JPH07310137A - Aluminum alloy sheet for warm forming and its production - Google Patents

Abstract

PURPOSE:To produce an aluminum alloy sheet excellent in warm formability as an aluminum alloy sheet for use in which warm forming is executed in a high temp. range, simultaneously excellent in stress corrosion cracking resistance after the warm forming and moreover having high strength. CONSTITUTION:An aluminum alloy sheet for warm forming having a compsn. contg. 2.0 to 3.5% Mg, >1.0 to 1.8% Mn, <=0.2% Fe, <=0.30% Cu, and the balance substantial Al, and in which the number of Al-Mn intermetallic compounds having 1 to 5mum grain size is regulated to >=1000 pieces per 0.1mm<2> and the average grain size is regulated to <=50mum is obtd. Next, the rolling finishing temp. in hot rolling, after homogenizing treatment of 500 to 600 deg.CX4 to 80hr, is regulated to <=280 deg.C, the rolling ratio at <=280 deg.C is regulated to >=30%, and after that, softening treatment is executed at 300 to 500 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy rolled sheet for warm forming, that is, an aluminum alloy sheet used by forming at a temperature in the range of 150 to 350 ° C. The present invention relates to an aluminum alloy sheet excellent in stress corrosion cracking resistance after hot forming (hereinafter referred to as "SCC resistance") and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, various superplastic materials have been developed which show a large elongation of about 300% or more without causing local deformation (neck) when tensile is applied at an appropriate strain rate at high temperature. As a result, superplastic materials have been developed for aluminum alloys. Conventionally, as such an aluminum-based superplastic material, Al-
78% Zn alloy, Al-33% Cu alloy, Al-6% C
u-0.4% Zr alloy ("SUPURAL"), Al-
Zn-Mg-Cu alloy (AA standard 7475 alloy, 7
075 alloy, etc.), Al-2.5 to 6.0% Mg-0.0
5 to 0.6% Zr alloy and the like are known. Since all of these materials can obtain a large deformation at a high temperature of 400 ° C. or higher, they have an advantage that a complicated shape can be easily molded.

These aluminum-based superplastic materials have three
In order to generate a large elongation of more than 00%, 40
It is necessary to give an appropriate strain rate at a high temperature of 0 ° C. or higher, and generally the strain rate showing the largest elongation (optimal strain rate) is 10
It is in the order of ^-3 / sec to 10 ^-4 / sec. However, such a strain rate is remarkably slow as compared with the case of a general molding process, and when such a strain rate is applied, one molding step requires several minutes to several tens of minutes, which is not suitable for a factory scale. In mass production, there is a problem that productivity is significantly hindered. Therefore, it has been hesitant to put the above-mentioned aluminum-based superplastic material into practical use on a mass production scale.

By the way, in the case of so-called warm forming in a temperature range of 150 to 350 ° C., which is lower than the superplastic working temperature range, the Al--Mg alloy has a relatively large elongation at a normal forming rate. It is known that the plate thickness distribution after deformation in that case is also uniform, and therefore Al-
If warm forming is performed using a Mg-based alloy, it is considered that forming a complicated shape becomes relatively easy without impeding productivity.

Conventionally, Al-Mg for such warm forming
As a system alloy, JIS 5182 alloy (4.5% Mg-0.3% M) having high strength and relatively good warm formability is used.
n), 5454 alloy (2.7% Mg-0.7% Mn),
Al-Mg based alloys containing 2.5-4.5% Mg, such as the 5083 alloy (4.5% Mn-0.7% Mg), have been considered.

[0006]

The application of the warm-formed parts is considered to be automobile parts such as oil pans of automobiles, but the automobile parts are often exposed to a severe corrosive environment, and therefore SCC resistance is high. Is required to be excellent. In addition, automobile parts are required to be thinned for the purpose of improving fuel efficiency by reducing the weight of the vehicle body and reducing material costs.In that case, high strength of automobile parts materials is required so as to have sufficient proof strength even when thin. Is desired.

Among the conventional materials considered for warm forming as described above, 5454 alloy has good SCC resistance, but lacks strength, while 5182 alloy and 5083 alloy have high strength. However, there was a problem of poor SCC resistance.

As a method for increasing the strength of the Al-Mg alloy, increasing the Mg content can be considered, but Mg is an element that adversely affects the SCC resistance,
Therefore, if the amount of Mg is increased, the S
Since the CC property is lowered, it is not practically preferable to increase the strength by increasing the amount of Mg.

Further, although the conventional Al--Mg type alloy has been obtained with a certain degree of warm formability, in consideration of the application of the warm formability on a mass production scale, a material having a more excellent warm formability is obtained. Development is strongly desired.

The present invention has been made in view of the above circumstances, and provides an aluminum alloy plate for warm forming which has excellent warm formability, excellent SCC resistance after warm forming, and high strength. The purpose is to do.

[0011]

Means for Solving the Problems The inventors of the present invention have made earnest experiments and studies to solve the above problems, and as a result, Al-M
Based on g-based alloy, M that adversely affects SCC resistance
n is not particularly increased, but the Mn amount is set to JIS 545
No. 4 alloy and the like, and by making the precipitate particles of the Al—Mn-based intermetallic compound that becomes the nucleus of recrystallized grain formation finer and the final crystal grains (recrystallized grains) finer, SCC resistance at the same time as obtaining excellent warm formability
The inventors have found that high strength can be obtained without impairing the properties and have completed the present invention. Further, here, by restricting the content of various elements contained as impurities in the Al-Mg-based alloy to a specific trace amount or less, as described above, the precipitate particles of the Al-Mn-based intermetallic compound are surely formed. It became possible to miniaturize and ensure excellent warm formability.

Specifically, the rolled aluminum alloy sheet for warm forming according to the invention of claim 1 has Mg 2.0 to 3.5%, M
n of more than 1.0% and 1.8% or less, Fe of 0.20% or less,
A grain size of 1 containing Cu 0.30% or less, the balance being Al and unavoidable impurities and being dispersed in the alloy plate 1
The number of Al-Mn-based intermetallic compound particles having a particle size of ~ 5 μm is 0.1.
More than 1000 pieces per mm ² and an average crystal grain size of 5
It is characterized by being 0 μm or less.

The rolled aluminum alloy plate for warm forming according to the invention of claim 2 is the aluminum alloy plate for warm forming according to claim 1, wherein Cr is 0.05 as an impurity.
% Or less, Zr is 0.05% or less, Si is 0.2% or less,
Zn is regulated to 0.05% or less, V is regulated to 0.05% or less, and the total amount of other impurities is regulated to 0.1% or less.

On the other hand, the manufacturing method of the aluminum alloy sheet for warm forming according to the third aspect of the present invention is Mg 2.0 to 3.5%, Mn
More than 1.0% and 1.8% or less, Fe 0.20% or less, C
A cast ingot of an alloy containing u of 0.30% or less and the balance of Al and unavoidable impurities was cast, and
A homogenization treatment is performed at a temperature in the range of 00 to 600 ° C. for 5 to 48 hours to deposit 1000 or more Al-Mn-based intermetallic compound particles having a particle size of 1 to 5 μm per 0.1 mm ² .
Then, when rolling is performed to obtain the required final plate thickness, the rolling end temperature in hot rolling is set to 280 ° C. or less, the rolling ratio in the temperature range lower than the recrystallization temperature is set to 30% or more, and the final plate thickness is further set. It is characterized in that the rolled steel sheet is subjected to a softening treatment at 300 to 500 ° C. so that the average crystal grain size becomes 50 μm or less.

[0015]

First, the reasons for limiting the components of the aluminum alloy for warm forming of the present invention will be explained.

Mg: Mg is an element that improves warm formability by promoting work softening or dynamic recrystallization during warm forming, and on the other hand, if contained in excess, it adversely affects SCC resistance. It is also an element that gives. M
If g is less than 2.0%, the warm formability will be insufficient and the strength as various molded parts will be insufficient. On the other hand, even if Mg exceeds 3.5%, the elongation in warm forming does not increase so much, the SCC resistance also deteriorates, and further the cost of the material increases. Therefore, the content of Mg is 2.0 to 3.5.
Within the range of%. The amount of Mg is preferably 2.5-
It is better to set it within the range of 3.2%.

Mn: Mn is forcibly solid-solved during casting and is effective not only for improving strength by solid solution strengthening, but also for Al such as Al ₆ Mn precipitated by high temperature soaking treatment (homogenization treatment) on the ingot. -Mn-based intermetallic compound particles serve as nuclei for recrystallized grain formation, and the recrystallized grains of the final plate are refined,
It effectively acts to improve strength and obtain good warm formability. However, when Mn is 1.0% or less, the solid solution amount of Mn is insufficient, and Al- which is precipitated by high temperature soaking treatment
The number and size of Mn-based intermetallic compound particles are not sufficient,
Therefore, the effect of refining the recrystallized grains of the final plate cannot be sufficiently obtained, and the strength and the warm formability cannot be sufficiently improved. On the other hand, if the Mn content exceeds 1.8%, Al-Fe
There is a possibility that the —Mn-based crystallized substance becomes coarse and the warm formability is impaired. Therefore, the amount of Mn exceeds 1.0% and 1.8%
Within the range of.

Fe: Fe is an element that imparts moldability, but as the content increases, coarse Al-Fe-
A Mn-based intermetallic compound is generated, which hinders the slip deformation during molding and reduces the elongation. In particular, if Fe is contained in excess of 0.2%, the warm formability becomes poor. Therefore Fe
The amount should be kept below 0.2%. It should be noted that Fe may be regulated to 0.2% or less (including 0%) as an impurity until it gets tired, or may be positively added in the range of 0.2% or less in expectation of the effect of addition.

Cu: Cu is an element that imparts SCC resistance and strength. As the content increases, the work hardenability increases, but on the contrary, the elongation during warming decreases. Especially C
If u is contained in excess of 0.3%, the warm formability becomes poor. Therefore, the Cu content needs to be suppressed to 0.3% or less. Cu may be regulated to 0.3% or less (including 0%) as an impurity until it gets tired, or may be positively added in the range of 0.3% or less in anticipation of its addition effect.

Cr, Zr, Si, Zn, V and other impurities: Cr, Zr, Si, Zn, and V all tend to form coarse intermetallic compounds during casting, and once formed, these intermetallic compounds are formed. Cannot be removed by subsequent processing or heat treatment. If the particle size of these intermetallic compounds exceeds 3 μm, they serve as the starting point of fracture during warm forming, and significantly deteriorate the warm formability. In order to prevent the formation of intermetallic compounds having a particle size exceeding 3 μm, Cr as an impurity is 0.05% or less, Zr is 0.05% or less,
Si is 0.2% or less, Zn is 0.05% or less, and V is 0.
It is preferable that the content of each of the other impurities (excluding Fe and Cu) is regulated to not more than 0.1% while controlling the content of each to be not more than 05%.

The balance of the above components may be substantially Al. However, in ordinary aluminum alloys, a minute amount of Ti or Ti and B may be added for refining the ingot crystal grains. In the case of the present invention, a small amount of Ti,
Alternatively, Ti and B may be contained. Where T
If the i content exceeds 0.15%, primary TiAl ₂ particles crystallize and impair the formability, and if the B content exceeds 0.05%, coarse particles of TiB occur and impair the formability.
Ti is preferably 0.15% or less and B is preferably 0.05% or less.

When a large amount of Mg is contained, the molten metal is likely to be oxidized, and Be is generally added to prevent the molten metal from oxidizing. However, in the case of the aluminum alloy for warm forming of the present invention, Alternatively, Be may be added to prevent the oxidation of the molten metal. However, the amount of Be added is 1 ppm
If it is less than 100 ppm, the effect cannot be obtained, and if it exceeds 100 ppm, the effect is saturated. Therefore, when Be is added, the addition amount is preferably in the range of 1 to 100 ppm.

Further, in the aluminum alloy sheet for warm forming of the present invention, not only the component composition thereof is specified as described above, but also the precipitation state of the Al-Mn based intermetallic compound in the final sheet and the crystal grain of the final sheet. The diameter (recrystallized grain size) is important. That is, the present invention aims to obtain excellent warm formability and at the same time improve strength without impairing SCC resistance. For that purpose, in the state of the final plate, it is dispersed in the alloy plate. Particle size of 1 μm or more 5
It is necessary that the number of particles of the Al-Mn-based intermetallic compound within the range of less than or equal to μm is 1000 or more per 0.1 mm ² , and the average crystal grain size is less than or equal to 50 μm.

Al-M dispersed in the alloy plate as described above
The reason for limiting the size and dispersion state of the n-based intermetallic compound particles will be described below. The Al-Mn-based intermetallic compound particles serve as nuclei for the formation of recrystallized grains during the softening treatment, and refine the recrystallized grains of the final plate to improve the strength and effectively obtain excellent warm formability. Although it has a function of acting, if the particle size is larger than 5 μm, the Al—Mn-based intermetallic compound particles themselves become the starting point of fracture during warm forming, and the warm formability is significantly deteriorated. Therefore, the diameter of the Al-Mn-based intermetallic compound particles in the final plate is preferably 5 μm or less as much as possible. On the other hand, Al-Mn-based intermetallic compound particles having a fine diameter of less than 1 μm do not serve as nuclei for recrystallized grain formation. The grain size of 1 to 1 effectively functions as the nucleus of recrystallized grain formation without impairing the warm formability.
It is an Al-Mn-based intermetallic compound particle within a range of 5 μm. If the number of Al-Mn-based intermetallic compound particles within the particle size range of 1 to 5 μm is 1000 or more per 0.1 mm ^2, most Al-Mn-based intermetallic compound particles having a particle size exceeding 5 μm exist. Since it does not exist, the warm formability is hardly deteriorated, and fine recrystallization is performed during the final softening treatment to obtain a fine structure having an average crystal grain size of 50 μm or less.
Further, by setting the average crystal grain size of the final plate (the plate after the final softening treatment) to 50 μm or less, excellent warm formability and high strength can be obtained. The average grain size of the final plate is 5
When it exceeds 0 μm, good warm moldability cannot be obtained, and the strength is not sufficiently improved.

Here, in order to make the recrystallized structure finer during the final softening treatment, as described above, in the state immediately before the final softening treatment, Al-having a grain size of 1 μm or more and 5 μm or less is used.
It is necessary that 1000 or more Mn-based intermetallic compound particles are present per 0.1 mm ^2, but if the Al-Mn-based intermetallic compound particles satisfy the above conditions after the final softening treatment, Since the conditions are inevitably satisfied immediately before the final softening treatment, the above conditions are defined as the plate after the final softening treatment in the inventions of claims 1 and 2.

The aluminum alloy plate satisfying the above-described component composition conditions and metallographic structure conditions (crystal grain size condition, Al--Mn type intermetallic compound condition) of the present invention is 150 to 350.
Formability (warm formability) in performing warm forming at a temperature in the range of ° C and SCC resistance after warm forming are significantly superior to those of conventional Al-Mg alloys. It has the high strength of high strength Al-Mg alloy.

Next, a method of manufacturing the aluminum alloy sheet for warm forming as described above, that is, the invention of claim 3 will be described.

First, an alloy having the above composition is cast. The casting method is not particularly limited, but in order to increase the solid solution amount of Mn and refine the crystallized substances of the Al-Mn intermetallic compound, a DC casting method (semi-continuous casting method) or the like is used. It is preferable to cast at a cooling rate of 0.5 ° C./sec or more.

The obtained ingot is subjected to a homogenizing treatment (soaking treatment). This soaking treatment is an important step for not only homogenizing the ingot structure but also precipitating Al-Mn-based intermetallic compound particles. That is, in the present invention, by performing soaking treatment at high temperature for a long time, a fine Al—Mn having a grain size of 1 μm or more and 5 μm or less, which becomes a nucleus of recrystallization, is obtained.
Precipitated 1000 or more particles of intermetallic compound per 0.1 mm ^{2 to make} recrystallized grains finer during the subsequent softening treatment, improve elongation during warm forming and SCC resistance after warm forming. And the strength can be improved. If the homogenization treatment temperature is less than 500 ° C. or the homogenization treatment time is less than 5 hours, the precipitation of Al—Mn-based intermetallic compound particles becomes insufficient, while the soaking temperature is 600.
If the temperature exceeds ℃, local melting will occur, and if the soaking time exceeds 48 hours, the effect of precipitation of Al-Mn intermetallic compound will be saturated and problems will occur in terms of economic efficiency, and surface oxidation will occur. It progresses and the surface quality deteriorates. Therefore, the soaking time needs to be within the range of 500 to 600 ° C. × 5 to 48 hours.

The Al-Mn-based intermetallic compound particles deposited by such soaking do not dissolve into the matrix in the subsequent process, and since they are fine in the first place, they are crushed by processing and further The diameter is almost never small. Therefore, if at least 1000 Al-Mn-based intermetallic compound particles having a particle size of 1 μm or more and 5 μm or less are precipitated per 0.1 mm ^{2 in the} soaking process, the recrystallization of the final plate is performed. Al-M even during processing
n-based intermetallic compound particles can satisfy the same conditions,
Therefore, as already described, by making the recrystallization structure a fine structure having an average crystal grain size of 50 μm or less, it is possible to improve the elongation during warm forming.

After soaking, hot rolling is performed. The hot rolling start temperature may be the same as that of a conventional Al-Mn-Mg-based alloy, and is usually 400 to 550 ° C. In carrying out this hot rolling, after soaking, it may be once cooled and then reheated to 400 to 550 ° C., or 400 to 550 without soaking after reheating.
You may perform hot rolling from the state of ℃. In this hot rolling, the hot rolling finish temperature is important. That is,
By setting the hot rolling end temperature to a relatively low temperature of 280 ° C. or lower, which is lower than the recrystallization temperature of the alloy targeted by the present invention, the rolling rate at a temperature lower than the recrystallization temperature of the Al—Mg-based alloy is 30%. As described above, the same effect as cold rolling can be provided without cold rolling, and the effect of refining recrystallized grains during the softening treatment of the final plate can be obtained. When the hot rolling finish temperature is higher than 280 ° C., the recrystallized grains are not refined, and therefore the effect of improving elongation during warm forming cannot be obtained.

The hot rolling finish temperature condition as described above will be explained in detail. The recrystallization temperature of the alloy of the present invention is about 280 ° C. to 300 ° C. If rolling at temperature, 2 during rolling
Since secondary recrystallized grains are generated, the rolling work structure does not occur and work hardening hardly occurs. On the other hand, by performing rolling in a temperature range of 280 ° C. or lower, which is lower than the recrystallization temperature, a rolling work structure is generated, work hardening occurs, and cold rolling is applied without cold rolling. The same effect can be obtained. Then, in the subsequent softening treatment in the final step, in the former case, newly generated recrystallized grains are not fine, whereas in the latter case, fine recrystallized grains are easily generated due to the rolling structure. It With respect to the recrystallized grains generated by this softening treatment, the larger the rolling ratio at the recrystallization temperature or lower, the easier it becomes to obtain fine recrystallized grains. If the rolling rate at the recrystallization temperature or lower is less than 30%, the size of the recrystallized grains exceeds 50 μm, a fine recrystallized structure cannot be obtained, and the warm elongation becomes insufficient. Therefore, in order to obtain sufficient elongation to improve the warm formability, the rolling rate at the recrystallization temperature (280 ° C to 300 ° C) or less in hot rolling is set to 30% or more. By applying such a method, it is possible to omit the cold rolling step, which brings about an advantage that the production cost can be reduced.

As described above, the softening treatment is applied to the rolled plate (final rolled plate) having the final plate thickness by the hot rolling in which the rolling end temperature is controlled. This softening treatment may be performed by either batch annealing or continuous annealing. This softening treatment is a step necessary to recrystallize the structure of the final rolled plate and obtain a required soft material, and the temperature is 30
If the temperature is lower than 0 ° C., recrystallization does not proceed sufficiently, and if the temperature exceeds 500 ° C., coarsening of recrystallized grains tends to occur. Therefore, the softening treatment needs to be performed at a temperature within the range of 300 to 500 ° C. The time for the softening treatment is not particularly limited, but it is usually preferably within the range of 0.5 to 5 hours. In such a softening treatment, as described above, the grain size is 1
Since 1000 or more Al-Mn-based intermetallic compound particles having a size of from 5 μm to 5 μm are dispersed per 0.1 mm ² , a fine recrystallized structure having an average crystal grain size of 50 μm or less can be obtained. Since such a fine recrystallized structure is obtained, it is possible to improve the elongation during warm forming.

The warm forming of the rolled plate of the product is 15
It is carried out at 0 to 350 ° C., in which case the rolled plate is set in a heated mold and held until the material temperature reaches a predetermined temperature before being formed, or in another preheating furnace. It is heated, then set in a mold and molded. In this case, it is not necessary to obtain the recrystallized structure by the final annealing under the conditions such that the recrystallization temperature or time for holding or preheating occurs, and in that case, the final annealing can be omitted.

When the thin plate continuous casting method is applied instead of DC casting, up to hot rolling can be omitted from the above-mentioned steps. However, in this case, in order to improve the rolling property, it is preferable that the cast coil is subjected to a homogenizing treatment and then cold-rolled to a desired plate thickness. The homogenization treatment in this case may be the same as the ingot heating conditions before hot rolling when the above DC casting is applied.

[0036]

[Example] Manufacturing condition No. 1 in Table 1 The aluminum alloys having the component compositions shown in 1 to 10, that is, the alloys within the component range of the present invention (Nos. 1 to 5) and the alloys of Comparative Examples outside the component range of the present invention (Nos. 6 to 10) were subjected to conventional methods Therefore, DC casting was performed, and the obtained ingot was manufactured under the manufacturing condition No. 2 shown in Table 2. 1
After soaking (homogenization treatment), preheating before hot rolling, and hot rolling under various conditions as shown in 10 to make a rolled plate having a thickness of 1.6 mm, 350 ° C. × 2 hours A softening treatment was performed to obtain a product plate.

Immediately after the soaking treatment and the softening treatment in the above-mentioned process, the number of Al-Mn-based intermetallic compound particles having a size of 1 μm or more and 5 μm or less per 0.1 mm ² was examined by using an image analyzer. The average crystal grain size immediately after the softening treatment was examined, and the results are also shown in Table 2.

Table 3 shows the manufacturing condition No. after the softening treatment.
The mechanical properties of each of the plates 1 to 10 at room temperature and the elongation in the warm tensile test at 150 ° C and 350 ° C are shown. As the conditions for this warm tensile test, test pieces as shown in FIG. 1 were used, and the test pieces of each material were heated in a heating furnace, and after the temperature of the test pieces reached 150 ° C. and 350 ° C., 5 Hold for minutes, then start pulling, and pulling speed is 10m
The distance between the reference points was 10 mm.

Further, Table 3 shows the manufacturing condition No. The result of having investigated the forming limit depth until it fracture | ruptures by the double sink warm forming drawing die of each board by 1-10 is shown. The molding conditions for this double-sink warm molding drawing die are as follows.

Punch: 60 mm × 60 mm × 2 double sinks Distance between punches: 60 mm Blank holder force: 300 kg Molding height limit: 60 mm (maximum height of mold that can be drawn) Molding speed: 100 mm / min Heating temperature: The test material was evaluated under two conditions: 1) holding the sample in the mold at 150 ° C for 1 minute, and 2) holding the sample in the mold at 350 ° C for 1 minute. Lubricant: Molybdenum disulfide lubricant applied to both sides of the plate

The break life of each plate after the softening treatment was examined by the SCC test. The results are also shown in Table 3.

Regarding the SCC resistance, it is generally known that the SCC susceptibility is low in the soft material as it is, and Mg ₂ Al ₃ is precipitated at the grain boundaries due to the change with time after the forming process, and the SCC susceptibility is increased. . So in this example,
After subjecting the plate (soft material) after the softening treatment to 50% tensile processing (elongation) by warm drawing at 350 ° C. under the same conditions as in FIG. 1 and Table 3, further, to this test piece, About 1
120 ℃, which is equivalent to the change in Mg ₂ Al ₃ precipitation for 0 years
A SCC test was carried out in a state in which the SCC sensitivity was increased by applying a heat treatment for 7 days.

In this SCC test, stress is applied by uniaxial tension in an aqueous NaCl solution and the SC resistance is increased.
5m DC on the test piece to evaluate C property in a relatively short time
A method of accelerating intergranular corrosion by passing a current of A / cm ² , that is, a current load uniaxial tension method was used. The applied stress is 100 N / mm ² and 150 N / mm.
^It was investigated as 2 levels of 2.

Furthermore, stress corrosion cracking is known to be brittle fracture due to the interaction between intergranular corrosion and stress. In the above-mentioned SCC test, the SCC resistance is evaluated only by the fracture life, but it is considered that it is necessary to evaluate the SCC resistance not only from the fracture life but also from the fracture mode of the fracture surface. Additional stress 15 in SCC test
Regarding the fracture surface of the test piece fractured at 0 N / mm ² , the fracture mode of the fracture surface was observed with a scanning electron microscope. The results are also shown in Table 3.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

As shown in Table 2, No. 1 within the component composition range of the present invention. 1-No. In each of the aluminum alloy plates of No. 5, the number of Al-Mn-based intermetallic compound particles having a size of 1 μm or more and 5 μm or less is 1000 or more per 0.1 mm ² , and the average crystal grain size is 50 μm or less in all cases. ing. And from Table 3, the aluminum alloy plate No. according to the embodiment of the present invention. 1-No. All 5 are 150 ℃
The elongation in the warm tensile test at 70 ° C. is 70% or more, and the elongation in the warm tensile test at 350 ° C. is 250% or more. 6-No. Compared with the alloy plate No. 10, the alloy plate No. 1-No. It can be seen that No. 5 has a remarkably large warm tensile elongation. Further, the forming limit of the double sink warm forming drawing die is the same as that of the alloy sheet No. 1 of the present invention. 1
~ No. No. 5 at 150 ℃ 30mm or more, also 350m
m is 60 mm or more, which is remarkably superior to the comparative example.
Therefore, it is clear from these results that the aluminum alloy sheet according to the present invention has excellent warm formability.

Further, as shown in Table 3, each of the aluminum alloy sheets of the present invention had a breaking life in the SCC test of 4000 min or more under the condition of an additional stress of 150 N / mm ² , and also the fracture mode of the cross section of the test piece. The dimple fracture surface exhibits ductile fracture, and it is clear from these results that the aluminum alloy sheet according to the present invention has excellent SCC resistance.

On the other hand, among the comparative examples, alloy plate No. 6, N
o. Although the chemical compositions of all the materials of No. 7 are within the composition range of the present invention, the alloy plate No. In the case of No. 6, since the end temperature of hot rolling was higher than the recrystallization temperature, the average crystal grain size became as large as 70 μm, so the warm tensile elongation was small and the limiting drawing height was insufficient. . In addition, the alloy plate No. In No. 7, since the soaking temperature is out of the range of the present invention, the number of Al-Mn-based intermetallic compound particles is small, and therefore the recrystallized particle size becomes a mixed particle, and sufficient elongation cannot be obtained in warm drawing. Moreover, the limit drawing height was also insufficient.

Further, No. The alloy plate of Comparative Example No. 8 has Mn
The amount of Al is less than the range specified in the present invention, and therefore Al to form nuclei for recrystallization generated in the soaking process.
There were few particles of -Mn-based intermetallic compound. Therefore, the average crystal grain size after the softening treatment became larger than the range specified in the present invention, the elongation due to warm drawing decreased, and the limiting drawing height became insufficient.

No. 9, No. In each of the alloy sheets of Comparative Example 10 of the comparative example, since the end temperature of hot rolling is the recrystallization temperature or higher,
The average grain size was large, and the elongation due to warm drawing was small. In addition, these No. 9, No. The alloy plate of Comparative Example 10 of Comparative Example 10 had a Mg content outside the range specified in the present invention, and thus had a short fracture life in the SCC test, and the fracture mode of the cross section of the test piece exhibited a grain boundary fracture surface showing brittle fracture. SC resistant
It is clear that the C property is inferior.

As described above, the alloy sheets (No. 1 to No. 5) according to the examples of the present invention are excellent in warm tensile elongation,
In addition, the double sink warm forming die has a high limit drawing height, which is excellent in warm formability as well as SCC resistance.
Moreover, it is clear that it has high strength.

[0054]

EFFECTS OF THE INVENTION The aluminum alloy sheet for warm forming according to the present invention is excellent in warm formability and SCC resistance after warm forming. Therefore, the warm forming in the temperature range of 150 to 350 ° C. A molded product with a complicated shape can be easily obtained by molding, stress corrosion cracking is less likely to occur even when exposed to a harsh corrosive environment, and strength is also compared to conventional Al-Mg alloys. Therefore, it is most suitable for automobile parts, aircraft parts, and various molded parts.

[Brief description of drawings]

FIG. 1 is a plan view showing the shape and dimensions of a test piece in a warm tensile test conducted in an example of the present invention.

Claims (3)

[Claims] 1. Mg 2.0 to 3.5% (weight%, the same hereinafter), Mn more than 1.0% and 1.8% or less, Fe 0.20
% Or less and Cu 0.30% or less, the balance of Al and unavoidable impurities, and the number of Al—Mn-based intermetallic compound particles having a particle size of 1 to 5 μm dispersed in the alloy plate is 0. The number of grains per 1 mm ^{2 is} 1000 or more, and the average crystal grain size is 50 μm or less.
An aluminum alloy plate for warm forming, which is excellent in warm formability during warm forming within a range of 350 ° C and stress corrosion cracking resistance after warm forming. 2. The aluminum alloy plate for warm forming according to claim 1, wherein Cr is 0.05% or less, Zr is 0.05% or less, Si is 0.2% or less, and Zn is Zn.
Is regulated to 0.05% or less, V is regulated to 0.05% or less, and the total amount of other impurities is regulated to 0.1% or less. Aluminum alloy sheet for warm forming, which is excellent in warm formability during warm forming and stress corrosion cracking resistance after warm forming. 3. Mg 2.0 to 3.5%, Mn more than 1.0% and 1.8% or less, Fe 0.20% or less, Cu 0.30.
% Or less, with the balance being Al and inevitable impurities, an ingot of the alloy is cast, and the obtained ingot is 500 to 60
A homogenization treatment is performed at a temperature in the range of 0 ° C. for 5 to 48 hours to deposit 1000 or more Al—Mn-based intermetallic compound particles having a particle diameter of 1 to 5 μm per 0.1 mm ² , and then perform rolling. In order to obtain the required final plate thickness, the rolling end temperature in hot rolling is set to 280 ° C or less, and the rolling ratio in the temperature range lower than the recrystallization temperature is set to 30% or more. On the other hand, the softening treatment is performed at 300 to 500 ° C., and the average crystal grain size is set to 50 μm or less. Warm formability and warm forming in warm forming in the range of 150 to 350 ° C. A method for producing an aluminum alloy sheet for warm forming, which is excellent in stress corrosion cracking resistance after forming.