JP6467154B2 - Manufacturing method of high strength and high ductility aluminum alloy sheet - Google Patents

Description

  The present invention relates to a method for producing a high-strength and high-ductility aluminum alloy plate suitable for use as a structural material for transport equipment such as automobiles, which has high strength and excellent formability and further has good pickling properties.

In recent years, an aluminum alloy plate tends to be used instead of a steel plate in a transport device such as an automobile because of a demand for weight reduction. Such materials for transportation equipment are required to have high strength and excellent formability (high ductility). Currently, Al-Mg-Si alloys that provide high strength tend to be used for automobile panels and the like. In this alloy, precipitates and Mg—Si clusters are formed by heat treatment, and the strength increases due to these formations. However, an increase in strength, on the other hand, causes a decrease in ductility, making it difficult or impossible to form a predetermined shape during press molding.
For this reason, Al-Mg-Si alloys that achieve both high strength and high ductility by controlling components and heat treatment have been proposed in Patent Documents 1 to 11 described later.

The technology described in these patent documents is basically a long-time heat treatment for several hours in a temperature range around 100 ° C. where the heat treatment temperature of the aluminum alloy is relatively low after the solution heat treatment. Is to do. Further, the characteristics are improved by controlling the cooling rate from the high temperature heat treatment before the low temperature heat treatment or by controlling the cooling rate of the low temperature heat treatment. The Al-Mg-Si alloy adjusts the characteristics represented by strength by fine precipitates and clusters made of Mg and Si formed in the material, so it can be said that the material control by heat treatment is reasonable, but it takes a long time. The heat treatment causes a dense and thick oxide film to be formed. If such a thick oxide film is formed, pickling becomes difficult, and the remaining oxide film that cannot be removed by a conventional pickling method makes it impossible to form a uniform chemical film. In order to completely remove such a film by pickling, a longer processing time than usual is required, and the manufacturing cost increases.
For this reason, no material has been proposed that satisfies the strength and elongation of the Al—Mg—Si alloy, and further satisfies the pickling properties at a high level.

JP 2004-323952 A JP 2008-303449 A Japanese Patent Laid-Open No. 2004-211177 JP-A 64-11937 Japanese Patent Laid-Open No. 2-122045 JP-A-4-259358 JP-A-4-318144 JP-A-5-125505 Japanese Patent Laid-Open No. 9-41062 Japanese Patent Laid-Open No. 7-18390 JP-A-7-166285

  The present invention makes it possible to provide a material having not only ductility and strength higher than those of conventional Al—Mg—Si alloys but also good pickling properties.

In order to simultaneously improve the strength and ductility of the aluminum alloy, it is effective to increase the work hardening rate. In order to increase the work hardening rate, it is necessary to effectively increase the dislocation density at the time of processing. To achieve this, the amount of solid solution atoms that affect the movement of dislocations is adjusted and generated by heat treatment. Cluster formation has been utilized.
However, in order to generate a sufficient amount of clusters, it is necessary to hold for a long time, and the long-time holding has a problem of forming an oxide film that thickly covers the surface of the alloy plate and causing the above-described adverse effects due to chemical formation.

In order to solve the above-mentioned problem, the present inventor studied a means for efficiently generating clusters in an aluminum alloy in as short a time as possible.
From the viewpoint of securing the pickling property of the aluminum alloy, it is desirable that the total heat treatment time is 100 hours or less. As a result, it was found that clusters can be formed efficiently before the oxide film develops excessively by dividing the generation of clusters into a nucleation process and a growth process and performing different heat treatments. Furthermore, in the nucleation process and growth process, more favorable work hardening behavior can be obtained by optimizing the heat treatment of each process and independently controlling the type, size, distribution density, etc. of precipitates and clusters. It was confirmed.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%, Mg: 0.5% or more and 1.2% or less, Si: 0.3% or more and 1.5% or less, with the balance of inevitable impurities and Al, Mg / Si T1 is 60 or more and 160 or less, and t1 is 63.5 exp (−0.038 T1) +2. The first heat treatment is performed at 5 to 24 and maintained at the temperature T1 ° C. Thereafter, the temperature T2 ° C exceeds the temperature T1 ° C and is 170 ° C or less, and the time t2 satisfies the relationship of 3 hours to 72 hours. A method for producing a high-strength, high-ductility aluminum alloy sheet having a tensile strength of 250 MPa or more and an elongation of 20% or more in a uniaxial tensile test, wherein a second heat treatment is performed at a temperature T2 ° C. for t2 hours.
(2) In addition to the above composition, Cu: 0.3% to 2.0%, Fe: 0.25% or less, Mn: 0.50% or less, Ti: 0.20% or less, Cr: 0.3 The method for producing a high-strength, high-ductility aluminum alloy sheet according to claim 1, comprising at least one or more of% or less.
(3) The high strength according to claim 1 or 2, wherein after the second heat treatment, a third heat treatment is performed at a temperature exceeding T2 ° C and not more than 180 ° C for 2 hours or less. A method for producing a highly ductile aluminum alloy sheet.

  According to the present invention, an Al-Mg-Si aluminum alloy plate having high strength, high formability, and good pickling properties can be provided, and applied as a steel plate substitute to a site where a conventional steel plate is used in transportation equipment such as automobiles. Is possible. As a result, it greatly contributes to weight reduction of transportation equipment.

Explanatory drawing which shows an example of the relationship between aging time and the yield stress in the case of manufacturing the aluminum alloy plate which concerns on this invention. The graph which shows the relationship between content of Mg and Si contained in the aluminum alloy plate used in the Example and the comparative example, and the quantitative ratio of Mg and Si.

In the Al—Mg—Si alloy, in order to control the material strength, it is generally recognized as an almost correct fact that the formation of Mg—Si clusters (hereinafter referred to as clusters) is essential.
In accordance with this recognition, in the following description, the requirements of the present invention will be described in relation to “cluster”. However, in the present invention, “cluster” itself is not defined quantitatively. This is because the “cluster” controlled by the present invention is very fine, so the observation area is narrowed, and the current analytical instrument can only obtain very local information, and reliable data can be obtained in comparative evaluation. This is because it was difficult to obtain. In the future, the development of analytical instruments is expected to enable quantitative definition based on a sufficient amount of data regarding the size, density, composition and structure of clusters, and the impact of the “cluster” on the effects of the present invention. There is a possibility that some wrinkles may occur in the contribution, but it should be noted that in the present invention, “cluster” is explained as the cause of the effect of the present invention.
The present inventor has found that Mg clusters, Si clusters, Mg—Si clusters, GP zones, and the like are generated as a study of the precipitation process at 175 ° C. or less in an Al—Mg—Si alloy. The GP zone means an Mg—Si cluster having a size of about 2 nm showing contrast in a transmission electron microscope. In Al-Mg-Si alloys, it can be estimated that Mg-Si clusters, GP zones, β phase, β 'phase, and β "phase precipitates have various effects on material strength and elongation. Control technology is important, and as a result of studying heat treatment conditions, aging conditions, etc. in Al—Mg—Si alloys, we have found out the effectiveness explained in this embodiment, and in the case of aging for Al—Mg—Si alloys. It was found that state changes such as cluster nucleation and growth, cluster size and distribution, etc. can be controlled by heat treatment in two stages at specific different temperature ranges.
Based on these findings, the present inventor adopts the following modes for the composition ratio of the Al—Mg—Si alloy to be applied.

(Components of aluminum alloy plate)
"Mg content: 0.5 mass% or more and 1.2 mass% or less"
In the aluminum alloy plate of the present embodiment, if the Mg content is less than 0.5% by mass, a cluster that sufficiently contributes to an increase in work hardening is not formed. On the other hand, when it exceeds 1.2 mass%, the Mg / Si ratio limited to the following is increased, the work hardening ability of the Mg—Si cluster is lowered, and the effect of increasing ductility is reduced. Furthermore, if Mg is added excessively, a precipitate of Mg alone is generated. This precipitate of Mg alone becomes a starting point of fracture and greatly reduces ductility.
“Si content: 0.3 mass% or more and 1.5 mass% or less”
In the aluminum alloy plate of the present embodiment, as in the case of Mg, if the content of Si is less than 0.3% by mass, clusters that sufficiently contribute to an increase in work hardening are not formed. When it exceeds 1.5 mass%, the Mg / Si ratio limited to the following is decreased, and also in this case, the work hardening ability of the Mg—Si cluster is decreased and the effect of increasing the ductility is decreased. Furthermore, if Si is added excessively, a precipitate of Si alone is generated. This precipitate of Si alone also serves as a starting point of fracture and greatly reduces ductility.

In the aluminum alloy plate of the present embodiment, in order to form clusters with the optimum size and distribution density for work hardening, it is also important to control the addition amount ratio in terms of mass% of Mg and Si. If Mg / Si is 1.0 or less, the cluster distribution can be controlled to a preferable state. Clusters are thought to form and grow with Si atoms as nuclei, so the number of Si atoms is larger than the number of Mg atoms, that is, Mg / Si is set to 1.0 or less so that Si atoms are the center. Cluster distribution density increases and work hardening ability improves.
In the aluminum alloy plate of the present embodiment, the balance is inevitable impurities and aluminum.

In the aluminum alloy plate of this embodiment, Cu may be added to further improve the formability. In this case, the amount of added Cu is 0.3% by mass or more and 2.0% by mass or less. If it is less than 0.3% by mass, sufficient improvement in moldability is not observed, and if it exceeds 2.0% by mass, ductility is lowered by forming a new precipitate.
In the aluminum alloy plate of this embodiment, Fe may be added to further improve the strength. In this case, the added Fe amount is 0.25% by mass or less. If the addition amount of Fe exceeds 0.25 mass%, ductility will fall.
In the aluminum alloy plate of the present embodiment, Ti may be added in order to further improve the strength. In this case, the amount of added Ti is 0.20% by mass or less. If the amount of Ti exceeds 0.20% by mass, the ductility is lowered.
In the aluminum alloy plate of this embodiment, Mn may be added in order to further improve the strength. In this case, the amount of added Mn is 2.5% by mass or less. If the amount of Mn added exceeds 2.5% by mass, the ductility decreases.
In the aluminum alloy plate of this embodiment, Cr may be added in order to further improve the strength. In this case, the amount of added Cr is 0.3% by mass or less. If the added amount of Cr exceeds 0.3% by mass, ductility decreases.

(Aluminum alloy plate manufacturing method)
Next, an example of the manufacturing method of the said aluminum alloy plate is demonstrated.
In general, an aluminum alloy sheet is manufactured by melting, casting, homogenizing heat treatment, hot rolling, cold rolling, solution heat treatment, and quenching treatment of an alloy having a target composition. In order to control the development of the crystal structure, cluster dispersion, and oxide film, which are the characteristics of the aluminum alloy plate of this embodiment, the thermal history after the solution heat treatment, which is the final heat treatment, is important in the manufacturing method described above. .
In the following, first, heat treatment after solution heat treatment will be described, and then a general manufacturing method before and after this thermal history will be described.

After the solution heat treatment is completed, the effects of the present embodiment can be obtained by controlling the clusters and the oxide film by passing through the following thermal history. This thermal history can be roughly divided into three stages.
Hereinafter, this heat history is referred to as a first heat treatment, a second heat treatment, and a third heat treatment in the order of execution.

After the solution heat treatment, a first heat treatment is performed by holding at a holding temperature T1 ° C. for t1 hours.
T1 is 60 or more and 160 or less, and t1 is 63.5exp (−0.038T1) +2.5 or more. In the aluminum alloy plate according to the composition of the present embodiment, the clusters necessary for high strength and high ductility are formed at a holding temperature of 60 ° C. or higher and 160 ° C. or lower, but in order to obtain high strength and high ductility in less than a predetermined holding time. Not enough cluster nuclei are formed. This holding time is a function of the temperature T1. That is, when held at a high temperature, the diffusion coefficient increases, so that it takes a short time to grow into a cluster of a predetermined size. On the other hand, holding at a low temperature requires a long time.
When the holding temperature is T1 ° C., a holding time of 63.5 exp (−0.038 T1) +2.5 or more is necessary, and when it is less than that, the nuclei of clusters necessary for high strength and high ductility are not formed and continued. The possibility of re-dissolution by heat treatment increases. However, holding for a long time increases the manufacturing cost, reduces industrial advantages, and forms a stronger oxide film. Therefore, it is reasonable to set the upper limit to 90 hours or less. Most preferably, the heat treatment time is within 24 hours in the first heat treatment in which the most time is spent for the heat treatment. Particularly preferably, it is within 18 hours.

The heat treatment conditions of the first heat treatment are the main points of the present invention. The idea is to perform heat treatment for cluster nucleation when classified into cluster nucleation and growth as described above. That is, the purpose of the first heat treatment of this embodiment is to carry out the heat treatment until the end of cluster nucleation.
The concept of this first heat treatment is shown in FIG. When heat treatment is performed at a predetermined heat treatment temperature, the strength (yield stress) increases rapidly from a specific temperature according to the holding time. Until the start of the increase in strength corresponds to nucleation, the first heat treatment is performed at least until that time, that is, until nucleation is completed. If the first heat treatment is completed in a shorter time than this, cluster growth does not occur in the subsequent heat treatment, and high strength and high ductility cannot be obtained in the aluminum alloy.

  According to conventional knowledge, the time when the yield stress value is below a predetermined value may be defined as the heat treatment time. Such a definition includes a case where the heat treatment is terminated without completing nucleation. On the contrary, in the present application, the heat treatment is performed until the strength increases beyond a predetermined yield stress. That is, the heat treatment is performed until the yield stress starts to increase from a value that was constant until then. For this purpose, a long holding time is required. However, long-term aging has few industrial advantages. Therefore, the time when the intensity increase as shown in FIG. 1 starts is determined as the minimum value of the holding time.

After that, the second heat treatment is performed for t2 hours at a temperature T2 ° C that satisfies the relationship that the temperature T2 exceeds the temperature T1 and is 170 ° C or less and the time t2 is 3 hours or more and 72 hours or less.
In the second heat treatment, the growth of clusters formed in the first heat treatment is aimed. The temperature necessary for the growth of the cluster is to be maintained at a temperature higher than that of the first heat treatment. Therefore, it is necessary to maintain a temperature exceeding T1 ° C. However, when the temperature exceeds 170 ° C., there is a high possibility that a precipitate having a structure different from that of the cluster is formed, and there is a high possibility that the cluster formed by the first heat treatment also grows into the precipitate. If a precipitate having a structure different from that of the cluster is generated, the high strength and high ductility obtained by forming the cluster cannot be achieved.
The concept of holding time is the same as the first heat treatment. As the holding temperature increases, the required holding time decreases. The upper limit can be defined as 72 hours. Even if the holding time exceeds 72 hours, sufficient cluster growth can be expected, but this is not desirable because it causes an increase in manufacturing cost due to high-temperature and long-time manufacturing. In addition, there is a concern that the strength is lowered after the dispersion and coarsening of the clusters due to Ostwald growth when the temperature is maintained for a long time. Further, there is a concern that the clusters grow sufficiently and change into the precipitates. Therefore, the upper limit holding time is 72 hours as a temperature range in which there is no such concern. The lower limit is 3 hours, and if it is less than 3 hours, the clusters formed by the first heat treatment cannot be expected to sufficiently grow into clusters necessary for high strength and high ductility at any holding temperature.

After the second heat treatment, it is preferable to perform the third heat treatment for 2 hours or less at a temperature of 180 ° C. or less exceeding the temperature T2. In the third heat treatment, the cluster growth that cannot be completed in the second heat treatment is completed. Even within the holding time specified by the second heat treatment, a certain degree of high strength and high ductility can be achieved, but further high strength and high ductility can be expected by the third heat treatment.
For this purpose, a longer heat treatment is required at the holding temperature of the second heat treatment. In order to achieve such high strength and high ductility in a short time, it is necessary to keep the temperature higher than that of the second heat treatment. As in the case after the second heat treatment, when the amount of remaining Mg atoms and Si atoms are very small, the temperature at which precipitates are formed rises slightly and exceeds 180 ° C.
Therefore, it is carried out in the holding temperature range of T2 ° C. or higher and 180 ° C. or lower. Below T2 ° C, it is necessary to hold for a long time to achieve further high strength and high ductility. At temperatures exceeding 180 ° C, precipitates having a structure different from that of clusters are formed or the clusters change into precipitates. Ductility cannot be achieved. Further, if the holding time exceeds 2 hours, the clusters formed up to the second heat treatment may be changed into precipitates even at a temperature of 180 ° C. or lower. Although there is no particular lower limit for the holding time, a holding time of 10 minutes or more is preferable because further growth of the cluster is less likely to occur when the holding time is less than 10 minutes.

The ingot of the Al—Mg—Si alloy having the above component composition is subjected to homogenization heat treatment, hot rolling, and cold rolling, and then subjected to heat treatment after solution heat treatment and solution heat treatment. These steps are the same as in the usual method. Note that one or more heat treatments may be performed during the cold rolling, or the hot-rolled sheet may be heat treated after the hot rolling.
First, in the melting and casting process, a melt casting method such as a continuous casting rolling method or a semi-continuous casting method (DC casting method) is selectively performed on the molten alloy.
The next homogenization heat treatment is aimed at homogenizing the material. The main purpose of the homogenizing heat treatment is to eliminate segregation of additive elements. For this purpose, heat treatment at a temperature of 560 ° C. or higher and a melting point or lower is required. Although the heat treatment time depends on the amount of added elements, it is sufficient if it is 20 minutes or longer and 8 hours or shorter within the above temperature range. If it is shorter than 20 minutes, it is difficult to sufficiently eliminate segregation. On the other hand, if it is 8 hours or more, the production cost increases. Further, after being held within the above temperature range for the above heating time, it is necessary to cool at a cooling rate of 20 ° C./sec or more. When the cooling rate is less than 20 ° C./sec, other elements form precipitates in addition to Mg and Si, and this lowers the efficiency of solid solution in the heat treatment in the subsequent step. Means for increasing the cooling rate include forced air cooling and water cooling, but the means is not particularly limited.

In the subsequent hot rolling, it is necessary to set a starting temperature, which should be 450 ° C. or higher. At temperatures below 450 ° C., the frequency of recrystallization during hot rolling decreases sharply, which increases the possibility of non-recrystallization in the final product. Preferably, if the starting temperature is 560 ° C. or higher, the precipitate remaining in the homogenization heat treatment can be dissolved. The final thickness is not particularly limited and is preferably 5 mm or less from the viewpoint of the ease of the subsequent cold rolling process.
In order to obtain reliable recrystallization, the hot-rolled sheet may be annealed before cold rolling. In that case, a condition of 20 minutes or longer at a temperature of 400 ° C. or higher is sufficient, but annealing for a long time is a drawback of increasing the manufacturing cost. In consideration of the entire manufacturing cost, this hot-rolled sheet annealing may be omitted.

Subsequent cold rolling may be performed by a standard method to a desired plate thickness.
Similar to hot-rolled sheet annealing, in order to obtain reliable recrystallization, one or more heat treatments (intermediate annealing) may be performed during the cold rolling. The temperature at this time may be the same as the hot rolling annealing before cold rolling at a temperature of 400 ° C. or more, and the holding time may be 20 minutes or more and a holding time not more than the time that does not increase the manufacturing cost.
It is preferable that the cold rolling rate from the intermediate annealing to the final plate thickness is large. By increasing the cold rolling rate, the recrystallized grains at the time of final annealing are refined. Desirably, the cold rolling rate from the intermediate annealing to the final thickness is 75% or more.

  After the cold rolling, solution heat treatment is performed. The solution heat treatment temperature is set to 550 ° C. or higher and the melting point or lower. The purpose of this annealing is to increase the amount of supersaturated solid solution of added Mg atoms and Si atoms. If the temperature is lower than 550 ° C., it is difficult to form a sufficient amount of clusters that contribute to work hardening in the subsequent heat treatment. Moreover, it is desirable to cool immediately after annealing. If the cooling is slow, Mg and Si precipitates are formed. For that purpose, it is necessary to cool to 50 ° C. or less at a cooling rate of 20 ° C./sec or more. When the cooling rate is less than 20 ° C./sec, precipitates of Mg and Si are formed, and desired strength and ductility cannot be obtained.

If the aluminum alloy plate is obtained by performing the first heat treatment and the second heat treatment described above, and performing the third heat treatment as necessary, the control of the number of cluster nuclei, the growth control of the clusters, the distribution of the clusters Since the control is suitably performed, the tensile strength in the short axis tensile test is 250 MPa or more, the tensile strength is excellent, the elongation is 20% or more, and the elongation is excellent. Moreover, since each heat processing temperature and aging time are suppressed and the film thickness of the surface oxide film can also be suppressed, the aluminum alloy plate which has favorable pickling property can be provided.
Therefore, if it is the aluminum alloy plate obtained by the above-mentioned heat treatment, an alloy plate having high strength and good formability can be provided as a structural material for a transport device such as an automobile, and transportation represented by an automobile. Contributes to weight reduction of equipment.

Table 1 shows the components (mass%) of various aluminum alloys used in this example.
Table 2 shows the heat treatment conditions after the solution heat treatment of each alloy listed in Table 1, and the tensile property values (tensile strength and elongation) of the obtained aluminum alloy sheet. All the aluminum alloys in Table 2 were subjected to a homogenization annealing treatment at 560 ° C. for 1 hour after casting. After homogenization annealing, it cooled to room temperature at 30 degreeC / sec. The subsequent hot rolling was started at 500 ° C. and the final thickness was 4 mm. After hot rolling, cold rolling up to a plate thickness of 1 mm was performed, and no intermediate annealing was performed during cold rolling.
A tensile test piece of JIS No. 5 (corresponding international standard ISO6892) was produced from an aluminum alloy plate obtained after cold rolling. The gauge length was 50 mm, and the tensile direction was parallel to the material rolling direction. In the subsequent solution heat treatment, holding treatment was performed at 560 ° C. for 1 minute using a salt bath. After holding, water quenching was performed. The cooling rate by water quenching is 20 ° C./sec or more. After water quenching, heat treatment was performed in an oil bath at a predetermined temperature and a predetermined holding time. After the heat treatment by the oil bath, it was cooled to room temperature by air cooling, and a tensile test was performed.

Table 1 shows the alloy composition, and Table 2 shows the manufacturing process and tensile properties of these alloy plates.
In Table 1, alloys A to D are alloys satisfying the component composition defined in the claims, and alloys E to M are alloys having compositions deviating from the component composition defined in the claims.
FIG. 2 is a graph in which the composition positions of alloys A to M shown in Table 1 are plotted in a chart in which the vertical axis is set to Si content and the horizontal axis is set to Mg content for reference. Further, a boundary line of Mg / Si ≦ 1.0 was drawn on this graph, and the range of Mg / Si ≦ 1.0 was indicated by an arrow.
The ranges of Mg: 0.5% to 1.2% and Si: 0.3% to 1.5% specified in the claims are rectangular regions surrounded by chain lines in FIG. Even inside, the ◆ marks plotted in the region above the boundary line of Mg / Si ≦ 1.0 indicate the compositions of the examples alloys AD.
In FIG. 2, the compositions of alloys E, G, I, K, and M fall outside the rectangular region surrounded by the chain line, and are within the rectangular region surrounded by the chain line and below the boundary line of Mg / Si ≦ 1.0. The composition of alloys F, J, H, and L corresponds to this region.

Alloys E, F, and G have a small composition of Mg and Si, and cannot secure a cluster amount necessary for ensuring strength or ductility.
In alloys I, K, and M containing excessive Mg or excessive Si, ductility is lowered due to the formation of precipitates that are the starting points of fracture. In the alloys H, J, and L with Mg / Si of 1.0 or more, the types of clusters change, so the contributions to the improvement of the strength and ductility of the clusters differ, and the strength decreases.
In alloy A which is a component according to claim 1, TS: 250 MPa or more and El: 20% or more cannot be obtained when the production process is outside the scope of claims.
Sample No. In No. 17, since T1 and t1 are not more than those defined in the claims, the cluster cannot grow to a size that contributes to the strength, and the strength is insufficient. Sample No. At 18, the temperature is sufficient, but the holding time is not sufficient for cluster growth, so the strength is insufficient.

Sample No. In No. 19, since the holding time in the heat treatment 2 is long, the clusters begin to change into precipitates, and the ductility characteristic of the cluster forming material cannot be ensured. On the other hand, sample No. At 20, the retention time is short, so the cluster does not grow to a size that exhibits sufficient strength.
Sample No. In No. 21, since the retention time in the heat treatment 3 was long, the cluster changed into a precipitate. As in the case of 19, sufficient ductility is not ensured. Sample No. In No. 22, since the holding temperature in the heat treatment 3 is high, the clusters change into precipitates, and sufficient ductility is not ensured even with this sample.
Sample No. 29 and sample no. In 30, since the holding time of the heat treatment 1 is short, clusters do not grow before contributing to strength, and sufficient strength cannot be obtained.
Sample No. In No. 31, the holding temperature of the heat treatment 2 is high, and the clusters change into precipitates, so that the ductility expressed by cluster formation cannot be secured. Sample No. In No. 32, since the holding temperature of the heat treatment 2 is low, cluster growth is insufficient, and high strength cannot be obtained.
In sample 33, since the holding temperature of heat treatment 1 is low, another type of cluster that does not contribute to high strength is formed. As a result, the strength was greatly reduced. Sample No. In 34, since the holding temperature of the heat treatment 1 is high, precipitates are formed instead of clusters. Therefore, high ductility cannot be obtained.

As described above, using an aluminum alloy having Mg: 0.5% to 1.2%, Si: 0.3% to 1.5%, and Mg / Si 1.0 or less, this composition In the case where T1 is 60 or more and 160 or less in the heat treatment held at a temperature T1 ° C. for t1 time after the solution heat treatment, the temperature T1 ° C. is 63.5 exp (−0.038 T1) +2.5 or more as t1. The first heat treatment is performed, and thereafter, the temperature T2 exceeds the temperature T1 ° C. and is 170 ° C. or less, and the time t2 is maintained at the temperature T2 ° C. satisfying the relationship of 3 hours to 72 hours for t2 hours. If the second heat treatment is performed, it becomes clear that an excellent high strength and high ductility aluminum alloy sheet having a tensile strength in a uniaxial tensile test of 250 MPa or more and an elongation of 20% or more can be obtained. It was.
Further, as shown in Table 1, the same conditions as described above may be applied to an aluminum alloy in which any one or more of Mn, Cu, Cr, Ti, and Fe are added to the above composition. It is clear that an excellent high strength and high ductility aluminum alloy sheet having a tensile strength of 250 MPa or more and an elongation of 20% or more can be obtained by performing the first heat treatment and the second heat treatment in FIG. It was.

  The alloy of the present invention achieves higher strength and higher ductility than before, facilitates the molding of parts that require high strength, promotes the application of parts using aluminum alloys, and reduces the weight of transportation equipment represented by automobiles. Is achieved.

Claims (3)

It contains Mg: 0.5% or more and 1.2% or less, Si: 0.3% or more and 1.5% or less, and the balance is inevitable impurities and Al, and Mg / Si is 1. For an aluminum alloy having a temperature of 0 or less, T1 is 60 or more and 160 or less and t1 is 63.5exp (−0.038T1) +2.5 or more and 24 in a heat treatment that is held at a temperature T1 ° C. for t1 hours after solution heat treatment. In the following, a first heat treatment is performed to maintain the temperature at T1 ° C., and then the temperature T2 ° C. exceeds the temperature T1 ° C. and is 170 ° C. or less, and the time T2 satisfies the relationship of 3 hours to 72 hours. A method for producing a high-strength, high-ductility aluminum alloy sheet having a tensile strength of 250 MPa or more and an elongation of 20% or more in a uniaxial tensile test, wherein a second heat treatment is performed for 2 hours.   In addition to the above composition, Cu: 0.3% to 2.0%, Fe: 0.25% or less, Mn: 0.50% or less, Ti: 0.20% or less, Cr: 0.3% or less Among them, the method for producing a high-strength, high-ductility aluminum alloy plate according to claim 1, comprising at least one kind or two or more kinds.   3. The high-strength, high-ductility aluminum alloy according to claim 1, wherein after the second heat treatment, a third heat treatment is performed at a temperature exceeding T2 ° C. and not more than 180 ° C. for 2 hours or less. A manufacturing method of a board.

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