JP4292070B2 - High toughness Al alloy casting and method for producing the same - Google Patents

Description

  The present invention relates to a high toughness Al alloy casting and a manufacturing method thereof. This type of Al alloy casting includes chassis components such as vehicle bodies, suspension members, subframe members, various joint members, and aluminum wheels.

Conventionally, high toughness Al alloy castings are known in which the content of Fe as an alloy element is set to Fe ≦ 0.2 wt% (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-272942

  However, setting the Fe content to Fe ≦ 0.2 wt% is effective in increasing the toughness of the Al alloy casting, but on the other hand, under the application of the pressure casting method, the inner surface of the cavity of the mold A new problem arises that the adhesion of the molten metal to the steel increases and seizure is likely to occur.

  In view of the above, an object of the present invention is to provide a sound Al alloy casting that has excellent toughness and does not cause seizure to a mold, and a method for producing the same.

In order to achieve the above object, according to the first invention, 2 wt% ≦ Si ≦ 4 wt%, 0.2 wt% ≦ Mg ≦ 0.5 wt%, 0.4 wt% ≦ Cu ≦ 0.8 wt%, 0.2 wt% < A high toughness Al alloy casting made of Fe ≦ 0.5 wt%, 0.1 wt% ≦ Ti ≦ 0.3 wt% and the balance Al containing inevitable impurities, and the α phase particle size d in the metal structure is d ≦ 45 μm. Provided.

According to the second invention, 2 wt% ≦ Si ≦ 4 wt%, 0.2 wt% ≦ Mg ≦ 0.5 wt%, 0.4 wt% ≦ Cu ≦ 0.8 wt%, 0.2 wt% <Fe ≦ 0.5 wt. %, 0.1 wt% ≦ Ti ≦ 0.3 wt% and the remaining Al alloy containing inevitable impurities is filled in the mold cavity under pressure, and then the solidification starts after the molten metal starts to solidify. Until completion, there is provided a method for producing a high toughness Al alloy casting in which the cooling rate C _R of the molten metal and the Al alloy casting produced from the molten metal is controlled to C _R ≧ 5 ° C./s.

  According to 1st invention, the sound Al alloy casting which has the outstanding toughness by comprising as mentioned above can be provided.

This is due to the following reason. That is, when the Fe content is set as described above, seizure of the molten metal to the mold is prevented even under the application of the pressure casting method, and the particle size d of the α phase is set to d ≦ 45 μm. The refinement of the crystal grain increases the abundance of α-phase grain boundaries, increases the amount of Fe accepted by the grain boundaries, and crystallizes and grows acicular and plate-like β-FeAlSi (Al5 FeSi). It is because it can suppress.

  According to the second invention, it is possible to provide the manufacturing method capable of mass-producing the Al alloy casting at low cost.

This is because the Fe content is relatively high and inexpensive bullion and return material (return) can be used, and the mold maintenance is reduced from avoiding seizure of the molten metal. This is due to the extended service life of the mold. If the cooling rate CR during the specific period is set as described above, the particle size d of the α phase can be set to d ≦ 45 μm.

High toughness Al alloy castings are 2wt% ≤Si≤4wt%, 0.2wt% ≤Mg≤0.5wt%, 0.4wt% ≤Cu≤0.8wt%, 0.2wt% <Fe≤0.5wt% , 0.1 wt% ≦ Ti ≦ 0.3 wt% and the balance Al containing inevitable impurities, and the α phase particle size d in the metal structure is set to d ≦ 45 μm.

  The reasons for the content of each alloy element and the reasons for limiting the content are as follows.

  Si: Has the effect of improving the fluidity of the molten metal and improving the mechanical properties of the Al alloy casting. However, when Si <2 wt%, the fluidity of the molten metal is deteriorated, so that casting defects such as nests are remarkably increased in Al alloy castings. On the other hand, when Si> 4 wt%, the abundance of Si crystals distributed in the α-phase grain boundaries increases, and the toughness of the Al alloy casting decreases.

Mg: Si has the effect of finely dispersing and precipitating Mg ₂ Si to improve the strength of the Al alloy casting. However, when Mg <0.2 wt%, the above effect is insufficient. On the other hand, when Mg> 0.5 wt%, the precipitation amount of Mg ₂ Si becomes excessive, and the toughness of the Al alloy casting is lowered.

  Based on the high solid solubility limit in Cu: Al, the metal structure of the Al alloy casting is strengthened by solid solution, and the metal structure is dispersed and strengthened by dispersion precipitation by T6 treatment. However, if Cu <0.4 wt%, the effect of improving the strength of the Al alloy casting is not sufficient, while if Cu> 0.8 wt%, the stress corrosion cracking resistance of the Al alloy casting is lowered and the corrosion resistance is also deteriorated.

  Fe: As described above, it has the effect of preventing seizure of the molten metal to the mold. However, when Fe ≦ 0.2 wt%, the effect of preventing seizure is insufficient, while when Fe> 0.5 wt%, the toughness of the Al alloy casting decreases because α-FeAlSi that crystallizes at a high temperature exists.

Ti: has an effect of refining crystal grains. However, when T <0.1 wt%, the above effect is insufficient. On the other hand, when Ti> 0.3 wt%, Al ₃ Ti, which is a TiAl-based high-temperature crystallization product, is generated, and the fluidity of the melt deteriorates. Casting defects are likely to occur.

  The effect of crystal grain refinement can also be obtained by Zr and B. In this case, the Zr content is set to 0.1 wt% ≦ Zr ≦ 0.3 wt%, and the B content is set to 0.02 wt% ≦ B ≦ 0.04 wt%. Note that B is used in combination with Ti and Zr in order to develop a composite fine particle effect in cooperation with Ti and Zr.

When the particle size d of the α phase in the metal structure is d> 45 μm, the abundance of the α phase grain boundary decreases, so that the Fe acceptance amount of the crystal grain boundary becomes small and crystals such as acicular β-FeAlSi are formed. The toughness of the Al alloy casting is lowered by the protrusion and its growth.

In manufacturing the high toughness Al alloy casting, 2 wt% ≦ Si ≦ 4 wt%, 0.2 wt% ≦ Mg ≦ 0.5 wt%, 0.4 wt% ≦ Cu ≦ 0.8 wt%, 0.2 wt% < Fill the mold cavity with molten Al alloy consisting of Fe ≦ 0.5wt%, 0.1wt% ≦ Ti ≦ 0.3wt% and the balance Al containing inevitable impurities, and then the molten metal starts to solidify Then, until the solidification is completed, the cooling rate C _R of the molten metal and the Al alloy casting produced from the molten metal is controlled to C _R ≧ 5 ° C./s.

  The reason for the content of each alloy element and the reason for limiting the content are the same as described above. As the casting method, for example, a laminar flow filling die casting method, a GDC method, or the like is applied.

In addition, by setting the cooling rate CR as described above, the particle size d of the α phase can be set to d ≦ 45 μm. However, at CR <5 ° C./s, d> 45 μm, so the intended purpose is achieved. I can't. The faster the cooling rate CR, the smaller the particle size d of the α phase. However, the upper limit value of the cooling rate CR is on the order of CR = 10 2 ° C./s because of the relationship with the cooling device.

  Specific examples will be described below.

Table 1 shows the composition, examples of the casting method, and the cooling rate from the start of solidification to the completion of solidification for the examples (1) to (12) in which the Fe content was changed in an Al alloy casting. _C.sub.R , .alpha.

  In the table, laminar flow DC means a laminar filling die casting method using a 200-ton die casting machine. The temperature was set to 730 ° C. and the casting pressure was set to 90 MPa. GDC means a gravity mold casting method, and the casting conditions were set to a mold temperature of 120 to 350 ° C and a pouring temperature of 730 ° C.

  The solidification start temperature of the molten metal, which is an index for starting cooling, is 656 to 630 ° C., while the temperature of the Al alloy casting at the completion of solidification, which is an index for ending cooling, is about 550 ° C. This is the same for molten metal and Al alloy castings having the compositions of Table 1 and molten metal and Al alloy castings having the compositions of Tables 3, 5 and 7 described later. Each Al alloy casting is subjected to T6 treatment. T6 treatment conditions were set at 540-510 ° C for 4-8 hours, followed by water quenching and 180-160 ° C for 6-15 hours.

1 and 2 are photomicrographs showing the metal structures of Example (8) and Example (3), respectively. In the example (8) shown in FIG. 1, the particle size d of the α phase is d ≦ 45 μm, and needle-like and plate-like β-FeAlSi was not crystallized at the crystal grain boundary. In the example (3) shown, the particle size d of the α phase was d> 45 μm, and a large number of acicular β-FeAlSi crystallized at the crystal grain boundaries. In Examples (8) and (3), crystallization of a plurality of Si crystals was observed at the α-phase grain boundaries.

  Tensile test pieces and Charpy test pieces were produced from the Al alloy casting examples (1) to (12). The tensile test piece has a flat plate shape, the gauge distance L 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. When a tensile test and a Charpy impact test were performed using each test piece, the results shown in Table 2 were obtained.

  3 and 4 are graphs showing the relationship between the Fe content and the Charpy impact value and the relationship between the Fe content and the tensile strength based on Tables 1 and 2, respectively. In the figure, (1) to (12) correspond to examples (1) to (12) of the Al alloy casting, respectively. Such a relationship is the same below.

As is clear from Tables 1 and 2 and FIGS. 3 and 4, examples (7), (8), and (9) correspond to the examples, and both the Charpy impact value and the tensile strength are large. It can be seen that it is healthy because it has high strength and toughness, and no seizure has occurred. The toughness required for chassis components is 12 J / cm ² or more in Charpy impact value.

On the other hand, examples (1), (2), (5), and (6) have a large Charpy impact value and tensile strength because the Fe content is Fe ≦ 0.2 wt%. This is a defective product because seizure occurs. Examples (3) and (4) have a large Fe content and a cooling rate C _R of 1 ° C./s. Examples (10) to (12) have a cooling rate C _R of 5 ° C./s. However, since the Fe content is extremely large, it can be seen that it has low strength and low toughness due to crystallization of α-FeAlSi.

Table 3 shows the compositions of Examples (13) to (17) and Example (8) in which the Si content was changed in the Al alloy casting, the type of pressure casting method, and solidification completed after the molten metal started solidification. The cooling rate C _R until the heat treatment, the α-phase particle size d, and the presence or absence of seizure on the mold are shown.

  In the table, laminar flow DC means a laminar flow filling die casting method using a 200-ton die casting machine, as described above, and the casting conditions are the same as described above. Each Al alloy casting is subjected to T6 treatment, and the T6 treatment conditions are the same as described above.

  From the Al alloy casting examples (13) to (17), the same tensile test pieces and Charpy test pieces were produced. When a tensile test and a Charpy impact test were performed using each test piece, and a fluidity confirmation test of the molten metal was performed, the results shown in Table 4 were obtained. In the test for confirming the fluidity of the molten metal, the test piece mold of the laminar flow filling die casting method is filled with each molten metal under the same conditions as described for the laminar flow DC, and the test piece is cast. When the casting defect occurred, it was judged as “bad”, and when it did not, it was judged as “good”.

  FIG. 5 is a graph showing the relationship between the Si content, the Charpy impact value, and the tensile strength based on Tables 3 and 4. As is apparent from Tables 3 and 4 and FIG. 5, Examples (14), (15), and (8) correspond to the Examples, and both the Charpy impact value and the tensile strength are large, and the high strength.・ It is high toughness and no casting defects due to the fluidity of the molten metal have occurred.

  Example (13) has casting defects due to poor fluidity of the melt, while examples (16) and (17) have low toughness due to Si> 4 wt%.

Table 5 shows the compositions of Examples (18) to (22) and Example (8) in which the Mg content was changed in an Al alloy casting, the type of pressure casting method, and solidification completed after the molten metal started solidification. The cooling rate C _R until the heat treatment, the α-phase particle size d, and the presence or absence of seizure on the mold are shown.

  In the table, laminar flow DC means a laminar flow filling die casting method using a 200-ton die casting machine, as described above, and the casting conditions are the same as described above. Each Al alloy casting is subjected to T6 treatment, and the T6 treatment conditions are the same as described above.

  From the examples (18) to (22) of Al alloy castings, the same tensile test pieces and Charpy test pieces as described above were produced. When a tensile test and a Charpy impact test were performed using each test piece, the results shown in Table 6 were obtained.

  FIG. 6 is a graph showing the relationship between Mg content, Charpy impact value, and tensile strength based on Tables 5 and 6.

  As is apparent from Tables 5 and 6 and FIG. 6, Examples (19), (20), and (8) correspond to the examples, and both the Charpy impact value and the tensile strength are large, and the high strength.・ It turns out to be high toughness.

  Example (18) has low strength because Mg <0.2 wt%, while Examples (21) and (22) have low toughness because Mg> 0.5 wt%.

Table 7 shows the compositions of Examples (23) to (27) and Example (8) in which the Cu content was changed in an Al alloy casting, the type of pressure casting method, and solidification completed after the molten metal started solidification. The cooling rate C _R until the heat treatment, the α-phase particle size d, and the presence or absence of seizure on the mold are shown.

  In the table, laminar flow DC means a laminar flow filling die casting method using a 200-ton die casting machine, as described above, and the casting conditions are the same as described above. Each Al alloy casting is subjected to T6 treatment, and the T6 treatment conditions are the same as described above.

  From the examples (23) to (27) of Al alloy castings, the same tensile test pieces and Charpy test pieces were produced. When a tensile test and a Charpy impact test were performed using each test piece, and a stress corrosion cracking test was performed, the results shown in Table 8 were obtained. The stress corrosion cracking test was performed according to JIS H 8711 using a 2B test piece and setting the stress load to 85% of the proof stress value.

  FIG. 7 is a graph showing the relationship between the Cu content, the Charpy impact value, and the tensile strength based on Tables 7 and 8, respectively.

  As is clear from Tables 7 and 8 and FIG. 7, examples (24), (25), and (8) correspond to the examples, and both the Charpy impact value and the tensile strength are large, and the high strength.・ It is found to be healthy because it has high toughness and no stress corrosion cracking has occurred.

  Example (23) had low strength because Cu <0.4 wt%, while Examples (26) and (27) had stress corrosion cracking because Cu> 0.8 wt%.

It is a copy of the microscope picture which shows the metal structure regarding the Example of Al alloy casting. It is a copy of the microscope picture which shows the metal structure regarding the comparative example of Al alloy casting. It is a graph which shows the relationship between Fe content and a Charpy impact value. It is a graph which shows the relationship between Fe content and tensile strength. It is a graph which shows the relationship between Si content, Charpy impact value, and tensile strength. It is a graph which shows the relationship between Mg content, Charpy impact value, and tensile strength. It is a graph which shows the relationship between Cu content, Charpy impact value, and tensile strength.

Claims (2)

2 wt% ≦ Si ≦ 4 wt%, 0.2 wt% ≦ Mg ≦ 0.5 wt%, 0.4 wt% ≦ Cu ≦ 0.8 wt%, 0.2 wt% <Fe ≦ 0.5 wt%, 0.1 wt% ≦ Ti A high toughness Al alloy casting characterized by comprising the balance Al containing ≦ 0.3 wt% and inevitable impurities, and the particle diameter d of the α phase in the metal structure being d ≦ 45 μm.   2 wt% ≦ Si ≦ 4 wt%, 0.2 wt% ≦ Mg ≦ 0.5 wt%, 0.4 wt% ≦ Cu ≦ 0.8 wt%, 0.2 wt% <Fe ≦ 0.5 wt%, 0.1 wt% ≦ Ti ≦ 0.3 wt% and the remaining Al alloy containing the inevitable impurities is filled in the mold cavity under pressure, and then the molten metal starts solidification until solidification is completed. And a method for producing a high toughness Al alloy casting, characterized in that the cooling rate CR of the Al alloy casting produced from the molten metal is controlled to CR ≧ 5 ° C./s.

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