JPS58213851A - Microcrystal grain material for stringer of airplane and its manufacture - Google Patents

Abstract

PURPOSE:To refine the grains of the structure of a material for the stringers of an airplane and to improve the mechanical properties, elongation, rupture toughness value, etc. by cold working an Al alloy at <=90% working rate and by subjecting it to soln. heat treatment. CONSTITUTION:Stringer members for reinforcing the belly of an airplane are manufactured using an Al alloy contg. 5.1-8.1% Zn, 1.8-3.4% Mg, 1.2-2.6% Cu, <0.2% Ti and 0.18-0.35% Cr. The Al alloy blank is subjected to soln. heat treatment, and it is worked to a prescribed thickness by hot rolling and cold rolling. The worked blank is rapidly heated to 320-500 deg.C at >=11 deg.C/min average heating rate, cold worked in steps at 0-90% different working rates, and subjected to soln. heat treatment. The grains are made as fine as <=100mum, and stringers having superior mechanical properties, elongation, rupture toughness value, chemical sealability and fatigue strength are obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a material for an aircraft stringer having fine grains and a method for manufacturing the same.

Aircraft stringers refer to the longitudinal and circumferential reinforcing members 2 and 3 used inside the aircraft fuselage 1, as shown in Figure 1, and their cross-sectional shape is (a) Hat type, (b) 7 type or (
C) It is of type J.

A typical manufacturing method for this stringer is as follows.

JIS 7075 alloy was subjected to homogenization heat treatment at approximately 60°C for approximately 16 hours, hot rolled at approximately 400°C to a thickness of approximately 61 mm, intermediate annealed at approximately 10°C for approximately 1 hour, and then furnace cooled. After cold rolling into a 3-4II 1m thick plate, 8-12
The temperature is raised to about 410℃ in an hour's heating time, and at that temperature about 1
After being heated and softened for an hour, it is cooled at a cooling rate of 25°C per hour to form a 7075 alloy O alloy, and the working degree is θ ~ 9.
0% stepped cold rolling, solution treatment and stringer
manufactured materials for use. For example, the above-mentioned middle stage cold working is
In other words, in the form shown in Fig. 3, the degree of rolling is changed in the length direction, and a part with a degree of work O is A, a part with a relatively low degree of work B, a part with an intermediate degree of work C, a part with a high degree of work, etc. Process it into the form that it has.

This is to reduce the overall weight of the aircraft by reducing the thickness of parts that do not require strength. The stringer material thus produced is formed into a hat shape, for example, as shown in FIG. 2, by seximine roll molding, and then subjected to T6 tempering to form a stringer.

When producing stringers using the above process, the following problems arise.

In other words, the 7075 alloy O produced as a stringer material by the conventional method has crystal grains of about 150 to 250μ, and this material is solutionized after cold working (taper rolling) with a low working degree of about 10 to 30%. When processing, the crystal grains become even coarser than the crystal grains of the material, approximately 20%
Based on our experience, the degree of machining has also become coarser. Of course, even when such a material is used, fine crystal grains with a grain size of about 50μ can be obtained in the part that is subjected to solution treatment after 50% or more cold working. Since there are parts with various cold working degrees from 0 to a maximum of 90%, the total length of the stringer is 10%.
It is extremely difficult to reduce the grain size to 100μ or less over the entire length of m.

FIG. 4 shows an example of the relationship between the working degree (upper row) and the crystal grain size (lower row) when existing stringer materials are subjected to solution treatment after cold working at various working degrees. The grains are fine in areas such as F and G where the degree of work is high, but A where the degree of work is small.

In areas such as B, C, and E, the crystal grains are very large.

For areas with crystal grains of 100μ or more, such as A, B, C, and E, mechanical properties, elongation, fracture toughness, chemical milling properties, fatigue strength, etc. decrease, and roughness or cracking occurs during section roll forming. Not only is it extremely difficult to manufacture a stringer for an IC where this occurs, but its functionality is also degraded.

The present invention aims to solve the above problems,
The object of the present invention is to provide a stringer material having a crystal grain size of 100 μm or less by performing solution treatment after cold working to a maximum of 90%, and a method for manufacturing the same.

That is, the first invention of the present invention has a Zn content of 5.1 to 8.1%.
, Mu 1.8-3.4%, Cu 1.2-2.6%,
It is a stepped cold-worked and solution-treated material that contains TiO, 2% or less, and 0.18 to 0.35% Cr, and the remainder is A1 and impurities. This is a material for aircraft stringers with fine crystal grains, characterized in that the particle size is 100 μm or less.

The reasons for limiting the alloy components of the stringer material of the present invention are shown below.

Zn: If it is less than 5.1%, the strength of the alloy after T6 treatment will be low, and if it exceeds 8.1%, there is a risk of decreased toughness or stress corrosion cracking.

M(1...If it is less than 1.8%, the strength of Alloy 6- after T6 treatment will be low, and if it exceeds 3.4%, the cold workability of the soft material will be poor, and after the below 6 treatment. The toughness of the alloy decreases.

Cu: If the content is less than 1.2%, the strength of the alloy after the 6th treatment below will be low, and if it exceeds 2.6%, the toughness of the alloy will be reduced.

Ti...addition of 0.20% or less will refine the casting structure,
It is effective in preventing cracks in the ingot during spinning, but if it exceeds 0.20%, large intermetallic compounds will crystallize.

Or... If it is less than 0.18%, there is a risk of stress corrosion cracking, and if it exceeds 0.35%, a huge intermetallic compound will crystallize, which is not preferable.

Note that Fe, Si, and Mn as impurity elements need to be regulated as follows.

Fe...Fe is effective in refining crystal grains, but 0.5
If it exceeds 0%, the amount of insoluble compounds in the alloy increases, resulting in a decrease in the toughness of the alloy.

Sl...3i is effective in refining crystal grains, but 0.
When it exceeds 40%, the amount of insoluble compounds in the alloy increases, resulting in a decrease in the toughness of the alloy.

Mn...Mn is effective in preventing stress corrosion cracking, but
If it exceeds 0.10%, hardenability and toughness will decrease.

When manufacturing aircraft stringers using the material of the present invention, since the crystal grains are as fine as 100μ or less over the entire length, not only no roughness or cracks occur during section roll forming, but also mechanical properties and elongation. , it becomes possible to obtain stringers with excellent fracture toughness, chemical milling properties, fatigue strength, etc.

A second invention of the present invention is a method for producing a material for an aircraft stringer, which is the same as the first invention, wherein the aluminum alloy as limited above is homogenized, hot-rolled and cold-rolled according to a conventional method. 320 to 500
This method is characterized by softening the material by rapidly heating it to a temperature of 11°C at an average temperature increase rate of more than 11°C/min, performing cold working to a maximum of 90%, and performing solution treatment. .

In the second invention, the above-described aluminum alloy is homogenized according to a conventional method. In this homogenization treatment, an aluminum alloy ingot is sufficiently heated at 400 to 490°C for 2 to 48 hours, and 7n, Mg, Cu, In this method, elements such as the following are sufficiently dissolved in solid solution, and Cr is precipitated as a fine intermetallic compound. If homogenization treatment is insufficient due to low temperature or short time, hot workability of the aluminum alloy ingot will be poor, stress corrosion cracking resistance will decrease, and crystal grains will become coarse. . Furthermore, if the homogenization treatment temperature is higher than 490° C., eutectic melting occurs, which is not preferable.

The hot rolling following the homogenization process is preferably started at a temperature of 350-470°C. When the temperature is less than 350°C, the deformation resistance is large, resulting in poor rolling workability, and when it exceeds 410°C, the rolling process becomes brittle, leading to processing cracks, which is not preferable.

9- After hot rolling, softening is performed as necessary.

The softening rate is 3 per hour after being maintained at a temperature of 300-460℃.
It is necessary to cool down to about 260°C at a cooling rate of 0°C or less. This softening step is particularly necessary when the subsequent cold rolling is to be performed at a high degree of working.

The working degree in cold rolling is preferably 20% or more, and if the working degree is low, the stringer material has crystal grains of 100% or more.
It becomes coarser than μ.

The cold-rolled material is softened by rapid heating to a temperature of 320 to 500°C at an average heating rate greater than 11°C/min. This is particularly important in obtaining

Traditionally, the softening method for 7075 alloy is 413-454℃.
heated to , held at this temperature for 2 hours, cooled in air,
This is done by reheating to 232°C, holding at this temperature for 6 hours, and then cooling to room temperature. This method is the method recommended in Section 5.2.7.2 of the U.S. Department of Defense's MIL-1-(6088E military standard),
All softening methods for 7075 alloy for aircraft are based on the above methods and are common knowledge to those skilled in the art. The above-mentioned softening step in the present invention breaks the common sense of those skilled in the art.

If the heating temperature exceeds 500° C. in this softening step, the material may melt or abnormal crystal grain growth may occur, resulting in significantly coarse recrystallized grains, which is not preferable.

If the heating temperature is lower than 320° C., the material will not be completely softened and recrystallized, so there is a problem that cracks will occur during stepped cold rolling (taper roll processing) when manufacturing slingers.

After all, it is possible to produce a stringer alloy having fine recrystallized grains of 100 μm or less only when the alloy is heated and softened at a temperature of 320 to 500° C.

Regarding the heating rate to 12°C, it is essential to perform rapid heating at an average rate higher than 11°C/min. In this case, precipitation of Mg-Zn compounds during heating is small, and cold rolling The introduced dislocation structure changes into a uniform fine cell structure by being softened by rapid heating. When a material with such a structure is subjected to a weak taper roll process (10 to 30%) and then subjected to solution treatment, recrystallization proceeds with the uniform fine keratinized structure as the core. Recrystallized grains are obtained. If the temperature increase rate is lower than 11°C/min, Mg-Zn compounds will precipitate non-uniformly during heating to a predetermined softening temperature, and the dislocation structure will either completely disappear or become coarse and non-uniform in size. Cell tissue remains. If such a material is subjected to solution treatment after weak tapered roll processing, the above-mentioned uniform and fine recrystallized grains cannot be obtained, and the crystal grains become extremely coarse.

Regarding the cooling rate after softening due to rapid heating, if the cooling rate is less than 30℃ per hour, a completely zero material can be obtained, so the cold workability of the material is good, and 90%
It is possible to perform tapered roll rolling to a certain degree.

On the other hand, if the cooling rate after softening due to rapid heating is fast, quenching occurs and age hardening occurs, resulting in a material with higher strength than ordinary O material, but in this case, the degree of workability is relatively low. Although it can be used as a stringer material, there are problems in terms of workability when it is applied to stringers that require a high degree of workability.

The third invention of the present invention is a countermeasure against this problem, and in the second invention, when the cooling rate during softening is 30°C or more per hour, it is reheated to 200 to 500°C, and in particular, the reheating temperature is If the temperature is less than 200-350℃, air cooling or
Cool at a rate of 30℃ or less per hour, and reheat at a temperature of 3
In the case of 50 to 500°C, this method is characterized by cooling at a rate of 30°C or less per hour.

In other words, the cooling rate after reheating is set at a relatively low temperature of 200 to 350 to prevent reheating.
If the temperature is below ℃, use air cooling or reduce the cooling rate to 3 per hour.
When cooling at a cooling rate of 0°C or less and reheating at a relatively high temperature of 350 to 500°C, the cooling rate is 3 per hour.
Cool at a cooling rate of 13- below 0°C. By doing so, even when the cooling rate after rapid heating is fast, a high degree of processing is possible.

In addition, the reheating temperature can affect the tensile strength of the obtained material and the grain size of the material (hereinafter sometimes referred to as W material) that is solution-treated after processing the material into a stepped taper roll. I found this out through experiment. An example of this relationship is shown in FIG.

Figure 5 shows the tensile strength of the O material obtained by reheating the material softened by rapid heating at various temperatures, and the tensile strength of the O material after 20% cold working, solution treatment at 470°C for 40 minutes, and water quenching. Did W
The relationship between the crystal grain size of the material and the reheating temperature is shown.

That is, a material that is air-cooled after being softened by rapid heating and left at room temperature has a high tensile strength because it is hardened, and when reheated, the tensile strength decreases as the reheating temperature increases. In addition, the crystal grain size of the material subjected to 20% cold working and solution treatment after reheating varies depending on the reheating temperature, and when the reheating temperature is less than 200 to 350'C, the crystal grain size is 14- The diameter is relatively small, about 25 to 35 μm, and the crystal grain size is 35 to 50 μm when the reheating temperature is less than 350 to 440 °C.
When the reheating temperature is 440 to 500° C., the crystal grain size becomes small again to 30 to 35 μm.

Example 1 Table 1 Alloys No. 001 and No. 4 shown in Table 1 were manufactured into stringer materials having a thickness of 301 DEG C. by the method of the present invention and the conventional method described below.

Method of the present invention; Homogenization treatment (460°C x 161°) → Hot rolling (40°C
Rolling from 300mm to 6mm at 0℃) → Cold rolling (6→
3ff1m) → Rapid heating (heating rate 215° to 450°C)
Heating at C/min and holding for 3 minutes) → Cooling (cooling at 5°C/min) -
>Heat softening at 300°C for 1 hr → Cooling to 200°C at a cooling rate of 20°C/hr → Cold working (working degree O ~ 90%, shown in Table 2) → Solution treatment (470°C x 40 minutes, using salt bath) )→Conventional water quenching method: Homogenization treatment (460℃ x 16hr)→Hot rolling (400℃
300-) rolled to 6 mm)-+420°C x 1
After heating for 3 hours, cool at a cooling rate of 3℃/h1゛→cold rolling (6−+3ml11)−+softening (heat to 420℃ at a temperature rate of 0.5~b and hold for 2hr→cooling at 25℃/11r Cooling at a high speed → Holding at 235°C for 6 hours → Air cooling) → Cold working (working degree O ~ 90%, shown in Table 2) → Solution treatment (47
Hold at 0° C. for 40 minutes, use vine 1 heat bath)→Water quenching The various properties of the material (referred to as W material) produced by the above method are shown in Table 2, along with the crystal grains and degree of cold work before solution treatment.

The present invention material has a fine grain size of 100μ or less over the entire working degree of 0 to 90%, so the bendability of the W material, T6
The elongation and fracture toughness of the material are superior to conventional materials.

Furthermore, since the present invention material has fine crystal grains, the roughness after chemical milling is smaller than that of conventional materials, and the material has excellent fatigue strength after chemical milling.

17- Example 2 (Shadow of temperature increase rate of rapid heating 1i') Alloy N051 shown in Table 1 was homogenized at 410°C for 24 hours.
Start hot rolling at 40°C and roll from 350mm to 5mm
Rolled into a thick plate. The finishing temperature of hot rolling was 340°C. Next, the 6 mm thick plate was cold rolled to a thickness of 3 mm, and heated to 450°C at various heating rates shown in Table 3.
After being held for a minute, it was cooled at a cooling rate of 25°C per hour to obtain a 3mmQ material. The plates were cold-worked at various working degrees and then solution-treated at 470° C. for 40 minutes using a salt bath, followed by water quenching. The grain size of these materials and 450
Table 3 shows the relationship of the u-adjustment speed to °C.

Table 3 Alloy 1 * Equivalent to heating time using conventional method As shown in Figure 3, if the average heating rate to 450°C is greater than 11°C/min, the crystal grains of the alloy and the solution after cold working are The crystal grains of the chemically treated material are uniformly fine grains of 100 μm or less, but when the average temperature increase rate is 11° C./min or less, the crystal grains become extremely coarse. Then, the temperature increase rate in Table 3 is 86°C/min, 21°C/min, 14°C/min, 118
Table 4 shows the various performances of the W material and the T6 material aged at 120°C for 24 hours after quenching, with representative selections of 0.9°C/min and 0.9°C/min. Materials with average heating rates greater than 11°C/min have good performance as stringer materials.

22- Table 4 Alloy 1 Average valve speed Cold work degree After solution treatment
Bending test results of W material *Grain size Appearance Crack ('C/min) (%) (μm)
Presence 0 30 1 No roughness
None 10 35 86 20 3530
35 50 30 80 27 0 35 10 40 21 20 4730
45 50 35 80 30 〃 0 70 10 80 14 20 8530
80 50 40 80 35 23- Mechanical properties of T6 material Proof strength Tensile strength Elongation (kg/m1+2) (kg/mtn2)
(%) 51.1 57.2 16 52.1 57.5 14 52.6 58.0 14 50.6 57.0 15 50.6 57.4 16 50.3 57.8 17 51.2 57. 1 16 52.4 57.4 13 53.2 '57.1 1351.0
56.9 14 50.2 57.5 16 50.2 57.2 16 51.1 57.0 16 52.1 57.1 14 52.5 56.8 13 50.6 56.6 14 50.4 57 .8 16 50.1 57.6 16 0 110 Rough skin Micro cracks 10 14.0 11 20 17030
165 50 40 No rough skin
80 40 0 200
10 240 0.9 20 310 30 220 50 50 No rough skin
80 40'*90' bending, bending radius 1.5t (t: plate thickness) Bending test conducted 4 hours after quenching.

24- 270- 50.3 56.4 14 51.7 56.3 13 51.6 57.1 13 50.8 56.8 13 50.4 56.6' 1650.0
56.0 15 50.2 56.6 11 50.9 56.8 10 50.0 56.9 12 49.9 56.3 12 Example 3 (Effect of heating temperature) Alloy N002 shown in Table 1 was carried out. It was rolled into a 3 mm cold rolled plate in exactly the same manner as in Example 2. This board is 320~
Heating at various heating rates to various humidity levels between 520°C, then cooling at a cooling rate of 5°C per minute, and then cooling to 300°C.
The mixture was heated for 1 hour and cooled at a cooling rate of 20°C per hour to 3n+m0IJ.

After cold working the above 3mm-0 material, the crystal grain size of the W material was water-quenched after solution treatment at 470°C for 40 minutes using a salt bath, and the heating temperature was increased for 2 minutes. The relationship is shown in Table 5. Even when solution treatment is performed after mild working, materials with fine grains can only be obtained by softening cold-rolled sheets by rapidly heating them to temperatures of 320 to 500°C, and heating humidity If it is outside this range, a material with fine crystal grains cannot be obtained even if solution treatment is performed after mild electric processing.

Three examples of 3 mm thick O material softened under the conditions shown in Table 5 were cold rolled to a maximum of 80%, solution treated at 470°C for 40 minutes, and then water quenched.WI! Tests were also conducted on T6 material that had been quenched and then aged at 122°C for 25 hours. The results are shown in Table 6, and each example had sufficient performance as stringer material #X31.

Table 5 Alloy 2 27- Example 4 (Effect of heating holding time)
2 Alloy N003 shown in Table 1 was rolled into a cold-rolled plate having a thickness of 3Il111 in exactly the same manner as in Example 2. This plate was heated to each temperature at the heating rate shown in Table 7, held for each time, cooled at a cooling rate of 5°C per minute, and then heated to 300°C per minute.
After heating at °C x Yur, it was air-cooled to a size of 3 mm0U.

This amm Q material has the largest tendency to coarsen grains.
4 at 470℃ using a salt bath after 0% cold rolling.
Table 7 shows the relationship between the crystal grain size, heating temperature, and holding time of the W material that was water-quenched after 0 minutes of solution treatment.

As can be seen from Table 7, it is clear that a material with fine crystal grains can be obtained over each holding time.

All the crystal grains of the W material, which was cold rolled from the above 3 mm O material plate by 0 to 90%, and then solution treated and water quenched, were 1.
00μ or less, and even when bent 90° with a bending radius of 1.5t (t・-plate thickness), no roughening or cracking occurs at all, making it suitable for stringer materials 29-272- Met.

=30- Table 7 Alloy 3 Example 5 (Influence of manufacturing conditions) The 400 mm thick ingot of alloy N 0.1 shown in Table 1 was
An O material plate having a thickness of 2 to 5 ml was obtained under the manufacturing conditions shown in .

Table E3 Soaking Hot rolling condition No. Condition Start temperature End temperature Plate thickness * Softening condition ('C) (℃) (, mm) 147
0℃x30hr 430 330 6
None 2 4.00
300〃370℃×1hr3465℃×161
) r425310〃 None 4475℃X24hr
n 3!30℃xlh
r5
n 400℃xlbr7470℃x24hr
440280 8 None 8
400 260 〃9
440 330 510
〃 360 l111 470℃x
16hr 435 325 l112
475℃×24hr 415 345
n 350℃X11+r13
N290 9
400℃×廿1r14
〃320 815 470℃×24hr
420 〃 10 None 16
〃335 8 4
00℃xlhr17
〃15* After softening is complete, cool at a cooling rate of 25°C per hour.

Alloy 1 Cold rolling conditions Rapid heating softening conditions Workability
Plate thickness Average heating rate Heating conditions Cooling rate
Softening conditions (%) (mm) ('C/min) 3
3 4 140 450℃×1 minute 5℃/
Minutes 300℃ x 1hr21 450℃ x 2
Minutes I 150 3
, 230 470℃×3 minutes17 480℃×
30 minutes 66 2 450 470℃ x 2 minutes 10
℃/min 230℃ x 3hr 38400℃ x 35 minutes
N * 1150 4 230
, 480℃×1 minute 〃 *470℃×1hr
24 380℃ x 40 minutes 〃 * 〃4
0357430℃×20 minutes 20℃/hr
None 140 455℃ x 2 minutes 50 2.5 1300 470℃ x 3 minutes 40
400'CX50 minutes 25℃/hr66 3 9
00460℃×4 minutes nll75
2 440 460℃ x 15 minutes 50 5
680 470℃ x 3 minutes 63 JJ
150 440℃ x 10 minutes ll80
3 220 450℃ x 2 minutes 30℃/h
r=33- After cold-rolling the O material plates manufactured under the manufacturing conditions of N011 to No. 17 in Table 8 by 20%, which has the largest tendency to coarsen grains, it was subjected to solution treatment at 470°C for 40 minutes using a salt bath. T that was water quenched after chemical treatment and aged at 120℃ for 24 hours.
Table 9 shows the test results of various performances of the six materials.

Table 9 Alloy 1 *Bending test conducted 4 hours after quenching with 90° bending and bending radius of 1.5t (t: plate thickness).

As is clear from Table 9, the crystal grain size of the stringer material manufactured under the conditions of the present invention is 100μ or less, and the crystal grain size of the material quenched after cold working is also 100μ.
It does not become coarse as below, and both W and T6 materials can be used as stringers.
It shows good performance as a material.

Although Table 9 shows only the results for the case of 20% working degree, the grain size after solution treatment is all 100 μ or less even when cold working is performed from 0 to 80%. T
All six materials had sufficient performance as stringer materials.

Example 6 (Influence of alloy composition) A 400 mm thick ingot of alloy No. 1-4 shown in Table 1 was
After homogenization treatment at 70° C. for 25 hours, hot rolling was started at 400° C. and rolled into a plate having a thickness of 6t+un.

The hot rolling end temperature was 300°C. Then, 13m
m-thick plate was cold rolled to 3mm thickness, and the average heating rate was 220.
°C/min to 460 °C, held at that temperature for 5 minutes, then cooled at a cooling rate of 10 °C per minute, then 30 °C per minute.
After heating at 0° C. for 1 hour, the material was cooled in air to obtain a 3Ill36-□1rrlO material.

For comparison, alloys No. 005, No. 6, and No. 6 shown in Table 1 were also made into O material plates in the same manner.

In order to examine the performance of these O material plates as stringer materials, each O material plate was cold rolled by θ~75%, and then 470
Tests were conducted on W material that had been solution treated at 120°C for 40 minutes and water quenched, and T6471 that had been aged at 120°C for 24 hours after quenching. Its various performances are shown in Table 10.

In each alloy, the crystal grain size is 100 μm or less over the entire working degree.

Table 11 shows the various performances of materials obtained by cold working, solution treatment at 470° C. for 40 minutes using a salt bath, and quenching, for the case of 20% working, which has the greatest tendency to coarsen the grain size.

37-i Table 10 Alloys No. 1 to 4 have good performance as stringer materials, but alloy No. 5 has low strength, and alloy No. 6 has the risk of stress corrosion cracking, so it is not suitable for stringers. There are problems with its use as a material.

[Brief explanation of drawings]

Figure 1 is a partial perspective view of the interior of the aircraft fuselage, Figure 2 is an example of the cross-sectional shape of a stringer, Figure 3 is a perspective view showing the processing state of the stringer material, and Figure 4 is the degree of processing and grain size. FIG. 5 is a graph showing the relationship between the tensile strength of the material, the crystal grain size of the W material, and the reheating temperature. 1...Body 2.3...Reinforcement material (stringer, stringer frame) Patent applicant Sumitomo Light Metal Industries Co., Ltd. Agent Patent attorney Hide Komatsu 41-years old 2 Figure

Claims (1)

[Claims] [11Zn5, 1 to 8.1%, MOI, 8 to 3.4%,
Cu1.2-2.6%, 'l io, 2% or less, Oro
, 18 to 0.35%, with the remainder consisting of AI and impurities, the material is stepped cold-worked and solution-treated, and has crystal grains of 100 μm or less. A material for aircraft stringers with fine grains. (21Zn5.1-8.1%, Mol, 8-3.4%,
Cu1.2-2.6%, Ti0.2% or less, Oro, 1
An alloy containing 8 to 0.35% and the remaining A1 and impurities is homogenized, hot rolled and cold rolled to a predetermined thickness according to a conventional method.
It is characterized by being softened by rapidly heating to a temperature of 11°C/min at an average temperature increase rate of more than 11°C/min, and after applying cold stage pressure at different degrees of working from 0 to 90%, solution treatment is performed. A method for manufacturing a material for aircraft stringers with fine grains. (31Zn5.1-8.1%, Mol, 8-3.4%,
Cul, 2-2.6%, Tio, 2% or less, CrO,
An alloy containing ~0.35% IB and the remainder A1 and impurities is homogenized, hot rolled, and cold rolled to a predetermined thickness according to a conventional method.
It is softened by rapid heating to a temperature of 00°C at an average heating rate of more than 11°C/min, and when the cooling rate during this softening is 30°C or more per hour, it is reheated to 200-500°C. If the reheating temperature is less than 200 to 350°C, cool by air or at a rate of 30°C or less per hour, and if the reheating temperature is 350 to 500°C, cool at a rate of 30°C per hour.
A method for producing an aircraft stringer material with fine grains, which comprises cooling at a rate of 0.degree.