Aluminum alloy sheet, method for manufacturing same, and heat exchanger

Abstract

An aluminum alloy sheet having a function of heat bonding in a single layer, the aluminum alloy sheet comprising an aluminum alloy containing 2.00-3.00 mass% of Si, 0.05-0.40 mass% of Fe, and 0.80-1.80 mass% of Mn, the Cu content being 0.20 mass% or less (including 0.00 mass%), the Zn content being 6.00 mass% or less (including 0.00 mass%), and the remainder being Al and unavoidable impurities, after a heating test in which the temperature is increased from 300 DEG C to 400 DEG C at an average temperature increase rate of 60 DEG C / min or less and held at 600 + / -3 DEG C for 5 + / -3 minutes, in a cross-section in a direction perpendicular to the rolling surface and a direction perpendicular to the rolling direction, a region having one or more grain boundaries in the plate thickness direction has a ratio of 25% or more and less than 90% in the width direction. And the average crystal grain diameter of the plate surface in the direction perpendicular to the rolling direction is 950 [mu] m or less.

Description

Technical Field

[0001] This invention relates to an aluminum alloy plate for single-layer heating bonding and a heat exchanger manufactured using the same. Background Technology

[0002] Brazing is commonly used in the manufacturing processes of products such as heat exchangers and / or radiators that are made of aluminum and have multiple metal joints. The aluminum materials used for brazing include brazing sheets and / or pre-applied brazing filler metals coated on an aluminum core. However, due to manufacturing and / or material costs, the use of multi-layered overlapping coating materials such as brazing sheets and / or additional bonding materials such as pre-applied brazing filler metals has become a major reason for the increased cost of heat exchangers and similar products.

[0003] Therefore, in recent years, aluminum alloy materials capable of being heat-bonded in a single layer have been proposed (for example, Patent Documents 1 and 2). These aluminum alloy materials are composed of Al-Si alloys, and the liquid phase generated within the alloy material through heating is used for bonding. According to this aluminum alloy material, since the aforementioned liquid phase acts as a solder, it can be bonded to other components even when it is a single layer and no pre-applied solder or other bonding materials are used. It should be noted that in this invention, the ability to bond by heating even without bonding materials is referred to as a "heat bonding function." Furthermore, the bonding using this aluminum alloy material with the function of heat bonding in a single layer is called "heat bonding," and the heating temperature is called the "heat bonding temperature."

[0004] For aluminum alloys capable of single-layer heat bonding, ensuring deformation resistance at the brazing temperature is crucial because the material becomes semi-molten during the heat bonding process. As a method to improve the deformation resistance of aluminum alloys, for example, patent documents 3 and 4 disclose an aluminum alloy that exhibits excellent deformation resistance and the ability to be heat-bonded in a single layer, by forming a metallographic structure where the grains become coarser after brazing heating, suppressing the formation of liquid phase at grain boundaries.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 5436714 Specification

[0008] Patent Document 2: International Publication No. 2022 / 176420

[0009] Patent Document 3: Japanese Patent No. 5345264 Specification

[0010] Patent Document 4: Description of Japanese Patent No. 5732594 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Aluminum alloys that can be joined to other components through their own action (liquid phase seeping from the base material) without the need for brazing filler metal or welding materials require less liquid phase in brazing compared to conventional brazed fins coated with filler metal.

[0013] Therefore, a small fillet area at the junction of the fin and the tube reduces the fin's weldability. Furthermore, a small fillet area shortens the corrosion lifespan when exposed to corrosive environments, causing the fin to peel off prematurely and failing to fully perform its sacrificial corrosion protection function. Additionally, there is the issue of material deformation due to fin peeling.

[0014] To increase the amount of liquid phase, one method is to increase the Si content. However, if the Si content is too high, excessive Si will seep out from the base material during brazing heating, resulting in a significant decrease in material strength and thus failing to achieve sufficient strength. Corrosion resistance is also reduced. Another method is to increase the Cu content to improve the liquid phase ratio, but this leads to problems such as a significant deterioration in corrosion resistance or an increase in the material strength of the billet but a decrease in formability. These issues are difficult to resolve by adjusting the composition.

[0015] Therefore, the present invention is made based on the background described above, and its object is to provide an aluminum alloy plate that ensures material strength and has excellent brazing properties when manufacturing various aluminum alloy structures.

[0016] Solution for solving the problem

[0017] Through in-depth research, the inventors discovered that the distribution of grain boundaries and the average grain diameter of aluminum alloy sheets after a specified heating test affect brazing properties and material strength. Furthermore, the inventors discovered an aluminum alloy material possessing both bonding ability and material strength. This material contains 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn, with a Cu content of 0.20% by mass or less (including 0.00% by mass) and a Zn content of 6.00% by mass or less (including 0.00% by mass). In a cross-section perpendicular to both the rolling surface and the rolling direction after a brazing heating test, the region with one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the sheet surface is 950 μm or less. This invention thus completes the present invention.

[0018] That is, the present invention (1) provides an aluminum alloy plate, characterized in that it has the function of heating and bonding in a single layer.

[0019] It is composed of an aluminum alloy containing 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn, with a Cu content of less than 0.20% by mass (inclusive), a Zn content of less than 6.00% by mass (inclusive), and optionally containing one or more of the following: less than 0.08% by mass of Mg, less than 0.30% by mass of Ti, less than 0.30% by mass of Zr, less than 0.30% by mass of Cr, less than 0.30% by mass of V, less than 0.10% by mass of Be, less than 0.10% by mass of Sr, less than 0.30% by mass of Bi, less than 0.10% by mass of Na, and less than 0.05% by mass of Ca, with the balance being Al and unavoidable impurities.

[0020] In a heating test conducted from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, the cross section perpendicular to the rolling surface and perpendicular to the rolling direction has a region with more than one grain boundary in the thickness direction of 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

[0021] In addition, the present invention (2) provides an aluminum alloy plate according to (1), characterized in that, in the cross section after the heating test, in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, there are more than 3% of the regions with two or more grain boundaries in the thickness direction in proportion to the width direction.

[0022] In addition, the present invention (3) provides an aluminum alloy plate according to (1) or (2), characterized in that, in the cross section in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction after the heating test, the maximum width of the region in the thickness direction where there are 0 grain boundaries is 2000 μm or less.

[0023] In addition, the present invention (4) provides an aluminum alloy plate according to (1) or (2), characterized in that the plate thickness is 0.08 mm or less.

[0024] In addition, the present invention (5) provides an aluminum alloy plate according to (3), characterized in that the plate thickness is 0.08 mm or less.

[0025] In addition, the present invention (6) provides a method for manufacturing an aluminum alloy plate, characterized in that it comprises: a casting process, wherein a cast-rolled plate of a cast aluminum alloy is continuously cast and rolled at a casting speed greater than 0.50 m / min and less than 0.70 m / min, wherein the cast-rolled plate of the aluminum alloy is composed of an aluminum alloy containing 2.00 to 3.00% by mass of Si, 0.05 to 0.40% by mass of Fe, and 0.80 to 1.80% by mass of Mn, and the Cu content is 0.20% by mass or less (including 0.00% by mass). The Zn content is 6.00% by mass or less (including 0.00% by mass), and optionally contains 0.08% by mass or less Mg, 0.30% by mass or less Ti, 0.30% by mass or less Zr, 0.30% by mass or less Cr, 0.30% by mass or less V, 0.10% by mass or less Be, 0.10% by mass or less Sr, 0.30% by mass or less Bi, 0.10% by mass or less Na, and 0.05% by mass or less Ca, with the balance being Al and unavoidable impurities; and

[0026] The cold rolling process involves subjecting the cast and rolled plate to cold rolling at least twice.

[0027] The process involves at least one annealing treatment between the casting process and the final cold rolling process.

[0028] The annealing conditions for all annealing processes are annealing temperature of 200–550°C and annealing time of 1–10 hours.

[0029] In addition, the present invention (7) provides a heat exchanger, characterized in that the heat exchanger has an aluminum alloy tube for flowing working fluid and aluminum alloy fins metal-joined to the tube.

[0030] The tube is formed using heat exchanger tubing made of aluminum alloy.

[0031] The fin is formed using an aluminum alloy plate capable of being heat-bonded in a single layer. The aluminum alloy plate is composed of an aluminum alloy containing 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn; a Cu content of 0.20% by mass or less (including 0.00% by mass); a Zn content of 6.00% by mass or less (including 0.00% by mass); and optionally containing 0.08% by mass or less of Mg, 0.30% by mass or less of Ti, 0.30% by mass or less of Zr, 0.30% by mass or less of Cr, 0.30% by mass or less of V, 0.10% by mass or less of Be, 0.10% by mass or less of Sr, 0.30% by mass or less of Bi, 0.10% by mass or less of Na, and 0.05% by mass or less of Ca, with the balance being Al and unavoidable impurities.

[0032] In the cross section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, the region having one or more grain boundaries in the thickness direction accounts for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

[0033] In addition, the present invention (8) provides a heat exchanger according to (7), characterized in that, in the cross section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, there are more than 3% of the regions in the thickness direction having two or more grain boundaries in the width direction.

[0034] In addition, the present invention (9) provides a heat exchanger according to (7) or (8), characterized in that, in the cross section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, the maximum width of the region in the plate thickness direction where there are 0 grain boundaries is 2000 μm or less.

[0035] Furthermore, the present invention (10) provides a heat exchanger, characterized in that the heat exchanger has an aluminum alloy tube for flowing working fluid and aluminum alloy fins metal-joined to the tube.

[0036] The heat exchanger is obtained by combining heat exchanger tubing made of aluminum alloy and heat exchanger fins made of aluminum alloy, followed by heating the resulting assembly.

[0037] The heat exchanger tubing and the heat exchanger fins are joined together, wherein the heat exchanger fins are formed from an aluminum alloy plate of any one of (1) to (5).

[0038] The effects of the invention

[0039] According to the present invention, an aluminum alloy plate can be provided that ensures material strength and has excellent brazing properties when manufacturing various aluminum alloy structures. Attached Figure Description

[0040] Figure 1 This is a schematic phase diagram of Al-Si alloy, a representative binary eutectic alloy.

[0041] Figure 2 This is an explanatory diagram illustrating the formation mechanism of the liquid phase in the aluminum alloy forming the aluminum alloy sheet of the present invention during the joining of aluminum alloys used in the present invention.

[0042] Figure 3 This is an explanatory diagram illustrating the formation mechanism of the liquid phase in the aluminum alloy forming the aluminum alloy sheet of the present invention during the joining of aluminum alloys used in the present invention.

[0043] Figure 4 This is a schematic phase diagram of Al-Si alloy, a representative binary eutectic crystal.

[0044] Figure 5 This is a diagram showing an example of grain boundary measurement in a cross section.

[0045] Figure 6 This is a diagram showing an example of grain boundary measurement in a cross section.

[0046] Figure 7 This is a diagram showing an example of measuring the average grain diameter on the surface of a plate. Detailed Implementation

[0047] The aluminum alloy plate of the present invention is characterized by its function of being heat-bonded in a single layer, and is composed of an aluminum alloy containing 2.00-3.00% by mass of Si, 0.05-0.40% by mass of Fe, and 0.80-1.80% by mass of Mn, with a Cu content of 0.20% by mass or less (including 0.00% by mass), a Zn content of 6.00% by mass or less (including 0.00% by mass), and optionally containing 0.08% by mass or less of Mg, 0.30% by mass or less of Ti, 0.30% by mass or less of Zr, 0.30% by mass or less of Cr, 0.30% by mass or less of V, and 0.10% by mass or less of Be. The plate contains one or more of the following: less than 0.10% by mass of Sr, less than 0.30% by mass of Bi, less than 0.10% by mass of Na, and less than 0.05% by mass of Ca, with the balance being Al and unavoidable impurities. In a heating test conducted from 300°C to 400°C at an average heating rate of less than 60°C / min and held at 600±3°C for 5±3 minutes, the cross section in the direction perpendicular to the rolling plane and in the direction perpendicular to the rolling direction has a region with more than one grain boundary in the thickness direction accounting for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

[0048] The aluminum alloy plate of the present invention contains Si, Fe, and Mn as essential elements. It should be noted that the aluminum alloy plate of the present invention is composed of the essential elements, any additional elements added as needed, and aluminum and unavoidable impurities as the balance.

[0049] The aluminum alloy plate of the present invention is composed of an aluminum alloy containing 2.00 to 3.00% by mass of Si, 0.05 to 0.40% by mass of Fe, and 0.80 to 1.80% by mass of Mn, with the balance being Al and unavoidable impurities. That is, the aluminum alloy plate of the present invention is composed of an aluminum alloy.

[0050] The aluminum alloy plate of the present invention may contain, as an optional additive element, less than 0.20% by mass of Cu and less than 6.00% by mass of Zn. That is, in the aluminum alloy plate of the present invention, the content of Cu is 0.00 to 0.20% by mass, and the content of Zn is 0.00 to 6.00% by mass.

[0051] Furthermore, the aluminum alloy in the aluminum alloy plate of the present invention may, as an optional additive element, contain any one or more of the following: Mg (less than 0.08 wt%), Ti (less than 0.30 wt%), Zr (less than 0.30 wt%), Cr (less than 0.30 wt%), V (less than 0.30 wt%), Be (less than 0.10 wt%), Sr (less than 0.10 wt%), Bi (less than 0.30 wt%), Na (less than 0.10 wt%), and Ca (less than 0.05 wt%). Additionally, the aluminum alloy in the aluminum alloy plate of the present invention may, as an optional additive element, contain In (less than 0.10 wt%), Sn (less than 0.10 wt%), and rare earth elements (less than 0.10 wt%).

[0052] Si is an element that forms a liquid phase in the Al-Si system and facilitates bonding. The aluminum alloy plate of the present invention has a Si content of 2.00–3.00% by mass, preferably 2.10–2.80% by mass, and more preferably 2.20–2.60% by mass. With the Si content of the aluminum alloy within the above range, a sufficient amount of liquid phase can be generated, and the amount of liquid phase seepage becomes sufficient, thus enabling good bonding. Furthermore, the material strength does not decrease excessively during heating, and the shape can be maintained. Moreover, with the Si content of the aluminum alloy within the above range, the temperature difference between the solidus and liquidus of the aluminum alloy increases, thus lengthening the time from casting to solidification near the center of the plate thickness. As a result, solute atoms are discharged from the vicinity of the surface to the center. Due to the higher concentration of solute atoms, second-phase particles are densely present, and grain growth is hindered in the center of the plate thickness. Therefore, during heat bonding, the number of grains in the thickness direction increases, and deformation caused by grain boundary slip is suppressed. It should be noted that, as the thickness of the plate increases and the heating temperature rises, the amount of liquid phase that seeps out increases. Therefore, the amount of liquid phase required for heat bonding is adjusted according to the structure or size of the heat exchanger fins, and the Si content of the aluminum alloy and / or the heat bonding temperature are adjusted based on the amount of liquid phase required for heat bonding. On the other hand, if the Si content of the aluminum alloy is below the above range, a sufficient amount of liquid phase cannot be generated, resulting in less liquid phase seepage and incomplete bonding. Furthermore, if it exceeds the above range, the amount of aluminum alloy material melted during brazing increases, potentially leading to a decrease in the strength of the aluminum alloy material. As a result, the anti-sagging property of the aluminum alloy material may decrease, and deformation and / or bending of the aluminum alloy material may easily occur during brazing due to its own weight.

[0053] Besides its effect of slightly dissolving in the matrix to increase strength, Fe also disperses as crystals and / or precipitates, particularly preventing strength reduction at high temperatures. The aluminum alloy sheet of the present invention has an Fe content of 0.05 to 0.40% by mass, preferably 0.08 to 0.35% by mass. With the Fe content of the aluminum alloy within the above range, the strength is increased, and strength reduction at high temperatures is prevented. On the other hand, if the Fe content of the aluminum alloy is lower than the above range, not only is the above effect less pronounced, but high-purity billets are required, increasing costs. Furthermore, if the Fe content of the aluminum alloy exceeds the above range, coarse intermetallic compounds are formed during casting, causing manufacturability problems. The corrosion resistance of the joint exposed to corrosive environments (especially those with flowing liquids) decreases, and furthermore, the grain refinement due to recrystallization during heating during joining reduces deformation resistance.

[0054] Mn dissolves in the aluminum matrix during casting and promotes the formation of Al-based intermetallic compounds with a circumequivalent diameter of 0.01 to 0.50 μm in subsequent processing steps. The aluminum alloy sheet of the present invention has an Mn content of 0.80 to 1.80% by mass, preferably 1.00 to 1.60% by mass. With the Mn content of the aluminum alloy within the above range, the presence of Al-based intermetallic compounds with a circumequivalent diameter of 0.01 to 0.50 μm becomes sufficient, resulting in a suitable pinning effect. Limited grain growth leads to coarse grains, thus suppressing grain boundary slip and increasing deformation resistance. On the other hand, if the Mn content of the aluminum alloy is below the above range, the above effect cannot be fully obtained, and deformation resistance decreases. Furthermore, if it exceeds the above range, coarse intermetallic compounds are formed during casting, causing manufacturability problems.

[0055] In addition to Si, Fe, and Mn, the aluminum alloy plate of the present invention may, as needed, contain any one or more of Cu, Zn, Mg, Ti, Zr, Cr, V, Be, Sr, Bi, Na, Ca, In, Sn, and rare earth elements.

[0056] Cu is an additive element that is dissolved in the matrix to increase strength. In the case where the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Cu, the Cu content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.20% by mass or less, preferably 0.01 to 0.18% by mass. When the Cu content of the aluminum alloy is within the above range, the strength increases. On the other hand, if the Cu content of the aluminum alloy exceeds the above range, the corrosion resistance decreases.

[0057] Zinc (Zn) is an effective element for improving corrosion resistance through sacrificial corrosion protection. Zn has the effect of lowering the spontaneous potential by being almost uniformly dissolved in the matrix. For example, when the aluminum alloy material of the present invention is used as a fin material, by lowering its spontaneous potential, a sacrificial corrosion protection effect can be achieved, relatively suppressing the corrosion of the tube connected to the fin. In the case where the aluminum alloy involved in the aluminum alloy plate of the present invention contains Zn, the Zn content of the aluminum alloy involved in the aluminum alloy plate of the present invention is 6.00% by mass or less, preferably 0.05 to 6.00% by mass, and particularly preferably 0.10 to 5.00% by mass. When the Zn content of the aluminum alloy is within the above range, the corrosion resistance is higher. On the other hand, if the Zn content of the aluminum alloy exceeds the above range, the corrosion rate becomes too fast, resulting in lower corrosion resistance and a lower sacrificial corrosion protection effect.

[0058] After being heat-bonded, Mg transforms into Mg₂Si, undergoing age-curing and thus increasing strength. Therefore, Mg is an additive element that enhances strength. In the case where the aluminum alloy of the aluminum alloy sheet of the present invention contains Mg, the Mg content of the aluminum alloy is 0.08% by mass or less, preferably 0.005 to 0.07% by mass. If the Mg content of the aluminum alloy exceeds the above range, Mg reacts with the flux to form a high-melting-point compound, thereby reducing the bonding strength. It should be noted that in the present invention, Mg and other alloying components below the specified content also include 0% by mass.

[0059] Cr enhances strength through solid solution strengthening. Furthermore, the precipitation of Al-Cr intermetallic compounds contributes to grain coarsening upon heating. In the case of the aluminum alloy containing Cr in the aluminum alloy sheet of the present invention, the Cr content of the aluminum alloy is 0.30% by mass or less, preferably 0.05 to 0.30% by mass. When the Cr content of the aluminum alloy is within the above range, the strength is higher. On the other hand, if the Cr content of the aluminum alloy exceeds the above range, coarse intermetallic compounds are more easily formed, resulting in lower plastic workability.

[0060] Zr, as an Al-Zr intermetallic compound, precipitates and strengthens through dispersion, thereby increasing the strength after heat bonding. In the case of the aluminum alloy containing Zr in the aluminum alloy sheet of the present invention, the Zr content of the aluminum alloy is 0.30% by mass or less, preferably 0.05 to 0.30% by mass. When the Zr content of the aluminum alloy is within the above range, the strength is higher. On the other hand, if the Zr content of the aluminum alloy exceeds the above range, coarse intermetallic compounds are more easily formed, resulting in lower plasticity and workability.

[0061] Besides increasing strength by dissolving in the matrix, Ti and V also have the effect of preventing corrosion propagation in the thickness direction due to their layered distribution. When the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Ti, the Ti content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.30% by mass or less, preferably 0.05 to 0.30% by mass. Similarly, when the aluminum alloy contains V, the V content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.30% by mass or less, preferably 0.05 to 0.30% by mass. With the Ti or V content of the aluminum alloy within the above ranges, the strength is increased, and corrosion propagation in the thickness direction can be prevented. On the other hand, if the Ti or V content of the aluminum alloy exceeds the above ranges, large crystals are formed, hindering formability and corrosion resistance.

[0062] Be, Sr, Bi, Na, and Ca can improve bonding properties by finely dispersing Si particles and increasing the fluidity of the liquid phase. When the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Be, the Be content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.10% by mass or less, preferably 0.0001 to 0.10% by mass. Furthermore, when the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Sr, the Sr content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.10% by mass or less, preferably 0.0001 to 0.10% by mass. Furthermore, when the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Bi, the Bi content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.30% by mass or less, preferably 0.0001 to 0.30% by mass. Furthermore, when the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Na, the Na content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.10% by mass or less, preferably 0.0001 to 0.10% by mass. Furthermore, when the aluminum alloy involved in the aluminum alloy sheet of the present invention contains Ca, the Ca content of the aluminum alloy involved in the aluminum alloy sheet of the present invention is 0.05% by mass or less, preferably 0.0001 to 0.05% by mass. When the Be, Sr, Bi, Na, or Ca content of the aluminum alloy is within the above range, the bonding strength is improved. On the other hand, if the Be, Sr, Bi, Na, or Ca content of the aluminum alloy exceeds the above range, it may sometimes result in reduced corrosion resistance. It should be noted that when the aluminum alloy contains one or more of Be, Sr, Bi, Na, and Ca, each added component must be within the above-mentioned component range. Additionally, the aluminum alloy involved in the aluminum alloy sheet of the present invention may also contain 0.10% by mass or less of In, 0.10% by mass or less of Sn, and 0.10% by mass or less of rare earth elements.

[0063] In a heating test of the aluminum alloy plate of the present invention, wherein the plate is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, and from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, the proportion of regions with one or more grain boundaries in the thickness direction is 25% or more and less than 90% in the width direction, preferably 30 to 85%, more preferably 35 to 80%, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is 950 μm or less, preferably 200 to 900 μm, more preferably 300 to 850 μm. That is, the aluminum alloy plate of the present invention is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes. The heating process produces a metallographic structure in which, in a cross-section perpendicular to both the rolling surface and the rolling direction after a heating test, the region having one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90%, preferably 30-85%, more preferably 35-80%, in proportion to the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is 950 μm or less, preferably 200-900 μm, more preferably 300-850 μm. The inventors have discovered that by heating from 300°C to 400°C at an average heating rate of 60°C / min or less and holding at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, heating from 400°C to 580°C for 8±3 minutes, and heating from 580°C to the holding temperature for 8±3 minutes and holding at 600±3°C for 5±3 minutes, an aluminum alloy sheet with the following metallographic structure can be heat-bonded in a single layer, ensuring both material strength and brazability, wherein in a cross-section perpendicular to the rolling surface and perpendicular to the rolling direction, the grain boundaries in the thickness direction are within the aforementioned range, and the average grain diameter in the direction perpendicular to the rolling direction on the sheet surface is within the aforementioned range.

[0064] In a heating test of the aluminum alloy sheet of the present invention, wherein the sheet is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, and from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, in a cross-section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, the region having one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90% in the width direction, preferably 30-85%, more preferably 35-80%. In the aluminum alloy sheet of the present invention, there are many flow paths of liquid phase seeping from the base material, i.e., many grain boundaries. Furthermore, in the aluminum alloy plate of the present invention, the flow paths of the liquid phase are increased, thereby increasing the filler area. Therefore, in a heating test in which the temperature is increased from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, the region in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, where there is one or more grain boundaries in the thickness direction, falls within the aforementioned range. This increases the flow paths of the liquid phase and thus increases the filler area. It should be noted that, since it is extremely difficult to observe the number of grain boundaries in the thickness direction of the plate cross-section during the heating process, the number of grain boundaries in the thickness direction of the plate cross-section after heating is used for judgment.

[0065] In a heating test of the aluminum alloy sheet of the present invention, wherein the sheet is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, more preferably at 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, the average grain diameter in the direction perpendicular to the rolling direction on the surface of the sheet after the heating test is 950 μm or less, preferably 900 μm or less, more preferably 850 μm or less. The finer the grain diameter, the more flow paths the liquid phase has, thus increasing the fill area. Therefore, in a heating test where the temperature is increased from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, the average grain diameter in the direction perpendicular to the rolling direction on the surface of the aluminum alloy sheet after the heating test falls within the above-mentioned range, which can increase the fill area. It should be noted that since it is extremely difficult to observe the average grain size during the heating process, the average grain diameter after heating is used for judgment.

[0066] Furthermore, in the heating test of the aluminum alloy sheet of the present invention, which involves heating from 300°C to 400°C at an average heating rate of 60°C / min or less and holding at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, more preferably 45°C / min or less, heating from 400°C to 580°C for 8±3 minutes, and heating from 580°C to the holding temperature for 8±3 minutes and holding at 600±3°C for 5±3 minutes, the average grain diameter in the direction perpendicular to the rolling direction on the surface of the sheet after the heating test is preferably 200 μm or more, more preferably 300 μm or more. When the grain diameter is too small, grain boundary slip and / or a significant reduction in material strength occur. Therefore, in the heating test where the temperature is increased from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, from 400°C to 580°C at 8±3 minutes, and from 580°C to the holding temperature at 8±3 minutes and held at 600±3°C for 5±3 minutes, the average grain diameter in the direction perpendicular to the rolling direction on the surface of the aluminum alloy sheet after the heating test is within the above range, making it difficult to produce grain boundary slip and / or a significant reduction in material strength.

[0067] In the aluminum alloy sheet of the present invention, in a cross-section perpendicular to both the rolling surface and the rolling direction after a heating test, regions having two or more grain boundaries in the thickness direction account for 3% or more, preferably 5% or more, in proportion to the width direction. The presence of these regions with two or more grain boundaries within the aforementioned range increases the flow path of the liquid phase seeping from the base material, resulting in excellent brazing properties.

[0068] In the aluminum alloy sheet of the present invention, in a cross-section perpendicular to both the rolling surface and the rolling direction after a heating test, the maximum width of the region with zero grain boundaries in the thickness direction is 2000 μm or less, preferably 1800 μm or less. Within this range, the flow path of the liquid phase seeping from the base material increases through the region with zero grain boundaries, resulting in excellent brazing properties.

[0069] In this invention, a heating test is conducted by heating from 300°C to 400°C at an average heating rate of 60°C / min or less and holding at 600±3°C for 5±3 minutes. Preferably, the heating rate is 45°C / min or less, from 300°C to 400°C. The heating rate is 8±3 minutes, from 400°C to 580°C. The heating rate is 8±3 minutes, from 580°C to the holding temperature and held at 600±3°C for 5±3 minutes. However, firstly, the aluminum alloy plate of this invention, which serves as the test specimen, is subjected to a heating test under the above heating conditions in an inactive gas atmosphere. Then, for the test specimen after the heating test, the number of grain boundaries in the thickness direction of the plate in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction is measured, as well as the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is measured. It should be noted that the heating test conditions are as follows: heating from 300°C to 400°C at an average heating rate of 60°C / min or less, followed by heating to 600°C. Preferably, the heating is from 300°C to 400°C at an average heating rate of 60°C / min or less, more preferably 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes.

[0070] In this invention, the number of grain boundaries in the thickness direction of a cross-section perpendicular to both the rolling surface and the rolling direction is determined as follows: A sample heated by brazing is cut along a direction perpendicular to both the rolling surface and the rolling direction, resin embedding and mirror polishing are performed, and the polished embedding resin is immersed in SWAAT test solution for 12 hours. Then, the resin surface is gently polished to remove contaminants. This process is used to etch the grain boundaries, making them easier to identify. Next, the cross-sectional structure is photographed at 200x using a metallographic microscope. For each photographed section, regions with one or more grain boundaries are enclosed by a frame. The length of each framed portion in the width direction is calculated, and the lengths of all enclosed portions are summed. The sum is then divided by the total length of the photographed section in the width direction to calculate the percentage of regions with one or more grain boundaries. Furthermore, for the cross-sectional photographs, regions with two or more grain boundaries are enclosed by frames. The length of each framed portion in the width direction is calculated, and the sum of all the lengths of the framed portions is divided by the total length of the cross-section in the width direction to calculate the percentage of regions with two or more grain boundaries. Additionally, in regions with zero grain boundaries (i.e., those not defined as having one or more boundaries), the length of the longest portion in the width direction is measured, and this is used to calculate the maximum width of the region with zero grain boundaries in the thickness direction. It should be noted that the number of grain boundaries in the thickness direction refers to the number of grain boundary lines intersecting a line drawn along the thickness direction (perpendicular to the rolling surface) on the cross-sectional photograph.

[0071] Figure 5 The figure shows an example of measuring the grain boundaries of the cross section of the aluminum alloy plate of the present invention. Figure 5 middle, Figure 5 A is a microscope image of the cross-section before image processing. Additionally... Figure 5 B is to Figure 5 Image processing was performed on a microscope photograph of A, and the grain boundaries are represented by black lines. Figure 5 In section B, grain boundaries are represented by black lines, and regions with more than one grain boundary in the thickness direction are enclosed by white frames. Figure 5 In the example of morphology B, there are three regions where there is one or more grain boundaries in the thickness direction. Then, the length in the width direction of each framed region is measured. Next, the lengths in the width direction of the framed regions where there is one or more grain boundaries in the thickness direction exist throughout the entire area being photographed are summed, and the result is calculated using the following formula:

[0072] The percentage (%) of regions with one or more grain boundaries in the thickness direction = ((the total length of the framed portion of the entire photographed region containing one or more grain boundaries in the thickness direction) / (the total length of the photographed region)) × 100. Additionally, Figure 5 In A, the unframed portion is the region with 0 or more grain boundaries in the thickness direction. The region with the longest width in the unframed portion of the entire area being photographed is the longest region in the width direction. Figure 5 In A, the length indicated by the white double arrows represents the maximum width of the region where the grain boundaries in the thickness direction are 0.

[0073] Figure 6 The figure shows an example of measuring the grain boundaries of the cross section of the aluminum alloy plate of the present invention. Figure 6 middle, Figure 6 A is a microscope image of the cross-section before image processing. Additionally... Figure 6 B is to Figure 6 Image processing was performed on a microscope photograph of A, and the grain boundaries are represented by black lines. Figure 6 In section B, regions with two or more grain boundaries along the thickness direction are outlined with white frames. Figure 6 In the morphological example of B, there are two regions where there are two or more grain boundaries in the thickness direction. Then, for each region enclosed by two or more grain boundaries in the thickness direction, the length in the width direction of each enclosed region is measured. Next, the lengths in the width direction of the enclosed regions with two or more grain boundaries in the thickness direction present in the entire area of ​​the photograph are added together, and the result is calculated using the following formula:

[0074] The percentage of regions with two or more grain boundaries in the thickness direction (%) = ((the total length of the width of the framed portion of the entire area where there are two or more grain boundaries in the thickness direction) / (the total length of the area being photographed)) × 100.

[0075] In this invention, the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is determined as follows: The sample, after brazing and heating, is cut into 20mm × 30mm pieces, and the plate surface is ground and milled to expose the center of the plate thickness. Next, mirror polishing and Parker etching are performed, followed by polarized light observation using a metal microscope. Six fields of view are captured at 20x magnification, and the crystal structure is observed continuously in these six fields of view (parallel to the rolling direction). Ten 6mm lines are drawn perpendicular to the rolling direction at 1mm intervals, the number of grains on the ten lines is counted, and the total number of grains is determined using the following formula:

[0076] The average grain diameter (μm) is calculated by the sum of the number of grains on 10 lines (6000 × 10).

[0077] Figure 7 An example of measuring the average grain diameter on the surface of the aluminum alloy plate of the present invention is shown. For example... Figure 7 As shown, ten 6mm lines are drawn perpendicular to the rolling direction at 1mm intervals. Next, the number of grains on each of the ten lines is counted. Then, the sum of the number of grains on each of the ten lines is determined using the following formula:

[0078] The average grain diameter (μm) is calculated by using (6000×10) / 10 the sum of the number of grains present on each line. Figure 7 In the diagram, the center of the crystal along each line is represented by a black dot. Additionally, Figure 7 The numbers above each line indicate the line number, and the numbers below each line indicate the number of grains on that line.

[0079] The thickness of the aluminum alloy plate of the present invention is preferably 0.08 mm or less. The thickness of the fin material used in the heat exchanger is preferably 0.08 mm or less. Furthermore, the aluminum alloy plate of the present invention exhibits excellent resistance to deformation even with a thickness as low as 0.08 mm or less.

[0080] The aluminum alloy sheet of the present invention is an aluminum alloy sheet that has the function of single-layer heat bonding at a temperature where the liquid phase fraction is 5.0% or more and 35.0% or less. That is, the aluminum alloy sheet of the present invention is a single-layer brazed sheet.

[0081] The following describes an aluminum alloy sheet (hereinafter also referred to as a single-layer brazed sheet) that has the function of being heat-bonded in a single layer at a temperature where the liquidus fraction is 5.0% or more and 35.0% or less.

[0082] Single-layer brazing sheets require bonding at a temperature where the ratio of the mass of the liquid phase generated in the aluminum alloy to the total mass of the aluminum alloy (hereinafter referred to as the "liquid phase ratio") is 5% or more and 35% or less. When the liquid phase ratio exceeds 35%, the amount of liquid phase generated is excessive, and the aluminum alloy becomes unable to maintain its shape, resulting in large deformation. On the other hand, if the liquid phase ratio is less than 5%, bonding becomes difficult. A preferred liquid phase ratio is 5% to 30%, and a more preferred liquid phase ratio is 10% to 20%.

[0083] The formation mechanism of the liquid phase is explained. Figure 1 The diagram schematically illustrates the phase diagram of an Al-Si alloy, a representative binary eutectic alloy. When an aluminum alloy with a Si concentration of c1 is heated, a liquid phase begins to form at a temperature T1 above the eutectic temperature (solid line temperature) Te. Below the eutectic temperature Te, as... Figure 2 As shown in (a), crystalline precipitates are distributed within a matrix defined by grain boundaries. Here, when the liquid phase begins to form, as... Figure 2 As shown in (b), the grain boundaries where the crystalline precipitates are more segregated melt into the liquid phase. Then, as... Figure 2 As shown in (c), the crystalline precipitates of Si, the main additive element dispersed in the aluminum alloy matrix, melt and spherical around the intermetallic compounds, forming a liquid phase. Furthermore, as... Figure 2 As shown in (d), the spherical liquid phase generated in the matrix, due to interfacial energy, dissolves back into the matrix over time and / or with increasing temperature, and migrates to the grain boundaries and / or surfaces via intra-solid diffusion. Then, as... Figure 1 As shown, when the temperature rises to T2, the amount of liquid phase increases according to the phase diagram. Figure 1 As shown, when the Si concentration of an aluminum alloy is less than the maximum solid solution limit concentration c2, a liquid phase begins to form near the solidus temperature Ts2. However, unlike the case of c1, the microstructure before melting is as follows: Figure 3 As shown in (a), sometimes crystalline precipitates are not present in the matrix. In this case, as... Figure 3 As shown in (b), after the grain boundaries first melt into a liquid phase, as Figure 3 As shown in (c), a liquid phase is generated in the matrix from areas of high local solute element concentration. Figure 3As shown in (d), the spherical liquid phase generated in the matrix, similar to that in c1, dissolves back into the matrix over time and with increasing temperature due to interfacial energy, and migrates to grain boundaries and / or surfaces via diffusion within the solid phase. When the temperature rises to T3, the amount of liquid phase increases according to the phase diagram. Therefore, the bonding in this invention utilizes the liquid phase generated by partial melting within a single-layer brazed sheet (the finned material for heat exchangers involved in this invention), achieving both bonding and shape maintenance.

[0084] The behavior of the metallographic structure from the generation of the liquid phase to the bonding is explained. A monolayer brazed sheet with a liquid phase generated and an aluminum alloy object material to which it is bonded are combined and heated at a temperature where the liquid phase fraction is 5.0% or more and 35.0% or less. Then, when the joint is observed under a microscope, as described above, a very small amount of liquid phase generated on the surface of the monolayer brazed sheet fills the gap between the aluminum alloy object material and the oxide coating that has broken due to flux or other factors. Next, the liquid phase located near the bonding interface of the two alloy materials moves into the aluminum alloy object material, and the grains of the solid α phase of the monolayer brazed sheet in contact with the bonding interface then grow into the aluminum alloy object material. On the other hand, the grains of the aluminum alloy object material also grow towards the monolayer brazed sheet side. Then, the structure of the monolayer brazed sheet is embedded in the aluminum alloy object material near the bonding interface, thus bonding occurs. Therefore, no metallographic structure other than the monolayer brazed sheet and the aluminum alloy object material is generated at the bonding interface.

[0085] On the other hand, when using brazed sheets coated with filler metal to bond with aluminum alloy materials via brazing heating, a filler layer is formed at the joint, revealing a eutectic structure. This results in a different joint structure compared to the case where a single-layer brazed sheet is used to bond with the aluminum alloy material via brazing heating. Specifically, when using brazed sheets coated with filler metal to bond with the aluminum alloy material via brazing heating, the liquid phase filler metal fills the joint, forming a filler layer, thus creating a eutectic structure different from the surrounding area. Furthermore, the joint also partially melts during the welding process, resulting in a metallographic structure different from other areas.

[0086] Therefore, when using a single-layer brazed sheet to heat-joint an aluminum alloy material, the metallographic structure of the joint is composed of only the two joined parts, or is composed of the two joined parts as a single unit. This is different from the case of using a brazed sheet covered with brazing filler metal and / or using welding.

[0087] Furthermore, due to this joining behavior, when using a single-layer brazed sheet to heat-bond an aluminum alloy material, almost no shape change occurs near the joint after the joining process. That is, the shape changes after joining, such as weld beads in welding and / or fillet welds in brazing, are almost non-existent when using a single-layer brazed sheet to heat-bond an aluminum alloy material. Nevertheless, as with welding and / or brazing, joining can be achieved using metal bonding. For example, when assembling a drawcup-type stacked heat exchanger using brazed sheets coated with filler metal (5% filler metal coverage on one side), the molten filler metal concentrates at the joint after brazing heating, thus reducing the height of the stacked heat exchanger by 5-10%. Therefore, this reduction needs to be considered in product design. In contrast, when using a single-layer brazed sheet to heat-bond an aluminum alloy material, the dimensional change after joining is minimal, thus enabling high-precision product design.

[0088] In this invention, determining the actual liquid phase fraction during the heating process of a single-layer brazed sheet is extremely difficult. Therefore, the liquid phase fraction specified in this invention is determined through equilibrium calculations. Specifically, it is calculated using thermodynamic equilibrium calculation software such as Thermo-Calc (registered trademark), manufactured by Thermo-Calc Software AB, based on the alloy composition and the highest temperature reached during heating.

[0089] based on Figure 4 The phase diagram shown illustrates the relationship between the liquid phase fraction and temperature. Figure 4 It is Figure 1 It is obtained through deformation. Figure 4 In the diagram, the line extending parallel to the horizontal axis through temperature Te (hereinafter referred to as "Solid Phase Line 1") and the line dividing the boundary with the α phase and extending upward and to the left from the left end of Solid Phase Line 1 to 660°C on the vertical axis (hereinafter referred to as "Solid Phase Line 2") both represent solid phase lines. Additionally, the line extending downward and to the right from 660°C on the vertical axis and connecting with Solid Phase Line 1 (hereinafter referred to as "Liquid Phase Line 1") and the line dividing the boundary with (Si + liquid phase) and extending upward and to the right from the point of connection both represent liquid phase lines.

[0090] Here, we designate point P0 at temperature T2, and draw a line passing through P0 parallel to the horizontal axis of the graph. The intersection of this line with liquidus line 1 is designated P1, and the intersection with solidus line 2 is designated P2. The Al-Si alloy with Si concentration C1 exists in a state of coexistence of liquid and solid phases at temperature T2. The Si concentration in the liquid phase is CP1 at point P1, and the Si concentration in the solid phase is CP2 at point P2. Furthermore, the ratio of the mass of the liquid phase to the total mass at temperature T2, i.e., the liquid phase ratio, is the ratio of the length of line segment P0 to P2 to the length of line segment P1 to P2.

[0091] As mentioned above, based on such Figure 1 and Figure 4 The phase diagram of the binary alloy shown is used to determine the liquidus fraction by plotting the alloy composition and temperature. Similarly, for multi-component systems of ternary or higher composition, the liquidus fraction can be determined by plotting the phase diagram based on the alloy composition and temperature. It should be noted that phase diagrams for multi-component systems of ternary or higher composition are difficult to obtain using... Figure 4 While it can be represented by a simple XY plane diagram, the liquid phase fraction can be calculated by computer using Thermo-Calc thermodynamic equilibrium calculation software.

[0092] The aluminum alloy sheet of the present invention has the following metallographic structure: after a heating test in which the sheet is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, in a cross section perpendicular to both the rolling surface and the rolling direction, the region having one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the sheet surface is 950 μm or less. Therefore, during brazing heating, there are many flow paths for the liquid phase seeping from the base material, i.e., many grain boundaries, thereby increasing the filler area generated by the heat-bonded joint. Therefore, the aluminum alloy sheet of the present invention exhibits excellent brazing properties even with a low Si content, thus achieving a balance between brazing performance and material strength.

[0093] The aluminum alloy sheet of the present invention is suitable for use as a material in the manufacture of heat exchangers. That is, the aluminum alloy sheet of the present invention is suitable as an aluminum alloy sheet for heat exchangers.

[0094] The aluminum alloy sheet of the present invention can be manufactured by any manufacturing method, for example, by the manufacturing method of the aluminum alloy sheet of the present invention described below.

[0095] The method for manufacturing an aluminum alloy plate according to the present invention is characterized by comprising: a casting process, wherein a cast-rolled plate of a cast aluminum alloy is continuously cast and rolled at a casting speed greater than 0.50 m / min and less than 0.70 m / min, wherein the cast-rolled plate of the aluminum alloy is composed of an aluminum alloy containing 2.00 to 3.00% by mass of Si, 0.05 to 0.40% by mass of Fe, and 0.80 to 1.80% by mass of Mn, wherein the Cu content is 0.20% by mass or less (including 0.00% by mass), the Zn content is 6.00% by mass or less (including 0.00% by mass), and optionally contains 0.08% by mass of Mg and 0.30% by mass of Fe. The composition comprises any one or more of the following: Ti, less than 0.30% by mass of Zr, less than 0.30% by mass of Cr, less than 0.30% by mass of V, less than 0.10% by mass of Be, less than 0.10% by mass of Sr, less than 0.30% by mass of Bi, less than 0.10% by mass of Na, and less than 0.05% by mass of Ca, with the balance being Al and unavoidable impurities; and a cold rolling process in which the cast rolled plate is cold rolled more than twice, and an annealing treatment is performed more than once from the casting process to the final cold rolling process, wherein the annealing conditions in all annealing treatments are an annealing temperature of 200 to 550°C and an annealing time of 1 to 10 hours.

[0096] The method for manufacturing the aluminum alloy plate of the present invention includes at least the following steps: casting, cold rolling and annealing.

[0097] The casting process is a process of casting a cast-rolled sheet of aluminum alloy with a specified chemical composition through continuous casting and rolling. In continuous casting, the cooling rate during solidification is rapid, thus making it difficult to form coarse crystals, and suppressing the formation of Si-based intermetallic compounds with a spherical equivalent diameter of 5.0–10 μm. As a result, the number of recrystallization nuclei can be reduced, thus allowing only specific grains to grow, resulting in coarse grains. Furthermore, compared to DC (Direct Chill) casting, which involves water cooling of thick ingots, the difference in cooling rate along the width direction is smaller in continuous casting, making it easier for the enrichment caused by the expulsion of solute atoms to become uniform along the width direction, thus ensuring the stability of the aluminum alloy quality. As for the continuous casting method, there are no particular limitations as long as it is a method of continuously casting sheet-shaped ingots, such as twin-roll continuous casting or twin-belt continuous casting. Twin-roll continuous casting rolling refers to a method of continuously casting and rolling thin sheets by supplying molten aluminum from a refractory nozzle between a pair of water-cooled rolls. Known methods include the Hunter process and / or the 3C process. Another method is twin-belt continuous casting, where molten aluminum is injected between two water-cooled, opposing rotating belts, solidifying the molten metal through cooling from the belt surface to form a slab. This slab is then continuously pulled out from the reverse injection side of the belt and wound into a roll. In twin-roll continuous casting rolling, the cooling rate during casting is several to hundreds of times faster than in semi-continuous casting. For example, the cooling rate in semi-continuous casting is 0.5–20 °C / s, while in twin-roll continuous casting rolling it is 100–1000 °C / s. Therefore, compared to semi-continuous casting, twin-roll continuous casting rolling is characterized by the formation of finer, more densely distributed dispersed particles during casting. This suppresses the formation of coarse crystals, thus reducing grain coarsening during the bonding heating process. Furthermore, the rapid cooling rate increases the solid solution content of the added elements. This allows for the formation of fine precipitates through subsequent heat treatment, which helps to coarsen the grains during the bonding heating process.

[0098] In the casting process, the cooling rate during twin-roll continuous casting is preferably 100–1000 °C / s. If the cooling rate is less than 100 °C / s, it is difficult to obtain the target metallographic structure; conversely, if it exceeds 1000 °C / s, it is difficult to manufacture stably. The rolling speed during twin-roll continuous casting is preferably greater than 0.50 m / min and less than 0.70 m / min, preferably 0.53–0.69 m / min, and more preferably 0.58–0.68 m / min. The casting speed affects the cooling rate. When the casting speed is less than 0.50 m / min, it is difficult to obtain a sufficient cooling rate as described above, resulting in coarser compounds and a lower solid solution content of additive elements in the base material. Consequently, fewer fine precipitates are formed during subsequent heat treatment, and the grain diameter becomes coarser. On the other hand, when the speed is 0.70 m / min or higher, the cooling rate is too fast, resulting in an excessive number of fine precipitates and a finer grain diameter. This easily leads to grain boundary slip, making deformation prone to occur during brazing heating. The preferred melt temperature for casting using a twin-roll continuous casting method is 650–800°C, more preferably 680–750°C. The melt temperature is the temperature of the headbox located directly in front of the melt supply nozzle. If the melt temperature is below this range, large, dispersed particles of intermetallic compounds are generated within the melt supply nozzle, which mix into the ingot and cause sheet breakage during cold rolling. Furthermore, if the melt temperature exceeds this range, the aluminum material cannot fully solidify between the rolls during casting, resulting in an ingot that does not form a normal sheet shape.

[0099] The thickness of the slab-shaped ingots cast by twin-roll continuous casting is preferably 2–10 mm, and particularly preferably 4–8 mm. Within this thickness range, the solidification rate in the center of the slab is also fast, making it easier to obtain a uniform microstructure. When the slab thickness is less than the above range, the amount of aluminum passing through the casting machine per unit time is small, making it difficult to stably supply molten metal in the width direction of the slab. On the other hand, if the slab thickness exceeds the above range, it becomes difficult to use the rolls for winding.

[0100] The casting speed is greater than 0.50 m / min and less than 0.70 m / min, preferably 0.53 to 0.69 m / min, and more preferably 0.58 to 0.68 m / min. By keeping the casting speed within the above range, it is easy to obtain the following aluminum alloy sheet: "In a heating test in which the temperature is raised from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably at 45°C / min or less, from 400°C to 580°C at 8±3 minutes, and from 580°C to the holding temperature at 8±3 minutes and held at 600±3°C for 5±3 minutes, in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, the area with one or more grain boundaries in the thickness direction accounts for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the sheet surface is less than 950 μm."

[0101] In the casting process, a cast rolled plate is cast from an aluminum alloy containing 2.00–3.00% by mass, preferably 2.10–2.80% by mass, more preferably 2.20–2.60% by mass of Si, 0.05–0.40% by mass, preferably 0.08–0.35% by mass of Fe, and 0.80–1.80% by mass, preferably 1.00–1.60% by mass of Mn, with the balance being Al and unavoidable impurities. Furthermore, the cast rolled plate obtained from the casting process may, as needed, contain, as optional additive elements, 0.20% by mass or less, preferably 0.01 to 0.18% by mass of Cu, 6.00% by mass or less, preferably 0.05 to 6.00% by mass, particularly preferably 0.10 to 5.00% by mass of Zn, 0.08% by mass or less, preferably 0.005 to 0.07% by mass of Mg, 0.30% by mass or less, preferably 0.05 to 0.30% by mass of Ti, 0.30% by mass or less, preferably 0.05 to 0.30% by mass of Zr, and 0.30% by mass or less, preferably... The composition may be selected from any one or more of the following: 0.05–0.30% by mass of Cr, 0.30% or less by mass of V, preferably 0.05–0.30% by mass of Be, 0.10% or less by mass of Be, preferably 0.0001–0.10% by mass of Sr, 0.30% or less by mass of Bi, 0.10% or less by mass of Na, preferably 0.0001–0.10% by mass of Na, and 0.05% or less by mass of Ca, preferably 0.0001–0.05% by mass of Ca. Additionally, the cast rolled plate obtained by the casting process may, as needed, contain 0.10% or less by mass of In, 0.10% or less by mass of Sn, and 0.10% or less by mass of rare earth elements. It should be noted that, in the casting process, by preparing a molten aluminum alloy with the above chemical composition and using the molten alloy for continuous casting and rolling, the chemical composition of the cast and rolled plate can be made to be the above chemical composition.

[0102] The cold rolling process is a process of cold rolling the cast and rolled sheet obtained from the casting process. In the cold rolling process, cold rolling is performed twice or more. That is, the cold rolling process involves two or more cold rolling passes. The number of cold rolling passes in the cold rolling process can be appropriately selected. Furthermore, in the cold rolling process, cold rolling continues until the thickness of the aluminum alloy sheet becomes the final sheet thickness. In other words, the thickness of the aluminum alloy sheet after the final cold rolling process is the final sheet thickness.

[0103] In the method for manufacturing the aluminum alloy sheet of the present invention, annealing is performed at least once during the period from after the casting process to before the final cold rolling process. In the method for manufacturing the aluminum alloy sheet of the present invention, the timing of annealing is as follows: (1) after the casting process and before the cold rolling process; and (2) when two or more cold rolling processes are performed, either (1) or (2) is performed at least once, preferably 1 to 3 times, more preferably 1 to 2 times, between cold rolling processes. In the case of three or more cold rolling processes, there are two or more cold rolling processes, but in this case, two or more annealing processes may also be performed during the cold rolling process. Annealing is performed to soften the aluminum alloy sheet so that the desired strength can be easily obtained in the final cold rolling. Through this annealing process, the size and density of the intermetallic compounds in the aluminum alloy sheet and the solid solution content of the added elements can be optimally adjusted. It should be noted that in the manufacturing method of the aluminum alloy plate of the present invention, no annealing treatment is performed after the final cold rolling process.

[0104] The annealing conditions in the annealing process are an annealing temperature of 200–550°C, preferably 250–450°C, and an annealing time of 1–10 hours. That is, in the annealing process, heating is carried out at an annealing temperature of 200–550°C, preferably 250–450°C, for an annealing time of 1–10 hours. If the annealing temperature is lower than the above range, the aluminum alloy sheet will not soften sufficiently, resulting in higher tensile strength before heat bonding. High tensile strength before heat bonding leads to poor formability and deterioration of core dimensions, resulting in lower durability. Furthermore, if the annealing temperature exceeds the above range, annealing will occur at excessively high temperatures exceeding the softening temperature of the aluminum alloy sheet, which is economically disadvantageous.

[0105] In the method for manufacturing aluminum alloy sheet of the present invention, the total reduction rate of cold rolling after the final annealing treatment is preferably 20-50%, and particularly preferably 25-40%. By ensuring that the total reduction rate of cold rolling after the final annealing treatment is within the above-mentioned range, it is easy to obtain an aluminum alloy sheet that meets the following criteria: "In a heating test in which the sheet is heated from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, preferably from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably at 45°C / min or less, from 400°C to 580°C for 8±3 minutes, and from 580°C to the holding temperature for 8±3 minutes and held at 600±3°C for 5±3 minutes, in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, the area with one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the sheet surface is 950 μm or less." It should be noted that, in this invention, the final annealing treatment refers to this single annealing treatment when only one annealing treatment is performed, and to the last annealing treatment among the two or more annealing treatments when only one annealing treatment is performed. Furthermore, the total reduction rate A (%) of cold rolling after the final annealing treatment is calculated using the following formula.

[0106] A(%) = ((BC) / B) × 100

[0107] A: Total reduction (%) during cold rolling after final annealing.

[0108] B: The thickness of the rolled plate after the final annealing treatment

[0109] C: Thickness of the rolled plate after final cold rolling

[0110] It should be noted that, in the case of only one cold rolling after the final annealing treatment, the thickness of the rolled plate before cold rolling is B, and the thickness of the rolled plate after cold rolling is C. Furthermore, in the case of multiple cold rolling after the final annealing treatment, the thickness of the rolled plate before the first cold rolling in each of the multiple cold rolling processes is B, and the thickness of the rolled plate after the final cold rolling is C.

[0111] The aluminum alloy sheet obtained by the manufacturing method of the present invention can be of O-type or H-type material. When the aluminum alloy sheet is H1n or H2n material, the final cold rolling rate is set to 50% or less, preferably 5 to 50%. When the final cold rolling rate is greater than 50%, multiple recrystallization nuclei are generated during heating, and the grain diameter becomes finer after bonding heating. It should be noted that if the final cold rolling rate is less than 5%, it is sometimes practically difficult to manufacture.

[0112] The aluminum alloy sheet obtained by the manufacturing method of the present invention has the function of being heat-bonded in a single layer at a temperature where the liquid phase fraction is 5.0% or more and 35.0% or less.

[0113] In the method for manufacturing aluminum alloy sheets of the present invention, in the casting process, a cast-rolled sheet is cast using continuous casting rolling, preferably twin-roll continuous casting rolling, and an annealing treatment is performed at least once from the casting process until the final sheet is obtained. All annealing conditions are set to an annealing temperature of 200–550°C, preferably 250–450°C, and an annealing time of 1–10 hours. Preferably, the total reduction rate in the cold rolling after the final annealing treatment is set to 20–50%, preferably 25–40%. This allows the manufacture of aluminum alloy sheets that are heated from 300°C to 400°C at an average heating rate of 60°C / min or less and then cooled to 600±... In the heating test of holding at 3°C ​​for 5±3 minutes, preferably heating from 300°C to 400°C at an average heating rate of 60°C / min or less, preferably 45°C / min or less, heating from 400°C to 580°C for 8±3 minutes, and heating from 580°C to the holding temperature for 8±3 minutes and holding at 600±3°C for 5±3 minutes, in the cross section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test, the region with one or more grain boundaries in the thickness direction accounts for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is 950 μm or less.

[0114] When using the aluminum alloy sheet of the present invention for heat bonding, the aluminum alloy sheet of the present invention is formed into a predetermined shape, then combined with the material to be bonded, and heated at a heat bonding temperature to perform heat bonding. A suitable heat bonding temperature for heat bonding using the aluminum alloy sheet of the present invention is a temperature range where the liquid phase fraction is 5% to 35%, and the holding time at a liquid phase fraction of 5% or higher is preferably 30 to 3600 seconds. If the liquid phase fraction is low, bonding may be difficult; therefore, a liquid phase fraction of 5% or higher is preferred. If the liquid phase fraction is greater than 35%, too much liquid phase is generated, resulting in significant deformation of the aluminum alloy material during heat bonding, making it impossible to maintain its shape. Furthermore, if the time with a liquid phase fraction of 5% or higher is less than 30 seconds, the liquid phase may not be sufficiently filled at the joint; and when the time exceeds 3600 seconds, deformation of the aluminum material may intensify. To achieve these conditions, the heating temperature is set to 580°C to 640°C, and the holding time at the heating temperature is set to approximately 0 to 10 minutes. Here, 0 minutes means that cooling begins immediately when the temperature of the components reaches the predetermined bonding temperature. For the heating conditions during heat joining, conditions adjusted to a suitable range can be used to achieve a healthy joint without deformation. Furthermore, the heating atmosphere during heat joining is preferably a non-oxidizing atmosphere substituted with nitrogen or argon. When a joint is obtained during heat joining, good bonding properties can be further obtained by using a non-corrosive flux. Moreover, heat joining can also be performed under vacuum and / or reduced pressure.

[0115] The heat exchanger of the present invention is characterized in that it has an aluminum alloy tube for flowing working fluid and aluminum alloy fins metal-joined to the tube. The heat exchanger is obtained by combining at least an aluminum alloy heat exchanger tube and an aluminum alloy heat exchanger fin, then heating the resulting assembly, and joining the heat exchanger tube and the heat exchanger fin, wherein the heat exchanger fin is a molded body of the aluminum alloy plate of the present invention.

[0116] As for the heat exchanger tube made of aluminum alloy involved in the present invention, there are generally no special limitations as long as the aluminum alloy material used as the tube of the aluminum alloy heat exchanger is made into the shape of a tube.

[0117] There are no particular restrictions on the chemical composition of the aluminum alloys used to form tubes for heat exchangers. Representative aluminum alloys used to form tubes for heat exchangers include 1000 series and 3000 series aluminum. That is, pure aluminum, as well as aluminum alloys containing one or more of the following relative to pure aluminum: less than 0.60% by mass of Si, less than 0.70% by mass of Fe, less than 0.70% by mass of Cu, and less than 2.00% by mass of Mn, with the balance being Al and unavoidable impurities.

[0118] The heat exchanger of the present invention relates to a heat exchanger fin material made of aluminum alloy, which is a molded body of the aluminum alloy plate of the present invention. The aluminum alloy plate for the heat exchanger fin material used in the heat exchanger of the present invention is the same as the aluminum alloy plate of the present invention described above.

[0119] The heat exchanger of the present invention is obtained by heating and joining together a combination of heat exchanger tubing made of aluminum alloy and heat exchanger fins made of aluminum alloy, and further combining necessary components such as manifolds, storage tanks, and piping materials.

[0120] The heating temperature for joining the assemblies can be appropriately selected based on the Si content. In addition to Si, Zn and Cu also affect the solidus temperature. Therefore, when the aluminum alloy plate of the present invention contains Zn and / or Cu in addition to Si, the heating temperature for joining the assemblies can be appropriately selected based on the Si and Zn and / or Cu content. Preferably, the heating temperature for joining the assemblies is in the temperature range where the liquidus fraction of the aluminum alloy plate of the present invention is 5-35%, and the holding time at a liquidus fraction of 5% or higher is preferably 30-3600 seconds. The heating rate for joining the assemblies is not specifically defined and can be appropriately selected based on the furnace structure and / or product design, but is generally 20-300°C / minute.

[0121] That is, the heat exchanger of the present invention is characterized in that it has an aluminum alloy tube for flowing working fluid and aluminum alloy fins metal-joined to the tube. The tube is formed using heat exchanger tubing made of aluminum alloy, and the fins are formed using an aluminum alloy plate having the function of single-layer heating bonding. The aluminum alloy plate is composed of an aluminum alloy containing 2.00 to 3.00% by mass of Si, 0.05 to 0.40% by mass of Fe, and 0.80 to 1.80% by mass of Mn, with a Cu content of 0.20% by mass or less (including 0.00% by mass), a Zn content of 6.00% by mass or less (including 0.00% by mass), and optionally containing 0.08% by mass or less of [unspecified ingredient]. The fin contains one or more of the following: Mg, Ti (less than 0.30% by mass), Zr (less than 0.30% by mass), Cr (less than 0.30% by mass), V (less than 0.30% by mass), Be (less than 0.10% by mass), Sr (less than 0.10% by mass), Bi (less than 0.30% by mass), Na (less than 0.10% by mass), and Ca (less than 0.05% by mass), with the balance being Al and unavoidable impurities. In the cross-section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, the region having one or more grain boundaries in the thickness direction accounts for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

[0122] The heat exchanger of the present invention is formed by heating and joining aluminum alloy plates with the function of single-layer heating and joining aluminum alloy heat exchanger tubes as the object material.

[0123] The fins of the heat exchanger of the present invention are formed using an aluminum alloy plate having the function of being heated and joined in a single layer. For example, the fins of the heat exchanger of the present invention are formed using the aluminum alloy described above.

[0124] The aluminum alloy used to form the fins of the heat exchanger of the present invention is an aluminum alloy containing 2.00 to 3.00% by mass, preferably 2.10 to 2.80% by mass, more preferably 2.20 to 2.60% by mass of Si, 0.05 to 0.40% by mass, preferably 0.08 to 0.35% by mass of Fe, and 0.80 to 1.80% by mass, preferably 1.00 to 1.60% by mass of Mn, with the balance being Al and unavoidable impurities. Furthermore, the aluminum alloy used to form the fin material of the heat exchanger of the present invention may, as needed, contain, as optional additive elements, 0.20% or less, preferably 0.01 to 0.18% Cu, 6.00% or less, preferably 0.05 to 6.00% Zn, particularly preferably 0.10 to 5.00% Zn, 0.08% or less, preferably 0.005 to 0.070% Mg, 0.30% or less, preferably 0.05 to 0.30% Ti, 0.30% or less, preferably 0.05 to 0.30% Zr, and 0.30% or less of other additives. The following are the components: preferably 0.05 to 0.30% by mass of Cr, preferably 0.30% by mass of V, preferably 0.05 to 0.30% by mass of Be, preferably 0.10% by mass of Be, preferably 0.0001 to 0.10% by mass of Sr, preferably 0.10% by mass of Bi, preferably 0.0001 to 0.30% by mass of Na, preferably 0.10% by mass of Na, and preferably 0.0001 to 0.10% by mass of Ca, and any one or more of the following components: preferably 0.05% by mass of Cr, preferably 0.0001 to 0.05% by mass of Na. In addition, the aluminum alloy plate of the present invention may also contain less than 0.10% by mass, preferably 0.0001 to 0.10% by mass of In, less than 0.10% by mass, preferably 0.0001 to 0.10% by mass of Sn, less than 0.10% by mass, preferably 0.0001 to 0.10% by mass of Be, and less than 0.10% by mass, preferably 0.0001 to 0.10% by mass of rare earth elements.

[0125] In the cross-section of the fins of the heat exchanger of the present invention, in the direction perpendicular to the rolling plane and in the direction perpendicular to the rolling direction, the region having one or more grain boundaries in the thickness direction accounts for 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is 950 μm or less. During brazing heating, there are many flow paths of liquid phase seeping from the base material, i.e., many grain boundaries, thus increasing the fillet area generated by the heat bonding. Therefore, the fins of the heat exchanger of the present invention have excellent brazing properties even with low Si content, and thus the heat exchanger of the present invention is a heat exchanger that balances brazing properties and material strength.

[0126] In the heat exchanger of the present invention, the fins, in a cross-section perpendicular to both the rolling plane and the rolling direction after a heating test, exhibit a region with two or more grain boundaries in the thickness direction comprising 3% or more, preferably 5% or more, in proportion to the width direction. The presence of two or more grain boundaries within the aforementioned range increases the flow path of the liquid phase seeping from the base material, resulting in excellent brazing properties.

[0127] In the heat exchanger of the present invention, the maximum width of the region with zero grain boundaries in the thickness direction of the fins, in a cross-section perpendicular to both the rolling surface and the rolling direction after a heating test, is 2000 μm or less, preferably 1800 μm or less. Within this range, the flow path of the liquid phase seeping from the base material increases, resulting in excellent brazing properties.

[0128] There are no particular limitations on the aluminum alloy used for the tubes in the heat exchanger of the present invention, as long as it is an aluminum alloy commonly used for tubes in aluminum alloy heat exchangers.

[0129] There are no particular restrictions on the chemical composition of the aluminum alloy forming the tube. Representative aluminum alloys for forming tubes for heat exchangers include 1000 series and 3000 series aluminum. That is, pure aluminum, as well as aluminum alloys containing one or more of the following relative to pure aluminum: less than 0.60% by mass of Si, less than 0.70% by mass of Fe, less than 0.70% by mass of Cu, and less than 2.00% by mass of Mn, with the balance being Al and unavoidable impurities.

[0130] The following examples illustrate the present invention in detail, but the present invention is not limited to the examples shown below.

[0131] Example

[0132] (Example 1, Comparative Examples 1-2)

[0133] Cast rolled sheets were produced using aluminum alloys with the alloy compositions shown in Table 1 via twin-roll continuous casting. It should be noted that in the alloy compositions of Table 1, "-" indicates below the detection limit, and "balance" includes unavoidable impurities. The melt temperature during twin-roll continuous casting was 600–800°C, and the thickness of the cast rolled sheet was 6.0 mm.

[0134] Next, the resulting plate-shaped cast and rolled sheet was annealed at 420°C for 2 hours, and then cold-rolled to the thickness shown in Table 2 (after the first cold rolling). Then, after annealing at 370°C for 2 hours, it was cold-rolled to a thickness of 0.070 mm to produce sample material (final plate).

[0135] For each of the above sample materials, the maximum width of regions with two or more grain boundaries, one or more grain boundaries, or zero grain boundaries in the thickness direction were measured in the cross-section perpendicular to the rolling surface and perpendicular to the rolling direction after the heating test; the average grain diameter in the direction perpendicular to the rolling direction as observed from the plate surface; the fillet area; and the tensile strength after brazing heating. The results are shown in Table 2.

[0136] <Heating Test>

[0137] The sample material was heated in an inert gas atmosphere from 300°C to 400°C at a heating rate of 41°C / min, from 400°C to 580°C for 7.2 minutes, and from 580°C to 600°C for 7.4 minutes. The temperature was then raised to 600±3°C and held for 4.7 minutes. Finally, the temperature was cooled to room temperature to obtain the test material after the heating test.

[0138] <Determination of grain boundaries in cross-section>

[0139] The sample after brazing and heating is cut out along a direction perpendicular to the rolling surface and the rolling direction, and then resin embedding and mirror polishing are performed.

[0140] Next, the ground embedding resin was immersed in SWAAT test solution for 12 hours. Then, the resin surface was gently mirror-polished to remove contaminants.

[0141] Next, the cross-sectional structure was photographed at 200x using a microscope for metallographic observation. The observation length was set to approximately 25 mm based on the total length.

[0142] The cross-sectional photographs were colored red to make the grain boundaries more clearly visible.

[0143] Enclose regions with one or more grain boundaries using frames. Calculate the width of each framed portion, sum all lengths, and divide the sum by the total width of the observed region to calculate the proportion of regions with one or more grain boundaries. Similarly, enclose regions with two or more grain boundaries using frames. Calculate the width of each framed portion, sum all lengths, and divide the sum by the total width of the observed region to calculate the proportion of regions with two or more grain boundaries.

[0144] For regions with zero grain boundaries, in the portion not defined as having more than one grain boundary, measure the length of the longest portion in the width direction, and calculate the maximum width of the region with zero grain boundaries in the thickness direction.

[0145] <Determination of grain boundaries on the surface>

[0146] After the sample was heated by brazing, it was cut into 20mm×30mm pieces, and then ground and milled from the surface of the plate to expose the center of the plate thickness.

[0147] Next, mirror polishing and Parker etching were performed, followed by polarized light observation using a metal microscope. Six fields of view were photographed at 20x magnification, and the crystal structure was observed continuously (parallel to the rolling direction) in six fields of view at 20x magnification.

[0148] Draw 10 lines, each 6 mm in diameter, perpendicular to the rolling direction and spaced 1 mm apart. Count the number of grains on each of the 10 lines and calculate the total number of grains using the following formula:

[0149] The average grain diameter (μm) is calculated by the sum of the number of grains on 10 lines (6000 × 10).

[0150] [Table 1]

[0151]

[0152] [Table 2]

[0153]

[0154] [Table 3]

[0155]

[0156] Casting method CC: Twin-roll continuous casting rolling

[0157] Average grain diameter: The average grain diameter in the direction perpendicular to the rolling direction on the surface of the plate after the heating test.

Claims

1. An aluminum alloy plate, characterized in that, It has the function of heating and bonding a single layer. It is composed of an aluminum alloy containing 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn, with a Cu content of less than 0.20% by mass (inclusive), a Zn content of less than 6.00% by mass (inclusive), and optionally containing one or more of the following: less than 0.08% by mass of Mg, less than 0.30% by mass of Ti, less than 0.30% by mass of Zr, less than 0.30% by mass of Cr, less than 0.30% by mass of V, less than 0.10% by mass of Be, less than 0.10% by mass of Sr, less than 0.30% by mass of Bi, less than 0.10% by mass of Na, and less than 0.05% by mass of Ca, with the balance being Al and unavoidable impurities. In a heating test conducted from 300°C to 400°C at an average heating rate of 60°C / min or less and held at 600±3°C for 5±3 minutes, the cross section perpendicular to the rolling surface and perpendicular to the rolling direction has a region with more than one grain boundary in the thickness direction of 25% or more and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

2. The aluminum alloy plate according to claim 1, characterized in that, In the cross section perpendicular to both the rolling surface and the rolling direction after the heating test, regions with two or more grain boundaries in the thickness direction account for more than 3% of the area in the width direction.

3. The aluminum alloy plate according to claim 1 or 2, characterized in that, In the cross section perpendicular to both the rolling surface and the rolling direction after the heating test, the maximum width of the region with zero grain boundaries in the thickness direction is less than 2000 μm.

4. The aluminum alloy plate according to claim 1 or 2, characterized in that, The plate thickness is less than 0.08mm.

5. The aluminum alloy plate according to claim 3, characterized in that, The plate thickness is less than 0.08mm.

6. A method for manufacturing an aluminum alloy plate, characterized in that, It has the following characteristics: The casting process involves continuously casting and rolling a cast aluminum alloy sheet at a casting speed greater than 0.50 m / min and less than 0.70 m / min. The cast aluminum alloy sheet is composed of an aluminum alloy containing 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn, with a Cu content of less than 0.20% by mass (including 0.00% by mass) and a Zn content of less than 6.00% by mass. Including 0.00% by mass), optionally containing 0.08% by mass or less of Mg, 0.30% by mass or less of Ti, 0.30% by mass or less of Zr, 0.30% by mass or less of Cr, 0.30% by mass or less of V, 0.10% by mass or less of Be, 0.10% by mass or less of Sr, 0.30% by mass or less of Bi, 0.10% by mass or less of Na and 0.05% by mass or less of Ca, with the balance being Al and unavoidable impurities; as well as The cold rolling process involves subjecting the cast and rolled plate to cold rolling at least twice. The process involves at least one annealing treatment between the casting process and the final cold rolling process. The annealing conditions for all annealing processes are annealing temperature of 200–550°C and annealing time of 1–10 hours.

7. A heat exchanger, characterized in that, The heat exchanger has an aluminum alloy tube through which the working fluid flows and aluminum alloy fins that are metal-joined to the tube. The tube is formed using heat exchanger tubing made of aluminum alloy. The fin is formed using an aluminum alloy plate capable of being heat-bonded in a single layer. The aluminum alloy plate is composed of an aluminum alloy containing 2.00–3.00% by mass of Si, 0.05–0.40% by mass of Fe, and 0.80–1.80% by mass of Mn; a Cu content of 0.20% by mass or less (including 0.00% by mass); a Zn content of 6.00% by mass or less (including 0.00% by mass); and optionally containing 0.08% by mass or less of Mg, 0.30% by mass or less of Ti, 0.30% by mass or less of Zr, 0.30% by mass or less of Cr, 0.30% by mass or less of V, 0.10% by mass or less of Be, 0.10% by mass or less of Sr, 0.30% by mass or less of Bi, 0.10% by mass or less of Na, and 0.05% by mass or less of Ca, with the balance being Al and unavoidable impurities. In the cross section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, the region having one or more grain boundaries in the thickness direction accounts for more than 25% and less than 90% in the width direction, and the average grain diameter in the direction perpendicular to the rolling direction on the plate surface is less than 950 μm.

8. The heat exchanger according to claim 7, characterized in that, In the cross section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, there are more than 3% of the regions with two or more grain boundaries in the thickness direction compared to the width direction.

9. The heat exchanger according to claim 7 or 8, characterized in that, In the cross-section of the fin in the direction perpendicular to the rolling surface and in the direction perpendicular to the rolling direction, the maximum width of the region with zero grain boundaries in the thickness direction is less than 2000 μm.

10. A heat exchanger, characterized in that, The heat exchanger has an aluminum alloy tube through which the working fluid flows and aluminum alloy fins that are metal-joined to the tube. The heat exchanger is obtained by combining at least an aluminum alloy heat exchanger tube and an aluminum alloy heat exchanger fin, then heating the resulting assembly to join the heat exchanger tube and the heat exchanger fin. The heat exchanger uses fins formed from the aluminum alloy plate as described in any one of claims 1 to 5.

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