ALUMINUM-BASED ALLOY

Description

TECHNICAL FIELD

The present invention relates to an aluminum-based alloy in which one or more special additive elements are solid-solved in an aluminum parent phase so as to impart a high Young's modulus.

BACKGROUND ART

Accompanied by increasing demand to reduce weight of vehicles or aircraft, aluminum alloys have been more widely used. When substituting a conventional iron-based material with an aluminum material, there is a major problem of decreasing stiffness due to decreasing Young's modulus. To solve this problem, conventionally, increasing stiffness has been attempted by a complex effect of aluminum and ceramics (See Japanese Patents Nos. 4825776, 4119357, 4119348 and 3391636).

However, there is a problem of high production cost because production process of such complex material including reinforcing ceramic material is complicated. Furthermore, since hard particles are contained, there is a problem in that machine processing is difficult.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an aluminum-based alloy which can have high stiffness without containing hard particles such as those of ceramics, which can be produced easily, and which is easily processed by machine processing.

The inventors have researched strengthening by solid solution and aging in order to improve Young's modulus of aluminum-based alloys. As a result of calculation, they found that stiffness can be increased by substituting Al with an element having smaller atomic radius than Al. That is, by adding the additive element, electron density is improved and distance between atoms (distance between lattices) is smaller, bonding energy is increased, and therefore, stiffness can be increased. As a result of researching the atomic radius of elements from the first row to the fifth row in the periodic table, atomic radius of Cu, Zn, Ag, and Li is −10.5%, −6.99%, +1.05% and +5.70% of atomic radius of Al, respectively.

Furthermore, the inventors have calculated Young's modulus of aluminum-based alloy in a case in which 25 atom % of the additive element is contained in Al, with respect to elements from the first row to the fifth row in the periodic table. The following formula 1 is used as the theoretical formula. In the formula 1, E is Young's modulus, r is distance between atoms in a crystal lattice (face centered cubic), and A, n, and in are constants, depending on element. In addition, Young's modulus was calculated by the formula 1 using analytical software (CASTEP, super cell model). It should be noted that settings of the analytical software are approximations of the general density gradient, 350 eV of energy cut off, and 6×6×6 of K point set.

E = A  ( n - m ) 0 r m Formula   1

Young's modulus of each of the aluminum-based alloys was calculated, and these alloys were compared to the Young's modulus of pure aluminum, and increase rate of Young's modulus was calculated in a condition in which added amount of additive element in each aluminum-based alloy is converted to 1 wt %. The increase rate of Young's modulus of Cu, Zn, Ag, and Li is respectively 0.65%, 0.04%, 0.24%, and 0.95%.

Furthermore, the inventors have understood that if there is oversaturation of an additive element solid-solved in Al, even higher stiffness can be exhibited by depositing an intermediate layer (intermetallic compound of Al and additive element, intermetallic compound of additive elements or the like) due to difference between the oversaturated solid-solution and solid solubility limit at aging temperature, and they have researched elements from the first row to the fifth row in the periodic table. As a result, they have found that the maximum solid solubility amount of Cu, Zn, Ag and Li in Al is respectively 2.48 wt %, 49.1 wt %, 23.9 wt %, and 13.9 wt %.

Since the high stiffness of the aluminum-based alloy was considered to be an synergic effect of the abovementioned increase ratio of Young's modulus and the maximum solid solubility amount, the product of both was calculated. Then, the products were Cu 1.612, Zn 1.964, Ag 5.736, Li 13.205, and the other elements less than 1.

The present invention was completed in view of the above findings, and the first aspect of the present invention is an aluminum-based alloy containing aluminum as a main element and is shown by the following general formula (1), wherein X and Y are respectively selected from Cu, Zn, Ag and Li, and a and b are values in mass % in which a solid solution is possible by solution heat treatment in this range.

Al-aX-bY   (1)

Furthermore, the second aspect of the present invention is an aluminum-based alloy containing aluminum as a main element and is shown by the following general formula (2), wherein X, Y, Z, and W are respectively selected from Cu, Zn, Ag, and Li, and a, b, c, and d are values in mass % in which a solid solution is possible by solution heat treatment in this range.

Al-aX-bY-cZ-dW   (2)

It should be noted that since at least one element is added in the aluminum-alloy of the present invention, one to three among a to d can be zero. In addition, the solution heat treatment is a treatment in which secondary phase particles or the like generated by a concentration gradient in a solid phase are solid solved by heat treatment. In the treatment, additive elements are solid solved by increasing temperature until monophasic domain in an equilibrium diagram and then rapidly cooling. Therefore, a “range in which solid solution is possible by solution heat treatment” means a range in which a monophasic solid phase (α phase) exists in an equilibrium diagram, and its upper limit is the content amount of additive elements of which the solid phase only exists in two phases (α phase+β phase).

Here, it is desirable that a, b, c, and d in the general formulas (1) and (2) be positive numbers satisfying the relationship 14≤(a+b+c+d)≤30.

A method for production of aluminum-based alloy of the present invention is characterized in that solution heat treatment and quenching of the above-mentioned aluminum-based alloy are performed, and this is aged at 90 to 170 ° C. for 120 to 240 hours.

According to the present invention, due to forming effects of the solid solution and the intermediate phase of the additive elements added to the aluminum parent phase, an aluminum-based alloy can be provided, in which the Young's modulus and stiffness are greatly improved. Therefore, by the present invention, due to high stiffness, for example, weight can be reduced by reducing thickness of parts that are influenced by stiffness, such as a braking caliper, and compact shape design can be realized by reducing thickness of parts.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing a measuring apparatus for Young's modulus.

FIG. 2 is a graph showing a relationship between aging time and Young's modulus of the aluminum-based alloy in an Example of the present invention.

EXAMPLES

1. First Examples

Hereinafter, the present invention is further explained by way of practical Examples.

Rectangular samples having a width of 10 mm, length of 60 mm, and thickness of 1.5 mm were prepared from the aluminum-based alloy having composition shown in Table 1. The samples were processed by solution heat treatment in which samples were held at 520° C. for 4 hours and then quenched in water, and they were processed by aging at 110° C. for 24 hours. Then, Young's modulus of the samples was measured multiple times, and each of maximum values among multiple measurements are shown in Table 1.

FIG. 1 shows an apparatus for measuring Young's modulus (trade name: JE-RT, produced by Nihon Techno-Plus Co. Ltd.). In this measuring apparatus, a sample TP is suspended by two hanging wires 1, a driving electrode 2 generates natural vibration by constructing a condenser at a gap between the driving electrode 2 and the sample TP, the vibration is detected by a non-contacting vibration sensor 3, and Young's modulus is calculated. This measuring method is regulated and understood under Japanese Industrial Standard Z 2280.

As shown in Table 1, Examples 1 to 5 exhibit higher Young's modulus than that of the reference material made of pure aluminum. In particular, in Example 5 containing Cu, Zn, Ag and Li, extremely high Young's modulus was obtained.

2. Second Examples

Samples were prepared under conditions similar to those in the First Examples, except that aging treatment was performed holding at 90° C. for 10 days, and Young's modulus thereof was measured. The results are shown in Table 2. In addition, Young's modulus calculated by the above formula 1 is also shown in Table 2.

As shown in Table 2, the Young's modulus calculated with the formula 1 was extremely close to the actual measured value thereof, and thus, the desirability of selecting Cu, Zn, Ag, and Li was confirmed.

3. Third Examples

Samples of aluminum-based alloy were prepared in a condition similar to that of the First Examples, except that composition and aging treatment conditions were as shown in FIG. 2. As shown in FIG. 2, in a case in which aging temperature was 170° C., it was confirmed that Young's modulus of not less than 77 GPa was obtained by aging for 240 hours. Furthermore, in a case in which aging temperature was 110° C., it was also confirmed that Young's modulus of not less than 78 GPa was obtained by aging for 1500 hours.

Since high stiffness is obtained in the present invention, it is possible to use it for a part of a vehicle that requires stiffness.