JPH03230859A - Manufacture of light aluminum casting - Google Patents

Abstract

PURPOSE:To stabilize sound absorption characteristic of a light aluminum alloy by casting the molten aluminum alloy absorbing hydrogen to the solubility in the solid-state or more in the specific temp. range and cooling velocity. CONSTITUTION:A special mold is constituted with a heater 2, air vessel 3, mold 4, cooling pipes 5, 6, air flow-in and exhaust pipes 7, 8, and thermocouple 9. In this mold, the molten aluminum alloy absorbing the hydrogen to the solubility in the solid-state or more, is cast while unidirectionally solidifying from lower part to upper part of the casting at 1-5 deg.C/min cooling velocity from casting temp. having m.p. or more to the m.p. or lower. By this method, the development of shrinkage hole at center part in the light and porous aluminum alloy casting suiting to acoustic material, building material, etc., is prevented and the casting having uniform blow holes can be manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing lightweight and porous aluminum castings that can be advantageously applied to sound absorbing materials, building materials, etc.
In particular, the present invention relates to a method for manufacturing aluminum castings having uniform cellularity without forming cavities in the center.

[Conventional technology]

Production of lightweight aluminum alloy castings was attempted in the United States, Japan, and other countries from around 1955 using many methods, including direct foaming using a foaming agent, precision casting using polyurethane foam as a pattern, bubble injection, and sintering, but the industry was unable to achieve this. It was not possible to put it into practical use as a product.

In recent years, industrial products have been manufactured by improving the direct foaming method, and the product name is foamed aluminum.

The production of foamed aluminum involves a thickening process in which molten aluminum is given an appropriate viscosity, a stirring and mixing process in which a blowing agent that generates gas is added and bubbles are uniformly dispersed, a foaming cooling process in which bubbles are generated and solidified, and foaming. The process consists of cutting the ingot.

Methods for thickening molten metal include air blowing, adding thickeners such as titanium, shirasu balloons, and calcium, and stirring. Foaming agents include titanium hydride and zirconium hydride. Metal hydride particles are used, the foaming cooling process is performed by cooling in the air in a required mold, and the cutting process is performed using a conventional cutting machine.

Foamed aluminum obtained by these methods is being developed as a new material that is made up of a large number of closed cells and is lightweight and has excellent acoustic, mechanical, and thermal properties.

However, the biggest drawback is that when large-scale materials are manufactured on an industrial scale, there is a problem that cavities occur in the center of the casting and the size of the bubbles is non-uniform.

Current aluminum foam has different cell diameters in the periphery and center, and the center is coarse, resulting in non-uniformity in sound absorption and other properties. For this reason, only the portions of the foamed aluminum ingots that have good cell diameters are used, making the product expensive and impeding its practical use.

Therefore, it has been desired to establish a method for manufacturing foamed aluminum castings that does not cause shrinkage cavities in the center even when large ingots are formed.

Furthermore, the above-mentioned problems are the same even when a method of increasing the amount of hydrogen in the molten metal involves directly blowing hydrogen into the molten metal, which is different from hydrogen generation using a blowing agent.

[Problem to be solved by the invention]

In view of the above-mentioned technical level, the present invention has been developed using lightweight aluminum that does not produce cavities in the center of the casting even when it is made into a large material, has uniform cell diameters in each part of the ingot regardless of its size, and has stable sound absorption properties. The purpose is to provide a method for manufacturing castings.

[Means to solve the problem]

The present invention provides molten aluminum or aluminum alloy with
After absorbing more hydrogen than the dissolved amount of hydrogen in the aluminum or aluminum alloy solid state, cooling from the casting temperature above the melting point of the aluminum or aluminum alloy to below the melting point from the bottom to the top of the casting at a cooling rate of 1°C/min to 5°C/min. This is a method for manufacturing lightweight aluminum castings characterized by casting while unidirectionally solidifying.

In the present invention, unidirectional solidification refers to a process in which the cooling capacity is varied by adjusting the amount of water in the cooling pipe at the bottom of the mold so that solidification proceeds from the bottom of the casting to the top (top of the mold), so that the bottom of the casting is oriented toward the top. say.

To explain in more detail with reference to FIG. 1, which will be mentioned in Examples below, the amount of cooling water in the bottom A is increased, and the solidification phase starts from A part, moves sequentially to B part, 6 part, and D part, and finally reaches the atmosphere. It is solidified in the contacting layer E.

The lightweight aluminum casting of the present invention is a material containing a large amount of bubbles and has an apparent specific gravity of 1 or less, and the large number of bubbles are caused by hydrogen gas.

[For production]

The principle by which porous aluminum castings can be produced by the method of the present invention is that the amount of hydrogen dissolved in aluminum and aluminum alloys is approximately 1 cc/100g above the melting point, whereas it is approximately 0.05 cc/100g below the melting point where it becomes a solid phase.
g, and the solubility of hydrogen in the molten state is smaller than that of other metals, and there is a large difference in solubility between the molten state and the molten state. For reference, Figure 2 shows the hydrogen solubility of aluminum. That is, when the amount of hydrogen dissolved in the molten state becomes solidified, it is not completely dissolved and is released to form bubbles. As described above, bubbles are hydrogen gas generated during solidification, and the large internal cavities that occur in large lightweight aluminum (including foamed aluminum) ingots are hydrogen gas bubbles generated in the slowest part of solidification. Therefore, in principle, it is necessary to control the melting state and solidification of aluminum and aluminum alloys in order to prevent cavities from forming on the inner surface.

The present invention applies to aluminum and molten aluminum alloys,
The amount of hydrogen dissolved in these reviews was 0.05cc/100
After absorbing more than g of hydrogen using a hydrogen compound (such as titanium hydride) or the hydrogen blowing method, the cooling rate between the melting state and recollection, where bubbles are generated when the amount of hydrogen exceeds the solubility, is appropriately adjusted. It is. Specifically, the cooling conditions are adjusted so that directional solidification proceeds from the bottom surface of the ingot to the top surface, and the final solidification position is moved to the top surface, creating a riser section where the nest position can be removed, and a final solidification section. This is to reduce the formation of cavities by optimizing the cooling rate.

In order to adjust the cooling rate below the melting point, it is necessary to use the molds conventionally used to produce foamed aluminum castings, such as graphite, steel, or molds without a cooling device as shown in FIGS. 3 and 4.
This is difficult with stainless steel molds. In addition, in FIGS. 3 and 4, 1 is a graphite, steel or stainless steel container,
2 is a heating heater.

One embodiment of the special mold used in the method of the present invention is shown in FIG. In Figure 1, 2 is a heater, 3 is an air tank, 4 is a stainless steel container (mold), 5 is a cooling pipe (for air), 6
is a cooling pipe (for water), 7 is an air inflow pipe, 8 is an air discharge pipe,
9 is a thermocouple. By using this special mold, the cooling rate below the melting point, which is a feature of the method of the present invention, can be adjusted to 1 to b, and a lightweight aluminum casting with no shrinkage cavities in the center and uniform cell diameter can be manufactured.

In this embodiment, stainless steel is used for the special mold in consideration of heat resistance and oxidation resistance, but the material of the mold is not limited to this.

If the cooling rate is high, as can be seen from the aluminum-hydrogen state in FIG. 2, hydrogen does not form bubbles but remains as a solid solution, making it impossible to obtain a lightweight aluminum casting with low density.

Furthermore, if the cooling rate is low, small bubbles will connect to form large bubbles, which will further expand into nests.

The container 4 of the special mold shown in FIG. 1 is made of stainless steel, and molten metal that has undergone hydrogen absorption treatment is first poured into it. After pouring,
Although the container 4 is preheated, it cools quickly at first due to heat absorption in the container 4, so compressed air is passed through the air tank 3 for cooling.

As solidification progresses and the solidified layer (foamed aluminum) from around the container 3 becomes thicker, foamed aluminum has a significantly lower thermal conductivity than pure aluminum (approximately 1/400), so the cooling rate inside the casting is reduced to that of pure aluminum. It is slower than that and tends to form a nest in the center.

In the method of the present invention, cooling can be controlled by placing water or air at the bottom of the container (mold) and passing water or air through a coiled cooling pipe (for water) 6 and a cooling pipe (for air) 5. In other words, after pouring the hydrogen-absorbed molten metal into the mold, water or air is passed through the cooling pipe at the bottom of the mold, and the temperature of the valley inside the molten metal is measured so that solidification starts from the bottom of the mold and progresses to the center and then to the top. At the same time, the amount of water and air is adjusted to achieve unidirectional solidification from the bottom of the mold to the top.

Cooling adjustment is performed by installing a thermocouple on the test molten metal in the container and adjusting the amount of water and air to achieve the target cooling rate. Cooling can be adjusted by changing the flow rate ratio of water and air, such as by flowing more water if the cooling rate is slow, or by flowing more air if it is faster. Therefore, it is preferable that the cooling pipes provided at the bottom of the mold be arranged so that those for water and those for air alternate.

The most important thing below the melting point is the melt-plane relationship determined by hydrogen absorption, and even considering that the solidified phase has the strength to not collapse due to gravity, it is sufficient to adjust the cooling rate to 50°C below the solidus point.

〔Example〕

The details of the present invention will be explained based on examples.

After maintaining the molten aluminum alloy at 700-720℃ and adding 1% magnesium and 1% calcium to give it viscosity, hydrogen is absorbed into the molten metal by hydrogen injection, addition of titanium hydride, zirconium hydride, etc. to increase the amount of hydrogen in the molten metal to 1 cc/100 g or more. after that,
The mixture was stirred and cooled in the mold shown in FIG. At that time, the flow rate of air and/or water in the cooling pipe installed in the mold was adjusted so that the temperature was 1 to b below the melting point. The purpose of controlling the amount of air and/or water is to regulate the cooling rate and to ensure that the solidified phase within the mold starts from the bottom of the mold, progresses sequentially to the center of the mold, and then to the top of the mold. In other words, the amount of water and air in the bottom cooling pipe is reduced within the molten metal so that unidirectional solidification occurs from the bottom of the mold to the top, and the evacuation cavities move to the top of the mold to obtain a large, healthy foamed aluminum casting. The temperature was adjusted according to the temperature of each part. In order to achieve unidirectional solidification, it is preferable to further provide a heating device, such as an electric heater, on the side wall of the mold, and to provide this with an automatic temperature control function so as to control the temperature of each part of the molten metal.

After solidification, the foaming height and weight were measured, the apparent density was measured, and the cross section was cut to examine the presence or absence of shrinkage cavities. 16 kg was melted in an electric furnace.

The results are shown in Table 1.

Nol material, No. 2 material, and No. 3 material were cast metals produced by the method of the present invention, and No. 4 material, No. 5 material, and N06 material were produced using the same molds as in the method of the present invention, but were cooled at a cooling rate outside the specifications of the present invention. NoT material is cooled using conventional molds, and cooling cannot be controlled.

From Table 1, the cooling rate from the melting point to 600°C is determined from No. 1 to b No. 2 within the specifications of the present invention. Na3 material has an apparent density of 1g/cm3 or less.
, 5 g/cm', and it was a lightweight casting and at the same time had good acoustic properties such as sound absorption. This is because 1. As can be seen from the cross-sectional survey results, there is no evacuation cavity in the center of the casting, and it has moved to the top, so it can be removed as a riser.

Even if cooling adjustment or a mold is used, if the cooling rate is outside the specifications of the present invention, (1) the cooling rate is 1°C/min or less, which is outside the scope of the present invention;
．． No. 4 at 5°C/min. Since the No. 5 alloy solidified slowly, the fine hydrogen bubbles that were generated were connected to form large elongation cavities. (2) No. 6 alloy with a cooling rate of 10°C/min or more than 5°C/min, which is outside the scope of the present invention, had a high cooling rate and did not generate enough bubbles, resulting in a density of 1 or more, making it impossible to obtain good lightweight aluminum. .

Also, with conventional molds, it was not possible to adjust the cooling rate of the casting.
o7. In the No. 8 alloy, as in the No. 7 alloy, large shrinkage cavities were generated in the center, and the bubble diameter was small at the early stage of solidification, and the bubble diameter was large and nonuniform at the late stage of solidification, which was unfavorable in terms of acoustic properties. It is also sensitive to the mold material and preheating, resulting in castings with high density and poor foaming, such as No. 8 alloy.

2 Effects of the Invention As explained above, the present invention allows unidirectional solidification of hydrogen bubbles, which are the cause of the formation of lightweight aluminum castings, by adjusting the cooling rate within a specified range, and removes the bubbles from the center. Since it is moved to the upper part where it can be cut and cooled at a constant cooling rate under atmospheric pressure, it is possible to produce lightweight aluminum castings consisting of cells of uniform size and shape. This makes it possible to produce large-sized, lightweight aluminum castings on an industrial scale, which was previously difficult.

Since this lightweight aluminum casting is lightweight and has high sound absorption properties, it is useful as a new material for housing construction materials and road wall materials, as it has excellent heat insulation effects, electromagnetic shielding properties, and impact properties.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment for carrying out the method of the present invention,
Figure 2 is a graph showing the hydrogen solubility of pure aluminum, Figures 3 and 4 are explanatory diagrams of molds for manufacturing conventional lightweight aluminum castings, and Figures 5 (a) to (f) are those manufactured in Examples. FIG. 4 is a schematic diagram of cross-sectional survey results of lightweight aluminum castings of the present invention material, 4 comparative materials, and conventional material.

Claims (1)

[Claims] After the molten aluminum or aluminum alloy absorbs more hydrogen than the amount of hydrogen dissolved in the aluminum or aluminum alloy solid state, the cooling rate is 1°C from the casting temperature above the melting point of the aluminum or aluminum alloy to below the melting point.
1. A method for producing a lightweight aluminum casting, characterized by casting while unidirectionally solidifying the casting from the bottom to the top at a rate of 5° C./min to 5° C./min.