Aluminium-silicon carbide composite, and power-module base plate

Abstract

To provide an aluminum-silicon carbide composite which is suitable for use as a power-module base plate. An aluminum-silicon carbide composite wherein a peripheral portion having, as a main component thereof, an aluminum-ceramic fiber composite containing ceramic fibers having an average fiber diameter of at most 20 m and an average aspect ratio of at least 100, is provided on the periphery of a flat plate-shaped aluminum-silicon carbide composite having a plate thickness of 2 to 6 mm formed by impregnating, with a metal containing aluminum, a porous silicon carbide molded body having a silicon carbide content of 50 to 80 vol %, and wherein the proportion of the aluminum-ceramic fiber composite occupied in the peripheral portion is at least 50 area %.

Claims

1. An aluminum-silicon carbide composite comprising a first phase comprising a flat plate-shaped aluminum-silicon carbide composite having a plate thickness of 2 to 6 mm formed by impregnating, with a metal containing aluminum, a porous silicon carbide molded body having a silicon carbide content of 50 to 80 vol %; and on a periphery of the first phase, a second phase comprising an aluminum-ceramic fiber composite containing, at a proportion of 3 to 20% by volume, ceramic fibers comprising alumina or silica and having an average fiber diameter of at most 20 m and an average aspect ratio of at least 100; wherein a proportion of the aluminum-ceramic fiber composite contained in the second phase is at least 50 area % of the peripheral area of the first phase.

2. The aluminum-silicon carbide composite according to claim 1, wherein a thermal expansion coefficient of the aluminum-ceramic fiber composite is less than 2010.sup.6/K, a strength at 25 C. is at least 200 MPa and a strength at 150 C. is at least 150 MPa.

3. The aluminum-silicon carbide composite according to claim 1, wherein both main surfaces of the first phase are covered by an aluminum alloy layer or an aluminum-ceramic fiber layer.

4. The aluminum-silicon carbide composite according to claim 1, wherein one main surface of the first phase is covered by an aluminum alloy layer or an aluminum-ceramic fiber layer.

5. The aluminum-silicon carbide composite according to claim 1, wherein a ceramic fiber content in the aluminum-ceramic fiber composite contained in the second phase is 5 to 20 vol % with respect to an entire aluminum-ceramic fiber composite.

6. The aluminum-silicon carbide composite according to claim 1, wherein the ceramic fiber comprises one or more materials chosen from among alumina, silica, boron nitride, and silicon nitride.

7. A power-module base plate formed by plating a surface of the aluminum-silicon carbide composite according to claim 1.

8. The aluminum-silicon carbide composite according to claim 1, wherein the aluminum alloy layer has an average thickness of 0.05 mm to 0.3 mm.

Description

EXAMPLES

(1) Herebelow, the present invention will be further explained based on examples and comparative examples, but the present invention is not to be construed as being limited thereto.

Example 1

(2) 100 g of silicon carbide powder A (manufactured by Pacific Rundum: NG-150, average particle diameter: 100 m), 100 g of silicon carbide powder B (manufactured by Pacific Rundum: NG-220, average particle diameter: 60 m), 100 g of silicon carbide powder C (manufactured by Yakushima Denko: GC-1000F, average particle diameter: 10 m) and 30 g of a silica sol (manufactured by Nissan Chemical Industries: Snowtex) were weighed out and mixed in a stirrer/mixer for 30 minutes, then press-molded at a pressure of 10 MPa into the shape of a flat plate with dimensions of 190 mm140 mm5.5 mm.

(3) The resulting molded body was dried for 2 hours at a temperature of 120 C., then baked for 2 hours at a temperature of 950 C. in air, to obtain a porous silicon carbide molded body with a relative density of 65%. The resulting porous silicon carbide molded body was surface-worked to a thickness of 4.8 mm using a surface grinding machine with a diamond grinding wheel, then the peripheral portions were worked to external shape dimensions of 183133 mm using a machining center. The three-point bending strength of the resulting porous silicon carbide molded body was measured to be 10 MPa.

(4) Mullite ceramic fibers (average fiber diameter 15 m, average aspect ratio 120, volume proportion 5 vol %) were arranged adjacent to both long sides of the periphery of the resulting porous silicon carbide molded body (proportion of aluminum-ceramic fiber composite occupied in peripheral portion: 58 area %), both surfaces were clamped by carbon-coated stainless steel plates with dimensions of 210 mm160 mm0.8 mm, 30 were stacked, after which iron plates with a thickness of 6 mm were disposed on both sides, connected with six M10 bolts, which were tightened with a torque wrench so that the tightening torque in the planar direction was 3 Nm, forming a single block. Next, the integrated block was preheated to 600 C. in an electric furnace, then placed in a preheated press mold with an inner diameter of 400 mm, and a molten aluminum alloy comprising 12 mass % of silicon and 0.8 mass % of magnesium was poured in and the silicon carbide porous body was impregnated with the aluminum alloy by pressurizing for 20 minutes at a pressure of 100 MPa. After cooling to 25 C., the block was cut along the shapes of the mold release plates using a wet bandsaw, the clamped stainless steel plates were stripped away, and thereafter, an annealing treatment was performed for 3 hours at a temperature of 530 C. in order to remove strain generated at the time of impregnation, to obtain an aluminum-silicon carbide composite.

(5) Through holes with a diameter of 7 mm were formed at eight locations and 10 to 4 mm countersinks were formed at four locations on the edge portions of the resulting aluminum-silicon carbide composite, and the aluminum portions and the aluminum-ceramic fiber composite portions of the periphery were worked with an NC lathe to a shape of 187 mm137 m5.0 mm. Next, in order to warp this aluminum-silicon carbide composite, a carbon concavo-convex mold provided with a spherical surface having a radius of curvature of 15000 mm was prepared. This concavo-convex mold was mounted on a hot press and heated to set the surface temperature of the mold to 470 C. The aforementioned composite was arranged between this concavo-convex mold and pressed at 400 KPa. At this time, a thermocouple was placed in contact with the side surface of the composite to measure the temperature. After holding for 3 minutes from the time the temperature of the composite reached 450 C., the pressure was released and the composite was naturally cooled to 50 C. Next, in order to remove strain, an annealing treatment was performed for 1 hour at a temperature of 350 C. in an electric furnace. The amount of warpage for every 10 cm of length in the resulting composite was measured using a contour shape measuring device (manufactured by Tokyo Seimitsu; Contourecord 1600D-22), and a warpage of 80 m had been applied for every 10 cm of length.

(6) After cleaning the resulting alumina-silicon carbide composite by performing a blast treatment using alumina abrasive grains at a pressure of 0.4 MPa and a transport speed of 1.0 m/min, electroless NiP and NiB plating was performed. A plating layer with a thickness of 8 m (NiP: 6 m+NiB: 2 m) was formed on the composite surface.

(7) The resulting aluminum-silicon carbide composite was ground to produce a sample for measuring the thermal expansion coefficient (plate-shaped body of length 20 mm, width 4 mm and thickness 4 mm), a sample for measuring the thermal conductivity (plate-shaped body of length 10 mm, width 10 mm and thickness 1 mm) and a sample for measuring the strength (plate-shaped body of length 40 mm, width 4 mm and thickness 3 mm). Using the respective samples, for the first phase, the thermal expansion coefficient from 25 C. to 150 C. was measured using a thermal expansion meter (manufactured by Seiko Instruments; TMA300), the thermal conductivity at 25 C. was measured by the laser flash method (manufactured by Rigaku; TC-7000) and the three-point bending strength at 25 C. was measured using a flexural strength meter (manufactured by Imada Seisakusho; SV-301). The obtained results are shown in Table 1.

(8) Next, the peripheral aluminum-ceramic fiber composite portion (second phase) of the resulting aluminum-silicon carbide composite was ground to produce a sample for measuring the thermal expansion coefficient (plate-shaped body of length 20 mm, width 4 mm and thickness 4 mm) and a sample for measuring the strength (plate-shaped body of length 40 mm, width 4 mm and thickness 3 mm). Using the respective samples, for the second phase, the thermal expansion coefficient from 25 C. to 150 C. was measured using a thermal expansion meter (manufactured by Seiko Instruments; TMA300), and the three-point bending strength at 25 C. and 150 C. was measured using a flexural strength meter (manufactured by Imada Seisakusho; SV-301). The obtained results are shown in Table 1.

(9) Using the plated product of Example 1, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C. After the heat cycle test of Example 1, no waving or depressions were observed in the aluminum-silicon carbide composite. Additionally, upon observing the peripheral portions by eye, there were no cracks, and upon performing internal flaw inspection using an ultrasonic flaw detector, there were no cracks in the aluminum-silicon carbide composite.

(10) Next, after joining an Al circuit board to the plated product of Example 1 using a lead-free solder, and after performing a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C., upon checking the external appearance and the joining state using an ultrasonic flaw detector, no cracks were observed in the solder which is the joining layer. The obtained results are shown in Table 2.

Example 2

(11) 100 g of silicon carbide powder A (manufactured by Pacific Rundum: NG-150, average particle diameter: 100 m), 100 g of silicon carbide powder B (manufactured by Pacific Rundum: NG-220, average particle diameter: 60 m), 100 g of silicon carbide powder C (manufactured by Yakushima Denko: GC-1000F, average particle diameter: 10 m) and 30 g of a silica sol (manufactured by Nissan Chemical Industries: Snowtex) were weighed out and mixed in a stirrer/mixer for 30 minutes, then press-molded at a pressure of 10 MPa into the shape of a flat plate with dimensions of 190 mm140 mm5.5 mm.

(12) The resulting molded body was dried for 2 hours at a temperature of 120 C., then baked for 2 hours at a temperature of 950 C. in air, to obtain a porous silicon carbide molded body with a relative density of 65%. The resulting porous silicon carbide molded body was surface-worked to a thickness of 4.8 mm using a surface grinding machine with a diamond grinding wheel, then the peripheral portions were worked to external shape dimensions of 183133 mm using a machining center. The three-point bending strength of the resulting porous silicon carbide molded body was measured to be 10 MPa.

(13) Mullite ceramic fibers (average fiber diameter 15 m, average aspect ratio 120, volume proportion 5 vol %) were arranged adjacent to both long sides and both short sides of the periphery of the porous silicon carbide molded body (proportion of aluminum-ceramic fiber composite occupied in peripheral portion: 100 area %), and an aluminum-silicon carbide composite was obtained in the same manner as Example 1.

(14) Using the plated product of Example 2, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(15) Next, after joining an Al circuit board to the plated product of Example 2 using a lead-free solder, a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. was performed. The obtained results are shown in Table 2.

Example 3

(16) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the volume proportion of the ceramic fiber was set to 20 vol %.

(17) Using the plated product of Example 3, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(18) Next, after joining an Al circuit board to the plated product of Example 3 using a lead-free solder, a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. was performed. The obtained results are shown in Table 2.

Example 4

(19) The aluminum-silicon carbide composite of Example 1 was ground by 1.0 mm using a planar grinding machine with a diamond grinding wheel to expose the aluminum-silicon carbide composite, to a shape of 1871374 mm. Next, the resulting workpiece was annealed for 1 hour at a temperature of 530 C. in an electric furnace in order to remove strain generated at the time of working. Next, after cleaning by performing a blast treatment using alumina abrasive grains at a pressure of 0.4 MPa and a transport speed of 1.0 m/min, electroless NiP and NiB plating was performed. A plating layer with a thickness of 8 m (NiP: 6 m+NiB: 2 m) was formed on the composite surface.

(20) Using the plated product of Example 4, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(21) Next, after joining an Al circuit board to the plated product of Example 4 using a lead-free solder, a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. was performed. The obtained results are shown in Table 2.

Examples 5 and 6

(22) Aluminum-silicon carbide composites were obtained in the same manner as Example 1 except that the silicon carbide contents in the aluminum-silicon carbide composites were set to 50 vol % and 80 vol %.

(23) Using the plated products of Examples 5 and 6, heat cycle tests were performed in 10 cycles wherein the plated products were placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the products were allowed to naturally cool to 25 C.

(24) Next, after joining Al circuit boards to the plated products of Examples 5 and 6 using a lead-free solder, heat cycle tests (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. were performed. The obtained results are shown in Table 2.

Examples 7 and 8

(25) Aluminum-silicon carbide composites were obtained in the same manner as Example 1, except that the porous silicon carbide composite molded bodies were surface-worked to thicknesses of 1.8 mm and 5.8 mm using a planar grinding machine with a diamond grinding wheel, to adjust the thicknesses of the aluminum-silicon carbide composites to 2.0 mm and 6.0 mm.

(26) Using the plated products of Examples 7 and 8, heat cycle tests were performed in 10 cycles wherein the plated products were placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the products were allowed to naturally cool to 25 C.

(27) Next, after joining Al circuit boards to the plated products of Examples 7 and 8 using a lead-free solder, heat cycle tests (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. were performed. The obtained results are shown in Table 2.

Example 9

(28) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the average fiber diameter of the ceramic fibers was 20 m, the average aspect ratio was 100 and the volume proportion was 5 vol %.

(29) Using the plated product of Example 9, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(30) Next, after joining an Al circuit board to the plated product of Example 9 using a lead-free solder, a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C. was performed. The obtained results are shown in Table 2.

Comparative Example 1

(31) 100 g of silicon carbide powder A (manufactured by Pacific Rundum: NG-150, average particle diameter: 100 m), 100 g of silicon carbide powder B (manufactured by Pacific Rundum: NG-220, average particle diameter: 60 m), 100 g of silicon carbide powder C (manufactured by Yakushima Denko: GC-1000F, average particle diameter: 10 m) and 30 g of a silica sol (manufactured by Nissan Chemical Industries: Snowtex) were weighed out and mixed in a stirrer/mixer for 30 minutes, then press-molded at a pressure of 10 MPa into the shape of a flat plate with dimensions of 190 mm140 mm5.5 mm.

(32) The resulting molded body was dried for 2 hours at a temperature of 120 C., then baked for 2 hours at a temperature of 950 C. in air, to obtain a porous silicon carbide molded body with a relative density of 65%. The resulting porous silicon carbide molded body was surface-worked to a thickness of 4.8 mm using a surface grinding machine with a diamond grinding wheel, then the peripheral portions were worked to external shape dimensions of 183133 mm using a machining center. The three-point bending strength of the resulting porous silicon carbide molded body was measured to be 10 MPa.

(33) Mullite ceramic fibers (average fiber diameter 15 m, average aspect ratio 120, volume proportion 5 vol %) were arranged adjacent to one long side of the periphery of the resulting porous silicon carbide molded body (proportion of aluminum-ceramic fiber composite occupied in peripheral portion: 29 area %), and an aluminum-silicon carbide composite was obtained in the same manner as Example 1.

(34) After cleaning the resulting aluminum-silicon carbide composite by performing a blast treatment using alumina abrasive grains at a pressure of 0.4 MPa and a transport speed of 1.0 m/min, electroless NiP and NiB plating was performed. A plating layer with a thickness of 8 m (NiP: 6 m+NiB: 2 m) was formed on the composite surface.

(35) Using the plated product of Comparative Example 1, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C., whereupon waving was observed after the test.

(36) Next, after joining an Al circuit board to the plated product of Comparative Example 1 using a lead-free solder, and after performing a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C., upon checking the external appearance and the joining state using an ultrasonic flaw detector, no cracks were observed in the solder which is the joining layer. The obtained results are shown in Table 2.

Comparative Example 2

(37) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the silicon carbide content in the aluminum-silicon carbide composite was set to 45 vol %.

(38) Using the plated product of Comparative Example 2, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(39) Next, after joining an Al circuit board to the plated product of Comparative Example 2 using a lead-free solder, and after performing a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C., upon checking the external appearance and the joining state using an ultrasonic flaw detector, cracks were observed in the solder which is the joining layer.

Comparative Example 3

(40) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the silicon carbide content in the aluminum-silicon carbide composite was set to 85 vol %. Upon performing internal flaw inspection of the resulting aluminum-silicon carbide composite using an ultrasonic flaw detector, cracks were observed in the aluminum-silicon carbide composite.

Comparative Example 4

(41) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the porous silicon carbide molded body was surface-worked to a thickness of 1.3 mm using a planar grinding machine with a diamond grinding wheel, and the thickness of the aluminum-silicon carbide composite was set to 1.5 mm. Upon performing internal flaw inspection of the resulting aluminum-silicon carbide composite using an ultrasonic flaw detector, cracks were observed in the aluminum-silicon carbide composite.

Comparative Example 5

(42) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the porous silicon carbide molded body was surface-worked to a thickness of 6.3 mm using a planar grinding machine with a diamond grinding wheel, and the thickness of the aluminum-silicon carbide composite was set to 6.5 mm.

(43) Using the plated product of Comparative Example 5, a heat cycle test was performed in 10 cycles wherein the plated product was placed on a hot plate heated to a temperature of 350 C., and after reaching a material temperature of 350 C. and holding for 10 minutes, the product was allowed to naturally cool to 25 C.

(44) Next, after joining an Al circuit board to the plated product of Comparative Example 5 using a lead-free solder, and after performing a heat cycle test (500 cycles) of holding for 30 minutes in thermostatic tanks of 40 C. and 125 C., upon checking the external appearance and the joining state using an ultrasonic flaw detector, cracks were observed in the solder which is the joining layer.

Comparative Example 6

(45) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the average fiber diameter of the ceramic fiber was 25 m, the average aspect ratio was 90 and the volume proportion was 5 vol %. Upon observing the periphery of the resulting aluminum-silicon carbide composite by eye, cracks were observed in the peripheral aluminum-ceramic fiber composite portion.

Comparative Example 7

(46) An aluminum-silicon carbide composite was obtained in the same manner as Example 1, except that the average fiber diameter of the ceramic fiber was 15 m, the average aspect ratio was 120 and the volume proportion was 25 vol %.

(47) After cleaning the resulting aluminum-silicon carbide composite by performing a blast treatment using alumina abrasive grains at a pressure of 0.4 MPa and a transport speed of 1.0 m/min, electroless NiP and NiB plating was performed. A plating layer with a thickness of 8 m (NiP: 6 m+NiB: 2 m) was formed on the composite surface.

(48) Upon observing the periphery of the plated product of Comparative Example 7 by eye, many unplated portions were observed in the peripheral aluminum-ceramic fiber composite portion.

(49) The principal conditions and results of the Examples and Comparative Examples are shown in Tables 1 and 2. For Examples 2 to 9 and Comparative Examples 1 to 7, the thermal expansion coefficient, thermal conductivity and three-point bending strength of the first phase were measured in the same manner as Example 1.

(50) TABLE-US-00001 TABLE 1 Aluminum-Ceramic Fiber Composite Aluminum-Silicon Carbide Composite Ceramic Fiber Silicon Plate Thermal Thermal Average Thermal Carbide Thick- Expansion Conduc- Strength: Fiber Expansion Strength: Strength: Content ness Coefficient tivity 25 C. Diameter Aspect Content Coefficient 25 C. 150 C. (vol %) (mm) (10.sup.6/K) (W/mK) (MPa) (m) Ratio (vol %) (10.sup.6/K) (MPa) (MPa) Example 1 65 5.0 7.2 208 412 15 120 5.0 19.0 270 221 Example 2 65 5.0 7.1 211 421 15 120 5.0 19.2 266 215 Example 3 65 5.0 7.2 201 395 15 120 20.0 17.5 345 302 Example 4 65 5.0 6.9 205 399 15 120 5.0 19.1 281 232 Example 5 50 5.0 8.8 173 365 15 120 5.0 18.8 260 211 Example 6 80 5.0 6.2 280 326 15 120 5.0 18.8 267 214 Example 7 65 2.0 7.3 207 409 15 120 5.0 19.0 273 226 Example 8 65 6.0 7.3 218 401 15 120 5.0 18.5 277 205 Example 9 65 5.0 7.2 222 395 20 100 5.0 18.7 279 210 Comparative 65 5.0 7.1 205 411 15 120 5.0 18.7 275 230 Example 1 Comparative 45 5.0 9.7 155 420 15 120 5.0 18.8 283 218 Example 2 Comparative 85 5.0 5.5 298 312 15 120 5.0 19.0 268 212 Example 3 Comparative 65 1.5 7.4 209 398 15 120 5.0 18.6 277 208 Example 4 Comparative 65 6.5 7.4 213 425 15 120 5.0 18.5 264 205 Example 5 Comparative 65 5.0 7.1 210 421 25 90 5.0 18.8 256 201 Example 6 Comparative 65 5.0 7.2 218 396 15 120 25.0 16.3 336 297 Example 7

(51) TABLE-US-00002 TABLE 2 Flaws in Heat Cycle (45 C. to 120 C.) After Flaws in Flaws in Mounting Aluminum-Silicon Heat Cycle on Circuit Carbide Composite (25 C. to 350 C.) Board Example 1 none none none Example 2 none none none Example 3 none none none Example 4 none none none Example 5 none none none Example 6 none none none Example 7 none none none Example 8 none none none Example 9 none none none Comparative none aluminum-silicon Example 1 carbide composite (first phase) was wavy Comparative none none solder cracks Example 2 Comparative aluminum-silicon Example 3 carbide composite (first phase) had cracks Comparative aluminum-silicon Example 4 carbide composite (first phase) had cracks Comparative none none solder cracks Example 5 Comparative aluminum-ceramic Example 6 fiber portion (second phase) had cracks Comparative aluminum-ceramic Example 7 fiber portion (second phase) was unplated

BRIEF DESCRIPTION OF THE DRAWINGS

(52) FIG. 1 An explanatory diagram showing an embodiment of the aluminum-silicon carbide composite used in the present invention.

(53) FIG. 2 An explanatory diagram showing an embodiment of the aluminum-silicon carbide composite used in the present invention.

DESCRIPTION OF REFERENCE SYMBOLS

(54) a) Aluminum-silicon carbide composite b) Peripheral portion including aluminum-ceramic fiber composite c) 7 mm through hole d) 10 to 4 mm countersink e) Surface aluminum alloy layer