Aluminum alloy sheet and method for producing same

Abstract

This aluminum alloy sheet has: a chemical composition that contains 0.40 mass% to 1.1 mass% inclusive of Si, 0 mass% to 0.70 mass% inclusive of Fe, 0 mass% to 1.1 mass% inclusive of Cu, 0.40 mass% to 1.2 mass% inclusive of Mg, 0 mass% to 0.35 mass% inclusive of Cr, 0 mass% to 0.80 mass% inclusive of Mn, 0 mass% to 0.25 mass% inclusive of Zn, and 0 mass% to 0.15 mass% inclusive of Ti, with the balance being made up of Al and inevitable impurities; a thickness of 0.1 mm to 2.5 mm inclusive; and a 0.2% proof stress of 385 MPa or more.

Description

Aluminum Alloy Sheet and Method for Producing the Same

[0001] The present disclosure relates to an aluminum alloy sheet and a method for producing the same.

[0002] 6000-series aluminum alloy sheets have relatively high strength among aluminum alloys, and are therefore used in various applications such as casings for electronic devices, exterior materials for vehicles, and construction materials.

[0003] For example, Patent Document 1 describes an aluminum alloy body containing 0.1 to 2.0 wt% of silicon and 0.1 to 3.0 wt% of magnesium, wherein at least one of silicon and magnesium is a main alloying element other than aluminum in the aluminum alloy body, the aluminum alloy body contains at least one selected from the group consisting of (A) at least 1.1 wt% of Mg, (B) 0.35 to 2.0 wt% of Cu, and (C) 0.35 to 2.0 wt% of Zn, a majority of the aluminum alloy body is not recrystallized, and the aluminum alloy body achieves a maximum normalized R-value of at least 3.0.

[0004] The aluminum alloy body of Patent Document 1 is obtained by performing a preparation step (a) including a solution treatment step, then performing a cold working step (b) of subjecting the aluminum alloy body to cold working of at least 50%, and further performing a heat treatment step (c) of subjecting the aluminum alloy body to heat treatment.

[0005] Japanese National Publication of International Patent Application No. 2013-542320

[0006] In recent years, further weight reduction of electronic devices, vehicles, and the like has been desired, and from this point of view, it has been desired to reduce the thickness of aluminum alloy sheets while maintaining their high strength.

[0007] The present disclosure has been made in view of such a background, and an object thereof is to provide an aluminum alloy sheet capable of being reduced in thickness while maintaining high strength, and a method for producing the same.

[0008] One aspect of the present disclosure is an aluminum alloy sheet having a chemical composition containing Si (silicon): 0.40% by mass or more and 1.1% by mass or less, Fe (iron): 0% by mass or more and 0.70% by mass or less, Cu (copper): 0% by mass or more and 1.1% by mass or less, Mg (magnesium): 0.40% by mass or more and 1.2% by mass or less, Cr (chromium): 0% by mass or more and 0.35% by mass or less, Mn (manganese): 0% by mass or more and 0.80% by mass or less, Zn (zinc): 0% by mass or more and 0.25% by mass or less, and Ti (titanium): 0% by mass or more and 0.15% by mass or less, with the remainder being Al (aluminum) and unavoidable impurities, a thickness of 0.1 mm or more and 2.5 mm or less, and a 0.2% yield strength of 385 MPa or more.

[0009] Another aspect of the present disclosure is a method for manufacturing an aluminum alloy sheet according to the above-described aspect, comprising: preparing an ingot having the above-described chemical components; performing hot rolling on the ingot when the temperature of the ingot is 490°C or higher at the start of rolling; performing solution treatment on the rolled sheet obtained by the hot rolling by heating and quenching the sheet after which the temperature of the sheet is in the range of 500°C to 580°C for 300 seconds or less; then performing cold rolling on the sheet after cold rolling by heating the sheet after cold rolling for 1 hour to 48 hours when the temperature of the sheet is in the range of 100°C to 220°C.

[0010] According to the above embodiment, it is possible to provide an aluminum alloy sheet and a method for manufacturing the same that can be made thinner while maintaining high strength.

[0011] (Aluminum alloy sheet) The chemical composition, properties, and reasons for limitations of the aluminum alloy sheet will be explained.

[0012] [Chemical Composition] ・Si: 0.40% by mass or more and 1.1% by mass or less The aluminum alloy sheet contains 0.40% by mass or more and 1.1% by mass or less of Si as an essential component. The Si in the aluminum alloy sheet forms a β'' phase together with Mg, and has the effect of improving the strength of the aluminum alloy sheet through precipitation strengthening. By setting the Si content in the aluminum alloy sheet to 0.40% by mass or more, the strength of the aluminum alloy sheet can be further improved.

[0013] Furthermore, in recent years, in order to reduce the environmental impact when manufacturing aluminum alloy sheets, it has been considered to use recovered materials, such as aluminum scrap and used aluminum products, that are recovered during the manufacturing, distribution, and disposal processes of aluminum products, as part of the casting raw materials. By setting the Si content in the aluminum alloy sheet to 0.40% by mass or more, even when recovered materials are used as the casting raw materials for aluminum alloy sheets, the Si content in the aluminum alloy sheet can be easily adjusted to a specific range.

[0014] From the viewpoint of further increasing the strength of the aluminum alloy sheet, the Si content in the aluminum alloy sheet is preferably 0.45% by mass or more, more preferably 0.50% by mass or more, and even more preferably 0.55% by mass or more. If the Si content in the aluminum alloy sheet is less than 0.40% by mass, it may lead to a decrease in the strength of the aluminum alloy sheet.

[0015] On the other hand, if the Si content in the aluminum alloy sheet is excessively high, coarse precipitates are more likely to form in the aluminum alloy sheet, which may lead to a decrease in the bendability of the aluminum alloy sheet. This problem can be easily avoided by setting the Si content in the aluminum alloy sheet to 1.1% by mass or less, preferably 1.0% by mass or less, more preferably 0.90% by mass or less, and even more preferably 0.80% by mass or less.

[0016] In determining the preferred range for the Si content in the aluminum alloy sheet, the aforementioned upper and lower limits for the Si content can be arbitrarily combined. For example, the preferred range for the Si content in the aluminum alloy sheet may be 0.45% by mass or more and 1.0% by mass or less, 0.50% by mass or more and 0.90% by mass or less, or 0.55% by mass or more and 0.80% by mass or less.

[0017] - Fe: 0% by mass or more and 0.70% by mass or less The aluminum alloy sheet may contain 0.70% by mass or less of Fe as an optional component. By keeping the Fe content in the aluminum alloy sheet within the specified range, the formation of coarse precipitates can be easily avoided. As a result, a decrease in the bendability of the aluminum alloy sheet can be easily avoided. Furthermore, in this case, even when using recovered material as a casting raw material for the aluminum alloy sheet, the Fe content in the aluminum alloy sheet can be easily adjusted to within the specified range.

[0018] From the viewpoint of more easily avoiding the formation of coarse precipitates, the Fe content in the aluminum alloy sheet is preferably 0.65% by mass or less, more preferably 0.60% by mass or less, even more preferably 0.55% by mass or less, and particularly preferably 0.50% by mass or less. On the other hand, the Fe content in the aluminum alloy sheet may be, for example, 0.05% by mass or more, or 0.10% by mass or more.

[0019] The preferred range for the Fe content in the aluminum alloy sheet can be any combination of the upper and lower limits of the preferred range for Fe content described above. For example, the preferred range for the Fe content in the aluminum alloy sheet may be 0.05% by mass or more and 0.65% by mass or less, 0.05% by mass or more and 0.60% by mass or less, 0.05% by mass or more and 0.55% by mass or less, or 0.10% by mass or more and 0.50% by mass or less.

[0020] - Cu: 0% by mass or more and 1.1% by mass or less The aluminum alloy sheet may contain 1.1% by mass or less of Cu as an optional component. Cu forms a Q phase together with Mg and Si and has the effect of improving the strength of the aluminum alloy sheet through precipitation strengthening. Therefore, by adding Cu to the aluminum alloy sheet, the strength of the aluminum alloy sheet can be further improved. From the viewpoint of obtaining this effect more reliably, the Cu content in the aluminum alloy sheet is preferably 0.05% by mass or more, and more preferably 0.15% by mass or more. Furthermore, by preferably setting the Cu content to 0.05% by mass or more, and more preferably 0.15% by mass or more, even when using recovered material as a casting raw material for the aluminum alloy sheet, the Cu content in the aluminum alloy sheet can be easily adjusted to the above specific range.

[0021] If the Cu content in the aluminum alloy sheet is excessively high, coarse precipitates are likely to form in the aluminum alloy sheet, which may lead to a decrease in the strength of the aluminum alloy sheet. This problem can be easily avoided by setting the Cu content in the aluminum alloy sheet to 1.1% by mass or less, preferably 1.0% by mass or less, and more preferably 0.90% by mass or less.

[0022] In determining the preferred range for the Cu content in the aluminum alloy sheet, the aforementioned upper and lower limits for the Cu content can be arbitrarily combined. For example, the preferred range for the Cu content in the aluminum alloy sheet may be 0.05% by mass or more and 1.0% by mass or less, or 0.15% by mass or more and 0.90% by mass or less.

[0023] - Mg: 0.40% by mass or more and 1.2% by mass or less The aluminum alloy sheet contains 0.40% by mass or more and 1.2% by mass or less of Mg as an essential component. The Mg in the aluminum alloy sheet forms a β'' phase together with Si and has the effect of improving the strength of the aluminum alloy sheet through precipitation strengthening. By setting the Mg content in the aluminum alloy sheet to 0.40% by mass or more, the strength of the aluminum alloy sheet can be further improved. In this case, even when using recovered material as a casting raw material for the aluminum alloy sheet, the Mg content in the aluminum alloy sheet can be easily adjusted to the above specific range.

[0024] From the viewpoint of further increasing the strength of the aluminum alloy sheet, the Mg content in the aluminum alloy sheet is preferably 0.45% by mass or more, more preferably 0.50% by mass or more, and even more preferably 0.55% by mass or more. If the Mg content in the aluminum alloy sheet is less than 0.40% by mass, it may lead to a decrease in the strength of the aluminum alloy sheet.

[0025] On the other hand, if the Mg content in the aluminum alloy sheet is excessively high, it may lead to a decrease in the conductivity of the aluminum alloy sheet. This problem can be easily avoided by keeping the Mg content in the aluminum alloy sheet to 1.2% by mass or less.

[0026] In determining a preferred range for the Mg content in the aluminum alloy sheet, the aforementioned upper and lower limits for the Mg content can be arbitrarily combined. For example, the Mg content in the aluminum alloy sheet may be 0.45% by mass or more and 1.2% by mass or less, 0.50% by mass or more and 1.2% by mass or less, or 0.55% by mass or more and 1.2% by mass or less.

[0027] - Cr: 0% by mass or more and 0.35% by mass or less The aluminum alloy sheet may contain 0.35% by mass or less of Cr as an optional component. By keeping the Cr content in the aluminum alloy sheet within the specified range, the formation of coarse precipitates can be easily avoided. As a result, a decrease in the strength of the aluminum alloy sheet can be easily avoided. Furthermore, in this case, even when using recovered material as the casting raw material for the aluminum alloy sheet, the Cr content in the aluminum alloy sheet can be easily adjusted to within the specified range.

[0028] From the viewpoint of more easily avoiding the formation of coarse precipitates, the Cr content in the aluminum alloy plate is preferably 0% by mass or more and 0.30% by mass or less, more preferably 0% by mass or more and 0.15% by mass or less, particularly preferably 0% by mass or more and 0.05% by mass or less, and most preferably 0% by mass or more and 0.01% by mass or less.

[0029] - Mn: 0% by mass or more and 0.80% by mass or less The aluminum alloy sheet may contain 0.80% by mass or less of Mn as an optional component. By keeping the Mn content in the aluminum alloy sheet within the specified range, the formation of coarse precipitates can be easily avoided. As a result, a decrease in the bendability of the aluminum alloy sheet can be easily avoided. Furthermore, in this case, even when using recovered material as a casting raw material for the aluminum alloy sheet, the Mn content in the aluminum alloy sheet can be easily adjusted to within the specified range.

[0030] From the viewpoint of more easily avoiding the formation of coarse crystals, the Mn content in the aluminum alloy sheet is preferably 0.60% by mass or less, more preferably 0.45% by mass or less, even more preferably 0.30% by mass or less, and particularly preferably 0.25% by mass or less. On the other hand, the Mn content in the aluminum alloy sheet may be, for example, 0.05% by mass or more, or 0.10% by mass or more.

[0031] The preferred range for the Mn content in the aluminum alloy sheet can be any combination of the upper and lower limits of the preferred range for the Mn content described above. For example, the preferred range for the Mn content in the aluminum alloy sheet may be 0% by mass or more and 0.60% by mass or less, 0.05% by mass or more and 0.45% by mass or less, 0.05% by mass or more and 0.30% by mass or less, or 0.10% by mass or more and 0.25% by mass or less.

[0032] - Zn: 0% by mass or more and 0.25% by mass or less The aluminum alloy sheet may contain 0.25% by mass or less of Zn as an optional component. By keeping the Zn content in the aluminum alloy sheet within the specified range, the formation of coarse precipitates can be easily avoided. As a result, a decrease in the strength of the aluminum alloy sheet can be easily avoided. Furthermore, in this case, even when using recovered material as the casting raw material for the aluminum alloy sheet, the Zn content in the aluminum alloy sheet can be easily adjusted to within the specified range.

[0033] From the viewpoint of more easily avoiding the formation of coarse crystals, the Zn content in the aluminum alloy plate is preferably 0% by mass or more and 0.20% by mass or less, more preferably 0% by mass or more and 0.15% by mass or less, even more preferably 0% by mass or more and 0.10% by mass or less, and particularly preferably 0% by mass or more and 0.05% by mass or less.

[0034] - Ti: 0% by mass or more and 0.15% by mass or less The aluminum alloy sheet may contain 0.15% by mass or less of Ti as an optional component. By keeping the Ti content in the aluminum alloy sheet within the specified range, the formation of coarse precipitates can be easily avoided. As a result, a decrease in the strength of the aluminum alloy sheet can be easily avoided. Furthermore, in this case, even when using recovered material as a casting raw material for the aluminum alloy sheet, the Ti content in the aluminum alloy sheet can be easily adjusted to within the specified range.

[0035] From the viewpoint of more easily avoiding the formation of coarse crystals, the Ti content in the aluminum alloy plate is preferably 0% by mass or more and 0.10% by mass or less, and particularly preferably 0% by mass or more and 0.05% by mass or less.

[0036] From the viewpoint of reducing the thickness of the aluminum alloy sheet while maintaining its high strength, the aluminum alloy sheet may contain Si: 0.40% to 1.1% by mass, Fe: 0% to 0.70% by mass, Cu: 0% to 1.1% by mass, Mg: 0.40% to 1.2% by mass, Mn: 0% to 0.80% by mass, Cr: 0% to 0.35% by mass, and Ti: 0% to 0.15% by mass, with the remainder being Al and unavoidable impurities.

[0037] [Thickness and 0.2% yield strength] The thickness of the aluminum alloy plate is 0.1 mm or more and 2.5 mm or less. The 0.2% yield strength of the aluminum alloy plate is 385 MPa or more. Despite having such a relatively thin thickness, the aluminum alloy plate has a high yield strength of 385 MPa or more. Therefore, by using the aluminum alloy plate, the mass of electronic equipment, vehicles, etc. can be reduced more easily. From the viewpoint of making the aluminum alloy plate thinner while maintaining high strength, the thickness of the aluminum alloy plate is preferably 0.1 mm or more and less than 2.0 mm, more preferably 0.1 mm or more and 1.5 mm or less, even more preferably 0.1 mm or more and 1.0 mm or less, and particularly preferably 0.1 mm or more and 0.8 mm or less.

[0038] [Elongation] The elongation of the aluminum alloy sheet is preferably 6% or more, more preferably 7% or more, and even more preferably 8% or more. In this case, the formability of the aluminum alloy sheet can be further improved.

[0039] (Method for Manufacturing Aluminum Alloy Sheets) The aluminum alloy sheet is obtained, for example, by preparing an ingot having the above chemical components, performing hot rolling on the ingot when the temperature of the ingot is 490°C or higher at the start of rolling, performing solution treatment on the rolled sheet obtained by hot rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 500°C to 580°C is 300 seconds or less, and then performing quenching, after which the rolled sheet is cold-rolled under conditions that the reduction ratio is 40% or higher, and performing artificial aging treatment on the cold-rolled rolled sheet by heating it under conditions that the time the temperature of the rolled sheet is in the range of 100°C to 220°C is 1 hour or more and 48 hours or less. The steps of the above manufacturing method will be described in detail below.

[0040] [Preparation of Ingot] The ingot used to produce the aluminum alloy plate can be obtained by various methods. For example, the ingot may be produced by DC casting or by continuous casting.

[0041] [Hot Rolling] In the above manufacturing method, a rolled sheet is produced by hot rolling the ingot while its temperature is 490°C or higher at the start of rolling. Coarse Mg2Si particles are present in the ingot having the above chemical composition, formed during the process of the ingot's temperature decreasing. If hot rolling and subsequent processes are carried out with the presence of such Mg2Si particles, it becomes difficult to form the β'' phase in the aluminum alloy sheet, which may lead to a decrease in the strength of the aluminum alloy sheet.

[0042] In contrast, by performing hot rolling on the ingot while its temperature is 490°C or higher at the start of rolling, the Mg2Si particles within the ingot can be dissolved in the Al matrix. Then, by performing hot rolling and subsequent processes in this state, a β'' phase can be formed in the aluminum alloy sheet, improving the strength of the aluminum alloy sheet.

[0043] From the viewpoint of more reliably dissolving Mg₂Si particles in the ingot into the solid solution in the Al matrix, the temperature of the ingot at the start of rolling is preferably 500°C or higher, more preferably 510°C or higher, still more preferably 520°C or higher, and particularly preferably 530°C or higher. If the temperature of the ingot at the start of rolling is lower than 490°C, the solid solution of Mg₂Si particles in the Al matrix becomes insufficient, which may lead to a decrease in the strength of the aluminum alloy sheet.

[0044] Further, the temperature of the ingot at the start of rolling is preferably 600°C or lower, more preferably 590°C or lower, still more preferably 580°C or lower, and particularly preferably 570°C or lower. In this case, local melting of the ingot during hot rolling can be more easily avoided, and a sound rolled sheet can be more easily produced.

[0045] The preferred range of the temperature of the ingot at the start of rolling can be any combination of the above-mentioned upper limit and lower limit of the temperature of the ingot. For example, the preferred range of the temperature of the ingot at the start of rolling may be 490°C or higher and 600°C or lower, 500°C or higher and 590°C or lower, 510°C or higher and 580°C or lower, 520°C or higher and 580°C or lower, or 530°C or higher and 570°C or lower.

[0046] When performing hot rolling, the hot rolling may be performed immediately after heating the ingot to a temperature of 490°C or higher, but it is preferable to perform hot rolling after holding the temperature at 490°C or higher for 1 hour or more. By holding the temperature of the ingot for 1 hour or more in this manner, coarse Mg₂Si particles can be sufficiently dissolved as a solid solution in the Al matrix, and the structure of the ingot can be homogenized. As a result, the strength of the aluminum alloy sheet can be more easily improved.

[0047] From the perspective of further enhancing such effects, the holding time of the ingot temperature before hot rolling is preferably 2 hours or more, and more preferably 3 hours or more. From the perspective of sufficiently dissolving Mg₂Si particles into the Al matrix and obtaining the effect of homogenizing the structure of the ingot, there is no upper limit to the holding time at the heating temperature of the ingot before hot rolling. However, from the perspective of further improving the productivity of the aluminum alloy sheet, the holding time of the ingot temperature before hot rolling is preferably, for example, 24 hours or less.

[0048] From the perspective of more easily maintaining the temperature of the ingot at the start of rolling within the aforementioned specific range, the holding temperature for heating the ingot before hot rolling is preferably 500°C or higher and 600°C or lower, more preferably 500°C or higher and 590°C or lower, and still more preferably 500°C or higher and 580°C or lower.

[0049] A rolled sheet is obtained by performing the aforementioned hot rolling. The thickness of the rolled sheet after hot rolling may be appropriately set according to the desired thickness of the aluminum alloy sheet and the reduction ratio in cold rolling after solution treatment. In order to adjust the thickness of the rolled sheet after hot rolling, cold rolling may be performed as necessary between the completion of hot rolling and the start of solution treatment.

[0050] [Solution treatment] In the solution treatment, first, the rolled sheet obtained by the aforementioned hot rolling is heated under the condition that the time during which its temperature is in the range of 500°C or higher and 580°C or lower is 300 seconds or less. Thereby, Mg₂Si particles, other precipitates and crystallized compounds formed in the rolled sheet after hot rolling are dissolved into the Al matrix. Thereafter, the rolled sheet is quenched to form a supersaturated solid solution. In this way, after forming the rolled sheet into a supersaturated solid solution in the solution treatment, cold rolling and artificial aging treatment are performed, thereby forming fine β'' phases in the aluminum alloy sheet and improving the strength of the aluminum alloy sheet.

[0051] If the maximum temperature of the rolled sheet during the solution treatment is too low, it becomes difficult to sufficiently solid-solve the Mg2Si particles and other elements within the sheet. This can lead to a decrease in the strength of the aluminum alloy sheet. Conversely, if the maximum temperature of the rolled sheet during the solution treatment is too high, there is a risk of localized melting of the aluminum alloy sheet due to eutectic melting. From the viewpoint of easily avoiding these problems and more easily obtaining an aluminum alloy sheet with high strength, the maximum temperature of the rolled sheet during the solution treatment is preferably 510°C to 575°C, and more preferably 520°C to 570°C.

[0052] If the heating time of the rolled sheet during the solution treatment, that is, the time from when the temperature of the rolled sheet reaches 500°C until it falls below 500°C, is too long, the productivity of the aluminum alloy sheet may decrease. Furthermore, especially when heating the rolled sheet using a batch furnace, if the heating time of the rolled sheet extends to several hours, distortion and waviness are likely to occur in the rolled sheet, making it difficult to obtain a flat aluminum alloy sheet. By setting the heating time of the rolled sheet during the solution treatment to 300 seconds or less, preferably 200 seconds or less, more preferably 120 seconds or less, even more preferably 100 seconds or less, particularly preferably 80 seconds or less, and most preferably 60 seconds or less, these problems can be easily avoided, and the aluminum alloy sheet can be obtained.

[0053] From the viewpoint of sufficiently solid-solving the Mg2Si particles and the like present in the rolled sheet, the heating time of the rolled sheet in the solution treatment is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more.

[0054] In determining the preferred range for the heating time of the rolled sheet in the solution treatment, the aforementioned upper and lower limits of heating time can be arbitrarily combined. For example, the preferred range for the heating time of the rolled sheet in the solution treatment may be 10 seconds or more and 300 seconds or less, 10 seconds or more and 200 seconds or less, 10 seconds or more and 120 seconds or less, 10 seconds or more and 100 seconds or less, 20 seconds or more and 80 seconds or less, or 30 seconds or more and 60 seconds or less.

[0055] In the solution treatment process, it is preferable to heat the rolled sheet using a continuous annealing line. The continuous annealing line includes a conveying device for transporting strips of rolled sheet and a heating furnace positioned along the strip's travel path, and is configured to allow continuous heating of the rolled sheet in the heating furnace. By heating the rolled sheet using a continuous annealing line, the temperature of the rolled sheet can be reliably heated to the desired temperature in a short time. As a result, the productivity of the aluminum alloy sheet can be increased, and rolled sheets with less distortion and waviness can be easily obtained.

[0056] The quenching method in solution treatment is not particularly limited and can take various forms. For example, in solution treatment, quenching can be performed by known cooling methods such as fan cooling, mist cooling, and shower cooling.

[0057] [Preliminary Aging Treatment] In the above manufacturing method, a preliminary aging treatment may be performed after the solution treatment is completed and before the cold rolling is performed. In the preliminary aging treatment, it is preferable to heat the rolled sheet within 10 minutes from the time when the temperature of the rolled sheet falls below 500°C in the solution treatment, under conditions that the time during which the temperature of the rolled sheet is in the range of 50°C to 140°C is 1 hour or more. By performing a preliminary aging treatment under these specific conditions between the completion of the solution treatment and the cold rolling, an aluminum alloy sheet with high strength can be obtained more reliably.

[0058] [Cold Rolling] In the above manufacturing method, the rolled sheet after solution treatment is cold-rolled under conditions that result in a reduction ratio of 40% or more. By cold-rolling under such conditions, appropriate strain is introduced into the rolled sheet, and the strength of the aluminum alloy sheet can be improved by work hardening. If the reduction ratio in cold rolling is too low, it may lead to a decrease in the strength of the aluminum alloy sheet. From the viewpoint of further increasing the strength of the aluminum alloy sheet, the reduction ratio in cold rolling is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more.

[0059] [Artificial Aging Treatment] In artificial aging treatment, the rolled sheet after cold rolling is heated under conditions that the temperature of the rolled sheet is within the range of 100°C to 220°C for 1 hour to 48 hours. By performing artificial aging treatment under these specific conditions, elements that are in a supersaturated state of solid solution in the rolled sheet are precipitated, and a fine β'' phase can be formed. As a result, an aluminum alloy sheet with high strength can be obtained.

[0060] From the viewpoint of more easily obtaining aluminum alloy sheets with high strength, the maximum temperature of the rolled sheet in the artificial aging treatment is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 130°C or higher. If the maximum temperature of the rolled sheet in the artificial aging treatment is too low, it becomes difficult to sufficiently precipitate the β'' phase, which may lead to a decrease in the strength of the aluminum alloy sheet.

[0061] On the other hand, if the maximum temperature of the rolled sheet during artificial aging is too high, it can lead to over-aging, which may actually decrease the strength of the aluminum alloy sheet. This problem can be easily avoided by setting the maximum temperature of the rolled sheet during artificial aging to 220°C or lower, preferably 200°C or lower, and more preferably 180°C or lower.

[0062] In determining the preferred range for the maximum temperature of the rolled sheet during artificial aging, the aforementioned upper and lower limits of the maximum temperature can be arbitrarily combined. For example, the preferred range for the maximum temperature of the rolled sheet during artificial aging may be 110°C to 220°C, 120°C to 200°C, or 130°C to 180°C.

[0063] Examples of the aluminum alloy sheet and its manufacturing method will now be described. The aluminum alloy sheet in this example has a chemical composition containing Si: 0.40% to 1.1% by mass, Fe: 0% to 0.70% by mass, Cu: 0% to 1.1% by mass, Mg: 0.40% to 1.2% by mass, Cr: 0% to 0.35% by mass, Mn: 0% to 0.80% by mass, Zn: 0% to 0.25% by mass, and Ti: 0% to 0.15% by mass, with the remainder being Al and unavoidable impurities, a thickness of 0.1 mm to 2.5 mm, and a 0.2% yield strength of 385 MPa or more.

[0064] Furthermore, the aluminum alloy sheet in this example is obtained by preparing an ingot having the above chemical composition, performing hot rolling on the ingot when the temperature of the ingot is 490°C or higher at the start of rolling, performing solution treatment on the rolled sheet obtained by hot rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 500°C to 580°C is 300 seconds or less, and then performing quenching, after which the rolled sheet is cold-rolled under conditions that the reduction ratio is 40% or higher, and performing artificial aging treatment on the cold-rolled rolled sheet by heating it under conditions that the time the temperature of the rolled sheet is in the range of 100°C to 220°C is 1 hour or more and 48 hours or less.

[0065] Tables 1 to 4 show specific examples of the aluminum alloy sheets used in this example. The manufacturing methods for these aluminum alloy sheets are as follows.

[0066] (Test materials A1 to A4) Test materials A1 to A4 have a chemical composition containing Si: 0.68 mass%, Fe: 0.26 mass%, Cu: 0.30 mass%, Mg: 1.02 mass%, Cr: 0.17 mass%, Mn: 0.07 mass%, Zn: 0.003 mass%, and Ti: 0.006 mass%, with the remainder being Al and unavoidable impurities. The thickness, tensile strength, 0.2% yield strength, and elongation of test materials A1 to A4 are shown in Table 1.

[0067] The methods for measuring the tensile strength, 0.2% proof stress, and elongation of the test material are as follows: First, a No. 5 test specimen, as specified in JIS Z2241:2011, is taken from each test material, with its longitudinal direction parallel to the rolling direction. A tensile test is then performed using this specimen according to the method specified in JIS Z2241:2011. The tensile strength, 0.2% proof stress, and elongation are then obtained based on the load-displacement curve obtained from the tensile test.

[0068] In preparing test materials A1 to A4, first, ingots having the aforementioned chemical composition are prepared by DC casting. Next, the ingots are heated by holding them at a temperature of 560°C for 6 hours, and then hot-rolled to produce rolled plates. The temperature of the ingot at the start of rolling is set at 540°C.

[0069] Next, cold rolling is performed to reduce the thickness of the rolled sheet to 0.75 mm. This rolled sheet is then immersed in a saltpeter bath and heated. After removing the rolled sheet from the saltpeter bath, it is immediately quenched to perform solution treatment. The maximum temperature of the rolled sheet during the solution treatment is 550°C. The heating time during the solution treatment, that is, the time from when the temperature of the rolled sheet reaches 500°C until the temperature of the rolled sheet falls below 500°C, is 25 seconds.

[0070] After the solution treatment is complete, the rolled sheet is left to stand for two days in a room maintained at approximately 20°C. During this standing period, natural aging occurs, and the strength of the rolled sheet increases compared to before standing. Subsequently, the rolled sheet is cold-rolled to a reduction ratio shown in Table 1, reducing the thickness of the rolled sheet to the values ​​shown in Table 1. After cold rolling, the rolled sheet is heated in a heating furnace and subjected to artificial aging treatment to obtain test materials A1 to A4. The maximum temperature of the rolled sheet during artificial aging treatment is set at 140°C. The heating time during artificial aging treatment, that is, the time from when the temperature of the rolled sheet reaches 100°C until the temperature of the rolled sheet falls below 100°C, is set at 17 hours.

[0071] (Test specimens A5-A6) Test specimens A5-A6 have the same configuration as test specimens A1-A4, except that they have the thickness, tensile strength, 0.2% yield strength, and elongation shown in Table 1. The method for preparing test specimens A5-A6 is the same as the method for preparing test specimens A1-A4, except that the thickness of the rolled sheet obtained by cold rolling after hot rolling, the period of resting of the rolled sheet after solution treatment, the thickness of the rolled sheet obtained by cold rolling after solution treatment, and the heating conditions in artificial aging treatment are changed as shown in Table 1.

[0072] (Test specimens A7-A8) Test specimens A7-A8 have the same structure as test specimens A5-A6, except that they have the tensile strength, 0.2% yield strength, and elongation shown in Table 1. The method for preparing test specimens A7-A8 is the same as that for test specimens A5-A6, except that the rolled sheet after solution treatment is left to stand for 8 days in a room maintained at approximately 5°C before cold rolling.

[0073] (Test specimens A9-A10) Test specimens A9-A10 have the same structure as test specimens A5-A6, except that they have the tensile strength, 0.2% yield strength, and elongation shown in Table 1. The method for preparing test specimens A9-A10 is the same as that for test specimens A5-A6, except that the rolled sheet after solution treatment is left to stand for 8 days in a room maintained at approximately 40°C before being cold-rolled.

[0074] (Test specimens B1 to B12) Test specimens B1 to B12 have the same chemical composition as test specimens A1 to A10. The thickness, tensile strength, 0.2% yield strength, and elongation of test specimens B1 to B12 are shown in Tables 2 and 3.

[0075] In preparing test materials B1 to B12, first, ingots having the aforementioned chemical composition are prepared by DC casting. Next, the ingots are heated by holding them at a temperature of 560°C for 6 hours, and then hot-rolled to produce rolled plates. The temperature of the ingot at the start of rolling is set at 540°C.

[0076] Next, cold rolling is performed to reduce the thickness of the rolled sheet to 1.5 mm. This rolled sheet is then immersed in a saltpeter bath and heated. After removing the rolled sheet from the saltpeter bath, it is immediately quenched to perform solution treatment. The maximum temperature of the rolled sheet during the solution treatment is 550°C, and the heating time is 30 seconds.

[0077] After the solution treatment is complete, the rolled plates are heated in a heating furnace for pre-aging treatment. The maximum temperature of the rolled plates during pre-aging treatment shall be 90°C. The heating time during pre-aging treatment, that is, the time from when the temperature of the rolled plates reaches 50°C until the temperature of the rolled plates falls below 50°C, shall be 15 hours.

[0078] After the preliminary aging treatment is completed, the rolled plates are left to stand for 8 days in a room maintained at approximately 20°C. During this standing period, natural aging occurs, and the strength of the rolled plates increases compared to before standing. Subsequently, the rolled plates are cold-rolled to the reduction ratio shown in Tables 2 and 3, reducing the thickness of the rolled plates to the values ​​shown in Tables 2 and 3. After cold rolling, the rolled plates are heated under the heating conditions shown in Tables 2 and 3 to perform artificial aging treatment, thereby obtaining test materials B1 to B12.

[0079] (Test specimens B13-B14) Test specimens B13-B14 have the same structure as test specimens B1-B2, except that they have the tensile strength, 0.2% yield strength, and elongation shown in Table 3. The method for preparing test specimens B13-B14 is the same as the method for preparing test specimens B1-B2, except that the rolled plates after preliminary aging treatment are left to stand for 8 days in a room maintained at approximately 5°C before being cold-rolled.

[0080] (Test specimens B15-B16) Test specimens B15-B16 have the same structure as test specimens B1-B2, except that they have the tensile strength, 0.2% yield strength, and elongation shown in Table 3. The method for preparing test specimens B15-B16 is the same as the method for preparing test specimens B1-B2, except that the rolled sheet after preliminary aging is left to stand for 8 days in a room maintained at approximately 40°C before cold rolling.

[0081] (Test materials C1-C2) Test materials C1-C2 are test materials for comparison with test materials A1-A10 and test materials B1-B16. Test materials C1-C2 have a chemical composition containing Si: 0.7 mass%, Fe: 0.37 mass%, Cu: 0.32 mass%, Mg: 1.1 mass%, Cr: 0.18 mass%, Mn: 0.06 mass%, Zn: 0.03 mass%, and Ti: 0.01 mass%, with the remainder being Al and unavoidable impurities. The thickness, tensile strength, 0.2% yield strength, and elongation of test materials C1-C2 are shown in Table 3.

[0082] In preparing test materials C1 to C2, first, ingots having the aforementioned chemical composition are prepared by DC casting. Next, the ingots are heated by holding them at a temperature of 490°C for more than one hour, and then hot-rolled to produce rolled plates. The temperature of the ingot at the start of rolling is set at 485°C.

[0083] Next, cold rolling is performed to reduce the thickness of the rolled sheet to 3 mm. After heating the rolled sheet using a continuous annealing line, solution treatment is performed by quenching the rolled sheet at the outlet of the heating furnace of the continuous annealing line. The maximum temperature of the rolled sheet during the solution treatment is 550°C, and the heating time is 50 seconds.

[0084] After the solution treatment is complete, the rolled sheet is heated in a heating furnace for pre-aging treatment. The maximum temperature of the rolled sheet during pre-aging treatment is 80°C, and the heating time is 12 hours.

[0085] After the preliminary aging treatment is completed, the rolled sheet is left to stand in a room maintained at approximately 20°C for more than one month. During this standing period, natural aging occurs, and the strength of the rolled sheet after standing increases compared to before standing. Subsequently, the rolled sheet is cold-rolled to a reduction ratio of 90%, reducing the thickness of the rolled sheet to 0.3 mm. After cold rolling, the rolled sheet is heated under the heating conditions shown in Table 3 to perform artificial aging treatment, thereby obtaining test materials C1 to C2.

[0086] (Test materials D1 to D4) Test materials D1 to D4 have a chemical composition containing Si: 0.65 mass%, Fe: 0.16 mass%, Cu: 0.80 mass%, Mg: 0.75 mass%, Cr: less than 0.01 mass%, Mn: 0.12 mass%, Zn: less than 0.01 mass%, and Ti: 0.01 mass%, with the remainder being Al and unavoidable impurities. The thickness, tensile strength, 0.2% yield strength, and elongation of test materials D1 to D4 are shown in Table 4.

[0087] In preparing test materials D1 to D4, first, ingots having the aforementioned chemical composition are prepared by DC casting. Next, the ingots are heated by holding them at a temperature of 560°C for 6 hours, and then hot-rolled to produce rolled plates. The temperature of the ingot at the start of rolling is set at 540°C.

[0088] Next, cold rolling is performed to reduce the thickness of the rolled sheet to 0.75 mm. This rolled sheet is then immersed in a saltpeter bath and heated. After removing the rolled sheet from the saltpeter bath, it is immediately quenched to perform solution treatment. The maximum temperature of the rolled sheet during the solution treatment is 550°C, and the heating time is 25 seconds.

[0089] After the solution treatment is complete, the rolled sheet is left to stand for two days in a room maintained at approximately 20°C. During this standing period, natural aging occurs, and the strength of the rolled sheet increases compared to before standing. Subsequently, the rolled sheet is cold-rolled to the reduction ratio shown in Table 4, reducing the thickness of the rolled sheet to the value shown in Table 4. After cold rolling, the rolled sheet is heated in a heating furnace and subjected to artificial aging treatment to obtain test materials D1 to D4. The maximum temperature of the rolled sheet during artificial aging treatment is 140°C, and the heating time is 17 hours.

[0090] (Test materials E1 to E3) Test materials E1 to E3 are test materials for comparison with test materials D1 to D4. Test materials E1 to E3 have a chemical composition containing Si: 0.65 mass%, Fe: 0.15 mass%, Cu: 0.80 mass%, Mg: 0.75 mass%, Cr: less than 0.01 mass%, Mn: 0.12 mass%, Zn: less than 0.01 mass%, and Ti: 0.03 mass%, with the remainder being Al and unavoidable impurities. The thickness, tensile strength, 0.2% yield strength, and elongation of test materials E1 to E3 are shown in Table 4.

[0091] In preparing test materials E1 to E3, first, ingots having the aforementioned chemical composition are prepared by DC casting. Next, the ingots are subjected to a homogenization treatment by holding them at a temperature of 540°C for 12 hours. After the homogenization treatment, the ingots are cooled to room temperature, and then heated by holding them at a temperature of 480°C for 3 hours. Then, hot rolling is performed on the ingots immediately after heating to produce rolled plates. The temperature of the ingots at the start of rolling is 480°C.

[0092] Next, the rolled sheet is held at 400°C for 1 hour for intermediate annealing. After intermediate annealing, the rolled sheet is cold-rolled to reduce its thickness to 1 mm. This rolled sheet is then immersed in a saltpeter bath and heated. The rolled sheet is then immediately quenched after being removed from the saltpeter bath for solution treatment. The maximum temperature of the rolled sheet during the solution treatment is 550°C, and the heating time is 30 seconds.

[0093] After the solution treatment is complete, the rolled sheet is left to stand for several days in a room maintained at approximately 20°C. During this standing period, natural aging occurs, causing the strength of the rolled sheet to increase compared to before standing. Subsequently, the rolled sheet is cold-rolled to a reduction ratio shown in Table 4, reducing the thickness of the rolled sheet to the values ​​shown in Table 4. After cold rolling, the rolled sheet is heated in a furnace and subjected to artificial aging treatment to obtain test materials E1 to E3. The maximum temperature of the rolled sheet during artificial aging treatment is 180°C, and the heating time is 6 hours.

[0094] (Test specimens E4-E5) Test specimens E4-E5 are test specimens for comparison with test specimens D1-D4. Test specimens E4-E5 have the same configuration as test specimens E2-E3, except that they have the thickness, tensile strength, 0.2% yield strength, and elongation shown in Table 4. The method for preparing test specimens E4-E5 is the same as the method for preparing test specimens E2-E3, except that the rolled plates after solution treatment are subjected to pre-aging treatment under the heating conditions shown in Table 4.

[0095]

[0096]

[0097]

[0098]

[0099] As shown in Tables 1 to 4, test materials A1 to A10, B1 to B16, and D1 to D4 are manufactured by the specified manufacturing method described above. Therefore, these test materials can be made thin while maintaining high strength. In addition, these test materials have high flatness and exhibit little waviness or distortion.

[0100] In contrast, as shown in Table 3, in the manufacturing process of test materials C1 to C2, hot rolling is performed at a temperature lower than the specified range of the ingot. Therefore, the 0.2% yield strength of test materials C1 to C2 is lower than that of test materials A1 to A10 and test materials B1 to B16.

[0101] Furthermore, in the manufacturing process of test materials E1 to E5, the ingots are cooled to room temperature after homogenization. As shown in Table 4, the heating temperature when the ingots are reheated is too low, resulting in the ingot temperature at the start of hot rolling being lower than the specified range. Therefore, the 0.2% yield strength of test materials E1 to E5 is lower than that of test materials D1 to D4.

[0102] Although embodiments of the aluminum alloy plate and its manufacturing method have been described above based on the examples, the specific embodiments of the aluminum alloy plate and its manufacturing method described herein are not limited to those described in the examples, and the configuration can be modified as appropriate without impairing the spirit of this disclosure.

[0103] For example, the aluminum alloy sheet relating to this disclosure may take the following forms [1] to [3].

[0104] [1] An aluminum alloy sheet having a chemical composition containing Si: 0.40% by mass or more and 1.1% by mass or less, Fe: 0% by mass or more and 0.70% by mass or less, Cu: 0% by mass or more and 1.1% by mass or less, Mg: 0.40% by mass or more and 1.2% by mass or less, Cr: 0% by mass or more and 0.35% by mass or less, Mn: 0% by mass or more and 0.80% by mass or less, Zn: 0% by mass or more and 0.25% by mass or less, and Ti: 0% by mass or more and 0.15% by mass or less, with the remainder being Al and unavoidable impurities, a thickness of 0.1 mm or more and 2.5 mm or less, and a 0.2% yield strength of 385 MPa or more.

[0105] [2] The aluminum alloy sheet according to [1], wherein the thickness of the aluminum alloy sheet is 0.1 mm or more and less than 2.0 mm. [3] The aluminum alloy sheet according to [1] or [2], having an elongation of 6% or more.

[0106] Furthermore, the method for manufacturing an aluminum alloy sheet according to this disclosure may take the forms described in [4] to [7] below.

[0107] A method for manufacturing an aluminum alloy sheet according to any one of [4] [1] to [3], comprising: preparing an ingot having the chemical components; performing hot rolling on the ingot when the temperature of the ingot is 490°C or higher at the start of rolling; performing solution treatment on the rolled sheet obtained by the hot rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 500°C to 580°C is 300 seconds or less, and then quenching it; then performing cold rolling on the rolled sheet under conditions that the reduction ratio is 40% or higher; and performing artificial aging treatment on the rolled sheet after cold rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 100°C to 220°C is 1 hour or more and 48 hours or less.

[0108] [5] The method for manufacturing an aluminum alloy sheet according to [4], wherein the ingot is held at a temperature of 490°C or higher for one hour or more before hot rolling. [6] The method for manufacturing an aluminum alloy sheet according to [4] or [5], wherein the rolled sheet is heated using a continuous annealing line in the solution treatment. [7] The method for manufacturing an aluminum alloy sheet according to any one of [4] to [6], wherein the rolled sheet is heated within 10 minutes from the time the temperature of the rolled sheet falls below 500°C in the solution treatment, under the condition that the time the temperature of the rolled sheet is in the range of 50°C to 140°C for one hour or more, and then cold rolling is performed.

Claims

1. An aluminum alloy sheet having a chemical composition containing Si: 0.40% to 1.1% by mass, Fe: 0% to 0.70% by mass, Cu: 0% to 1.1% by mass, Mg: 0.40% to 1.2% by mass, Cr: 0% to 0.35% by mass, Mn: 0% to 0.80% by mass, Zn: 0% to 0.25% by mass, and Ti: 0% to 0.15% by mass, with the remainder being Al and unavoidable impurities; a thickness of 0.1 mm to 2.5 mm; and a 0.2% yield strength of 385 MPa or more.

2. The aluminum alloy plate according to claim 1, wherein the thickness of the aluminum alloy plate is 0.1 mm or more and less than 2.0 mm.

3. The aluminum alloy sheet according to claim 1, having an elongation of 6% or more.

4. A method for manufacturing an aluminum alloy sheet according to any one of claims 1 to 3, comprising: preparing an ingot having the chemical components; performing hot rolling on the ingot when the temperature of the ingot is 490°C or higher at the start of rolling; performing solution treatment on the rolled sheet obtained by the hot rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 500°C to 580°C is 300 seconds or less, and then quenching it; then performing cold rolling on the rolled sheet under conditions that the reduction ratio is 40% or higher; and performing artificial aging treatment on the rolled sheet after cold rolling by heating it under conditions that the time the temperature of the rolled sheet is in the range of 100°C to 220°C is 1 hour or more and 48 hours or less.

5. The method for manufacturing an aluminum alloy sheet according to claim 4, wherein the ingot is held at a temperature of 490°C or higher for one hour or more before hot rolling is performed.

6. The method for manufacturing an aluminum alloy sheet according to claim 4, wherein the rolled sheet is heated using a continuous annealing line in the solution treatment.

7. A method for manufacturing an aluminum alloy sheet according to claim 4, wherein, within 10 minutes from the time when the temperature of the rolled sheet falls below 500°C in the solution treatment, the rolled sheet is heated under conditions that the time during which the temperature of the rolled sheet is in the range of 50°C to 140°C is 1 hour or more, thereby performing a preliminary aging treatment, and then cold rolling is performed.

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