JP2002275567A - PRECIPITATION-HARDENING Al ALLOY, AND METHOD OF HEAT TREATMENT FOR PRECIPITATION-HARDENING ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precipitation-hardening Al alloy having well-balanced three properties, tensile strength, proof stress and elongation and also to provide a method for heat-treating precipitation-hardening alloys by which solution treatment can be performed at higher temperature while shortening temperature- rise time and reducing temperature deflection. SOLUTION: The precipitation-hardening Al alloy is obtained by heat-treating an Al alloy having forming strain and has a structure in which recrystallized grains and subgrains are formed and further has three characteristics of: >=320 MPa tensile strength, >=220 MPa 0.2% proof stress, and >=19% elongation; or >=350 MPa tensile strength, >=300 MPa 0.2% proof stress, and >=15% elongation. In the method for heat-treating the precipitation-hardening alloys, the precipitation-hardening alloys including the above Al alloy are subjected to solution treatment using a fluidized bed for <=60 min at a holding temperature ranging between a temperature lower by 10 deg.C and a temperature higher by 5 deg.C than the melting temperature of the alloy as the object to be heat-treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to, for example, cold working, that is, plastic deformation at or below the recrystallization temperature, or plastic deformation in an extremely short time even at or above the recrystallization temperature, Precipitation hardening type A in which recrystallized grains and sub-crystal grains are formed, obtained by heat-treating an Al alloy that has been subjected to processing strain and allowing recrystallization to proceed.
The present invention relates to a method for heat-treating a precipitation hardening alloy including an aluminum alloy and a precipitation hardening Al alloy.

[0002]

2. Description of the Related Art It is said that global warming, which is one of the global environmental problems, is greatly affected by carbon dioxide generated by all human activities, and it is necessary to reduce carbon dioxide emitted directly from factories and power plants. There is a strong global demand for reduction of automobile fuel consumption, which leads to carbon dioxide emission. Among them, measures to improve fuel efficiency of automobiles include using new power sources such as fuel cells, natural gas, and electricity, or
The combined use of these technologies, or the technical improvement of motor systems such as lean fuel engines and direct injection engines, as well as the reduction of power transmission systems and the reduction of running resistance by improving the body shape, are the most effective. Means that can be applied in combination with any other technology is to reduce vehicle weight.

[0003] Techniques for reducing the weight of automobiles are broadly classified into structural design techniques and material techniques, but changing the materials used is a more lightweight approach than tackling drastic improvements in vehicle body structures and components. . Examples of the lightening material include an aluminum (Al) alloy, a magnesium (Mg) alloy, a titanium (Ti) alloy, and the like. Inexpensive Al alloy
Already used as parts for automobiles and the like. For example, Al alloy castings are often used for engine cylinder heads, engine cylinder blocks, and the like, and forged parts of Al alloys are often used for underbody parts that require higher strength.

[0004] Recently, there has been an increasing demand for lighter weight of underbody parts, and it has been desired to provide products that have higher mechanical strength and can be made thinner. In particular,
Damage to undercarriage components directly leads to important safety issues, and there is a need for products having mechanical properties that combine strength and ductility.

By the way, generally, an Al alloy is heated,
By performing cooling, it is possible to change mechanical properties such as tensile strength and elongation. This is because the Al alloy is A
1 is an alloy obtained by adding Mg, Si (silicon), Cu (copper), Cr (chromium), etc., to form a solid solution in Al by heat treatment or to react with Al to form an intermediate phase. This is realized because the amount of various metals changes.

For example, as an Al alloy for forging, Al
Al-Mg-Si-based Al alloys containing several mass% of Mg and Si are known. The basic composition is an Al-Mg-Si-based Al alloy, and other elements such as Cu, Cr, etc. The contained multi-element Al-Mg-Si alloy is used as an alloy for forging. This means that the extensibility, ductility, toughness, corrosion resistance, etc., which are important properties in forging, are superior to other alloys, and that high strength alloys can be obtained by combining with other elements, This is because the thermal expansion coefficient is small and the wear resistance is good.

[0007] These Al alloys are mainly composed of Mg ₂ Si
Is a precipitation hardening type Al alloy whose strength is enhanced by a heat treatment effect by precipitation of an intermediate phase. Further, an alloy obtained by adding a small amount of Cu and Cr to an Al-Mg-Si alloy is also used. For example, as an effect of adding Cu, in addition to precipitation hardening due to the intermediate phase of Mg ₂ Si, The precipitation hardening by the intermediate phase of Al ₂ Cu, the solid solution hardening of Cu, and the like can improve the strength.

[0008] Precipitation effect type Al by such heat treatment
The strengthening of the alloy is obtained by the addition of other elements and the aging precipitation of the intermediate phase due to the addition of the other elements. The heat treatment for the aging precipitation comprises a solution treatment and an aging treatment. The solution treatment is a heat treatment in which a solute atom such as a non-equilibrium crystallization phase crystallized at the time of solidification at a high temperature is solid-dissolved and then rapidly cooled to obtain a solid solution in which the solute atom is dissolved in the matrix at room temperature. It is. The aging treatment subsequent to the solution treatment causes precipitation hardening due to the intermediate precipitation phase, and the heat treatment can improve the mechanical properties of the Al alloy.

Conventionally, as such a solution treatment and an aging treatment of an Al alloy, an atmosphere furnace such as a tunnel furnace using air as a heat medium has been used. Alternatively, there is a problem that the solution treatment at a higher temperature cannot be performed because the temperature fluctuation is as large as about ± 5 ° C. even if the fluctuation is small.

[0010] Also, as an Al alloy, conventionally, as described above, Al-containing several mass% of Mg and Si in Al is used.
Although an Mg-Si based forging Al alloy is used, the upper limit of the mechanical properties is that the tensile strength is about 33%.
The 0 MPa, 0.2% proof stress was about 300 MPa, and the elongation at this time was about 18%. Further, in the treatment such as changing the aging treatment temperature, the elongation is reduced if the strength is to be further increased, and the strength is reduced if the elongation is to be further improved. Was.

With respect to Al alloys used for undercar parts for automobiles, if the mechanical properties such as tensile strength, 0.2% proof stress and elongation are well-balanced and further improved, the thinner, that is, the lighter the weight. It is possible to reduce the weight of the vehicle as a whole, which contributes not only to improved fuel efficiency but also to improved driving stability, which is extremely preferable.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object the three mechanical properties of tensile strength, proof stress, and elongation. An object of the present invention is to provide a precipitation-hardened Al alloy having a good balance. Another object of the present invention is to provide a precipitation-hardening alloy including the above-described precipitation-hardening Al alloy, which can increase the temperature rising time, reduce the temperature fluctuation, and perform the solution treatment at a higher temperature. To provide a heat treatment method.

[0013]

That is, according to the present invention, first, a precipitation hardening type Al obtained by heat-treating an Al alloy having a work strain and having recrystallized grains and subcrystal grains formed therein.
Alloy with tensile strength of 320MPa or more, 0.2%
A first precipitation hardening type Al alloy characterized by a proof stress of 220 MPa or more and an elongation of 19% or more, and an Al alloy having a work strain are obtained by heat treatment, and recrystallized grains and subcrystal grains are obtained. A formed precipitation hardening type Al alloy,
Tensile strength is 350MPa or more, 0.2% proof stress is 300M
A second precipitation hardening type Al alloy having a Pa or more and an elongation of 15% or more is provided.

First and second precipitation hardening type Al of the present invention
The alloy preferably contains 0.4 to 1.2% by mass of Mg and 0.2 to 1.3% by mass of Si. Further, 0.10 to 0.40% by mass of Cu and 0.35% of Cr
It is also preferable that the content is not more than mass%. Also, the first of the present invention
The working strain in the second precipitation hardening type Al alloy is preferably given by cold working.

First and second precipitation hardening type Al of the present invention
The alloy is obtained by heat-treating an Al alloy having a working strain. This heat treatment includes a solution treatment and an aging treatment.
The heat treatment is preferably performed at a holding temperature of −10 ° C. to + 5 ° C. from the melting point of the alloy, and the solution treatment is performed within 60 minutes including a heating time and a holding time. It is preferable that the temperature rise time in the chemical treatment be performed within 20 minutes.

The above-mentioned solution treatment is preferably performed by causing an Al alloy to be heat-treated to be present in a fluidized bed. The aging treatment performed subsequent to the solution treatment is also preferably performed by causing the Al alloy to be heat-treated to be present in the fluidized bed. This fluidized bed is preferably formed by direct blowing of hot air.

First and second precipitation hardening type Al of the present invention
Since the alloy has both tensile strength and elongation, it is suitably used as underbody parts for vehicles such as automobiles.

Next, in the present invention, a heat treatment of a precipitation hardening type alloy for improving the mechanical properties of a workpiece by subjecting a workpiece made of an alloy having a work strain to a solution treatment and then performing an aging treatment. A method for heat treating a precipitation hardenable alloy, wherein a holding temperature in a solution treatment is −10 ° C. to + 5 ° C. from a melting point of a workpiece. At this time, the solution heat treatment time includes the temperature rise time and the holding time, and is preferably 60 minutes or less, and it is preferable to perform rapid temperature rise in which the solution heat treatment time is 20 minutes or less. .

In the heat treatment method for a precipitation hardening alloy according to the present invention, at least the solution treatment is preferably performed by causing the work piece to be present in the fluidized bed. It is also preferable that the reaction be carried out by allowing the compound to be present in the reaction. This fluidized bed is preferably formed by direct blowing of hot air.

As the above-mentioned precipitation hardening type alloy, a precipitation hardening type Al alloy containing 0.4 to 1.2% by mass of Mg and 0.2 to 1.3% by mass of Si can be mentioned. When heat-treating the precipitation hardening type Al alloy, the solution treatment temperature is preferably set to 540 to 562 ° C,
In the solution treatment, the solid solution rate of Mg and / or Si in the α phase is preferably set to 60% or more. In the case where the precipitation hardening type Al alloy is heat-treated, the aging treatment temperature is preferably 150 ° C to 200 ° C.

The precipitation hardening type Al thus heat-treated
A workpiece made of an alloy has both tensile strength and elongation, and thus can be suitably used as a vehicle underbody part.

[0022]

Hereinafter, embodiments of the present invention will be described in detail. However, it goes without saying that the present invention is not limited to the following embodiments.

The precipitation hardening type Al alloy of the present invention is obtained by heat-treating an Al alloy having a work strain, and has a precipitation hardening type having recrystallized grains and subcrystal grains formed in the course of recrystallization. It is an Al alloy having mechanical properties such as tensile strength, 0.2% proof stress, and elongation of a predetermined value or more. The precipitation hardening type Al alloy according to the present invention has a first precipitation hardening type Al alloy which is more improved in elongation and a second precipitation hardening type A which is more improved in tensile strength and 0.2% proof stress.
1 alloy. Specifically, the first precipitation hardening type Al alloy with further improved elongation has a tensile strength of 320 MPa.
a, a 0.2% proof stress of 220 MPa or more, and an elongation of 19% or more. In addition, the second precipitation hardening type Al alloy, which has improved tensile strength and 0.2% proof stress, has a tensile strength of 350 MPa or more and a 0.2% proof stress of 30%.
It shows 0 MPa or more and elongation of 15% or more. Note that the term “precipitation hardening type Al alloy” of the present invention simply refers to both the first precipitation hardening type Al alloy and the second precipitation hardening type Al alloy described above.

An Al alloy having a work strain is a state having a high internal energy, and recrystallization, which is a phenomenon that replaces the original crystal grains even when the generation and growth of a new crystal without the internal strain starts, may occur. It means Al alloy. For example, it is a cold-worked Al alloy that is plastically worked in a very short time even at a recrystallization start temperature or lower or at a recrystallization temperature or higher. The recrystallization initiation temperature varies depending on the metal, but is approximately 200 ° C. for an Al alloy. In general, as recrystallization proceeds, strength and hardness decrease, the material softens, and elongation increases. The present invention is directed to a precipitation hardening type Al alloy having such a processing strain.

The first precipitation hardening type Al alloy according to the present invention has an elongation of 19% or more, preferably 23% or more. It has such a large elongation and has a tensile strength of at least 320 MPa, preferably at least 330 MPa. The 0.2% proof stress is 220 MPa or more, and preferably 230 MPa or more. Further, the second precipitation hardening type Al alloy according to the present invention has a tensile strength of 350 MPa or more, preferably 355 MPa or more, and a 0.2% proof stress of 300 MPa or more, preferably 310 MPa or more. It has such high tensile strength and 0.2% proof stress, and elongation is 15% or more, preferably 16% or more. Here, the tensile strength of the Al alloy, 0.2% proof stress,
And the mechanical properties of elongation are based on Japanese Industrial Standard Z2201.
It was determined according to the test method specified in.

The first and second precipitation hardening type Al alloys of the present invention, having the above-mentioned predetermined mechanical properties,
Its composition is based on Al and Mg is 0.4-1.
Preferably, it contains 2% by mass and 0.2 to 1.3% by mass of Si. Further, Cu is 0.10 to 0.4.
0 mass%, containing 0.35 mass% or less of Cr,
More preferred.

By containing Mg, Si
And precipitated in the matrix as Mg ₂ Si,
It is an element that improves mechanical strength such as elongation, tensile strength, and proof stress. However, if the amount is too large, the improvement in strength not only reaches a plateau, but if it is too large, the solid solubility decreases, leading to a decrease in mechanical properties, which is not preferable.

By containing Si, Mg
Precipitates as Mg ₂ Si when mixed with elongation, tensile strength,
Although it is an element that also contributes to the improvement of mechanical strength such as proof stress,
If it is added too much, the eutectic Si structure is crystallized, resulting in a decrease in mechanical strength such as tensile strength. If Si is less than 0.2% by mass, the effect of precipitating Mg ₂ Si is not sufficient and mechanical strength cannot be improved. If it is more than 1.3% by mass, the eutectic Si structure increases. This is not preferred because the strength and ductility tend to decrease.

Cu is an element that can improve the strength by containing Cu. In a forged product containing Cu, Al-Cu or Al-Cu-Mg-based precipitates expressed by a so-called aging treatment can be obtained by T6 heat treatment. _The strength is improved by promoting the strength improving action of 2Si. However, considering the application to products in which corrosion resistance is of paramount importance, such as undercarriage parts for vehicles such as automobiles, the addition of Cu deteriorates the corrosion resistance. It is. If Cu is less than 0.10% by mass, it does not contribute to the improvement of the strength, which is not preferable. If it is more than 0.40% by mass, the corrosion resistance is reduced, and the strength cannot be maintained for a long time due to intergranular corrosion and the like. It is not preferable.

Cr is an element that, when contained, suppresses the recrystallization of the aluminum alloy and the growth of crystal grains. As a result, the structure in the aluminum alloy is maintained fine, and the strength is maintained. For example, when applied to underbody parts for vehicles such as automobiles, it is necessary to maintain mechanical strength such as elongation, tensile strength, and proof stress for a long period of time. Therefore, it is preferable to contain a small amount of Cr.

[0031] The Al alloy of the present invention is
_{This is} a precipitation hardening type alloy in which an intermediate phase such as a 2Si phase is precipitated. The mechanical properties such as tensile strength, 0.2% proof stress and elongation are superior to specified values or more, and the three properties are well-balanced, making them extremely effective as underbody parts for vehicles such as automobiles. Can be used for According to Japanese Industrial Standards, for example, A6061 alloy is Si0.4
0.8 mass%, Fe 0.7 mass% or less, Mg 0.8
1.2 mass%, Cu 0.15 to 0.4 mass%, Cr0.
04 to 0.35% by mass, the balance being Al. Therefore, as long as the above composition of the present invention is satisfied and the heat treatment described below is performed,
It can be said that this is an effective Al alloy.

Next, the precipitation hardening type Al alloy of the present invention having the above-mentioned mechanical properties and composition can be manufactured by the following heat treatment method. First, a work piece of an Al alloy manufactured by a normal manufacturing method is shown in FIG.
In the schedule shown in FIG. 1, after the temperature is raised and maintained at a predetermined temperature to perform a solution treatment, generally, it is rapidly cooled, and then the temperature is raised again to maintain the predetermined temperature and perform an aging treatment.
By performing these treatments on the work piece, the mechanical properties of the Al alloy can be improved so that the work piece can be applied to a desired use such as a vehicle underbody part even if the work piece is made thinner.

In the present invention, in the solution treatment, the workpiece is rapidly heated to the solution treatment temperature in a short time of 20 minutes or less, and thereafter, is maintained at the solution treatment temperature. Solution treatment within one hour. At this time, it is important to perform the heat treatment while maintaining a high temperature of −10 ° C. to + 5 ° C. from the melting point of the alloy constituting the workpiece to be heat-treated. In the case where the solution treatment is performed in a very short time of 1 hour or less including the heating time, even if the heat treatment is performed at a temperature higher than the melting point temperature of the alloy, the alloy does not immediately melt. As a result of treating at a higher solution treatment temperature, the solution treatment can solidify the non-equilibrium phase crystallized at the time of solidification more, in a short time, and harden by aging after the solution treatment, that is, The precipitation hardening is further promoted, and the strength such as tensile strength and 0.2% proof stress can be greatly improved. This means that hardness and strength are improved, but on the other hand, ductility is reduced.

However, the work piece to be heat-treated in the present invention is an alloy having a processing strain and a high internal energy, and is an alloy in which recrystallization has progressed further. Recrystallization is a phenomenon in which, for example, when a metal with internal strain is heated by cold working or the like, the generation and growth of a new crystal without internal strain starts and replaces the original crystal grains. Proceeding, if the whole is replaced with new crystal grains, ductility is improved by releasing strain. As described above, in the present invention, since the solution treatment is performed at a higher temperature and in a shorter time, the recrystallization proceeds more rapidly. Therefore, the decrease in ductility caused by the solution hardening and the precipitation hardening is compensated for, and the tensile strength caused by the solution hardening and the precipitation hardening is set to 0.1.
An alloy having more excellent elongation can be obtained without impairing the effect of improving the 2% proof stress.

The above heat treatment does not limit the metal to be heat treated to an Al alloy. If the metal is a metal having a high internal energy that is strained by cold working or the like and has a precipitation effect, the tensile strength, 0.2% proof stress, And it is possible to improve the three mechanical properties of elongation in a well-balanced and high level.

The melting point temperature varies depending on the metal, but is, for example, about 557 ° C. for an Al—Mg—Si alloy. Therefore, when heat-treating an Al-Mg-Si precipitation hardening type Al alloy, the solution treatment temperature is set to 547-5.
It is preferable that the temperature is raised to 62 ° C. in a few minutes to 20 minutes, and that the total solution treatment time is within 1 hour. By forming a solution at a high temperature around the melting point, solid solution progresses. More specifically, the solid solution rate of Mg and / or Si in the α phase is 6%.
It can be 0% or more. As a result, the resulting Al
The strength of the alloy is greatly improved.

In the solution treatment in the heat treatment of the present invention, it is sufficient that the work piece can be rapidly heated, and the method is not particularly limited. That is, the temperature of the atmosphere may be controlled so that the workpiece can be rapidly heated,
For example, high-frequency heating, low-frequency heating, and far-infrared heating can be applied, but rapid heating using a fluidized bed is more preferable.

The rapid heating by the fluidized bed is performed by allowing the workpiece to be present in the fluidized bed. The fluidized bed is heated by a blown gas to a granular material such as a granular material, and
It is formed by being uniformly mixed, and has a feature that the temperature inside the fluidized bed is substantially uniform and the heat transfer efficiency is good. The present invention utilizes the characteristics of the fluidized bed in the solution treatment of a workpiece, and achieves a uniform temperature (about ± 2 to 3 ° C.) inside the fluidized bed at a higher temperature around the melting point. And the heat transfer efficiency is high, so that the time required to raise the temperature to the solution treatment temperature can be shortened. These features are a great advantage over a conventional atmosphere furnace using air as a heating medium.

After the workpiece is subjected to solution treatment, it is rapidly cooled to return to room temperature, and then subjected to aging treatment. The specific method of the aging treatment is not particularly limited, and a conventional atmosphere furnace (tunnel furnace) using air as a heat medium can be used. However, similarly to the solution treatment, a fluidized bed can be used. More preferred. This is because, in addition to shortening the aging treatment time, when using a fluidized bed for the solution treatment, it is preferable to use the same fluidized bed from the viewpoint of control and operation of the entire process. In addition, fluidized bed systems are generally indirect heating systems such as a container heating system in which a fluidized bed container is heated from the outside, a radiant tube system in which a radiant tube is built in a fluidized bed, and a direct heating system by direct blowing of hot air. Although any method can be applied, it is preferable to form the fluidized bed by a direct heating method by direct blowing of hot air, since the temperature distribution in the fluidized bed becomes good.

Next, the processing conditions of the heat treatment method of the present invention will be described by taking as an example the case of heat-treating an Al—Mg—Si-based alloy. First, in the solution treatment of the workpiece, the temperature is raised to 540 to 562 ° C. in about 5 to 20 minutes, and the temperature is raised for several minutes to 40 minutes, preferably within 1 hour in total of the temperature raising and holding. To process. The solution treatment temperature is more preferably 547 to 562 ° C. Next, the workpiece is rapidly cooled and cooled to room temperature. Next, the workpiece is aged, and the aging process takes 150 to 20 minutes in a few minutes.
It is preferable to raise the temperature to 0 ° C. and hold at that temperature for several tens of minutes to several hours. The aging treatment temperature is more preferably 170 to 190 ° C. in order to improve the productivity by shortening the time.

Next, the heat treatment method of the present invention will be described in more detail with reference to the drawings. FIG. 3 is a schematic view showing an example of a fluidized bed of a hot air direct blowing system used in the present invention. Reference numeral 10 denotes a container. In the container 10, a granular material 12 such as a granular material is filled on a perforated plate 16, and the granular material 1
2 are fluidized by hot air 14 blown from below the perforated plate 16 and uniformly mixed to form a fluidized bed 18. FIG. 4 is a schematic view showing an example of a fluidized bed type solution treatment furnace used in the present invention. In FIG.
Is a hot-air generator, and the air sent from a blower (not shown) is heated to 700-800 ° C. hot air by the flame from the burner 22. This hot air is supplied to a hot air temperature monitoring device 24.
Is blown into the fluidized bed type solution treatment furnace 26. In the fluidized bed type solution treatment furnace 26, hot air is passed through the perforated pipe 2.
8 is blown into the fluidized bed 30 to fluidize the granular material 32 and heat the granular material 32. In this way, the inside of the fluidized bed 30 is heated to 547 to 562 ° C., and the fluctuation of the furnace temperature is within 6 ° C. (± 3 ° C.), and the fluctuation at one point is about 3 ° C. (± 1.5 ° C.). (° C.), and the temperature inside the furnace does not greatly exceed the melting point even if the temperature set point is set as the melting point. Thus, the fluidized bed 30
The workpiece 34 present therein is quickly and stably heated. Reference numeral 36 denotes a particulate matter discharge valve, which discharges the particulate matter 32 to the outside as appropriate.

Although not shown, a fluidized bed as shown in FIGS. 3 and 4 can be used for the aging treatment of the present invention.

[0043]

EXAMPLES Hereinafter, the present invention will be described more specifically based on examples. (Example 1) Using a fluidized bed type solution treatment furnace shown in FIG.
The heat treatment method of the present invention was carried out using a fluidized bed treatment furnace having the same configuration as the aging treatment furnace. The fluidized bed type solution treatment furnace has an inner diameter of 1500 mm x 1500 mm.
The tank has a straight body height of 750 mm, and the lower portion is formed of an inverted conical fluidized bed container. The aging treatment furnace also has the same configuration as the solution treatment furnace. Sand having an average particle size of 50 to 500 μm was used as the granular material.

As an object of the heat treatment, a test piece having a shape and a size shown in FIG. 2 was used. The composition of this test piece was as follows: 1.0% by mass of Mg, 0.6% by mass of Si, Cu
0.2% by mass and 0.1% by mass of Cr, with the balance being A
l. The heat treatment conditions include a solution treatment temperature of 55
At 0 ° C., the solution was heat-treated at a temperature rising time to the solution treatment temperature of 10 minutes and a holding time at the solution treatment temperature of 50 minutes, and then rapidly cooled.
The aging treatment for 210 minutes including the temperature rise and the holding was performed. Tensile test (tensile strength, 0.2%
Proof stress, elongation). The results obtained are shown in FIG.
FIG. 7 shows a photograph in which the metal microstructure of the test piece is enlarged by an optical microscope.

Example 2 A solution treatment was performed at a solution treatment temperature of 560 ° C., an aging treatment temperature of 180 ° C., and an aging treatment of 120 minutes including heating and holding was performed.
A heat treatment was performed under the same conditions as in Example 1, and a tensile test (tensile strength, 0.2% proof stress, elongation) was performed on the heat-treated test piece. The results obtained are shown in FIG.

Comparative Example 1 A conventional atmosphere furnace was used as a solution treatment furnace and an aging treatment furnace, and the solution treatment temperature was set to 53.
At 0 ° C., the aging temperature was set to 180 ° C., the heat-up time to the solution treatment temperature was 60 minutes, and the holding time at the solution treatment temperature was 120 minutes to perform the solution treatment.
The test was performed for 180 minutes including holding. Other conditions were the same as in Example 1.
Is the same as A tensile test (tensile strength, 0.2% proof stress, elongation) was performed on the heat-treated test piece. The results obtained are shown in FIG. FIG. 6 shows a photograph in which the metal microstructure of the test piece is enlarged by an optical microscope.

(Comparative Example 2) A heat treatment was performed under the same conditions as in Comparative Example 1 except that the aging treatment was performed for 360 minutes including the temperature increase and the holding, and the heat-treated test piece was subjected to a tensile test (tensile strength). , 0.2% proof stress, elongation). The results obtained are shown in FIG.

(Consideration) From the results of the tensile tests in Examples 1 and 2 and Comparative Examples 1 and 2, the following became clear. The heat-treated test piece obtained in Example 1 had a tensile strength of 330 MPa, a 0.2% proof stress of 230 MPa, an elongation of 23%, and a high level of tensile strength and 0.2% proof stress. However, in particular, it was confirmed that the elongation was significantly improved as compared with the conventional case. The heat-treated test piece obtained in Example 2 had a tensile strength of 355MP.
a, the 0.2% proof stress is 310 MPa, and the elongation is 17%.
It was confirmed that the% proof stress was significantly improved as compared with the conventional method.

When comparing the metal microstructure of the test piece with an optical microscope enlarged photograph, in Comparative Example 1, recrystallization has begun, but has not yet been completely replaced by recrystallized grains. While crystal grains elongated in a pancake shape are observed, in Example 1, it can be confirmed that recrystallization has progressed considerably despite the short-time solution treatment. . Also, it can be confirmed that many sub-crystal grains are present in the crystal grains. It is considered that the sub-crystal grains have a function of stopping dislocations and are resistant to deformation, and thus contributed to improvement in ductility and strength in recrystallization. Also, it should be noted that when the fluidized-bed type solution treatment furnace and the aging treatment furnace employed in Examples 1 and 2 are used, the total heat treatment time is significantly reduced as compared with the conventional atmosphere furnace. is there.

[0050]

As described above, according to the heat treatment method for a precipitation hardening type alloy of the present invention, since the solution treatment is performed at a higher temperature and at a higher temperature rising time, the total heat treatment time is reduced. It can be greatly reduced as compared with the conventional case. And, for example, in an Al alloy, it is possible to improve both while improving the strength by increasing the amount of solid solution and improving the ductility by recrystallization. Therefore, it is possible to provide a precipitation hardening type Al alloy having three mechanical properties of tensile strength, proof stress and elongation in a well-balanced manner.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of tensile tests (tensile strength, 0.2% proof stress, elongation) in Comparative Examples 1 and 2 and Examples 1 and 2.

FIG. 2 is an explanatory diagram showing shapes and dimensions of test pieces used in Comparative Examples 1 and 2 and Examples 1 and 2.

FIG. 3 is a schematic view showing an example of a fluidized bed of a hot air direct blowing system used in the present invention.

FIG. 4 is a schematic view showing an example of a fluidized bed type solution treatment furnace used in the present invention.

FIG. 5 is a graph showing heat treatment schedules in Comparative Examples 1 and 2 and Examples 1 and 2.

FIG. 6 is a photograph obtained by enlarging a metal microstructure of a test piece in Comparative Example 1 with an optical microscope.

FIG. 7 is a photograph obtained by enlarging a metal microstructure of a test piece in Example 1 with an optical microscope.

[Explanation of symbols]

DESCRIPTION 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 type solution treatment furnace, 28 ... perforated pipe, 30 ... fluidized bed, 32 ... particulate matter, 34 ... workpiece, 36 ... valve for discharging particulate matter,
41: test piece, 51: solution treatment time, 52: aging treatment time, 53: holding time (solution treatment), 54: temperature rising time (solution treatment).

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22F 1/00 630 C22F 1/00 630A 630K 685 685Z 686 686B 691 691A 691B 691C

Claims (23)

[Claims] 1. A precipitation hardening type Al alloy obtained by heat-treating an Al alloy having a working strain and having recrystallized grains and sub-crystal grains formed therein, having a tensile strength of 320 MPa or more and a 0.2% proof stress. Is 220M
A precipitation hardening type Al alloy having a Pa or more and an elongation of 19% or more. 2. A precipitation hardening type Al alloy obtained by heat-treating an Al alloy having a working strain and formed with recrystallized grains and subcrystal grains, wherein the tensile strength is 350 MPa or more and 0.2% proof stress. Is 300M
A precipitation hardening type Al alloy characterized by having Pa or more and elongation of 15% or more. 3. The precipitation hardening type Al alloy according to claim 1, comprising 0.4 to 1.2% by mass of Mg and 0.2 to 1.3% by mass of Si. 4. An amount of 0.10 to 0.40 mass% of Cu,
The precipitation hardening type Al alloy according to any one of claims 1 to 3, containing 0.35% by mass or less of r. 5. The precipitation hardening type A according to claim 1, wherein the processing strain is imparted by cold working.
1 alloy. 6. The heat treatment comprises a solution treatment and an aging treatment, wherein in the solution treatment, a heat treatment is performed at a holding temperature which is -10 ° C. to + 5 ° C. from the melting point of the Al alloy to be heat treated. 6. The precipitation hardening type Al alloy according to any one of 5. 7. The precipitation hardening type Al alloy according to claim 6, wherein the solution treatment is performed within 60 minutes, including a heating time and a holding time. 8. A heating time in the solution treatment is 2 hours.
The precipitation hardening type Al alloy according to claim 6 or 7, which is performed within 0 minutes. 9. The precipitation hardening type Al alloy according to claim 6, wherein at least the solution treatment is performed by causing the Al alloy to be heat-treated to be present in a fluidized bed. 10. The aging treatment is performed by causing an Al alloy to be heat-treated to be present in a fluidized bed.
The precipitation hardening type Al alloy according to any one of the above. 11. The precipitation hardening type Al alloy according to claim 9, wherein the fluidized bed is formed by direct blowing of hot air. 12. The precipitation hardening type Al alloy according to claim 1, which is used as a vehicle underbody part. 13. A precipitation-hardening alloy heat treatment method for improving the mechanical properties of a work piece made of an alloy having a work strain by subjecting the work piece to a solution treatment and then performing an aging treatment, A heat treatment method for a precipitation hardening alloy, wherein a holding temperature in the solution treatment is −10 ° C. to + 5 ° C. from a melting point of the workpiece. 14. The heat treatment method for a precipitation hardening alloy according to claim 13, wherein the solution heat treatment time includes a heating time and a holding time and is within 60 minutes. 15. The heat treatment method for a precipitation hardening alloy according to claim 13, wherein a rapid temperature rise in the solution treatment is performed within a time period of 20 minutes or less. 16. The heat treatment method for a precipitation hardening alloy according to claim 13, wherein at least the solution treatment is performed by causing the workpiece to be present in a fluidized bed. 17. The method according to claim 13, wherein the aging treatment is performed by causing the workpiece to be present in a fluidized bed.
A method for heat treating a precipitation hardening type alloy according to any one of claims 16 to 16. 18. The heat treatment method for a precipitation hardening alloy according to claim 16, wherein the fluidized bed is formed by direct blowing of hot air. 19. The alloy having a working strain includes Mg of 0.4 to 1.2% by mass and Si of 0.2 to 1.
The heat treatment method for a precipitation hardening alloy according to any one of claims 13 to 18, which is an Al alloy containing 3% by mass. 20. A solution treatment temperature of 540 to 562.
20. The method for heat treating a precipitation hardening alloy according to claim 19, wherein the temperature is ° C. 21. In the solution treatment, Mg and S are added.
The heat treatment method for a precipitation-hardenable alloy according to claim 19 or 20, wherein the solid solution ratio of i in the α phase is 60% or more. 22. An aging temperature of 150 ° C. to 200 ° C.
22. The method for heat treating a precipitation-hardening alloy according to claim 19, wherein the temperature is ℃. 23. The undercarriage component for a vehicle, wherein the workpiece made of the alloy having a processing strain is a vehicle underbody part.
3. The heat treatment method for a precipitation hardening type alloy according to any one of 2.