JPH057460B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an aluminum alloy plate with excellent bake hardenability, and more specifically, the present invention relates to a method for producing an aluminum alloy plate that has excellent moldability and has good bake hardenability due to heating during painting baking after molding. Concerning a manufacturing method for excellent aluminum alloy plates. [Prior art] Conventionally, in order to maintain the strength of the coating film applied to aluminum alloy materials used for automobile parts and other purposes, heating (baking) is applied after coating.
At the same time, this heating is used to improve the strength of aluminum alloy materials. This aluminum alloy material includes 6009,
6010 was used, and the coating was baked at a high temperature of 200°C for 60 to 90 minutes, which was a long-term high-temperature process, so 6009 and 6010 had the effect of improving strength. Recently, however, there has been a trend to lower the baking temperature and shorten the heating time in order to save energy and reduce costs during baking. For example, Tokuko Sho 59-039499 and Tokuko Sho No.
Publication No. 50-001910 discloses that an Al-Mg-Si-Cu based alloy is heated to 200°C after being left at room temperature after heat treatment.
The strength is improved by baking at a high temperature for 60 minutes at a temperature of Even if it were, it would be a slight increase of about 2Kg/mm ² and would have no effect. In addition, in the "Aluminum Alloy Plate with Excellent Formability and Bake Hardenability and Method for Producing the Same", which the present inventor has previously completed, it is possible to reduce the temperature to 200°C for 30 minutes, which is a short period of time. However, after being left at room temperature for three days or more after tempering, the strength was only slightly improved by short-time baking at a low temperature of 175° C. for 30 minutes, and the effect was small. In order to reduce the thickness of the plate, reduce the weight of the product, and reduce the cost of painting and baking, there is a strong demand for aluminum alloy plates that can be baked at low temperatures for a short time to improve strength and have excellent formability. [Problems to be Solved by the Invention] As explained above, the present invention has been made in view of various problems in conventional bake hardening of aluminum alloy plates, and is the result of intensive research by the inventor. , it has the effect of improving strength by high-temperature long-term heating of 200℃ held for 60 to 90 minutes, which has been done up until now, and furthermore, it has the effect of improving strength by holding it at a high temperature of 175℃ for 30 minutes. They have developed a method for manufacturing aluminum alloy sheets that have excellent formability with improved strength and excellent bake hardenability. [Means for Solving the Problems] The method for manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention is characterized by: Mg0.4-1.5wt%, Si0.3-1.5wt%, Cu0 Contains .2~0.8wt%, and furthermore, Ti0.005~0.1wt%, B0.0005~0.03wt%, Mn0.4wt% or less, Cr0.4wt% or less, Fe0.3wt% or less, Zr0.2wt%. The following Al-Mg- contains one or more selected from V0.1wt% or less, contains 0.2wt% or less of unavoidable impurities, and the remainder is substantially Al.
The Si-Cu based alloy ingot is subjected to normal homogenization treatment at a temperature below the burning temperature, hot rolled and cold rolled to the desired thickness, and heated at a heating rate of 100℃/min as tempering treatment. After performing rapid heating to 480 to 580℃ and holding it in this temperature range for more than 3 seconds, heat treatment is performed to rapidly cool down to 100℃ at a rate of 300℃/min or more, and further, within 72 hours, 40 to 580℃
A final heat treatment is carried out at a temperature of 120° C. for 8 to 36 hours. Note that rough annealing and/or intermediate annealing may be performed between hot rolling and cold rolling as necessary. The method for manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention will be described in detail below. First, the components and component ratios of the aluminum alloy used in the method of manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention will be explained. Mg is an element that imparts reinforcement in cooperation with Si,
If the content is less than 0.4wt%, the strength will be low, and
If the content exceeds 1.5wt%, moldability will deteriorate.
Therefore, in order to achieve a balance between formability, strength, and strength improvement by baking, the Mg content was set to 0.4.
~1.5wt%. Si is an element that works together with Mg to impart reinforcement,
If the content is less than 0.3wt%, the strength will be low, and
If the content exceeds 1.5wt%, moldability will deteriorate.
Therefore, in order to achieve a balance between formability, strength, and strength improvement by baking, the Si content was set to 0.3.
~1.5wt%. Cu is an element that increases strength and increases strength by baking in proportion to its content, but it is also an element that reduces corrosion resistance, and when the content is less than 0.2wt%, corrosion resistance is not good. However, the effect of improving strength and strength by baking is small, and when it is contained in excess of 0.8 wt%, the effect of improving strength and strength by baking is large, but it reduces corrosion resistance and moldability. Therefore, the Cu content is set to 0.2 to 0.8 wt%. Ti is an element that makes the crystal grains of the ingot fine and improves the formability.If the content is less than 0.005wt%, this effect will be small, and if the content is less than 0.1wt%
If the content exceeds 100%, coarse crystallized substances will be formed and the moldability will be deteriorated. Therefore, Ti content is 0.005~
The content shall be 0.1wt%. Like Ti, B is an element that refines the crystal grains of the ingot and improves formability, and the content is 0.0005wt.
If it is less than %, this effect is small, and
If the content exceeds 0.03 wt%, coarse crystallized substances are formed and moldability is reduced. Therefore, the B content is
The content should be 0.0005 to 0.03wt%. Note that Ti and B are preferably contained in an Al-Ti-B intermediate alloy or an Al-Ti intermediate alloy and an Al-B intermediate alloy. Mn, Cr, Zr, and V have the effect of improving strength, but when their content increases, they produce coarse crystallized substances and reduce formability, and Fe has a small strength-improving effect.
Generates coarse crystallized substances and reduces moldability. Therefore, from a balance between strength improvement and formability, the Mn content is 0.4wt% or less, the Cr content is 0.4wt% or less, the Fe content is 0.3wt% or less, the Zr content is 0.2wt% or less, and the V
The content should be 0.1wt% or less, and it is preferable to include one or more selected from among these. In particular, in order to maintain formability and bake hardenability, the content of Mn, Cr, Zr, V, and Fe must be controlled individually.
0.1wt% or less, or Mn+Cr+Zr+
It is preferable to control the total amount of V to 0.2wt% or less. The unavoidable impurities may be contained alone in an amount of up to 0.2 wt% as long as they do not impair bake hardenability and formability. In addition, in the method of manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention, the size of the crystallized material affects the formability, and the longest side length of the crystallized material is 13 μm.
If it exceeds m, the moldability deteriorates, so if bake hardenability and moldability are to be achieved at the same time, the length of the longest side of the crystallized product after the final heat treatment must be controlled to 13 μm or less. Next, heat treatment in the method for producing an aluminum alloy plate with excellent bake hardenability according to the present invention will be explained. The homogenization treatment of aluminum alloy ingots with the above-mentioned components and component ratios has a small effect on improving strength during baking at low temperatures and short periods of time, so it is best to perform it at a temperature below the burning temperature. Composition with hardenability and bake hardenability (Mn, Cr, Zr, V and Fe are 0.1wt alone)
% or less or the total amount of Mn + Cr + Zr + V is 0.2wt
% or less. ), the heating rate to the target temperature may be 200°C/hour or less, or a multi-stage homogenization process of two or more stages may be performed. Subsequently, hot rolling and cold rolling are performed, but these conditions do not need to be particularly limited because their effects on bake hardenability are small, as in the case of homogenization. Further, rough annealing and intermediate annealing may be performed after hot rolling. Thermal treatment involves rapid heating at high temperatures for a short period of time, followed by rapid cooling to improve the strength of the material.
It is a treatment that improves high formability and strength after baking, i.e., at a heating rate of 100℃/min or more.
Rapidly heat to a high temperature of 480 to 580℃, and keep at this temperature for 3
If the heating temperature is lower than 480°C, the strength of the material and the strength after baking will be low, and if the heating temperature is higher than 590°C, burning will occur and the moldability will deteriorate. Note that, at a heating temperature of less than 480° C., if the heating time is held for 3 seconds or less, the strength after baking will not improve much, but if the heating time is held for 30 minutes, the strength after baking will improve. Therefore,
In order to improve the strength after baking, it is recommended to hold for a long time, and in order to achieve both moldability and baking, it is preferable to hold for about 3 to 30 seconds. Next, the cooling rate up to 100℃ is rapidly cooled at 300℃/min or more, but the cooling rate up to 100℃ is
If it is less than 300℃/min, the moldability will decrease and the strength after baking will be less improved.
By setting the cooling rate to 300° C./min or more, moldability and strength after baking are greatly improved. Therefore, thermal refining treatment involves rapid heating to a temperature of 480 to 580°C at a heating rate of 100°C/min or more, and a holding time of 3.
The cooling rate up to 100°C is 300°C/min or more. By performing a final heat treatment following this tempering treatment, the conventional high temperature and long baking conditions can be improved.
It has the effect of improving strength by holding at a temperature of 200°C for 60 minutes, and can also have the effect of improving strength even under low-temperature and short-time baking conditions (for example, 175°C x 30 minutes). That is, after tempering treatment, the material is heated to a temperature of 40 to 120°C within 72 hours, regardless of the heating rate and cooling rate, and maintained at this temperature for 8 to 36 hours.
Formability is good at temperatures below 40°C, and although baking at a high temperature of 200°C for 60 minutes has the effect of improving strength, the effect of baking at a lower temperature and short time than conventional baking has little effect. Moreover, when the temperature exceeds 120°C, although it has the strength improvement effect of conventional high temperature for a long time and lower temperature for a short time than conventional, it reduces moldability. If the holding time is less than 4 hours, baking at high temperature for a long time will improve the strength, but baking at low temperature for a short time will have a small strength improvement effect, and if it exceeds 48 hours, the moldability will decrease and the baking time at low temperature for a short time will improve the strength. The strength improvement effect of baking is small. Therefore, the final heat treatment after the tempering treatment is carried out at a temperature of 40 to 120° C. for 8 to 36 hours within 72 hours after the tempering treatment. In addition, when straightening distortion using a leveler or skin pass after final heat treatment, the processing rate is 1.5.
% or less is desirable from the viewpoint of preventing deterioration of moldability. [Example] An example of the method for manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention will be described. Example 1 An aluminum alloy having the components and proportions shown in Table 1 was melted and cast using a normal method, and the ingot was face-faced and heated to a heating temperature of 530°C at a heating rate of 40°C/hour.
After homogenization treatment, which was held at a temperature of 100°C for 4 hours, hot rolling and cold rolling were performed to obtain a 1.0 mm thick plate, which was then held at a temperature of 550°C for 10 seconds at a heating rate of 200°C/min. , conduct heat treatment to cool down to 100℃ at a cooling rate of 800℃/min, then leave at temperature for 1 day,
A final heat treatment is carried out by holding it at a temperature of ℃ for 24 hours.
Characteristics of the alloy manufactured by the method of manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention after being left at room temperature for 30 days and comparative alloys, and the comparison with conventional baking conditions of holding at a temperature of 200°C for 60 minutes and To a temperature of 175℃ for conventional low temperature short time baking conditions
Table 2 shows the yield strength after holding for 30 minutes. As is clear from Table 2, alloys No. 1 to No. 12 manufactured by the method of manufacturing an aluminum alloy plate with excellent bake hardenability according to the present invention are different from comparative alloys No. 1 to No. 1. It has superior strength and formability compared to Type 8, and can be maintained at high temperatures for a long period of time (maintained at a temperature of 200℃ for 60 minutes).
It can be seen that this is a well-balanced material that has bake hardenability at a low temperature of 175°C for 30 minutes in addition to bake hardenability at a temperature of 175°C for 30 minutes. Comparative alloy No. 1, which has a low content of Mg, Si, and Cu, shows little improvement in strength and strength due to baking, and comparative alloy No. 2, which has a high content of Mg, Si, and Cu, elongates and has a low Erichsen value. , deterioration of moldability is too large. In addition, Mn content 0.8wt%, Cr content 0.4wt%,
Zr content 0.2wt%, V content 0.1wt%, Fe content
Adding 0.5wt% to wt% has the effect of improving strength, but
It can be seen that the elongation and Erichsen value decreased significantly, and the moldability deteriorated significantly. In addition, the Ti content is 0.1wt% and the B content is 0.05wt.
%, coarse crystallized substances are formed, elongation and Erichsen value are decreased, and moldability is greatly deteriorated. Nos. 2, 3, 4 manufactured by the method for manufacturing aluminum alloy plates with excellent bake hardenability according to the present invention,
10, the longest side length of the crystallized material is 13 μm or less,
It has high formability and improved strength by baking at a temperature of 175℃ for 30 minutes.

【table】

【table】

【table】

[Table] Example 2 The alloy No. 4 shown in Table 1 of Example 1 was melted and cast by a normal method, and the ingot was face-milled.
The heating temperature was set to 500°C at a heating rate of 40°C/hour, and after homogenization treatment, which was maintained at this temperature for 6 hours, hot rolling and cold rolling were performed to form a 1.0 mm thick plate. The plate is heated from 475℃ at a heating rate of 300℃/min.
After heating to a temperature of 590°C and varying the holding time at this temperature, forced air cooling was performed at a cooling rate of 200°C/min and 800°C/min to cool it to a temperature of 100°C. Alternatively, it can be cooled down to water temperature by water cooling (quenching in water), which has a much faster cooling rate, left at room temperature for one day, then subjected to a final heat treatment at a temperature of 100°C for 8 hours, and then left at room temperature for 30 days. The characteristics of
For comparison, Table 3 shows a comparison with the characteristics when no final heat treatment is performed. As is clear from Table 3, when the tempering treatment temperature is 475°C, the yield strength is improved by the conventional baking at 200°C for 60 minutes, but the effect is small at 175°C for 30 minutes. In addition, at 590℃, the moldability (elongation, Erichsen value) is low due to burning, and the strength improvement effect due to baking is small when the holding time is 0 seconds, but the effect is observed when the holding time is 5 seconds, and furthermore, the cooling rate is 200℃/min. Although the yield strength can be improved by baking at 200°C for 60 minutes at high temperatures,
It can be seen that the improvement in yield strength is small when baking for a short time at a low temperature of minutes. Therefore, in the thermal refining treatment, the heating temperature should be 480 to 580°C, the holding time should be 3 seconds or more, and the cooling rate should be 300°C/min or more. In addition, when emphasis is placed on moldability, it is preferable to perform heating for a long time of 3 to 120 seconds, and when emphasis is placed on strength, heating is performed for a long time of 30 minutes.

【table】

[Table] Example 3 Alloy No. 5 in Table 1 of Example 1 was melted and cast using the usual method, and the ingot was face-milled, and the heating rate was
Homogenization treatment is carried out by heating at 150℃/hour to a temperature of 530℃ and maintaining this temperature for 4 hours.The plate is then hot rolled and cold rolled to a thickness of 1.0mm, and this plate is heated from 475℃ to
After heating to a temperature of 590°C and varying the holding time at this temperature, forced air cooling was performed at a cooling rate of 200°C/min and 800°C/min to cool it to a temperature of 100°C. Alternatively, it can be cooled down to water temperature by water cooling (quenching in water), which has a much faster cooling rate than that, left at room temperature for one day, then subjected to a final heat treatment at 70°C for 24 hours, and then cooled to room temperature. Table 4 shows the characteristics after being left for 20 days and, for comparison, the characteristics after conventional heat treatment without low-temperature heating. As is clear from Table 4, when the tempering temperature is 475°C, the yield strength is improved by the conventional baking at 200°C for 60 minutes, but at 175°C for 30 minutes, the effect is small; At a temperature of , the moldability (elongation, Erichsen value) is low due to burning, and when the holding time is 0 seconds, the effect of baking is small, but when the holding time is 5 seconds, a baking effect is observed, and when the cooling rate is 200℃/min, it is 200℃ x 60 minutes. Although the yield strength can be improved by baking at high temperature for a long time,
It can be seen that the improvement in yield strength is small when baking for a short time at a low temperature of 800°C/min, but at 800°C/min, there is a sufficient improvement in yield strength not only for baking at a high temperature for a long time but also for a short time at a low temperature, and the improvement rate is large. Therefore, in the thermal refining treatment, the heating temperature should be 480 to 580°C, the holding time should be 3 seconds or more, and the cooling rate should be 300°C/min or more. If moldability is important, the holding time should be set to 3.
It is best to hold for ~120 seconds, or 30 minutes if strength is important.

[Table] Example 4 An ingot made by melting and casting the alloys No. 4 and No. 5 in Table 1 of Example 1 by a normal method was milled and heated to 530°C at a heating rate of 40°C/hour. After homogenization treatment, which was maintained at this temperature for 6 hours, the plate was made into a 1.8 mm thick plate by hot rolling and cold rolling, and this plate was heated at a temperature of 350°C for 3 hours.
1.0mm by cold rolling after intermediate annealing
The plate thickness is then 520℃ at a heating rate of 200℃/min.
temperature, perform a high-temperature and short-time heat treatment by holding this temperature for 15 seconds, cool to room temperature at a cooling rate of 600℃/min, leave at room temperature for 0 to 96 hours, and heat for 30 to 30 seconds.
A final heat treatment is performed at a temperature of 150℃ for 4 to 48 hours.
Table 5 shows the properties and baking properties after being left at room temperature for 30 days. As is clear from Table 5, the shorter the time left at room temperature after the tempering treatment until the final heat treatment, the better the baking properties.For 96 hours, the baking properties at high temperatures for 60 minutes at 200°C improve the yield strength. Yes, but 175
Baking for a short time at a low temperature for 30 minutes at a final heat treatment temperature of 30°C improves the yield strength. At ℃, elongation decreases, but it is improved by baking at a high temperature for a long time and at a low temperature for a short time.When the heating time is 4 hours, the yield strength improves by baking at a high temperature for a long time, but the yield strength does not improve by baking at a low temperature for a short time. The elongation is low after 48 hours, and there is no improvement in yield strength when baking at a low temperature for a short time. Furthermore, if the final heat treatment is not performed, the yield strength will be improved by baking at high temperature for a long time, but the yield strength will not be improved by baking at low temperature for a short time. Therefore, the final heat treatment after the tempering treatment is performed at a temperature of 40 to 120° C. for 8 to 36 hours within 72 hours after the tempering treatment.

[Table] [Effects of the Invention] As explained above, since the method for producing an aluminum alloy plate with excellent bake hardenability according to the present invention has the above configuration, the produced aluminum alloy plate has excellent formability, And high temperature for a long time (200℃ x 60 minutes)
It also exhibits excellent bake hardenability with improved strength in both low-temperature and short-time baking (175°C x 30 minutes).

Claims (1)

[Claims] 1 Contains 0.4 to 1.5 wt% Mg, 0.3 to 1.5 wt% Si, 0.2 to 0.8 wt% Cu, and further contains 0.005 to 0.1 wt% Ti, and 0.0005 to 0.03 wt% B. %, Mn 0.4wt% or less, Cr 0.4wt% or less, Fe 0.3wt% or less, Zr 0.2wt% or less, V0.1wt% or less, and unavoidable impurities. Al-Mg- containing 0.2wt% or less, with the remainder consisting essentially of Al
The Si-Cu based alloy ingot is subjected to normal homogenization treatment at a temperature below the burning temperature, hot rolled and cold rolled to the desired thickness, and heated at a heating rate of 100℃/min as tempering treatment. After rapidly heating to 480-580℃ and holding at this temperature for more than 3 seconds,
Heat treatment is performed to rapidly cool down to 100°C at a cooling rate of 300°C/min or more, and furthermore, within 72 hours,
A method for producing an aluminum alloy plate with excellent bake hardenability, which comprises performing a final heat treatment at a temperature of 8 to 36 hours.