage
content of Zr would be 0.25 wt % or less and that of Ti would be
0.25 wt % or less. Further, in the case where Zr and Ti are both
included, the total of Zr and Ti would be 0.3 wt % or less. Hereby,
a crystal grain can be made minute and the durability can be
enhanced, while inhibiting the generation of a bulky crystallized
substance.
[0031] Furthermore, in the forged piston to which the inventive
concepts may be applied, at least either of Mn or Cr can be
included in the aluminum alloy. In this case, as for the percentage
content of Mn, the total of Fe and Mn would be 2.0 wt % or less and
as to the percentage content of Cr, the total of Fe and Cr.times.5
would be 2.0 wt % or less, where "Cr.times.5" is five times a wt %
of Cr. Hereby, in a range in which no bulky compound is generated,
the metallographic structure can be made minute and the
malleability can be enhanced.
[0032] Moreover, in the forged piston to which the inventive
concepts may be applied, the particle size of eutectic Si and
pro-eutectic Si in the metallographic structure of the aluminum
alloy can be 10 to 100 .mu.m. Hereby, sufficient toughness and
productivity are secured and the sliding performance of the piston
can be enhanced.
[0033] Descriptions as to why each element may be added to the
aluminum alloy for making the forged piston, their added amounts,
and the metallographic structure of the aluminum alloy are provided
below.
(Si: 8 to 18 wt %)
[0034] Si is an element that can inhibit the linear expansion of
the piston used at high temperature, minimize its dimensional
change and resist sliding at high speed. However, when Si is added
in a large quantity, bulky pro-eutectic Si is crystallized, and the
toughness and the workability of the material are deteriorated.
Therefore, in the invention, to acquire sufficient effect, its
lower limit is 8 wt % and to secure sufficient toughness and
workability as a piston, its upper limit is 18 wt %.
(Cu: 0.5 to 3 wt %)
[0035] Cu is an element for enhancing material strength between
room temperature to approximately 200.degree. C. by the
strengthening of solid solution. However, when Cu is added in a
large quantity, the crystallization of the Al--Ni compound is
hindered, the enhancement of material strength at 250.degree. C. or
higher temperatures is hindered, and a light piston cannot be
acquired because the specific gravity of the material
increases.
[0036] Therefore, to acquire strength minimally required at
200.degree. C., the lower limit of Cu is 0.5 wt % and to inhibit
the increase of the specific gravity without preventing the
crystallization of the Al--Ni compound, its upper limit is 3 wt
%.
(Ni: 1 to 5 wt %)
[0037] Ni is an element for crystallizing the Al--Cu--Ni ternary
compound by coexisting with Cu and enhancing strength at high
temperature. The effect can act up to 250.degree. C. However, to
enhance strength up to 250.degree. C. or higher temperatures, the
Al--Ni compound is required to be crystallized. To crystallize the
Al--Ni compound, Ni is required to be added in a larger quantity
than Cu. However, when Ni is added in a large quantity, a
crystallized substance is made bulky, the toughness of the material
is deteriorated, which causes cracking and defects in forging.
Therefore, to crystallize the Al--Ni compound required for strength
at high temperature, the lower limit of Ni is 1 wt % and to inhibit
the crystallization of a bulky compound, its upper limit is 5 wt %.
Further, Ni is added in a larger quantity than Cu.
(Fe: 2.0 wt % or less)
[0038] Fe is an element for crystallizing a compound with Al like
Ni and enhancing strength at high temperature and can be
arbitrarily added, however, to inhibit bulking a crystallized
substance, Fe equivalent to 2 wt % maximum can be included. As the
Al--Ni--Fe compound is crystallized in the case where Fe and Ni are
simultaneously added, the total of Ni and Fe would be 5 wt % or
less. Further, the total of Ni and Fe would be more than Cu.
(Mg: 2.0 wt % or less)
[0039] Mg is an element for enhancing the strength of the material
by the strengthening of solid solution and can be arbitrarily
added, however, as the toughness of the material is deteriorated by
the crystallization of Mg.sub.2Si when Mg is added in a large
quantity, a maximum of 2.0 wt % of Mg would be included.
(Zr: 0.25 wt % or less)
(Ti: 0.25 wt % or less)
[0040] Zr and Ti are both elements that contribute to making a
crystal grain minute and enhancing heat resistance. However, when
Zr and Ti are added in a large quantity, either or both crystallize
a bulky compound with Al. Therefore, the percentage of Zr and Ti
included would be respectively 0.25 wt % maximum to inhibit the
generation of a bulky crystallized substance. The total of Zr and
Ti when they are both included would be 0.3 wt % or less.
(Mn: total of Fe and Mn: 2.0 wt % or less)
(Cr: total of Fe and Cr.times.5: 2.0 wt % or less)
[0041] Mn and Cr are elements for enhancing strength at high
temperature and making the metallographic structure minute,
however, when they are added at the same time as Fe, a bulky
compound is generated together with Al and Fe and the malleability
is deteriorated. Therefore, an upper limit for the total of these
Mn, Cr and Fe is preferred. That is, the total of Fe and Mn would
be 2.0 wt % or less and the total of Fe and Cr.times.5 would be
2.0% less.
[0042] Next, the metallographic structure of the aluminum alloy
will be described.
(Intermetallic Compound)
[0043] An intermetallic compound of Al, Ni and a transition element
such as Fe enhances material strength up to high temperature by
inhibiting the transformation of material. However, as the effect
of the intermetallic compound decreases when the intermetallic
compound is made too minute, a lower limit of the maximum length is
3 .mu.m. In the meantime, as cracking and defects are caused in
forging when the intermetallic compound is made too excessive, an
upper limit of the maximum length is 100 .mu.m so that the
intermetallic compound can be resistant to forging.
(Eutectic Si, Pro-Eutectic Si)
[0044] Eutectic Si and pro-eutectic Si are effective to enhance
sliding performance, however, when the particle sizes of them are
made too excessive, cracking and defects are caused in forging.
Therefore, a lower limit of the particle sizes of eutectic Si and
pro-eutectic Si would be 3 .mu.m to gain sufficient effect and an
upper limit would be 100 .mu.m to resist forging.
[0045] The effects of the invention are detailed by exemplary
embodiments below. The invention is not limited to the following
embodiments and can be suitably changed in a range in which the
outline is not changed.
[0046] First, an aluminum alloy including each additional element
shown in Table 1 is forged into the shape of a piston and forged
pistons of samples 1 to 12 are produced. As for the forged piston
of each sample 1 to 12, a mechanical characteristic and
malleability are evaluated. The samples 1 to 5 of these are the
embodiments that meet conditions of the inventive principles and
the samples 6 to 10 are comparative examples that do not meet the
conditions of the inventive principles. The sample 11 shows JIS
A4032 and the sample 12 shows JIS AC8A.
[0047] As for mechanical characteristics out of the results of
evaluation shown in Table 1, each test piece is cut from the forged
piston of each sample 1 to 12, after it is kept at 300.degree. C.
for 100 hours, a tension test is made in an atmosphere of
300.degree. C., and the tensile strength and the extension of each
test piece are measured. As for malleability, each sample 1 to 12
is heated at 350.degree. C. or higher and it is checked whether a
crack is made or not in forging the shape of the piston. In Table
1, .smallcircle. shows a case that no crack is made and .times.
shows a case that a crack is made. TABLE-US-00001 TABLE 1 Tensile
Compound Strength Extension Size Specific No Si Cu Ni Fe Mg Mn Cr
Zr Ti (Mpa) (%) (.mu.m) Malleability Gravity Embodiment 1 12 1 3 --
1 -- -- -- -- 72 21 10-30 .largecircle. 2.71 2 12 1 3 -- 1 1 -- --
-- 81 17 10-40 .largecircle. 2.73 3 12 1 3 -- 1 -- -0.2 -- -- 78 18
10-20 .largecircle. 2.71 4 12 1 2 0.6 0.5 -- -- 0.1 0.1 73 24 3-30
.largecircle. 2.71 5 12 1 2 -- 1 -- -- 0.1 0.1 71 23 3-30
.largecircle. 2.69 Comparative 6 12 5 5 -- 1 -- -- -- -- 84 15
100< X 2.83 Example 7 12 5 3 -- 1 -- -- -- -- 80 22 10-30
.largecircle. 2.79 8 12 1 3 1 1 -- -- -- -- 78 16 100< X 2.73 9
12 1 2 0.6 1 0.5 -- 0.1 0.1 84 19 100< X 2.71 10 12 1 2 0.6 1 --
0.2 -- 0 81 18 100< X 2.70 A4032 11 12 1 1 -- 1 -- -- -- -- 60
35 -- .largecircle. 2.67 AC8A 12 12 1 1 -- 1 -- -- -- -- 76 15 --
-- 2.67
[0048] The results of evaluation shown in Table 1 show that the
samples 1 to 6 (the embodiments) higher tensile strength than A4032
and show larger extension than AC8A. Besides, the samples 1 to 6
have no problem in relation to malleability and also show no
increase in specific gravity to the extension that the specific
gravity has an effect upon each actual piston. Further, the
embodiments 2 and 3 show higher tensile strength and larger
extension than AC8A. In the meantime, the embodiments 1, 4 and 5
show higher strength than AC8A in relation to fatigue strength
which is important in each actual piston and owing to the
enhancement of each internal quality by minute metallographic
structure and malleability, though each tensile strength is
inferior to that in AC8A.
[0049] In the meantime, in the samples 6, 8, 9 and 10 (the
comparative examples), though they show a high value in relation to
mechanical strength, a crack is caused in forging in any case.
Tests of the metallographic structure of these samples 6, 8, 9 and
10 show that in the comparative example 6, Al--Ni bulky compound is
crystallized, in the comparative example 8, an Al--Ni--Fe bulky
compound is crystallized, in the comparative example 9, an
Al--Ni--Fe--Mn bulky compound is crystallized, and in the
comparative example 10, an Al--Ni--Fe--Cr bulky compound is
crystallized. These bulky compounds exceed 100 .mu.m in length in
any case.
[0050] JP-A No. 54053/2000 shows the effect of micronizing a
crystallized substance by Mn and shows that the maximum length of
the crystallized substance is reduced by changing the shape of the
crystallized substance from a sharp and narrow shape to a lump.
However, in the reference, the volume itself of an individual
crystallized substance is not reduced and the maximum length is
also at a level of 100 .mu.m. Therefore, the effect of
micronization to the extent that malleability is enhanced, cannot
be recognized as in the presently disclosed inventive concepts.
[0051] In the sample 7 (the comparative example), the strength is
high, no bulky crystallized substance is caused, and the
malleability is also satisfactory. However, the specific gravity is
larger by approximately 5%, compared with that in conventional type
A4032 and AC8A. This is contrary to the object of the invention of
manufacturing the light piston. In the meantime, in the samples 1
to 6 (the embodiments), each specific gravity is 2.75 or less and
further lightening is enabled by inhibiting the increase of the
specific gravity, maintaining high strength resistant to high
temperature and excellent malleability.
[0052] Next, a fatigue strength test is made for the forged pistons
in the sample 4 (the invention), the sample 11 (A4032) and the
sample 12 (AC8A). In this fatigue strength test, a fatigue curve
under pulsating tension near to stress generated in each actual
piston in an atmosphere of 300.degree. C. is measured. FIG. 2 shows
the results of the measurement.
[0053] The results of the measurement shown in FIG. 2 show that in
the sample 4, though the tensile strength is lower than that in
AC8A, the fatigue strength is higher by 10% or more than that in
AC8A. The results also show that the fatigue strength in the sample
4 is higher by 40% or more than that in A40432 and that the
strength of sample 4 is greatly enhanced.
[0054] Next, FIG. 3 shows a photograph of a microstructure showing
the forged piston in the sample 4 (the invention) and FIG. 4 shows
a photograph of a microstructure in the sample 9 (the comparative
example). These photographs of the microstructures shown in FIGS. 3
and 4 show that in the forged piston in the comparative example,
the maximum length of an intermetallic compound in metallographic
structure is 100 .mu.m or longer, while in the forged piston
according to the present inventive concepts, the intermetallic
compounds in the metallographic structure are minutely and
homogeneously dispersed and are controlled at a level at which the
malleability is not hindered.
* * * * *