JP2000096175A - Aluminum alloy sheet excellent in ridging mark resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aluminum alloy free from the occurrence of ridging mark. SOLUTION: The aluminum alloy sheet is an Al-Mg-Si type aluminum alloy sheet which has a composition containing, by mass, 0.2-1.8% Si and 0.2-1.6% Mg and is prepared by carring out hot rolling, successive cold rolling after process annealing if necessary, solution heat treatment, and hardening treatment. Moreover, the alloy sheet has a microstructure composed of equiaxed recrystallized grains. Further, the rate of earing of a cup becomes >=-4% when the alloy sheet is subjected to forming into a cup shape at 150 kgf blank holder pressure and 60 mm/min forming rate by the use of #700 lubricating oil by using a 40 mm diameter punch (3 mm shoulder radius) and a die in which the ratio of the clearance between punch and die to the thickness of the Al alloy sheet is 1.3-1.4. It is desirable that this Al alloy sheet has <=45 μm grain size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al-Mg-Si-based aluminum alloy plate which has excellent ridging mark resistance and is suitable for use as a panel for a transport device such as an automobile, a railway vehicle and an aircraft.

[0002]

2. Description of the Related Art A 6000 (Al-Mg-Si) aluminum alloy sheet is relatively excellent in corrosion resistance and formability at room temperature, and has high strength by artificial aging. It is suitable for applications requiring thinning. Al-Mg-Si based alloy sheet materials are usually
After the homogenization treatment, hot rolling is performed, and then, if necessary, intermediate annealing is performed, and then cold rolling is performed to obtain a plate having a predetermined thickness, which is subjected to a solution treatment and a quenching treatment. , Stretched, etc.

However, when a forming process is performed on an Al-Mg-Si alloy sheet material, a ridging mark is formed on the surface of the sheet as described in JP-A-7-228956 or JP-A-8-23252. The problem is that surface roughness called "surface roughness" occurs. When this ridging mark occurs, it cannot be used as a poor appearance for applications such as automotive skin panels that require a very beautiful surface, and passenger aircraft fuselage skin panels, and ridging marks must be painted. If it is performed, it becomes particularly noticeable, so it proceeds to the painting process without noticing after the molding process, and it may be recognized for the first time after painting. In other words, it has the troublesome characteristic that it sometimes appears only when it is a product.

Japanese Patent Application Laid-Open Nos. Hei 7-228956 and Hei 8-23205 relate to a method for preventing the generation of ridging marks on an Al-Mg-Si alloy sheet material. Cooling to a temperature of 200 ° C. starts hot rolling, ends hot rolling at a temperature of 200 to 300 ° C., performs intermediate annealing as necessary, and then performs cold rolling, solution treatment, and quenching. That is, the latter is cooled to a temperature of 450 ° C. or less after the homogenization treatment, and starts hot rolling, finishes hot rolling at a temperature of 200 to 350 ° C., and intermediates the temperature of 350 to 420 ° C. as necessary. After annealing, cold rolling, solution quenching, and final heat treatment are performed.In each case, the hot rolling temperature is set lower, and at the same time, the processing conditions in each of the other steps are strictly controlled. It depends It is that you try to prevent the occurrence of ridging marks Te.

[0005]

On the other hand, the present inventors have
First, Japanese Patent Application Nos. 9-287906 and 9-36772.
In No. 3, Si: 0.2 to 1.8%, Mg: 0.2
It has been found that the occurrence of ridging marks can be prevented by regulating the size of the macrostructure or the degree of integration of the cube orientation of the Al-Mg-Si-based aluminum alloy sheet for forming containing up to 1.6% to a predetermined range. Was. However, to statistically process the form of the macrostructure or the degree of integration of the cube orientation and to estimate the variation in the characteristics of the entire product (for example, the entire length of the coil) based on the statistical processing, in an actual manufacturing line in terms of time and cost, it is not practical. Not a target.

In this regard, if the characteristics of a large number of samples of an aluminum alloy plate can be measured in a short time and evaluated with high reliability, for example, if it is determined that the product plate is prone to produce ridging marks, it will not be used in a factory. Can be stopped. In addition, such a product plate can be diverted to a member that is not subjected to a large tensile deformation at the time of molding and can be shipped, and the quality and the yield can be improved. The definition of the macrostructure size or the degree of integration of the cube orientation in the prior application is a necessary condition for preventing the occurrence of ridging marks. Ridging marks may be discovered in rare cases, which may not always be sufficient. Therefore, a more reliable index that can evaluate the presence or absence of a ridging mark is desired. That is, an object of the present invention is to make it possible to reliably and quickly evaluate whether or not ridging marks are generated in an aluminum alloy plate.

[0007]

Means for Solving the Problems The present inventors have proposed Al-M
If the g-Si based aluminum alloy is hot-rolled under specific temperature and strain rate conditions, and the microstructure after hot rolling is set as equiaxed recrystallized grains, it is necessary to perform intermediate annealing or not. Cold rolling is performed in accordance with, then solution treatment and quenching are performed, and when the microstructure is a product plate with equiaxed recrystallized grains, it is found that ridging marks can be prevented from being generated on the product plate, I applied for a patent earlier. In addition, this equiaxed recrystallized grain means that the average aspect ratio of the recrystallized grain observed in both the plane parallel to the plate surface and the plane perpendicular to the rolling direction is in the range of 1 to 3. means. Specifically, the following condition is satisfied. 1 ≦ dL / dLT ≦ 3 1 ≦ dL / dST ≦ 3 dL; particle size measured in the plate length direction dLT; particle size measured in the plate width direction dST; particle size measured in the plate thickness direction

[0008] Thereafter, Al-Mg-Si-based aluminum alloys are subjected to hot rolling and, if necessary, intermediate annealing, and then cold rolled, and then subjected to a solution treatment and a quenching treatment to make the microstructure equiaxed recrystallized grains. As a result of various studies on the characteristics of the product plate, it was found that there was a specific relationship between the presence or absence of ridging marks and the ear height generated when this product plate was formed into a cup shape. . The present invention has been made based on this finding, and Si: 0.2 to 1.8.
%, Mg: 0.2 to 1.6%, an Al-Mg-Si-based aluminum alloy plate that has been hot-rolled and subsequently subjected to intermediate annealing if necessary, then cold-rolled, and then solution-hardened and quenched. The microstructure is composed of equiaxed recrystallized grains, and the ratio of the Al alloy sheet thickness to the punch having a diameter of 40 mm (shoulder radius of 3 mm) and the gap between the punch and the die is 1.3 to 1.
When a die in the range of 4 is used to form a cup under the conditions of a wrinkle holding force of 150 kgf, a forming speed of 60 mm / min, and a used lubricating oil # 700, the cup ear ratio is -4% or more. I do. The equiaxed meaning is the same as that described above.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Ears generated when an Al-Mg-Si based aluminum alloy plate is formed into a cup shape are 0 °, 90 °, 18 ° with respect to a rolling direction called a minus ear.
0 °, 270 ° ears and 45 °, 135 °, 225 °, 315
It is roughly divided into ears that occur in the ゜ direction. And ear rate (%)
Is generally defined as follows: Ear ratio (%) = {(average value of plus ear height) − (average value of minus ear height)} × 100 / (average ear height)

[0010] As shown in the prior application, ridging in an Al-Mg-Si-based aluminum alloy plate which has been hot-rolled, and subsequently subjected to intermediate annealing as required, then cold-rolled, and then solution-hardened and quenched. The presence or absence of the mark is related to the degree of integration of the cube orientation. If the degree of integration of the cube orientation is high, there is a difference in the anisotropy and degree of deformation between the accumulation area and the non-accumulation area of the cube orientation during molding, which causes the generation of ridging marks. The use of ear ratios that more directly represent the anisotropy of the resulting deformation may allow more accurate assessment of the presence or absence of ridging marks. From that point of view, the present inventors performed hot rolling and subsequently intermediate annealing, then cold rolled, and then subjected to solution treatment and quenching treatment to make the microstructure an equiaxed recrystallized Al-Mg-Si based aluminum alloy. When the plate was formed into a cup shape under a certain processing condition (in the above "") and examined, the ear ratio defined above was -4%.
It was found that in the above plate, the occurrence of ridging marks was reliably prevented. In addition, since the ear ratio at the time of forming into a cup shape varies depending on the processing conditions, the processing conditions must be constant.

[0011] The Al-Mg-Si-based aluminum alloy sheet having a microstructure of equiaxed recrystallized grains by hot rolling, and then, if necessary, intermediate annealing and then cold rolling, solution treatment and quenching, is used. When the ear ratio at that time is within the above range, the ridging mark resistance of the product plate is guaranteed. However, when the ear rate is outside the above range,
Ridging mark resistance is not completely guaranteed. Therefore,
In this case, a countermeasure such as turning the product plate to a molding use at a level at which ridging marks are not generated or a use at which ridging marks may be generated is taken. In any case, since the measurement of the ear height can be performed easily and in a short time, quick measures can be taken. The conditions for forming into a cup shape do not necessarily have to be the same as the above-mentioned "". However, it is necessary to clarify the relationship between the ear ratio and the occurrence of ridging marks when molding is performed under these conditions.

The Al-Mg-Si-based aluminum alloy sheet is subjected to hot rolling after homogenizing heat treatment, intermediate annealing as necessary, followed by cold rolling, solution treatment and quenching. Are as follows. In the hot rolling, the hot rolling end temperature is equal to or higher than the recrystallization temperature, and the strain rate during the final pass of the hot rolling is 7000 to 2
After the completion of hot rolling, the rolled sheet is immediately rolled up to obtain a hot-rolled sheet having microstructure of equiaxed recrystallized grains.
Here, the strain rate is defined as: strain rate = rolling rate (%) by final roll / time (second) that the sheet passes through the final roll. More specifically, the rolling start temperature is set to 450
° C or higher and a homogenization treatment temperature (for example, 470 to 540 ° C) or lower, and the hot rolling end temperature is higher than the recrystallization temperature, for example, 3 ° C.
Set to 00-450 ° C. In the case where the finishing hot rolling is performed in a continuous manner in a plurality of stages, the minimum strain rate of the continuous hot rolling is set to 2% or more of the strain rate at the time of the final pass, and recrystallization is repeatedly performed during the finishing hot rolling. If this is the case, the recrystallized grains become finer, and this is more effective in preventing ridging marks on the product plate. The preferred size of the recrystallized grains at this stage is 45
μm or less. Further, in order to cause recrystallization in the finish hot rolling, it is desirable that the rolling ratio of each pass is 40% or more.

The intermediate annealing conditions are as follows: heating rate: up to 400 ° C., 30 ° C./min. To 500 ° C./sec.
１００100 ° C./min, holding condition: 500-580 ° C. × 10 seconds to 10 minutes, cooling rate: 30 ° C. from holding temperature to 50 ° C.
/ Min or more. In the case where the intermediate annealing is performed, the rolling end temperature of the hot rolling can be made lower than the temperature range described in the previous hot rolling, for example, to 150 to 300 ° C. Further, the strain rate during the final pass of hot rolling can be set as low as, for example, 5,000 to 20,000% / sec. The cold rolling rate is preferably set to 50% or more in order to reduce the particle diameter of equiaxed recrystallized grains of the aluminum alloy sheet after solution treatment to 45 μm or less. Thereby, the occurrence of orange peel during molding is prevented. When the above-described intermediate annealing is performed, the solid solubility is high, the work hardening degree in cold rolling is high, and the recrystallized grains in the solution treatment are easily refined. Therefore, a cold rolling reduction of 30% or more is sufficient. Preferred solution treatment conditions are as follows: heating rate up to 400 ° C. is 30 ° C./min or more;
C./min or more, at 530-580.degree. C. for 10 seconds to 10 minutes. For heating, a nitrite furnace, a continuous annealing furnace, an induction heating furnace, or the like may be used to increase the heating rate. The quenching is performed from the holding temperature to a temperature of 70 to 140 ° C. or lower.
C./min. Or at a holding temperature of 70 to 1
The cooling may be performed at a temperature of 40 ° C. at a cooling rate of 30 ° C./min or more, and may be maintained at a temperature of 70 to 140 ° C. for 0.5 to 48 hours.

[0014] In terms of the component composition, the present invention relates to Si:
0.2-1.8%, Mg: 0.2-1.6%,
In addition to the aluminum alloy comprising the balance of Al and inevitable impurities, if necessary, Zn: 0.005 to 1.0
%, Cu: 0.005 to 1.0%, Ti: 0.001 to
0.1% of one or more of B, 1 to 30
0 ppm, Be: one or more of 0.1 to 100 ppm
Seed, Mn: 1.0% or less, Cr: 0.3% or less, Z
r: 0.15% or less, V: 1 out of 0.15% or less
0.01 to 1.5% in total of two or more species or more,
, Or an aluminum alloy containing a combination thereof, Si: 0.2 to 1.8%, Mg: 0.
It can be applied to all Al-Mg-Si-based aluminum alloys containing 2 to 1.6%. The reason for defining the composition of the Al-Mg-Si-based alloy as described above is as follows.

Mg: Mg is an element that imparts strength together with Si, but if it is less than 0.2%, sufficient strength cannot be obtained by artificial aging, while if it exceeds 1.6%, formability decreases. Therefore, the Mg content is in the range of 0.2 to 1.6%. Si: Si is an element that imparts strength together with Mg, but if it is less than 0.2%, sufficient strength cannot be obtained by artificial aging, while if it exceeds 1.8%, elongation decreases and moldability decreases. I do. Therefore, the Si content is in the range of 0.2 to 1.8%. In order to obtain high strength by artificial aging, M
It is desirable that the ratio of the content of g and Si be Si / Mg ≧ 0.65.

Zn: Zn is MgZn during artificial aging.
₂ is finely and densely deposited to realize high strength.
However, if less than 0.005%, sufficient strength cannot be obtained,
On the other hand, if it exceeds 1.0%, the corrosion resistance is significantly reduced,
The content is in the range of 0.005 to 1.0%. Cu: Cu precipitates Mg ₂ Si finely and at high density during artificial aging, and realizes high strength. However, 0.0
If it is less than 0.05%, there is no effect, while if it exceeds 1.0%, the corrosion resistance and weldability are remarkably reduced.
005 to 1.0%. Ti: Ti is an element added for refining the crystal grains of the ingot and improving formability. However, if it is less than 0.001%, there is no effect, and if it is added more than 0.1%, it is not effective. It forms coarse crystals and reduces moldability. For this reason,
The Ti content is in the range of 0.001 to 0.1%.

B: Similar to Ti, B is an alloy added for refining the crystal grains of the ingot and improving the formability. However, if less than 1 ppm is added, there is no effect.
If contained in excess of the above, a coarse crystallized product is formed and the moldability is reduced. Therefore, the B content is in the range of 1 to 300 ppm. Be: Be is contained in an amount of 0.1 ppm or more, if necessary, to prevent reoxidation of the aluminum melt in the air. However, if the content exceeds 100 ppm, the hardness of the material increases and the formability decreases.
ppm range.

Mn, Cr, Zr, V: These components are Al ₂₀ Cu ₂ during the homogenizing heat treatment and during the subsequent hot rolling.
Mn ₃ , Al ₁₂ Mg ₂ Cr, Al ₃ Zr, Al ₂ Mg
It generates dispersed particles of ₃ Zn ₃ and the like. Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains can be obtained. However, excessive addition tends to generate a coarse insoluble intermetallic compound at the time of melting casting, becomes a starting point of destruction at the time of forming, and causes a reduction in formability. In addition, excessive addition of Zr tends to make the microstructure needle-like, deteriorating fracture toughness and fatigue characteristics in a specific direction, and further deteriorating formability. Therefore, the addition amounts of Mn, Cr, Zr, and V are 1.0%, 0.30%, 0.15%,
0.15% or less, and a total of 1.5% or less.

Fe: Fe contained as impurities is Al
₇ Cu ₂ Fe, Al ₁₂ (Fe, Mn) ₃ Cu ₂ , (F
e, Mn) generating a crystallized substances such as Al _6. These precipitates are harmful to fracture toughness, fatigue properties, and formability. If the Fe content exceeds 0.5%, fracture toughness, fatigue properties, and formability are significantly reduced. The amount is 0.5% or less. In addition, as a crystallized substance, there are soluble substances such as Al ₂ Cu ₂ Mg, Al ₂ Cu ₂ , and Mg ₂ Si other than Fe-based substances, and these are sufficiently reconstituted in the Al matrix by solution treatment and quenching. It is desirable to form a solid solution. Other impurities: Ni is limited to 0.05% or less.

[0020]

Embodiments of the present invention will be described below. (Example 1) Mg: 0.5%, Si: 1.2%, Mn:
0.05%, Fe: 0.15%, Cr: 0.01%, N
i: 0.001%, Zn: 0.03%, Cu: 0.03
%, Ti: 0.06%, Bi: 10 ppm, Be: 30
ppm, and an aluminum alloy consisting of the balance Al and impurities was melt-cast into a 480 mm thick ingot,
After performing homogenizing heat treatment at 40 ° C. × 8 hr, rough hot rolling (reverse) and finish continuous hot rolling (4 tandem)
A 3.5 mm-thick plate was wound around a coil, subjected to intermediate annealing or not, and cold-rolled into a 1.2 mm-thick plate, followed by solution treatment and quenching. Solution treatment and quenching are performed at an average temperature increase rate of 300 ° C to 400 ° C by continuous annealing.
After heating at 550 ° C. for about 1 minute, the mixture was cooled to 30 ° C. by forced air cooling at an average cooling rate of 40 ° C./min. Table 1 shows the processing conditions of each step.

[0021]

[Table 1]

Sampling was performed from this plate, and each material property was measured in the following manner. Micro crystal grains: The recrystallized grain size was determined by measuring the L-LT surface (the surface layer portion was polished by 0.1 mm) for the sampled plate material in terms of the L-direction crystal grain size (dL) and the LT direction crystal grain size (dLT). The crystal grain size (dST) in the ST direction is determined by mechanically polishing the L-ST surface, and then performing electrolytic etching (tetrafluoroboric acid: water = 15: 400, voltage 30 V, solution temperature 20 to 3).
The film was evaluated at 0 ° C. and an etching time of 60 to 90 seconds by an optical microscope (using a polarizing plate, magnification of 50 ×) by a line intercept method (based on JIS H0501). Tensile properties: After aging the quenched plate at room temperature for 3 months, JIS
Based on -Z2241, using a JIS No. 5 test piece in a normal temperature atmosphere, the test was performed in the LT direction (90 ° direction with respect to the rolling direction) at a tensile speed of 5 mm / min.

Evaluation of ridging mark; JIS from product plate
After preparing a No. 5 test piece (the longitudinal direction was perpendicular to the rolling direction and the length of the parallel portion was 60 mm), the parallel portion was mirror-finished by buffing. This is subjected to a 15% tensile deformation (cage length 50 mm,
After a deformation rate of 5 mm / min), the degree of unevenness of the plate surface at the parallel portion was visually observed, and a case where a ridging mark was generated was evaluated as x, and a case where it was difficult to distinguish the ridging mark was evaluated as ○.

As can be seen from Table 1, the sample No. having an ear ratio of -4% or more. No ridging marks were generated in Nos. 1 to 3 and 6. Furthermore, the size of recrystallized grains is 45
No. which was less than μm. No orange peel was generated in 1 to 3. On the other hand, the ear ratio was less than -4%.
Ridging marks occurred on 4 and 5.

[0025]

According to the present invention, Al is hot-rolled, then, if necessary, is subjected to intermediate annealing, then cold-rolled, and then is subjected to a solution treatment and a quenching treatment so that the microstructure becomes equiaxed recrystallized grains. −
By defining the ear ratio generated when the Mg-Si-based aluminum alloy plate is formed into a cup shape, the ridging mark resistance of the product plate can be guaranteed.
In addition, since the ridging mark resistance of a product plate can be reliably evaluated in a short time, the result of the evaluation is immediately reflected in the manufacturing process to prevent a situation in which an aluminum alloy plate with poor ridging mark resistance is manufactured in large quantities. Becomes possible.

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Claims (5)

[Claims] 1. Si: 0.2 to 1.8% (mass%,
The same applies hereinafter), Mg: 0.2 to 1.6%, Al-Mg-Si which is cold-rolled after hot rolling and, if necessary, intermediate annealing, and then solution-treated and quenched. -Based aluminum alloy plate, the microstructure of which is composed of equiaxed recrystallized grains, and a punch having a diameter of 40 mm (shoulder radius 3
mm) and a die having a ratio between the gap between the punch and the die and the thickness of the Al alloy in the range of 1.3 to 1.4, and a wrinkle holding force of 15 mm.
0 kgf, molding speed 60 mm / min, lubricating oil used # 70
An aluminum alloy sheet having excellent ridging mark resistance, wherein the cup ear ratio is -4% or more when formed into a cup under the condition of "0". 2. The aluminum alloy sheet having excellent ridging mark resistance according to claim 1, which has a crystal grain size of 45 μm or less. 3. The Al-Mg-Si-based aluminum alloy further contains 0.005% to 1.0% of Zn and 0.1% of Cu.
005 to 1.0%, one or more of Ti: 0.001 to 0.1%, B: 1 to 300 ppm, Be: 0.1
1 to 2 ppm of Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.15% or less, V:
3. The method according to claim 1, wherein one or more of 0.15% or less are contained in a total of 0.01 to 1.5%, and any one or more of these or a combination thereof. 4. An aluminum alloy sheet from which the sheet material for forming process having excellent ridging mark resistance described can be obtained. 4. An aluminum alloy sheet from which the sheet material for forming process excellent in ridging mark resistance according to claim 1 is obtained for an automotive panel. 5. Si: 0.2-1.8%, Mg: 0.2
About 1.6%, the Al-Mg-Si-based aluminum alloy sheet which was cold-rolled after being subjected to hot rolling and, if necessary, intermediate annealing as needed, and then subjected to solution treatment and quenching treatment,
A method for evaluating the ridging mark resistance of an Al-Mg-Si-based aluminum alloy plate, which comprises forming the cup in a cup shape and measuring its ear height.