Aluminum alloy pipe and method for manufacturing the same

Abstract

To provide an aluminum alloy pipe which is excellent in corrosion resistance and workability.SOLUTION: An aluminum alloy pipe is composed of an aluminum alloy which contains 0.30 mass% or more and 1.50 mass% or less Mn, 0.001 mass% or more and 0.24 mass% or less Mg, 0.001 mass% or more and 1.0 mass% or less Zn, 0.001 mass% or more and 0.50 mass% or less Si, more than 0 mass% Fe, and more than 0 mass% Cu, in which a content x (mass%) of Fe and a content y (mass%) of Cu satisfy a relation of the following expression (1): x+7y≤0.70, and optionally contains one or two or more of 0.30 mass% or less Cr, 0.20 mass% or less Zr, and 0.15 mass% or less Ti, and the balance Al with impurities.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy tube for automotive heat exchangers, which has excellent corrosion resistance and workability, among aluminum alloys used in heat exchangers for automobiles and various industrial applications, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, JIS 1000 series alloys, JIS 3000 series alloys, JIS 6000 series alloys, etc. have been commonly used as materials for piping of this type of heat exchanger, etc. In order to improve the corrosion resistance of piping materials, a method has been proposed in which a sacrificial material that is electrically less noble than the core material is clad on the 3000 series alloy or other core material, and the sacrificial anticorrosive effect of the sacrificial material is used to suppress the progress of corrosion in the plate thickness direction (Patent Document 1).

[0003] However, the heat exchanger piping material disclosed in Patent Document 1 is not a material that has been comprehensively optimized as an aluminum alloy piping material for heat exchangers. In the manufacturing process of the piping material clad with a sacrificial material, it is necessary to separately prepare the core alloy and the skin alloy and combine them, which makes the manufacturing process complicated. Therefore, it is desired to obtain good corrosion resistance with a single-layer aluminum alloy pipe.

[0004] Aluminum alloys having good corrosion resistance in a single layer (Patent Documents 2 to 4) have also been proposed. Patent Document 2 specifies an aluminum alloy material that is an aluminum alloy containing about 0.05 to 0.5% (mass%, the same below), about 0.1% to a maximum of 1.0% Fe, a maximum of about 2.0% Mn, about 0.06 to 1.0% Zn, about 0.03 to 0.35% Ti, and the balance aluminum and unavoidable impurities, in which the ratio of Mn to Fe is maintained at more than about 0.5% to about 6.0% or less, and the total amount of Fe and Mn is maintained at more than about 0.30%, so as to contain intermetallic compounds dispersed throughout the aluminum matrix at a volume fraction of at least 0.5%, and the electrolytic potential difference between the aluminum matrix of the article and the intermetallic compounds is less than about 0.2 volts, and the intermetallic compounds have an aspect ratio of less than about 5.0.

[0005] Patent Document 3 specifies an aluminum alloy piping material containing 0.05-0.6% Si, 0.05-0.7% Fe, 0.04-0.2% Cu, 0.6-1.0% Mn, 0.01-0.15% Mg, 0.1-3.0% Zn, with the balance being Al and unavoidable impurities. Furthermore, Patent Document 4 specifies an aluminum alloy containing Cu: about 0.01% to about 0.6%, Fe: about 0.05% to about 0.40%, Mg: about 0.05% to about 0.8%, Mn: about 0.001% to about 2.0%, Si: about 0.05% to about 0.25%, Ti: about 0.001% by weight to about 0.20%, Zn: about 0.001% to 0.20%, Cr: 0% to about 0.05%, Pb: 0% to about 0.005%, Ca: 0% to about 0.03%, Cd: 0% to about 0.004%, Li: 0% to about 0.0001%, Na: 0% to about 0.0005%, other elements up to about 0.03% individually and up to about 0.10% in total, and the balance Al. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-65588 [Patent Document 2] JP 2002-53923 A [Patent Document 3] JP 2005-89788 A [Patent Document 4] Special Publication No. 2018-536088 Summary of the Invention [Problem to be solved by the invention]

[0007] However, there is a concern that the alloys of Patent Documents 2 to 4 may have insufficient corrosion resistance in severe corrosive environments, and further improvement in corrosion resistance is desired.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to solve the above-mentioned problems in the conventional aluminum alloy pipes used for piping, etc., and to provide an aluminum alloy pipe having excellent corrosion resistance and a method for manufacturing the same. [Means for solving the problem]

[0009] As a result of intensive research, the present inventors have found that when the Fe content and Cu content of an aluminum alloy tube are both high, there is a risk of the corrosion resistance being significantly reduced, and that an aluminum alloy tube having excellent corrosion resistance can be provided by either satisfying a specific relational expression in which the relationship between the Fe content and the Cu content of the aluminum alloy tube is not both high, or by having both the Fe and Cu contents of the aluminum alloy tube not high and having a number density of intermetallic compounds of the aluminum alloy tube not more than a predetermined value, or by having the Cu content of the aluminum alloy tube not higher than a predetermined amount, and have completed the present invention.

[0010] That is, the present invention (1) is Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass of Fe, and more than 0% by mass of Cu, The Fe content x (mass%) and the Cu content y (mass%) are expressed by the following formula (1): x+7y≦0.70 (1) Satisfying the relationship, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is an aluminum alloy containing Al and unavoidable impurities. The present invention provides an aluminum alloy tube characterized by the above.

[0011] The present invention (2) also provides Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.40% by mass or less of Fe, and more than 0% by mass and 0.10% by mass or less of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The aluminum alloy is made of the balance Al and unavoidable impurities. The number density of intermetallic compounds with a circle equivalent diameter of 1.0 μm or more in a cross section perpendicular to the circumferential direction of the pipe is 1.4 × 10 4 pieces / mm 2 That is: The present invention provides an aluminum alloy tube characterized by the above.

[0012] The present invention (3) also provides Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.70% by mass or less of Fe, and more than 0% by mass and less than 0.04% by mass of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is Al and unavoidable impurities. The present invention provides an aluminum alloy tube characterized by the above.

[0013] The present invention (4) provides an aluminum alloy tube according to any one of (1) to (3), characterized in that the average crystal grain size in a cross section perpendicular to the circumferential direction of the tube is 100 μm or less.

[0014] The present invention (5) is a method for producing an aluminum alloy tube according to any one of (1) to (3), The present invention provides a method for producing an aluminum alloy tube, comprising at least a casting step of casting an ingot having the composition of an aluminum alloy according to any one of claims 1 to 3, and an extrusion step of extruding the ingot to produce an extruded tube.

[0015] The present invention (6) provides a method for producing an aluminum alloy tube as set forth in (5), further comprising an annealing step of annealing the extruded tube, or a drawing step of drawing the extruded tube, or a drawing step of drawing the extruded tube and an annealing step of annealing the tube after the drawing step.

[0016] The present invention (7) also provides a method for producing an aluminum alloy tube as set forth in (6), characterized in that in the annealing step, the temperature rise rate is 60° C. / h or more. Effect of the Invention

[0017] According to the present invention, it is possible to provide an aluminum alloy pipe having excellent corrosion resistance and a manufacturing method thereof. The aluminum alloy pipe of the present invention is an aluminum alloy pipe having a single layer, has excellent corrosion resistance, is less susceptible to localized corrosion in the thickness direction, and can extend the period until penetration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The aluminum alloy tube of the first embodiment of the present invention comprises: Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass of Fe, and more than 0% by mass of Cu, The Fe content x (mass%) and the Cu content y (mass%) are expressed by the following formula (1): x+7y≦0.70 (1) Satisfying the relationship, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is an aluminum alloy containing Al and unavoidable impurities. The aluminum alloy tube is characterized by the above.

[0019] The aluminum alloy tube of the first embodiment of the present invention is made of a single layer of aluminum alloy. That is, the aluminum alloy tube of the first embodiment of the present invention is a bare tube made of an aluminum alloy. Also, the aluminum alloy tube of the first embodiment of the present invention is an extrusion-molded tube manufactured by extrusion molding.

[0020] The aluminum alloy according to the first embodiment of the present invention contains Mn, Mg, Zn, Si, Fe, and Cu as essential elements, and is composed of the essential elements, optional elements added as necessary, and aluminum and unavoidable impurities as the balance.

[0021] The aluminum alloy according to the first embodiment of the present invention contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass of Fe, and more than 0% by mass of Cu, and the Fe content x (mass%) and the Cu content y (mass%) satisfy the following formula (1): x+7y≦0.70 (1) Satisfy the relationship.

[0022] The aluminum alloy for the aluminum alloy tube of the first embodiment of the present invention may contain, as optional added elements, one or more of 0.30 mass% or less of Cr, 0.20 mass% or less of Zr, and 0.15 mass% or less of Ti. That is, in the aluminum alloy for the aluminum alloy tube of the first embodiment of the present invention, the Cr content is 0.00 to 0.30 mass%, the Zr content is 0.00 to 0.20 mass%, and the Ti content is 0.00 to 0.15 mass%.

[0023] Mn functions to improve the strength of the aluminum alloy pipe. The Mn content of the aluminum alloy according to the first embodiment of the present invention is 0.30% by mass or more and 1.50% by mass, preferably 0.30-1.20% by mass, more preferably 0.30-1.00% by mass, even more preferably 0.30-0.80% by mass, and even more preferably 0.30-0.70% by mass. If the Mn content of the aluminum alloy is less than the above range, a sufficient strength improving effect cannot be obtained, and if it exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired.

[0024] Mg functions to improve the strength of the aluminum alloy pipe. The Mg content of the aluminum alloy according to the first embodiment of the present invention is 0.001% by mass or more and 0.24% by mass or less. The upper limit of the Mg content is preferably 0.20% by mass, more preferably 0.15% by mass. The lower limit of the Mg content is preferably 0.01% by mass, more preferably 0.02% by mass, more preferably 0.03% by mass, more preferably 0.04% by mass, more preferably 0.05% by mass, more preferably 0.06% by mass. The Mg content can be set to a range that combines the upper and lower limits. If the Mg content of the aluminum alloy exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired. If the Mg content of the aluminum alloy is less than the above range, sufficient strength improvement effect cannot be obtained.

[0025] Zn is added to suppress pitting corrosion of the aluminum alloy pipe and to make the corrosion form general corrosion. The Zn content of the aluminum alloy according to the first embodiment of the present invention is 0.001% by mass or more and 1.0% by mass or less. The upper limit of the Zn content is preferably 0.80% by mass, more preferably 0.60% by mass, and more preferably 0.40% by mass. The lower limit of the Zn content is preferably 0.01% by mass, more preferably 0.05% by mass, more preferably 0.10% by mass, more preferably 0.15% by mass, and more preferably 0.20% by mass. The Zn content can be within a range that combines the upper and lower limits. If the Zn content of the aluminum alloy exceeds the above range, the corrosion rate increases significantly and the corrosion resistance decreases. If the Zn content of the aluminum alloy is less than the above range, a sufficient pitting corrosion suppression effect cannot be obtained.

[0026] Fe contributes to improving the strength of the aluminum alloy tube. The Fe content of the aluminum alloy according to the first embodiment of the present invention exceeds 0 mass% and satisfies the following formula (1). The lower limit of the Fe content is preferably 0.05 mass%, more preferably 0.10 mass%, and more preferably 0.15 mass%. The upper limit of the Fe content is preferably 0.60 mass%, more preferably 0.50 mass%, more preferably 0.40 mass%, more preferably 0.39 mass%, more preferably 0.35 mass%, more preferably 0.30 mass%, and more preferably 0.28 mass%.

[0027] Cu contributes to improving the strength of the aluminum alloy tube. The Cu content of the aluminum alloy according to the first embodiment of the present invention exceeds 0 mass% and satisfies the following formula (1). The lower limit of the Cu content is preferably 0.001 mass%. The upper limit of the Cu content is preferably 0.08 mass%, more preferably 0.06 mass%, more preferably 0.05 mass%, more preferably 0.04 mass%, and more preferably 0.03 mass%.

[0028] The Fe content x (mass%) and Cu content y (mass%) of the aluminum alloy according to the first embodiment of the aluminum alloy pipe of the present invention are expressed by the following formula (1): x+7y≦0.70 (1) Satisfy the relationship. When the contents of Fe and Cu satisfy the relationship of formula (1), an aluminum alloy tube with excellent corrosion resistance is obtained. When the contents of Fe and Cu do not satisfy the relationship of formula (1), for example, when the contents of Fe and Cu are both high, many coarse intermetallic compounds that act as cathodes and promote corrosion are present at the crystal grain boundaries, and intermetallic compounds containing Cu are precipitated near the crystal grain boundaries, forming a Cu-deficient layer in the aluminum matrix that is electrically less noble than the surrounding area, resulting in many intermetallic compounds with a large potential difference in the aluminum matrix, and there is a risk of the corrosion being promoted and the corrosion resistance being significantly reduced.

[0029] Si functions to improve the strength of the aluminum alloy tube. The Si content of the aluminum alloy according to the first embodiment of the present invention is 0.001% by mass or more and 0.50% by mass or less. The upper limit of the Si content is preferably 0.45% by mass, more preferably 0.40% by mass, more preferably 0.35% by mass, more preferably 0.30% by mass, more preferably 0.25% by mass, more preferably 0.20% by mass, more preferably 0.15% by mass, more preferably 0.12% by mass, and more preferably 0.10% by mass. The lower limit of the Si content is preferably 0.01% by mass, more preferably 0.03% by mass, and more preferably 0.05% by mass. The Si content can be set to a range that combines the upper limit and the lower limit. If the Si content of the aluminum alloy exceeds the above range, the crystal grains become coarse and the bending workability is reduced. If the Si content of the aluminum alloy is less than the above range, a sufficient strength improvement effect cannot be obtained.

[0030] The aluminum alloy according to the first embodiment of the present invention may contain Cr, Zr, and Ti from the viewpoints of optimizing corrosion resistance and improving scrap blendability. However, excessive addition of these elements may cause a decrease in extrudability. The Cr content of the aluminum alloy according to the first embodiment of the present invention is 0.30% by mass or less, preferably 0.20% by mass or less, and more preferably 0.10% by mass or less. The Zr content is 0.20% by mass or less, preferably 0.15% by mass or less, and more preferably 0.10% by mass or less. The Ti content is 0.15% by mass or less, and more preferably 0.10% by mass or less.

[0031] Impurity elements other than those mentioned above may be contained within a range that does not affect the effects of the present invention. The content of other impurity elements is permitted to be within a range of 0.05 mass % each and 0.15 mass % in total.

[0032] The aluminum alloy tube according to the second embodiment of the present invention comprises: Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.40% by mass or less of Fe, and more than 0% by mass and 0.10% by mass or less of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The aluminum alloy is made of the balance Al and unavoidable impurities. The number density of intermetallic compounds with a circle equivalent diameter of 1.0 μm or more in a cross section perpendicular to the circumferential direction of the pipe is 1.4 × 10 4 pieces / mm 2 That is: The aluminum alloy tube is characterized by the above.

[0033] The aluminum alloy tube of the second embodiment of the present invention is made of a single layer of aluminum alloy. That is, the aluminum alloy tube of the second embodiment of the present invention is a bare tube made of an aluminum alloy. Also, the aluminum alloy tube of the second embodiment of the present invention is an extrusion-molded tube manufactured by extrusion molding.

[0034] The aluminum alloy according to the second embodiment of the present invention contains Mn, Mg, Zn, Si, Fe, and Cu as essential elements, while the aluminum alloy according to the first embodiment of the present invention is composed of the essential elements, optional elements added as necessary, and aluminum and unavoidable impurities as the balance.

[0035] The aluminum alloy for the aluminum alloy pipe of the second embodiment of the present invention contains 0.30 mass% or more and 1.50 mass% or less of Mn, 0.001 mass% or more and 0.24 mass% or less of Mg, 0.001 mass% or more and 1.0 mass% or less of Zn, 0.001 mass% or more and 0.50 mass% or less of Si, more than 0 mass% and 0.40 mass% or less of Fe, and more than 0 mass% and 0.10 mass% or less of Cu.

[0036] The aluminum alloy for the aluminum alloy tube of the second embodiment of the present invention may contain, as optional added elements, one or more of 0.30 mass% or less of Cr, 0.20 mass% or less of Zr, and 0.15 mass% or less of Ti. That is, in the aluminum alloy for the aluminum alloy tube of the second embodiment of the present invention, the Cr content is 0.00 to 0.30 mass%, the Zr content is 0.00 to 0.20 mass%, and the Ti content is 0.00 to 0.15 mass%.

[0037] Mn functions to improve the strength of the aluminum alloy pipe. The Mn content of the aluminum alloy according to the second embodiment of the present invention is 0.30% by mass or more and 1.50% by mass, preferably 0.30-1.20% by mass, more preferably 0.30-1.00% by mass, even more preferably 0.30-0.80% by mass, and even more preferably 0.30-0.70% by mass. If the Mn content of the aluminum alloy is less than the above range, a sufficient strength improving effect cannot be obtained, and if it exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired.

[0038] Mg functions to improve the strength of the aluminum alloy pipe. The Mg content of the aluminum alloy according to the second embodiment of the present invention is 0.001% by mass or more and 0.24% by mass or less. The upper limit of the Mg content is preferably 0.20% by mass, more preferably 0.15% by mass. The lower limit of the Mg content is preferably 0.01% by mass, more preferably 0.02% by mass, more preferably 0.03% by mass, more preferably 0.04% by mass, more preferably 0.05% by mass, more preferably 0.06% by mass. The Mg content can be set to a range that combines the upper and lower limits. If the Mg content of the aluminum alloy exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired. If the Mg content of the aluminum alloy is less than the above range, sufficient strength improvement effect cannot be obtained.

[0039] Zn is added to suppress pitting corrosion of the aluminum alloy pipe and to make the corrosion form general corrosion. The Zn content of the aluminum alloy according to the second embodiment of the present invention is 0.001% by mass or more and 1.0% by mass or less. The upper limit of the Zn content is preferably 0.80% by mass, more preferably 0.60% by mass, and more preferably 0.40% by mass. The lower limit of the Zn content is preferably 0.01% by mass, more preferably 0.05% by mass, more preferably 0.10% by mass, more preferably 0.15% by mass, and more preferably 0.20% by mass. The Zn content can be within a range that combines the upper and lower limits. If the Zn content of the aluminum alloy exceeds the above range, the corrosion rate increases significantly and the corrosion resistance decreases. If the Zn content of the aluminum alloy is less than the above range, a sufficient pitting corrosion suppression effect cannot be obtained.

[0040] Fe contributes to improving the strength of the aluminum alloy tube. The Fe content of the aluminum alloy according to the second embodiment of the present invention is more than 0% by mass and not more than 0.40% by mass. If the Fe content exceeds 0.40% by mass, roughness is likely to occur during hot working in the manufacturing process of the material. The upper limit of the Fe content is preferably 0.39% by mass, more preferably 0.35% by mass, more preferably 0.30% by mass, and more preferably 0.28% by mass. In addition, if the Fe content is low, the crystal grains may become coarse, and bending workability may decrease. The lower limit of the Fe content is preferably 0.05% by mass, more preferably 0.10% by mass, and more preferably 0.15% by mass. The Fe content may be within a range that is a combination of the upper limit and the lower limit.

[0041] Cu contributes to improving the strength of the aluminum alloy tube. The Cu content of the aluminum alloy according to the second embodiment of the present invention is more than 0% by mass and not more than 0.10% by mass. If the Cu content exceeds 0.10% by mass, the action of Cu as a cathode becomes significant, and the corrosion resistance is reduced. The upper limit of the Cu content is preferably 0.08% by mass, more preferably 0.06% by mass, more preferably 0.05% by mass, more preferably 0.04% by mass, and more preferably 0.03% by mass. If the Cu content exceeds the above range, intermetallic compounds containing Cu are precipitated near the grain boundaries, and a Cu depletion layer that is more base in potential than the surroundings is formed in the aluminum parent phase. If these occur simultaneously, many intermetallic compounds with a large potential difference in the aluminum parent phase are present, and corrosion is promoted, resulting in a significant reduction in corrosion resistance. The lower limit of the Cu content is preferably 0.001% by mass. The Cu content can be within a range that combines the above upper and lower limits.

[0042] The aluminum alloy according to the second embodiment of the present invention has an Fe content of more than 0% by mass and not more than 0.40% by mass, and a Cu content of more than 0% by mass and not more than 0.10% by mass. Since the Fe and Cu contents are not high, the corrosion resistance is excellent. For example, when the Fe content and the Cu content are both high, a large amount of coarse intermetallic compounds that act as a cathode and promote corrosion are present at the grain boundaries, and intermetallic compounds containing Cu are precipitated near the grain boundaries, forming a Cu depleted layer in the aluminum matrix that is more base in potential than the surroundings. This results in a large amount of intermetallic compounds with a large potential difference in the aluminum matrix, and corrosion is promoted, which may significantly reduce the corrosion resistance.

[0043] In the aluminum alloy tube of the second embodiment of the present invention, the number density of intermetallic compounds having a circle equivalent diameter of 1.0 μm or more in a cross section perpendicular to the circumferential direction of the tube is 1.4 × 10 4 pieces / mm 2In the aluminum alloy tube of the second embodiment of the present invention, the number density of intermetallic compounds having a circle-equivalent diameter of 1.0 μm or more in a cross section perpendicular to the circumferential direction of the tube is within the above range, so that the aluminum alloy tube has excellent corrosion resistance. 4 pieces / mm 2 If the temperature exceeds this range, the grain boundaries will contain many coarse intermetallic compounds that act as cathodes and promote corrosion, resulting in low corrosion resistance. Examples of intermetallic compounds include Al-Mn, Al-Fe, Al-Mn-Fe, Al-Mn-Si, Al-Fe-Si, Al-Mn-Fe-Si, Al-Cu, Al-Mn-Cu, Al-Fe-Cu, Al-Mn-Fe-Cu, Al-Mn-Si-Cu, Al-Fe-Si-Cu, and Al-Mn-Fe-Si-Cu compounds.

[0044] Si functions to improve the strength of the aluminum alloy tube. The Si content of the aluminum alloy according to the second embodiment of the present invention is 0.001% by mass or more and 0.50% by mass or less. The upper limit of the Si content is preferably 0.45% by mass, more preferably 0.40% by mass, more preferably 0.35% by mass, more preferably 0.30% by mass, more preferably 0.25% by mass, more preferably 0.20% by mass, more preferably 0.15% by mass, more preferably 0.12% by mass, and more preferably 0.10% by mass. The lower limit of the Si content is preferably 0.01% by mass, more preferably 0.03% by mass, and more preferably 0.05% by mass. The Si content can be set to a range that combines the upper and lower limits. If the Si content of the aluminum alloy exceeds the above range, the crystal grains become coarse and the bending workability is reduced. If the Si content of the aluminum alloy is less than the above range, a sufficient strength improvement effect cannot be obtained.

[0045] The aluminum alloy according to the second embodiment of the present invention may contain Cr, Zr, and Ti from the viewpoint of optimizing corrosion resistance and improving scrap blendability. However, excessive addition of these elements may cause a decrease in extrudability. The aluminum alloy according to the first embodiment of the present invention may contain Cr, Zr, and Ti in a range of 0.30% by mass or less, preferably 0.20% by mass or less, and more preferably 0.10% by mass or less. The Zr content is 0.20% by mass or less, preferably 0.15% by mass or less, and more preferably 0.10% by mass or less. The Ti content is 0.15% by mass or less, and more preferably 0.10% by mass or less.

[0046] Impurity elements other than those mentioned above may be contained within a range that does not affect the effects of the present invention. The content of other impurity elements is permitted to be within a range of 0.05 mass % each and 0.15 mass % in total.

[0047] The aluminum alloy tube of the third embodiment of the present invention comprises: Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.70% by mass or less of Fe, and more than 0% by mass and less than 0.04% by mass of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is Al and unavoidable impurities. The aluminum alloy tube is characterized by the above.

[0048] The aluminum alloy tube of the third embodiment of the present invention is made of a single layer of aluminum alloy. That is, the aluminum alloy tube of the third embodiment of the present invention is a bare tube made of an aluminum alloy. Also, the aluminum alloy tube of the third embodiment of the present invention is an extrusion-molded tube manufactured by extrusion molding.

[0049] The aluminum alloy according to the third embodiment of the present invention contains Mn, Mg, Zn, Si, Fe, and Cu as essential elements, while the aluminum alloy according to the first embodiment of the present invention is composed of the essential elements, optional elements added as necessary, and aluminum and unavoidable impurities as the balance.

[0050] The aluminum alloy for the aluminum alloy pipe of the third embodiment of the present invention contains 0.30 mass% or more and 1.50 mass% or less of Mn, 0.001 mass% or more and 0.24 mass% or less of Mg, 0.001 mass% or more and 1.0 mass% or less of Zn, 0.001 mass% or more and 0.50 mass% or less of Si, more than 0 mass% and 0.70 mass% or less of Fe, and more than 0 mass% and less than 0.04 mass% of Cu.

[0051] The aluminum alloy for the aluminum alloy tube of the third embodiment of the present invention may contain, as optional added elements, one or more of 0.30 mass% or less of Cr, 0.20 mass% or less of Zr, and 0.15 mass% or less of Ti. That is, in the aluminum alloy for the aluminum alloy tube of the second embodiment of the present invention, the Cr content is 0.00 to 0.30 mass%, the Zr content is 0.00 to 0.20 mass%, and the Ti content is 0.00 to 0.15 mass%.

[0052] Mn functions to improve the strength of the aluminum alloy pipe. The Mn content of the aluminum alloy according to the third embodiment of the present invention is 0.30% by mass or more and 1.50% by mass, preferably 0.30-1.20% by mass, more preferably 0.30-1.00% by mass, even more preferably 0.30-0.80% by mass, and even more preferably 0.30-0.70% by mass. If the Mn content of the aluminum alloy is less than the above range, a sufficient strength improving effect cannot be obtained, and if it exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired.

[0053] Mg functions to improve the strength of the aluminum alloy pipe. The Mg content of the aluminum alloy according to the third embodiment of the present invention is 0.001% by mass or more and 0.24% by mass or less. The upper limit of the Mg content is preferably 0.20% by mass, more preferably 0.15% by mass. The lower limit of the Mg content is preferably 0.01% by mass, more preferably 0.02% by mass, more preferably 0.03% by mass, more preferably 0.04% by mass, more preferably 0.05% by mass, more preferably 0.06% by mass. The Mg content can be set to a range that combines the upper and lower limits. If the Mg content of the aluminum alloy exceeds the above range, the deformation resistance during extrusion increases and extrudability is impaired. If the Mg content of the aluminum alloy is less than the above range, sufficient strength improvement effect cannot be obtained.

[0054] Zn is added to suppress pitting corrosion of the aluminum alloy pipe and to make the corrosion form general corrosion. The Zn content of the aluminum alloy according to the third embodiment of the present invention is 0.001% by mass or more and 1.0% by mass or less. The upper limit of the Zn content is preferably 0.80% by mass, more preferably 0.60% by mass, and more preferably 0.40% by mass. The lower limit of the Zn content is preferably 0.01% by mass, more preferably 0.05% by mass, more preferably 0.10% by mass, more preferably 0.15% by mass, and more preferably 0.20% by mass. The Zn content can be within a range that combines the upper and lower limits. If the Zn content of the aluminum alloy exceeds the above range, the corrosion rate increases significantly and the corrosion resistance decreases. If the Zn content of the aluminum alloy is less than the above range, a sufficient pitting corrosion suppression effect cannot be obtained.

[0055] Fe contributes to improving the strength of the aluminum alloy tube. The Fe content of the aluminum alloy according to the third embodiment of the present invention is more than 0% by mass and not more than 0.70% by mass. If the Fe content exceeds 0.70% by mass, Al3Fe compounds are excessively precipitated, lowering the corrosion resistance. The upper limit of the Fe content is preferably 0.65% by mass, more preferably 0.60% by mass, more preferably 0.55% by mass, more preferably 0.50% by mass, and more preferably 0.45% by mass. Also, if the Fe concentration is low, the crystal grains may become coarse, and bending workability may decrease. The lower limit of the Fe content is preferably 0.05% by mass, more preferably 0.10% by mass, and more preferably 0.15% by mass. The Fe content may be within a range that is a combination of the upper and lower limits.

[0056] Cu contributes to improving the strength of the aluminum alloy tube. The Cu content of the aluminum alloy according to the third embodiment of the present invention is more than 0% by mass and less than 0.04% by mass. When the Cu content is high, the action of Cu as a cathode becomes significant, and the corrosion resistance is reduced. The upper limit of the Cu content is preferably 0.03% by mass. When the Cu concentration exceeds the above range, intermetallic compounds containing Cu are precipitated near the grain boundaries, and a Cu depletion layer that is more base in potential than the surroundings is formed in the aluminum parent phase. When these occur simultaneously, many intermetallic compounds with a large potential difference in the aluminum parent phase are present, and corrosion is promoted, resulting in a significant reduction in corrosion resistance. The lower limit of the Cu content is preferably 0.001% by mass. The Cu content can be within a range that combines the above upper and lower limits.

[0057] The aluminum alloy according to the third embodiment of the present invention has an Fe content of more than 0% by mass and not more than 0.70% by mass, and a Cu content of more than 0% by mass and less than 0.04% by mass. Since the Fe and Cu contents are not high, the corrosion resistance is excellent. For example, when the Fe content and the Cu content are both high, a large amount of coarse intermetallic compounds that act as a cathode and promote corrosion are present at the grain boundaries, and intermetallic compounds containing Cu are precipitated near the grain boundaries, forming a Cu depleted layer in the aluminum matrix that is more base in potential than the surroundings. This results in a large amount of intermetallic compounds with a large potential difference in the aluminum matrix, and corrosion is promoted, which may significantly reduce the corrosion resistance.

[0058] Si functions to improve the strength of the aluminum alloy tube. The Si content of the aluminum alloy according to the third embodiment of the present invention is 0.001% by mass or more and 0.50% by mass or less. The upper limit of the Si content is preferably 0.45% by mass, more preferably 0.40% by mass, more preferably 0.35% by mass, more preferably 0.30% by mass, more preferably 0.25% by mass, more preferably 0.20% by mass, more preferably 0.15% by mass, more preferably 0.12% by mass, and more preferably 0.10% by mass. The lower limit of the Si content is preferably 0.01% by mass, more preferably 0.03% by mass, and more preferably 0.05% by mass. The Si content can be set to a range that combines the upper limit and the lower limit. If the Si content of the aluminum alloy exceeds the above range, the crystal grains become coarse and the bending workability is reduced. If the Si content of the aluminum alloy is less than the above range, a sufficient strength improvement effect cannot be obtained.

[0059] The aluminum alloy according to the third embodiment of the present invention may contain Cr, Zr, and Ti from the viewpoints of optimizing corrosion resistance and improving scrap blendability. However, excessive addition of these elements may cause a decrease in extrudability. The aluminum alloy according to the first embodiment of the present invention may contain Cr, Zr, and Ti in a range of 0.30% by mass or less, preferably 0.20% by mass or less, and more preferably 0.10% by mass or less. The Zr content is 0.20% by mass or less, preferably 0.15% by mass or less, and more preferably 0.10% by mass or less. The Ti content is 0.15% by mass or less, and more preferably 0.10% by mass or less.

[0060] Impurity elements other than those mentioned above may be contained within a range that does not affect the effects of the present invention. The content of other impurity elements is permitted to be within a range of 0.05 mass % each and 0.15 mass % in total.

[0061] In the aluminum alloy tubes of the first, second and third embodiments of the present invention, the average crystal grain size in a cross section perpendicular to the circumferential direction of the tube is preferably 100 μm or less, more preferably 80 μm or less. When the average crystal grain size is within the above range, defects such as roughness are unlikely to occur during bending, tube expansion and other processes, and the aluminum alloy tube has excellent processability.

[0062] The aluminum alloy tube of the present invention may be produced by any production method, and is preferably produced, for example, by the production method of the aluminum alloy tube of the present invention described below.

[0063] The method for producing an aluminum alloy tube of the present invention is a method for producing an aluminum alloy tube according to any one of the first, second and third embodiments of the present invention, and is characterized by comprising at least a casting step of casting an ingot having an aluminum alloy composition according to any one of the first, second and third embodiments of the present invention, and an extrusion step of extruding the ingot to produce an extruded tube. The method for producing an aluminum alloy tube of the present invention may further comprise an annealing step and / or a drawing step.

[0064] The method for producing an aluminum alloy tube according to the present invention will be described below. In the method for producing an aluminum alloy tube of the present invention, a casting step is performed in which a molten aluminum alloy having a composition of any one of the aluminum alloy tubes of the first, second, or third embodiment of the present invention is cast in an ordinary manner, the resulting ingot (billet) is homogenized, and then the billet is reheated and extruded to produce an extruded tube, which is then subjected to an annealing step and / or a drawing step, as necessary.

[0065] The aluminum alloy ingot of the first type to be cast in the casting step contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass of Fe, and more than 0% by mass of Cu, The Fe content x (mass%) and the Cu content y (mass%) are expressed by the following formula (1): x+7y≦0.70 (1) Satisfying the relationship, Optionally, the aluminum alloy contains one or more of 0.30 mass % or less of Cr, 0.20 mass % or less of Zr, and 0.15 mass % or less of Ti, with the remainder being Al and unavoidable impurities. The aluminum alloy ingot of the second type cast in the casting step contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.40% by mass or less of Fe, and more than 0% by mass and 0.10% by mass or less of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The aluminum alloy is made up of the balance Al and unavoidable impurities. Also, the aluminum alloy ingot of a third type cast in the casting step contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.70% by mass or less of Fe, and more than 0% by mass and less than 0.04% by mass of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance consists of Al and unavoidable impurities.

[0066] The composition of the aluminum alloy ingot of the first embodiment cast in the casting process is the same as the composition of the aluminum alloy for the aluminum alloy pipe of the first embodiment of the present invention. The composition of the aluminum alloy ingot of the second embodiment cast in the casting process is the same as the composition of the aluminum alloy for the aluminum alloy pipe of the second embodiment of the present invention. The composition of the aluminum alloy ingot of the third embodiment cast in the casting process is the same as the composition of the aluminum alloy for the aluminum alloy pipe of the third embodiment of the present invention.

[0067] The homogenization of the ingot (billet) is preferably performed for 2 hours or more in a temperature range of 450°C to 620°C. If the homogenization temperature is lower than 450°C or the homogenization time is shorter than 2 hours, the diffusion energy is insufficient, and the microsegregation of the ingot structure of the billet is not eliminated, and the workability such as bending workability and pipe expansion workability is likely to decrease. If the homogenization temperature is higher than 620°C, the temperature may exceed the solidus temperature and the billet may partially melt. Although the required performance can be obtained by performing the homogenization for 2 hours or more, it is preferable to perform the homogenization for 24 hours or less in practical terms, taking into account the manufacturing cost.

[0068] The extrusion process is preferably carried out at a temperature of 400°C to 550°C. If the extrusion temperature is lower than 400°C, the extrusion pressure becomes high, which may make extrusion difficult. If the extrusion temperature is higher than 550°C, the extruded aluminum alloy pipe is likely to have a tear defect during extrusion.

[0069] The drawing process after extrusion is preferably performed with a reduction in area of ​​30% or more. If the reduction in area is less than 30%, the degree of cold working is small, so that the crystal grain size after softening becomes coarse, and there is a risk of problems such as rough surface occurring during bending, expanding, or other processes.

[0070] The softening treatment in the annealing step is preferably performed in a temperature range of 300 to 560°C for more than 0 hours and not more than 3 hours, and the heating rate in the temperature range of 300 to 560°C is preferably 60°C / h or more. If the softening temperature is lower than 300°C, the softening is insufficient, the strength becomes partially non-uniform, and workability such as bending workability and tube expansion workability decreases. If the softening temperature is higher than 560°C, if the softening time is longer than 3 hours, or if the heating rate is less than 60°C / h, the crystal grains may become coarse, causing problems such as rough surfaces during bending and tube expansion.

[0071] In the method for producing an aluminum alloy tube of the present invention, drawing after extrusion may or may not be performed, and an annealing step may or may not be included. Examples of combinations of steps in the method for producing an aluminum alloy tube of the present invention include combinations of steps performed in the order of (1) casting step → extrusion step, (2) casting step → extrusion step → annealing step, (3) casting step → extrusion step → drawing step, and (4) casting step → extrusion step → drawing step → annealing step. EXAMPLES

[0072] Examples of the present invention will be described below to demonstrate the effects of the present invention. These examples are merely illustrative of one embodiment of the present invention, and the present invention is not limited thereto.

[0073] [Example 1] <Manufacturing method of test material> Aluminum alloys A to D having the compositions shown in Table 1 were melted and cast into billets with a diameter of 254 mm by semi-continuous casting. The resulting billets were homogenized at 600°C for 10 hours, and then extruded at 450°C into pipes with an outer diameter of 47 mm and a wall thickness of 3.5 mm. The billets were then drawn to have an outer diameter of 17 mm and a wall thickness of 1.0 mm, and annealed at 400°C for 1 hour. These were designated test materials 1 to 4.

[0074] [Table 1]

[0075] <Method for measuring the number density of intermetallic compounds> For test materials 1 to 4, the cross section perpendicular to the circumferential direction of the tube was cut out and polished to adjust the surface. Next, a secondary electron image of an 86 μm × 127 μm area in the center of the tube wall thickness was taken using a SEM (scanning electron microscope). From the area S of the intermetallic compound in the obtained secondary electron image, the circle equivalent diameter D was calculated using formula (2). D = (4S / π)1 / 2 Equation (2) The number density was calculated as shown in Table 2 by dividing the number of intermetallic compounds with a circle equivalent diameter of 1.0 μm or more by the area of ​​the observation region. <Corrosion resistance evaluation method> Samples of 120 mm in length were cut from test materials 1 to 4, both ends were masked to leave an exposed section of 100 mm in length, and the SWAAT specified in ASTM-G85-Annex A3 was carried out for 480 hours. After the test, the samples were acid-washed according to the procedure specified in the test method to remove corrosion products, and samples without penetration were rated as passing (◯), and samples with penetration were rated as failing (×). <Corrosion resistance evaluation results> The results of the corrosion resistance evaluation of the test materials are shown in Table 3. Test materials 1, 2, and 3 according to the present invention did not suffer from corrosion penetration and were excellent in corrosion resistance. On the other hand, test material 4 suffered from corrosion penetration in the corrosion resistance evaluation because the Fe concentration, Cu concentration, and number density of intermetallic compounds were outside the ranges of the present invention.

[0076] [Table 2]

[0077] [Table 3]

[0078] [Example 2] <Manufacturing method of test material> Aluminum alloy A having the composition shown in Table 1 was melted and cast into a billet with a diameter of 254 mm by continuous casting. The resulting billet was homogenized at 600°C for 10 hours, and then extruded at 450°C into a pipe with an outer diameter of 47 mm and a wall thickness of 3.5 mm. It was then drawn to an outer diameter of 17 mm and a wall thickness of 1.0 mm, and softened by heating to 400°C at the heating rate shown in Table 4. These were designated as test materials 5 and 6, and their grain sizes were evaluated. <Crystal grain size evaluation method> Samples 20 mm long were cut from test materials 5 and 6, and the structure of the cross section parallel to the length of the tube was observed. The samples were polished and etched, and an arbitrary field of view of each was photographed at 50x using a polarizing microscope. The crystal grain sizes in the length and thickness directions of the tube were measured using the cross method, and the average crystal grain size was calculated from the average of these measurements. <Evaluation Results> The results of the crystal grain size evaluation are shown in Table 4. Test material 5 had an average crystal grain size of 100 μm or less, and there was little concern about defects such as roughness during bending and tube expansion (evaluated as ◎). On the other hand, test material 6 had an average crystal grain size of over 100 μm due to the slow heating rate during the softening treatment, and although it had lower workability than test material 5, it is presumed that it can still be worked (evaluated as ◯).

[0079] [Table 4]

Claims

1. Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass of Fe, and more than 0% by mass of Cu, The Fe content x (mass%) and the Cu content y (mass%) are expressed by the following formula (1): x+7y≦0.70 (1) Satisfying the relationship, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is an aluminum alloy containing Al and unavoidable impurities. An aluminum alloy tube characterized by:

2. Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.40% by mass or less of Fe, and more than 0% by mass and 0.10% by mass or less of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The aluminum alloy is made of the balance Al and unavoidable impurities. The number density of intermetallic compounds with a circle equivalent diameter of 1.0 μm or more in a cross section perpendicular to the circumferential direction of the tube is 1.4 × 10 ４ pieces / mm ２ That is: An aluminum alloy tube characterized by:

3. Contains 0.30% by mass or more and 1.50% by mass or less of Mn, 0.001% by mass or more and 0.24% by mass or less of Mg, 0.001% by mass or more and 1.0% by mass or less of Zn, 0.001% by mass or more and 0.50% by mass or less of Si, more than 0% by mass and 0.70% by mass or less of Fe, and more than 0% by mass and less than 0.04% by mass of Cu, Optionally, one or more of 0.30% by weight or less Cr, 0.20% by weight or less Zr, and 0.15% by weight or less Ti; The balance is Al and unavoidable impurities. An aluminum alloy tube characterized by:

4. 4. The aluminum alloy tube according to claim 1, wherein the average crystal grain size in a cross section perpendicular to the circumferential direction of the tube is 100 μm or less.

5. 4. A method for producing an aluminum alloy tube according to claim 1, comprising at least a casting step of casting an ingot having a composition of the aluminum alloy, and an extrusion step of extruding the ingot to produce an extruded tube.

6. 6. The method for producing an aluminum alloy tube according to claim 5, further comprising: an annealing step of annealing the extruded tube; or a drawing step of drawing the extruded tube; or a drawing step of drawing the extruded tube and an annealing step of annealing the tube after the drawing step.

7. 7. The method for producing an aluminum alloy tube according to claim 6, wherein in the annealing step, a temperature rise rate is set to 60° C. / h or more.

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