US20030051784A1 - Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products - Google Patents

Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products Download PDF

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Publication number
US20030051784A1
US20030051784A1 US10/103,273 US10327302A US2003051784A1 US 20030051784 A1 US20030051784 A1 US 20030051784A1 US 10327302 A US10327302 A US 10327302A US 2003051784 A1 US2003051784 A1 US 2003051784A1
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Prior art keywords
hours
aging
alloy
aluminum
product
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Abandoned
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US10/103,273
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English (en)
Inventor
Diana Denzer
Dhruba Chakrabarti
John Liu
Lynn Oswald
Robert Westerlund
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Howmet Aerospace Inc
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Alcoa Inc
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Priority to US10/103,273 priority Critical patent/US20030051784A1/en
Assigned to ALCOA INC. reassignment ALCOA INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: WESTERLUND, ROBERT W., DENZER, DIANA K., CHAKRABARTI, DHRUBA J., OSWALD, LYNNE, LIU, JOHN
Publication of US20030051784A1 publication Critical patent/US20030051784A1/en
Priority to US11/003,650 priority patent/US20050269000A1/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/053—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with zinc as the next major constituent

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  • This invention relates to the field of aluminum alloys for aerospace applications, typically 7000 Series or 7xxx alloys as designated by the Aluminum Association. More particularly, this invention relates to an improved method for imparting better yield strengths to 7000 Series aluminum alloys tempered in a known, preferred manner. This method achieves such strength improvements without detrimentally effecting corrosion resistance, particularly exfoliation corrosion resistance. Conversely, the method of this invention can be used to impart better corrosion resistance performance in these 7000 Series aluminum aerospace alloys at or about the same yield strength levels. For the sheet and plate varieties of these products, the invention may be practiced on products situated in their respective dies for further achieving some age forming improvements thereon. It is to be understood that analogous improvements in the strength/corrosion properties of 7000 Series extrusions and forgings should also take place.
  • a typical age forming practice for large aircraft wing panels usually involves starting with a W51 tempered (solution heat treated and stress relieved) plate product.
  • that same W51-tempered part may be subjected to the first of several multiple step tempering practices while still flat, either by the material supplier, an intermediate distributor/handler, or the end user/customer, i.e. the ultimate aircraft manufacturer/assembler.
  • this first artificial aging step is not typically performed while the alloy material is kept in its ultimate forming die. Instead, the latter plate product is sawed and machined to a desired shape and thickness for a making given wing panel component part therefrom.
  • That machined panel is then aligned over a forming die whereupon pressure is applied to force said panel to assume its final or near-final shape, that of the die itself.
  • the die and panel may then be artificially aged together per prescribed practices. Alternately, this first tempering in a multiple step aging practice could take place with a sawed and machined part situated “in” its forming die, after which both part and die are further artificially aged together.
  • a typical 7xxx age forming practice entails one or two steps. If a two step practice is used, the first step is usually performed at a lower temperature than the second. That first step is typically about 200-250° F. for about 3 to 12 hours. The second step of that two-step practice targets one or more temperatures between about 280-350° F. for about 6 to 24 hours, and in some instances for as high as 30 hours. If only a one step practice is used, that typically transpires at one or more target temperatures between about 280-320° F. for about 6 to 24 hours.
  • the preferred first of two, or second of three, aging practice steps of this invention proceed at a significantly lower, first or second step temperature as compared to the prior art temperings described above, lower by about 40 to 50° F.
  • the results of this invention were even more surprising since strength increases were not expected using a lower temperature aging treatment following the 300°+ practices of the preferred embodiments herein.
  • this invention relates to an improved method for artificially aging 7000 Series aluminum aerospace alloys.
  • This method imparts improved strength performance at the same corrosion resistance performance level, or improved corrosion resistance performance at the same strength level. It accomplishes these property improvements by purposefully adding a second aging step or stage to a typical one-step tempering process, or a purposeful third step/stage to a known two-step aging operations.
  • the purposefully added step/stage (second of two or third of three) extends at about 225-275° F. for about 3-24 hours, or more preferably at about 250° F. for about 6 hours or more.
  • the invention especially imparts improved combinations of strength and exfoliation corrosion resistance to 7055 aluminum alloy products (Aluminum Association designation) in sheet, plate, extrusion or even forged product forms.
  • this same invention entails adding a third step to the two-step aging practice for “ ⁇ T7951”. That third step likewise extends at about 225-275° F. for about 3-24 hours, or more preferably at about 250° F. for about 6 hours. With the addition of that third aging step following a lower than usual second temperature aging practice, a surprising and significant increase in strength was observed at the same level of corrosion resistance, especially exfoliation corrosion resistance. Or restated once more, the addition of this third aging step above imparts a significant increase in corrosion resistance, especially exfoliation corrosion resistance, at about the same strength level.
  • adding a second step to a one-step aging practice for 7000 Series aluminum alloys, or adding a third step to a known two-step aging practice is: (1) always lower than the aging step that it follows; AND (2) that preceding step, itself, whether the first of now TWO aging steps; or the second of now THREE aging steps, takes place at temperatures lower than what is otherwise known to be practiced for other T77 aging practices for 7000 Series alloys.
  • FIGS. 1 ( a ) through ( c ) are graphic representations of three, 2-step aging schemes according to the invention.
  • FIGS. 2 ( a ) through ( g ) are graphic representations of seven representative 3-step aging schemes according to the invention.
  • FIG. 3 is a graph depicting the relative improvement in strength, particularly longitudinal tensile yield strength (TYS), versus electrical conductivity (in % IACS) both measured at T/2 as representative of exfoliation corrosion resistance performance, for various samples of 0.75 inch thick, 7055 plate after artificial aging by known 1- and 2-step practices (hollow triangular data points) versus the preferred aging practice of this invention to which a controlled second or third step, as appropriate was purposefully added to the aforesaid known practices (shown with solid circular data points);
  • FIG. 4 is the same graph of FIG. 3 through which solid curves A-A and B-B were drawn using a quadratic statistical equation approach for predicting the strength/EC slopes of the Invention versus known (1- and 2-step aged) 7055 plate product and around which 95% confidence bands were drawn in dotted lines;
  • FIG. 5 is a graph depicting the numerical increase in tensile yield strength (ksi) values predicted for 7055 Plate aged by the invention over its known (1- and 2-step aged) counterparts per the quadratic curves in FIG. 4 above;
  • FIG. 6 is a graph depicting the increase in tensile yield strength values predicted (by percent improvement) for 7055 Plate aged by the invention over its known (1- and 2-step aged) counterparts;
  • FIG. 7 is a graph numerically depicting the improvement in electrical conductivity (% IACS) predicted for 7055 Plate aged by the invention over its known (1- and 2-step aged) counterparts;
  • FIG. 8 is a graph depicting that same improvement in predicted electrical conductivity values (by percentages) for 7055 Plate aged by the invention versus its known (1- and 2-step aged) counterparts.
  • FIGS. 1 ( a ) through ( c ) are graphic representations of three, 2-step aging schemes according to the invention, with 1 ( a ) representing a 2-step or staged method with a partial (air) cooling between controlled steps/stages.
  • FIG. 1( b ) there is shown a representative 2-step method that has a controlled, furnace ramping down between first and second steps/stages.
  • FIG. 1( c ) schematically depicts a 2-step or staged method with a distinct, fully separated cooling (via air or cold water quenching “CWQ”) between steps/stages.
  • CWQ cold water quenching
  • FIGS. 2 ( a ) through ( g ) are graphic representations of seven representative 3-step aging schemes according to the invention.
  • FIG. 2( a ) a 3-step or staged method is shown with a partial (air) cooling between controlled steps 2 and 3.
  • FIG. 2( b ) illustrates a 3-step method that has a controlled, furnace ramping down to achieve the same effect as the isothermal 3 rd step described earlier.
  • FIG. 2( c ) represents a variation on 2 ( b ) with a controlled temperature ramping up as step 1.
  • FIG. 2( d ) a variation on 2 ( a ) is shown with a controlled interrupted cool down between steps 1 and 2.
  • FIG. 2( e ) depicts a variation on 2 ( b ) with a full cool down between steps 1 and 2 and a controlled, furnace ramping down to achieve the same effect as the isothermal 3 rd step described earlier.
  • FIG. 2( f ) illustrates a variation on the 3 step practice of 2 ( c ) above, but with a distinct, fully separated cooling (via air or cold water quenching “CWQ”) between steps 2 and 3.
  • representative FIG. 2( g ) shows still another variation on 2 ( f ) with distinct, fully separated cooling (via air or cold water quenching “CWQ”) between each of steps 1, 2 and 3. It is important to note that in each of the foregoing aging examples, both FIGS. 1 and 2, that the latter stages of any such practice according to the invention can be performed either in or out of a forming die.
  • One main means for evaluating the data of Table 1 is to compare relative sample strengths at a constant electrical conductivity EC value.
  • FIGS. 3 through 7 facilitate such a comparison.
  • TYS values ran about 1.5 ksi higher when another step (the second of two or third of three steps) was employed per the present invention.
  • An alternative evaluation from Table 1/FIG. 3 leads to another conclusion about this invention, namely that at a constant TYS value, relatively higher electrical conductivity values (and hence, relatively improved corrosion resistance performances) were observed per the added step or stage of this invention (again, the second of two or third of three steps).
  • TYS Increase due to Inv. 1.678 ksi over range of EC (36.0 to 39.2% IACS)
  • FIG. 5 shows the numerical increase in tensile yield strength (ksi) values predicted for 7055 Plate aged by the invention over its known (1- and 2-step aged) counterparts.
  • FIG. 6 predicts that same improvement in strength as a function of electrical conductivity by percentage rather than in actual ksi values observed.
  • Table 3 The data supporting FIGS. 5 and 6 is found in Table 3 that follows: TABLE 3 Predicted Increase in Tensile Yield Strength due to Invention Quadratic Model EC (% IACS) (Numerical ksi) (Percentage Increase) 36 1.91 36.5 1.91 37 1.92 37.5 1.678 1.93 38 1.96 38.5 1.98 39 2.02
  • FIG. 7 shows the numerical EC improvement predicted (in % IACS values) for the invention over its known (1- and 2-step aged) counterparts.
  • FIG. 8 predicts that same improvement in strength as a function of electrical conductivity by percentage rather than in actual EC (% IACS) values observed. Note that for both FIGS 7 and 8 , EC increases could not be determined over the entire range of tensile yield strengths due to the mathematical consequence of inverting quadratic calculations.
  • Wing skins are typically made from thinner gauge plates as compared to the wing spars made from thick plate products. Thinner gauge plate products possess thin, narrow width grains brought about by greater rolling reductions, Such grains tend to be highly laminated. Unfortunately, corrosion induces delamination along these grain boundaries during service. Hence, resistance to exfoliation corrosion is an important requirement for the upper wing skins of today's larger aircrafts. As with SCC, exfoliation resistance improves with progressive overaging. This invention attempts to maintain exfoliation corrosion resistance performance while still managing to improve strength values, particularly those of a TYS variety. Alternately, this invention will impart improved exfoliation corrosion resistance performance at or about the same strength value levels.
  • the method of this invention includes adding a third aging step to a known two step aging practice, like “T79” tempering, it is not always necessary to practice the invention in separate, distinct stages.
  • the method of this invention may just as easily be practiced on an aging operation that includes slowly ramping up, in a controlled manner, through one or more, first stage temperatures without any true stopping, or holding point. By gradually passing through the first “stage”, one may still accomplish the effects of a first heat treatment temperature without really imposing a separately distinct furnace operation thereon.
  • the same effect of this method may be achievable by slowly, yet controllably, ramping down from the first of two, or second of three heat treatment steps/stages without having a purposeful cooling off period or quench (air, cold water or otherwise) thereafter.
  • the same relative property improvements may be observed ramping controllably down from the higher, preceding heat treatment (either the first of two; or second of three) stage and through the preferred added heat treatment times and temperatures of THIS invention ultimately achieving a total, cumulative effect of 7000 Series aluminum alloy product exposure of about 225-275° F. for about 3-24 hours.

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  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Testing Resistance To Weather, Investigating Materials By Mechanical Methods (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
US10/103,273 2001-03-20 2002-03-20 Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products Abandoned US20030051784A1 (en)

Priority Applications (2)

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US10/103,273 US20030051784A1 (en) 2001-03-20 2002-03-20 Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products
US11/003,650 US20050269000A1 (en) 2001-03-20 2004-12-03 Method for increasing the strength and/or corrosion resistance of 7000 Series AI aerospace alloy products

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US27740301P 2001-03-20 2001-03-20
US10/103,273 US20030051784A1 (en) 2001-03-20 2002-03-20 Method for increasing the strength and/or corrosion resistance of 7000 series Al aerospace alloy products

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US (1) US20030051784A1 (fr)
EP (1) EP1373591A2 (fr)
CN (1) CN1531603A (fr)
AU (1) AU2002245705A1 (fr)
BR (1) BR0208271A (fr)
CA (1) CA2441168A1 (fr)
WO (1) WO2002075010A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2015063747A (ja) * 2013-08-30 2015-04-09 株式会社Uacj 高強度アルミニウム合金押出薄肉形材およびその製造方法

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050006010A1 (en) * 2002-06-24 2005-01-13 Rinze Benedictus Method for producing a high strength Al-Zn-Mg-Cu alloy
US7666267B2 (en) 2003-04-10 2010-02-23 Aleris Aluminum Koblenz Gmbh Al-Zn-Mg-Cu alloy with improved damage tolerance-strength combination properties
CN100547098C (zh) 2003-04-10 2009-10-07 克里斯铝轧制品有限公司 一种铝-锌-镁-铜合金
US20050034794A1 (en) * 2003-04-10 2005-02-17 Rinze Benedictus High strength Al-Zn alloy and method for producing such an alloy product
JP5409125B2 (ja) * 2009-05-29 2014-02-05 アイシン軽金属株式会社 耐ｓｃｃ性に優れる７０００系アルミニウム合金押出材及びその製造方法
EP2518173B1 (fr) 2011-04-26 2017-11-01 Benteler Automobiltechnik GmbH Procédé de fabrication d'un composant de structure en tôle ainsi que composant de structure en tôle
EP3559293A4 (fr) * 2016-12-21 2020-05-13 Arconic Technologies LLC Produits d'alliage d'aluminium à teneur élevée en zinc

Citations (4)

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Publication number Priority date Publication date Assignee Title
US5221377A (en) * 1987-09-21 1993-06-22 Aluminum Company Of America Aluminum alloy product having improved combinations of properties
US5341303A (en) * 1991-08-12 1994-08-23 Avco Corporation Method of developing complex tool shapes
US5865911A (en) * 1995-05-26 1999-02-02 Aluminum Company Of America Aluminum alloy products suited for commercial jet aircraft wing members
US6048415A (en) * 1997-04-18 2000-04-11 Kabushiki Kaisha Kobe Seiko Sho High strength heat treatable 7000 series aluminum alloy of excellent corrosion resistance and a method of producing thereof

Family Cites Families (6)

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Publication number Priority date Publication date Assignee Title
IL39200A (en) * 1972-04-12 1975-08-31 Israel Aircraft Ind Ltd Method of reducing the susceptibility of alloys,particularly aluminum alloys,to stress-corrosion cracking
US4477292A (en) * 1973-10-26 1984-10-16 Aluminum Company Of America Three-step aging to obtain high strength and corrosion resistance in Al-Zn-Mg-Cu alloys
US4863528A (en) * 1973-10-26 1989-09-05 Aluminum Company Of America Aluminum alloy product having improved combinations of strength and corrosion resistance properties and method for producing the same
FR2409319A1 (fr) * 1977-11-21 1979-06-15 Cegedur Procede de traitement thermique de produits minces en alliages d'aluminium de la serie 7000
US5108520A (en) * 1980-02-27 1992-04-28 Aluminum Company Of America Heat treatment of precipitation hardening alloys
CN1489637A (zh) * 2000-12-21 2004-04-14 �Ƹ��� 铝合金产品及人工时效方法

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5221377A (en) * 1987-09-21 1993-06-22 Aluminum Company Of America Aluminum alloy product having improved combinations of properties
US5341303A (en) * 1991-08-12 1994-08-23 Avco Corporation Method of developing complex tool shapes
US5865911A (en) * 1995-05-26 1999-02-02 Aluminum Company Of America Aluminum alloy products suited for commercial jet aircraft wing members
US6048415A (en) * 1997-04-18 2000-04-11 Kabushiki Kaisha Kobe Seiko Sho High strength heat treatable 7000 series aluminum alloy of excellent corrosion resistance and a method of producing thereof

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2015063747A (ja) * 2013-08-30 2015-04-09 株式会社Uacj 高強度アルミニウム合金押出薄肉形材およびその製造方法

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EP1373591A2 (fr) 2004-01-02
BR0208271A (pt) 2004-03-09
WO2002075010A3 (fr) 2003-03-13
CN1531603A (zh) 2004-09-22
AU2002245705A1 (en) 2002-10-03
CA2441168A1 (fr) 2002-09-26
WO2002075010A2 (fr) 2002-09-26

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