JPS602644A - Aluminum alloy - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to aluminum/lithium (A/!, /L+) alloys which are particularly suitable for aerospace vehicle construction.

PRIOR ART Such alloys are attractive because they allow for a notable weight reduction of less than 20 inches over other aluminum alloys, and because these alloys have high strength and stiffness and good corrosion resistance properties. have

However, to date, At/Li alloys have suffered from reductions in other properties such as fracture toughness and have been difficult to cast and subsequently process compared to other aircraft alloys.

Most At/L+ alloys proposed so far are
At/I, tzMg systems (e.g. Li2.1 and Mg
5.5 Ti) or by using relatively high levels of lithium additions to conventional aerospace alloys in powder metallurgy, e.g., 3 or more Li additions to alloy 2024. It was based on crab. Recently, addition of Mg and Cu has been proposed, for example, L13% or more, Cu about 1.5%.
%, about 2% Mg and about 0.18% Zr.

This gives the alloy improved fracture toughness and facilitates hot and cold working.

SUMMARY OF THE INVENTION We have discovered that additional improvements in ease of manufacture and subsequent processing can be made by further modifying the lithium, magnesium and copper content of the alloy and by subjecting hot rolled blanks made from cast innits to specific heat treatments. I discovered that this can be accomplished by rubbing.

According to one aspect of the invention, the composition ranges in weight percent: Lithium 2.3 ~ 29 Magnesium 0.5 ~ 1.0 Copper 1.6 ~ 2.4 Zirconium 0.05-0.25 Titanium 0 ~ 0.5 Manganese O~0.5 Nickel 0 ~ 0.5 Zinc O~2.0 Aluminum balance (including incidental impurities) An aluminum alloy is provided.

It is desirable that the ratio of copper to magnesium be much higher than previously proposed, with a preferred ratio of about 3=1.
It can vary from 1.6:1 to 4.8:1,
This has been found to significantly improve the precipitation strengthening behavior of the alloy giving increased strength with acceptable fracture toughness.

Zirconium is included because of its known properties in controlling grain size, and the optional addition of one or more of the elements titanium, manganese, nickel and chromium may also control grain size and grain growth upon recrystallization. It will be controlled. The optional addition of zinc enhances the superplastic properties of the alloy and provides strength contributions.

It has long been recognized that mechanical deformation by methods such as hot and cold rolling leads to the development of crystallographically preferred orientations in metallic materials in sheet or slip form. This has been proven in several ways, many of which are quite detrimental to the properties of the product. especially,
Anisotropy in mechanical properties results in the strength and ductility of a fabricated or fabricated and annealed product varying appreciably with direction in the plane of the sheet or strip; these properties are measured. be done. Torera's result is 1
000.000 is common in simple aluminum-based alloys such as the 3000 or 5000 series alloys (named by the Aluminum Institute of America), but in the 2000 and 7000 series aluminum alloys commonly used in aircraft construction. No harmful consequences.

However, experiments in the development of aluminum-lithium based alloys have shown that the anisotropy of properties poses a significant challenge when the alloys are processed through processes similar to those used for the 2000 and 7000 series alloys. In addition, anisotropy control techniques traditionally applied to 1000°3000 and 5000 series alloys, such as controlling the Fe to St ratio, cannot be applied to aluminum-lithium based alloys because iron levels are This is because it is kept relatively low. Therefore, special thermal and mechanical processing techniques need to be developed to control the mechanical properties anisotropy and especially elongation within acceptable limits in the alloy.

In our pending UK Application No. 8308907, filed on March 31, 1983, we disclose a heat treatment technique commonly applicable to A4/Li alloys, and which is particularly suitable for the alloys of the present invention. ing.

Therefore, the method of manufacturing a sheet or strip provided by the present invention includes (a) hot rolling an ingot of the aluminum alloy according to the present invention in one or multiple stages to produce a hot blank; (C) ensuring cooling of the hot blank; (d) further heat treating the cooled blank; to precipitate these age-hardened phases in solid solution; (e) continue the heat treatment to create a coarse-grained overaged structure; and (f) cold-roll the blank to form a sheet or A method of manufacturing a sheet or strip, comprising: forming a strip, the elongation properties of which at every position and in every direction of the sheet or stop vary by a factor of 2.0 or less from the elongation properties in the rolling direction. . At every position and in every direction of the sheet or strip, its tensile strength properties vary by no more than 25 MPa (0.2% stress plus tensile stress) from the properties in the rolling direction.

The initial holding temperature of the hot blank is between 480°C and 540°C and the time varies between 20 and 120 minutes, depending on the thickness of the blank and the previous thermal history of the blank. ing. Once the hot blank has dropped to a temperature below 480°C, the blank is reheated to
+ Mg! Solutionize Cu and some Zr.

Preferably, the hot blank is 12.5 inches to 3 inches thick. The sheet or strip will be less than 10 mm thick, preferably less than 5 wn thick. Desirably, the hot blank is reliably cooled.

Reliable cooling is achieved through further heat treatment.
treatment), so that a definite cooling step and a further heat treatment step may be combined. Further heat treatment with generally 300 to 40
The period will be 8 to 16 hours at a temperature between 0°C.

This heat treatment of the blank not only controls the anisotropy of the cold rolled sheet or strip, but also facilitates subsequent cold rolling and, in the case of superplastic alloys, enhances its superplastic properties.

The invention will be further described in connection with the following examples and with reference to the accompanying drawings.

The copper-to-magnesium ratio has been found to be a key feature in alloys that are able to achieve increased strength with satisfactory fracture toughness compared to previously proposed alloy compositions.

This is illustrated in Figure 1, which shows differential scanning calorimetry curves for three alloy compositions. 2.5%L
1 +2-0%Cu, 0.7%Mg and 0.12
The first curve for aluminum alloy with %Zr (
) shows aging peaks at about 200°C and about 325°C. The peak at 200°C is due to the A'7'Li3 phase, and the peak at 325°C is due to the S phase (At-
C11-Mg) and the combinatorial precipitation of the equilibrium AL/Li phase. The curve of aluminum alloy with 2.51Li, 2.0%Cu, 0.454Mg and 0.12%Zr lower than the inventive limit for Mg (b
), there is a flat bottom between 250°C and 285°C, indicating a lack of precipitation of the S phase.

Finally, regarding Mg, 2.5% is higher than the limitation of the present invention.
Li, 2.0% Cu, 1.1% Mg and 0.12% Z
In curve (c) for the aluminum alloy with r, an At-Cu-Mg addition precipitation mechanism exists at about 140°C.

It was well established that AL/Li-based alloys have low ductility and low fracture toughness due to Az/Li3 precipitation without dispersing slip during deformation. The alloy according to the invention maximizes the precipitation of S phase which disperses slip and increases strength, ductility and toughness.

Example 1 Alloy composition (wt%) Lithium 2.5 Magnesium 0.6 Copper 2.1 Zirconium 0.14 Chromium 0.05 Titanium 0.013 Aluminum Balance (including incidental impurities) Alloy 5
A 08 mm x 178 m 300 kll ingot was cast by a direct rapid cooling casting method. Next, 54 ingots
Homogenization was carried out at 0° C. for 16 hours, and surface defects were removed by peeling. Then, the ingot was reheated to 540℃, and
5. Hot rolled into a plate.

The plate was solution-treated at 540°C for 1 hour, quenched with cold water, and
Stretch to % permanent elongation and reduce the tensile strength of the material to 1
Evaluations were made after aging at 70°C for various periods. Comparing longitudinal tensile properties of alloys 2014-T651 and 7010-T7
A comparison with the minimum specified characteristic level of 651 is shown in FIG.

The alloy has been shown to have strength levels well in excess of the minimum requirements of comparative alloys. Peak aging solutionization (170
℃ aging for 60 hours), the alloy is 0.2%
The yield strength is about 100 MPa higher than typical for 2014-T651 plate of the same thickness and the tensile strength is 2014-
Approximately 80 MPa higher than typical for T651 plate.

Additionally, the alloy was found to have 20% higher fracture toughness than 2014-T651 (both materials tested in their fully heat treated condition).

All heat treated alloys have a density of 8-1 compared to all specified aerospace aluminum alloys.
0% lower and coefficient 10-15% higher. Below are blank spaces Example 2 Lithium 2.8% Magnesium 0.9T Copper 1.8% Zirconium Q, 12q6 Aluminum Balance (including incidental impurities) Alloy 5
A 08mX 178WII300kl+ ingot was cast using a direct quench casting method. Next, add 5 ingots
It was homogenized at 40° C. for 16 hours and peeled to remove surface defects. Then, the ingot was reheated to 540℃,
It was hot rolled into a hot blank with a thickness of 5WrIn.

Blank our pending UK Application No. 830890
The heat treatment was performed according to the heat treatment schedule detailed in No. 7. Specifically, a 5-cm thick hot blank was solution treated at 540°C for 1 hour, air cooled, and overaged at 350°C for 16 hours.

The blank is then cold rolled to a thickness range of 4 to 0,8.
2mXim size sheets were produced in wrrM with necessary intermediate annealing. The rolled sheets were solution treated at 540°C for 20 minutes, cold water quenched, and aged at 170°C. Table 1 shows the changes in tensile properties of 1.6mm thick sheets with aging time in T6 (no stretching) Tenno 4- and TS (2nd stretch before aging) tempers, and the tensile properties were measured in the longitudinal and transverse directions. The direction was measured.

Similar characteristic level is 4. It has also been achieved in sheet materials in the thickness range of Own to 0.8 fog.

Below margin 0.2% PS = 0.2% stress resistance TS = tensile stress El = elongation MPa = megapascal At peak aging under T6 condition, the alloy has 0.2% PS of 440 MPa, tensile strength of 520 MPa and 6- 7
．． An elongation of 5% can be achieved. These properties are the most widely used high-strength 2000 series alloy (201
4-T6 0.2% proof stress = 380 MPa, tensile strength = 440 MPa, elongation = 7 inches, minimum specified properties for sheet) are also noteworthy and high.

This material also exceeds the minimum property requirements of 7075 sheet at T73 temper.

At peak aging at T8 conditions, the alloy is able to achieve a 0.2 tensile strength of 475 MPa and a tensile strength of 535 MPa in both longitudinal and transverse tests, and these values are higher than those of the 7075 alloy (T6 Tennoku). Approximately comparable to the fully heat-treated minimum sheet regulations at

Figure 3 shows the tensile properties at peak aging under T8 conditions.

170 for 25 plates of the alloy of Example 1 in Figure 3.
Changes in longitudinal tensile properties with aging time at °C in 2014
- Shown in comparison with 25m boards specified by T651 and 7010-T7651. In the drawings, TS = Tensile 9 Strength ps = Yield Strength EL = Elongation DTD5120F and B52L93 are the relevant prescribed standards for the two comparison alloys. Figure 3 shows statistical changes in 0.2% proof stress and tensile stress for sheets manufactured in the 5.0 to 0.8 m thickness range from 508 mm x 178 mm cast ingots within the specific composition limits of the present application. . Most of the sheets manufactured from these results have a 0.2% proof stress greater than the minimum specified value of 0.2% stress resistance of 7075-T6 and a tensile strength of 7075-T6 that is at the minimum specified tensile strength of 7075-T6. It can be seen that it is about 50 times larger. Reduced density of the alloy (8-10 compared to 7075)
%), the specific strength level of the alloy is 7075-T6
The size of the material is also noteworthy.

Example 3 Alloy composition (wt%) Lithium 2.39 Magnesium 0.70 Copper 1.81 Zirconium 0.16 Titanium 0.014 Aluminum The balance (including incidental impurities) was made into an ingot with a diameter of 216wn and was directly quenched and cast. It was cast at. The ingot was then homogenized at 540° C. for 16 hours and peeled to remove surface defects.

The ingot was divided into two pieces with a diameter of 185 mm and a length of 600 mm. These were preheated to 440°C and extruded using a 212 diameter chamber. One was extruded through a die with a cross section of 95 mm x 20 m at a speed of 5 ml'm t n, and the other one was extruded through a die with a diameter of 54 mm and a cross section of 5 ml.
/mln.

The extrudates were solution treated at 535° C. for 1 hour and quenched in cold water. The material was controlled 2.5% stretched and aged at 190°C for 16 hours.

Tensile specimens were taken from the front and rear of the extrusion. The results of the tensile test are as follows.

These results indicate that the alloy is capable of achieving 7075-T6 strength levels in extruded form.

Example 4 Alloy composition (weight -11%) Lithium 2.56 Magnesium 0.66 Copper 1.98 Zirconium 0.12 Titanium 0.026 Aluminum The balance (including incidental impurities) was produced directly from the alloy as an ingot with a diameter of 216 mm. Cast using the rapid cooling casting method. The ingot was then homogenized at 540° C. for 16 hours and peeled to remove surface defects.

Preheat the ingot to 480℃, and 1100gX1
oo+ Forged into a rectangular bar. The bars were solution heated at 540°C for 2 hours, cold water quenched, and aged at 190°C for 16 hours. The tensile properties of the forged bars were as follows.

Longitudinal direction 0.2%PS = 459 MPaTS =
546 MPa EL=6% Lateral direction 0.2% PS=401 MPaTS=
468 MPa EL=3% These results show that the alloy can achieve 7075-T73 properties in forged form.

All heat treated as-is alloys offer an 8-10% density savings and a 10-12 inch increase in modulus compared to all existing specified aerospace aluminum alloys.

The fracture toughness and fatigue life of the sheet materials were measured. 1.
Longitudinal-lateral (L-T) fracture toughness (Kc) of 6 simple sheets is 4
68.5 MPa y'F at proof stress value of 25 MPa;
was measured. Average L-T fatigue life at proof stress of 425 MPa is 3.14 at maximum test stress of 140 MPa
×105 cycles (average of 3 samples) was determined. The test was performed on a sample without notch (xt==2.5)
and tested in uniaxial tension at a stress ratio of +0.1.

The alloy was found to exhibit superplastic behavior with an elongation of 400-700% in cold rolled 1.6 sheet heat treated in a hot blank prior to cold rolling in accordance with the above-described aspect of the invention.

Furthermore, it was found that the superplastic behavior of the alloy was further enhanced to over 700 by addition of 1.6-Zn.

We have found that when the alloy according to the invention is cast and extruded in round billet form, the resulting tensile properties are 10 to 15 inches higher than those obtained for sheet material under the same heat treatment conditions. was also shown.

The alloy according to the invention has properties that are acceptable for forging.

[Brief explanation of the drawing]

Figure 1 is a diagram showing differential scanning calorimetry curves for three types of alloy compositions, and Figures 2 and 3 are diagrams showing variations in tensile properties with aging time and statistical data on the tensile properties. It is. Patent applicant Alkan International Limited Patent agent Akira Aoki Patent attorney Kazuyuki Nishidate 1) Yukio Patent attorney Akira Yamaguchi Patent attorney Masaya Nishiyama 0.2% proof stress (MPa) Fto, 2 (v!dW) To'f4 G Hei 1 & Procedural amendment (method) % formula % 1, Indication of the case 1982 Patent application No. 61260 2, Name of the invention Aluminum alloy 3, Person making the amendment Relationship with the case Patent applicant name Alkan International Limited 4
, Agent 6, Subject of amendment (1) Drawings (2) Specification 7, Contents of amendment (1) Engraving of drawings (no change in content) (2) Engraving of specification (no change in content) 8, Attached List of documents (1) 1 copy of engraving drawings (2) 1 copy of engraving specification

Claims (1)

[Claims] 1. Composition in the following ranges by weight: Lithium 2.3 to 2.9 Magnesium 0.5 to 1.0 Copper 1.6 to 2.4 Zirconium 0.05 to 0.25 Titanium O -0.5 Manganese 0-0.5 Nickel 0-0.5 Chromium 0-0.5 Zinc 0-2.0 Aluminum balance (including incidental impurities). 2. An alloy according to claim 1, wherein the copper to magnesium ratio is between 1.6:1 and 4.8:1, preferably 3:1. 3. Steps (a) to (f): (a) 2.3% by weight
~2.9% lithium, 0.5-1.0% magnesium, 1.6-2.4% copper, 0.05-0.25% zirconium, 0-0.5% titanium, Aluminum alloy consisting of 0-0.5% manganese, 0-0.5% nickel, 0-0.5% chromium, 0-2.0% zinc and balance aluminum (with incidental impurities) (b) the temperature and time to bring substantially all of the lithium, magnesium and copper, and zinc into a solid solution in the hot blank; (C) reliably cool the hot blank; (d) further heat-treat the cooled blank to precipitate these age hardening phases in a solid solution; (e
) continuing the heat treatment to create a coarse-grained overaged structure, and then (f) cold-pressing the blank to form a sheet or strip, and at any location and in any direction of the sheet or stop. The elongation properties of the sheet or strip vary by 2.0% or less from the elongation properties in the rolling direction. 4. At every position and in every direction on said sheet or strip, its elongation properties vary from the elongation properties in the rolling direction by less than 25 MPa (0.2% stress plus tensile stress). The method described in Section 3. 5. The initial holding temperature of the hot blank is between 480°C and 540°C, depending on the thickness of the blank and the previous thermal history, and the holding time varies between 20 and 120 minutes; A method according to claim 3 or 4. 6. The method of claim 5, wherein the hot blank is positively cooled by blast air cooling. 7. Once the hot blank has cooled down to a temperature below 480°C, the blank is reheated to form Li, M
7. A method according to any one of claims 3 to 6, characterized in that: g, Cu and some Zn. 8. The method according to any one of claims 3 to 7, wherein the hot blank has a thickness of between 12.5 and 3 gyo. 9. A method according to any one of claims 3 to 8, wherein the sheet or strip has a thickness of less than 1011 III+, preferably less than 5 mm. 4. The method of claim 3, wherein: io, the positive cooling ends at the temperature of the further heat treatment, so that the positive external cooling step and the further heat treatment step are combined. ]1. 11. A method according to claim 10, wherein the further heat treatment is for a period of 8 to 16 hours at a temperature between 300<0>C and 400<0>C.