JPH0547615B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is applicable to body sheets and frame materials for automobiles,
Heat-treated aluminum alloy used for molded products that require high strength and excellent formability (especially bendability and extensibility), such as air cleaners, oil tanks, and housings for home appliances, such as VTR chassis. Regarding rolled plates and their manufacturing methods, in particular, they can be used for forming processing as T4-treated materials without being heat-treated after rolling, yet have no change in material properties due to room temperature aging, and have stress corrosion cracking resistance (hereinafter referred to as SCC properties). The present invention relates to a T4-treated aluminum alloy rolled plate for high-strength forming processing that has excellent properties and does not generate Lyuders marks during forming processing, and a method for manufacturing the same. Conventional technology In the past, cold-rolled steel sheets were commonly used as automobile sheet materials for forming automobile body seats, etc., but recently, in order to reduce the weight of automobiles and improve their fuel efficiency, conventional cold-rolled steel sheets have been replaced. There is an increasing demand for the use of rolled aluminum alloy plates. Aluminum alloy rolled sheets used for such purposes have conventionally been Al-Mg-based 5052 alloy O material or 5182 alloy O material, or Al-Cu-based 2036 alloy O material.
T4 treated material and Al-Mg-Si based 6009 alloy
T4 treated materials, 6010 alloy T4 treated materials, etc. are used. However, the aforementioned 5052 alloy O material and 5182 alloy O
The material does not have sufficient strength after being baked and painted after forming, and has poor SCC resistance as an automotive body sheet material.
Because of its poor properties, there are safety issues when using it in areas exposed to corrosive environments under high stress, and there is also the problem of poor appearance due to the generation of reuders marks during molding. Also
2036 alloy T4 treated material has poor formability, and
The 6009 alloy T4 treated material has insufficient strength, and the 6010 alloy T4 treated material has poor formability. Furthermore, Al-Cu system, Al-Mg-Si system and Al-Mg
-Zn-Cu alloys have the disadvantage that material properties change significantly over time due to aging at room temperature, and formability deteriorates over time after manufacture, making inventory management and lot management during forming complicated. There's a problem. Therefore, in order to solve the above-mentioned problems, the inventors of the present invention, in Japanese Patent Application Laid-Open No. 62-27544 and Japanese Patent Application No. 63-50029, based on Al-Mg alloy known as JIS 5000 series alloy, A small amount of this
Al-Mg-Cu alloys are made by actively adding Cu and undergoing T4 treatment, which is solution treatment and rapid cooling, which has not been done with conventional Al-Mg alloys.
We are proposing a T4 treated rolled plate and its manufacturing method. Problems to be solved by the invention Al-Mg proposed by the inventors as described above
-Cu-based T4 treated material has superior strength and formability compared to conventional alloys, has no change in material properties after manufacturing, can prevent the occurrence of Lyuders marks during forming process, and is resistant to SCC. However, in order to withstand molding into complex shapes, it is desired to further improve moldability. This invention was made against the background of the above circumstances, and is based on the idea of using an Al-Mg alloy (JIS 5000 series alloy) as a base, actively adding a small amount of Cu to this to make a T4 treated material, and making it even more effective. It has excellent formability, especially excellent bendability and stretchability, has strength comparable to cold-rolled steel sheets, has SCC resistance, and does not generate reuders marks during forming process. The object of the present invention is to provide a hot-molten T4-treated aluminum alloy rolled sheet and a method for manufacturing the same, which does not cause changes in material properties over time due to aging at room temperature. Means for Solving the Problem The invention of claim 1 provides strength, formability, and SCC resistance.
The purpose of the present invention is to provide a heat-treated aluminum alloy rolled sheet for forming processing that has excellent properties and does not generate reuders marks during forming processing, and whose material properties do not change over time due to aging at room temperature. In addition to adding Cu, the amount of Fe, Si, and other impurities that adversely affect moldability, that is, the total amount of Mn, Cr, Zr, etc., is controlled to an extremely small amount, and the crystal grains in the final plate are optimized. It is specified in the value. Specifically, T4 for molding according to the invention of claim 1
Processed aluminum alloy rolled plate contains Mg1.5~5.5%,
Cu0.15~1.5%, Fe0.05~0.30%, Si0.05~0.40%
and other impurities are regulated to 0.05% or less in total, the remainder consists of Al, and the average crystal grain size is within the range of 30 μm to 150 μm. Moreover, the invention of claim 2 provides a method for manufacturing the above-mentioned T4-treated aluminum alloy rolled plate. Specifically, T4 for molding according to the invention of claim 2
The manufacturing method of treated aluminum alloy rolled plate is as follows:
Mg1.5~5.5%, Cu0.15~1.5%, Fe0.05~0.30%,
Contains 0.05 to 0.40% Si, and other impurities are regulated to 0.05% or less in total, with the remainder consisting of Al.
After casting the Al alloy ingot, the ingot has 450~580
When applying homogenization treatment at a temperature within the range of °C, further hot working and cold rolling, and then solution recrystallization treatment, the cold rolling rate immediately before the solution treatment recrystallization treatment must be 30% or more. and solution recrystallization treatment at a heating temperature of 450 to 570℃ and a heating rate of 50℃/min.
The above is characterized in that the holding time is 5 minutes or less and the cooling rate is 50° C./min or more. Function First, the reason for limiting the alloy components in this invention will be explained. Mg: Mg is a basic alloying component in the aluminum alloy of the present invention, and contributes to improving strength and formability, particularly elongation and extensibility. If the Mg content is less than 1.5%, the strength and moldability will be insufficient, making it unsuitable for use as automobile body sheets, etc. On the other hand, if Mg exceeds 5.5%, elongation decreases and rollability deteriorates.
It was set within the range of 1.5 to 5.5%. Cu: Cu is a basic alloying element for making T4 treated materials, and by sufficiently solutionizing it through solution treatment and rapid cooling, it can be used to form the S phase (Al-
It is an element that contributes to improving strength and bendability through the precipitation of Mg-Cu phase) and is effective in preventing the occurrence of Lyuders marks during molding. Furthermore, in Al alloys containing Mg and 3% or more, there is a risk that the SCC resistance will be reduced, but by adding Cu, the SCC resistance can be dramatically improved. Furthermore, if 5000 series alloys are baked and painted after machining, they will become significantly softer.
Adding Cu will cause age hardening during baking treatment.
The amount of softening can be suppressed slightly. These effects cannot be obtained sufficiently when the amount of Cu is 0.15% or less;
If Cu is added in excess of 20%, the strength will improve, but the moldability will deteriorate, and the material properties will change significantly over time due to room temperature aging after solution treatment. Therefore
The amount of Cu was limited within the range of 0.15 to 1.5%. Fe: Since Fe is an element that deteriorates moldability, particularly bendability and stretchability, it is preferable that its content be as low as possible. If the amount of Fe exceeds 0.30%, the amount of crystallized substances will increase, impairing moldability.
Must be 0.30% or less. Although good performance can be obtained even if the Fe content is less than 0.05%, the cost increases economically, so the Fe content is set within the range of 0.05 to 0.30%. Si: Si is also an element that increases the amount of crystallized compounds and reduces moldability. If Si exceeds 0.40%, moldability deteriorates, while if Si is less than 0.05%, it becomes uneconomical, so Si was set within the range of 0.05 to 0.40%. Other impurities: Since impurities other than Fe and Si also have a negative effect on moldability and corrosion resistance, the total amount was limited to a maximum of 0.05%. In particular, transition elements such as Mn, Cr, and Zr contribute to improving strength, but they impair formability, especially bendability, and these transition elements have a strong effect of refining crystal grains, so the grain size is reduced to 30 μm. It becomes difficult to increase the size beyond that. In addition to the above elements, Ti or Ti and B may be added to refine the crystal grains in the ingot. However, in order to prevent the crystallization of primary _TiAl3 particles, it is desirable to keep Ti at 0.15% or less, and
To prevent the generation of TiB ₂ particles, B is 500ppm.
The following is desirable. Furthermore, in Al alloy molten metal containing 1.5% or more of Mg, Be is added to prevent oxidation of the molten metal, and in this invention, Be is added to prevent oxidation of the molten metal. It does not exclude. The amount of Be added is 50ppm
The following is common, and if this amount of Be is added, other performances will not deteriorate even in this invention. Furthermore, in the aluminum alloy rolled sheet of the present invention, in addition to specifying each component element as described above, in particular, the crystal grains in the final sheet state are on average.
It must be 30 μm or more and 150 μm or less. Crystal grains have a strong correlation with the occurrence of Lyuders' marks during molding, and the smaller the crystal grains, the more easily Lyuders' marks occur. Especially when crystal grains
If the thickness is less than 30 μm, Reuders marks are likely to occur, spoiling the appearance of the molded product. On the other hand, crystal grains
If it exceeds 150 μm, the surface will become rough during molding, which will impair the appearance of the molded product as described above and will also reduce moldability. Note that the crystal grain size here is measured by the "Intercept Method" (cutting method) according to ASTM, and the observation plane of the crystal grains is a plane parallel to the plate surface (rolling surface). Next, a method for manufacturing an aluminum alloy rolled plate of the present invention will be explained. First, a molten alloy having the above-mentioned composition is cast. Here, as the casting method, when manufacturing the aluminum alloy rolled plate of the invention of claim 1,
Either a casting method (semi-continuous casting method) or a continuous casting method may be used, but in the case of the invention of claim 2, the DC casting method is applied because of the homogenization treatment. For the obtained Al alloy ingot, 450 to 580℃
The homogenization process is carried out at a temperature within the range of . By performing such homogenization treatment, molding workability and hot workability can be improved. If the temperature of the homogenization treatment is less than 450°C, the above-mentioned effects cannot be obtained, while if it exceeds 580°C, crystal melting may occur. Note that the time for the homogenization treatment is preferably 1 to 48 hours. If the treatment time is less than 1 hour, the above-mentioned effects cannot be sufficiently obtained, while treatment for a long time exceeding 48 hours is not economical. After the homogenization treatment, hot rolling is performed in accordance with a conventional method, and cold rolling is further performed one or more times to obtain the required thickness. Note that intermediate annealing may be performed between hot rolling and cold rolling or between cold rolling. After the cold rolling, a solution recrystallization treatment is performed later, and the cold rolling immediately before the solution recrystallization treatment must have a cold rolling ratio (reduction ratio) of 30% or more. Cold rolling rate just before solution recrystallization treatment is 30
%, the recrystallized grains after solution recrystallization treatment are
This results in mixed grains containing coarse grains exceeding 150 μm, resulting in poor moldability. The solution recrystallization treatment after cold rolling has the following roles. That is, first, the material is recrystallized to provide favorable moldability. Here, the recrystallization size is controlled to an appropriate size (30 μm or more and 150 μm or less) in order to prevent the occurrence of reuders marks during molding and at the same time to prevent rough skin. Second, the Al-Mg-Cu phase (S phase) is made into a solution to improve strength, moldability, and SCC resistance. Here, in the alloy system targeted by this invention, Fe, which is originally useful for stabilizing recrystallized grains,
Since the content of transition elements such as Mn, Cr, and Zr is kept as low as possible to improve moldability, the solution recrystallization treatment conditions must be met in order to stabilize the recrystallized grain size within a certain range. It is necessary to strictly keep the value within the range of conditions specified in this invention. In other words, the temperature increase rate (heating rate) is 50°C/min or more, the heating temperature (achieved temperature) is 450 to 570°C, and the holding time at a temperature within that range is 5 minutes or less (including zero). Furthermore, it is necessary to set the cooling rate to 50°C/min or more. The reasons for limiting the conditions for these solution recrystallization treatments are as follows. First, regarding the heating rate, the recrystallized grain size
In order to stabilize the thickness at 150 μm or less, it is preferable that the temperature increase rate be high. If the heating rate is less than 50℃/mm, crystal grains will interlock during heating and the temperature will increase to 150μ.
This results in a mixed grain structure containing coarse grains exceeding m, and coarse grains tend to form throughout. Therefore, the temperature increase rate needs to be 50°C/min or more. Regarding the heating temperature, if the heating temperature is lower than 450°C, the recrystallized grains become fine and become less than 30 μm, and Lyuders marks are likely to occur. On the other hand, if the temperature exceeds 570°C, recrystallized grains will grow and become coarse grains exceeding 150 μm, and local melting may also occur. Therefore, the heating temperature should be within the range of 450 to 570°C. Regarding the holding time, since the alloys targeted by this invention have few elements that stabilize the recrystallized grains, if the holding time exceeds 5 minutes, the recrystallized grains will become coarse. Therefore, the holding time must be 5 minutes or less. Note that there is a close relationship between the heating temperature and the holding time, and it is preferable that the higher the heating temperature is, the shorter the holding time is. Regarding the cooling rate, it is necessary to set the cooling rate to 50° C./min or more in order to cause precipitation of the S phase and other second phases. There are forced air cooling, water cooling, etc. as cooling methods to obtain such cooling speed.
From the viewpoint of reducing quenching distortion as much as possible, it is desirable to apply forced air cooling. Note that the solution recrystallization treatment and quenching described above is the final heat treatment, and after that, the required strength is obtained without substantially performing cold working except for strain correction. Quality is JIS
Corresponds to tempering symbol T4. Here, conventional Al-Mg alloys (JIS 5000 series alloys) are known as non-heat treatable alloys, and conventionally it was generally not considered to perform T4 treatment on Al-Mg alloys. It wasn't. On the other hand, one feature of the present invention is that it is based on an Al-Mg system, and a small amount of Cu, which contributes to precipitation hardening, is actively added to produce a T4-treated alloy. After cooling in the solution recrystallization treatment as described above, it is normal to perform strain correction, but leveling, stretching, skin pass, etc. % or less. Furthermore, in order to remove the processing strain during the above-mentioned strain correction and obtain better moldability, the heating rate, cooling rate, temperature, and holding time are within the range shown by the shaded areas in Figures 1 and 2. Even after the final heat treatment, other properties such as SCC resistance do not deteriorate. The aluminum alloy rolled sheet obtained under the above conditions and method has excellent formability superior to that of 5052 alloy O material and 5182 alloy O material, particularly excellent bendability and stretchability, and also has excellent bendability and stretchability. It has high strength comparable to rolled steel sheets, does not produce Lyuders marks during forming, has excellent SCC resistance, and does not change material properties over time due to aging at room temperature. Examples Example 1 Alloys having the composition shown in alloy numbers 1 to 5 in Table 1 were cast into slabs with cross-sectional dimensions of 500 mm x 1200 mm using the DC casting method, and the ingots were homogenized at 530°C for 10 hours. After applying the coating, it was hot rolled to a thickness of 4 mm, and further cold rolled to a thickness of 1 mm. In addition, some products were subjected to intermediate annealing at 350℃ x 2 hours at the stage of cold rolling to a plate thickness of 1.2 mm after hot rolling, and then cold rolling to a plate thickness of 1 mm (cold rolling after intermediate annealing). rolling rate 20%). Thereafter, each cold-rolled sheet was subjected to solution recrystallization treatment under the conditions shown in heat treatment numbers A to F in Table 2. After solution recrystallization treatment and aging at room temperature for two weeks, mechanical properties, formability (including the presence or absence of Lyuders marks and rough skin during molding), and resistance
Table 3 shows the results of investigating SCC properties. In Table 3, LDR is the limit drawing ratio,
Bending (mm) indicates the minimum bending radius. Also, SCC is
30% after the above solution recrystallization treatment for each material
After cold rolling, sensitization treatment was performed at 120°C for 7 days, loop bending test pieces according to DIN50908 were prepared, and stress corrosion cracking was observed when an alternate immersion test was conducted in 3.5% NaCl for 1 month. Indicates the presence or absence of occurrence.

【table】

【table】

[Table] As is clear from Table 3, Alloys 1 and 2 within the composition range of this invention were subjected to solution recrystallization treatment within the process condition range specified in this invention. Grain size after 30 ~
If it is within the range of 150μm, the conventional example 5182
It has better formability (especially stretchability and bendability) than the O material (heat treatment code F) of the alloy (alloy number 5), and does not cause reuders marks or rough skin during forming. It also has excellent SCC resistance. Example 2 Casting, homogenization heat treatment, and cold rolling were performed under the same conditions as in Example 1 for each alloy No. 1 of the present invention example and Alloy No. 5 of the conventional example (5182 alloy) in Table 1. After aging, Alloy No. 1 was subjected to solution recrystallization treatment according to heat treatment symbol A in Table 2,
Alloy No. 5 was subjected to solution recrystallization treatment according to heat treatment symbol F in Table 2. For each material, the decrease in yield strength due to processing and baking was investigated in the following manner. In other words, cold working was carried out at various degrees of working (0%, 5%, 10%) and the yield strength was investigated in that state, and the plates of each degree of working were baked at 175°C for 1 hour. The subsequent strength was investigated. The results are shown in Table 4.

[Table] As is clear from Table 4, in the case of the alloy according to the present invention, the decrease in yield strength after processing and baking is much smaller than that of the conventional alloy, 5182 alloy (alloy number 5), and therefore, after forming It is found that it is most suitable for automotive body sheet materials that undergo paint baking. Example 3 The alloy No. 1 of the invention examples shown in Table 1 was cast, homogenized, hot rolled, and cold rolled under the same conditions as in Example 1, and then Solution recrystallization treatment with heat treatment symbol A was performed. The yield strength of the material when aged at room temperature for various times and the height of the spherical surface of φ100 mm by pressing were investigated and the results are shown in Table 5.

[Table] As is clear from Table 5, it was found that in the alloy according to the present invention, no change in strength and stretchability over time due to aging at room temperature was observed. Effects of the Invention As is clear from the above explanation, the present invention has excellent moldability, particularly excellent bendability and extensibility, and has sufficient stress resistance suitable for automobile body sheets, etc. It is possible to obtain an Al alloy rolled sheet that has corrosion cracking resistance, does not generate reuders marks during forming processing, and does not change material properties over time due to aging at room temperature, and is therefore suitable for automobile body sheets and other applications. It has become possible to expand the use of Al alloys in automobile parts, etc., and to further promote weight reduction of automobile bodies.
It can bring about remarkable effects. It goes without saying that the Al alloy rolled sheet according to the present invention is suitable not only for automobile parts but also for various molded parts such as container materials for various electronic and electrical devices, such as chassis materials.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between heating rate/cooling rate and temperature in the final heat treatment, and FIG. 2 is a diagram showing the relationship between the holding time and temperature in the final heat treatment.

Claims (1)

[Claims] 1. Mg1.5-5.5% (weight%, same hereinafter), Cu0.15
~1.5%, Fe0.05~0.30%, Si0.05~0.40%, and other impurities are regulated to 0.05% or less in total, the balance is Al, and the average crystal grain is 30μ
A T4-treated aluminum alloy rolled plate for forming processing, characterized in that the thickness is within the range of m to 150 μm. 2 Mg1.5~5.5%, Cu0.15~1.5%, Fe0.05~
0.30%, Si0.05-0.40%, and other impurities are regulated to a total of 0.05% or less, with the balance being Al.
After casting an Al alloy ingot consisting of
Homogenization treatment is carried out at a temperature within the range of 450-580℃,
Furthermore, when performing solution recrystallization treatment after hot working and cold rolling, the cold rolling rate immediately before the solution recrystallization treatment is set to 30% or more, and the solution treatment is carried out at a heating temperature of 450%. ~570℃, heating rate 50
℃/min or more, holding time 5 minutes or less, cooling rate 50
A method for producing a T4-treated aluminum alloy rolled plate for forming processing, characterized in that the process is carried out at a temperature of ℃/min or higher.