EP0229075B1 - High strength, ductile, low density aluminum alloys and process for making same - Google Patents

High strength, ductile, low density aluminum alloys and process for making same Download PDF

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Publication number
EP0229075B1
EP0229075B1 EP19860902711 EP86902711A EP0229075B1 EP 0229075 B1 EP0229075 B1 EP 0229075B1 EP 19860902711 EP19860902711 EP 19860902711 EP 86902711 A EP86902711 A EP 86902711A EP 0229075 B1 EP0229075 B1 EP 0229075B1
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EP
European Patent Office
Prior art keywords
alloy
composite
aluminum
precipitates
hours
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Expired
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EP19860902711
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German (de)
English (en)
French (fr)
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EP0229075A1 (en
Inventor
Nack Joon Kim
Colin Mclean Adam
Richard Lister Bye, Jr.
Santosh Kumar Das
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Honeywell International Inc
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AlliedSignal Inc
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium

Definitions

  • the invention relates to a process for making high strength, high ductility, low density aluminum-based alloys that, in particular are characterized by a homogeneous distribution of composite precipitates in the aluminum matrix thereof.
  • the microstructure is developed by heat treatment method consisting of initial solutionizing treatment followed by multiple aging treatments.
  • Aluminum-lithium alloys offer the potential of meeting the weight savings due to the pronounced effects of lithium on the mechanical and physical properties of aluminum alloys.
  • the addition of one weight percent lithium (-3.5 atom percent) decreases the density by ⁇ 3% and increases the elastic modulus by ⁇ 6%, hence giving a substantial increase in the specific modulus (E/p).
  • heat treatment of alloys results in the precipitation of a coherent, metastable phase, 8' (Al 3 Li) which offers considerable strengthening.
  • development and widespread application of the Al-Li alloy system have been impeded mainly due to its inherent brittleness.
  • PFZ precipitate free zone
  • precipitate-induced intergranular fracture can be reduced by controlling processing to avoid the intergranular precipitation of stable AI-Li, Al-Cu-Li, Al-Mg-Li phases.
  • the problem of planar slip can be partly alleviated by promoting slip dispersion through the addition of dispersoid forming elements and the controlled co-precipitation of Al-Cu-Li, AI-Cu-Mg and/or Al-Li-Mg intermetallics.
  • the dispersoid forming elements include Mn, Fe, Co, etc.
  • the processed for developing a homogeneous distribution of such phase has required the strict control of processing parameters during the thermomechanical processing, as well as prolonged solutionizing and/or aging treatments. From the practical point of view, this process is quite undesirable and may also result in undesirable microstructural features such as recrystallization and wide precipitate free zones. Moreover, the process cannot be effectively applied to low Zr (e.g., 0.2 wt% Zr) containing alloys which produce a small volume fraction of heterogeneously distributed coarse composite precipitates (P.L. Makin and B. Ralph, Journal of Materials Science, vol. 19, pp. 3835-3843, 1984; P.J. Gregson and H.M. Flower, Journal of Materials Science Letters, vol. 3, pp. 829-834, 1984; P.L. Makin, D.J. Lloyd, and W.M. Stobbs, Philosophical Magazine A, vol. 51, pp. L41-L47, 1985).
  • low Zr e.g., 0.2 wt% Zr
  • the present invention provides a process for making aluminum-lithium alloys containing a high density of substantially uniformly distributed shear resistant dispersoids which markedly improve the strength and ductility thereof.
  • the low density aluminum-base alloys, of the invention consist essentially of the formula AI bal Zr a Li b X c , wherein X is at least one element selected from Cu, Mg, Si, Sc, Ti, U, Hf, Be, Cr, V, Mn, Fe, Co and Ni, «a» is from 0.15-2 wt%, «b» is from 2.5-5 wt%, «c» is from 0-5 wt% and the balance is aluminum.
  • microstructure of these alloys is characterized by the precipitation of composite A1 3 (Li, Zr) phase in the aluminum matrix thereof.
  • This microstructure is developed in accordance with the process of the present invention by subjecting an alloy having the formula delineated above to solutionizing treatment followed by multiple aging treatments. An improving process for making high strength, high ductility, low density aluminum-based alloy is thereby provided wherein the aluminum-based alloy produced has an improved combination of strength and ductility (at the same density).
  • the solutionizing and aging treatments according to the invention comprise the steps of:
  • the number of aging treatments can be from 2 to 10, more preferably from 2 to 5.
  • the solutionized alloy can be stretched.
  • the high strength, high ductility, low density aluminum-based alloy produced in accordance with the present invention has a controlled composite A1 3 (Li, Zr) precipitate which, advantageously, offers a wide range of strength and ductility combinations.
  • the present invention relates to the process of making high strength, high ductility, and low density AI-Li-Zr-X alloys.
  • the process involves the use of multiple aging steps during heat treatment of the alloy.
  • the alloy is characterized by a unique microstructure consisting essentially of «composite» A1 3 (Li, Zr) precipitate in an aluminum matrix (Fig. 1) due to the heat treatment as hereinafter described.
  • the alloy may also contain other Li, Cu and/ or Mg containing precipitates provided such precipitates do not significantly deteriorate the mechanical and physical properties of the alloy.
  • the factors governing the properties of the Al-Li-Zr-X alloys are primarily its Li content and microstructure and secondarily the residual alloying elements.
  • the microstructure is determined largely by the composition and the final thermomechanical treatments such as extrusion, forging and/or heat treatment parameters. Normally, and alloy in the as- processed condition (cast, extruded or forged) has large intermetallic particles. Further processing is required to develop certain microstructural features for certain characteristic properties.
  • the alloy is given an initial solutionizing treatment, that is, heating at a temperature (T i ) for a period of time sufficient to substantially dissolve most of the intermetallic particles present during the forging or extrusion process, followed by cooling to ambient temperature at a sufficiently high rate to retain alloying elements in said solution.
  • T i a temperature
  • the time at temperature T 1 will be dependent on the composition of the alloy and the method of fabrication (e.g., ingot cast, powder metallargy processed) and will typically range from 0.1 1 to 10 hours.
  • the alloy is then reheated to an aging temperature, T 2 , for a period of time sufficient to activate the nucleation of composite A1 3 (Li, Zr) precipitates, and cooled to ambient temperature, followed by a second aging treatment at temperature, T s , for a period of time sufficient for the growth of the composite A1 3 (Li, Zr) precipitate and a dissolution of 8' precipitate whose nucleation is not aided by Zr.
  • the alloy at this point is characterized by a unique microstructure which consists essentially of composite A1 3 (Li, Zr) precipitate. This composite Al 3 (Li, Zr) precipitate is resistant to dislocation shear and quite effective in dispersing dislocation motion (Fig. 2).
  • Fig. 3(b) clearly shows the homogeneous mode of deformation in an alloy subjected to the process claimed in this invention
  • Fig. 3(a) shows the severe planar slip observed in a conventionally processed alloy due to the shearing of 8' precipitates by dislocations (see Fig. 4).
  • the combination of ductility with high strength is best achieved in accordance with the invention when the density of the shear resistant dispersoids ranges from 10 to 60 percent by volume, and preferably from 20-40 percent by volume.
  • the exact temperature, T 1 , to which the alloy is heated in the solutionizing step is not critical as long as there is a dissolution of intermetallic particles at this temperature.
  • the exact temperature, T 2 in the first aging step where the nucleation of composite A1 3 (Li, Zr) precipitate is promoted, depends upon the alloying elements present and upon the final aging step.
  • the optimum temperature range for T z is from 100°C to 180°C.
  • the exact temperature, T 3 whose range is from 120°C to 200°C, depends on the alloying elements present and mechanical properties desired. Generally, the times at temperatures T 2 and T 3 are different depending upon the composition of the alloy and the thermomechanical processing history, and will typically range from 0.1 to 100 hours.
  • Fig. 2 is a weak beam dark field transmission electron micrograph showing microstructure of a deformed alloy (Al-3.7Li-0.5Zr) which has been solutionized at 540°C for 4 hours and subsequently aged at 160°C for 4 hours followed by final aging at 180°C for 16 hours.
  • a deformed alloy Al-3.7Li-0.5Zr
  • Such heat treatment promotes the precipitation of composite Al 3 (Li, Zr) which is highly resistant to dislocation shear and is quite effective in dispersing the dislocation movement.
  • Fig. 3(a) shows a bright field electron micrograph showing microstructure of a deformed alloy (Al-3.7 Li-0.5Zr) which has not been given the claimed process.
  • the alloy had been aged, for 16 hours at 180 ° C after solutionizing at 540°C for 4 hours. This alloy showed the pronounced planar slip which is the common deformation characteristic of brittle alloy.
  • Fig. 3(b) illustrates the beneficial effect of the claimed process on the deformation behavior of an alloy having the composition AI-3.7Li-0.5Zr. After solutionizing at 540°C for 4 hours, the alloy had been subjected to the double aging treatment of 160°C for 4 hours and 180°C for 16 hours. The deformation mode of this alloy is quite homogeneous indicating high ductility.
  • An alloy having a composition of Al-3.1Li-2Cu-1 Mg-0.5Zr was developed for medium strength applications as shown in Table I.
  • the alloy was solutionized at 540°C for 2.5 hours, quenched into water at about 20°C and given conventional single aging and the claimed double aging treatments.
  • a high strength AI-Li alloy was made to satisfy the requirements for high strength applications for aerospace structure.
  • An alloy having a composition of AI-3.2Li-2Cu-2Mg-0.5Zr was solutionized at 542°C for 4 hours.
  • conventional aging treatment 190°C for 16 hours
  • yield strength 521 MPa
  • ductility 3.6%
  • double aging of the alloy 160°C for 4 hours followed by 180°C for 16 hours
  • yield strength yield strength of 554 MPa
  • ductility 5.5%), which meets property requirements for high strength alloys needed for aerospace structural applications.
  • This example illustrates the beneficial effect of the claimed process on the mechanical properties of a simple ternary alloy Al-3.7Li-0.5Zr.
  • the alloy was solutionized at 540°C for 4 hours, and subsequently aged as shown in Table III.
  • the resulting tensile properties show that the claimed results in improved strength and ductility compared to the conventional process.
  • a wide range of mechanical properties can be achieved by using multiple aging conditions. For example, a triple aging treatment (120°C, 4 hours + 140°C, 16 hours + 160°C, 4 hours) produced yield strength of 446 MPa and ultimate tensile strength of 464 MPa with 4.6% elongation. As a result, a variety of heat treatments of the alloys according to the claims can be employed to produce alloys having a variety of mechanical properties.
  • FIG. 5 shows the dark field electron micrograph of a typical alloy AI-3.2Li-3Cu-1.5Mg-0.2Zr which had been solutionized at 540°C for 4 hours, reheated to 170°C for 4 hours followed by final aging at 190°C for 16 hours.
  • the large volume fraction of composite AI 3 (Li,Zr) precipitate observed in such an alloy indicates that the claimed process in also quite effective in Al-Li alloys having low Zr content of 0.2%.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Laminated Bodies (AREA)
  • Manufacture Of Alloys Or Alloy Compounds (AREA)
EP19860902711 1985-07-08 1986-04-11 High strength, ductile, low density aluminum alloys and process for making same Expired EP0229075B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US75243385A 1985-07-08 1985-07-08
US752433 1985-07-08

Publications (2)

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EP0229075A1 EP0229075A1 (en) 1987-07-22
EP0229075B1 true EP0229075B1 (en) 1989-09-27

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EP (1) EP0229075B1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
JP (1) JPS62502295A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
AU (1) AU578828B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CA (1) CA1280342C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (1) DE3665884D1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
WO (1) WO1987000206A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007056298A1 (de) * 2007-11-22 2009-05-28 Bayerische Motoren Werke Aktiengesellschaft Kolben

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5178695A (en) * 1990-05-02 1993-01-12 Allied-Signal Inc. Strength enhancement of rapidly solidified aluminum-lithium through double aging
RU2163938C1 (ru) * 1999-08-09 2001-03-10 Государственное предприятие "Всероссийский научно-исследовательский институт авиационных материалов" Коррозионно-стойкий сплав на основе алюминия, способ получения полуфабрикатов и изделие из него
RU2163940C1 (ru) * 1999-08-09 2001-03-10 Государственное предприятие "Всероссийский научно-исследовательский институт авиационных материалов" Сплав на основе алюминия и изделие, выполненное из него
AUPQ485399A0 (en) 1999-12-23 2000-02-03 Commonwealth Scientific And Industrial Research Organisation Heat treatment of age-hardenable aluminium alloys
AUPR360801A0 (en) 2001-03-08 2001-04-05 Commonwealth Scientific And Industrial Research Organisation Heat treatment of age-hardenable aluminium alloys utilising secondary precipitation
RU2513492C1 (ru) * 2013-02-21 2014-04-20 Открытое акционерное общество "Всероссийский институт легких сплавов" (ОАО "ВИЛС") Деформируемый термически неупрочняемый сплав на основе алюминия
CN104694786B (zh) * 2015-01-29 2016-09-07 东莞劲胜精密组件股份有限公司 一种铝合金
CN106756272A (zh) * 2016-12-14 2017-05-31 张家港市广大机械锻造有限公司 一种用于航空器壳体的合金制造方法
WO2019152664A1 (en) * 2018-01-31 2019-08-08 Arconic Inc. Corrosion resistant aluminum electrode alloy
KR102494830B1 (ko) * 2022-03-22 2023-02-06 국방과학연구소 다단 시효처리를 이용한 Al-Li 합금의 제조방법

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0088511B1 (en) * 1982-02-26 1986-09-17 Secretary of State for Defence in Her Britannic Majesty's Gov. of the United Kingdom of Great Britain and Northern Ireland Improvements in or relating to aluminium alloys
CA1198656A (en) * 1982-08-27 1985-12-31 Roger Grimes Light metal alloys
JPS59118848A (ja) * 1982-12-27 1984-07-09 Sumitomo Light Metal Ind Ltd 電気抵抗を高めた構造用アルミニウム合金
US4624717A (en) * 1983-03-31 1986-11-25 Alcan International Limited Aluminum alloy heat treatment
US4661172A (en) * 1984-02-29 1987-04-28 Allied Corporation Low density aluminum alloys and method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007056298A1 (de) * 2007-11-22 2009-05-28 Bayerische Motoren Werke Aktiengesellschaft Kolben

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AU5774986A (en) 1987-01-30
WO1987000206A1 (en) 1987-01-15
JPS62502295A (ja) 1987-09-03
AU578828B2 (en) 1988-11-03
JPS648066B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1989-02-13
EP0229075A1 (en) 1987-07-22
DE3665884D1 (en) 1989-11-02
CA1280342C (en) 1991-02-19

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