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
  • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
• • 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
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent

Definitions

• the magnesium content is controlled in relation to the copper and manganese content in accordance with the following equation:
• Mg min. 0.32 Cu where Mn is not greater than 0.5%
• Mg min. 0.2+0.32 Cu0.4 Mn where Mn is greater than 0.5%
• This invention relates to aluminum base alloy plate having improved short transverse tensile elongation and resistance to stress corrosion.
• heat treatable aluminum base alloy plate containing copper, magnesium and manganese has found considerable acceptance for various structural members.
• Such an alloy known in the art contains nominally 4.5% copper, 1.5% magnesium and 0.6% manganese and carries the Aluminum Association designation of 2024 alloy.
• This alloy plate at least in relatively thin section, is noted for its very good strength to weight ratio, its outstanding toughness and tear resistance and its good resistance to general and stress corrosion effects. It has been commercially produced by conventional rolling procedures wherein an ingot having a rectangular transverse cross section of say about 14 to 16 inches by 45 .to 50 inches is hot rolled to the desired thickness of plate.
• Plate so produced is marked by a rather limited level of ductility across the short transverse, or thickness, dimension, generally exhibiting short transverse tensile elongation values as low as /2% and very rarely over 2%. Also notable is the relatively low level of toughness or tear resistance exhibited across the plate thickness.
• One reliable measure of toughness or tear resistance is the Kahn tear test described in the American Society for Testing Materials publication, Materials Research and Standards, vol. 4, No. 4, April 1964. In this test conventionally hot rolled plate exhibits a short transverse unit propagation energy of about 80 inch pounds per square inch compared to long transverse and longitudinal levels of about 110 and 150 respectively.
• plate members of the described aluminum base alloy type which are characterized by a high level of elongation, resistance to stress corrosion and tear resistance in the short transverse direction.
• Another object of the invention is to provide forged and hot rolled plate of the aluminum base alloy type described having a high level of resistance to stress corrosion in the short transverse direction.
• Yet another object of the invention is to provide a method of producing forged and hot rolled plate of the described aluminum base alloy type having improved isotropy of mechanical properties and resistance to stress corrosion.
• Another object of the invention is to provide a method of producing plate of the aluminum base alloy type described, the plate exhibiting a high level in elongation, resistance to stress corrosion and tear resistance in the short transverse direction.
• the invention resides in imparting to the alloy body or ingot, prior to hot rolling, a severe forging upset whereby an ingot or other body having a greater length than the cross sectional dimension is compressed in an plate thickness, solution heat treated and artificially aged.
• the magnesium content generally must be at least 0.32 times the copper content.
• the alloy consists essentially of aluminum and, on a weight basis, 3 to 6% copper, 1 to 3% magnesium and 0.3 to 1% manganese together with impurities.
• a preferred composition is one consisting essentially of aluminum, 3.5 to 5% copper, 1 to 2% magnesium and 0.3 to 1% manganese together with impurities.
• the plate which is benefited by the controlled composition and forging practice generally ranges in thickness from 1" to 8", but more often from 2" to 6" in most applications where short transverse properties are of substantial significance.
• the alloy body or stock to which the forging steps are applied is generally a relatively large continuously cast ingot which has its surface discontinuities removed by scalping and its ends cropped to remove end defects.
• an alloy body is intended to include both ingot and other suitable stock.
• the body Prior to forging, the body is gradually heated to a temperature above 800 F. but generally short of incipient melting, and most often between 900 and 925 F., and then soaked at that temperature for a prolonged period principally to homogenize its internal structure and also relieve some of the internal stresses introduced in casting. The soaking time is generally over hours and more often between and hours, although much longer soak times of 50 hours and more are often used.
• the degree to which the alloy body is compressed or upset in an axial direction is at least 60% and preferably over 75% of the original length.
• An additional factor which has a very significant effect upon the degree of upset achieved is the ratio of the length of the body to the base dimensions.
• the base dimension is considered the diameter for round bodies and the mean base dimension for rectangular or other shaped bodies. For instance, a body 20" by 40" in cross section is considered to have a base dimension of the same as a 30" square or round body.
• the length to base ratio should be at least 2:1 and is preferably at least 2' /z:1.
• an alloy body is upset by a forging operation, at a temperature which most often ranges from 700 to 900 R, which decreases the length of a body having a length to base ratio of at least 2:1, and preferably at least 2 /211, by at least 60%,
• the forged biscuit is generally reheated to a temperature of about 800 to 850 F., flattened slightly on its sides and then further compressed in the original A direction on a forging press, hammer, or the like to form in an elongated slab, the thickness of which is not more than three fourths the height (thickness) of the biscuit and more often ranges from A to /2 the biscuit height.
• the forged slab is cooled to room temperature and reheated when it is to be rolled.
• the elongated slab is hot rolled, generally at 800 to 900 F. to the final plate thickness.
• the hot rolling generally reduces the thickness of the slab by 20% or more, but most often the thickness reduction ranges from 35% to Thus the initial ingot length is converted to the final plate thickness.
• the forging operations, together with the hot rolling operations are performed at elevated temperatures within the approximate range of 600 to 900 F., and more often between 700 and 900 F., the temperature generally diminishing somewhat between the start and completion of any hot working operation, and hence temperature generally refers to the level at the start of the operation.
• the ranges set forth above for the individual operations are those which have been used most often in practicing the invention. If the stock cools excessively during a hot working operation, such may be interrupted for purposes of reheating in accordance with the general practice in the art.
• the hot rolled plate is solution heat treated, for example, at about 800 to 950 F., or preferably at about 900 to 925 F., for about one to twelve hours or more depending on the plate thickness. This time is expressed functionally as being of sufficient duration to effect substantial solution of the soluble alloy constituents.
• the plate is then rapidly quenched, generally by spray quenching especially where the plate is of relatively thick cross section, and artificially aged, at about 300 to 400 F. for about 6 to 24 hours, but more often within narrower ranges of 360 to 390 F. for 10 to 13 hours, by methods currently practiced in the art.
• the artificial aging step is preferably preceded by a mechanical stress relief treatment by means of working at substantially room temperature sufficiently to efifect a 1 /2 to 3% permanent stretch for example, the plate is often cold stretched to effect a permanent stretch of about 1%
• solution heat treatment, quench, cold stretching and artificial aging operations as performed in the practice of the invention are much the same as those currently practiced in the art of treating 2024 type aluminum alloy.
• temperature levels, holding times at temperature and other factors can be determined for specific plate thicknesses by those practicing the art and need not be further developed here.
• Plate produced as set forth above exhibits short transverse tensile elongation generally ranging from 3% to 6% and tear resistance characterized by unit propagation energy of to in. lb./sq. in. thus rendering the plate entirely suitable for design applications where it is stressed in that direction.
• the plate is considered as exhibitmg more isotropy, or less directionality, in tensile and elongation properties than the hot rolled plate of the prior art.
• Typical average mechanical strength values of conventional hot rolled 2024 alloy plate compared with the values of special forged and rolled plate of the invention are listed in Table I where the abbreviation K s.i. represents 1000 pounds per square inch.
• the plate thicknesses ranged from 1%" to 5" and the plates of both series were given the same solution heat treatment, quench, stretch and artificial aging.
• Table II lists typical average tear test results comparing conventional and specially forged and hot rolled plates within 2024 alloy composition limits.
• the plate temper and thickness ranges are the same as for Table I.
• the Kahn type of test, referred to earlier in this description, is considered to offer a good measure of the toughness of an article in that the resistance to initiating and propagating a crack at a stressed notch is measured.
• the specially preforged plate exhibits a marked improvement in toughness as measured by the tear test. Also, as with the tensile tests, tear resistance was not significantly affected by variations in composition. It can be seen that the over-all toughness is considerably upgraded, the short transverse performance being improved to a level comparable to the long transverse .and longitudinal values for conventional plate. This improved short transverse toughness or tear resistance enables the plate to perform where conventional hotrolled plate was previously considered inadequate.
• Example I A round ingot can be cast by any of the conventional continuous casting methods and is composed of an aluminum base alloy nominally containing 4.8% copper, 1.5% magnesium and 0.5% manganese together with incidental impurities.
• the ingot has a diameter of about 37 inches and a length of about 100 inches after scalp-ing and cropping.
• the ingot is gradually heated to about 915 F. in a conventional furnace and then soaked at that temperature for about 24 hours to homogenize its internal structure and prepare it for hot Working. Upon removal from the furnace and before the temperature drops to 800 F., it is placed on end in a large forging press .and compressed in the A direction, the 100 inch long ingot being reduced to a biscuit about 36 inches high and about 75 inches in its swelled diameter.
• This biscuit is reheated to a temperature of a little over 850 F. squared slightly by compression on its sides which also reduces the lateral swelling at mid-height and then further compressed by drawing down on a forging press, again in the original A direction, to form an elongated slab about 14 inches thick, 50 inches wide and to inches long.
• the slab is then reheated to about 850 to 900 F. and hot rolled to a'thickness of about 4 inches.
• the plate is solution heat treated at a metal temperature of slightly over 900 F. and a soak time of about 4 to 5 hours and then quenched. For this thick plate it is preferable to spray quench the plate to assure reasonably rapid cooling throughout its thickness.
• the plate is cold stretched at room temperature to effect a 1 /2 to 3 permanent stretch principally to relieve some of the internal stresses.
• the plate is then artificially aged by a ten to thirteen hour soak at .a metal temperature of about 370 to 380 F.
• This plate is tested for short transverse mechanical properties and is found to exhibit a marked improvement over conventionally hot rolled plate. Average elongation and unit propagation energy values for this plate are a little over 4% and about 125 in. lb./sq. in. as contrasted to average values of about 1.4% and 75 to 80 for conventionally hot rolled 4" plate.
• the basic alloy composition embodied in the invention consists essentially of aluminum, 3 to 6%, preferably 3.5 to 5%, copper l to 3%, preferably 1 to 2%, magnesium and 0.3 to 1% manganese together with impurities.
• impurity limits associated with the described type alloys preferably apply to the practice of the invention.
• maximum impurity limits are preferably followed: silicon 0.5%, iron 0.5 chromium 0.1% and zinc 0.25%.
• Another composition limit, over the above that practiced in the prior art, which is required by the practice of the invention is the highly critical relation between the principal alloying constituents, copper and magnesium.
• the minimum magnesium content is equal to 0.32 times the copper content except that this minimum is lessened slightly where manganese exceeds 0.5% as explained hereinafter; preferably the magnesium content is at least 0.2% over and above this minimum.
• the alloy plate will exhibit very good resistance to stress corrosion for loads up to and slightly exceeding 50% of the yield strength, a stress level of about 30 K s.i. based on a nominal yield strength of 60 K s.i. for 2024 aluminum alloy.
• the additional 0.2% magnesium in accordance with the preferred practice of the invention, raises the permissible stress level to and above 75% of the yield strength, that is a stress level of about 45 K s.i. based on the nominal 60 K s.i.
• Example 11 Ingots were prepared from aluminum base alloys having compositions within the following limits: 4.15 to 4.6% copper, 1.4 to 1.7% magnesium, 0.5 to 0.65% manganese, and impurities Within the maximum stated amounts: silicon 0.15%, iron 0.25%, chromium 0.10%, zinc 0.20%, and nickel 0.05%. In some instances up to 0.05% titanium and up to 0.002 boron are added for grain refining purposes. It is noteworthy that this composition range inherently satisfies the minimum magnesium requirements of Equations 1 and 2.
• the cropped and scalped ingots generally had a length of over 110 inches and a diameter around 37 inches. These ingots were soaked at about 900 to 925 F.
• the plates were solution heat treated by soaking them for 4 to 5 hours at about 910 to 925 F., spray quenched, cold stretched at room temperature to effect about a 1%% permanent stretch and artificially aged for about 11 hours at a temperature of about 370 to 380 F.
• the resulting plate exhibited short transverse tensile elongation values ranging from 3% to 8%, most often 4% to 6%, and a general improvement in toughness and tear resistance characterized by unit propagation energy levels consistently over 110 inch pounds per square inch.
• the plate where the magnesium content exceeded that set forth in Equations 3 and 4 exhibited substantial immunity to stress corrosion at stress levels of up to and over 45,- 000 p.s.i. yield) as evidenced by the accelerated thirty day alternate immersion test in 3.5% NaCl solution.
• the fabrication cycle was altered so that the ingot was compressed in the 18 inch direction at a temperature of 850 to 900 F. by drawing down in a forging press to form an elongated slab about 10 inches thick.
• the forged slab was reheated and hot rolled at about 850 F. to form the plate, the other steps being the same as with the conventionally hot rolled plate.
• This forging step did not impart any consistent or significant improvement in short transverse properties.
• this plate was found to exhibit generally inadequate resistance to short transverse stress corrosion in that few, if any, specimens survived the accelerated alternate immersion test for more than thirty days, many specimens failing in as little as three to ten days and at stress levels considerably below 50% yield.
• the method of producing improved aluminum base alloy plate comprising:
• the resulting plate exhibiting improved short transverse elongation, ranging from 3% to 6%, improved short transverse tear resistance characterized by a unit propagation energy of at least 100, and substantial immunity to stress corrosion in the short transverse direction at a stress of 50% of the yield strength in the short transverse direction.
• Mg min. 0.2+0.32 Cu where Mn is not greater than 0.5%
• Mg min. 0.4+0.32 Cu0.4 Mn where Mn is greater than 0.5%
• the plate produced exhibits substantial immunity to stress corrosion in the short transverse direction at a stress of 75% of the yield strength in the short transverse direction.
• the method of producing improved aluminum base alloy plate comprising:
• the resulting plate exhibiting improved short transverse elongation, ranging from 3% to 6%, improved short transverse tear resistance characterized by a unit propagation energy of at least 100, and substantial immunity to stress corrosion in the short transverse direction at a stress of 50% of the yield strent gh in the short transverse direction.
• the plate produced exhibits substantial immunity to stress corrosion in the short transverse direction at a stress of 75% of the yield strength in the short transverse direction.
• Mg Min. 0.2-
• the resulting plate exhibiting improved short transverse elongation, ranging from 3% to 6%, improved short transverse tear resistance characterized by a unit propagation energy of at least 100, and substantial immunity to stress corrosion in the short transverse direction at a stress of 50% of the yield strength in the short transverse direction.
• Improved aluminum base alloy plate ranging in thickness from 2 to 6 inches and composed of an alloy consisting essentially of aluminum, 3 to 6% copper, 0.8 to 3% magnesium, 0.3 to 1% manganese, the minimum magnesium content being governed by the relation:
• Mg min. 0.32 Cu where Mn is not greater than 0.5%
• Mg min. 0.2+0.32 Cu0.4 Mn where Mn is greater than 0.5%
• the plate exhibiting improved short transverse elongation, ranging from 3 to 6%, improved short transverse tear resistance characterized by a unit propagation energy of at least 100, and substantial immunity to stress corrosion in the short transverse direction at a stress of 50% of the alloy yield strength in the short transverse direction.

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• 1965
  • 1965-02-05 US US430743A patent/US3333989A/en not_active Expired - Lifetime
• 1966
  • 1966-02-03 GB GB4868/66A patent/GB1122912A/en not_active Expired
  • 1966-02-04 DE DE19661533497D patent/DE1533497B1/de active Pending

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