JPH0225972B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to an Al alloy ingot for rolling which prevents the occurrence of fir tree structure. <Prior art> Pure known as JIS Al××× or 5×××
Al-based or Al-Mg-based Al alloys for rolling crystallize Al-Fe-based intermetallic compounds inside the ingot. This intermetallic compound crystallizes in the semi-continuous cast ingot and produces a unique ingot texture often referred to as fir wood texture as seen in FIGS. 1 and 2. In the figure, A indicates the inner region of the fir tree tissue, and B indicates the outer region of the fir tree tissue. As seen in Figure 2, its shape resembles the natural shape of a fir tree, so it is called a fir tree in this technical field. When an ingot containing this fir tree structure is rolled and then subjected to anodizing treatment, a band-like striped pattern is generated corresponding to the fir tree pattern in the ingot, resulting in poor appearance and the product cannot be commercialized. By the way, once the fir tree structure is generated, it cannot be removed sufficiently in the subsequent process, so in order to solve this problem, it is necessary to use an ingot that consists entirely of the inner region of the fir tree structure, or It is desirable to produce an ingot consisting of an external region of fir wood tissue. It is known that the occurrence of fir wood structure is controlled by the cooling rate during solidification of the ingot, and if casting is performed at a slow casting speed, the internal region of fir wood structure is more likely to occur. On the other hand, if the casting speed is increased, the outer region of the fir wood structure will develop more easily. In other words, this fir tree structure pattern is caused by the difference in solidification rate of Al-Fe intermetallic compounds in each part of the ingot, which results in FeAl _{3 phases} , FeAl 6 phases, FeAl ₆ phases,
It is known that the cause is a phase change in FeAl _n . Generally, the internal region of fir tree tissue is
Consisting of FeAl ₃ + FeAl ₆ phases, the outer region is FeAl _n
Since the electrochemical properties of each phase are different, there are differences in etching characteristics and anodizing characteristics, resulting in a fir tree pattern. This transformation of FeAl ₃ phase → FeAl ₆ phase → FeAl _n phase is
Since this is a transformation from an equilibrium phase to a non-equilibrium phase, it is not only accelerated as the solidification rate is faster, but also accelerated by the presence of a third element. That is, it is known that addition of Si, Mg, Ca, Sr, Co, Ni, V, etc. makes it easier for the external region of the fir tree tissue to develop. Of these, Ca, Sr,
The addition of Co, Ni, V, etc. is very effective, and by adding a small amount, it is possible to obtain an ingot without a fir tree pattern consisting of the entire outer region at a normal casting speed. As an example of measures from this aspect,
15186, Tokukowa 58-6774, etc. However, the addition of Ca, Sr, Co, Ni, V, etc. may promote contamination of the boiling water or use relatively special elements that are not normally used in commercially available aluminum alloys, so it is not economical. There were disadvantages such as high price and restrictions on its use as return material. Therefore, it is commonly used
It has been strongly desired to obtain an ingot with a fir tree structure by controlling the amount of Si and Mg added, but
Because the effects of Mg and Mg on the fir tree structure had not been quantitatively understood,
The reality is that it is not possible to stably obtain an ingot in which no fir tree structure is formed. In view of this situation, the inventors have developed this Si and
A detailed study of the influence of Mg on the formation of fir tree tissue revealed that the ratio of Si to Fe is important;
When (%)/Si (%) is small, the external region develops, and when it is large, the internal region develops, but for Mg, the greater the amount added, the more the external region of the fir tree tissue develops, regardless of the amount of Fe. We found that Fe (%) / Si (%)
By appropriately adjusting the amount of Mg, even at normal casting speeds, the entire ingot can be made into the outside area of the fir tree structure, or the entire area can be made into the inside area, making it possible to stabilize the ingot without the fir tree pattern. We have already filed an application for this patent. (Tokukōwa 58−
26421). <Problems that Hatsuhatsu attempts to solve> However, in Japanese Patent Publication No. 58-26421, Fe and Si
The ratio of Fe (%) / Si (%) ≦ 2.0 + 0.5 × Mg (%)
Or, since Fe (%) / Si (%) ≧ 6.5 + 3.0 × Mg (%), even if Mg is not included, 2.0 < Fe (%) / Si
(%)<6.5, an ingot without fir wood structure cannot be obtained, and this range expands if even a small amount of Mg is contained. The present invention is for obtaining an ingot without a fir tree pattern and a rolled plate without a fir tree pattern even in the range of 3.0 < Fe (%) / Si (%) < 6.5,
Due to other reasons (color tone after anodization, required mechanical properties, economic efficiency, etc.),
This is particularly effective when the Si and Mg amounts cannot be adjusted within a certain range. <Means for Solving the Problems> The present invention has the following configuration to solve the above problems. That is, Fe0.05~1.0%, Si0.05~1.0%,
Mg0.3~1.5%, Cu0.01~0.5%, Ti0.005~0.3%,
It consists of Cr0.05~0.3%, Mn0.005~0.3%, the balance Al and unavoidable impurities, and the ratio of Fe and Si is
Al alloy for rolling that prevents the occurrence of fir pattern, characterized by 3.0 < Fe (%) / Si (%) < 6.5 and the dendrite arm spacing within 20 mm from the skin of the ingot is 30 μm or less It is an ingot. In addition, this value of dendrite arm spacing was determined by taking a photo of a sample that had been electrolytically polished after buffing using an optical microscope, measuring the spacing of crystallized compounds using a random cutting method on photographic paper, and applying the average value. . <Function> The reason for limiting the composition range of each alloy component is as follows. Fe is set at 0.05 to 1.0%. Regulating it to less than 0.05% requires high-purity metal, which is not economical. 1.0%
If the amount is larger than this, the corrosion resistance will decrease, which is not preferable. Si is set at 0.05 to 1.0%. Regulating it to less than 0.05% requires high-purity metal, which is not economical. If it exceeds 1.0, the color tone of the anodic oxide film becomes dark, which is undesirable, and the corrosion resistance also decreases. Mg is added to increase strength, but from 0.3 to
The rate shall be 1.5%. If it is less than 0.3%, the effect is not sufficient and 1.5
%, Mg ₂ Si-based crystallized substances take priority and Al−Fe
The crystallization of type intermetallic compounds is eliminated, resulting in an alloy that is not subject to the prevention of fir tree structure according to the present invention. Cu is added to increase strength, but from 0.01 to
Set at 0.5%. If it is less than 0.01%, the effect is not sufficient.
If it exceeds 0.5%, corrosion resistance will decrease. Ti is added to refine grains, but
Set at 0.005-0.3%. If it is less than 0.005%, the effect is not sufficient, and if it exceeds 0.3%, the effect is saturated, and furthermore,
The formation of giant intermetallic compounds deteriorates the formability and corrosion resistance of the anodic oxide film. Cr is added for the purpose of stably developing the outer region, improving strength, and refining recrystallized grains in combination with the casting conditions described later, and is added in an amount of 0.05 to 0.3%. If it is less than 0.05%, the effect is not sufficient, and if it exceeds 0.3%, giant intermetallic compounds are formed, which deteriorates the formability and corrosion resistance of the anodic oxide film. Mn is added for the purpose of improving strength and refining recrystallized grains, and is added in an amount of 0.005 to 0.3%. If it is less than 0.005%, the effect is not sufficient, and if it exceeds 0.3%, Al−Fe−
Crystallization of Mn-based intermetallic compounds takes precedence, and crystallization of Al--Fe-based intermetallic compounds disappears, resulting in an alloy that is not subject to the prevention of fir tree structure according to the present invention. The ratio of Fe and Si is 3.0<Fe(%)/Si(%)<6.5
shall be. If this value is less than 3 or more than 6.5,
Since the invention described in Japanese Patent Publication No. 58-26421 can prevent fir wood structure, it is outside the scope of the present invention. An alloy with the above chemical composition is extracted from the surface of an ingot.
Cast at a cooling rate that results in dendrite arm spacing of 30 μm or less within 20 mm. Thereafter, this ingot may be subjected to normal rolling to form a rolled plate. As described above, by adding Cr within a certain range and increasing the cooling rate during casting, the present invention can stabilize the alloy composition from only the external region, which was not possible in Japanese Patent Publication No. 58-26421. It is possible to obtain an ingot that looks like this, and to prevent the fir tree pattern on the rolled plate. <Example> The present invention will become clearer through the following example. In other words, an ingot having the chemical composition shown in Table 1 and the dendrite arm spacing of the ingot is
DC cast. The size of the ingot is 1200mm wide x 400mm thick
It was mm x length 3500mm. Each ingot obtained by the above casting is
After cutting at the 500mm position and cutting out the slices, soak the sliced surface in 10% caustic soda solution for 60 minutes.
Etched at ℃ for 10 minutes, washed with water, pickled with 30% nitric acid, and then heated to a current of 2.5 A/dm ² in a 15% sulfuric acid solution.

[Table] Anodization treatment was performed under electrolytic conditions of 50 minutes of electrolysis time and 15°C of electrolysis temperature. The results of observing each sliced surface anodized in this way were as shown in the right column of the first table. As can be seen from this result, all of the comparative examples lacking any of the constituent features of the present invention exhibited a fir tree texture, whereas the examples satisfying all of the constituent features of the present invention exhibited a fir wood texture. Does not occur. <Effects of the Invention> The alloy of this invention can prevent the occurrence of fir tree patterns even in alloys that do not fall within the composition range specified in Japanese Patent Publication No. 58-26421. It has great significance in industrial production because it expands the selection range.

[Brief explanation of drawings]

The drawings show the fir tree structure that appears in the cross section of an aluminum alloy ingot for rolling. Figure 1 is a cross-sectional view of the ingot, and Figure 2 is a cross-sectional view of the ingot taken along the line X-X' in Figure 2. FIG.

Claims (1)

[Claims] 1 Fe0.05-1.0% (by weight, same below), Si0.05
~1.0%, Mg0.3~1.5%, Cu0.01~0.5%, Ti0.005
~0.3%, Cr0.05~0.3%, Mn0.005~0.3%, balance
Consisting of Al and unavoidable impurities, the ratio of Fe and Si is 3.0 < Fe (%) / Si (%) < 6.5, and the dendrite arm spacing within 20 mm from the skin of the ingot is 30 μm or less. An aluminum alloy ingot for rolling that prevents the occurrence of fir tree structure.