Patent Application
20140076263
The present invention relates to an aluminum alloy member and a manufacturing method thereof and, more particularly, to a piston for an internal combustion engine a manufacturing method thereof.
There is conventionally known a piston for an internal combustion engine, which has a piston body made of an aluminum alloy material. It is common practice to anodize a top ring groove of the piston (in which a top ring is fitted) and thereby form an anodic oxide film on a surface of the top ring groove for improvements in wear resistance and corrosion resistance. This type of aluminum alloy piston faces a technical problem that there occur clearances between the anodic oxide film and silicon particles contained in the aluminum alloy material due to the growth and expansion of the anodic oxide film.
As a solution to such a problem, Japanese Laid-Open Patent Publication No. 2010-90427 proposes a technique for reinforcing an anodic oxide film on an aluminum alloy material by, after the formation of the anodic oxide film, immersing the anodic oxide film in an aqueous solution containing magnesium ions, ammonium ions and fluoride ions for a predetermined time and thereby allowing a compound containing magnesium and fluorine to be deposited in clearances between the anodic oxide film and silicon particles contained in the aluminum alloy material.
In the above-proposed reinforcement technique, however, the deposited magnesium/fluorine-containing compound is not still sufficient in strength so that it is impossible to secure the sufficient strength of the anodic oxide film.
It is accordingly an object of the present invention to provide an aluminum alloy piston for an internal combustion engine or an aluminum alloy member, in which an anodic oxide film is formed with sufficient strength.
According to one aspect of the present invention, there is provided a piston for an internal combustion engine, comprising: a piston body made of an aluminum alloy material containing silicon and having a piston ring groove formed therein; and an anodic oxide film formed on the piston ring groove, wherein a metal containing nickel and zinc is deposited around silicon particles in the anodic oxide film.
According to another aspect of the present invention, there is provided a method of manufacturing a piston for an internal combustion engine, comprising: producing a piston with a piston ring groove from an aluminum alloy material containing silicon; forming an anodic oxide film on the piston ring groove; and electrolyzing, in an electrolytic solution, a part of the piston on which the anodic oxide film has been formed so as to allow a metal containing nickel and zinc to be deposited around silicon particles in the anodic oxide film.
According to still another aspect of the present invention, there is provided an aluminum alloy member, comprising: a base body made of an aluminum alloy material containing silicon; and an anodic oxide film formed on at least a part of the base body, wherein a metal containing nickel and zinc is deposited around silicon particles in the anodic oxide film.
It is possible according to the present invention to secure the sufficient strength of the anodic oxide film by the deposition of the high-strength metal around the silicon particles in the anodic oxide film.
The other objects and features of the present invention will also become understood from the following description.
Hereinafter, the present invention will be described in detail below with reference to the drawings.
The following embodiment specifically refers to a piston 1 for an automotive internal combustion engine. In the internal combustion engine, the piston 1 is in sliding contact with a substantially cylindrical cylinder wall 3 of a cylinder block 2 such that a combustion chamber C is defined by the piston 1, the cylinder wall 3 and a cylinder head (not shown) as shown in
As shown in
The crown portion 6 is disc-shaped with a relatively large thickness and has a crown surface 6a defining thereon the combustion chamber C. A plurality of valve recesses 10 are made in the crown surface 6a for prevention of interference with intake and exhaust valves (not shown). Further, three ring grooves 11, 12 and 13 are cut in the outer circumference surface of the crown portion 6 such that three piston rings PL1, PL2 and PL3 (such as a compression ring, an oil ring etc.) are fitted in the ring grooves 11, 12 and 13, respectively.
Among these ring grooves 11, 12 and 13, the top ring groove 11 is located closest to the combustion chamber C and is thus more susceptible to the influence of combustion in the combustion chamber C.
In the present embodiment, the piston 1 has an anodization treatment region 14 in which known anodization treatment is performed on the inside and periphery of the top ring groove 11 and an electrolytic deposition treatment region 15 in which electrolytic deposition treatment (as secondary electrolytic treatment after the anodization treatment) is performed on a given area within the anodization treatment region 14 as shown in
In the anodization treatment region 14, an anodic oxide film 20 is formed on the piston base material 1b as shown in
In the electrolytic deposition treatment region 15, a relatively high-strength metal 16 such as nickel and zinc is deposited around the silicon particles 24 in the clearances 25 and in surface recesses 26 of the anodic oxide film 20 as shown in
The above-structured piston 1 can be manufactured through the following steps: (1) casting the aluminum alloy material 1b into a given shape, thereby forming the piston body 1a with the piston rings 11, 12 and 13 etc.; (2) performing the anodization treatment on the top ring groove 11; and (3) performing electrolytic nickel plating treatment as the electrolytic deposition treatment on the given area of the anodization treatment region 14.
As shown in
The electrolytic nickel plating treatment can be performed by electrolysis using the piston base material 1b with the anodic oxide film 20 as a cathode X and using pure nickel as an anode Y in a predetermined electrolytic solution 18 containing nickel ions (Ni2+) and zinc ions (Zn2+) as shown in
It is herein feasible to perform the electrolytic nickel plating treatment with the use of an apparatus in which the electrolytic solution 18 is stored in an electrolytic bath 19 as shown in
The effects of the present invention have been be verified by the following experiments.
In the following experiments, two types of test samples: one type of which was subjected to only anodization treatment (referred to as “test sample 1”) and the other type of which was subjected to anodization treatment and electrolytic nickel plating treatment according to the present invention (referred to as “test sample 2”) were prepared and used.
[Experiment 1: Comparison Between Anodic Oxide Film According to the Present Invention and Conventional Anodic Oxide Film]
Test samples 1 and 2 were prepared as follows by using aluminum alloy casting AC8A (according to JIS H5202) as a base material 1b. Herein, each of the test samples of types 1 and 2 had a rectangular plate shape with a length of 19 mm, a width of 15 mm and a thickness of 5 mm. The composition of the aluminum alloy material AC8A is indicated in TABLE 1.
First, the test samples 1 and 2 were subjected to degreasing pretreatment by ultrasonic cleaning in acetone for 5 minutes at room temperature.
After the degreasing pretreatment, the anodization treatment was performed on the test samples 1 and 2 by immersing the test sample as an anode and pure titanium as a cathode in an electrolytic solution of sulfuric acid (sulfuric acid concentration: 200 g/L, temperature: 25±5° C.) and supplying a direct current with a current density of 10.0 A/dm2 for 5 minutes. There was thus formed an anodic oxide film 20 having a thickness of 20 μm on the base material 1b in each of the test samples 1 and 2.
The resulting anodized test samples 1 and 2 were subjected to washing with water of pH 5.8 to 8.6 for 1 minute so as to wash away the electrolytic solution therefrom, and then, dried with air blow.
After the washing/drying treatment, the electrolytic nickel plating treatment was performed on the test sample 2 by immersing the test sample as a cathode and pure nickel as an anode in an electrolytic solution and supplying a direct current with a current density of 2.1 A/dm2 for 9 minutes. The electrolytic solution herein used was of the type containing nickel sulfamate, zinc sulfate and boric acid (nickel sulfamate concentration: 300 g/L, zinc sulfate concentration: 30 g/L, boric acid concentration: 30 g/L, temperature: 35±5° C.). By this electrolytic nickel plating treatment, a metal 16 was deposited inside the anodic oxide film 20.
The resulting electrolyzed test sample 2 was subjected to washing with water of pH 5.8 to 8.6 for 1 minute so as to wash away the electrolytic solution therefrom, and then, dried with air blow.
The treatment conditions are summarized in TABLE 2.
The thus-obtained test samples 1 and 2 were tested for the damage resistance, composition and surface roughness of the anodic oxide film.
The damage resistance of the anodic oxide film was determined by a counter vibration test method (cavitation/erosion test method) using a test machine 30 as shown in
The damage resistance test conditions are summarized in TABLE 3.
The degree of damage to the anodic oxide film was observed with a microscope. Then, the maximum width of the damage center (where damage was heavier in a thickness direction than other parts) was determined as a damage width. The ratio of the damage width of the test sample 2 to the damage width of the test sample 1 was further determined as a damage ratio. The damage resistance of the anodic oxide film was evaluated based on the damage ratio.
The composition of the anodic oxide film was determined by EDX quantitative analysis.
The surface roughness of the anodic oxide film was determined by SEM observation. In this experiment, the test sample 2 was subjected to surface roughness measurement when it was confirmed by EDX quantitative analysis that the nickel content of the test sample was 0.3 atomic % or more. The ratio of the surface roughness of the test sample 2 to the surface roughness of the test sample 1 was determined as a roughness ratio on a percentage basis. The surface roughness of the anodic oxide film was evaluated based on the roughness ratio.
The test/evaluation methods are summarized in TABLE 4.
The test/evaluation results of the test samples 1 and 2 are indicated in TABLE 5 and
It is noted that, in the test sample 2, not only nickel (Ni) but also zinc (Zn) were confirmed as being contained as the metal deposit 16 in the anodic oxide film 20.
As is seen from TABLE 5 and
The reason for the above results is considered that, by the electrolytic deposition treatment, the metal 16 such as nickel and zinc is deposited and filled in weak, crack-prone clearances 25 and recesses 26 of the anodic oxide film 20 so as to reinforce the clearances 25 and recesses 26 of the anodic oxide film 20 for improvement of damage resistance and, at the same time, smoothen the surface of the anodic oxide film 20 for improvement of surface roughness.
[Experiment 2: Influence of Si Content of Base Material on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiment 1 by using aluminum alloy materials a to i of different silicon contents as a base material 1b. The compositions of the respective aluminum alloy materials a to i used are indicated in TABLE 6.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiment 1.
The test/evaluation results of the test samples 1 and 2 are indicated in TABLE 7 and
In Experiment 2, not only nickel (Ni) but also zinc (Zn) were confirmed as being contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 as in the case of Experiment 1, except for the case where the silicon content of the base material 1b was 0 wt %”.
As is seen from TABLE 7 and
The reason for the above results is considered as follows. When the silicon content of the base material 1b is too low, there occur less clearances 25 and recesses 26 in the anodic oxide film 20. The anodic oxide film 20 is thus unlikely to be deteriorated in damage resistance and surface roughness even in the case where only the anodization treatment is performed. In the case where the electrolytic deposition treatment is performed in combination with the anodization treatment, however, there arises a difficulty in the passage of electric current due to the less clearances 25 of the anodic oxide film 20 so that the anodic oxide film 20 becomes damaged (e.g. broken) by the application of a high voltage during the electrolytic deposition treatment. Further, the metal 16 cannot be deposited adequately due to the less clearances 25 and recesses 26 of the anodic oxide film 20 and becomes a cause of surface roughness. On the other hand, when the silicon content of the base material 1b is too high, there occur many clearances 25 and recesses 26 in the anodic oxide film 20. The anodic oxide film 20 is thus likely to be deteriorated in damage resistance and surface roughness in the case where only the anodization treatment is performed. In the case where the electrolytic deposition treatment is performed in combination with the anodization treatment, the metal 16 cannot deposited in a sufficient amount to fill the many clearances 25 and recesses 26 of the anodic oxide film 20 so that the anodic oxide film 20 becomes deteriorated in damage resistance and surface roughness.
[Experiment 3: Influence of Thickness of Anodic Oxide Film on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiments 1 and 2 by varying the thickness of the anodic oxide film 20 in a range of 5 to 60 μm.
The treatment conditions are summarized in TABLE 8.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiments 1 and 2.
The test/evaluation results of the test samples 1 and 2 are indicated in TABLE 9 and
In Experiment 3, not only nickel (Ni) but also zinc (Zn) were confirmed as being contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 as in the case of Experiments 1 and 2.
As is seen from TABLE 9 and
The reason for the above results is considered as follows. Regardless of whether the electrolytic deposition treatment is performed in combination with the anodization treatment or not, the anodic oxide film 20 is high in rigidity and shows high damage resistance when the thickness of the anodic oxide film 20 is relatively small. However, there occur many clearances 25 and recesses 26 in the anodic oxide film 20 when the thickness of the anodic oxide film 20 is too large. In the case where only the anodization treatment is performed, the anodic oxide film 20 is likely to be damaged (e.g. cracked) by impact due to the many clearances 25 and recesses 26 and thus be deteriorated in damage resistance. Even in the case where the electrolytic deposition treatment is performed in combination with the anodization treatment, the anodic oxide film 20 becomes deteriorated in damage resistance as the amount of the deposited metal 16 does not keep up with the amount of the clearances 25 and clearances 26 in the anodic oxide film 20.
[Experiment 4: Influence of Ni Content of Anodic Oxide Film on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiments 1 to 3 by using aluminum alloy materials a to h of different component ratios as a base material 1b and, in the case of the test sample 2 using the aluminum alloy material e as the base material 1b, varying the treatment area, current density and treatment time of the electrolytic deposition treatment. The compositions of the respective aluminum alloy materials a to h used are indicated in TABLE 10.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiments 1 to 3.
The test/evaluation results of the test sample 2 are indicated in TABLE 11 and
In Experiment 4, not only nickel (Ni) but also zinc (Zn) were confirmed as being contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 as in the case of Experiments 1 to 3.
As is seen from TABLE 11 and
[Experiment 5: Influence of Electrolytic Deposition Conditions on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiments 1 to 4 by varying the current density and treatment time of the electrolytic deposition treatment. In this experiment, the maximum limit of the electrolytic deposition treatment time was set to 9 minutes because the electrolytic deposition treatment time exceeding 9 minutes would cause a large deviation from the appropriate manufacturing time of the piston 1 and thus would not be practical.
The treatment conditions are summarized in TABLE 12.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiments 1 to 4.
The test/evaluation results are indicated in TABLE 13 and
It is assumed based on the results of Experiments 1 to 4 that nickel (Ni) and zinc (Zn) were contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 even in Experiment 5 although the nickel content of the anodic oxide film 20 was not measured and indicated for every sample.
As is seen from TABLE 13 and
The reason for the above results is considered as follows. The metal 16 cannot be deposited sufficiently in the clearances 25 and recesses 26 of the anodic oxide film 20 so that the anodic oxide film 20 becomes deteriorated in damage resistance and surface roughness when the current density is too low. When the current density is too high, by contrast, the deposition of the metal 16 is concentrated on the place where the electric current is easy to pass (that is, the metal 16 is concentratedly deposited on the surface of the anodic oxide film 20 where the electrical resistance is relatively small, rather than in the clearances 25 of the anodic oxide film 20 where the electrical resistance is relatively large) so as to cause significant deterioration in surface roughness. The metal 16 cannot also be deposited sufficiently so that the anodic oxide film 20 becomes deteriorated in damage resistance and surface roughness when the treatment time is too short.
[Experiment 6: Influence of Electrolytic Solution Concentration on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiments 1 to 5 by varying the electrolytic solution and current density of the electrolytic deposition treatment. The reagent concentrations of the respective electrolytic solutions used are indicated in TABLE 14.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiments 1 to 5.
The test/evaluation results are indicated in TABLE 15 and
It is assumed based on the results of Experiments 1 to 4 that nickel (Ni) and zinc (Zn) were contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 even in Experiment 6, although the nickel content of the anodic oxide film 20 was not measured and indicated for every sample, as in the case of Experiment 5.
As is seen from TABLE 15 and
The reason for the above results is considered that the Ni content of the anodic oxide film 20, i.e., the amount of the metal deposit 16 in the anodic oxide film 20 is increased as the nickel sulfamate concentration of the electrolytic solution is high. In particular, the deposition of nickel is effectively accelerated by the coexistence of zinc during the electrolytic deposition treatment.
[Experiment 7: Influence of Electrolytic Solution Concentration on Film Performance]
Test samples 1 and 2 were prepared in the same manner as in Experiments 1 to 6 by varying the reagent concentration of the electrolytic solution. The reagent concentrations of the respective electrolytic solutions used are indicated in TABLE 16.
The thus-obtained test samples 1 and 2 were tested and evaluated in the same manner as in Experiments 1 to 6.
The test/evaluation results are indicated in TABLE 17 and
In Experiment 7, not only nickel (Ni) but also zinc (Zn) were confirmed as being contained as the metal deposit 16 in the anodic oxide film 20 of the test sample 2 as in the case of Experiments 1 to 4.
As is seen from TABLE 17 and
The reason for the above results is considered as follows. When the nickel sulfamate concentration of the electrolytic solution is too low, the anodic oxide film 20 cannot obtain sufficient improvement in damage resistance and surface roughness due to less nickel content of the anodic oxide film 20, i.e., insufficient amount of the deposited metal 16 in the anodic oxide film 20. When the nickel sulfamate concentration of the electrolytic solution is too high and exceeds a given level, the deposition speed of the metal 16 becomes increased with the amount of nickel ions (Ni2+) in the electrolytic solution. In this ease, the deposition of the metal 16 is concentrated on the place where the electric current is easy to pass (the metal 16 is concentratedly deposited on the surface of the anodic oxide film 20 where the electrical resistance is relatively small, rather than in the clearances 25 of the anodic oxide film 20 where the electrical resistance is relatively large) so as to cause significant deterioration in surface roughness, as in the case where the current density is too high during the electrolytic deposition treatment.
As described above, the anodic oxide film 20 in which the high-strength metal 16 such as nickel and zinc is deposited around the silicon particles 24 in the clearances 25 is formed by combination of the anodization treatment and the electrolytic deposition treatment in the present embodiment. In general, it is likely that the anodic oxide film 20 will be broken from the clearances 25 in the occurrence of cracking. In the present embodiment, however, such breakage-prone clearances 25 are filled with and reinforced by the deposited high-strength metal 16. It is therefore possible for the anodic oxide film 20 to secure sufficient strength such as resistance to damage/impact by explosive combustion in the combustion chamber C.
In addition, not only the clearances 25 inside the anodic oxide film 20 but also the recesses 26 in the surface of the anodic oxide film 20 are filled with the deposited metal 16. It is thus possible to impart surface smoothness to the anodic oxide film 20.
It is further possible to improve the heat radiation properties of the piston 1 as the metal 16 deposited in the recesses 26 of the anodic oxide film 20 is in contact with the piston base material 1b so as to allow radiation of heat from the piston 1 (piston base material 1b) to the outside (cylinder block 2) through the piston ring PL1.
For effective reinforcement of the anodic oxide film 20, the silicon content of the piston base material 1b is preferably 7 to 25 wt % based on the total weight of the piston base material 1b. One specific example of the Al—Si piston base material 1b is, but is not limited to, AC8A. When the silicon content of the piston base material 1b is too high, there are formed many clearances 25 around the silicon particles 24 so that the amount of the deposited metal 16 may not keep up with the amount of the clearances 25. This leads to deterioration in damage/impact resistance of the anodic oxide film 20. When the silicon content of the piston base material 1b is too low, on the other hand, there are formed less clearances 25 around the silicon particles 24 in the anodic oxide film 20. This raises a difficulty in the passage of electric current so that the anodic oxide film 20 may be broken under the application of a high voltage during the electrolytic deposition treatment. It is possible to keep balance between the amount of the clearances 25 and the amount of the deposited metal 16 and secure the sufficient strength of the anodic oxide film 20 when the silicon content of the piston base material 1b is controlled to within the above-specified relatively-low content range.
The silicon content of the piston base material 1b is more preferably 10 to 25 wt % based on the total weight of the piston base material 1b in order to keep balance between the amount of the clearances 25 and recesses 26 and the amount of the deposited metal 16 and thereby secure not only the sufficient strength but also adequate surface smoothness of the anodic oxide film 20.
Further, the thickness of the anodic oxide film 20 is preferably 5 to 50 μm. The amount of the clearances 25 in the anodic oxide film 20 increases with the thickness of the anodic oxide film 20. The amount of the deposited metal 16 may thus not keep up with the amount of the clearances 25 when the thickness of the anodic oxide film 20 is too large. This leads to deterioration in damage/impact resistance of the anodic oxide film 20 due to the clearances 25. When the thickness of the anodic oxide film 20 is too small, the anodic oxide film 20 itself may not secure sufficient strength and may become poor in damage/impact resistance. It is possible to keep balance between the amount of the clearances 25 and the amount of the deposited metal 16, while ensuring the minimum thickness of the anodic oxide film 20 required for sufficient damage/impact resistance, and secure the sufficient strength of the anodic oxide film 20 when the thickness of the anodic oxide film 20 is controlled within the above-specified relatively-small thickness range.
The nickel content of the anodic oxide film 20 is preferably 0.3 atomic % or more. It is possible to achieve proper reinforcement of the anodic oxide film 20 by the metal 16, limit the occurrence of damage to the anodic oxide film 20 by impact to within an acceptable range and secure the sufficient strength of the anodic oxide film 16 when the nickel content of the anodic oxide film 20 is controlled to be 0.3 atomic % or more.
Furthermore, the electrolytic deposition treatment is preferably performed at a current density of 0.4 to 3.5 A/dm2. When the current density is too high, the deposition of the metal 16 is concentrated on the place where the metal 16 is easy to deposit (the electric current is easy to pass) so as to cause deterioration in surface roughness. The amount of the deposited metal 16 may become insufficient to fill the clearances 25 and recesses 26 of the anodic oxide film 20 so as to cause deterioration in damage/impact resistance and surface roughness when the current density is too low. When the current density is controlled to be 0.4 to 3.5 A/dm2 in the electrolytic deposition treatment, it is possible to keep balance between the amount and distribution of the deposited metal 16 so that the anodic oxide film 20 can combine sufficient strength with surface smoothness.
One preferred example of the electrolytic solution 18 used in the electrolytic deposition treatment is an electrolytic solution containing nickel sulfamate at a concentration of 100 to 600 g/L. As the deposition of nickel is effectively accelerated by the coexistence of zinc during the electrolytic deposition treatment, it is preferable that the electrolytic solution contains zinc sulfate in addition to the nickel sulfamate. It is also preferable that the electrolytic solution contains boric acid.
Although the engine piston 1 is exemplified in the above embodiment, the present invention is applicable to any other aluminum alloy member such as a spool valve body or pump housing. It is possible to obtain the same effects as above even when the present invention is embodied as any other aluminum alloy member.
The entire contents of Japanese Patent Application No. 2012-203882 (filed on Sep. 18, 2012) and No. 2013-160028 (filed on Aug. 1, 2013) are herein incorporated by reference.
Although the present invention has been described with reference to the above exemplary embodiments, the present invention is not limited to these exemplary embodiments. Various modification and variation of the embodiments described above will occur to those skilled in the art in light of the above teachings.
Depending on the specifications of the target product, it is feasible to provide the electrolytic deposition treatment region 15 on the entire area of the anodization treatment region 14 although the electrolytic deposition treatment region 15 is provided to the given area within the anodization treatment region 14 in the above embodiment. Although the anodization treatment region 14 and the electrolytic deposition treatment region 15 are provided on the top ring groove 11 in the above embodiment, it is feasible to provide the anodization treatment region 14 and the electrolytic deposition treatment region 15 on any part of the piston 1 such as the crown surface 6a and outer circumferential surface of the crown portion 6. The ranges of formation of the anodization treatment region 14 and the electrolytic deposition treatment region 15 can be set as appropriate depending on the specifications of the target product.
The scope of the present invention is defined with reference to the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-203882 | Sep 2012 | JP | national |
| 2013-160028 | Aug 2013 | JP | national |
