JP7096690B2 - Aluminum alloys for die casting and aluminum alloy castings - Google Patents

Description

The present invention relates to an aluminum alloy (simply referred to as "Al alloy") or the like, which can be used for die casting with excellent mechanical properties.

In recent years, Al alloys have been widely used due to the demand for weight reduction. Al alloy products (members) mass-produced are often manufactured by die casting. According to the die casting method, it is possible to manufacture a highly accurate product in a short cycle time while significantly reducing cutting work and the like.

Typical Al alloys used for die casting include Al—Si based alloys (for example, JIS ADC12) and Al—Mg based alloys. Al—Si alloys have excellent castability, but their castings have very low ductility. Therefore, Al—Mg-based alloys are used for members that require high strength and high ductility. Many proposals have been made regarding such Al—Mg-based alloys, and for example, there are descriptions related to the following patent documents.

Japanese Unexamined Patent Publication No. 9-268340 Japanese Unexamined Patent Publication No. 11-193434 Japanese Unexamined Patent Publication No. 11-293375 Japanese Patent No. 4145242 Japanese Patent No. 4155509

Some of them are excellent in strength and ductility, such as Al alloys for die casting shown in Patent Document 4 and Patent Document 5. However, there is still a lot of room for improvement in other Al alloys.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an Al alloy having a new composition capable of obtaining a die-cast casting capable of achieving both strength and ductility at a high level.

As a result of diligent research to solve this problem, the present inventor has decided to obtain high-strength and high-development die-casting by using an Al-Mg (-Mn) -based alloy having a new composition different from that of the conventional Al alloy. Successful. By developing this result, the present invention described below was completed.

《Aluminum alloy for die casting》
(1) The present invention is an aluminum alloy used for die casting, which satisfies the following composition with 100% by mass (simply referred to as "%") as a whole.
Mg: 3 to 6%, Mn: 0.7 to 1.5%, Fe: 0.2 to 0.6%,
Ti: 0.1-0.3%, Zr: 0.1-0.3%, balance: Al and impurities

(2) By using the Al alloy of the present invention, a die-cast casting having high strength and high ductility (simply referred to as "casting") can be obtained. Incidentally, since the Al alloy of the present invention contains a predetermined amount of Fe, the seizure resistance at the time of die casting can be improved. Further, since the Al alloy of the present invention allows the content of Fe exceeding the impurity level, it is possible to use a recycled material as a raw material.

By the way, the reason why a high-strength and high-ductility casting can be obtained by the Al alloy of the present invention is considered as follows. First, the Al alloy of the present invention contains both Ti and Zr, unlike the Al alloy used for conventional die casting. Ti and Zr exert a synergistic effect by coexistence and can contribute to a significant miniaturization of the cast structure. The present inventor has confirmed that such an excellent effect cannot be sufficiently obtained with either Ti or Zr.

Next, the Al alloy of the present invention contains a relatively large amount of Mn, and a large amount of Mn compound is crystallized to improve the strength of the casting. However, when the Mn compound becomes coarse, the Mn compound becomes a fracture starting point, and on the contrary, the strength and ductility of the casting may decrease. Here, in the Al alloy of the present invention, the crystallization time of the Mn compound is delayed by containing a predetermined amount of Fe (more specifically, the crystallization time of the Mn compound is brought closer to the crystallization time of α-Al. ), It has succeeded in suppressing the coarsening thereof and dispersing a large amount of fine Mn compounds around α-Al. At that time, the amount of Al—Fe eutectic crystallization is also suppressed, and its coarsening is also suppressed.

In this way, according to the Al alloy of the present invention, both α-Al and each compound phase have a fine cast structure, and a casting having both strength and ductility at a high level can be obtained.

《Aluminum alloy casting (die casting)》
(1) The present invention can also be grasped as a die-cast casting made of the above-mentioned Al alloy. For example, the present invention may be an aluminum alloy casting made of the above-mentioned Al alloy and having a cast structure having a crystal grain size of 0.15 mm or less, 0.1 mm or less, and further 0.05 mm or less.

The crystal grain size referred to in the present specification is measured by mirror polishing the measurement sample, subjecting it to electrolytic etching in Barker's solution, observing it with an optical microscope, and measuring the average crystal grain size using the section method. Identified by.

(2) In the cast structure according to the present invention, it is preferable that the Mn compound phase (Al—M-based crystallized product) and the Al—Fe eutectic phase are finely crystallized around the α—Al crystal grains. ..

Further, the casting of the present invention preferably has an elongation of 12% or more, 13% or more, and further preferably 14% or more. Further, the proof stress (0.2% proof stress) is preferably 140 MPa or more, 150 MPa or more, and more preferably 160 MPa or more.

"others"
(1) The Al alloy of the present invention may be a raw material alloy used for die casting or a casting cast using the raw material alloy. Impurities referred to in the present specification include, in addition to unavoidable impurities, elements that are difficult to remove due to reasons such as cost. The amount of such impurity elements is preferably 0.1% or less, more preferably 0.05% or less, respectively.

(2) Unless otherwise specified, "x to y" in the present specification includes a lower limit value x and an upper limit value y. A range such as "a to b" may be newly established with any numerical value included in the various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

It is a structure photograph which shows the influence of Ti and Zr on a cast structure. It is a structure photograph which shows the influence of Fe on a cast structure. It is a graph obtained by analyzing the influence of Fe on the crystallization process. It is a bar graph comparing the yield strength and elongation of die castings having different alloy compositions.

One or more components arbitrarily selected from the present specification may be added to the components of the present invention described above. The contents described in the present specification appropriately apply not only to the Al alloy of the present invention but also to castings. A component related to a manufacturing method can also be a component related to a product. Which embodiment is the best depends on the target, required performance, and the like.

《Al alloy》
The Al alloy of the present invention contains Mg, Mn, Fe, Ti and Zr as essential alloying elements in addition to Al. Hereinafter, the alloying elements and the contents will be described in detail. Unless otherwise specified, the alloy composition referred to in the present specification is a mass ratio with respect to the entire Al alloy, and is simply indicated by "%".

Mg dissolves in the Al matrix and contributes to the improvement of the mechanical strength (tensile strength, etc.) of the Al alloy. Mg also affects the ductility and castability of Al alloys. Therefore, it is preferable that Mg is contained in an amount of 3 to 6%, 3.5 to 5.5%, more preferably 4 to 5%. If the amount of Mg is too small, the strength of the Al alloy will be insufficient. If the amount of Mg is excessive, the ductility of the Al alloy may decrease due to the coarsening of the Mn compound or Fe compound that crystallizes.

Mn not only dissolves in the matrix of Al, but also forms a compound (Al ₆ Mn, etc.) with Al to improve the strength of the Al alloy. Mn can also improve the seizure resistance with the mold. Therefore, Mn is preferably contained in an amount of 0.7 to 1.5%, 0.8 to 1.3%, more preferably 0.9 to 1.2%. If Mn is too small, the strength of the Al alloy may be insufficient. When Mn is excessive, the strength and ductility of the Al alloy may decrease due to the coarsening of the Mn compound.

Fe affects the crystallization process of Al alloy and contributes to the miniaturization of Mn compounds and the like. Fe can also improve the seizure resistance with the mold. Further, in the Al alloy of the present invention, the Fe content is considerably higher than the impurity level. Therefore, it is also possible to use a recycled material (recycled Al alloy or the like) that easily contains Fe as the Al alloy itself of the present invention or as a raw material thereof. Therefore, Fe is preferably contained in an amount of 0.2 to 0.6%, 0.25 to 0.55%, more preferably 0.3 to 0.5%. If Fe is too small, the above-mentioned effect is poor, and if Fe is too large, the strength and ductility of the Al alloy may decrease due to the coarsening of the crystallized products (Mn compound, Fe compound, etc.).

Ti and Zr become nucleation sites for primary crystal Al (α-Al) and contribute to the miniaturization of the entire cast structure. Therefore, Ti and Zr are preferably contained in an amount of 0.1 to 0.3% (further less than 0.3%), 0.14 to 0.25%, and further 0.15 to 0.2%, respectively. If one of Ti and Zr is too small, the casting structure will be insufficiently miniaturized. If Ti or Zr is excessive, coarse compounds (Al ₃ Ti, etc.) may crystallize and the ductility may decrease. As described above, in the Al alloy of the present invention, the cast structure is significantly miniaturized by the coexistence of Ti and Zr, but the total amount (Ti + Zr) is 0.25 to 0.5% and further 0. It is more preferably .29 to 0.4%.

《Casting method》
The Al alloy of the present invention can be used in general casting methods (sand casting, mold casting, etc.), but is particularly preferably used for die casting. With the Al alloy of the present invention, a die-cast casting having high strength and high ductility can be obtained.

In die casting, in general, the molten Al alloy is supplied to the cavity of the set mold while pressurizing it with a plunger or the like (pouring step), and then quenching and solidifying (solidification step). In such die casting, for example, the injection speed: 0.1 to 5 m / sec, further 0.2 to 2 m / sec, the casting pressure: 10 to 100 MPa, further 20 to 80 MPa, and the injection temperature: the liquidus line of the Al alloy. The temperature is preferably +60 to 140 ° C., more preferably 80 to 120 ° C. The cooling rate cannot be specified uniformly because it varies depending on the site, but it is preferably 20 ° C./sec or higher, and more preferably 50 ° C./sec or higher at the latest.

《Use》
Since the casting of the present invention has high strength and high ductility, it is used for various products and members. For example, the casting of the present invention is suitable for the skeleton portion (body, chassis, etc.) of a vehicle (automobile, motorcycle), suspension member, wheel, joint, suspension tower, pillar, and the like.

Samples (die-cast castings) made of Al alloys having different compositions were produced, and the metallographic structure (casting structure) of each sample was observed or the mechanical properties were measured. The present invention will be described in more detail based on such a specific example.

[First Example / Effect of Ti and Zr]
(1) Production A large number of samples consisting of Al-4.5% Mg-1.0% Mn-0.5% Fe-x% Ti-y% Zr were produced. The Ti and Zr contents (x, y) related to each sample are summarized in Table 1. The alloy composition is a mass ratio (mass%) with respect to the entire Al alloy, and is simply indicated by "%".

Each sample was produced as follows. The molten metal (720 ° C.) prepared for each alloy composition was poured into a wedge-shaped mold (manufactured by S55C) and solidified. At this time, the molten metal containing Ti and Zr was prepared by adding Ti and Zr to the molten metal heated to 760 ° C. The cooling rate of the mold casting according to this embodiment is about the same as that of general die casting (about 200 to 300 ° C./s).

(2) Observation The test material cut out from each sample was macrocorroded by electrolytic etching using Barker's solution. The cast structure of each sample after this treatment was observed with an optical microscope. An example of the obtained macrostructure is shown in comparison with FIG.

The crystal grain size of each sample was specified by the method described above based on each cast structure. The results of comparing the crystal grain sizes of each sample are summarized in Table 1. The comparison of crystal grain size is based on the crystal grain size of the reference sample (Ti: 0.14%, Zr: 0%), when it is finer than that: ○, when it is coarse: ×, when it is about the same. : △.

(3) Evaluation As is clear from FIGS. 1 and 1, it was found that the cast structure was remarkably miniaturized by the combined addition of a predetermined amount of Ti and Zr. On the contrary, it was also found that the cast structure cannot be sufficiently miniaturized not only when Ti and Zr are not contained but also when only one of them is contained.

For example, in the case of no Ti / Zr, the crystal grain size was about 0.4 to 0.6 mm, and in the case of only Zr, the crystal grain size was about the same. When only Ti is used, the crystal grain size is refined to more than 0.15 to 0.2 mm, but when Ti and Zr are combined (total amount: 0.26%), the crystal grain size is 0.15 mm. Below, it was remarkably miniaturized to 0.1 mm or less.

It is presumed that such miniaturization of the cast structure occurs because Ti and Zr become nucleation of primary crystals (α-Al). However, the reason (mechanism) that the crystal grain size is significantly different due to the difference in the micronizing agent (difference between Ti and Zr) and the compounding is not clear at present, and can be said to be a phenomenon peculiar to the Al alloy of the present invention.

No coarse crystallization was observed in the cast structure of the sample with Ti: 0.23% and Zr: 0.20%, but it was more than 0.3% in either Ti or Zr. It has also been confirmed that coarse crystallization is observed in the sample.

[2nd Example / Effect of Fe]
(1) Manufacture Al-4.5% Mg-1.0% Mn-0.5% Fe-0.15% Ti-0.15% Zr and Al-4.5% Mg-1.0% Mn A sample consisting of −0.7% Fe −0.15% Ti −0.15% Zr was produced by die casting.

Die casting was performed using a vertical die casting machine. The molten metal prepared for each composition was pressure-injected into the cavity of the mold with a plunger (φ40 mm) (injection step) and then solidified (coagulation step). The casting conditions were casting pressure: 65 MPa, injection (plunger) speed: low speed 0.2 m / s, high speed 1.0 m / s, injection (melting) temperature: liquidus temperature + 100 ° C. The mold temperature was room temperature, and the cooling rate was about 100 ° C./s. In this way, a plate-shaped die-cast casting (simply referred to as "casting") having a size of 200 mm × 40 mm × t3 to 5 mm was obtained. The structure of the sample cut out from this casting was observed.

(2) Observation The cast structure of each sample was observed with an optical microscope. The microstructure of each sample thus obtained is shown in comparison with FIG.

(3) Evaluation As is clear from FIG. 2, crystallization of coarse Al—Mn compounds and Al—Fe eutectic crystals was observed in the cast structure having an Fe content of 0.7%. On the other hand, in the cast structure having an Fe amount of 0.5%, no such coarse crystallized material was observed.

(4) Consideration For Al-4.5% Mg-1.0% Mn-z% Fe-0.15% Ti-0.15% Zr, the Fe amount (z) is 0.3% and 0.5%. FIG. 3 shows the results of analysis of the crystallization process at 0.7% and using Thermo Calc according to Scheil's equation. In the graph shown in FIG. 3, the horizontal axis is the solid phase ratio and the vertical axis is the temperature.

As is clear from FIG. 3, when the Fe amount is 0.7%, the crystallization start temperature of the Al ₆ Mn phase is higher than that of α-Al. Therefore, the Al ₆ Mn phase crystallizes before α-Al and tends to be coarsened.

On the other hand, when the Fe amount is 0.5% or 0.3%, the crystallization start temperature of the Al ₆ Mn phase approaches the crystallization start temperature of α-Al, and the Al ₆ Mn phase is at about the same time as α-Al. Will crystallize in. Therefore, the Al ₆ Mn phase is restricted to α-Al particles, and its coarsening is suppressed. It can also be seen that when the Fe amount is within such a range, the Al—Fe eutectic amount also decreases, so that the coarsening of the eutectic phase is also suppressed.

In this way, in the Al alloy having an Fe amount of less than 0.7%, 0.6% or less, and further 0.5% or less, a cast structure in which the Al—Mn compound phase and the Al—Fe eutectic phase are finely dispersed can be obtained. It is thought that it was done.

[Third Example]
A die-cast casting having the following three alloy compositions was produced in the same manner as in the case of the second embodiment. 0.2% proof stress and elongation were measured using the test material (sample) cut out from each casting. The results are summarized in FIG.
(Example)
Al-4.5% Mg-1.0% Mn-0.5% Fe-0.15% Ti-0.15% Zr
(Comparative Example A)
Al-3.5% Mg-1.2% Mn-0.1% Fe
(Comparative Example B)
Al-4.5% Mg-0.3% Mn-0.75% Fe-0.15% Ti

As is clear from FIG. 4, when an Al alloy containing a predetermined amount of Ti, Zr and Fe is used, the 0.2% proof stress is 140 MPa or more, further 150 MPa or more, and the elongation is 12% or more, further 13% or more. It was found that a high-strength and high-ductility casting can be obtained.

From the above, the coexistence of a predetermined amount of Ti and Zr contributes to the overall miniaturization of the cast structure (particularly α-Al), and at the same time, contributes to the miniaturization of the compound in which a predetermined amount of Fe is crystallized. It was confirmed that the die-cast casting made of the Al alloy of the present invention exhibits high strength and high ductility.

Claims (4)

An aluminum alloy used for die casting that satisfies the following composition with the whole being 100% by mass (simply referred to as "%").
Mg: 3-6%,
Mn: 0.7-1.5%,
Fe: 0. 3 to 0.6%,
Ti: 0.1-0.3%,
Zr: 0.1-0.3%,
Remaining: Al and impurities An aluminum alloy casting comprising the aluminum alloy according to claim 1 and having a cast structure having a crystal grain size of 0.15 mm or less. The aluminum alloy casting according to claim 2, wherein the cast structure is a Mn compound phase and an Al—Fe eutectic phase crystallized around α—Al crystal grains. The aluminum alloy casting according to claim 2 or 3, wherein the elongation is 12% or more and the proof stress is 140 MPa or more.

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