JP2003147498A - Method for producing semi-molten cast billet of aluminum alloy for transport apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a semi-molten billet of an aluminum alloy for a transport apparatus in a simple process by which the cost reduction is promoted, and the product becomes homogeneous. SOLUTION: An aluminum alloy containing, by weight, 3.5 to 7.5% Zn, 0.50 to 4.0% Mg, <=0.50% Si, <=0.55% Fe, at least one or more kinds selected from 0.001 to 0.50% Ti and 0.0001 to 0.5% B, and at least one or more kinds selected from 0.30 to 3.0% Cu, 0.03 to 0.80% Mn, 0.03 to 0.35% Zr, 0.03 to 0.35% Cr, and 0.03 to 0.2% V, and the balance substantially Al, and in which the intervals of dendrites are <=200 μm is produced. Next, working strains are introduced at a strain ratio of 5 to 50%, at a working introduction rate of <=50 mm/sec., and, at less than a recrystallization temperature by cold frame mold forging. After that, the temperature of the alloy is raised to a solidus temperature or higher, and is held to a temperature in which a liquid phase ratio reaches 20 to 80%, and semi-molten working is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semi-molten molded billet of an aluminum alloy used for transportation equipment.

[0002]

2. Description of the Related Art The thixocasting method using a semi-molten billet has recently attracted attention because it has advantages such as less casting segregation / defects and longer die life than the conventional die casting method. As a billet casting method used for this, in order to make the primary α (Al) phase into a spherical shape at the billet stage known as the Pennesey Almax method, a method of performing electromagnetic / mechanical stirring in the semi-melting temperature range (method A) or a larger amount of Al-Ti- than is usually added during casting.
B was added, and the temperature was raised to the melting temperature range in the latter half and the primary crystal α (A
1) There is a method of making the phase spherical (method B). Further, a method (method C) in which the temperature is raised to spherical as in method B after introducing strain by extrusion / rolling is widely known.

[0003]

[Problems to be Solved by the Invention]
In case of method A, the process is very complicated and the manufacturing cost is high.
There was a problem of sticking. In the method B, a large amount of Al
-TiB in the melting furnace to add Ti-B _TwoFor settling
Quality instability occurs, and distortion occurs due to rolling of method C.
It is difficult to introduce uniform strain in the method of introducing
At room temperature extrusion, the work process is complicated, and the strain is uniform.
It is difficult to introduce only the product, and both strain introduction methods are product processing after processing
Is required, and mass production and cost reduction cannot be achieved.
There was a problem.

Japanese Patent No. 2976073 discloses an improved method. That is, there is a step in the first paragraph "a step of deforming a completely solidified metal or metal alloy material at a temperature lower than its recrystallization temperature, and heating the deformable material to cause recrystallization of the microstructure of the material. And partially melting the recrystallized structure to form free-standing particles in a liquid matrix that behaves thixotropically by raising the temperature of the material above its solidus temperature. A method including a step of
This method comprises heating a deformed material to cause recrystallization of the microstructure of the material, and raising the temperature of the material above its solidus temperature, so to speak 2.
The heating which should be called stepwise heating is performed. Although such a method can be said to be an improved technique as compared with the conventional technique, it still requires two steps of heating, and has a problem that the process is complicated and heating control is difficult.

The present invention solves the above-mentioned drawbacks of the prior art,
It is an object of the present invention to provide a method for manufacturing a semi-molten cast billet of an aluminum alloy for transportation equipment, which has a simple process, can promote cost reduction, and has a homogeneous product.

[0006]

In order to achieve the above object, a method for producing a semi-molten cast billet of an aluminum alloy for transportation equipment of the present invention is Zn 3.5 to 7.5 wt%, Mg.
0.50 to 4.0 wt%, Si 0.50 wt% or less, F
e 0.55 wt% or less and Ti 0.001 to 0.50 w
t% and B 0.0001 to 0.5 wt% of at least 1
Species or more, Cu 0.30 to 3.0 wt%, Mn 0.03
~ 0.80wt%, Zr0.03-0.35wt%, C
r0.03 to 0.35 wt% and V0.03 to 0.2w
At least one of t% is included, and the balance is substantially composed of Al, and the dendrite branch spacing is 200 μm.
The following aluminum alloy is manufactured and then strain rate 5
˜50%, processing introduction speed 50 mm / sec. At a temperature below the recrystallization temperature, a working strain is introduced by cold die forging, and then the temperature is raised to above the solidus temperature to obtain a liquid phase ratio of 20 to 8
This is a method of holding at a temperature of 0% and performing semi-melt processing.

[0007] In this case, in order to homogenize the segregation of the components and release the casting stress, 400-
It is preferable to perform the homogenization treatment at a temperature of 520 ° C. for 1 to 24 hours.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Various reasons for limiting numerical values such as limiting the numerical values of the amounts of aluminum alloy components used in the present invention will be described in detail below.

When the Zn component coexists with the Mg component, it contributes to the improvement of mechanical properties and machinability.
If it is less than 5 wt%, the effect is small, while on the other hand, 7.5 wt%
If it exceeds the range, the cold forgeability deteriorates and the corrosion resistance deteriorates, so the content was made 3.5 to 7.5 wt%.

The Mg component, when coexisting with the Zn component, contributes to the improvement of mechanical properties, but if it is less than 0.50 wt%, its effect is small, while if it exceeds 4.0 wt%, cold forgeability is poor. 0.50 to 4.0 wt because it gets worse
%.

If the amount of the Si component exceeds 0.50 wt%, the elongation and toughness deteriorate and the cold forgeability deteriorates, so the content was made 0.50 wt% or less.

The Fe component forms an intermetallic compound with the Al component, and if it is contained in a large amount, it becomes an Al-Fe-Si type compound, which adversely affects elongation, toughness and corrosion resistance.
It was set to t% or less.

The Ti component refines the structure of the ingot and prevents the occurrence of ingot cracking. However, if it is less than 0.001 wt%, its effect is small, while if it exceeds 0.5 wt%, TiAl.
_{3 It} promotes the generation of huge crystallized substances, leading to cracking during cold forging and deterioration of mechanical properties of transportation equipment parts.
It was set to 0.001 to 0.5 wt%.

The B component, together with the Ti component, refines the structure of the ingot and prevents the occurrence of ingot cracks.
If it is less than t%, the effect is small, while if it exceeds 0.5% by weight, cracking during cold forging and deterioration of mechanical properties of parts for transportation equipment are caused, so 0.0001 to 0.5% by weight is set.

The Cu component improves not only mechanical properties but also stress corrosion cracking resistance and fatigue resistance.
If it is less than 0.30 wt%, the effect is small, while it is 3.0.
If it exceeds 0.3 wt%, cracking during cold forging and deterioration of corrosion resistance will occur, so the content was made 0.30 to 3.0 wt%.

The Mn component improves not only mechanical properties by suppressing recrystallization and refining recrystallized grains but also improving stress corrosion cracking resistance and fatigue resistance, but if it is less than 0.03 wt%, The effect is small, while on the other hand, if it exceeds 0.80 wt%, the ductility will decrease, so 0.03 to 0.80 wt%
And

The Cr, Zr, and V components suppress the refinement or recrystallization of recrystallized grains similarly to the Mn component, improve strength, elongation, and toughness, and at the same time contribute to the improvement of stress corrosion cracking resistance. Cr less than 0.03 wt%, Zr 0.03 wt
%, Less than V0.03 wt%, the effect is small,
Cr 0.35 wt%, Zr 0.35 wt%, V0.2w
If it exceeds t%, ductility is adversely affected.
Cr 0.03 to 0.35 wt%, Zr 0.03 to 0.3
5 wt% and V0.03-0.2 wt%.

The dendrite branch spacing (DAS) is 200μ
Although the billet having a diameter of m or less is cast, if the dendrite branch spacing (DAS) exceeds 200 μm, it becomes difficult to make the primary α (Al) phase into a uniform fine spheroid when heated to the semi-melting temperature range, and the homogeneous When the homogenization treatment is performed, it takes time to perform the homogenization treatment, so the dendrite branch interval (DAS) is set to 20
It was set to 0 μm or less.

By homogenizing the billet obtained by casting, MgZn ₂ crystallized at the grain boundaries during casting,
Crystallized substances such as MgSi _{2 form a} solid solution in the matrix. When the homogenization treatment temperature is lower than 400 ° C. or the heating time is shorter than 1 hour, solid solution cannot be sufficiently obtained and casting strain is not sufficiently removed. However, at a processing temperature higher than 520 ° C., eutectic melting occurs and the workability during forging is impaired. Further, when the heating time exceeds 24 hours, the effect of homogenization corresponding to the long heating time is not increased, and the heating energy is lost.
Therefore, the homogenization treatment condition was heating at a temperature of 400 to 520 ° C. for 1 to 24 hours.

Next, the working strain is introduced by cold forging so that the process can be simplified and the strain can be effectively introduced with a small working rate, and the strain is uniformly introduced to the entire forging billet. The frame is forged so that The distortion rate is
If it is less than 5%, the introduction of strain is small, and even if the temperature is raised to the semi-melting temperature range, the primary spheroidal α (Al) phase cannot be made uniform spheroidization, while if it exceeds 50%, the primary crystal α (Al) is spheroidized. The phase size does not change, and cracks occur during cold forging, so the content was set to 5 to 50%. The strain rate here is (L ₁ −L ₂ ) / L ₁ × 100 (%) when the original length of the forging billet is L ₁ and the length of the forged billet is L _2.
Defined in.

The processing introduction speed can be greatly increased by adding crystal grain refining and homogenizing treatment to the billet ingot. From the viewpoint of productivity, it is preferable that the processing introduction speed is as fast as possible. However, 50 mm / sec. If it exceeds 50 mm / sec., Cracks may occur during forging, or forging dead zones may occur, and strain may not be uniformly introduced.
Below. Also, the billet temperature during cold formwork forging is
Above the recrystallization temperature, the introduction of strain for a predetermined processing rate was insufficient, and the primary crystal α (Al) phase did not have a granular structure even when the temperature was raised to the semi-melting temperature, so the temperature was set below the recrystallization temperature.

After that, the billet is heated to a temperature above the solidus temperature and held at a temperature at which the liquid phase ratio is 20 to 80% for semi-melt molding, but when the liquid phase ratio is less than 20%, the primary crystal α (Al ) A uniform spheroidization of the phase cannot be achieved, and the deformation resistance of the semi-molten molding is large, making pressure molding difficult. Further, if it exceeds 80%, a molded product having a uniform structure cannot be obtained. Therefore, the liquid phase ratio in the semi-melting temperature range above the solidus temperature is set to 20 to 80%.

[0023]

EXAMPLES Specific examples of the present invention will be described below. FIG. 1 is a schematic view of cold formwork forging used in the method of the present invention. In the figure, reference numeral 1 is a forging die, 2 is a forging die punch, and 3 is an aluminum alloy billet.

Si, Mg, Zn, Fe, Ti, B, C
A molten metal was prepared so that u, Cr, and Zr had the compositions shown in Table 1 below, and an aluminum alloy billet was cast by continuous casting.

[0025]

[Table 1]

The aluminum alloy billets shown in Table 1 were treated under the conditions shown in Table 2 to evaluate the moldability of semi-melt molding and the shape of the primary crystal α (Al) phase after semi-melt molding. Also described in.

[0027]

[Table 2]

With respect to the moldability shown in Table 2 when the processing strain was introduced, the moldability that did not cause cracks when molded under the molding conditions shown in Table 2 was good, and the moldability was good. It was judged by. Regarding the moldability of the semi-melt molding, the good one was evaluated as ◯, and the poor moldability was evaluated as x. Primary crystal α after semi-melt molding
The shape of the (Al) phase was evaluated as ◯ when spheroidization was recognized, and as x when spheroidization was insufficient. In the homogenization of the primary α (Al) phase after semi-melt molding, the primary α (A
l) A phase size of 100 μm or less is defined as ◯, and 100 μm
Those having a size exceeding 0.1 were judged as x.

FIG. 2 shows a photograph of a representative example in which the fine homogenization of the primary crystal α (Al) phase was evaluated as ◯.

[0030]

As described above, according to the method of the present invention, the process can be simplified and the cost can be reduced as compared with the conventional semi-molten billet. Further, the obtained structure is also primary crystal α (Al).
Phase size average 100μm or less and primary crystal α (Al)
It has a uniform spheroidized structure with a phase area ratio of 50% and can be used for transportation equipment such as automobile parts.

[Brief description of drawings]

FIG. 1 is a schematic view of cold formwork forging.

FIG. 2 is a photomicrograph of a typical example in which fine homogenization of primary crystal α (Al) phase is evaluated as ◯, and the magnification is 50 times.

[Explanation of symbols]

1 Forging die 2 Forging die punch 3 Aluminum alloy billet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 681 C22F 1/00 681 682 682 685 685A 691 691B 691C 694 694A (72) Inventor Yasuyuki Murayama 80, Shiyama-cho, Omuta-shi, Kyushu Within Kyushu Mitsui Aluminum Industry Co., Ltd. (72) Inventor Tsuneki Iwashita, F-Term, 80, Yoyama-cho, Omuta-shi, Fukuoka Kyushu Mitsui Aluminum Industry Co., Ltd. (reference) 4E087 AA01 BA04 BA24 CA11 CB03 DB15 GA09 HB17

Claims (2)

[Claims] 1. Zn3.5-7.5 wt%, Mg0.5
0-4.0 wt%, Si 0.50 wt% or less, Fe0.
55 wt% or less, at least one or more of Ti 0.001 to 0.50 wt% and B 0.0001 to 0.5 wt%, Cu 0.30 to 3.0 wt%, Mn 0.03 to 0.
80 wt%, Zr 0.03 to 0.35 wt%, Cr0.
An aluminum alloy containing at least one of 03 to 0.35 wt% and V0.03 to 0.2 wt%, the balance being substantially composed of Al, and having a dendrite branch interval of 200 μm or less, Then distortion rate 5 to 50
%, Processing introduction speed 50 mm / sec. In the following, a working strain was introduced by cold mold forging at a temperature lower than the recrystallization temperature, then the temperature was raised to above the solidus temperature, and the liquid phase ratio was maintained at a temperature of 20 to 80% to maintain a half. A method for producing a semi-molten molded billet of an aluminum alloy for transportation equipment, characterized by performing melt processing. 2. The aluminum alloy for transportation equipment according to claim 1, wherein the aluminum alloy is manufactured and subjected to a homogenizing treatment at a temperature of 400 to 520 ° C. for 1 to 24 hours before introducing a working strain. Method for producing semi-molten molded billet.