US20240018632A1

US20240018632A1 - Aluminum alloy and aluminum alloy casting material

Info

Publication number: US20240018632A1
Application number: US18/039,829
Authority: US
Inventors: Shinya Miwa; Hiroshi Horikawa
Original assignee: Nikkei MC Aluminium Co Ltd
Current assignee: Nikkei MC Aluminium Co Ltd
Priority date: 2020-12-15
Filing date: 2020-12-15
Publication date: 2024-01-18
Also published as: WO2022130484A1; JP7472318B2; JPWO2022130484A1; CN116635549A

Abstract

The present invention provides an aluminum alloy that has exceptional casting properties and that can exhibit high mechanical properties without being subjected to a heat treatment, and an aluminum alloy casting material. More specifically, the present invention provides: an aluminum alloy that has exceptional casting properties, and that has a high 0.2% proof stress and exceptional ductility without being subjected to a heat treatment; and an aluminum alloy casting material. The aluminum alloy according to the present invention is characterized by containing 7.0-9.0 mass % of Si, 2.0-4.0 mass % of Cu, 0.8-1.2 mass % of Mg, 0.3-0.5 mass % of Fe, 0.3-0.5 mass % of Mn, and. 2.0-4.0 mass % of Zn, the balance being Al and unavoidable impurities.

Description

TECHNICAL FIELD

The present invention relates to an aluminum alloy for casting and an aluminum alloy casting material made of the aluminum alloy.

PRIOR ARTS

Aluminum alloy materials are used for housings of portable electronic devices and electronic terminals because they are lightweight and have excellent texture. The demand for thinness and weight reduction for these portable electronic devices is increasing year by year, and higher strength is required for the aluminum alloys used for the housings.
In particular, smartphones are often kept in a pocket or the like when not in use, and bending stress is often applied in this situation. That is, aluminum alloys used for the housings of portable electronic devices must have high strength and ductility (toughness) in addition to exceptional casting properties.
On the other hand, for example, Patent Literature 1 (Japanese Unexamined Patent Publication No. S48-32719) discloses, for the purpose of obtaining an alloy having strength comparable to that of conventional high-strength aluminum alloy for casting by taking advantage of the exceptional casting properties of Al-Cu-Si or Al-Si-Cu-Mg alloys, a high-strength aluminum alloy for casting having exceptional casting properties comprising silicon of 7.5 to 1.2%, copper of 4.0 to 5.5%, magnesium of 0.2 to 1.0% by weight, the balance being aluminum and impurities.
In the high-strength aluminum alloy for casting described in Patent Literature 1, it is said that excellent mechanical properties can be imparted to the aluminum alloy casting material by subjecting age hardening treatment after performing solution treatment at about 500° C.
Further, Patent Literature 2 (Japanese Unexamined Patent Publication No. S60-57497) discloses, for the purpose of obtaining a heat-treated high-strength aluminum alloy having good casting property, high toughness, and excellent heat resistance, a heat-resistant high-strength aluminum alloy comprising silicone of more than 6% to 13%, copper of more than 3% to 5.5%, zinc of more than 1% to 4%, magnesium of more than 0.2% to 1% and antimony of more than 0.03% to 1% and the balance being aluminum and impurities.
In the heat-resistant and high-strength aluminum alloy described in Patent Literature 2, it is said that when the Al-Si-Cu-Zn-Mg alloy contains more than 3% of copper, if antimony is added to the alloy, during aging treatment, the age hardening of the alloy is accelerated and the strength of the alloy is significantly improved without significantly deteriorating the toughness, and the thermal shock resistance of the alloy is significantly improved.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No. S48-32719
Patent Literature 2: Japanese Unexamined Patent Publication No. S60-57497

SUMMARY OF THE INVENTION

Technical Problem

In the high-strength aluminum alloy for casting described in Patent Literature 1 and the heat-resistant high-strength aluminum alloy described in Patent Literature 2, though it is said that excellent mechanical properties are imparted in addition to exceptional casting properties, in order to realize the mechanical properties, heat treatment such as artificial aging is essential.
However, the heat treatment process not only increases manufacturing costs and manufacturing time, but also affects the dimensions and shape of the aluminum alloy casting material. Particularly, since the housings of portable electronic devices are thin and require high dimensional accuracy, it is desirable to achieve high strength and excellent ductility without being subjected to heat treatment.
In view of the problems in the prior art as described above, an object of the present invention is to provide an aluminum alloy and an aluminum alloy casting material that have exceptional casting properties and can exhibit high mechanical properties without being subjected to heat treatment. More specifically, the object of the present invention is to provide an aluminum alloy and an aluminum alloy casting material that have exceptional casting properties, high 0.2% proof stress and excellent ductility without being subjected to heat treatment.

Solution to Problem

In order to achieve the above object, as a result of extensive study as to the composition range of aluminum alloys, the present inventors have found it is effective that all of the addition amounts of Si, Cu, Mg, Fe, Mn and Zn are strictly controlled, and then reached the present invention.
Namely, the present invention provides an aluminum alloy which contains

- Si: 7.0 to 9.0% by mass,
- Cu: 2.0 to 4.0% by mass,
- Mg: 0.8 to 1.2% by mass,
- Fe: 0.3 to 0.5% by mass,
- Mn: 0.3 to 0.5% by mass,
- Zn: 2.0 to 4.0% by mass, and the balance being Al and unavoidable impurities.

It is preferable that the aluminum alloy of the present invention contains at least one of Sr: 0.008 to 0.04% by mass, Be: 0.001 to 0.004% by mass, Ti: 0.05 to 0.005% by mass, and B: 0.01 to 0.005% by mass,
The present invention also provides an aluminum alloy casting material which comprises the aluminum alloy of the present invention, and has a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more.
The aluminum alloy casting material of the present invention can develop a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more after forming into a desired shape by casting without being subjected to heat treatment. A more preferable 0.2% proof stress is 240 MPa or more, and a more preferable elongation at break is 3.0% or more.

Effect of the Invention

According to the present invention, it is possible to provide an aluminum alloy and an aluminum alloy casting material that have exceptional casting properties and can exhibit high mechanical properties without being subjected to heat treatment. More specifically, according to the present invention, it is possible to provide an aluminum alloy and an aluminum alloy casting material that have exceptional casting properties, high 0.2% proof stress and excellent ductility without being subjected to heat treatment.

Embodiments for Achieving the Invention

Hereinafter, representative embodiments of the aluminum alloy and aluminum alloy casting material of the present invention will be described in detail, but the present invention is not limited to these examples.

1. Aluminum Alloy

The aluminum alloy of the present invention is an aluminum alloy which has Si: 7.0 to 9.0% by mass, Cu: 2.0 to 4.0% by mass, Mg: 0.8 to 1.2% by mass, and Fe: 0.3 to 0.5% by mass, Mn: 0.3 to 0.5% by mass, Zn: 2.0 to 4.0% by mass, and the balance being Al and unavoidable impurities. Each component will be described in detail hereinbelow.

(1) Essential Additive Element

Si: 7.0 to 9.0% by Mass

Si has the effect of improving the casting property of aluminum and also has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Si: 7.0% by mass or more. Conversely, when Si: 9.0% by mass or more, the crystallized eutectic Si and primary crystal Si tend to coarsen. When these compounds are coarsened, they tend to serve as starting points for breakage, which tends to lead to decrease in elongation. A more preferable addition amount of Si is 7.5 to 8.5% by mass.

Cu: 2.0 to 4.0% by Mass

Cu has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Cu: 2.0% by mass or more. Conversely, when more than 4.0% by mass, the Cu-based crystallized substances tend to coarsen, and the elongation tends to decrease. Further, when the content of Cu increases, the corrosion resistance also decreases. Furthermore, when anodized, the color tends to be yellowish. A more preferable addition amount of Cu is 2.5 to 3.7% by mass, and further preferable is 3.5% by mass or less.

Mg: 0.8 to 1.2% by Mass

Mg has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Mg: 0.8% by mass or more. Conversely, when more than 1.2% by mass, the coarse compounds tend to be formed, and the elongation tends to decrease.
Though Si, Mg, and Cu are elements that precipitate as compounds during aging treatment and contribute to precipitation strengthening, since the aluminum alloy of the present invention is mainly used as the non-heat treated materials, the strengthening mechanism of these elements is basically solid-solution strengthening.

Fe: 0.2 to 0.5% by Mass

Fe has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Fe: 0.2% by mass or more. It also has the effect of preventing seizure in mold casting such as die casting. When more than 0.5% by mass, it is easy to form coarse needle-like Al-Si, Fe, Mn)-based compounds that serve as fracture starting points.

Mn: 0.3 to 0.5% by Mass

Mn has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Mn: 0.3% by mass or more. It also has the effect of making the Al—(Si, Fe, Mn)-based compound into particles. Conversely, when more than 0.5% by mass, the Al—(Si, Fe, Mn)-based compounds tend to coarsen.

Zn: 2.0 to 4.0% by Mass

Zn has the effect of improving mechanical properties such as tensile strength. This effect becomes remarkable when Zn: 2.0% by mass or more. Conversely, when more than 4.0% by mass, stress corrosion cracking tends to occur. Further, discoloration and color unevenness are likely to occur when subjecting to anodized film treatment.

(2) Optional Additive Element

Sr: 0.008 to 0.04% by Mass

Sr has the effect of making the eutectic Si fine and granular, and this effect is remarkable when Sr: 0.008% by mass or more. When added more than 0.04% by mass, since the effect is not significantly improved, it is preferably less than 0.04% by mass.

Be: 0.001 to 0.004% by Mass

Be has the effect that an oxide film is formed on the surface of the molten metal when melted, and the depletion of other elements such as Mg can be suppressed. Further, it also has the effect of suppressing the blackening of the casting surface. This effect becomes remarkable when Be is 0.001% by mass or more. When added more than 0.004% by mass, since the effect is not significantly improved, it is preferably less than 0.004% by mass.

Ti: 0.05 to 0.005% by Mass

Ti mainly contributes to toughness by making the structure fine. When less than the lower limit, the effect is small, and when containing beyond the upper limit, since it is already sufficiently fine and has no effect, and in addition thereto, when adding excess amount, since coarse crystalline compounds are formed to give adverse effect on elongation, it is necessary to limit it within the above range.

B: 0.01-0.005% by Mass

B mainly contributes to toughness by making the structure fine. When less than the lower limit, the effect is small, and when containing beyond the upper limit, since it is already sufficiently fine and has no effect, and in addition thereto, when adding excess amount, since coarse crystalline compounds are formed to give adverse effect on. elongation, it is necessary to limit it within the above range.
As long as the effects of the present invention are not impaired, the method for producing the aluminum alloy of the present invention is not particularly limited, and conventionally known various production methods may be used.

2. Aluminum Alloy Casting Material

The aluminum alloy casting material of the present invention is made of the aluminum alloy of the present invention, and is characterized by having a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more. A more preferable 0.2% proof stress is 240 MPa or more, and a more preferable elongation at break is 3.0% or more.
The excellent mechanical properties are basically realized by rigorously optimizing the composition, and the mechanical properties are owned without depending on the shape and size of the aluminum alloy casting material and further without depending on the portion and direction of the aluminum alloy casting material.
Further, the aluminum alloy casting material of the present invention can develop a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more without being subjected to heat treatment such as aging treatment.
As long as the effects of the present invention are not impaired, the shape and size of the aluminum alloy casting material are not particularly limited, and can he used as various conventionally known members. Examples of such members include an electronic terminal housing.
Further, as long as time effects of the present invention are not impaired, the method for producing the aluminum alloy casting material of the present invention is not particularly limited, and the aluminum alloy of the present invention may be cast by various conventionally known methods. Furthermore, the casting material by using the alloy of the present invention has excellent mechanical properties, particularly toughness, even without heat treatment, but heat treatment such as aging treatment may be performed. When aging treatment is performed, higher mechanical properties can be obtained due to precipitation strengthening of compounds such as Si, Mg, Cu, and Zn.
The representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design changes are possible, and all such design changes are included in the technical scope of the present invention.

EXAMPLE

Example

In Table 1, aluminum alloys having the compositions described as Examples 1 to 5 were produced by melting and die-cast at a casting pressure of 120 MPa, a molten metal temperature of 730° C., and a mold temperature of 170° C. The mold shape is a plate of 55 mm×110 mm×3 mm. The aluminum alloy has excellent die-casting property, and a good aluminum alloy casting material (die-cast material) was obtained. The unit of the numerical values shown in Table 1. is % concentration by mass.

TABLE 1

Si	Cu	Mg	Fe	Mn	Zn	Be	Sr	Al

Ex. 1	8.0	3.0	1.0	0.4	0.4	3.0	0.003	0.020	Bal.
Ex. 2	9.0	2.2	1.2	0.3	0.5	2.1	0.001	0.025	Bal.
Ex. 3	7.2	3.9	0.8	0.5	0.3	3.9	—	0.038	Bal.
Ex. 4	8.2	3.1	0.9	0.4	0.4	3.1	—	0.008	Bal.
Ex. 5	7.7	2.8	1.1	0.5	0.5	2.8	0.004	0.012	Bal.
Com. Ex. 1	11.0	4.5	0.8	0.25	1.0	—	—	0.015	Bal.
Com. Ex. 2	11.0	4.5	1.0	0.4	1.0	—	—	0.010	Bal.
Com. Ex. 3	11.0	4.5	1.0	0.4	1.0	1.0	—	0.010	Bal.
Com. Ex. 4	10.5	4.5	1.0	0.4	1.0	3.0	—	0.010	Bal.
Com. Ex. 5	10.0	4.5	1.0	0.4	1.0	5.0	—	0.010	Bal.
Com. Ex. 6	9.0	3.5	2.0	0.8	—	—	0.003	0.020	Bal.
Com. Ex. 7	9.0	3.5	2.0	0.8	—	3.0	0.003	0.020	Bal.
Com. Ex. 8	9.0	3.5	2.0	0.8	—	5.0	0.003	0.020	Bal.
Com. Ex. 9	9.0	3.5	1.0	0.8	—	—	—	0.020	Bal.
Com. Ex. 10	9.0	3.5	1.5	0.8	—	—	—	—	Bal.
Com. Ex. 11	8.0	3.0	0.5	0.4	0.4	—	0.003	0.020	Bal.
Com. Ex. 12	8.0	3.0	0.5	0.4	0.4	3.0	0.003	0.020	Bal.
Com. Ex. 13	8.9	3.6	0.51	0.78	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 14	8.9	3.6	1.1	0.79	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 15	8.8	3.6	1.5	0.79	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 16	8.8	3.7	0.79	0.81	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 17	7.3	3.6	0.6	0.76	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 18	7.3	3.6	0.9	0.77	<0.01	<0.01	0.002	0.020	Bal.
Com. Ex. 19	7.3	3.6	1.2	0.77	<0.01	<0.01	0.003	0.020	Bal.
Com. Ex. 20	1.9	<0.01	7.1	0.19	0.7	<0.01	0.003	—	Bal.
Com. Ex. 21	6.8	3.0	1.0	0.4	0.6	1.8	0.003	0.020	Bal.
Com. Ex. 22	7.9	1.7	0.9	0.4	0.1	2.9	0.003	0.020	Bal.

A No. 14B test piece defined in JIS-Z2241 was taken from each of the obtained aluminum alloy casting materials, and when the tensile test was performed at room temperature, the values shown in Table 2 of the tensile strength, the 0.2% proof stress and elongation at break were obtained. Further, when the Rockwell hardness of the obtained aluminum alloy casting materials were measured, the values shown in Table 2 were obtained. Here, the aluminum alloy casting materials were die-cast as they were, and was not subjected to heat treatment such as aging treatment.

TABLE 2

Tensile	0.2% Proof
strength	stress	Elongation	Hardness
(MPa)	(MPa)	(%)	(HRB)

Ex. 1	369	241	3.3	73
Ex. 2	362	237	2.7	—
Ex. 3	383	247	2.6	—
Ex. 4	365	242	3.2	—
Ex. 5	371	245	3.0	—
Com. Ex. 1	336	230	1.6	77
Com. Ex. 2	362	237	2.0	77
Com. Ex. 3	317	231	1.2	76
Com. Ex. 4	347	241	1.6	78
Com. Ex. 5	330	251	1.3	79
Com. Ex. 6	357	298	1.1	77
Com. Ex. 7	385	301	1,5	78
Com. Ex. 8	366	302	1.0	79
Com. Ex. 9	357	239	2.2	76
Com. Ex. 10	385	253	1.6	77
Com. Ex. 11	—	—	—	59
Com. Ex. 12	—	—	—	59
Com. Ex. 13	328	227	2.4	—
Com. Ex. 14	328	271	1.5	—
Com. Ex. 15	333	325	1.0	—
Com. Ex. 16	333	241	1.8	—
Com. Ex. 17	316	207	2.4	—
Com. Ex. 18	347	244	2.4	—
Com. Ex. 19	350	282	1.5	—
Com. Ex. 20	294	190	4.1	—
Com. Ex. 21	366	241	2.2	—
Com. Ex. 22	349	225	2.3	—

Comparative Example

Comparative aluminum alloy casting materials (die cast materials) were obtained in the same manner as in the Examples, except that the molten material was prepared so as to have the components described in Table 1 as Comparative Examples 1 to 22. Further, the tensile properties and Rockwell hardness were measured in the same manner as in Examples. The values obtained are shown in Table 2. In addition, when there is no description of a numerical value, it means that the measurement was not performed.
Comparing the tensile properties of the aluminum alloy casting materials obtained in Examples and Comparative Examples, it can be seen that only the aluminum alloy casting materials obtained in Examples have a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more. Further, it can be seen that Example 1 with Sr added has higher tensile strength and elongation than Example 4 with no Sr added (extremely low Sr content).
The aluminum alloy casting materials having the compositions of Comparative Examples 1 to 5, which contain a large amount of Si, Cu and Mn, exhibit a high 0.2% proof stress, but the elongation at break is 2.0% or less. Further, the elongation at break of the aluminum alloy casting materials having the compositions of Comparative Examples 6 to 10 and Comparative Examples 13 to 19, which contain a large amount of Fe, does not reach 2.5%.
Further, the hardness of the aluminum alloy casting materials having the compositions of Comparative Example 11, in which the amount of Mg added is small and does not contain Zn, and Comparative Example 12, in which the amount of Mg added is small, are low values, and it can be seen that sufficient strength is not obtained.
Furthermore, the aluminum alloy casting material having the composition of Comparative Example 20 with low Si and Cu contents has an elongation at break of 2.5% or more, but a low 0.2% proof stress. Further, in Comparative Example 21, in which the Si and Zn contents are low and the Cu and Mn contents are high, the tensile strength and 0.2% proof stress are high, but the elongation at break is as low as less than 2.5%. Further, in Comparative Example 22, in which the Cu and Mn contents are high, the elongation at break is as low as less than 2.5%, and in addition the 0.2% proof stress does not reach 230 MPa.
From the above results, in order to develop the 0.2% proof stress of 230 MPa or more and the elongation at break of 2.5% or more without subjecting the aluminum alloy casting material to heat treatment, it can be seen that it is necessary to strictly control the addition amounts of Si, Cu, Mg, Fe, Mn and Zn.

Claims

1. An aluminum alloy comprising:

Si: 7.0 to 9.0% by mass,

Cu: 2.0 to 4.0% by mass,

Mg: 0.8 to 1.2% by mass,

Fe: 0.3 to 0.5% by mass,

Mn: 0.3 to 0.5% by mass,

Zn: 2.0 to 4.0% by mass, and the balance being Al and unavoidable impurities.

2. The aluminum alloy according to claim 1, which contains at least one of

Sr: 0.008 to 0.04% by mass,

Be: 0.001 to 0.004% by mass,

Ti: 0.05 to 0.005% by mass,

B: 0.01 to 0.005% by mass.

3. An aluminum alloy casting material which comprises the aluminum alloy according to claim 1, has a 0.2% proof stress of 230 MPa or more and an elongation at break of 2.5% or more.