JP3685973B2 - Al-Mg-based Al alloy plate with excellent formability - Google Patents

Description

【００３６】
【表２】

【００３７】
【表３】

【００３８】
表３中、試料No. １２はＭｇが過多のため、試料No. ２２は鋳造条件が不適切であるため、熱延時に割れが生じた。試料No. ２２と同成分系（成分No. ５）の試料No. ５とにつき、鋳造帯板（鋳塊）の幅方向の冷却速度（板厚中心部）を測定したところ、No. ５では幅中央部（板端から５００ｍｍ位置）では３．０℃/sec、１／４幅部（板端から２５０ｍｍ位置）では２．５℃/secであり、幅方向の冷却速度のばらつきは小さかったが、No. ２２では幅中央部が３．０℃/sec、１／４幅部が１．６℃/secであり、１／４幅部の冷却速度が幅中央部の約５３％と幅方向の冷却速度のばらつきが大きかった。このため、No. ２２では、１／４幅部にＭｇ、Ｆｅ、Ｓｉ等の合金元素の濃縮が起こり、このため加工性が劣化したか、あるいは融点の低下を招来して部分溶融が生じて割れが発生したものと推察された。
【００３９】
また、No. １１、１３〜１８は、成分が発明範囲外であるため、耐食性が良好なものもあるが、概ね成形性が劣っている。もっとも、No. １５はＣｕ含有量が０．６％と多いため、成形性は良好であるが、耐食性の劣化が著しい。また、No. １９〜２１および２３は発明成分を満足するが、製造条件が不適切であるため、本発明の組織条件を満足せず、やはり成形性が低下している。
【００４０】
これらの比較例に対して、実施例のNo. １〜１０は、耐食性、成形性が共に優れていることが確認された。
【００４１】
【発明の効果】
本発明のＡｌ−Ｍｇ系Ａｌ合金板によれば、Ｍｇ、Ｓｉ、Ａｌのほか、所定量のＦｅあるいはさらにＣｕを本質的成分として含み、晶出物の平均晶出物径、平均アスペクト比および平均結晶粒径を所定の値以下に制限したので、優れた成形性あるいはさらに耐食性を兼ね備えることができ、これらの特性が要求される、例えば自動車パネル等の素材として好適に使用することができる。また、本発明のＡｌ合金板は、高純度のＡｌ地金を用いることなく製造することができるので、製造コストを低減することができ、アルミ材料のリサイクルにも資することができる。[0001]
[Technical field to which the invention belongs]
The present invention relates to an Al—Mg-based Al alloy plate excellent in formability or further corrosion resistance, and relates to an Al alloy plate suitable as a material for an automobile panel or the like.
[0002]
[Prior art]
Due to global environmental problems, demands for reducing the weight of automobiles for the purpose of improving fuel efficiency are increasing, and the application of aluminum materials instead of steel materials such as steel sheets to automobile body panel materials has been studied. Yes.
In an automobile panel material, an Al—Mg-based Al alloy (5000-based alloy) containing a relatively large amount of Mg is attracting attention as an Al alloy plate replacing a cold-rolled steel plate because of its excellent strength and ductility.
[0003]
[Problems to be solved by the invention]
However, it is said that press formability is insufficient when a 5000 series alloy plate produced by DC casting and rolling as in the prior art is applied to a complicated shape member such as a door panel or a roof panel. The reason is that an intermetallic compound of Fe and Si, which are impurity elements unavoidably present in the Al alloy, is generated as a crystallized substance, which becomes a starting point of fracture during molding and deteriorates formability.
[0004]
As a means for improving the formability of such an Al—Mg alloy, it is only necessary to limit the contents of Fe and Si, which are impurity elements that cause generation of the crystallized substance, as much as possible. However, in order to limit these impurity elements as much as possible, high-purity Al ingots are required, resulting in high costs and poor practicality.
[0005]
On the other hand, Japanese Patent Application Laid-Open No. 7-278716 proposes a technique for improving the formability by setting the average size of crystallized material to 15 μm or less. However, casting defects, segregation, and coarse crystallized material are proposed. In addition, a crystallized product having a large aspect ratio inevitably remains, so that a sufficient effect cannot be obtained.
[0006]
Japanese Patent Laid-Open No. 7-252572 has proposed a technique for improving moldability by containing 0.5 to 1.5% of Cu and setting the maximum size of the insoluble compound to 2 μm or less. Further, since a large amount of Cu is added, there is a problem that the corrosion resistance is deteriorated.
[0007]
The present invention has been made in view of such problems, and an object thereof is to provide an Al—Mg-based Al alloy plate that can be manufactured without using a high-purity Al metal and has excellent formability.
[0008]
[Means for Solving the Problems]
The Al alloy plate of the present invention is mass%,
Mg: 3.0-6.0%,
Si: 0.1 to 0.6%,
Fe: 0.1 to 1.0%,
Alternatively, Cu: 0.4% or less and the balance Al are essential components. The average equivalent circle diameter of the crystallized product containing Fe or Si is 2 μm or less, and the average aspect ratio of the crystallized product is 1.8. This is an Al—Mg-based Al alloy plate excellent in formability and having an average crystal grain size of 30 μm or less.
[0009]
As the components of the Al alloy plate, as described in claim 3, Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% Hereinafter, one or more kinds of components selected from the group consisting of Ti: 0.03% or less can be contained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor pays attention to the fact that Fe and Si, which have been treated as impurities in the past, have the effect of refining crystal grains, and in addition, the form of crystallized crystals inevitably generated because of the inclusion of the elements is precisely controlled. As a result of earnest research based on the idea that the moldability may be improved, the present invention has been completed.
[0011]
That is, as described in Japanese Patent Application Laid-Open No. 7-278716, there is a limit to improving the moldability only by considering the average size of the crystallized product. The average equivalent circle diameter of the product exceeds 2 μm, and the average aspect ratio of the crystallized product (ratio L1 / L2 of the length L1 in the rolling direction and the length L2 in the thickness direction of the crystallized product) is 1.8. It has been found that a remarkable effect of improving the characteristics can be obtained by suppressing the crystallized material in a region exceeding 20 nm and making the average crystal grain size 30 μm or less.
[0012]
Regarding the refinement of the crystallized material, in the technique of the above publication, the steel product thickness is continuously cast to 1 to 10 mm, and the crystallized product is refined by cooling at a cooling rate of 10 ° C./sec or more. However, with such a steel slab thickness, the rolling reduction rate cannot be sufficiently obtained during hot rolling, so casting defects and segregation remain in the plate material, and it is good enough by simply increasing the cooling rate. It is hard to get.
[0013]
In this regard, in the present invention, as will be apparent from the examples described later, not only the cooling rate is increased, but also the thickness of the steel ingot is increased to a certain level, while the ingot structure is soundened, and the ingot structure is further increased. By controlling the distribution of the crystallized product and the rolling conditions, the present invention succeeded in eliminating the coarse crystallized product and the crystallized product having a large aspect ratio that were inevitably left. In particular, casting the ingot to a certain thickness and controlling the ingot structure to a columnar crystal extending in the direction of the center of the plate thickness is very effective in refining the crystallized material and reducing the aspect ratio. Was found. In other words, by setting the ingot to a certain thickness, the crystallized crystals crystallized at the grain boundaries can be arranged in a line from the surface portion toward the center of the plate thickness, thereby enabling the subsequent hot rolling and cooling. The crystallized product can be easily and finely crushed by hot rolling.
[0014]
The Al alloy plate of the present invention made by the above knowledge is mass%,
Mg: 3.0-6.0%,
Si: 0.1 to 0.6%,
Fe: 0.1 to 1.0%,
Alternatively, Cu: 0.4% or less and the balance Al are essential components, and the average equivalent circle diameter (hereinafter referred to as the average crystallite diameter) of the crystallized product containing Fe or Si is 2 μm or less, The crystallized product has an average aspect ratio of 1.8 or less and an average crystal grain size of 30 μm or less.
[0015]
First, the reasons for limiting the components of the Al alloy plate of the present invention will be described.
Mg: 3.0-6.0%
Mg is added in order to improve the strength by solid solution in the Al matrix and to secure ductility. If it is less than 3.0%, the effect is too small. On the other hand, if it exceeds 6.0%, hot workability is reduced, hot rolling becomes extremely difficult, the solid-liquid coexistence area is expanded, and casting is difficult. As a result, productivity is significantly reduced.
[0016]
Si: 0.1-0.6%
Fe: 0.1 to 1.0%
Si and Fe generate crystallized substances such as Mg-Si and Al-Fe-Si, and have an effect of refining crystal grains. Therefore, 0.1% or more of each is added. On the other hand, when Si exceeds 0.6% and Fe exceeds 1.0%, the crystallization is coarsened, and this does not become fine due to rolling or the like after casting. The remaining coarse crystallization is the starting point of fracture, and the formability is reduced. Deteriorate. Further, when Si crystallizes as Mg ₂ Si, the amount of Mg dissolved in the Al matrix decreases, and the strength and toughness deteriorate. Therefore, from this point, Si can be kept at 0.6% or less. . In the present invention, Si and Fe are positively added in order to utilize the Si and Fe crystal grain refining effect. However, as an incidental effect, an inexpensive Al ingot containing a large amount of Fe is inevitable. Scrap material can be used, which can contribute to cost reduction.
[0017]
Cu: 0.4% or less Cu has an effect of improving moldability, but excessive addition deteriorates corrosion resistance. In the present invention, it is limited to 0.4% or less mainly from the viewpoint of ensuring corrosion resistance. In the present invention, the amount of Cu added is low and the amount of Cu that contributes to the improvement of the formability is small. However, the present invention succeeds in improving the formability by satisfying specific structure conditions described later.
[0018]
The Al alloy plate of the present invention is composed of the above Mg, Si, Fe, or even Cu and the balance Al, and is composed of the balance inevitable impurities, and further improves the characteristics of the Al alloy plate of the present invention. As mentioned above, one or more of the following element groups can be added.
[0019]
Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less, Ti: 0.03% or less These elements have a crystal grain refining effect. Effective in improving moldability. When the upper limit of each element is exceeded, a coarse compound is formed, which becomes a starting point of destruction and deteriorates moldability. In addition, Ti also has the refinement | miniaturization ability at the time of casting, and when the upper limit is exceeded, columnar crystal formation of an ingot will be prevented and the crystallized substance dividing effect will deteriorate. More preferably, Mn: 0.6% or less, Cr: 0.2% or less, Zr: 0.2% or less, V: 0.2% or less, Ti: 0.01% or less.
[0020]
Next, the structure of the Al alloy plate of the present invention will be described.
In the present invention, the average crystallite size of the crystallized product containing Fe or Si is 2 μm or less, the average aspect ratio of the crystallized product is 1.8 or less, and the average crystal grain size is 30 μm or less. .
[0021]
As for the form of the crystallized material, even if the average particle size is small, if there is a crystallized material having a large particle size and aspect ratio, it becomes a starting point of fracture, and thus has a great influence on the formability of the alloy plate. For this reason, in the present invention, the average crystallite diameter is limited to 2 μm or less, and the average aspect ratio of the crystallized product is limited to 1.8 or less, preferably 1.5 or less. When the average crystallized substance diameter exceeds 2 μm, it tends to be a starting point of fracture. Also, even if the average crystallite diameter is 2 μm or less, stress concentration tends to occur when the aspect ratio exceeds 1.8, so that such a crystallized substance is likely to be a starting point of fracture and the formability is lowered. Become.
[0022]
It was also found that the crystal grain size greatly affected the moldability, as is clear from the examples described later. Therefore, in the present invention, not only the crystallized form but also the crystal grain size is limited. That is, when the average crystal grain size exceeds 30 μm, the deterioration of the moldability becomes remarkable. Therefore, in the present invention, the average crystal grain size is set to 30 μm or less, preferably 20 μm or less. These form conditions ensure good moldability even if the amount of Cu is reduced.
[0023]
The Al—Mg-based Al alloy sheet of the present invention is manufactured through processes of hot rolling, intermediate annealing, cold rolling, and final annealing after casting. However, it is desirable to pay attention to the following points so that a predetermined organization can be obtained.
[0024]
The higher the solidification rate at the time of casting, the finer the crystallized material in the ingot. However, it is effective for minimizing the crystallized material to suppress defects and segregation in the ingot. It is preferable that the cooling rate at the center of the mass is not too high. When the cooling rate is too high, supply of the molten metal for solidification shrinkage is insufficient, and defects are likely to be generated. Therefore, in consideration of the balance between the refinement of the crystallized material and the suppression of defects and segregation in the casting stage, it is desirable to set the cooling rate at the ingot plate thickness center to 1 to 5 ° C./sec.
[0025]
Further, it is desirable to suppress the variation in the cooling rate in the ingot width direction within ± 30%, preferably within ± 20%. If there is a part with a slow cooling rate, that part becomes the final solidified part, where defects and segregation are concentrated, degrading the properties of that part, particularly the processing characteristics in the subsequent rolling process, resulting in coarse crystals and aspect. It becomes a factor which a crystallized substance with a large ratio remains.
[0026]
In order to obtain a sound structure in which the crystallized material is divided into a predetermined size and is uniformly dispersed, it has become clear that the structure at the time of solidification is preferably a columnar crystal. The reason is that by making the structure during solidification into columnar crystals, a structure form in which the crystal grains are elongated in the direction of the center of the plate thickness from the surface layer portion is obtained. In order to make the crystallized material finer effectively by rolling at a relatively high reduction ratio in the subsequent hot rolling and cold rolling. It is because it is divided. For this reason, the ingot thickness is preferably 15 mm or more, more preferably 25 mm or more.
[0027]
As a casting process for realizing the cooling rate and ingot thickness of the ingot plate thickness center as described above, a thin slab continuous casting such as a twin belt type or twin block type for producing a cast piece having a thickness of 15 to 35 mm. A process can be used. Further, as a method of suppressing the variation in the cooling rate in the ingot width direction, in the belt continuous casting method, it is necessary to prevent deformation of the belt, and preheating of the belt, application of tension, and application of a belt coating agent are effective. The preheating of the belt may be performed at a belt temperature of 60 ° C. or higher, desirably 80 ° C. or higher. Tension applied to the belt is preferably in the stress at 5.0 kgf / mm ² or more, 7.5 kgf / mm ² or more is more preferable. Moreover, as a coating agent, a thing with heat insulation is desirable, and oxide type mold release agents, such as an alumina type, are suitable. Of course, a carbon mold release agent can also be used.
[0028]
As the hot rolling condition of the ingot, it is desirable to carry out in a high temperature range for fine fragmentation of crystallized material in the ingot and reduction of the aspect ratio, but if it is too high, partial melting occurs. Accordingly, the hot rolling start temperature is preferably 450 ° C. or higher and 590 ° C. or lower, more preferably 500 ° C. or higher and 570 ° C. or lower. Further, an increase in the rolling reduction during hot rolling is effective for fine crystallization and reduction of the aspect ratio, and the total rolling reduction is preferably 80% or more, more preferably 90% or more.
[0029]
The intermediate annealing conditions and the final annealing after cold rolling are not particularly specified, and may be performed by a normal annealing method (continuous annealing or batch annealing).
[0030]
As the cold rolling conditions, as the rolling reduction (cold rolling ratio) during cold rolling increases, the crystallized material is more finely divided and the aspect ratio is reduced. However, increasing the rolling rate during hot rolling has a greater effect on the refinement of the crystallized matter. On the other hand, reduction during cold rolling is effective for crystal grain refinement after cold rolling or after final annealing. Taking these effects into consideration, the total rolling reduction during cold rolling is preferably 60% or more, more preferably 70% or more. Note that the intermediate annealing during the cold rolling is not necessarily performed.
[0031]
EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not restrictively interpreted by these Examples.
[0032]
【Example】
An aluminum alloy having the composition shown in Table 1 below is melted, and as shown in Table 2, various methods are employed by the twin belt type continuous casting method so that the cooling rate at the center of the plate thickness is 0.5 to 30 ° C./sec. A thick moving strip (plate width 1000 mm) was prepared, and this strip was immediately hot-rolled to obtain a plate having a thickness of 1.5 to 5 mm. Regarding the continuous casting conditions, in Table 2, for Sample Nos. 1 to 20 and 23, the belt preheating temperature during casting was 70 ° C., the belt tension was 7.5 kgf / mm ² , and an alumina release agent was applied to the belt. . On the other hand, Sample No. 21 produced a plate having a thickness of 8 mm by a twin roll continuous casting method, and processed it to a final thickness of 1 mm by performing only cold rolling without performing hot rolling. Sample No. 22 was cast at a belt preheating temperature of 40 ° C. and a belt tension of 2.5 kgf / mm ² , with no release agent applied, and immediately hot-rolled.
[0033]
As shown in Table 2, the hot rolling (excluding No. 21) was performed at a rolling start temperature of 430 to 570 ° C. and a rolling reduction of 90 to 75%. The hot-rolled sheet thus obtained was subjected to intermediate annealing at 500 ° C. for 1 minute, and then cold-rolled at the cold rolling rate shown in Table 2 to obtain an Al alloy sheet having a thickness of 1 mm. This alloy plate was subjected to final annealing at 550 ° C. for 1 minute and water quenching was performed.
[0034]
The Al alloy plate sample thus produced was subjected to observation with an optical microscope and image analysis to determine the equivalent circle diameter and aspect ratio of the crystallized product. In addition, the crystal grain size was measured by the section method by observation with an optical microscope. In addition, pitting corrosion after 100 hours immersion in 0.5 mol NaCl aqueous solution at 40 ° C. was evaluated in five stages (AA: excellent, A: good, B: acceptable, C: inferior, D: not possible), and corrosion resistance was evaluated. did. Further, the formability was evaluated by measuring the overhang height when the test piece was broken by the LDH test. The test conditions were 100 mm in diameter and using a ball-head punch, the application of lubricating oil R-303P, and a wrinkle holding force of 200 kN. Table 3 shows the results of these investigations. In the table, sample Nos. 1 to 10 are examples, and Nos. 11 to 23 are comparative examples.
[0035]
[Table 1]

[0036]
[Table 2]

[0037]
[Table 3]

[0038]
In Table 3, Sample No. 12 was excessive in Mg, and Sample No. 22 was not suitable for casting, so cracking occurred during hot rolling. For sample No. 22 and sample No. 5 of the same component system (component No. 5), the cooling rate in the width direction of the cast strip (ingot) was measured. The width central part (500 mm position from the end of the plate) was 3.0 ° C / sec, and the quarter width section (position 250 mm from the end of the plate) was 2.5 ° C / sec. The variation in the cooling rate in the width direction was small. However, in No. 22, the width center part is 3.0 ° C./sec, the 1/4 width part is 1.6 ° C./sec, and the cooling speed of the 1/4 width part is about 53% of the width center part. The variation in the cooling rate in the direction was large. For this reason, in No. 22, the concentration of alloy elements such as Mg, Fe, and Si occurs in the ¼ width portion, so that the workability is deteriorated or the melting point is lowered and partial melting occurs. It was inferred that cracking occurred.
[0039]
Nos. 11 and 13 to 18 have good corrosion resistance because the components are outside the scope of the invention, but generally have poor moldability. However, since No. 15 has a high Cu content of 0.6%, the moldability is good, but the corrosion resistance is remarkably deteriorated. Nos. 19 to 21 and 23 satisfy the components of the invention, but the manufacturing conditions are inappropriate. Therefore, the structural conditions of the present invention are not satisfied, and the moldability is also lowered.
[0040]
In contrast to these comparative examples, it was confirmed that Nos. 1 to 10 of the examples were excellent in both corrosion resistance and moldability.
[0041]
【The invention's effect】
According to the Al-Mg-based Al alloy plate of the present invention, Mg, Si, Al, in addition to a predetermined amount of Fe or further Cu as an essential component, the average crystallite diameter, average aspect ratio and Since the average crystal grain size is limited to a predetermined value or less, it can have excellent moldability or further corrosion resistance, and can be suitably used as a material for, for example, an automobile panel, which requires these characteristics. Moreover, since the Al alloy plate of the present invention can be manufactured without using high-purity Al metal, the manufacturing cost can be reduced and the aluminum material can be recycled.

Claims (3)

mass%
Mg: 3.0-6.0%,
Si: 0.1 to 0.6%,
Fe: 0.1 to 1.0%
And the balance Al is an essential component, and the average equivalent circle diameter of the crystallized product containing Fe or Si is 2 μm or less, the average aspect ratio of the crystallized product is 1.8 or less, and the average crystal grain size An Al—Mg-based Al alloy plate excellent in formability, having a thickness of 30 μm or less. mass%
Mg: 3.0-6.0%,
Si: 0.1 to 0.6%,
Fe: 0.1 to 1.0%,
Cu: 0.4% or less and the balance Al as an essential component, the average of the equivalent circle diameter of the crystallized product containing Fe or Si is 2 μm or less, and the average aspect ratio of the crystallized product is 1.8 or less An Al—Mg-based Al alloy plate having excellent formability and having an average crystal grain size of 30 μm or less. further,
Mn: 1.0% or less,
Cr: 0.3% or less,
Zr: 0.3% or less,
V: 0.3% or less,
3. The Al—Mg-based Al alloy plate according to claim 1, comprising at least one component selected from the group consisting of Ti and 0.03% or less.