Aluminum die casting alloy

Abstract

The thermal conductivity of the alloy of the invention can achieve 146 W/m·K, an increase of 45% compared with that of common aluminum die casting alloy-ADC12. The casting defects like shrinkage cavity, micro-porosity and amount of dross also become much less than those of pure aluminum. Further, the fluidity and mold erosion resistance of this alloy is also better than that of pure aluminum and almost equivalent to that of ADC12. When the aluminum die casting alloy of the invention is applied to a heat sink, the thermal resistance is even lower than that of ADC12 and 1070 pure aluminum.

Description

[0001] This is a continuation-in-part of Ser. No. 09/527,879, filed Mar. 20, 2000, now pending.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an aluminum die casting alloy, and more particularly to an aluminum die casting alloy used for a heat sink. The aluminum die casting alloy possesses good castability, high thermal conductivity and minor mold erosion.

[0004] 2. Description of the Prior Art

[0005] As the power dissipation of IC components and assemblies such as CPU, chipsets and the like increases, so does the demand for thermally conductive materials. The heat generated by the increasing power dissipation of the IC component, if not effectively dispensed with, will easily cause the IC component or even the entire system to experience instability or failure. In order to dissipate the heat from the IC component and keep the junction temperature below the operating limit, a heat sink or heat dissipation apparatus is always mounted on the top surface of IC components.

[0006] Heat sink units are mainly fabricated by either extrusion or die casting. Among these, aluminum die casting is widely employed to produce very compact heat sink units despite their complex shape and flexible design. However, the common aluminum die casting alloys such as ADC12 and ADC10 possess an inferior thermal conductivity (K=96 W/m·K) as compared one of pure aluminum (220 W/m·K). Therefore, the common aluminum die casting alloy is gradually becoming unable to meet the requirements of high speed and high power CPUs. Although the raw material of pure aluminum has a superior thermal conductivity, when used as a die casting material, its poor melt fluidity and serious casting defects such as shrinkage cavity, micro-porosity and dross will eliminate the substantial thermal conductivity of the original raw material. Consequently, the total thermal performance of the pure aluminum heat sink is counterbalanced by the casting defects. Further, the die casting mold is easily eroded by the molten pure aluminum as casting proceeds, thus reducing the lifetime of the metal mold.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is to solve the above-mentioned problems and to provide a suitable aluminum die casting alloy which possesses superior thermal conductivity, better casting soundness and mechanical properties; as well as a good erosion resistance to the metal mold process.

[0008] To achieve this object, a new aluminum die casting alloy is developed by metallurgical design. The thermal conductivity of the aluminum die casting alloy of the present invention can achieve 146 W/m.K, an increase of 45% compared with the commercial aluminum alloy—ADC12 . When this aluminum die casting alloy is used as a heat sink material, the casting defects like shrinkage cavity, micro-porosity and amount of dross become much less than those of pure aluminum. Consequently, the thermal resistance of this alloy is even lower than that of pure aluminum. That is to say, the thermal performance of the heat sink of this alloy is better than that of pure aluminum and ADC12. Further, the melt fluidity and mold erosion resistance of this alloy is also better than that of pure aluminum and almost equivalent to that of ADC12. Therefore, the aluminum die casting alloy of the present invention has the potential to substitute for the pure aluminum and the common die casting alloys for a heat sink material of CPUS, DRAMs, BGAs, and chipsets. The alloy of the present invention can even be used as a chassis material for computer, hard disk, CD-ROM, power supply and other IC-related applicationss.

BRIEF DESCRIPION OF THE DRAWINGS

[0009] The present invention will be described in detail with reference to the illustrated embodiments and the accompanying drawings, in which:

[0010] FIG. 1 shows a photograph of the cross section of a die cast heat sink using 1070 pure aluminum;

[0011] FIG. 2 shows a photograph of the cross section of a die cast heat sink using the aluminum alloy of this invention;

[0012] FIG. 3 shows a photograph of the die cast microstructure of the A514 aluminum alloy (with micro-shrinkage and porosity);

[0013] FIG. 4 shows a photograph of the die cast microstructure of the invented aluminum alloy (with no micro-shrinkage);

[0014] FIG. 5 shows a photograph of a misrun that occurred when using A514 alloy as heat sink material; and

[0015] FIG. 6 shows a photograph of sound casting by using the invented alloy as heat sink material; and

[0016] FIG. 7 shows the X-ray diffraction pattern of A383, A384 and the invented alloy.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The aluminum die casting alloy of this invention possesses good casting soundness as a commercial aluminum die casting alloy, high thermal conductivity between that of ADC12 and pure aluminum, and minor mold erosion.

[0018] Table 1 is the chemical composition of the aluminum die casting alloy of the present invention and the commercial aluminum die casting alloys. 1 TABLE 1 Aluminum alloy Composition (wt %) ASTM (JIS) Si Cu Mg Zn Fe Mn Ni Sn Al A413 11.0˜1.30 <1.0 <0.3 <0.5 <1.3 <0.3 <0.5 <0.1 Bal. (ADC1) A360  9.0˜10.0 <0.6 0.4˜0.6 <0.5 <1.3 <0.3 <0.5 <0.1 Bal. (ADC3) A518 <0.3 <0.2 4.0˜8.5 <0.1 <1.8 <0.3 <0.5 <0.1 Bal. (ADC5) A514 <1.0 <0.1 2.5˜4.0 <0.4 <0.8 <0.3 <0.5 <0.1 Bal. (ADC6) A380 7.5˜9.5 2.0˜4.0 <0.3 <1.0 <1.3 <0.3 <0.5 <0.3 Bal. (ADC10) A383  9.6˜12.0 <1.0 <0.3 <1.0 <1.3 <0.3 <0.5 <0.3 Bal. (ADC12) A390 16˜18 4˜5 0.45˜0.65 <0.1 <1.3 <0.1 <0.1 <0.1 Bal. (ADC14) The alloy of 10.5   6.0  0.24  0.6  0.68  0.15   0.005  0.01 Bal. the invention

[0019] Table 2 is the thermal conductivity of the aluminum die casting alloy of the present invention and commercial aluminum die casting alloys. 2 TABLE 2 Aluminum alloy Thermal ASTM (JIS) conductivity (W/M · K) A413 (ADC1) 121 A360 (ADC3) 113 A518 (ADC5)  96 A514 (ADC6) 138 A380 (ADC10)  96 A383 (ADC12)  96 A390 (ADC14) 134 The alloy of the invention 146

[0020] From the results, it can be seen that thermal conductivity of the alloy of the invention can achieve 146 W/m·K, an increase of 45% compared with that of ADC12.

[0021] When the aluminum die casting alloy of the invention is applied to a CPU heat sink for a desktop PC, it can be seen that thermal resistance decreases from 1.03° C./W to 0.89° C./W, which is less than that of ADC12, as shown in Table 3. 3 TABLE 3 Input Ambient Case Power Temperature Temperature Rca* Material (W) (° C.) (° C.) (° C./W) Mark ADC12 19.46 24.2 44.3 1.03 Forced 27.4  24.3 55.2 1.02 convection 34.89 24.4 60.4 1.03 with cooling fan The 19.98 24.3 42   0.89 Forced alloy of 28.07 24.7 49.6 0.89 convection the in- 35.8  24.9 56.5 0.89 with vention cooling fan *Rca: Thermal resistance

[0022] When the aluminum die casting alloy of the invention is applied to a CPU heat sink of a notebook PC, it can be seen that the case temperature is lower than that using 1070 pure aluminum by about 4° C., as shown in Table 4. Moreover, the castability of the aluminum die casting alloy of the invention is better than 1070 pure aluminum. FIG. 1 is the cross section of a die cast heat sink using 1070 pure aluminum. It shows a greater macro-shrinkage cavity inside the heat sink, which forms a thermal barrier and minimize the thermal performance. Using the aluminum alloy of this invention, the internal macro-shrinkage of the die cast heat sink becomes much less as shown in FIG. 2. Thus, the heat sink fabricated with the aluminum die casting alloy of the invention is suitable for use in CPUs, DRAMs, BGAs, and chipsets. 4 TABLE 4 Input Ambient Case Power Temperature Temperature Rca Material (W) (° C.) (° C.) (° C./W) Mark The alloy 6.625 23.4 90   10.05 Natural of the convection invention 1070 22.2 94.1 10.85 The alloy 4.2  23.8 70.6 11.14 Natural of the convection invention 1070 24.1 74.1 11.9 

[0023] Table 5 shows the fluidity of common die casting aluminum alloys and the alloy of the invention. Table 6 shows the measurement of thermal resistance of a heat sink employing the alloy of the invention and ASTM material A514. It is found that the alloy of the invention has superior thermal conductivity and fluidity compared to those of common die casting alloys.

[0024] A514 alloy has a higher thermal conductivity of 138 W/m.K among the common die casting aluminum alloys, as shown in Table 2. However, when it is used as a heat sink material, the heat sink has a serious internal casting defect including micro-shrinkage and porosity as seen in FIG. 3. In contrast, when the alloy of the invention is employed, there are no casting defects in the heat sink as shown in FIG. 4.

[0025] FIG. 5 and FIG. 6 also show respectively the die cast heat sinks employing the A514 and the alloy of the invention. It is found that misrun occurs when using A514 alloy, but none when using the alloy of the invention. Therefore the alloy of the invention has notably superior thermal conductivity and castability characteristics compared to common die casting alloys. 5 TABLE 5 Aluminum alloy Fluidity length (mm) A514 250 A380 305 A383/A384 320 The alloy of the 350 invention

[0026] 6 TABLE 6 Input Ambient Case Power Temperature Temperature Rca Material (Watt) (° C.) (° C.) (° C./W) The 4.95  22.5  90.4 13.72 invented Alloy A514 23.2 91  13.70 The 6.625 19.5 102.9 12.59 invented Alloy A514 23.2 107.7 12.75 The 9.45 23.4 130.1 11.29 invented Alloy A514 23.3 136   11.93

[0027] Moreover, the alloy of the invention contains 0.5-1.2 wt % Fe, which inhibits the metal mold (die) erosion and increases the life cycle of the die. The life cycle between the alloy of the invention and 1070 is shown in Table 7. 7 TABLE 7 Material Life cycle of die (metal mold) 1070 5,000˜10,000 shots/mold The alloy of the invention Over 50,000 shots/mold

[0028] The X-ray diffraction pattern as shown in FIG. 7 it reveals that the alloy of the invention exhibited a CuAl2 phase as compared with the ASM Al—Si—Cu reference (eg. A383, A384). The precipitated phase is possessed of a high thermal conductivity and hardness, which will improve the thermal behavior and surface flatness when used as a heat sink material. Note that the surface flatness of the heat sink material also plays an important role in thermal transfer as it is mounted on the surface of electric components such as CPU VGA and MCM (Multiple Chip Modules).

[0029] While the invention has been described with reference to various illustrative embodiments, the description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as may fall within the scope of the invention defined by the following claims and their equivalents.

Claims

1. An aluminum die casting alloy comprising 80-90 wt % of aluminum, 9.1-12 wt % of silicon, 4.3-8 wt % of copper, less than 0.3 wt % of magnesium, 0.5-1.2 wt % of iron, less than 1.0 wt % of zinc, and less than 0.9 wt % of manganese.

2. The aluminum die casting alloy as claimed in

claim 1 further comprising less than 0.1 wt % of nickel, less than 0.1 wt % of chromium, less than 0.1 wt % of lead, less than 0.1 wt % of tin, less than 0.1 wt % of titanium, and less than 0.1 wt % of strontium.

3. The aluminum die casting alloy useful for a heat sink comprising 80-90 wt % of aluminum, 9.1-12 wt % of silicon, 4.3-8 wt % of copper, less than 0.3 wt % of magnesium, 0.5-1.2 wt % of iron, less than 1.0 wt % of zinc, and less than 0.9 wt % of manganese.

4. The aluminum die casting alloy useful for a heat sink as claimed in

claim 3 further comprising less than 0.1 wt % of nickel, less than 0.1 wt % of chromium, less than 0.1 wt % of lead, less than 0.1 wt % of tin, less than 0.1 wt % of titanium, and less than 0.1 wt % of strontium.

5. The aluminum die casting alloy useful for a heat sink as claimed in

claim 3, wherein said heat sink is applied to CPUs, DRAMs, BGAs, or chipsets.