Architectural aluminum alloy material and process for manufacturing the same

Abstract

There is provided an architectural Al alloy material which undergoes minor loss of proof stress even after a baking finish treatment at a high temperature of 260 to 280° C. and which can be subjected to acute-angle bending, as well as, a process for manufacturing the same. This architectural Al alloy material, which is a hot rolled JIS A3003 material, contains a fiber structure and a recrystallized grain structure having an area ratio of 20 % or less after a baking finish treatment at 300° C. or lower, and undergoes a proof stress loss of 10% or less after the baking finish treatment. The Al alloy material is manufactured only by hot rolling which is carried out under control such that the temperature at the end of rolling be in the range of 290 to 340° C.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an architectural aluminum (Al) alloy material and a process for manufacturing the same. More specifically, the present invention relates to an architectural Al alloy material, which is to be put into practical uses as a building material with the premise that it is subjected to a baking finish treatment in a high temperature region of 260 to 280° C. and which undergoes minor loss of proof stress and retains sufficient elongation even after the baking finish treatment to show excellent bendability, as well as, to a process for manufacturing the same.

[0003] 2. Prior Art

[0004] Since Al alloy materials are light, they are used as exterior wall materials and interior finishing materials for high-rise buildings or as curtain wall materials.

[0005] In such cases, an Al alloy plate 1 is subjected to 90-degree bending, for example, as shown in FIG. 1. These days, acute-angle bending is on the increase to bend Al alloy plates by beyond 90° (&thgr;>90°), as shown in FIG. 2. In such acute-angle bending treatments, it is pursued to enhance ornamental design by forming a sharp bend 2. An example of bending treatment is shown in FIG. 3, in which a notch 3 is formed on an Al alloy material 1, and the alloy material 1 is bent along this notch 3.

[0006] Before the Al alloy material 1 is bent as described above, it is subjected to a baking finish treatment using a coating material such as a fluorine coat, an acrylic resin coating and a urethane resin coating at a predetermined temperature so as to enhance decorative design and corrosion resistance of the material 1.

[0007] Those architectural Al alloy materials practically used according to such a mode are required to show the following performances:

[0008] First, since they are building materials, they should show appropriate strength properties even after application. More specifically, in the case where an Al alloy material is used as an exterior wall material for buildings, it is required to have a proof stress of 95 N/mm2 or more even after application.

[0009] Further, they are required to have appropriate elongation properties to enhance smooth bending treatment and form sharp angles at bends.

[0010] As architectural Al alloy materials, for example, A3004-H24 (3004 defined by B209 of ASTM) and A3004-H32 (3004 defined by B209 of ASTM) materials have conventionally been used, primarily in view of their strength properties.

[0011] In manufacturing such materials, an Al alloy material of predetermined specifications is melted first to form an ingot thereof. The ingot is then subjected to a soaking treatment at a predetermined temperature for a predetermined time, followed by a hot rolling treatment at a predetermined processing rate.

[0012] In this hot rolling process, the solidification structure of the ingot is converted into a fiber structure as it is rolled out in the rolling direction.

[0013] Subsequently, the resulting rolled alloy material is subjected to cold rolling to effect finely dividing of the crystal grains and thickness adjustment, and after the alloy material is annealed to remove processing strain, it is subjected again to cold rolling and heat treatment for removing the strain occurred in the cold rolling. The thus treated Al alloy material is used in practical applications.

[0014] Here, in the series of steps in the manufacturing process described above, rolling strains accumulate in the workpiece at the end of the hot rolling treatment and cold rolling treatment. When the resulting workpiece is then heated to a temperature not lower than the recrystallization temperature thereof, the energy of processing strain triggers growth of grains of recrystallization in the structure. Each grain of the recrystallized structure usually does not assume the form of fiber but of a grain of a certain size.

[0015] The A3004-H24 material and the like described above are those which are all subjected finally to the cold rolling treatment, so that they have finely divided grains of recrystallized structure. In addition, fiber structures remain in these materials, so that they can be subjected to sharp 90-degree bending.

[0016] When they are subjected to more than 90-degree acute-angle bending and cracking occurs at the bends of the alloy materials, the cracked portions are mended by welding.

OBJECT AND SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to provide an architectural Al alloy material used as a building material on the premise that it is subjected to baking finish treatment, wherein cracking does not occur even when it is subjected to sharp bending or acute-angle bending, since it undergoes minor loss of the proof stress and also has appropriate elongation properties even after the baking finish treatment, and to provide a process for manufacturing it.

[0018] In order to attain the above object, the present invention provides an architectural Al alloy material, which is a hot rolled material defined by JIS A3003 (3003 defined by B209 of ASTM); the material containing, in terms of a structure after a baking finish treatment at a temperature of not higher than 300° C., a fiber structure and a recrystallized grain structure having an area ratio of 20% or less; wherein the material undergoes a proof stress loss of 10% or less after the baking finish treatment.

[0019] The present invention also provides a process for manufacturing an architectural Al alloy material including the steps of subjecting an ingot of JIS A3003 (3003 defined by B209 of ASTM) to a soaking treatment; and subjecting the resulting ingot to hot rolling to be carried out in such a way that it has a temperature of 290 to 340° C. at the end of rolling; wherein the thus treated ingot is as such applied to a practical use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a schematic drawing showing 90-degree bending of a plate material;

[0021] FIG. 2 is a schematic drawing showing acute-angle bending of a plate material;

[0022] FIG. 3 is a schematic drawing showing 90-degree bending of a notched plate material;

[0023] FIG. 4 shows a photomicrographic structure of a plate material in Example 9;

[0024] FIG. 5 shows a photomicrographic structure of a plate material in Comparative Example 8;

[0025] FIG. 6 is a schematic view of a plate material bent at right angles to the rolling direction; and

[0026] FIG. 7 is a schematic view of a plate material bent parallel to the rolling direction.

DETAILED DESCRIPTION

[0027] The Al alloy material according to the present invention is prepared merely by subjecting an A3003 material having excellent strength properties to a hot rolling treatment under the conditions to be described later and is put into practical uses directly after the treatment. In other words, unlike the conventional Al alloy materials, the alloy material of the present invention is not manufactured by going through the hot rolling, followed by cold rolling, process annealing, cold rolling and heat treatment.

[0028] The Al alloy material of the present invention is manufactured typically as follows:

[0029] First, an A3003 material having a predetermined composition is melted to form an ingot thereof. The ingot is then subjected to soaking and then to hot rolling.

[0030] The soaking treatment is preferably carried out in a temperature range of 500 to 630° C. for about 1 to 15 hours. If the soaking treatment is carried out at a temperature of lower than 500° C., intermetallic compounds containing substantially, for example, AlMn decreases in quantity, and grains of recrystallized structure growing from the solidification structure are coarsened, to be likely to cause drop in bendability of the material and to mar appearance thereof. Further, if the soaking treatment is carried out at a temperature of higher than 630° C., deformation, blisters and the like occur in the ingot, which are causative of structural defects in the subsequent step (hot rolling). Therefore, the soaking treatment is carried out preferably at a temperature of 600 to 630° C.

[0031] Meanwhile, if the soaking treatment is carried out for less than one hour, the ingot cannot be soaked entirely, making it difficult to carry out homogeneous hot rolling. On the other hand, even if the soaking treatment is carried out for more than 15 hours, the soaking effect is saturated, and it is nothing but waste of thermal energy, uneconomically. The soaking treatment is desirably carried out for 2 to 6 hours.

[0032] The ingot having undergone the soaking treatment as described above is then subjected immediately to hot rolling, where the solidification structure of the ingot is converted to a fiber structure and also finely divided secondary structure (subgrains) is caused to grow.

[0033] The A3003 material according to the present invention can be put into practical uses as a building material directly after completion of the hot rolling treatment. Therefore, at the point when the material is put into a practical use, the thus hot-rolled A3003 material assumes substantially the fiber structure formed by the rolling treatment and has a predetermined amount of finely divided secondary structure dispersed therein.

[0034] This A3003 material having the structure as described above exhibits the following effects:

[0035] For example, in carrying out acute-angle bending, if the material has the fiber structure only, cracking or the like can occur at the bend along the grain boundary of the fiber structure. However, the A3003 material of the present invention contains the finely divided secondary structure, so that such cracking can be prevented from occurring. In other words, the material ensures acute-angle bending.

[0036] In addition, in the case of the A3003 material, even if it is subjected to a baking finish treatment at a high temperature of 300° C. or lower, more typically at 260 to 280° C., % loss of proof stress after the baking finish treatment is controlled to 10% or less. Even after the baking finish treatment of the material, it secures an absolute proof stress value of 95 N/mm2 or more, satisfying requirements for the exterior wall material for buildings. Besides, elongation of the material is increased to 27% or more, enabling excellent bending treatment.

[0037] The properties described above, particularly that % loss of proof stress after the baking finish treatment is controlled to 10% or less are the effects to be brought about by the finely divided structure and the fiber structure coexisting in the material. This secondary structure naturally grows into recrystallized grain structure during the baking finish treatment at a high temperature to have increased diameters respectively, and also the quantity of precipitated crystal grains thereof increases.

[0038] However, in the case of the A3003 material according to the present invention, it is controlled so that it contains the recrystallized grain structure in an amount of not more than 20% of the entire structure in terms of area ratio even after the baking finish treatment, and that the rest remains as the fiber structure. Thus, loss of proof stress to be caused by the baking finish treatment can be held within 10%.

[0039] Such attribute can be realized by controlling the hot rolling treatment such that the temperature of the workpiece be in the range of 290 to 340° C. at the end of the treatment.

[0040] If the temperature at the end of rolling is higher than 340° C., the workpiece comes to have an elongation of about 35%. However, it is substantially of the recrystallized grain structure, which causes rough surface at the bend.

[0041] Meanwhile, if the temperature at the end of rolling is lower than 290° C., the finely divided secondary structure to be formed decreases in quantity, and the elongation becomes smaller than 27%, inducing cracking in acute-angle bending.

[0042] In order to control the temperature at the end of rolling to be in the range of 290 to 340° C., the temperature at the beginning of rolling is set to be in the range of 350 to 450° C.

[0043] A temperature at the beginning of rolling of lower than 350° C. cannot secure a temperature of 290° C. or higher at the end of rolling. This can increase the strength but reduces elongation, causing cracking and the like in bending.

[0044] Meanwhile, if the temperature at the beginning of rolling is higher than 450° C., it is difficult to attain a temperature of 340° C. or lower at the end of rolling. At the end of rolling, coarse grains of recrystallized structure predominate the material to cause rough surface at a bend in a bending treatment. In addition, the resulting workpiece comes to have a proof stress of smaller than 95 N/mm2.

EXAMPLE

Examples 1 to 16, Comparative Examples 1 to 9

[0045] (1) Al Alloy Material

[0046] Al alloy materials were melted to form ingots thereof respectively (thickness: 500 mm). The materials had the following compositions respectively:

[0047] A3003 Material:

[0048] Si: 0.58 mass %; Fe: 0.68 mass %; Cu: 0.18 mass %; Mn: 1.48 mass %; Mg: 0.02 mass %; Zn: 0.09 mass %; Al and unavoidable impurities: q.s.

[0049] A3004 Material:

[0050] Si: 0.58 mass %; Fe: 0.68 mass %; Cu: 0.20 mass %; Mn: 1.48 mass %; Mg: 1.01 mass %; Zn: 0.23 mass %; Al and unavoidable impurities: q.s.

[0051] (2) Formation of Plate Material

[0052] Plate materials each having a thickness as shown in Table 1 were made according to the methods having the following conditions respectively:

[0053] Process of the Invention (A):

[0054] Each ingot was subjected to a soaking treatment at 600° C. for 6 hours in a holding furnace, followed by hot rolling at a temperature at the beginning of rolling of 550° C. and under temperature control such that the temperature at the end of rolling is as shown in Table 1. The resulting product was used as such as a plate material.

[0055] Process of the Prior Art (B):

[0056] Each ingot was subjected to a soaking treatment at 600° C. for 6 hours in a holding furnace, followed successively by hot rolling at a temperature at the beginning of rolling of 550° C. and under temperature control such that the temperature at the end of rolling is 310° C. and cold rolling at 80° C.

[0057] Subsequently, the resulting workpiece was subjected successively to process annealing at a temperature of 360° C. for 3 hours, cold rolling at a temperature of 80° C., and a heat treatment at 230° C. for 3 hours. Then, the thus treated workpiece was used as a plate material.

[0058] (3) Determination of Properties

[0059] Loss of Proof Stress (%) After Baking Finish Treatment:

[0060] Proof stress (&Ggr;0) and elongation of each plate material were determined before the baking finish treatment.

[0061] Subsequently, a fluorine coat was applied to each plate material, and the resulting plate material was subjected to baking finish treatment at a temperature as shown in Table 1 to measure proof stress (F) and elongation after the treatment.

[0062] Loss of proof stress (%) after the baking finish treatment was calculated according to the following equation: 100×(&Ggr;0-&Ggr;)/&Ggr;0.

[0063] The results are as shown in Table 1.

[0064] Area Ratio of Recrystallized Grain Structure:

[0065] Grain structures were observed according to the Barker's method.

[0066] More specifically, each plate material was ground to expose the surface of the plate material, and the thus exposed surface was subjected to electropolishing. The polished surface was etched using an HBF4 solution, followed by polariscopic image data processing to integrate the surface area of the grains of the recrystallized structure. Then, rate (percentage) of the integrated value within a scope (5 mm×5 mm) was determined. The results are shown in Table 1.

[0067] Meanwhile, referring to plate materials of Example 9 and Comparative Example 8, photomicrographs (50 power) of them are shown in FIGS. 4 and 5 respectively.

[0068] (4) Bending Test

[0069] Each plate material having been subjected to baking finish treatment was bent to visually observe whether or not there occurred rough surface (lifting of the coating) and cracking.

[0070] With respect to determination of rough surface, each plate material was bent in two modes, i.e. orthogonal to the rolling direction 4 (in the longitudinal direction of the plate material) as shown in FIG. 6 and parallel to the rolling direction (in the width direction of the plate material) as shown in FIG. 7, to determine bending angles when occurrence of rough surface was observed.

[0071] Meanwhile, with respect to determination of cracking as shown in FIG. 7, each plate material was bent by 90° and 180° parallel to the rolling direction (in the width direction of the plate material) to observe whether or not there occurred cracking.

[0072] In Table 1, ∘ means that there occurred no cracking; &Dgr; means that there occurred slight cracking that is not significant in practical uses; and × means that notable cracking occurred. 1 TABLE 1 Formation of plate material Baking Finish Property Property Temp. at the Plate (before baking) (after baking) Kind of end of thickness Proof stress Baking Proof stress Alloy Process rolling (° C.) (mm) (N/mm2) Elongation (%) temp. (° C.) (N/mm2) Elongation (%) Example 1 A3003 A 290 1.5 146 26.2 180 146 27.1 Example 2 A3003 A 290 1.5 146 26.2 260 141 27.6 Example 3 A3003 A 290 5.0 142 26.5 260 138 27.4 Example 4 A3003 A 300 1.0 137 26.5 260 136 27.2 Example 5 A3003 A 310 1.5 125 28.5 200 125 28.9 Example 6 A3003 A 310 3.0 124 28.6 200 123 29.1 Example 7 A3003 A 310 5.0 123 28.8 200 122 29.1 Example 8 A3003 A 310 1.5 125 28.5 260 124 29.0 Example 9 A3003 A 310 3.0 124 28.6 260 122 29.5 Example 10 A3003 A 310 5.0 123 28.8 260 121 29.8 Example 11 A3003 A 310 3.0 124 28.6 300 120 30.0 Example 12 A3003 A 330 1.5 114 30.4 200 114 30.6 Example 13 A3003 A 330 1.5 114 30.4 260 112 31.4 Example 14 A3003 A 340 5.0 105 31.0 260 103 32.0 Example 15 A3003 A 340 6.0 104 31.2 260 102 32.3 Example 16 A3003 A 340 5.0 105 31.0 300 99 32.7 Comparative A3003 A 250 3.0 170 19.8 260 168 21.2 Example 1 Comparative A3003 A 310 3.0 124 28.6 340 85 33.6 Example 2 Comparative A3003 A 330 3.0 106 31.0 340 78 38.1 Example 3 comparative A3003 A 360 3.0 87 33.3 260 82 34.1 Example 4 Comparative A3003 B 310 3.0 95 34.1 180 94 34.1 Example 5 Comparative A3003 B 310 3.0 95 34.1 260 93 34.3 Example 6 Comparative A3004 B 310 3.0 225 8.8 180 20 8.8 Example 7 Comparative A3004 B 310 3.0 225 8.8 260 160 15.2 Example 8 Comparative A3004 B 310 3.0 225 8.8 340 77 22.0 Example 9 Bending test Baking finish Rough surface Surface ratio Orthogonal Parallel to Cracking of recrystallized Loss of to the rolling the rolling 90° 180° grain structure (%) proof stress (%) direction (°) direction (°) Bending Bending Example 1 0 0 none 180 ◯ &Dgr; Example 2 0 3.4 none 180 ◯ &Dgr; Example 3 0 2.8 none 180 ◯ &Dgr; Example 4 0 0.7 none 180 ◯ &Dgr; Example 5 0 0 none 180 ◯ ◯ Example 6 0 0.8 none 180 ◯ ◯ Example 7 0 0.8 none 180 ◯ ◯ Example 8 0 0.8 none 180 ◯ ◯ Example 9 0 1.6 none 180 ◯ ◯ Example 10 0 1.6 none 180 ◯ ◯ Example 11 0 3.2 none 180 ◯ ◯ Example 12 0 0 none 180 ◯ ◯ Example 13 0 1.8 none 180 ◯ ◯ Example 14 5 1.9 none 180 ◯ ◯ Example 15 5 1.9 none 180 ◯ &Dgr; Example 16 0 5.7 none 180 ◯ ◯ Comparative 0 1.2 none 180 X X Example 1 Comparative 55 31.5 180 140 ◯ ◯ Example 2 Comparative 60 26.4 180 140 ◯ ◯ Example 3 Comparative 80 5.7 110 110 ◯ ◯ Example 4 Comparative 100 1.1 140 140 ◯ ◯ Example 5 Comparative 100 2.1 140 110 ◯ ◯ Example 6 Comparative 100 10.7 110 110 X X Example Comparative 100 28.9 140 110 X X Example 8 Comparative 100 65.8 140 110 &Dgr; X Example 9

[0073] The following became apparent from Table 1:

[0074] (1) As is clearly shown in a comparison between Example 9 and Comparative Example 6, using the same material and the same temperature at the end of rolling and having the same plate thickness, Comparative Example 6, obtained through hot rolling, followed by cold rolling, process annealing, etc., came to have a proof stress lower than 95 N/mm2 after the baking finish treatment, which is lower than that of Example 9 in spite of the same baking finish temperature of 260° C. In addition, in the bending test, Comparative Example 6 was more likely to have rough surface than Example 9. This is because the structure of Comparative Example 6 was converted into recrystallized grain structure through a series of steps after the hot rolling and further during the baking finish treatment.

[0075] The above description obviously shows effectiveness of the process of the present invention employing only hot rolling under conditions where even the subsequent baking finish treatment does not induce growth of recrystallized grain structure.

[0076] (2) A fiber structure and a finely divided secondary structure (subgrains) coexist in Example 9 after the baking finish treatment as shown in FIG. 4, and Example 9 showed a high proof stress of 122 N/mm2 and a high elongation of 29.5% after the baking finish treatment but a very low proof stress loss of 1.6%, thus showing excellent results in the bending test.

[0077] Meanwhile, a coarse recrystallized grain structure was observed instead of the fiber structure in Comparative Example 8 shown in FIG. 5. Although Comparative Example 8 showed a high proof stress of 160 N/mm2 after the baking finish treatment, it showed a small elongation of 15.2% and an extremely great % loss of proof stress. As a result, there were obtained significantly bad results in the bending test in terms of rough surface and cracking.

[0078] The above description obviously shows effectiveness of the architectural Al alloy material according to the present invention containing a mixture of a fiber structure and a finely divided secondary structure.

[0079] As is clearly explained above, the hot rolled A3003 material obtained under control such that the temperature at the end of rolling be in the range of 290 to 340° C. maintained the state that it contains substantially the fiber structure with no growth of recrystallized grain structure even after the baking finish treatment, and it also showed a proof stress loss of 10% or less and also secured an absolute proof stress value of 95 N/mm2 or more and an elongation of 27% or more. Therefore, the Al alloy material according to the present invention enjoys high industrial value as a building material having excellent bendability and undergoing no loss of proof stress.

[0080] It should be noted here that while the baking finish treatment was carried out in a temperature range of 260 to 280° C. in the above description, the architectural Al alloy material according to the present invention can be employed suitably whether the temperature of the baking finish treatment is 260° C. or lower or in the range of 280 to 300° C.

Claims

1. An architectural Al alloy material, which is a hot rolled material defined by JIS A3003 (3003 defined by B209 of ASTM); the material comprising, in terms of a structure after a baking finish treatment at a temperature of not higher than 300° C., a fiber structure and a recrystallized grain structure having an area ratio of 20% or less; wherein the material undergoes a proof stress loss of 10% or less after the baking finish treatment.

2. The architectural Al alloy material according to claim 1, having a proof stress and an elongation of 95 N/mm2 or more and 27% or more, respectively, after the baking finish treatment.

3. The architectural Al alloy material according to claim 1 or 2, wherein the baking finish treatment is carried out at a temperature of 260 to 280° C.

4. A process for manufacturing an architectural Al alloy material comprising the steps of:

subjecting an ingot of JIS A3003 (3003 defined by B209 of ASTM) to a soaking treatment; and

subjecting the resulting ingot to hot rolling to be carried out in such a way that it has a temperature of 290 to 340° C. at the end of rolling;

wherein the thus treated ingot is as such applied to a practical use.