JPH04147957A - Heat insulating aluminum-based member - Google Patents

Abstract

PURPOSE:To prevent a film from being damaged even under high-temp. conditions and to impart a sufficient heat insulating property by forming a ceramic film contg. hollow balloons and with the porosity and thermal conductivity specified on an Al alloy base material by coating with a thermally sprayed ceramic film in between. CONSTITUTION:The film of an Al alloy powder contg. 20% Ni and 5% Cr is thermally sprayed in 0.1mm thickness on a flat base material 1 consisting of a calcined alumina material contg. 12% Si and which has been shot-blasted to obtain a thermally sprayed substrate layer 2. A powder of ZrO2.8Y2O3 is plasma-sprayed thereon to form a ceramic film 3 having 0.2mm thickness. A ceramic slurry contg. 40-60vol.% SiO2-based ceramic balloons, 5-20vol.% SiC fiber and the balance SiO2-based ceramic material is prepared, and the slurry is applied on the film 3 in 0.2mm thickness, dried for one hour, allowed to stand and then sintered at 400 deg.C for 3min. A ceramic film 4 having 30-50% porosity and 0.2-0.8W/m.K thermal conductivity is obtained in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat insulating aluminum member. This heat-insulating aluminum-based member uses an aluminum-based alloy as a base material,
It can be used for members having parts that are heated to high temperatures, such as the pistons of automobile engines.

[Prior Art] Among heat-insulating aluminum-based members, a piston for an automobile engine, for example, will be described in detail below.

In recent years, as pistons used in engines, pistons cast from aluminum-based alloys have been increasingly used, with a focus on weight reduction in order to reduce the inertia of reciprocating motion in the engine. However, since aluminum alloy is a material with high thermal conductivity, in engines using pistons made only of aluminum alloy, the combustion heat generated by combustion of fuel in the combustion chamber is transferred to the outside of the combustion chamber through the piston. This tends to worsen the thermal efficiency of the engine and reduce the output and fuel efficiency of the engine. Therefore,
In order to reduce heat loss transferred to the outside of the combustion chamber, a piston has been proposed that consists of a piston body made of an aluminum alloy and a thermally sprayed ceramic coating formed on the top surface (piston head) of this piston body ( for example,
“Cumm+ns/TACOM AdVarlded
Adiabatic Engine, JR, Kamo
et at, SAE Paper No.
.

840428 etc.>. In this piston, the thermally sprayed ceramic coating is formed by thermally spraying a ceramic material with low thermal conductivity and excellent heat resistance, so that the heat insulation and heat resistance are improved.

[Problems to be Solved by the Invention] However, even with a piston made of the piston body made of an aluminum alloy and a thermally sprayed ceramic coating, there is a difference between the thermal expansion coefficient of the aluminum alloy and that of the thermally sprayed ceramic coating. Because of the large difference, cracks tend to occur at the interface between the piston body and the sprayed ceramic coating due to thermal stress during repeated heating and cooling during engine operation, and eventually the sprayed ceramic coating peels off and falls off from the piston body. There was a risk that the

For this reason, among the various ceramic materials used for thermal sprayed ceramic coatings, zirconia (zirconia), which has a coefficient of thermal expansion closest to that of aluminum alloys, has recently been used.
Zr02) is increasingly being selected. However, even in pistons on which a thermally sprayed ceramic coating is formed using zirconia, it is still difficult to reliably prevent the thermally sprayed ceramic coating from peeling off or falling off due to slight differences in thermal expansion coefficients.

In addition, as a means to prevent the thermal sprayed ceramic coating from peeling off due to differences in thermal expansion coefficients, a thin base thermal sprayed layer called a bond layer or intermediate layer is formed on the surface of the base material in advance by thermal spraying, and the base thermal sprayed layer is Methods of forming a thermally sprayed ceramic film on the surface of the material have also been considered (for example, the above-mentioned publication).
. The base thermal sprayed layer used here is a metal whose thermal expansion coefficient is intermediate between that of the base material and the thermal sprayed ceramic coating, and which has good adhesion to the thermal sprayed ceramic coating, such as N.
i-0r-A1 alloy, Ni-0r-AY gold alloy Ni
-Co-Cr-AI-Y alloy etc. are adopted.

However, even when a base thermal spray layer is formed,
Peeling of the sprayed ceramic coating due to the difference in thermal expansion
It was still not sufficient to prevent falling off.

On the other hand, due to the increase in engine output in recent years, the temperature of the combustion chamber of the engine is increasing, and pistons having a thermally sprayed ceramic coating are required to have better heat insulation than before.

Increasing the thickness of the thermally sprayed ceramic coating is generally considered as one means of achieving high thermal insulation properties. Here, for the same heat flux, the relationship between the degree of insulation and the film thickness is expressed by the formula (
1) shows a proportional relationship.

ΔT=Q−j! /λ...Formula (1) % Formula %: If the thermal sprayed ceramic coating is made thicker to improve the thermal insulation, the thickness (am) and thermal insulation degree ('C) of the thermal sprayed ceramic coating are The relationship is shown in FIG. In FIG. 7, 8% by weight (wt) yttria-stabilized zirconia (ZrO2.8Y203) is used as the ceramic material, and 0.0% is used as the base sprayed layer.
1sn nickel aluminum chromium alloy (Ni-20wt%
Qr-5wt%A+> is employed and used by coating the top surface of an aluminum piston body of a diesel engine. Also, the engine horsepower at this time (
Figure 8 shows the relationship between the thermal sprayed ceramic coating's surface temperature ("C") and the thermally sprayed ceramic coating's surface temperature. Figure 9 shows the relationship between the thickness (III!I) and the ratio of thermal stress to the strength of the sprayed ceramic coating.The vertical axis shows the ratio, and damage is expected when this is 1.0 or more. From Figure 9, it can be seen that 0.7 am is the limit thickness at which the current thermal sprayed ceramic coatings can no longer be used.Also, Figures 7 and 8
From the figure, the surface temperature of the sprayed ceramic coating at this time is 90
It can be seen that the temperature is 0°C (insulation degree 550°C), and the maximum possible engine horsepower is 120 horsepower.

However, due to the trend toward higher engine output, the engine
It is well predicted that the output will be as high as 20 horsepower or more, and the surface temperature of the sprayed ceramic coating will exceed 900℃.In this case, there is a limit to the ability to increase the thermal insulation properties by increasing the thickness of the sprayed ceramic coating. With conventional pistons that have a thermally sprayed ceramic coating on the piston body, the coating is easily damaged.
Moreover, it cannot provide sufficient insulation.

In addition, as a second means of achieving high thermal insulation other than thickening the film,
As is clear from the above equation (1), it is also possible to reduce the thermal conductivity. Here, for example, Zroz・8Y
When spraying 203, the porosity (%) and thermal conductivity (W/
The relationship with m-K> at room temperature is as shown in Figure 10.
Increasing the porosity within the sprayed ceramic coating reduces thermal conductivity. Further, a thermally sprayed ceramic film containing many pores has a lower thermal conductivity than a sintered ceramic film produced by sintering. Therefore, it can be seen that the thermal conductivity can be lowered by increasing the pores of the thermally sprayed ceramic coating.

However, even if the number of pores in the sprayed ceramic coating is increased by thermal spraying using conventional techniques such as low-pressure spraying, this will reduce the adhesion between the particles. formation becomes impossible, and it becomes impossible to include pores beyond a certain value. For this reason, until now, as a means of improving the thermal insulation properties of thermally sprayed ceramic coatings, it has been necessary to rely on increasing the thickness.

Furthermore, as a third means of improving heat insulation, ceramic slurry containing many pores 91a is used as shown in FIG.
It is also conceivable to form a coated ceramic film by applying 91 to the base material 90. ceramic slurry
As the material 91, in order to form pores 91a in the applied ceramic film, a silicon carbide (SiC)-based hollow balloon and a silicon carbide-based ceramic material, that is, a silica (SiO2)-based material is mainly employed. The porosity of the applied ceramic film thus formed is 30 to 50.
%, which is more than three times that of the thermal sprayed ceramic coating using ZrO2.8Y203. Therefore, the thermal conductivity is also approximately 0.4 W/m-K (W: Watt, K:
(absolute temperature), which is less than 1/2 that of the ZrO2.8Y203 thermal sprayed ceramic coating. In other words, the above (
According to equation 1), when comparing a thermally sprayed ceramic film and a coated ceramic film of the same film thickness, it can be said that the latter has a thermal insulation degree that is more than twice that of the former.

However, even though the coated ceramic film has excellent heat insulation properties, the main component of the ceramic slurry is 3i02.
Since the coefficient of thermal expansion is as small as 5X10-6/"C, combustion parts made of aluminum alloy (Al: 23x10
-6/'C) and Ni-based heat-resistant steel (Ni-based: 15 to 1
When applied to a base material with a large coefficient of thermal expansion such as 8X10-6/'C), damage may occur and there is a problem in terms of durability.

For this reason, until now, it has only been used for base materials with a small coefficient of thermal expansion, such as cast iron, to prevent peeling due to the difference in thermal expansion with the base material. In addition, it is impossible to use the coating on the top surface of the piston body made of aluminum alloy in an environment where the temperature is expected to exceed 900℃ because the difference in thermal expansion will be greater than at low temperatures. Environmental temperature is also limited. Therefore, although the current coated ceramic coatings have high heat insulating properties, they cannot be used in high temperature ranges where higher heat insulating properties are required.

The present invention was made in view of the above-mentioned conventional problems, and provides a heat-insulating aluminum-based member that exhibits heat-insulating properties with sufficient durability and without film damage even under higher-temperature conditions. The purpose is to

[Means for Solving the Problems] The heat insulating aluminum member of the present invention comprises a base material made of an aluminum alloy, a sprayed ceramic coating formed on the base material, and a coating formed on the sprayed ceramic coating. A heat insulating aluminum member comprising a ceramic film, the applied ceramic film having a porosity including hollow balloons of 30 to 50% and a thermal conductivity of 0.2 to 0.8 W/m.
K.

The base material is made of an aluminum alloy. It is preferable to provide an uneven treated surface by shot blasting or the like at a portion of the base material to be heated at a high temperature. In addition, Ni-C
r-Al alloy, N-Cr-AI-Y alloy, Ni-C
It is preferable to form the base sprayed layer using an o-Cr-A I-Y alloy or the like. This base material is used, for example, as a piston body for an automobile engine.

The sprayed ceramic coating is formed by plasma spraying a ceramic material such as zirconia or ittria-stabilized zirconia onto a portion of the base material that is heated to a high temperature.

The applied ceramic coating is formed on the thermally sprayed ceramic coating. This coated ceramic film has a porosity of 30 to 50% including hollow balloons, and a thermal conductivity of 0.2 to 0.
．． It is 8W/m-. If the porosity is less than 30%, the heat insulation degree is insufficient according to the above equation (1), and if the porosity exceeds 50%, the strength is insufficient. Thermal conductivity is 0.2W/m-
If it is less than , the strength is not sufficient and the thermal conductivity is 0.8W.
/m-K, the degree of insulation is insufficient. This coated ceramic film can be formed by applying, for example, a silica-based ceramic material consisting of a ceramic balloon made of 5i02 and a matrix made of 5i02 ceramic, followed by drying and firing. It is preferable to add ceramic fibers such as silicon carbide (SiC) fibers to the ceramic material.

There is a gap between the thermal sprayed ceramic coating and the applied ceramic coating.
It is preferable to provide a diffusion layer that is a mixed layer of both.

[Function] The insulating aluminum member of the present invention has a porosity of 3 including hollow balloons on the base material through a thermally sprayed ceramic coating.
A coated ceramic film having a thermal conductivity of 0 to 50% and a thermal conductivity of 0.2 to 0.8 W/m- is formed. Therefore, it is possible to sequentially change the coefficient of thermal expansion from the thermally sprayed ceramic coating to the coated ceramic coating. Furthermore, the thicknesses of the thermally sprayed ceramic coating and the coated ceramic coating can be reduced while maintaining the same degree of heat insulation. Therefore, the thermal stress due to the difference in thermal expansion between the base material and the sprayed ceramic coating and the thermal stress due to the difference in thermal expansion between the sprayed ceramic coating and the coated ceramic coating are alleviated, and peeling and falling off are prevented. In addition, since the applied ceramic film has a high porosity, high machinability can be obtained.

When a diffusion layer is provided between the thermally sprayed ceramic film and the coated ceramic film, the adhesion between the two is improved, and the coefficient of thermal expansion can be changed sequentially from the sprayed ceramic film to the coated ceramic film. Thermal stress due to the difference in thermal expansion between the ceramic film and the applied ceramic film is further relaxed, and peeling and falling off are more effectively prevented.

In addition, when an uneven treated surface is provided by shot blasting or the like on a portion of the base material that is heated to a high temperature, the adhesion of the thermally sprayed ceramic coating is improved.

In general, when a base thermal sprayed layer is formed on a portion of the base material that is heated to a high temperature or on the treated surface of this portion, the adhesion of the thermally sprayed ceramic coating is improved and thermal stress due to the difference in thermal expansion is alleviated.

In addition, when ceramic fibers are added to the ceramic material forming the applied ceramic coating, the strength of the applied ceramic coating is improved.

[Examples, Comparative Examples] Examples 1 to 5 embodying the present invention will be described below as Comparative Examples 1.2.
This will be explained with reference to the drawings.

(Example 1) A shot blasting treatment is performed on a flat plate made of aluminum alloy (A112%Si) as the base material 1.

This base material 1 has a coefficient of thermal expansion of 23.4X10-6 at room temperature.
Thermal conductivity is 105 (W/m-K).

The blasting material used is calcined alumina, 1200 to 1400 μm. NiCrA 1 alloy (N+-
20%Cr-5%AI> powder (50 to 100 μm) was formed to a thickness of 0.11Nr1 by plasma spraying, and this was used as the base sprayed layer 2. This base sprayed layer 2 has a thermal expansion coefficient of 15.0 x 10-6 and a thermal conductivity of 6.0 (W/
m-K).

ZrO2.8Y203 powder (44-7
4 μm) to form a thermal sprayed ceramic coating 3 having a thickness of 0°2IIIn. This thermal sprayed ceramic coating 3 has a thermal expansion coefficient of 10°0XIO-6 and a thermal conductivity of 1.0 (W/m-K) at room temperature.

Ceramic balloon consisting of SiO2 40-60 volume (
vol)%, 5 to 20 VO 1% of ceramic fibers made of SIC fibers, and the remainder of the matrix made of SiO2-based ceramic to prepare a ceramic slurry, and apply 0.2% of this ceramic slurry onto the thermal sprayed ceramic coating 3.
After applying the coating and leaving it to dry for 1 hour, it was held at 400°C for 30 minutes and fired. This is referred to as a coated ceramic film 4.

This coated ceramic film 4 has a coefficient of thermal expansion of 5.0 at room temperature.
X10-6, thermal conductivity is 0.4 (W/m-K), and porosity is 40 to 60%.

A schematic sectional view, a 50x cross-sectional photograph, and a 100x cross-sectional photograph of the heat-insulating aluminum-based member produced by the above procedure are shown in FIGS. 1, 2, and 3.

(Example 2) A heat-insulating aluminum-based member is produced which is basically the same as in Example 1 except that the thickness of the thermally sprayed ceramic coating 3 is 0.5 IrIm.

(Example 3) A heat-insulating aluminum-based member basically the same as in Example 1 was prepared except that the following treatment was performed to increase the adhesion between the thermal sprayed ceramic coating 3 and the coated ceramic coating [14].

That is, in order to make the lower 0.1 am of the applied ceramic film a mixed structure of ceramic slurry and zirconia,
Ceramic slurry is applied on the thermal sprayed ceramic coating in advance.
and Zr'02.8Y203 powder (particle size 44-74μm)
0.1 ml+ of a mixture of 50% by volume was applied, and 0.1 m of ceramic slurry was applied thereon to form a ceramic slurry. This mixed structure is used as the diffusion layer 51.

FIG. 4 shows a schematic cross-sectional view of the heat-insulating aluminum-based member produced by the above procedure.

(Example 4) A heat-insulating aluminum-based member basically the same as in Example 1 was prepared except that the following treatment was performed to increase the adhesion between the thermally sprayed ceramic coating 3 and the coated ceramic coating 4.

That is, AI is applied to the upper 0.1M of the thermal sprayed ceramic coating 3.
Powder (particle size 44 to 74 μTrL) is contained in a volume ratio of 50%. After that, a strong alkaline solution such as a sodium hydroxide solution is impregnated from the upper part of the thermal sprayed ceramic coating 4, and A1
Chemically dissolve the powder. After neutralizing and cleaning the surface, the ceramic slurry is applied and placed in a vacuum chamber.
The portion from which the AI powder has been removed: the diffusion layer 52) is forcibly impregnated with ceramic slurry.

FIG. 5 shows a schematic cross-sectional view of the heat-insulating aluminum-based member produced by the above procedure.

(Example 5) A heat-insulating aluminum-based member basically the same as Example 1 was prepared except that the following treatment was performed to increase the adhesion between the thermally sprayed ceramic coating 3 and the coated ceramic coating 4.

That is, as in Example 4, the thermal sprayed ceramic coating 4 is impregnated with ceramic slurry, but at this time, polyester resin powder (particle size 44 to 74 μm) is used instead of A1 powder.
), and before applying the ceramic slurry, it is burnt out with flame to provide a diffusion layer 53 with pores in the sprayed ceramic coating.

A schematic cross-sectional view of the heat insulating aluminum member produced by the above procedure is also shown in FIG.

(Comparative Example 1) As a conventional heat insulating aluminum member, a thermal sprayed ceramic coating 3 was formed on a base thermal sprayed layer 2, and a coated ceramic coating 4 was formed on the base thermal sprayed layer 2.
A heat-insulating aluminum-based member that is basically the same as in Example 1 except that it is not formed is produced.

(Comparative Example 2) As a conventional heat-insulating aluminum-based member, a heat-insulating aluminum-based member that is basically the same as in Example 1 except that a coated ceramic film 4 is only formed on the base material 1 is created.

[Heat Cycle Test Evaluation] A heat cycle test was conducted to confirm how much improvement in durability the heat insulating aluminum members of Examples 1 to 5 exhibited compared to those of Comparative Example 1.2.

The survey targets are shown below.

Sample No. 1...Insulating aluminum member sample No. of Comparative Example 1, 2.3...Insulating aluminum member sample No. 004 of Example 2.1...Insulating aluminum member sample No. of Comparative Example 2, 5 to 7...Insulating aluminum-based members of Examples 2 to 4 The degrees of insulation of these objects to be investigated were calculated to be the same.

Test conditions were water cooling and burner flame (top surface temperature 900℃)
This is a thermal cycle evaluation. The test results are shown in FIG.

As mentioned above, Comparative Example 1 (Sample No. 1>, that is, a conventional heat-insulating aluminum-based member without coating ceramic film 4, requires a film thickness of 0.7 m to insulate a surface temperature of 900°C. As expected, 150
Peeling occurred during cycling.

Comparative Example 2 (Sample No. 4), that is, a conventional heat-insulating aluminum-based member in which a coated ceramic film 4 was formed on the base thermal sprayed layer 2, showed the same heat insulation properties with a film thickness of 0.281111, but 60. Peeling occurred during cycling.

On the other hand, Example 2 (sample No. 2>, that is, the base thermal sprayed layer 2 has a thermally sprayed ceramic coating 3 of 0.5#I and a thermally sprayed ceramic coating 3 of 0.087
In the heat insulating aluminum member formed with the coated ceramic film 4 of No. 11111, peeling occurred after 700 cycles.

In addition, in Example 1 (sample No. 3), that is, in a heat-insulating aluminum member in which a 0.2 m long thermal sprayed ceramic film 3 and a 0.2 m long applied ceramic film 4 were formed on the base thermal sprayed layer 2, peeling occurred after 1700 cycles. occured.

From this result, it can be said that the heat insulating aluminum member of Example 1 is advantageous in terms of durability under these test conditions, but it is thought that the optimal combination will vary depending on the usage environment.

In addition, Examples 3 to 5 (Samples Nos. 5 to 7), that is, heat-insulating aluminum-based members in which diffusion layers 51 to 53 were provided between the thermally sprayed ceramic film 3 and the applied ceramic film 4,
No peeling occurred even after 2000 cycles.

Therefore, the durability of these heat-insulating aluminum-based members is improved compared to that of Example 1.2 (sample N003.2), in which the coated ceramic film 4 was simply formed on the thermally sprayed ceramic film 3. it is obvious.

From the above evaluation, the durability of a heat-insulating aluminum-based member having a thermally sprayed ceramic film 3 and a coated ceramic film 4 is improved compared to a heat-insulating aluminum-based member having only a conventional thermally sprayed ceramic film 3 or a coated ceramic film 4. Recognize.

It can also be seen that even in the case of having the thermally sprayed ceramic coating 3 and the coated ceramic coating 4, the durability is further improved by forming the diffusion layers 51 to 53 between them.

[Actual machine test evaluation] Here, an actual machine test was conducted in which the piston body was actually used as the base material and the top surface of the piston body was coated with a thermally sprayed ceramic coating or the like. The survey targets are listed below.

Sample No. 1... Piston sample No. 3, formed in the same manner as the heat insulating aluminum member of Comparative Example 1. Piston sample No. 4, formed in the same manner as the heat insulating aluminum member of Example 1. Comparison Piston sample No. 005 formed in the same manner as the heat insulating aluminum member of Example 2...Piston formed in the same manner as the heat insulating aluminum member of Example 5 These were assembled into a diesel engine, 50 horsepower, 95
Continuous operation was performed for 500 hours at horsepower, 120 horsepower, and 150 horsepower, respectively, and the presence or absence of film damage was confirmed. The results are shown in Table 1.

In the piston of Comparative Example 1 (Sample No. 001), cracks were observed at 95 horsepower, and complete peeling of the coating occurred at 120 horsepower.

In addition, the piston of Comparative Example 2 (Sample No. 4>
Even at 0 horsepower, peeling occurred.

On the other hand, in the piston of Example 1 (sample No. 3), 1
Good results were shown up to 20 horsepower, but Table 1: ○: No damage to the coating, good condition △:: Cracks were observed in the membrane, and there is a possibility of peeling in the future.X: Peeling and cracks of the coating were observed. .

At 50 horsepower, some cracks were observed in the film.

In addition, in the piston of Example 5 (sample No. 5>), 1
Even after a 50 horsepower durability test, no defects such as film cracks were observed.

The above evaluation shows that the piston of Example 1.5 can be used satisfactorily even at high horsepower, which conventional pistons cannot withstand.

Further, in the piston of Example 1.5, the top surface is a coated ceramic film having many pores and excellent machinability. Therefore, in the piston of Example 1.5,
Post-processing is easier than with conventional pistons, cutting torque is less than 1/10 of conventional pistons, and tool life (wear) is reduced.
improved by more than 10 times. Therefore, the time required for machining can be reduced compared to the conventional method, and the cost of cutting tools can be reduced.

[Effects of the Invention] As detailed above, the heat-insulating aluminum member of the present invention has a thermally sprayed ceramic film and a coated ceramic film formed on a base material made of an aluminum alloy, and the coated ceramic film includes a hollow balloon. Since the porosity is 30 to 50% and the thermal conductivity is 0.2 to 0.8 W/m-, the film will not be damaged and will exhibit sufficient heat insulation even under higher temperature conditions. can.

Therefore, if this heat-insulating aluminum-based member is adopted for the piston of an automobile engine, the engine will be
Even with high output that exceeds horsepower, it can exhibit sufficient durability.

Additionally, since the surface of this heat-insulating aluminum-based member is coated with a ceramic coating, the time required for processing can be shortened.
Moreover, the cutting tool cost can also be reduced.
\

[Brief explanation of the drawing]

Figures 1 to 3 relate to the heat insulating aluminum member of Example 1. Figure 1 is a schematic cross-sectional view, Figure 2 is a 50x photomicrograph showing the particle structure, and Figure 3 is a 1100x photomicrograph showing the particle structure. This is a microscopic photograph. FIG. 4 is a schematic sectional view showing a heat insulating aluminum member of Example 2. FIG. 5 is a schematic sectional view showing the heat insulating aluminum member of Example 3.4. 6th
The figure is a graph showing the results of thermal cycle tests of Examples and Comparative Examples. Figures 7 to 11 relate to conventional heat-insulating aluminum members, Figure 7 is a graph showing the relationship between the thickness of the thermally sprayed ceramic coating and the degree of insulation, Figure 8 is a graph showing the relationship between engine horsepower and temperature; FIG. 9 is a graph showing the relationship between the thermal sprayed ceramic coating and the thermal stress of the strength valve, FIG. 10 is a graph showing the relationship between porosity and thermal conductivity, and FIG. 11 is a schematic cross-sectional view. 1... Base material 2... Base sprayed layer 3... Thermal sprayed ceramic coating 4... Coated ceramic coating 51.52.53... Diffusion layer

Claims (1)

[Claims] (1) A heat insulating aluminum member comprising a base material made of an aluminum alloy, a thermally sprayed ceramic film formed on the base material, and a coated ceramic film formed on the sprayed ceramic film, wherein the The ceramic film is a heat insulating aluminum member characterized by having a porosity of 30 to 50% including hollow balloons and a thermal conductivity of 0.2 to 0.8 W/m·K.