Classifications

• • 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
• • 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
  • C22F1/047—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 magnesium as the next major constituent
• • 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
• • 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
  • C22F1/057—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 copper as the next major constituent

Definitions

• the present invention discloses a method for producing a high damage tolerant aluminium rolled alloy having a good toughness and an improved fatigue crack growth resistance while maintaining good strength levels and to an aluminium alloy sheet or plate product having such a high toughness and an improved fatigue crack growth resistance. Furthermore, the invention relates to the use of an alloy product obtained by the method of this invention. It is known in the art to use heat treatable aluminium alloys in a number of applications involving relatively high strength such as aircraft fuselages, vehicular members and other applications. Aluminium alloys AA2024, AA2324 and AA2524 are well-known heat treatable aluminium alloys which have useful strength and toughness properties in T3, T39 and T351 tempers.
• aluminium alloys AA6013 and AA6056 are well-known heat treatable aluminium alloys which have useful strength and toughness properties as well as a good fatigue crack growth resistance in both T4 and T6 tempers. It is known that the T4 temper condition refers to a solution heat treated and quenched condition, naturally aged to a substantially stable property level, whereas T6 tempers refer to a stronger condition produced by artificially aging. Several other AA2000 and AA6000 series alloys are generally unsuitable for the design of commercial aircraft which require different sets of properties for different types of structures.
• US-5,213,639 discloses a method for producing an aluminium alloy of the AA2000-series with an aluminium base alloy which is hot rolled, heated and again hot rolled, thereby obtaining good combinations of strength together with high fracture toughness and a low fatigue crack growth rate. It is disclosed to apply an inter-annealed treatment after hot rolling the casted ingot with a temperature between 479°C and 524°C and again hot rolling the inter-annealed alloy. Such alloy is reported to have a 5% improvement over the conventional AA2024-series alloys in T-L fracture toughness and an improved fatigue crack growth resistance at certain ⁇ K-levels. It has been reported that the known AA6056 alloy is sensitive to inter-crystalline corrosion in the T6 temper condition.
• US-5,858,134 provides a process for the production of rolled or extruded products having a defined chemical composition, and whereby the products are brought in an over-aged temper condition requiring time and money consuming processing times at the end of the manufacturer of aerospace components.
• the Mg/Si ratio is less than 1.
• US-4,589,932 discloses an aluminium wrought alloy product for e.g. automotive and aerospace constructions, which alloy was subsequently registered under the AA designation 6013.
• Such aluminium alloy has been solution heat treated at a temperature in a range of 449°C to 582°C, approaching the solidus temperature of the alloy.
• EP-A-1143027 discloses a method for producing an Al-Mg-Si alloy of the AA6000-series having a defined chemical composition and wherein the products are subjected to an artificial aging procedure to improve the alloy and to meet high damage tolerance ("HDT") characteristics similar to those of the AA2024-series which are preferably used for aeronautical applications but which are not weldable. The aging procedure is being optimised using a respective function of the composition.
• EP-1170394-A2 discloses an aluminium alloy sheet product with improved fatigue crack growth resistance having an anisotropic microstructure defined by grains having an average length to width aspect ratio of greater than about 4. Such alloy has an improvement in compressive yield strength properties which is achieved by respective sheet products in comparison with conventional AA2524-sheet products.
• WO-97/22724 discloses a method and an apparatus for producing an aluminium alloy sheet product, typically for automotive application, with improved yield strength by continuously and rapidly heating the hot rolled and cold rolled sheet, which has been solution heat treated and quenched, to a pre-aging temperature prior to the continuous coiling step. After rapidly heating, the sheet in coil form is ambiently cooled, the rapid heating and ambient cooling improving the paintbake response of the aluminium alloy sheet. It is disclosed that it is preferred to rapidly heating the coiled sheet to between 65°C and 121 °C and to choose an ambient cooling rate and which is preferred to be between 1.1°C/h and 3.3°C/h.
• the HDT-properties should preferably be better than those of conventional manufactured AA6013-T6, 6056-T6 alloys and preferably better than AA2024-T3 or AA2524-T3 alloys.
• FCGR fatigue crack growth rate
• the present invention solves one or more of the above mentioned objects by the features of independent claims.
• a method for producing a high damage tolerant aluminium alloy having a high toughness and an improved fatigue crack growth resistance comprising the steps of a.) casting an ingot having a composition selected from the group consisting of AA2000, AA5000, AA6000, and AA7000-series alloys; b.) homogenising and/or pre-heating the ingot after casting; c.) hot rolling the ingot into a hot rolled product, and optionally further cold rolling the hot rolled product into a cold rolled product, characterized in that the hot rolled product leaves the hot rolling mill at an hot-mill exit temperature (T Exit ) and cooling the hot rolled product from said
• T Exit hot-mill exit temperature
• T(t) 50 - (50 - T E ⁇ it)e t and wherein T(t) is the temperature (°C) as function in time (expressed in hours), t is the time (expressed in hours) and ⁇ (expressed in hrs -1 ) is a parameter defining the cooling rate and is in the range of -0.09 ⁇ 0.05 (hrs -1 ), and more preferably in a range of -0.09 ⁇ 0.03 (hrs "1 ). It has been found that below the temperature of 150°C the cooling rate is no longer relevant to achieve one or more of the advantages found according to this invention.
• Typical hot-mill exit temperatures in an industrial scale practice are in a range of 350 to 500°C and are alloy dependent, for example for an AA6xxx the exit temperature will be at the higher end of this range of about 420 to 500°C, whereas for AA2xxx and AA7xxx-series alloys this would be at the lower end of this range of about 350 to 425°C.
• a further cold rolling of the cooled hot rolled product in coil form is optional.
• the cold rolling can be straight or cross rolling. Further steps of inter-annealing before, during or after cold rolling are also optional.
• a second alternative for subjecting the hot rolled product to a controlled cooling cycle is the step of continuously moving the alloy through a furnace after hot rolling, wherein said furnace is adjustable to apply heat and/or coldness to the alloy while passing to its cold rolling station or coiling station.
• the rolled product is first hot rolled to a desired gauge and then cooled to room temperature using conventional cooling.
• the cooled hot rolled product is reheated to a hot-mil exit temperature and then allowed to cool to below 150°C using the controlled cooling cycle according to the invention and followed by further processing.
• the hot rolled product is either fed to said furnace after hot rolling or coiled after hot rolling wherein the further processing is done on coils (sheet route). If the product is cut into plates during or after hot rolling the further processing is done on thereby produced plates.
• the furnace is preferably adjustable to apply various amounts of heat close to the hot rolling station and other amounts of heat at a greater distance from the hot rolling station, depending on the cooling rate, thickness and other dimensions of the hot rolled product leaving the hot rolling station.
• the hot rolled product When the hot rolled product is subjected to the controlled cooling cycle by coiling it is possible to coil the alloy after hot rolling in a respective furnace, wherein said furnace is then also preferably adjustable to apply heat to control the cooling cycle.
• the hot rolled product has a gauge in a range of up to 12 mm while leaving the hot rolling mill at the hot-mill exit temperature, and preferably in a range of 1 to 10 mm, and most preferably in the range of 4 to 8 mm.
• the total cold roll reduction is in a range of 40 to 70% to further optimise the mechanical properties.
• the final gauge of the rolled alloy product is preferably in a range of about 2 to 7 mm.
• the method in accordance with the present invention may further include one or more of the following steps: d.) solution heat treating of the hot rolled product after being subjected to the controlled cooling cycle or of the cold rolled product at a temperature and time sufficient to place into solid solution soluble constituents in the alloy; e.) quenching the solution heat treated alloy product by one of spray quenching or immersion quenching in water or other quenching media; f.) optionally stretching or compressing of the quenched alloy product or otherwise cold worked to relieve stresses, for example levelling of sheet products; g.) optionally ageing the quenched and optionally stretched or compressed alloy product to achieve a desired temper, which is dependent of the alloy chemistry, but includes the tempers T3, T351 , T6, T4, T74, T76, T751 , T7451, T7651 , T77, T79, Furthermore, it is possible to anneal and/or reheat a hot rolled ingot after a first hot rolling operation and then again hot rolling the product to a final
• the average cooling rate when using the controlled cooling cycle according to the invention is in a range of 12 to 20°C/hour.
• the cast ingot for the processing route of the method as disclosed herein comprises the following composition (in weight.%): Si 0.6 - 1.3, Cu 0.04 - 1.1 , Mn 0.1 - 0.9, Mg 0.4 - 1.3, Fe 0.01 - 0.3, Zr ⁇ 0.25, Cr ⁇ 0.25, Zn ⁇ 0.6, Ti ⁇ 0.15, V ⁇ 0.25, Hf ⁇ 0.25, other elements, in particular impurities, each less than 0.05 and less than 0.20 in total, balance aluminium. And more preferably alloys within the compositional range of AA6013 orAA6056.
• Another embodiment of the present invention uses an ingot comprises the following composition (in weight.%): Cu 3.8 - 5.2, Mg 0.2 -1.6, Cr ⁇ 0.25, Zr ⁇ 0.25, and preferably 0.06 -
• the method uses an ingot comprises the following composition (in weight.%): Zn 5.0 - 9.5, Cu 1.0 - 3.0, Mg 1.0 - 3.0, Mn ⁇
• an aluminium alloy sheet or plate product which has high toughness and an improved fatigue crack growth resistance and which is made of an alloy product which is produced according to a method which has been described above and which will be described in more details herein below.
• Fig. 1 is a typical cooling curve of an aluminium alloy cooled down after hot rolling using the method according this invention.
• Example 1 In a first preferred embodiment of the present invention, two conventional alloys (AA6013 and AA6056) were cast and processed to a sheet product. Here, two processing variants were used: Route 1. A normal processing route by lab-casting ingots of conventional AA6013 and AA60156-alloy compositions was used. Blocks of 80x80x100mm were sawn, homogenised, preheated and hot rolled to 4.5 mm sheet.
• the alloy has been processed to a sheet product with a hot rolling gauge of 4.5mm.
• the following three processing variants were then applied: Route 1. A standard processing route. (No coiling step after hot rolling).
• Route 2. The inventive processing route with coiling after hot rolling and hot rolling and cold rolling in the same direction.
• Route 3. The inventive processing route with coiling after hot rolling and hot rolling and cold rolling in dissimilar directions (cross rolling). All three above mentioned processing variants were applied to the following general processing route: a. DC-casting of ingots of an alloy composition in accordance with Table 3. b. Homogenising the cast ingots. c.
• Table 6 Values of Table 5, relative to standard (Route 1).
• Fig. 1 shows a typical continuous cooling down curve for an aluminium AA7050 alloy when cooled down from a hot-mill exit temperature of 440°C to a temperature below 150°C, whereby the metal sheet has a gauge of 4.5 mm and being immediately coiled when leaving the hot-mill in accordance with an embodiment of the method of this invention.
• the width of the coil was 1.4 meter.
• the temperatures of the coil as function of time is also given in Table 7 for the hottest spot of a coil (being the centre, and indicated as HotSpt in Fig.1) and the coldest spot (being the edge of a coil, and indicated as ColdSpt in Fig.1)). Table 7 provides also the temperatures in case a coil having a width of 2.8 meter.
• the ⁇ is about -0.084 hrs "1 .
• the ⁇ would typically be in the range of -0.5 to -2 hrs ⁇ and resulting in the such a plate would cool down from the hot mill exit temperature to a temperature of 150°C or less in a time period of less than 3 hours.
• the controlled cooling cycle follows the equation set out above and in the claims, and the average cooling rate of the coiled product form from 440 to 150°C is within the range of 12 to 20°C/hour.

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• Chemical & Material Sciences (AREA)
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• Engineering & Computer Science (AREA)
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• 2004
  • 2004-10-29 JP JP2006537227A patent/JP5052895B2/ja active Active
  • 2004-10-29 CN CN200480030024A patent/CN100577848C/zh active Active
  • 2004-10-29 RU RU2006118354/02A patent/RU2326181C2/ru active
  • 2004-10-29 DE DE112004001985T patent/DE112004001985T5/de not_active Withdrawn
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