JP4510541B2 - Aluminum alloy casting molding method - Google Patents

Description

The present invention relates to a molding how the A aluminum alloy casting.

In order to reduce the weight of automobiles, aluminum alloy castings (hereinafter referred to as Al alloys) are used for vehicle chassis structural members such as suspension members, subframe members, various joint members, and aluminum wheels.
For the molding of Al alloy castings, a semi-molten casting method is used which can be easily molded even with complicated shapes. In order to ensure the fluidity of the semi-molten aluminum composition, the billet used in the semi-molten casting method has a high Si material of Si 6.0 to 8.0% by mass as shown in Patent Document 1. Commonly used. However, as pointed out in Patent Document 1, if the Si content is large, the toughness is lowered, and if the content is insufficient, the fluidity of the molten metal is lowered.
If a semi-molten casting method can be performed with aluminum having a low Si content, a cast product with high toughness can be obtained. However, since toughness and fluidity are in a trade-off relationship as described above, it has not been realized.
So far, studies have been made to obtain high toughness with an Al alloy having a low Si content. For example, Patent Document 2 discloses a technique in which an Al alloy casting is subjected to an aging treatment after a high-temperature solution treatment.
In the technique disclosed in Patent Document 2, an Al alloy casting having Si of 1.65 to 4.0% is heated to 550 to 575 ° C., and then rapidly cooled to form a solution treatment, and then an aging treatment at 140 to 200 ° C. Is.
JP 2001-252754 A (paragraph 0014) JP-A-9-272742 (paragraphs 0014 to 0019)

  However, since casting such as disclosed in Patent Document 2 is cast by a normal casting method, there is a problem that the molten metal temperature becomes high and the mold life is shortened. It is desired to be able to produce alloy castings.

Therefore, in the present invention to solve the aforementioned problems, and an object thereof is to provide a molded how the A l alloy castings that high toughness semi-molten casting is obtained.

The invention according to claim 1, S I2.0～4.0 wt%, pouring the residue portion A l and unavoidable impurities was either Ranaru molten metal vessel, solid fraction the molten metal at a temperature of the eutectic point near The molten metal is adjusted to 25 to 45% by mass , and the molten metal is loaded onto the injection sleeve from the split surface of the casting mold together with the container, and the casting mold is closed, and then the container and the molten metal Is pressed by a plunger to fill the cavity of the casting mold with the molten metal, and then rapidly cools the molten metal filled in the cavity of the casting mold at a cooling rate of 5 ° C./second or more. It was set as the molding method of the aluminum alloy casting to do.
According to invention of Claim 1, Si content is 2.0-4.0 mass %, Si content (5.5-8.0 mass) of Al alloy used for the conventional semi-molten casting method %), An Al alloy having higher toughness than the conventional semi-molten casting method can be obtained.

Further, when the Si content to prepare solid fraction of 2.0 to 4.0 mass% of Al alloy 25-45 wt%, the liquid phase of the semi-molten melt becomes hypoeutectic composition of Al-rich.
For this reason, when the above-mentioned semi-molten molten metal is rapidly cooled, in the metal structure of the Al alloy casting, a fine Al crystal different from the Al crystal phase generated in the semi-molten state (this is referred to as the first α phase). A phase (referred to as the second α phase) precipitates in the Al—Si eutectic phase. The presence of this fine second α-phase prevents crack growth through the interface between the Al crystal phase and the Al-Si eutectic phase (hereinafter referred to as grain boundaries), resulting in a machine such as toughness of the Al alloy. The physical properties are improved.

Therefore, according to the invention of claim 1, since the semi-molten molten metal is loaded into the injection sleeve from the split surface of the casting mold together with the container, the time from loading to injection is shortened, and the temperature drop can be minimized, Even a semi-molten molten metal that is easily solidified or a semi-molten molten metal having poor fluidity can be molded in one step. Furthermore, since the quenching is performed at a cooling rate of 5 ° C./second or more, the fine second α-phase can be reliably formed. Further, by adjusting the solid phase rate in the 25 to 45 mass%, even solidified easily poor fluidity Si2.0~4.0 wt% of aluminum semi-molten melt, it becomes possible to mold in one step .

According to the method for molding an Al alloy casting of the present invention, it is possible to mold even an aluminum semi-molten molten metal of Si 2.0 to 4.0% by mass which is easy to solidify and has poor fluidity.

Next, embodiments of the present invention will be described with reference to the drawings as appropriate.
Al alloy of the present embodiment Si2.0~4.0 wt%, consists composition containing the remaining portion A l and unavoidable impurities, obtained by rapid cooling from semi-molten melt state of the solid fraction from 25 to 45 wt% It is done.
The obtained Al alloy includes a first α phase having an equivalent circle diameter of 20 μm or more and an average equivalent circle diameter of 50 μm or more, and a second α phase having an equivalent circle diameter of less than 20 μm.
As the rapid cooling condition, the cooling rate is preferably 5 ° C./second or more.

  The reason for containing Si constituting the Al alloy and the reason for limiting the content are as follows.

Si: 2.0-4.0 mass %
Si improves the fluidity of the molten metal and affects the toughness of Al alloy castings. When Si <2.0% by mass , the fluidity of the molten metal is insufficient, so that casting defects called nests and sink marks are remarkably increased in the Al alloy casting. On the other hand, when Si> 4.0 mass %, the amount of Si eutectic distributed at the α-phase grain boundaries becomes excessive, and the toughness of the Al alloy casting is lowered.

  This Al alloy may further contain the following components. The reason for the inclusion of each component and the amount that can be contained will be described below.

Mg: 0.2 to 0.5% by mass
Mg becomes Mg ₂ Si and affects the strength of the Al alloy casting. If Mg <0.2% by mass , the strength is not sufficiently improved. On the other hand, if Mg> 0.5% by mass , Mg ₂ Si precipitates excessively and the toughness decreases.

Cu: 0.4-0.8 mass %
Cu contributes to improving the strength by solid-solution strengthening the metal structure of the Al alloy casting, but reduces the corrosion resistance. If Cu <0.4% by mass , the strength is not sufficiently improved. On the other hand, when Cu> 0.8% by mass , the corrosion resistance decreases and the stress corrosion cracking resistance decreases.

Ti: 0.1 to 0.3% by mass
Ti refines the crystal of the Al alloy casting to improve the strength. When Ti <0.1% by mass , the effect of reducing the size of the crystal and improving the strength is insufficient. On the other hand, when Ti> 0.3% by mass , Al ₃ Ti is generated and the fluidity of the molten metal is deteriorated, so that casting defects are likely to occur.

The effect of refining the crystal can also be obtained with Zr and B. In this case, it is preferable to add Zr in the range of 0.1 to 0.3% by mass and B in the range of 0.2 to 0.4% by mass . B exhibits the effect of making crystals finer in cooperation with Ti and Zr.

The Al alloy casting is obtained by making the Al alloy having the above composition into a semi-molten molten metal having a solid phase ratio of 25 to 45 mass % and rapidly cooling it.
If the solid phase ratio is less than 25% by mass, the amount of the liquid metal is excessive, so that handling is difficult, and it is extremely difficult to form. On the other hand, if the solid phase ratio exceeds 45% by mass , the solid content is large and molding becomes difficult.

The solid phase ratio is determined by pouring a molten metal maintained at a temperature near the eutectic point, preferably at a superheating temperature of less than 50 ° C. with respect to the liquidus temperature, into the container, and holding the molten metal in the container for a predetermined time. Adjust by crystallizing Al crystal while cooling. When pouring molten metal into the container, it is necessary to tilt the container and pour it gently so that the molten metal does not get out of control. This is because if the molten metal becomes violent, an oxide film or the like is involved and the quality of the product is deteriorated. After pouring, for example, it is preferable to achieve uniform temperature in the container by, for example, partially insulating the container.
The cooling rate is preferably in the range of 5 to 30 ° C./second. When the cooling rate exceeds 30 ° C./second, the temperature is lowered too much during the transportation and setting of the container, and it becomes impossible to mold at the target solid phase rate. If it is less than 5 ° C./second, the first α phase grows abnormally and the toughness of the Al alloy decreases.

FIG. 1 is created based on the eutectic equilibrium diagram of Al and Si, and shows the relationship between the Si content and the solid fraction during eutectic. That is, the lower right line in FIG. 1 indicates the maximum proportion of Al crystal (α phase) that can be crystallized from the molten metal, and above this line, the Al crystal (α phase) does not crystallize. Yes.
As shown in FIG. 1, the present embodiment is in a region where the Si content is 2.0 to 4.0 mass % and the solid phase ratio is 25 to 45 mass %. On the other hand, the alloy used in the conventional semi-molten casting method is in a region where the Si content is 6.0 to 8.0 mass % and the solid phase ratio is 40 to 60 mass %.

As is clear from FIG. 1, the Si content range of 2.0 to 4.0 mass % and the solid phase ratio of 25 to 45 mass % of the present embodiment are below the line in FIG. Has a hypoeutectic composition that can be crystallized. For this reason, the second α phase having a fine particle size shown in FIG. 2 separates from the first α phase generated in the semi-molten state by rapid cooling.
As apparent from FIG. 2, the Al alloy of the present embodiment has a first α phase having an equivalent circle diameter of 20 μm or more and an average equivalent circle diameter of 50 μm or more, and a second α phase having an equivalent circle diameter of less than 20 μm. α phase is included. As described above, the presence of the second α phase having a finer particle diameter than the first α phase having an equivalent circle diameter of 20 μm or more and an average equivalent circle diameter of 50 μm or more causes the growth of cracks through the grain boundaries. As a result of being more effectively blocked, the toughness of the Al alloy is improved. Here, the equivalent circle diameter is a diameter of a pseudo circle calculated from the particle area of the α phase observed with a microscope, and the average equivalent circle diameter is a number average value of equivalent circle diameters.
FIG. 2 is a photomicrograph of the metallographic structure of a semi-molten molten Al alloy of 3 mass % Si when rapidly cooled at a cooling rate of 10 ° C./second from a solid phase ratio of 30 mass %.

On the other hand, since the conventional Al alloy is almost on the right-downward line in FIG. 1, there is almost no Al that can be crystallized in the liquid phase, and even if it is rapidly cooled as shown in FIG. The second α phase having a fine particle size does not crystallize. More specifically, since the liquid phase immediately before forming has an eutectic composition of Al-Si, there is no surplus Al even in the rapid cooling process, and the second α phase having a fine particle size cannot be precipitated. . And after shaping | molding, it becomes the metal structure which the eutectic phase of Al-Si produced in the cooling process and the spherical alpha phase with the large particle size produced | generated in the semi-molten molten metal were mixed.
FIG. 3 is a photomicrograph of the metallographic structure when the Al alloy semi-molten molten metal in the conventional forming region is rapidly cooled at a cooling rate of 10 ° C./second.

  The first α phase is generated by adjusting the cooling rate of the molten metal in the container by the above-described method so that the equivalent circle diameter is 20 μm or more and the average equivalent circle diameter is 50 μm or more. If the equivalent circle diameter is less than 20 μm or the average equivalent circle diameter is less than 50 μm, there is a problem that it is difficult to maintain the shape of the Al alloy in the container and the conveyance set is impossible.

The second α phase having an equivalent circle diameter of less than 20 μm is generated by cooling the semi-molten molten metal at a cooling rate of 5 ° C./second or more. Thus, when the semi-molten molten metal is rapidly cooled at a cooling rate of 5 ° C./second or more, crystallization is promoted, and as a result, the above-described fine second α-phase can be reliably formed. When the cooling rate is less than 5 ° C./second, the second α-phase is only slightly formed as is apparent from the comparison between FIG. 2 (cooling rate 5 ° C./second) and FIG. 4 (cooling rate 1 ° C./second). Not. In the case of molding using a casting mold, the cooling rate can be adjusted by a known method such as the cooling water temperature of the casting mold or the design of the casting mold.
The average equivalent circle diameter of the second α phase is preferably 1/5 or less of the average equivalent circle diameter of the first α phase in order to obtain an Al alloy having good toughness. If the average equivalent circle diameter of the second α phase is 1/5 or less of the average equivalent circle diameter of the first α phase, the result is that crack growth can be more effectively prevented by the presence of the fine second α phase. Further, an Al alloy having further excellent toughness can be obtained. Furthermore, the average equivalent circle diameter of the second α phase is preferably 1/7 or less of the average equivalent circle diameter of the first α phase in order to obtain an Al alloy having better toughness.
FIG. 4 is a photomicrograph of the metallographic structure when an Al alloy having the same Si content and solid phase ratio as in FIG. 2 is used and the cooling rate is slow.

  The area occupied by the second α phase observed under a microscope is 5% or more, more preferably 20% or more of the total area including the area of the first α phase. It is preferable when improving toughness. Furthermore, in order to obtain an Al alloy having better toughness, the area of the second α phase is preferably in the range of 20% to 50% with respect to the total area.

In the conventional semi-molten casting method, the metal structure of the Al alloy casting after forming has a structure in which an Al—Si eutectic phase and a spherical α phase having a large particle size (Al crystal phase) are mixed as described above. (See FIG. 3). It is known that the crystal structure is different between the Al—Si eutectic phase and the spherical α phase of aluminum, so that cracks easily propagate through the grain boundaries.
However, by generating a fine second α-phase in the metal structure, the progress of cracks through the grain boundary is prevented, and as a result, mechanical properties such as toughness of the Al alloy are improved.

Next, a method for producing an Al alloy casting will be described with reference to the drawings as appropriate.
FIG. 5 is a diagram schematically showing a method for producing an Al alloy casting.

From a melting furnace (not shown), molten metal maintained at a degree of superheat of less than 50 ° C. with respect to the liquidus temperature is poured into the container 1. As the container 1, a container 1 having a fragile part 7 provided on the bottom (the surface facing the gate of the casting mold 2) as disclosed in Japanese Patent Application Laid-Open No. 2002-307153 is suitably used. be able to.
Moreover, when pouring a molten metal into the container 1, the method disclosed in JP-A-11-138248 can be used (FIG. 6). When this method is used, the molten metal is once received in the container C, the container 1 is inclined, and the molten metal is injected along the inner peripheral surface of the inclined container 1 while raising the inclined container 1. Thereby, a molten metal can be poured gently into the container 1, and the fall of the quality of the product by involvement of an oxide film etc. can be prevented.

The molten metal, Si2.0～4.0 wt%, can be used having the composition containing the remaining portion A l and unavoidable impurities. Even if it is a molten aluminum which does not have this composition, it is possible to manufacture an Al alloy casting using the manufacturing method of this embodiment.
A semi-molten molten metal 6 having a target solid phase ratio can be adjusted by cooling the molten metal for a predetermined time while keeping the molten metal at a predetermined cooling rate by a method such as putting the container 1 in a heat insulating container whose periphery is insulated. . The solid phase ratio is adjusted to be in the range of 25 to 45% by mass .

After a predetermined time has elapsed, the container 1 containing the semi-molten molten metal 6 is taken out from the heat insulating container, and the semi-molten molten metal 6 is loaded into the injection sleeve 3 from the split surface of the casting mold 2 together with the container 1 as shown in FIG.
At this time, if the solid phase ratio of the semi-molten molten metal 6 is 25% by mass or more, the semi-molten molten metal 6 on the surface that comes into contact with air is solidified, so that the semi-molten molten metal 6 is not spilled from the container 1. One can be loaded into the injection sleeve 3.
The injection sleeve 3 is preferably kept warm with a heat insulating material in order to prevent the semi-molten molten metal 6 from solidifying. In addition, the loading may be performed manually or automatically by a transport device.

  When the container 1 is loaded on the injection sleeve 3, the casting mold 2 is immediately closed, and the semi-molten molten metal 6 in the container 1 is pressed together with the container 1 by the plunger 4. Thereby, the weak part 7 provided in the bottom part of the container 1 is broken, and the molten metal 6 is filled in the cavity 5 of the casting mold 2.

In addition, it is preferable that the material of the container 1 is aluminum, and 1000 series pure aluminums, such as JIS name 1080 and 1070, can be used especially suitably.
Next, the semi-molten molten metal 6 inside the cavity 5 is rapidly cooled at a cooling rate of 5 ° C./second or more to obtain an Al alloy casting. The semi-molten molten metal 6 inside the cavity 5 can be cooled by known means such as circulating cooling water through a cooling water channel 11 provided in the casting mold 2.

If the Al alloy of this embodiment is used, a high toughness Al alloy casting can be obtained. Furthermore, if the Al alloy casting molding method of the present embodiment is applied, for example , a suspension member, a subframe member, various joint members, a member having a complicated shape, such as a vehicle chassis structure member such as an aluminum wheel. However, it can be molded without impairing the high toughness.

As mentioned above, although embodiment was described, this invention is not limited to above-described embodiment.
For example, as a method for adjusting the solid phase ratio, a heat-insulated container having a thermally insulated periphery has been described as an example, but a method of placing it in a furnace or tunnel maintained at a constant temperature for a predetermined time may be used.
In the present embodiment, the injection sleeve 3 is preferably kept warm by a heat insulating material in order to prevent the semi-molten molten metal 6 from solidifying. However, in order to agitate the semi-molten molten metal 6, Stirring or electromagnetic stirring means may be provided. Alternatively, the semi-molten molten metal 6 can be directly injected from the melting furnace into the empty container 1 loaded in the injection sleeve 3 and held for a predetermined time in the injection sleeve 3 to adjust the target solid phase ratio.

  Although the vehicle chassis structural member is taken up as a suitable material for the Al alloy of the present invention, the present invention is not limited to this. For example, various cast products such as a rotating member such as a blower fan, a machine housing, etc. Can be applied to. In particular, when the Al alloy of the present invention is applied to a cast iron product, the effect of weight reduction can be remarkably exhibited.

  Next, examples in which the effects of the present invention have been confirmed will be described. Using the Al alloy and Al alloy casting method of the above-described embodiment, the case where the Si content and the solid phase ratio fall within the scope of the present invention is taken as an example, and the case where it does not enter is a comparative example, toughness, tensile strength And the moldability were compared.

The Charpy test piece and the tensile test piece used in Examples and Comparative Examples were produced by a 200 t die casting machine using a semi-molten molten metal whose solid phase ratio was adjusted by the method described above. The casting conditions were set to a casting mold temperature of 90 to 250 ° C., an initial speed of 0.15 m / second, an injection speed of 0.3 m / second, and a casting pressure of 90 MPa.
The tensile test piece has a flat plate shape, the gauge distance is 25 mm, the thickness t is 3 mm, and the width w is 6 mm. The Charpy test piece corresponds to a JIS No. 3 test piece.

Table 1 shows the Si concentration, molding conditions, and evaluation results of the alloys used in the examples and comparative examples.
(Note that “solid phase ratio adjustment temperature” in Table 1 refers to the temperature when pouring the molten metal into the container, and refers to the temperature of the degree of superheat below 50 ° C. with respect to the liquidus temperature described above. For the average equivalent circle diameter, the equivalent circle diameter was obtained for 10 or more samples, and the number average was calculated.
The evaluation of “formability” was “◯” when the cavity of the casting mold was completely filled with the alloy and there was no minute defect inside the alloy.

<Influence of Si content>
In Examples 1 to 3 and Comparative Examples 1 and 2, only the Si content is changed and the other conditions are the same.
When the Si content was less than the range of the present invention (2.0 to 4.0% by mass ) (Comparative Example 2), many minute defects were observed inside the alloy. Further, due to this minute defect, the impact value and the proof stress varied greatly, and only a molded product that could not be properly evaluated was obtained. On the other hand, when the Si content is 6.5% higher than the range of the present invention (Comparative Example 1), the formation of the second α phase is not recognized in the alloy, and the molded product has a low impact value, yield strength, and the like. Only obtained.
On the other hand, in Examples 1 to 3 in which the Si content is within the range of the present invention (2.0 to 4.0% by mass ), the formability is good and the impact value and elongation are both conventional alloys (Comparative Example 1). ) The alloy has higher toughness. Also, the tensile strength and proof stress were superior to those of conventional alloys.

<Influence of solid fraction>
In Examples 2 and 4 and Comparative Examples 3 to 5, evaluation results of toughness and formability represented by elongation and impact values when only the solid phase ratio is changed and the other conditions are the same are shown.
In Comparative Example 3 where the solid phase ratio was lower than the range of the present invention, the liquid metal was excessive, and it was difficult to handle the semi-molten molten metal, so that molding could not be performed. On the other hand, in Comparative Examples 4 and 5 having a solid phase ratio of 50% or higher higher than that of the present invention, the fluidity of the semi-molten molten metal was inferior because the Si content was low. For this reason, when the solid phase ratio is 50% by mass and 60% by mass , there remains a portion in which the cavity of the casting mold is not completely filled.
In contrast, Examples 2 and 4 (solid fraction 30 mass%, 40 mass%) that the solid phase ratio is within the range of the present invention the filling of the casting mold cavity was good.

<Influence of cooling rate>
Example 2 and Comparative Example 6 show the evaluation results of formability, toughness, etc. when only the cooling rate is changed and the other conditions are the same (see FIGS. 2 and 4).
In any case, the moldability was good. However, in Comparative Example 6 in which the cooling rate was outside the range of the present invention, the generation of the second α phase was not observed. For this reason, not only the elongation and impact values, but also the tensile strength and proof stress were inferior to those of Example 2.

<Influence of second alpha phase>
When the Si content is within the range of the present invention and the cooling rate is 5 ° C./second, the formation of the second α-phase is recognized and good toughness is shown, but the cooling rate is outside the range of the present invention. At a certain 1 ° C./second (Comparative Example 6) and a conventional alloy (Comparative Example 1) whose Si content is outside the scope of the present invention, the second α phase is not formed and the toughness is also inferior. It was.
Further, in the Al alloys according to the present invention of Examples 1 to 4, the average equivalent circle diameter of the first α phase is 50 μm or more, and the average equivalent circle diameter of the second α phase is that of the first α phase. It is a value of 1/5 or less of the average equivalent circle diameter, and in this example, it was about 1/7 or less.
In Comparative Example 3, since the molding could not be performed as described above, the average equivalent circle diameter could not be measured. In Comparative Examples 2, 4, and 5, good first and second α phases were observed, but as described above, evaluation of toughness and the like could not be performed due to molding problems. This suggests that it can be used as an Al alloy having high toughness even in the range of Comparative Examples 2 to 5 by optimizing the processing conditions.

It is a figure which shows the relationship between Si content and the solid-phase rate at the time of eutectic. It is a copy of the microscope picture which shows a metal structure when the semi-molten molten metal of Al alloy of this invention is rapidly cooled with the cooling rate of 10 degree-C / sec. It is a copy of the microscope picture which shows a metal structure when the semi-molten molten metal of Al alloy in the conventional shaping | molding area | region is rapidly cooled with the cooling rate of 10 degree-C / sec. It is a copy of the microscope picture which shows the metal structure at the time of cooling the semi-molten molten metal of Al alloy of this invention at the cooling rate of 1 degree-C / sec. It is a schematic diagram of the method of manufacturing an Al alloy casting. It is a schematic diagram of the method of injecting molten metal into a container.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Container 2 Casting die 3 Injection sleeve 4 Plunger 5 Cavity 6 Semi-molten molten metal

Claims (1)

S I2.0～4.0 wt%, pouring the residue portion A l and unavoidable impurities was either Ranaru melt into the vessel,
Adjusting the molten metal to a semi-molten molten metal having a solid phase ratio of 25 to 45 mass % at a temperature near the eutectic point;
The semi-molten molten metal is loaded into the injection sleeve from the split surface of the casting mold together with the container,
After closing the casting mold,
The container and the semi-molten molten metal are pressed by a plunger to fill the semi-molten molten metal into a cavity of the casting mold,
Next, the aluminum alloy casting molding method characterized by quenching the semi-molten molten metal filled in the cavity of the casting mold at a cooling rate of 5 ° C./second or more.

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