JP2003147497A - 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, <=0.20% Cu, <=0.50% Si, 2.0 to 6.0% Mg, <=0.35% Zn, <=0.50% Fe, at least one or more kinds selected from 0.001 to 0.5% Ti and 0.0001 to 0.5% B, and at least one or more kinds selected from 0.05 to 1.5% Mn, 0.03 to 0.35% Zr and 0.03 to 0.40% Cr, 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, and is held at 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-melt molding billet has advantages such as less casting segregation / defects and longer die life than the conventional die casting method. is there. The billet casting method used for this is to perform electromagnetic / mechanical stirring in the semi-melting temperature range in order to make the primary α (Al) phase in the billet stage known as the Pennesey Almax method spherical. (Method A), or a larger amount of A than that normally added during casting
There is a method (method B) of adding 1-Ti-B and raising the temperature to the latter half melting temperature range to make the primary crystal α (Al) phase spherical. 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 manufacturing a semi-molten cast billet of an aluminum alloy for transportation equipment of the present invention is Cu 0.20 wt% or less, Si
0.50 wt% or less, Mg 2.0 to 6.0 wt%, Zn
0.35 wt% or less, Fe 0.50 wt% or less, Ti
0.001-0.5 wt% and B 0.0001-0.5
At least one or more of wt% and Mn 0.05 to 1.5
wt%, Zr 0.03 to 0.35 wt% and Cr 0.0
At least one of 3 to 0.40 wt%,
An aluminum alloy having the balance substantially consisting of Al and having a dendrite branch interval (DAS) of 200 μm or less is manufactured, and then the strain rate is 5 to 50% and the processing introduction speed is 50.
mm / sec. A process strain is introduced by cold mold forging at a temperature lower than the recrystallization temperature below, and then the temperature is raised to above the solidus temperature and maintained at a temperature at which the liquidus rate becomes 20 to 80%. It is a method of melt processing.

In this case, in order to homogenize the segregation of the components and release the casting stress, 450 to 450% before introducing the working strain.
It is preferable to perform the homogenization treatment at a temperature of 550 ° C. for 1 to 10 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.

If the Cu content exceeds 0.20 wt%,
Since the corrosion resistance deteriorates, it was set to 0.20 wt% or less.

If the amount of the Si component exceeds 0.5 wt%, the elongation and toughness deteriorate and the cold forgeability deteriorates, so the Si content was made 0.5 wt% or less.

The Mg component contributes to the improvement of mechanical properties as a solid solution strengthening, the improvement of machinability and the improvement of corrosion resistance, but if it is less than 2.0 wt%, its effect is small, while on the other hand, 6.0 wt% is added. When it exceeds the above range, the oxidation of the molten metal is promoted and casting becomes difficult, so the content was made 2.0 to 6.0 wt%.

Since the Zn component deteriorates the corrosion resistance, it has a .0.
The upper limit was 35 wt%.

The Fe component forms an intermetallic compound with Al. 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, but if it is less than 0.001 wt%, its effect is small, while if it exceeds 0.5 wt%, TiA is produced.
to promote the formation of huge crystallized substance of l _3, and a 0.005 to 0.5% because lowering the mechanical properties of the cracks and transportation equipment components during cold forging.

The B component, together with the Ti component, also refines the structure of the ingot and prevents the occurrence of ingot cracking.
If it is less than 0.5% by weight, the effect is small, and if it exceeds 0.5% by weight, cracking during cold forging and deterioration of mechanical properties of parts for transportation equipment may occur, so the content was made 0.0001 to 0.5% by weight.

The Mn, Cr and Zr components suppress the refinement or recrystallization of recrystallized grains and improve the strength, elongation and toughness. It also contributes to the improvement of corrosion resistance, moldability, and weldability, but Mn is less than 0.05 wt% and Cr is 0.03 wt%.
Less, less than Zr 0.03 wt%, the effect is small,
Mn1.5wt%, Cr0.40wt%, Zr0.35
If the content exceeds Wt%, MnAl ₆ , CrA during forging
Since a coarse intermetallic compound of l ₇ and ZrAl ₃ crystallizes and adversely affects ductility and workability, Mn 0.05 to 1.5 wt
%, Cr 0.03 to 0.4 wt% and Zr 0.03 to
It was set to 0.35 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 a semi-melting temperature range. 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 subjecting the billet obtained by casting to homogenization treatment, Al ₂ Cu crystallized at the grain boundaries during casting,
Crystallized substances such as Mg ₂ Si dissolve in the matrix. When the homogenization treatment temperature is lower than 450 ° C. or the heating time is shorter than 1 hour, sufficient solid solution cannot be obtained and removal of casting strain is insufficient. However, at a processing temperature exceeding 550 ° C., eutectic melting occurs, and the workability during forging is impaired. Further, when the heating time exceeds 10 hours, the effect of homogenization commensurate with the long heating time is not increased and the heating energy is lost. For this reason, the homogenization treatment conditions were heating at a temperature of 450 to 550 ° C. for 1 to 10 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 into the entire casting 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 is not changed, and cracks occur during cold forging, so the content is set to 5 to 50%. The strain rate here is (L ₁ −L ₂ ) / L ₁ × 100 (%), where L ₁ is the original length of the forging billet and L ₂ is the length of the forged billet. Defined.

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. Further, the billet temperature at the time of cold form forging is such that when the recrystallization temperature or higher, the introduction of strain for a predetermined processing rate becomes insufficient, and even if the temperature is raised to the semi-melting temperature, the primary crystal α
Since the (Al) phase does not have a granular structure, 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 ( Although the Al) phase cannot be formed into a uniform sphere, semi-melt molding is performed, but the deformation resistance of the semi-melt molding is large and pressure molding becomes difficult. Also, 8
If it exceeds 0%, 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%.

[0022]

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.

Cu, Si, Mg, Zn, Fe, Ti,
A molten metal was prepared so that each of B, Mn, Cr and Zr had a composition shown in Table 1 below, and an aluminum alloy billet was cast by continuous casting.

[0024]

[Table 1]

The aluminum alloy billets shown in Table 1 above 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.

[0026]

[Table 2]

The moldability shown in Table 2 when the processing strain was introduced was ◯ when the moldability did not cause cracks when molded under the molding conditions shown in Table 2 and the moldability was good, and x when cracks were observed. 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 crystal α (Al) phase after semi-melt molding,
When the size of the (Al) phase is 100 μm or less, it is defined as ◯ and 100
Those having a size exceeding μm 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 ◯.

[0029]

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 front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C22C 21/06 C22C 21/06 C22F 1/00 681 C22F 1/00 681 682 682 685 685A 691 691B 691C 694 694A (72) Inventor Yasuyuki Murayama 80 Yoyama-cho, Omuta-shi, Fukuoka Within Kyushu Mitsui Aluminum Industry Co., Ltd. (72) Inventor Tsuneki Iwashita 80 Yoyama-cho, Omuta-shi, Fukuoka Kyushu Mitsui Aluminum Industry Co., Ltd. Inner F term (reference) 4E087 AA01 BA04 BA14 CA11 CB14 DB15 DB22 HB17

Claims (2)

[Claims] 1. Cu 0.20 wt% or less, Si 0.50
wt% or less, Mg 2.0 to 6.0 wt%, Zn 0.35
wt% or less, Fe 0.50 wt% or less, Ti 0.00
1 to 0.5 wt% and B 0.0001 to 0.5 wt% at least one or more, and Mn 0.05 to 1.5 wt%,
Zr 0.03 to 0.35 wt% and Cr 0.03 to 0.
40 wt% of at least one kind, and the balance is substantially composed of Al, and the dendrite branch interval is 20.
An aluminum alloy having a thickness of 0 μm or less is manufactured, then a strain rate is 5 to 50%, and a processing introduction speed is 50 mm / sec. At the 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, and the liquid phase ratio becomes 2
A method for producing a semi-molten molded billet of an aluminum alloy for transportation equipment, characterized by holding at a temperature of 0 to 80% for semi-melt processing. 2. The aluminum for transportation equipment according to claim 1, wherein the aluminum alloy is produced and subjected to a homogenizing treatment at a temperature of 450 to 550 ° C. for 1 to 10 hours before introducing a working strain. A method for producing a semi-molten cast billet of an alloy.