Aluminum alloy, continuously cast aluminum alloy rod, method for manufacturing a continuously cast aluminum alloy rod

Abstract

This invention provides an aluminum alloy, a continuously cast aluminum alloy rod, and a method for manufacturing a continuously cast aluminum alloy rod, which contribute to the efficient use of resources at low cost by increasing the proportion of scrap containing a high amount of iron (e.g., 0.4% by mass or more). [Solution] The alloy has a composition containing Si in a range of 0.6 mass% or less, Fe in a range of 1.0 mass% or less, Cu in a range of 0.2 mass% or less, Mn in a range of 1.0 mass% to 1.5 mass%, Zn in a range of 0.30 mass% or less, and Ca in a range of 0.0005 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities.

Description

Technical Field

[0005]

[0001] The present invention relates to an aluminum alloy, a continuously cast bar of an aluminum alloy, and a method for producing a continuously cast bar of an aluminum alloy.

Background Art

[0002] A3003, an aluminum alloy defined by JIS, has slightly higher strength than pure aluminum and has excellent formability, weldability, and corrosion resistance by adding Mn as an additive element. Such A3003 aluminum alloys are widely used in aluminum containers, photosensitive drums, building materials such as panels, shipbuilding materials, fin materials, aluminum cans, and the like.

[0003] Generally, when producing an aluminum alloy, from the viewpoints of cost and effective use of resources, recycled aluminum alloy (scrap) is often used. However, most of such scrap contains more than 0.7% by mass of Fe. When casting an A3003 aluminum alloy using such scrap containing more than 0.7% by mass of Fe, excessive Fe combines with Al to form a metal compound such as Al6Fe.

[0004] Al6Fe causes, for example, a fir tree structure (Tannen-baumgefuge) similar to the appearance of a fir tree in the longitudinal section of a cast bar of an A3003 aluminum alloy (see, for example, FIG. 5). When such a fir tree structure occurs in an aluminum alloy, it does not disappear even after undergoing various processes such as stretching and heat treatment, which are post-processing steps. When chemical conversion treatment or anodic oxidation treatment is applied, the color of that part becomes different and a pattern appears on the surface. When such a fir tree structure occurs, it not only impairs the aesthetics of the manufactured product but also causes a problem that the workability decreases due to a partial change in hardness caused by the generation of Al6Fe.

[0005] For this reason, for example, Patent Document 1 describes that when adding Ca, Ti, and B to the molten metal during the casting of aluminum alloy, the formation of fir wood-like structures can be stably suppressed by setting the molten metal temperature to 675-740°C. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-174182 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, Patent Document 1 specifies that the Fe content should be between 0.03 and 2.5% by mass. Since many scrap materials exceed this Fe content, it became necessary to use a very small proportion of scrap in the molten metal, requiring the use of a large amount of pure aluminum that does not contain Fe. This increased the manufacturing cost of A3003 aluminum alloy and hindered the effective utilization of scrap.

[0008] This invention has been made in view of the above technical background, and aims to provide an aluminum alloy, a continuously cast aluminum alloy rod, and a method for manufacturing a continuously cast aluminum alloy rod that contribute to the effective use of resources at low cost by improving the proportion of scrap containing a large amount of iron (for example, 0.4% by mass or more). [Means for solving the problem]

[0009] To solve the above problems, the following means are proposed in the aluminum alloy, the continuously cast aluminum alloy rod, and the method for manufacturing the continuously cast aluminum alloy rod according to one embodiment of the present invention. (1) The aluminum alloy according to embodiment 1 of the present invention has an alloy composition containing Si in a range of 0.6 mass% or less, Fe in a range of 1.0 mass% or less, Cu in a range of 0.2 mass% or less, Mn in a range of 1.0 mass% or more and 1.5 mass% or less, Zn in a range of 0.30 mass% or less, and Ca in a range of 0.0005 mass% or more and 0.01 mass% or less, with the remainder being Al and unavoidable impurities.

[0010] (2) Embodiment 2 of the present invention further comprises the aluminum alloy of Embodiment 1, wherein Ti is included in a range of 0.005% by mass or more and 0.10% by mass or less.

[0011] (3) Embodiment 3 of the present invention further comprises B in an aluminum alloy according to Embodiment 1 or 2 in an amount of 0.001% by mass or more and 0.02% by mass or less.

[0012] (4) Embodiment 4 of the present invention is an aluminum alloy according to any one of embodiments 1 to 3, wherein the Al6Fe compound is not included.

[0013] (5) The continuously cast aluminum alloy rod of embodiment 5 of the present invention is made of any one of the aluminum alloys of embodiments 1 to 4, is a cylindrical continuously cast rod, and has a diameter in the range of 30 mm to 300 mm.

[0014] (6) A method for manufacturing a continuously cast aluminum alloy rod according to aspect 6 of the present invention is a method for manufacturing a continuously cast aluminum alloy rod according to aspect 5, comprising: a molten metal injection step of injecting molten alloy having the alloy composition of the aluminum alloy into the mold body of a continuous casting mold; a lubrication step of supplying lubricating oil and gas into the mold body; a primary cooling step of circulating a cooling medium through a cavity formed in the mold body to solidify the molten alloy and form the continuously cast rod; and a secondary cooling step of directly injecting the cooling medium toward the continuously cast rod that has undergone the primary cooling step, wherein the cooling rate at the center of the continuously cast rod from the molten metal injection step to the completion of the primary cooling step is controlled to be within the range of 2°C / second or more and 20°C / second or less.

[0015] (7) Embodiment 7 of the present invention is a method for manufacturing a continuously cast aluminum alloy rod according to Embodiment 6, wherein in the lubrication step, the temperature of the gas is controlled to be within the range of 5°C to 50°C and the temperature of the lubricating oil is controlled to be within the range of 5°C to 45°C.

[0016] (8) Embodiment 8 of the present invention is a method for manufacturing a continuously cast aluminum alloy rod according to Embodiment 6 or 7, wherein in the lubrication step, the lubricating oil used has a viscosity of 80 (mPa·s (25℃)) or more and 1100 (mPa·s (25℃)). [Effects of the Invention]

[0017] According to the present invention, it is possible to improve the proportion of scrap containing a large amount of iron (for example, 0.4% by mass or more) and provide an aluminum alloy, a continuously cast aluminum alloy rod, and a method for manufacturing a continuously cast aluminum alloy rod that contribute to the effective use of resources at low cost. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic cross-sectional view showing an example of a vertical casting apparatus used in the manufacturing method of continuously cast aluminum alloy rods according to this embodiment. [Figure 2] This is a flowchart illustrating the step-by-step method for manufacturing a continuous cast aluminum alloy rod according to this embodiment. [Figure 3] This is a schematic diagram showing the position of the observation surface of a continuously cast rod. [Figure 4] These are photographs of the observation surfaces of Example 1 and Comparative Example 1. [Figure 5] This is a schematic diagram showing an example of fir tree tissue. [Modes for carrying out the invention]

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may enlarge and show characteristic parts for ease of understanding of the characteristics, and the dimensional ratios of each component are not necessarily the same as the actual ones. Also, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and it can be appropriately modified and implemented within a range that does not change its effects.

[0020] [Aluminum alloy] An aluminum alloy according to an embodiment of the present invention will be described. The aluminum alloy of an embodiment of the present invention corresponds to A3003 aluminum alloy in that it contains Mn and Cu. The aluminum alloy of an embodiment of the present invention contains Si within a range of 0.6 mass% or less, Fe within a range of 1.0 mass% or less, Cu within a range of 0.2 mass% or less, Mn within a range of 1.0 mass% or more and 1.5 mass% or less, Zn within a range of 0.30 mass% or less, and Ca within a range of 0.0005 mass% or more and 0.01 mass% or less, and the balance consists of Al and inevitable impurities.

[0021] (Si: 0.6 mass% or less) Si has the effect of improving corrosion resistance along with mechanical properties at room temperature. However, if Si is added excessively to the aluminum alloy, there is a risk that the tensile strength of the aluminum alloy will decrease due to the crystallization of coarse primary Si grains. By setting the Si content to 0.6 mass% or less, the crystallization of primary Si can be suppressed.

[0022] (Fe: 1.0 mass% or less) Fe (Fe) improves the tensile strength of aluminum alloys by crystallizing as fine precipitates containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe in aluminum alloys. On the other hand, excess Fe can generate hard intermetallic compounds such as Al6Fe, which may reduce workability. By keeping the Fe content within the range of 1.0 mass% or less, along with the addition of Ca (described later), the formation of Al6Fe, which causes the formation of the fir-like structure, can be suppressed.

[0023] (Cu: 0.2% by mass or less) Cu has the effect of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating as Al-Cu-Mg-Si compounds, including the Q phase. However, excess Cu can cause the formation of unnecessary intermetallic compounds. By keeping the Cu content within the above range, it is possible to improve the room-temperature mechanical properties of the aluminum alloy forged product 1a without forming unnecessary intermetallic compounds.

[0024] (Mn: 1.0 mass% or more and 1.5 mass% or less) Mn improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si within the alloy. By keeping the Mn content within the specified range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0025] (Ca: 0.0005 mass% or more and 0.01 mass% or less) Ca can suppress the formation of a fir-like structure caused by metallic compounds such as Al6Fe, even when the proportion of Fe-containing scrap and other materials used as raw materials for aluminum alloy production is increased. By keeping the Ca content within the above range, the formation of a fir-like structure can be suppressed even if, for example, the Fe content is 1.0 mass%.

[0026] The aluminum alloy of one embodiment of the present invention may further contain Ti in an amount of 0.005% by mass or more and 0.10% by mass or less.

[0027] (Ti: 0.005 mass% or more and 0.10 mass% or less) Ti has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. If the Ti content is less than 0.005 mass%, the grain refinement effect may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.10 mass%, coarse precipitates may form, which may reduce wroughtability. In addition, if a large amount of coarse precipitates containing Ti are mixed into the aluminum alloy, the toughness may decrease.

[0028] The aluminum alloy of one embodiment of the present invention may further contain B in an amount of 0.001% by mass or more and 0.02% by mass or less.

[0029] (B: 0.001 mass% or more, 0.02 mass% or less) B has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. Adding B to aluminum alloys together with Ti, as described above, enhances the crystal grain refinement effect. If the B content is less than 0.001 mass%, the crystal grain refinement effect may not be sufficiently obtained. On the other hand, if the B content exceeds 0.02 mass%, coarse precipitates may form and be mixed into the aluminum alloy as inclusions. Furthermore, if a large amount of coarse precipitates containing B are mixed into the final aluminum alloy product, the toughness may decrease.

[0030] The aluminum alloy of one embodiment of the present invention preferably contains no Al6Fe compound at all. Al6Fe causes a fir-like structure in aluminum alloys. This fir-like structure not only impairs the aesthetic appearance of the manufactured product, but also reduces workability due to localized changes in hardness caused by the formation of Al6Fe. In the aluminum alloy of this embodiment, by including Ca in the range of 0.0005% by mass or more and 0.01% by mass or less, even if Fe is included at a high content, such as 1.0% by mass, the formation of Al6Fe compounds is suppressed, resulting in an aluminum alloy in which no fir-like structure is formed at all.

[0031] According to the aluminum alloy of this embodiment, which has the above configuration, even if scrap with a Fe content exceeding 0.3 mass% is used as a raw material, the formation of Al6Fe compounds is suppressed and an aluminum alloy without a fir tree structure is obtained by including Ca in a range of 0.0005 mass% to 0.01 mass%.

[0032] This makes it possible to create an aluminum alloy that produces aesthetically pleasing aluminum products without localized color variations. Furthermore, it is possible to create an aluminum alloy with excellent workability that does not exhibit localized hardness changes due to the formation of Al6Fe compounds.

[0033] [Continuously cast aluminum alloy rods] A continuously cast aluminum alloy rod according to one embodiment of the present invention can be obtained by casting an aluminum alloy having the above-described alloy composition, for example, using a vertical continuous casting apparatus. Such a continuously cast aluminum alloy rod has the above-described alloy composition of the aluminum alloy, has a cylindrical shape, and has a diameter in the range of, for example, 30 mm to 300 mm.

[0034] [Method for manufacturing continuously cast aluminum alloy rods] Next, an embodiment of the method for manufacturing a continuous cast aluminum alloy rod according to this embodiment will be described. First, an example of a vertical casting apparatus used in the manufacturing method of the continuously cast aluminum alloy rod according to this embodiment will be described. Figure 1 is a schematic cross-sectional view showing an example of a vertical casting apparatus used in the manufacturing method of continuously cast aluminum alloy rods according to this embodiment.

[0035] The vertical continuous casting apparatus 10 for continuous casting has a continuous casting mold 100. The continuous casting mold 100 has a cylindrical mold body 100A, one end of which is an inlet 12 for molten alloy and the other end of which is an outlet 13 for the continuous casting rod (ingot) S. The mold body 100A is made of an aluminum alloy containing a large amount of Mg. Alternatively, a Cu alloy can also be suitably used.

[0036] The mold body 100A has a cavity 21 through which a cooling medium, such as cooling water C, flows. An inlet 22 to the cavity 21 is provided at the top, and a nozzle 23 surrounds the casting outlet 13. The cooling water (cooling medium) C introduced from the inlet 22 flows through the cavity 21 and cools the molten metal M in the molding hole 11 through the mold body 100A, causing the molten alloy to solidify (primary cooling). Furthermore, this cooling water C is ejected from the nozzle 23 and sprayed onto the continuously cast rod S as it is being cast, cooling the continuously cast rod S (secondary cooling).

[0037] Furthermore, a carbon ring 30 is provided above (upstream of) the cavity 21 of the mold body 100A, facing the inner circumferential surface 100Aa of the molding hole 11. This carbon ring 30 has a lubricating oil supply path 31 and a gas supply path 32 positioned spaced apart from the lubricating oil supply path 31.

[0038] Lubricating oil Q is supplied to the inside of the mold body 100A from the lubricating oil supply path 31. The type of lubricating oil Q is not particularly limited, but it is preferable to use one with a viscosity in the range of 80 (mPa·s (25℃)) to 1100 (mPa·s (25℃)).

[0039] Furthermore, gas G is supplied to the inside of the mold body 100A from the gas supply path 32. Examples of the supplied gas include air, a gas mixture (e.g., oxygen + inert gas), and an inert gas. In this embodiment, air was used as the gas supplied from the gas supply path 32.

[0040] Figure 2 is a flowchart illustrating the step-by-step method for manufacturing a continuous cast aluminum alloy rod according to this embodiment. The method for manufacturing a continuously cast aluminum alloy rod according to this embodiment includes, for example, a molten metal injection step S1 in which molten metal M having the alloy composition of the aluminum alloy described above is injected into the inside of a mold body 100A using a vertical continuous casting apparatus 10 as described above; a lubrication step S2 in which lubricating oil Q and gas G are supplied to the inside of the mold body 100A; a primary cooling step S3 in which cooling water C, which is a cooling medium, is circulated in the cavity 21 to solidify the molten metal M and form a continuously cast rod S; and a secondary cooling step S4 in which cooling water C is directly sprayed onto the continuously cast rod S that has gone through the primary cooling step S3.

[0041] Then, the cooling rate at the center E of the continuous casting rod S from the molten metal injection process S1 to the completion of the primary cooling process S3 is controlled to be within the range of 2°C / second to 20°C / second. In this embodiment, the cooling rate was set to 10°C / second.

[0042] Furthermore, in the lubrication process S2, the temperature of the air G supplied from the gas supply path 32 is controlled to be within the range of 5°C to 50°C, and the temperature of the lubricating oil Q supplied from the lubricating oil supply path 31 is controlled to be within the range of 5°C to 45°C. It is preferable to use a lubricating oil Q with a viscosity in the range of 80 (mPa·s (25°C)) to 1100 (mPa·s (25°C)).

[0043] The molten alloy injected in the molten metal injection process S1 is made by melting an aluminum material having the alloy composition of the aluminum alloy described above. By including Ca in this alloy composition within the range of 0.0005% by mass to 0.01% by mass, even if the molten alloy contains a high concentration of Fe, for example 10% by mass, Al6Fe compounds will not be formed. Therefore, the continuously cast aluminum alloy rod S obtained by casting does not develop the fir wood structure shown in Figure 5.

[0044] The continuously cast aluminum alloy rod S produced by the manufacturing method of the aluminum alloy rod of this embodiment does not contain a fir wood structure, making it possible to produce aluminum products with excellent aesthetics and no color unevenness. Furthermore, since Al6Fe compounds, which are harder than aluminum, are not formed, it is possible to maintain good workability.

[0045] Although one embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0046] The effects of the present invention were verified. For verification, continuous casting rods of Examples 1-6 and Comparative Examples 1-9 were cast using aluminum alloy materials with the compositions shown in Table 1, with the vertical continuous casting apparatus 10 shown in Figure 1. Casting conditions such as casting speed, cooling rate, gas supply temperature, and lubricating oil supply temperature were the same for both the examples and comparative examples, as shown in Table 2, with only the composition of the aluminum alloy forming the molten metal being changed.

[0047] [Table 1] [Table 2]

[0048] The continuous casting rods obtained from Examples 1-6 and Comparative Examples 1-9 were cut in half along the casting direction, and the cross-sections were etched with a sodium hydroxide solution to form observation surfaces (see Figure 3). Each observation surface was then visually inspected to check for the presence or absence of fir wood structure. In Table 1, ○ indicates that no fir wood structure was observed, and × indicates that fir wood structure was present. Figure 4 also shows photographs of the observation surfaces of Example 1 and Comparative Example 1.

[0049] According to the results shown in Table 1, no fir-like tissue was observed in Examples 1-5, where 0.0005% by mass of Ca was added, and in Example 6, where 0.0010% by mass of Ca was added. On the other hand, in Comparative Examples 1-9, where Ca was not added, fir tree tissue was observed in all cases. Therefore, it was confirmed that the growth of fir tree tissue can be reliably suppressed by including Ca in a range of 0.0005% by mass or more and 0.01% by mass or less. [Explanation of symbols]

[0050] 10…Vertical continuous casting apparatus 12…Inlet 13…Casting outlet 21... Cavity 31… Lubrication oil supply route 32...Gas supply path 100... Mold for continuous casting

Claims

1. An aluminum alloy having an alloy composition containing Si in a range of 0.6 mass% or less, Fe in a range of 1.0 mass% or less, Cu in a range of 0.2 mass% or less, Mn in a range of 1.0 mass% or more and 1.5 mass% or less, Zn in a range of 0.30 mass% or less, and Ca in a range of 0.0005 mass% or more and 0.01 mass% or less, with the remainder being Al and unavoidable impurities.

2. The aluminum alloy according to claim 1, further comprising Ti in an amount of 0.005% by mass or more and 0.10% by mass or less.

3. The aluminum alloy according to claim 1 or 2, further comprising B in an amount of 0.001% by mass or more and 0.02% by mass or less.

4. Al ６ An aluminum alloy according to claim 1 or 2, which does not contain an Fe compound.

5. A continuous cast aluminum alloy rod made of the aluminum alloy described in claim 1 or 2, having a cylindrical shape and a diameter in the range of 30 mm to 300 mm.

6. A method for manufacturing a continuous cast aluminum alloy rod according to claim 5, A molten metal injection step in which molten alloy having the alloy composition of the aluminum alloy is injected into the mold body of a mold for continuous casting, A lubrication step in which lubricating oil and gas are supplied into the mold body, A primary cooling step involves circulating a cooling medium through a cavity formed within the mold body to solidify the molten alloy and form the continuous casting rod, The process includes a secondary cooling step in which the cooling medium is directly injected onto the continuous casting rod that has undergone the primary cooling step, A method for manufacturing a continuously cast aluminum alloy rod, comprising controlling the cooling rate at the center of the continuously cast rod from the molten metal injection step to the completion of the primary cooling step so that it is within the range of 2°C / second or more and 20°C / second or less.

7. A method for manufacturing a continuously cast aluminum alloy rod according to claim 6, wherein in the lubrication step, the temperature of the gas is controlled to be within a range of 5°C to 50°C and the temperature of the lubricating oil is controlled to be within a range of 5°C to 45°C.

8. The method for manufacturing a continuously cast aluminum alloy rod according to claim 6, wherein in the lubrication step, the lubricating oil has a viscosity in the range of 80 (mPa·s (25°C)) to 1100 (mPa·s (25°C)).

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