JP4341453B2 - Aluminum alloy casting excellent in thermal conductivity and method for producing the same - Google Patents

Description

  The present invention generally relates to an aluminum alloy casting excellent in thermal conductivity, and more particularly to an aluminum alloy casting suitable for use in a heat sink having a complicated shape or a thin portion in order to improve heat dissipation. Moreover, it is related also with the manufacturing method of this aluminum alloy casting.

Conventionally, pure aluminum or an aluminum alloy is used for a member such as a heat sink that requires thermal conductivity. Although pure aluminum has high thermal conductivity, it is difficult to form a complicated shape due to low castability. In addition, when the strength is low and the shape becomes complicated, it may be cracked or deformed when it is taken out from the mold or handled for other processing or assembly. Therefore, in a heat sink that needs to have a complicated shape or thin portion in order to improve heat dissipation, Al-Si system that has high strength and excellent castability even at the expense of thermal conductivity to some extent Aluminum alloy castings such as these are particularly preferably used.
JP 2001-316748 A JP 2002-3972 A JP 2002-105571 A

  However, with the recent high performance of electronic devices, a higher performance heat sink has been demanded. For this reason, development of an alloy having further higher thermal conductivity than that of a conventional aluminum alloy casting has been awaited.

The present invention has been made in view of the above circumstances, and provides an aluminum alloy casting in which thermal conductivity is further improved while having mechanical strength and castability equivalent to or higher than those of conventional aluminum alloy castings. Objective.
It is another object of the present invention to provide a method for producing such an aluminum alloy casting.

As a result of intensive studies to solve the above problems, the present inventors have found that the amount of Si solid solution in the matrix of the Al-Si aluminum alloy casting and the area ratio of the crystallized material in the metal structure are the heat of the casting. If the Si solid solution amount and the crystallized area ratio are both optimized, the aluminum alloy casting having a sufficient mechanical strength and particularly excellent thermal conductivity can be obtained. I found out that
Moreover, it turned out that the amount of Si solid solution and the area ratio of a crystallized substance can be controlled by the heat holding process after casting.

Thus, according to the present invention, Si: 6.0 to 8.0% by mass, elements other than Si and Al alone are 0.6% or less, and the amount of Si solid solution in the aluminum matrix is small. It is adjusted to 0.5 to 1.1% by mass, preferably 0.55 to 1.05% by mass, more preferably 0.6 to 1.0% by mass, and the area ratio of crystallized matter in the metal structure is adjusted. Provided is an aluminum alloy casting excellent in thermal conductivity, characterized by being adjusted to 5 to 8%, preferably 5.5 to 7.5%, more preferably 6.0 to 7.0%. The
Here, in the aluminum alloy casting, preferably, elements other than Si and Al are Mg: 0.2 to 0.5 mass%, Fe: 0.6 mass% or less, and the total amount is 0.2 mass% or less. The composition is composed of other elements.

Moreover, when the said aluminum alloy casting contains Ti and / or Zr in said other element, it is preferable that the quantity of Ti and / or Zr is adjusted to 0.03 mass% or less.
Such an aluminum alloy casting has a thermal conductivity superior to that of a conventional aluminum alloy casting, and preferably exhibits a thermal conductivity of 160 W / m · k or more, more preferably 165 W / m · k or more.

Furthermore, in the present invention, an aluminum alloy casting material containing 6.0 to 8.0% by mass of Si and containing only 0.6% by mass of elements other than Si and Al alone is heated at 400 to 510 ° C. for 1 hour or more. There is provided a method for producing an aluminum alloy casting excellent in thermal conductivity, characterized by performing a holding treatment.
Here, the aluminum alloy casting material preferably contains Si: 6.0 to 8.0% by mass, Mg: 0.2 to 0.5% by mass, Fe: 0.6% by mass or less, and the balance is aluminum. And the total amount is 0.2 mass% or less of other elements, and Ti and / or Zr in the aluminum alloy casting material is adjusted to 0.03% by mass or less. The time for the heat holding treatment of the aluminum alloy casting material is 1 hour or more. In addition, since the improvement of the characteristic beyond it cannot be acquired even if it heat-processes for 7 hours or more, it is preferable to make it 7 hours or less.

  According to the present invention, it is possible to obtain an aluminum alloy casting in which thermal conductivity is further improved while having mechanical strength and castability. Therefore, a higher performance heat sink or the like can be manufactured.

In a preferred embodiment of the present invention, the aluminum alloy casting excellent in thermal conductivity of the present invention contains Si: 6.0 to 8.0% by mass, and elements other than Si and Al alone are 0.6%. The amount of Si solid solution in the aluminum matrix is adjusted to 0.5 to 1.1% by mass, and the area ratio of the crystallized substance in the metal structure is adjusted to 5 to 8%.
Here, in the aluminum alloy casting, preferably, elements other than Si and Al are Mg: 0.2 to 0.5 mass%, Fe: 0.6 mass% or less, and the total amount is 0.2 mass% or less. The composition is composed of other elements.

  Below, the effect | action and limitation reason of each composition and a crystallized material area ratio are demonstrated.

(Si: 6.0-8.0 mass%)
Si has an effect of improving castability. When casting a complicated shape such as a heat sink or a thin part, it is necessary to set Si to 6.0% by mass or more in order to achieve sufficient castability. This Si crystallizes as a Si-based crystallized product, and also has an effect of improving the mechanical strength, wear resistance, and vibration-proof property of the casting. Further, as the Si amount is further increased, the castability and the like are improved, but when the Si amount exceeds 8.0% by mass, the thermal conductivity is lowered. Therefore, for the purposes of the present invention, the Si content must be in the range of 6.0 to 8.0 mass%.

(Mg: 0.2-0.5% by mass)
Mg is not an essential element in the present invention. However, Mg forms an Mg-based crystallized substance and has an effect of improving mechanical strength. Therefore, when mechanical strength is particularly required, Mg is preferably contained. This effect becomes significant at 0.2% by mass or more, and conversely, when it exceeds 0.5% by mass, the thermal conductivity decreases. Further, part of Mg forms an Mg—Si based precipitate and has an action of improving mechanical strength. Therefore, when it contains Mg, it is preferable to set it as the range of 0.2-0.5 mass%.

(Fe: 0.6 mass% or less)
Fe is an impurity inevitably mixed in, but improves the mechanical strength and also has the effect of suppressing die seizure when cast by the die casting method. However, as Fe increases, the thermal conductivity and extensibility decrease, and when the amount of Fe exceeds 0.6 mass%, the plastic workability becomes insufficient. Therefore, even if Fe is inevitably mixed, the content is preferably 0.3% by mass or less.

(Total amount of other elements other than Si, Al, Mg and Fe)
The aluminum alloy casting according to the present invention may contain elements other than Si, Mg, Fe, and Al as long as the total is 0.2% by mass or less. These elements are usually inevitable impurities, but need not be recognized as such. Specific examples of these elements include Ti, Mn, Cr, B, Zr, P, Ca, Na, Sr, Sb, and Zn.
Here, since Ti, Mn, and Zr have a large influence on the thermal conductivity, their amount is preferably suppressed to 0.05% by mass or less.

(Si solid solution amount: 0.5 to 1.1% by mass) (preferable range: 0.55 to 1.05% by mass, more preferable range: 0.6 to 1.0% by mass)
In an aluminum alloy casting, the amount of Si solid solution greatly affects its thermal conductivity, and if the amount of Si solid solution exceeds 1.1% by mass, the thermal conductivity decreases. On the other hand, when the Si solid solution amount is less than 0.5% by mass, sufficient mechanical strength cannot be obtained.

(Area ratio of crystallized product: 5 to 8%) (Preferable range: 5.5 to 7.5%, more preferable range: 6.0 to 7.0%)
As the inventors have newly found out, in an aluminum alloy casting, when the area ratio of the crystallized substance exceeds 8%, the crystallized substance inhibits heat conduction. Also, the elongation is low. On the other hand, when the area ratio of the crystallized product is as small as less than 5%, sufficient strength cannot be obtained.

The present inventors have found that the above-described aluminum alloy casting can be obtained by further heat-holding a conventional aluminum alloy casting having excellent castability to a predetermined temperature.
That is, the manufacturing method according to the present invention first manufactures an aluminum alloy casting material having a predetermined composition. As the casting method, any conventionally known casting method such as a molten metal casting method, a DC method, a mold casting method, or the like can be used. In some cases, a commercially available aluminum alloy casting is used as a material of the method of the present invention. It can also be used as The aluminum alloy casting material to be used contains 6.0 to 8.0% by mass of Si, and elements other than Si and Al alone are 0.6% by mass or less, more preferably Si: 6.0 to 8 0.0% by mass, Mg: 0.2 to 0.5% by mass, Fe: 0.6% by mass or less, with the balance being aluminum and other elements with a total amount of 0.2% by mass or less . Examples of such aluminum alloy castings include castings cast from JIS standard AC4C and AC4CH alloys.

  Next, the aluminum alloy casting material is heated and held at 400 to 510 ° C. By such heating and holding treatment, Si dissolved in the matrix phase is precipitated, and the amount of Si solution in the matrix phase is in the range of 0.5 to 1.1% by mass. A part is dissolved in the matrix, and the area ratio of the crystallized product is in the range of 5 to 8%.

Here, when the heating and holding temperature exceeds 510 ° C., the crystallized product is often dissolved in the matrix, and as a result, the area ratio of the crystallized product decreases and the amount of Si solid solution increases. , Thermal conductivity decreases. Also, the mechanical strength is reduced. On the contrary, when the heating and holding temperature is 400 ° C. or lower, Si in the matrix phase does not precipitate and the amount of Si solid solution does not decrease, so the thermal conductivity is not improved. In addition, since a part of the crystallized product does not dissolve in the matrix, the area ratio of the crystallized product increases and the thermal conductivity decreases.
The heat holding treatment is preferably performed for 1 hour or longer. Moreover, even if it heat-maintains over 5 hours, the amount of Si solid solution and the area ratio of a crystallized substance will hardly change beyond it. Therefore, the holding time is preferably less than 5 hours from the viewpoint of cost.

  After heating and holding, it is cooled to room temperature, but the subsequent cooling may be water cooling or slow cooling with furnace cooling. The amount of precipitate varies depending on the cooling rate, and the solid solution amount of Si also changes. However, in the case of the alloy of the present invention, Si is already precipitated during the heat holding treatment, and the Si solid solution amount is reduced. The effect is small. Water cooling is preferred when it is desired to increase the strength as much as possible. However, in the case of water cooling, the cooling rate differs depending on the portion, and deformation is likely to occur during cooling. Therefore, slow cooling is preferable in the case of a thin part such as a heat sink.

Hereinafter, the present invention will be described in more detail by way of examples.
(Example 1)
Aluminum alloy casting material (JIS standard) consisting of 7.1 mass% Si, 0.32 mass% Mg, 0.2 mass% Fe and aluminum, and the total amount of other elements being 0.2 mass% or less (Corresponding to AC4C) was cast to 203φ × 2000 mm by the DC casting method. The obtained as-cast material (No. 1) was held at 380 ° C., 420 ° C., 450 ° C., 500 ° C., 535 ° C., 550 ° C. for 5 hours, then cooled to room temperature by water cooling, and an aluminum alloy casting (No. .2-7) were obtained.

  The as-cast material (No. 1) and the aluminum alloy castings (No. 4 to 6) obtained by performing the heating and holding treatment as described above were observed with a microscope. A part of the result is shown in FIG.

Furthermore, about the said as-cast material and aluminum alloy casting, the thermal conductivity, the tensile strength, the amount of Si solid solution, and the area ratio of the crystallized substance were measured, respectively.
Here, about the amount of Si solid solution, the amount of Si in the alloy and the amount of Si in the hot phenol residue were obtained by chemical analysis, and the amount of Si in the obtained alloy was subtracted from the amount of Si in the phenol residue. It was set as the amount of Si solid solution. The hot phenol dissolution residue was recovered by filtering an alloy dissolved with hot phenol through a membrane filter (0.1 μm).
Further, the area ratio of the crystallized material was measured after mirror-polishing the mineral and setting it in an image processing / analyzing apparatus. In the measurement, 10 visual fields (0.014 mm ² ) were measured, and the average value was taken.

The results of the above measurements are summarized in Table 1.

As can be seen from the results in Table 1, the as-cast material (No. 1) not subjected to the heat holding treatment and the comparative aluminum alloy casting (No. 2) having a low heat holding treatment temperature have a crystallized area ratio. Large, and therefore have low thermal conductivity and elongation. From this, it is confirmed that the crystallized substance inhibits heat conduction.
Moreover, it turns out that the comparative aluminum alloy casting (No. 6-7) with high heat retention processing temperature has increased the amount of Si solid solution, and has low thermal conductivity.
On the other hand, in the aluminum alloy castings (Nos. 3 to 5) according to the present invention, the Si solid solution amount and the area of the crystallized material are in the optimum ranges, and the thermal conductivity, tensile strength, and elongation are high. It turns out that all are high numbers.

(Example 2)
The as-cast material obtained in Example 1 was heated and held at 450 ° C. for 0.5 hours, 1 hour, 3 hours and 7 hours, and then slowly cooled to room temperature, and then casted aluminum alloy. (Nos. 8 to 11) were obtained. About the obtained aluminum alloy casting, the amount of Si solid solution, the area ratio of the crystallized product, the thermal conductivity, the tensile strength and the elongation were measured by the same method as in Example 1.

The results are shown in Table 2.

  As can be seen from the results in Table 2, when the heat retention treatment time is 0.5 hours, the crystallized product does not sufficiently dissolve, and as a result, the thermal conductivity, tensile strength, and elongation are low. I understand.

It is a microscope picture for drawing substitutes which shows the structure of an as-cast material and an aluminum alloy casting (No. 1, 4-6).

Claims (4)

Si: 6.0 to 8.0% by mass , Mg: 0.2 to 0.5% by mass, Fe: 0.6% by mass or less, and the balance is made of aluminum and unavoidable impurities . The amount of Si solid solution is adjusted to 0.5 to 1.1% by mass, and the area ratio of crystallized matter in the metal structure is adjusted to 5 to 8%, which is excellent in thermal conductivity. Aluminum alloy castings. The aluminum alloy casting according to claim 1 , wherein Ti and / or Zr is adjusted to 0.03% by mass or less. The aluminum alloy casting according to claim 1 or 2 , having a thermal conductivity of 160 W / m.k or more. A method for producing an aluminum alloy casting excellent in thermal conductivity, comprising heat-treating the aluminum alloy casting material having the composition according to claim 1 or 2 at 400 to 510 ° C for 1 hour or more.