JPH0713276B2 - Heat treatment type aluminum alloy rolled plate Soft material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a soft material of an aluminum alloy rolled plate used for various forming applications, and particularly to an Al--Cu system,
Al-Cu-Mg system, Al-Zn-Mg system, Al-Zn-Mg-Cu system, Al-
Rolled sheet soft material before forming of Mg-Si heat-treatable high-strength aluminum alloy, therefore, obtain a high-strength molded product by subjecting the soft material to solution quenching and natural aging or artificial aging The present invention relates to a rolled plate used for the following purposes.

Conventional technology Heat-treatable high-strength alloys include Al-Cu, Al-Cu-Mg, and Al-Zn.
-Mg system, Al-Zn-Mg-Cu system, Al-Mg-Si system,
Typical examples of these are Al-Cu-based alloys such as 2219 alloys, Al-Cu-Mg-based alloys such as 2017 alloys and 2024 alloys.
JIS-N01 alloy etc. for Zn-Mg system, Al-Zn-Mg-Cu system
60 for Al-Mg-Si system such as AA standard 7075 alloy and 7050 alloy
61 alloys and the like are known, and in each case, elements that contribute to age hardening are solid-solved by solution treatment, and after quenching, these elements are strengthened by fine precipitation by natural aging or artificial aging.

Such heat-treatable high-strength aluminum alloys generally have significantly poor formability when finally subjected to natural aging or artificial aging. On the other hand, it is usual that a forming process is performed, and then a solution hardening treatment is performed, and then a required strength is obtained by natural aging or artificial aging.

By the way, as a conventional method for obtaining a soft material for forming the heat-treated high-strength aluminum alloy rolled sheet, a method of annealing in a batch furnace after rolling is generally used. Annealing in such a batch furnace is to heat at a slow temperature rising rate, hold at about 400 ° C. for 1 to 3 hours, and then gradually cool, and to age-harden elements as large precipitates that do not contribute to hardening. It is intended for sufficient precipitation.

Problems to be Solved by the Invention The heat treatment type high strength aluminum alloy rolled sheet soft material obtained by the conventional method as described above has the following problems. That is, first of all, there is a drawback that roughening is likely to occur during the subsequent molding process, which is unfavorable in appearance, and microcracks are likely to occur. Secondly, there is a problem that the molding processability represented by Erichsen value, elongation, and bending is insufficient and the molding process with high strength cannot be endured. Thirdly, when the molded product is subjected to solution treatment, abnormal growth of crystal grains occurs in a low strain portion where the workability is about 3 to 20%, resulting in coarsening of the crystal grains. As a result, strain after quenching There have been problems that roughening occurs during processing for correction, roughening occurs during chemical milling, and mechanical properties, particularly fatigue strength, are reduced.

This invention was made against the background of the above circumstances.
-Cu system, Al-Cu-Mg system, Al-Zn-Mg system, Al-Zn-Mg-Cu
System, or Al-Mg-Si-based heat treatment type aluminum alloy rolled plate soft material, i.e., as a rolled plate soft material at the stage before being subjected to molding processing, without roughening or microcracking during molding processing, It is an object of the present invention to provide a heat-treatable aluminum alloy rolled sheet soft material that has good moldability and can withstand high-strength molding, and that can prevent crystal grain coarsening due to solution treatment after molding. It is a thing.

Means for Solving the Problems The inventors of the present invention have conducted various experiments and studies in order to solve the above-mentioned problems, and as a result, the conventional heat treatment type aluminum alloy rolled sheet soft material has a rough crystal grain size. In most cases, coarse precipitates mainly composed of age hardening elements exist over a considerable area of the crystal grain boundary of the soft material. It was found that the precipitates were responsible for the above mentioned problems. As a result of further experiments and examinations, the average grain size of the soft material was regulated to 100 μm or less and the grain boundary precipitate area on the grain boundaries was regulated to 1/3 or less of the total grain boundary area. By doing so, it was found that the moldability during the subsequent molding process is good, and that there is no occurrence of surface roughness or microcracks, and that the crystal grain coarsening during the solution treatment after the molding process can be prevented, and the present invention was achieved. It was.

Therefore, the heat treatment type aluminum alloy rolled plate soft material of the present invention includes Al-Cu system, Al-Cu-Mg system, Al-Zn-Mg system, and Al.
-Zn-Mg-Cu-based or Al-Mg-Si-based heat-treatable aluminum alloy, which is used before being subjected to solution treatment / quenching and used for forming before use. , The average grain size is 100 μm or less, and the area of the grain boundary precipitates on the grain boundaries is less than the total grain boundary area.
It is characterized by being 1/3 or less.

Here, the average crystal grain size means the average crystal grain size in a plane parallel to the rolled surface, and typically represents a value measured by the average cutting method.

DETAILED DESCRIPTION OF THE INVENTION First, the knowledge about the conventional heat-treatment type aluminum alloy rolled sheet soft material which is the basis for forming the present invention will be explained.

As described above, most of the conventional soft materials of heat-treated aluminum alloy rolled plate have coarse crystal grains, especially those having a grain size of more than 100 μm, and the grain boundary precipitates over a considerable area on the grain boundaries. It was found that these grain sizes and grain boundary precipitates affect the deterioration of moldability and the coarsening of crystal grains during solution treatment as follows.

That is, if the crystal grains are large in the soft material state, the surface becomes rough during the molding process and the surface appearance is impaired, and microcracks are likely to occur due to the strong molding process. If coarse precipitates are continuously present on the crystal grain boundaries, this portion is likely to be a starting point of cracks during the molding process, which makes it difficult to perform the strength molding process. For this reason, the conventional heat treatment type aluminum alloy rolled plate soft material in which the crystal grains are coarse and many of the crystal grain boundaries have precipitates is inferior in surface appearance during the forming process, and the Erichsen value, Molding workability represented by elongation and bending was insufficient, and it was not possible to endure strong molding work.

On the other hand, not only heat-treatable alloys, but if soft materials are cold-worked with a low workability and then heated at high temperatures, strain-induced grain boundary migration occurs and specific crystal grains grow selectively. Then, the phenomenon of coarsening is observed. In particular, it is known that the crystal grain boundaries tend to concentrate strain during cold working with a low working degree, and that the activity is higher than that within the grains. Larger grain boundaries, that is, grain boundaries with a low degree of conformity, tend to concentrate strain during cold work with low strain, and thus, grain boundaries that are more locally activated within the grain and other grain boundaries will follow. Selective growth is likely to occur during heating. By the way, if the grain size is large, the number of grain boundaries decreases, so that the degree of concentration of strain on the grain boundaries increases, and the number of grain boundaries activated by a certain degree of processing decreases, so that the crystals preferentially grow. The grain boundaries where the growth occurs are limited, and as a result, local grain growth occurs during the solution treatment, and the crystal grains tend to become coarse. In addition, when a coarse and hard precipitate is present, deformation strain is accumulated around the coarse hard precipitate during cold working, and that portion may be a place where recrystallization nuclei are generated during subsequent heating. Are known.

In the conventional heat-treated aluminum alloy rolled plate soft material, since the crystal grain size is coarse and hard coarse precipitates are present on the crystal grain boundaries as described above, the crystal grain boundaries themselves are formed by the mechanism described above. The accumulation of strain in the grain boundary and the accumulation of strain due to the precipitate of this grain boundary are superposed, and as a result, the accumulation of strain in the grain boundary becomes more remarkable than in the grain. Is more likely to occur, and crystal grain coarsening becomes remarkable during the solution treatment after low strain processing.

The inventors of the present invention who have found the above phenomenon, further in the heat treatment type aluminum alloy rolled plate soft material, the specific size of the crystal grain size and the ratio of the grain boundary precipitate area to the total grain boundary area is formability and As a result of detailed examination of the effect on the crystal grain coarsening during solution treatment, the average grain size was 100
It has been found that if the ratio is not more than μm and the ratio is not more than ⅓, excellent moldability can be obtained and the crystal grain coarsening in the solution treatment can be suppressed to such an extent that it does not substantially interfere.

Here, when the average crystal grain size exceeds 100 μm, roughening is likely to occur during the forming process, and crystal grain coarsening is likely to occur due to selective growth of crystal grains during the solution treatment after the forming process. The area of grain boundary precipitates is 1 / of the total grain boundary area.
When it exceeds 3, the moldability is deteriorated, and the crystal grains are likely to become coarse due to the selective growth of the crystal grains during the solution treatment. Therefore, in order to achieve the object of the present invention, the average grain size is set to 100 μm or less as described above, and the area of the grain boundary precipitates on the grain boundaries is 1/3 or less of the total grain boundary area. Need to live.

The heat-treatable aluminum alloy that is the subject of the present invention, as described above, Al-Cu system, Al-Cu-Mg system, Al-Zn-
Mg type, Al-Zn-Mg-Cu type, Al-Mg-Si type,
The typical composition of the components is as follows.

In other words, Al-Cu alloys have Cu2 ~ 7 as their main alloying components.
In addition, the Al-Cu-Mg-based alloy contains Cu2 to 7 wt% and Mg 0.2 to 2 wt% as its main alloying components, and Mn is 0.8 wt% or less and Cr is 0.3 wt% as necessary. Below, Zr
It is an alloy containing at least one of 0.3 wt% or less, Ti 0.15 wt% or less, and V 0.15 wt% or less. The Al-Zn-Mg alloy contains Zn3 to 8 wt% and Mg0.5 to 3 wt% as main alloying components.
-Zn-Mg-Cu system alloy is Zn3 ~ 8 wt% as the main alloy component,
Contains 0.5 to 3 wt% Mg and 0.3 to 3 wt% Cu, all of which are Mn 0.8 wt% or less, Cr 0.3% or less, Zr 0.3 wt% or less, Ti 0.15 wt% or less, V0.15 wt % Is an alloy containing one or more kinds. Further, the Al-Mg-Si alloy contains Mg 0.3 to 1.5 wt% and Si 0.2 to 1.5 wt% as main alloy components, and if necessary, Mn 1.0% or less, Cr 0.4% or less, Cu0 .Four%
Hereafter, it is an alloy containing at least one of Zr 0.3 wt% or less, Ti 0.15 wt% or less, and V 0.15 wt% or less.

Next, a method for producing a heat-treated aluminum alloy rolled sheet soft material of the present invention as described above, that is, an average crystal grain size of 10
A method for obtaining a heat-treatable aluminum alloy rolled sheet soft material having a grain boundary precipitate area of 0 μm or less and 1/3 or less of the total grain boundary area will be described.

Although various methods for obtaining such a soft material are conceivable, the basic method is to apply the following three steps i), ii), and iii) in that order.

i) First, a hot rolling step or an annealing step after hot rolling,
Alternatively, a step of performing intermediate annealing by performing primary cold rolling after hot rolling, and in any of the above steps, with a large precipitate size that does not contribute to hardening of elements that should eventually contribute to hardening by aging treatment. Perform a treatment to deposit as much as possible.

ii) Next, the final cold rolling gives a working strain, and the coarse precipitates precipitated in the preceding stage are divided to be aligned in the rolling direction.

iii) After the final cold rolling, heating is performed under the condition that re-dissolution of precipitates is not substantially performed, and only recrystallization is performed.

The processing in each of the steps i) to iii) will be described more specifically below. First, the step i) (hereinafter referred to as the first step) will be described.
Examples of the treatment), such as Al-Cu system, Al-Cu
-Mg system, Al-Zn-Mg system, Al-Zn-Mg-Cu system or Al-
When hot-rolling a Mg-Si heat-treatable aluminum alloy ingot, the hot rolling rising temperature may be 300 ° C or higher, and the hot rolling coil may be gradually cooled at an average cooling rate of less than 30 ° C / hr. .

Alternatively, as the first-stage treatment, a hot rolling uphill which is hot-rolled according to a conventional method, or a plate which is hot-rolled and primary cold-rolled according to a conventional method is subjected to the following heat treatment. Is also good. That is, for these plates Al
-Mg-Zn system or Al-Mg-Zn-Cu system alloy 15
0-500 ℃, Al-Cu system, Al-Cu-Mg system, or Al
In the case of -Mg-Si alloys, each is heated and held at 200 to 580 ° C, and then slowly cooled at a cooling rate of less than 30 ° C / hr, or, for example, 450 ° C × 2hr → 400 ° C × 2hr → 350 ° C × 5hr → 30
A heat treatment is performed in which the temperature is gradually reduced and maintained, such as 0 ° C × 5 hrs → 250 ° C × 5 hrs → room temperature.

By performing such a first-stage treatment, it is possible to deposit a precipitate phase consisting of an element that should contribute to hardening in the final aging treatment in a coarse size that does not contribute to hardening and in a large amount as much as possible. . Here, making precipitates in a coarse size not only softens the plate without hardening it by fine precipitates, but also re-solidifies the precipitates in the heat treatment (annealing) in the subsequent third stage. It helps prevent melting and refines the grains in the final soft material.
Therefore, in this first step, it is desirable to deposit the grains in the coarsest size possible. The purpose of this first-stage treatment is to precipitate the precipitate phase in a size as large as possible so as not to contribute to hardening as described above, so that the crystal grains of the matrix need not be recrystallized. good. Coarse precipitates precipitated by such a first-stage treatment are present both at the grain boundaries and within the grains, but especially the grain boundary precipitates are much coarser than the intragrain precipitates. It is normal.

Next, in the step ii) (hereinafter referred to as the second step), the first
Cold rolling is performed on a plate softened by coarse precipitates sufficiently precipitated in the step treatment at a rolling rate of 40% or more, and more optimally a rolling rate of 50% or more. This cold rolling is essential for refining the crystal grains of the soft material. By performing cold rolling at a rolling rate of 40% or more on a plate in which coarse precipitates have been precipitated in the grain boundaries and grains in the first stage treatment, the coarse precipitates are decomposed and aligned in the rolling direction.

As described above, the cold rolled sheet in which the coarse precipitates are lined up in the rolling direction is subjected to the treatment of iii) (hereinafter, this is referred to as the third stage treatment). That is, rapid reheating is carried out at a temperature and holding time in a range in which re-dissolution of precipitates is practically hardly performed, and only recrystallization is carried out. In this way, the temperature range for causing only recrystallization without substantially re-dissolving the precipitate that has been sufficiently precipitated in advance includes alloy components, soaking and heating conditions, precipitate size, and cold rolling. As a guide, the heating rate is 300, although it varies depending on the rate, heating rate, etc.
C./min or more rapid heating, the temperature may be about 325 to 430.degree. C., and it is preferable that the temperature is as low as possible within the range where recrystallization occurs.

A fine recrystallized structure can be obtained by such a treatment in the third stage, but coarse precipitates lined up in the rolling direction do not form a solid solution again, so that in this state, a phase composed of elements that should contribute to hardening is formed. It is possible to obtain a rolled sheet soft material of a heat-treatment type aluminum alloy in which the size is such that it does not contribute to hardening and is sufficiently precipitated, and the matrix has a recrystallized structure.
Here, since the precipitates are lined up in the rolling direction regardless of the recrystallized grain boundary, unlike the case of the conventional heat-treatable aluminum alloy soft material, almost no precipitate exists at the grain boundaries.

In addition, when coarse precipitates and fine precipitates are mixed in the rolled plate before the third-stage treatment, some of the fine precipitates are generated during the third-stage heat treatment for recrystallization. Re-dissolution may occur, but re-dissolution of coarse precipitate hardly occurs. In this case, in order to obtain a completely soft material, in the cooling process of the heat treatment in the third stage, the elements of the fine precipitates once re-dissolved in the cooling process are gradually cooled at a cooling rate of less than 30 ° C / hr. Re-precipitation, or rapid cooling in the cooling process of the third stage heat treatment, and then low-temperature re-heating for re-precipitation. The conditions of low temperature reheating for the latter reprecipitation include Al-Zn-Mg system or Al-Zn-
In the case of Mg-Cu alloy, reheat to a temperature of 150-350 ℃, Al
-Cu-based, Al-Mg-Cu-based or Al-Mg-Si-based 20
Reheat to a temperature of 0 to 350 ° C, and
When the temperature is 0 to 250 ° C, the material is reheated and then rapidly cooled or gradually cooled, while when the reheating temperature is 250 to 350 ° C, the material is reheated and then slowly cooled at a cooling rate of less than 30 ° C / hr. The precipitate re-precipitated by such a reheating treatment is derived from the element re-dissolved in the previous third heating treatment, but the re-dissolved amount is small, so The amount of precipitates re-precipitated by the heat treatment is also small, so there is almost no re-precipitation on the crystal grain boundaries, and even if they are re-precipitated on the crystal grain boundaries, the amount is extremely small, and the degree is As specified in this invention, the area of grain boundary precipitates is 1/3 of the total grain boundary area.
It is well within the following.

As described above, the basis of the above-described method described as a typical method for obtaining the heat-treatable aluminum alloy rolled sheet soft material of the present invention is that the elements contributing to hardening should be sufficiently large and sufficiently coarse in advance. After precipitation, cold rolling gives cold working strain and coarse precipitates are lined up in the rolling direction, and then the precipitates are rapidly heated to a range that does not substantially re-dissolve, and fine re-formation is performed. A recrystallized structure composed of crystal grains is formed, and if necessary, some of the re-dissolved elements are reprecipitated. Specific means and specific conditions for obtaining the aluminum alloy rolled sheet soft material of the present invention in accordance with such a method can be variously considered in addition to the means and conditions described above. Means for satisfying material size and grain boundary precipitate conditions,
Of course, it can be applied if it is a condition.

Here, if the difference between the typical method for obtaining the heat treatment type aluminum alloy rolled sheet soft material of the present invention as described above and the method for obtaining the conventional heat treatment type aluminum alloy rolled sheet soft material is clarified , In the conventional method, the basic idea is to first recrystallize at a sufficiently high temperature, and then,
It is in the point of achieving complete softening by sufficiently coarsening the hardening-contribution elements that are excessively solid-solved. In such a method, a softness that simultaneously satisfies the crystal grain size and the grain boundary precipitate conditions as specified in the present invention. No material is obtained, and in particular, precipitates are deposited over many regions of the grain boundaries. On the other hand, in the typical method for obtaining the soft material of the present invention described above, on the contrary, the elements contributing to the hardening are preliminarily coarsely precipitated in advance, and thereafter, the elements are re-formed under the condition that they are not substantially re-dissolved. Crystallization is performed, and by applying such a method, it is possible to simultaneously satisfy the grain size and grain boundary precipitate conditions specified in the present invention.

In the third-step heat treatment (recrystallization annealing), since coarse precipitates do not substantially re-dissolve, the subsequent cooling rate has essentially no effect, and even if it is rapidly cooled, it is hardened. Instead, it becomes a soft material as it is. When fine precipitates are slightly re-dissolved by heating, they may be slightly hardened, but the extent thereof is slight, and sufficient molding workability is exhibited as they are. In this case, of course, if necessary, an appropriate reheating treatment for reprecipitation may be performed as described above. However, when performing this reprecipitation treatment, it is important to set the heating temperature to a low temperature. That is, even though the re-dissolved elements are re-precipitated, this is a treatment to be performed on a plate in which most of the precipitation has already occurred. Re-dissolution progresses in the precipitation treatment, and in this case, a new precipitate is generated in the grain boundary in the cooling process of the re-precipitation treatment, and the object of the present invention cannot be achieved. From this point of view, it is appropriate that the heating temperature in the case of performing the reprecipitation treatment as described above is 350 ° C. or lower.

The heat treatment type aluminum alloy rolled plate soft material obtained by the typical process as described above has an average crystal grain size of 100.
Since it is less than μm and the area of grain boundary precipitates is less than 1/3 of the total grain boundary area, it has good moldability and prevents the crystal grains from becoming coarse during the subsequent solution treatment. it can. That is, the crystal grain coarsening at the time of the subsequent solution treatment is caused by the selective growth of the strain-integrated grain boundaries by the low strain cold working by the strain-induced grain boundary movement. Since there are few precipitates existing in the boundaries, strain does not easily accumulate at the crystal grain boundaries even when subjected to cold working with low strain, and since there are many grain boundaries because the crystal grains are fine, the strain at the grain boundaries is dispersed,
On the other hand, since there are few precipitates at the grain boundaries, on the contrary, large precipitates are also scattered within the grains, and strain is accumulated to some extent around the coarse precipitates within the grains. Since the distribution is averaged, it is possible to prevent the crystal grains from becoming coarse during the solution treatment due to the strain accumulation of the crystal grain boundaries.

Examples Representative heat-treatable aluminum alloys shown by alloy codes A to E in Table 1 were melted and continuously cast by a conventional method, homogenized under the conditions shown in Table 2, and then similarly. 2 Hot rolling was performed at the hot rolling start temperature and the hot rolling temperature shown in the table to obtain a hot rolled sheet (coil) having a thickness of 6.0 mm. Here, alloy A
Had recrystallized due to thermal expansion.

Next, the following heat treatments were performed on the hot-rolled sheets of each of the alloys A to E as the first-stage heat treatment.

Regarding alloy: After heating at 300 ° C for 10 hours, it was cooled to below 200 ° C at a cooling rate of 15 ° C / hr.

Regarding alloy B: After heating at 450 ° C. for 2 hours, it was cooled to 200 ° C. or less at a cooling rate of 15 ° C./hr.

Regarding alloys C and D: After heating at 450 ° C. for 2 hours, it was cooled to 260 ° C. at a cooling rate of 15 ° C./hr, held at that temperature for 5 hours, and then cooled to 200 ° C. or less at a cooling rate of 15 ° C./hr.

Regarding Alloy E: After heating at 450 ° C. for 2 hours, it was cooled to 260 ° C., held at that temperature for 5 hours, and then cooled to 200 ° C. or less at a cooling rate of 15 ° C./hr.

The soft coil thus obtained was then cold-rolled (rolling rate 75%) to a thickness of 1.5 mm.

Then, for the coil after cold rolling, as the above-described third stage processing, the following processing symbols A-1, ..., E-1; and the processing symbols A-2 ,. , E-2 were heat-treated under the conditions. Here, each processing code (A-1 etc.)
The letter at the beginning of the letter corresponds to the alloy code, so that for example A-
Both 1 and A-2 mean the treatment for the cold rolled coil of alloy A.

A-1: Continuous rapid heating was performed using a continuous annealing line.
The heating rate was 1500 ° C./min, the heating temperature was 400 ° C., and the temperature was not maintained. Ie 40
Upon reaching 0 ° C, it was immediately cooled. The cooling was air cooling, and the cooling rate at that time was about 1000 ° C / min. Further, the coil was heated at 300 ° C. for 5 hours and cooled at a cooling rate of 20 ° C./hr.

B-1: Continuous rapid heating was performed using a continuous annealing line.
The heating rate and the cooling rate are the same as in A-1. The heating temperature was 380 ° C., and the temperature was not maintained. Further, the coil was heated at 230 ° C. for 5 hours and cooled.

B-3: Continuous rapid heating was performed using a continuous annealing line.
The heating rate and cooling rate are the same as in A-1. The heating temperature was 425 ° C. and the holding was performed for 3 seconds. Further, the coil was heated at 330 ° C. for 5 hours and cooled at a cooling rate of 30 ° C./hr.

B-4: Continuous rapid heating was performed using a continuous annealing line.
The heating rate was 1500 ° C./min, the heating temperature was 520 ° C., and the holding time was 15 seconds. The cooling rate was 1000 ° C / min. Further, this coil was heated and held at 380 ° C. × 2 hr at a heating rate of 50 ° C./hr, and then cooled at a cooling rate of 35 ° C./hr.

C-1: Continuous rapid heating was performed using a continuous annealing line.
The heating rate and the cooling rate were the same as those in A-1, the heating temperature was 380 ° C., and the holding at that temperature was 0. The coil was heated at 190 ° C. for 10 hours and then cooled in the furnace.

D-1: The cut plate was rapidly heated by an infrared heater. The heating temperature is 350 ° C, and the heating rate is 1000 ° C / sec or more. Hold time at 350 ° C for 30 seconds, then 200 ° C
It was gradually cooled to 20 ° C / hr.

E-1: The plate was heated rapidly with a salt bath. The temperature of the salt bath was 500 ° C, a thermometer was attached to the cutting plate, and when the material temperature reached 420 ° C, it was taken out of the furnace and allowed to cool.
Therefore, the holding time was practically 0, and the heating rate was over 1000 ° C / sec.

A-2: Heated up to 400 ℃ × 2hr by batch furnace, up to 200 ℃ 25
Cooled at ° C / hr. The heating rate is 20 ° C / hr.

B-2: Processed under the same conditions as A-2.

C-2: Treated under the same conditions as A-2.

D-2: Continuous rapid heating was performed using a continuous annealing line. The heating rate was 1500 ° C./min, the heating temperature was 480 ° C., the holding time was substantially 0, and the cooling rate was 1000 ° C./min. Furthermore, this coil was gradually cooled to room temperature at a cooling rate of 400 ° C. × 2 hr heating retention number of 15 ° C./hr.

E-2: Continuous rapid heating was performed using a continuous annealing line. The conditions are the same as in the case of D-2 except that the heating temperature was 520 ° C.

About the heat treatment type aluminum alloy rolled plate soft material obtained by the above respective treatments A-1, ..., E-1; A-2, ..., E-2,
The average crystal grain size and the ratio of the area of grain boundary precipitates to the total grain boundary area were investigated, and various material properties and formability were also investigated. Further, the total grain boundary area and the area of the grain boundary precipitate were observed by a transmission electron microscope. That is, the cross section is observed with a transmission electron microscope, the observed image is directly or photographed, and the grain boundary area within a certain observation area (the area including 4 to 5 crystal grains as a standard) and the precipitation on the grain boundary by an image processing device. The area of the product was calculated, and the ratio of the area of the grain boundary precipitate on the crystal grain boundary to the total grain boundary area was determined. Further, the soft material was subjected to 15% cold working corresponding to the forming work, and then solution treatment and quenching were performed, and the degree of crystal grain coarsening was confirmed by the degree of rough skin. The solution treatment was performed at 500 ° C. × 1 hr for alloys A and B, 470 ° C. × 1 hr for alloys C and D, and 530 ° C. × 1 hr for alloy E. The results of those investigations are shown in Table 3.

As is clear from Table 3, A-1, B-1, B-3, C-1, D-
The soft material obtained by performing the treatment of 1, E-1 has a fine average particle size of about 30 μm, and fully satisfies the condition of 100 μm or less specified in the present invention, and The number of grain boundaries where precipitates are present is extremely small, and the area ratio of the grain boundary precipitates sufficiently satisfies the condition of 1/3 or less of the total grain boundary area as defined in the present invention. And all of these soft materials satisfying the present invention have an elongation of 20% or more and an Erichsen value of 9.1 mm or more, which are excellent in moldability, and
% It is clear that the surface roughness after the solution treatment / quenching treatment after cold working is small, in other words, the tendency of crystal grains to coarsen due to solution treatment is small.

On the other hand, when the A-2, B-2, and C-2 treatments were performed, the crystal grains were coarse and the grain boundary precipitates were remarkably large, so that elongation,
The Erichsen value is low and the moldability is poor, and the surface roughness after 15% cold working-solution treatment / quenching is remarkable, and it can be seen that the crystal grains are coarsened by the solution treatment. Also B-
When treated with 4, D-2, E-2, the crystal grain is 100μm
Although it was fine as below, there were many grain boundary precipitates, and therefore the formability was good, but 15% cold working-roughening after solution hardening, roughening of crystal grains by solution treatment It is understood that the change has occurred.

Incidentally, FIG. 1 is a transmission electron micrograph of a soft material (inventive material) obtained by subjecting alloy B to treatment B-1 and a soft material (comparative material) obtained by subjecting alloy B to treatment B-2. It is shown in FIG. As is clear from these figures, in the B-2 treated material (Fig. 2), precipitates are present over almost the entire grain boundary, whereas in the B-1 treated material (Fig. 1), the precipitates are present. It can be seen that there are almost no precipitates in the boundary.

Effects of the Invention As is clear from the above examples, the heat treatment type aluminum alloy rolled plate soft material of the present invention is Al-Cu system, Al-Cu system.
-Mg system, Al-Zn-Mg system, Al-Zn-Mg-Cu system, Al-Mg-Si
As a soft material in the stage before being subjected to the forming process for a rolled plate for the purpose of being used after being subjected to the forming process before solution treatment / quenching, it has a remarkably good forming processability. During the solution treatment, it can withstand high-strength molding processing, can prevent the occurrence of surface roughening and minute cracks during molding processing, and can prevent crystal grain coarsening due to solution treatment after molding processing. Can prevent the occurrence of rough skin and deterioration of mechanical properties due to the coarsening of crystal grains of
Compared with the conventional heat-treatment type aluminum alloy soft material, it is possible to exert a remarkably excellent effect.

[Brief description of drawings]

FIG. 1 is a transmission electron micrograph for showing the precipitation state of deposits of the B-1 treated material (material of the present invention) in Examples, and FIG.
The figure is a transmission electron micrograph for showing the state of deposits of the B-2 treated material (comparative material).

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Claims (1)

[Claims] 1. An Al-Cu system, an Al-Cu-Mg system, an Al-Zn-Mg system,
A soft material before forming, which is made of an Al-Zn-Mg-Cu-based or Al-Mg-Si-based heat-treatable aluminum alloy and which is used after being subjected to solution-treatment / quenching before forming. , The average crystal grain size is 100 μm or less, and the area of the grain boundary precipitates on the grain boundaries is 1/3 or less of the total grain boundary area. A heat-treated aluminum alloy rolled sheet soft material that does not cause crystal grain coarsening in the solution treatment after working.