JP2003239054A - HEAT TREATMENT METHOD FOR PRECIPITATION HARDENING TYPE Al ALLOY - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method for a precipitation hardening type Al alloy with which in applying to a thick member (20-50 μm value of DASII) mechanical properties, particularly, the elongation, can be improved. <P>SOLUTION: This heat treatment method for precipitation hardening type Al alloy, is the one with which the heat treatment is performed to a crude material obtained by casting the precipitation hardening type Al alloy. The heat treatment of the crude material is applied by performing a solution treatment and successively, performing an aging treatment, and the solution treatment is performed at 520-562°C for 50-180 min. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a precipitation hardening type Al.
It relates to a heat treatment method for an alloy.

[0002]

2. Description of the Related Art Aluminum for casting and die casting (A
l) As an alloy, Al-containing a few mass% of Si in Al-
Si-based Al alloys are known, and Al-Si-based Al
Multi-element Al containing alloy as basic composition and other elements
-Si-based alloys are used as casting alloys. This is because fluidity of the molten metal, which is an important property in casting of castings and die castings, mold filling property, etc. are superior to other alloys, casting cracks hardly occur, and they are combined with other elements. The reason is that an alloy with high strength can be obtained, the coefficient of thermal expansion is small, and the wear resistance is good.

For example, a small amount of Mg is added to an Al-Si alloy.
AC4A, AC4 as precipitation hardening alloys containing
C and AC4CH are present, and these alloys precipitate the intermediate phase of Mg ₂ Si by heat treatment of the crude product and enhance the mechanical properties (age hardening by the intermediate phase of Mg ₂ Si). In particular, AC4CH in which Fe is limited to 0.20 mass% or less to enhance toughness is used as a vehicle underbody component (for example, a vehicle wheel) or the like.

As described above, the increase in strength of the precipitation hardening type Al alloy is obtained by the addition of other elements and the age hardening of the intermediate phase by the addition of the other elements. The heat treatment for age hardening is the solution treatment, Consists of aging treatment. The solution treatment is
In this heat treatment, the non-equilibrium phase crystallized during solidification is solidified and the precipitated phase precipitated during cooling is re-solidified to obtain a solid solution having a uniform composition at high temperature. The aging treatment subsequent to the solution treatment is a heat treatment for refining and homogenizing the intermediate precipitation phase and causing precipitation hardening by the intermediate precipitation phase. By these heat treatments, the mechanical properties of the Al alloy are improved.

[0005]

However, when the conventional heat treatment method is applied to a vehicle wheel or the like having a relatively thin wall thickness among vehicle underbody parts, the cooling rate is high, so that the DASII (dendrites) is used. The value of the arm spacing secondary branch distance: center distance between adjacent secondary arms) is less than 20 μm, and although mechanical properties can be sufficiently improved, it was applied to a thick member having a wall thickness of 20 mm or more. In this case, the cooling rate becomes slower, so DAS
The value of II is 20 μm or more (20 ~ 5 for general suspension parts)
0 μm), and the elongation, which is an index of mechanical properties, in particular, the property against static tensile load, is about 3 to 5%, which is not sufficient.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide mechanical properties, particularly mechanical properties when applied to a thick member (having a DASII value of 20 to 50 μm). It is an object of the present invention to provide a heat treatment method for a precipitation hardening type Al alloy capable of improving its elongation.

[0007]

That is, according to the present invention, there is provided the following heat treatment method for a precipitation hardening type Al alloy.

(1) A heat treatment method for a precipitation-hardening Al alloy, comprising heat-treating a crude product formed by casting a precipitation-hardening Al alloy, wherein the heat treatment of the crude product is a solution heat treatment of the crude product, A heat treatment method for a precipitation hardening type Al alloy, characterized in that an aging treatment is carried out, and the solution treatment is carried out at a temperature of 520 to 562 ° C. for 50 to 180 minutes.

(2) The heat treatment method for a precipitation hardening type Al alloy according to the above (1), wherein the temperature rising time to reach the solution treatment temperature is 5 to 20 minutes.

(3) The aging treatment is 160 to 18
The heat treatment method for a precipitation hardening type Al alloy according to the above (1) or (2), which is held at a temperature of 0 ° C. for 2.5 to 6 hours.

(4) The precipitation hardening type A according to any of (1) to (3) above, wherein the solution treatment and the aging treatment are performed by allowing the crude product to exist in a fluidized bed.
1 Heat treatment method for alloy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The precipitation hardening type Al of the present invention will be described below.
The heat treatment method for the alloy will be specifically described.

The precipitation hardness that is the subject of the heat treatment method of the present invention
The chemical conversion Al alloy is not particularly limited, but, for example,
For example, Al-Si-based Al containing a few mass% of Si in Al
A precipitation hardening alloy in which a small amount of Mg is added to the alloy, A
C4A, AC4C, AC4CH, etc. are mentioned. these
The alloy of₂Si intermediate phase
That can be deposited and enhance its mechanical properties.
Yes (Mg ₂Age hardening by the intermediate phase of Si).

The crude product which is the object of the heat treatment method of the present invention is preferably a thick member having a wall thickness of 20 mm or more (DASII value is 20 to 50 μm). This is because the heat treatment method of the present invention can sufficiently improve the mechanical properties of such a thick member, particularly the elongation, which is an index of the properties with respect to a static tensile load.

The above-mentioned crude product is preferably cast by the following method. First, the above-mentioned precipitation hardening type Al
The alloy is melted into a molten metal, the molten metal is poured into a mold, the mold is cooled, and the molten metal is made into a crude product. In this case, it is preferable that the mold is cooled with water. Since the thick member requires time to be cooled, when cooling the mold by air cooling, the metal structure may become large and mechanical properties may deteriorate, but the mold is rapidly cooled by water cooling. By cooling
The metal structure becomes dense, and the mechanical properties of the crude product can be improved.

As a casting method in the present invention, it is preferable to use a horizontal stationary casting method and to inject a molten metal without moving the mold with the mold splitting surface of the mold arranged in the horizontal direction. This horizontal stationary casting method is a method of arranging a hanging weir on a sprue provided on a horizontal mold split surface of a mold. The horizontal stationary casting method is used
By injecting the molten metal into the mold by injecting it into the mold, the molten metal can be gently injected into the mold, and since the oxide removal net is easy to arrange, impurities such as oxides can be removed. This is because it was judged to be preferable in that a crude product having high mechanical properties without being mixed in the crude product can be obtained. Needless to say, casting can be performed by a tilt pouring method or a low pressure casting method.

Generally, the heat treatment of the crude product is performed by subjecting the crude product to a solution treatment, followed by quenching and then aging treatment. In the present invention, the solution treatment is performed at 520 to 520. It is preferable to hold at a temperature of 562 ° C. for 50 to 180 minutes. And, it is preferable that the temperature rising time from room temperature to the temperature of the solution treatment is 5 to 20 minutes, and the aging treatment is 160 to
It is preferable to keep the temperature at 180 ° C. for 2.5 to 6 hours. Under these conditions, the eutectic structure can be made spherical and the eutectic structure can be prevented from coarsening.
As a result, the mechanical properties of the thick cast product obtained, in particular the elongation, are improved.

The solution treatment and the aging treatment described above are preferably performed by allowing the crude product to exist in the fluidized bed. The fluidized bed is formed by granules such as powder particles being heated by a blowing gas and uniformly mixed, and has a characteristic that the temperature inside the fluidized bed is substantially uniform and the heat transfer efficiency is good. There is. By uniformizing the temperature inside the fluidized bed (about ± 2 to 3 ° C), solution treatment at a higher temperature becomes possible, and heat transfer efficiency is good, so the temperature rises from room temperature to the solution treatment temperature. The time can be shortened. These characteristics are a great advantage over the conventional atmospheric furnace using air as a heat medium.

The fluidized bed system is generally based on a container heating system in which the fluidized bed container is heated from the outside, an indirect heating system such as a radiant tube system in which a radiant tube is built in the fluidized bed, and a direct blowing of hot air. A direct heating method is known, and any method can be applied. However, it is preferable to form the fluidized bed by a direct heating method by direct blowing of hot air because the temperature distribution in the fluidized bed becomes good.

Next, the heat treatment method of the present invention will be described more specifically with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a hot-air direct blowing type fluidized bed used in the present invention.
Reference numeral 10 denotes a container. In the container 10, a granular material 12 such as a powder or granular material is filled on a perforated plate 16, and the granular material 12 is fluidized by a hot air 14 blown from under the perforated plate 16 to be uniform. To form the fluidized bed 18.

FIG. 2 is a schematic view showing an example of a fluidized bed furnace used in the heat treatment method of the present invention. In FIG.
Reference numeral 20 is a hot air generator, and air sent from a blower (not shown) is 700 to 8 due to the flame from the burner 22.
It can be warmed up to hot air of 00 ℃. This hot air is blown into the fluidized bed furnace 26 via the hot air temperature monitoring device 24. In the fluidized bed furnace 26, hot air flows from the perforated pipe 28 to the fluidized bed 30.
The particles 32 are blown in to fluidize the particles 32 and heat the particles 32. In this way, the inside of the fluidized bed 30 is heated, and the fluctuation range of the temperature inside the furnace is about 6 ° C. (± 3
(° C), the fluctuation of temperature at one point is about 3 ° C, the uniformity of the temperature in the furnace is achieved, and the crude product 34 existing in the fluidized bed 30 is rapidly heated. Reference numeral 36 denotes a particulate matter discharge valve, which appropriately discharges the particulate matter 32 to the outside. Such a fluidized bed furnace 26 can be used for both solution treatment and aging treatment.

The thick cast product obtained by the heat treatment method of the present invention has improved mechanical properties such as a tensile strength of 280 MPa or more and a 0.2% proof stress of 220 MPa or more, and particularly its elongation is 8 to 12 % Is excellent. The mechanical properties such as tensile strength, 0.2% proof stress, and elongation of the thick cast product are obtained according to the test method specified in JIS Z2201.

[0023]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples. (Example) As a precipitation hardening type Al alloy used as a casting raw material, 0.02 mass% of Cu, 7.2 mass% of Si, and Mg
Is 0.31% by mass, Fe is 0.15% by mass, and Ti is 0.
1 mass%, Mn 0.01 mass%, Ni 0.0052
Mass%, 0.01 mass% Zn, 0.003 mass% Sr, 0.0005 mass% Ca, balance Al
C4CH was used.

The object to be cast was a vehicle underbody part having a wall thickness of 20 mm. As a casting method, the above precipitation hardening Al alloy was injected into the mold by a horizontal stationary casting method, and further, the above precipitation hardening Al alloy was injected into the weir. Then, the mold was cooled by water cooling.
By doing so, a crude product of vehicle underbody parts was obtained (the value of DASII was 30 to 40 μm).

Next, the above-mentioned crude product was heat-treated using a fluidized bed furnace. The fluidized bed furnace shown in FIG. 2 was used for solution treatment and aging treatment. Fluidized bed furnace has an inner diameter of 1500 mm ×
It has a rectangular tank shape of 1500 mm and a straight body height of 7
The fluidized-bed container is 50 mm in diameter, and the lower part is in the shape of an inverted quadrangular prism. As the granular material, the average particle diameter is 50 to 500 μ.
m sand was used.

As heat treatment conditions, the solution treatment is 55
The temperature is maintained at 0 ° C (± 3 ° C) for 3 hours, and the temperature rise time from room temperature to the solution treatment temperature is 2
It was set to 0 minutes. In addition, the aging treatment was to hold at a temperature of 160 ° C. (± 3 ° C.) for 3 hours. Test pieces were taken from the heat-treated underbody parts for vehicles and subjected to a tensile test (tensile strength, 0.2% proof stress, elongation).

(Results) The underbody parts for vehicles obtained in the examples have improved mechanical properties such as a tensile strength of 280 MPa or more and a 0.2% proof stress of 220 MPa or more. It was excellent at 12%.

[0028]

EFFECTS OF THE INVENTION As described above, the heat treatment method of the present invention can improve mechanical properties, particularly elongation thereof, when applied to a thick member.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a hot air direct blowing type fluidized bed used in the present invention.

FIG. 2 is a schematic view showing an example of a fluidized bed type solution treatment furnace used in the present invention.

[Explanation of symbols]

10 ... Container, 12 ... Granular material, 14 ... Hot air, 16 ... Perforated plate, 18 ... Fluidized bed, 20 ... Hot air generator, 22 ... Burner, 24 ... Hot air temperature monitoring device, 26 ... Fluidized bed furnace, 28 ...
Perforated pipe, 30 ... Fluidized bed, 32 ... Granular material, 34 ... Crude product, 36 ... Valve for discharging granular material.

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Claims (4)

[Claims] 1. A heat treatment method for a precipitation-hardening Al alloy, comprising heat-treating a crude product obtained by casting a precipitation-hardening Al alloy, wherein the heat treatment of the crude product is a solution heat treatment of the crude product and then an aging treatment. The solution treatment is performed at a temperature of 520 to 562 ° C. for 50 to 1
A heat treatment method for a precipitation hardening type Al alloy, characterized in that it is held for 80 minutes. 2. The heat treatment method for a precipitation hardening type Al alloy according to claim 1, wherein the temperature rising time until the temperature of the solution heat treatment is reached is 5 to 20 minutes. 3. The aging treatment according to claim 1, wherein the aging treatment is performed at a temperature of 160 to 180 ° C. for 2.5 to 6 hours.
The heat treatment method for the precipitation hardening type Al alloy according to. 4. The heat treatment method for a precipitation hardenable Al alloy according to claim 1, wherein the solution heat treatment and the aging treatment are performed by allowing the crude product to exist in a fluidized bed.