US3333989A

US3333989A - Aluminum base alloy plate

Info

Publication number: US3333989A
Application number: US430743A
Authority: US
Inventors: Melvin H Brown; Bernard W Lifka; Stillman D Pitts
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1965-02-05
Filing date: 1965-02-05
Publication date: 1967-08-01
Anticipated expiration: 1984-08-01
Also published as: GB1122912A; DE1533497B1

Description

United States Patent M 3,333,989 ALUMINUM BASE ALLOY PLATE Melvin H. Brown, Leechburg, Bernard W. Lifka, New

Kensington, and Stillman D. Pitts, Pittsburgh, Pa., assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Feb. 5, 1965, Ser. No. 430,743 Claims. (Cl. 14812.7)

ABSTRACT OF THE DISCLOSURE- Improved aluminum alloy plate containing 3 to 6% copper, 0.8 to 3% magnesium and 0.3 to 1% manganese and exhibiting improved short transverse properties characterized by an elongation of 3 to 6%, a tear resistance unit propagation energy of at least 100 can be provided by a fabrication cycle which includes an A forging reduction of elongated stock which is then drawn out and hot rolled to form the plate. In addition, 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%

to impart substantial immunity to stress corrosion in the short transverse direction.

This invention relates to aluminum base alloy plate having improved short transverse tensile elongation and resistance to stress corrosion.

For some time, 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. For

3,333,989 Patented Aug. 1, 1967 relatively thin plate this deficiency is of little consequence since such is generally not stressed in that direction. Potential new applications for the alloy, however, indicate that relatively thick plate, eg 2" to 6", would olfer substantially increased utility if its short transverse ductility and toughness or tear resistance could be improved so that substantial tensile stresses might be imposed across its thickness in multi-directionally stressed members. One known manner for improving short transverse mechanical properties in plate is to forge the ingot to a suitable shape prior to the hot rolling operation. For example, the forging practice may consist of reducing the alloy type described, this technique has produced to 10 inches thick and then hot rolling this slab. With thea lloy type described, this technique has produced transverse properties that are inconsistent and the elongation still rarely exceeds 2% and very little, and more often, no consistent improvement in toughness or tear resistance. As a futher complication a decrease in resistance to stress corrosion is associated in the art with such preliminary forging methods which consequently are generally viewed with caution.

In accordance With the invention it has been found that by the practice of a special preliminary forging operation highly repeatable and reliable improvements in short transverse tensile elongation and toughness or tear resistance are realized such that the finished plate exhibits an elongation level of about 3% to 6% and a unit propagation energy of at least and more often about to in. 1b./sq. in. Further by virtue of certain critical composition limits the plate exhibits entirely satisfactory resistance to stress corrosion, even where the stress is applied across the plate thickness.

Accordingly it is a primary object of the invention to provide 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.

Other objects will, in part, be obvious and will, in part, appear hereinafter.

Basically 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.

While plate so produced will exhibit greatly improved short transverse properties, certain critical composition limits must be imposed over and above those currently applied by the art to the described type aluminum base alloys to avoid an adverse effect in resistance to corrosion. This limit is explained in more detail hereinafter but in its most simple terms is stated that the magnesium content generally must be at least 0.32 times the copper content. From a composition standpoint 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. Of course, the critical magnesium and copper relationship must be followed in order to avoid serious impairment of resistance to stress corrosion in the short transverse direction. 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.

While the initial forging step is relatively simple, it yields unexpected results in combination with subsequent hot working operations in that highly repeatable improvements in short transverse mechanical properties are achieved when applied to bodies of the above-described alloys. As suggested above, this upset is accomplished by compressing a relatively long ingot in an axial direction and further processing the ingot such that the length in an axial direction becomes the short transverse dimension of the final plate. In view of such a drastic reduction in the direction which eventually becomes the plate thickness, it is entirely unexpected that such improvements in short transverse properties would result since the art generally associates severe short transverse reductions with impairing properties in that direction and such a practice is therefore foreign to the art of producing plate of the described alloy type. 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. However, such is not intended as a limit on the invention which includes the application of the described forging steps to any body whose shape and dimensions are consistent with the method. Hence reference herein to an alloy body is intended to include both ingot and other suitable stock. 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. Thus in accordance with the invention, 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%,

and preferably at least 75%, to form a biscuit the height of which is not greater than 40%, preferably not over 25%, the length of the initial body. An upset in this, the axial, direction is generally termed an A upset; that is, an upset compressing the body length, referred to here as the A dimension. 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. Since forging and rolling facilities are not usually beside each other, 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. Of course, as indicated above, 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.

To develop a high strength and hardness 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% It might be noted that the 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. Thus 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. As the mechanical properties in the other directions, long transverse and longitudinal, are not impaired, and the short transverse properties are improved, 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.

Long Transverse It is quite apparent that the specially forged and hot rolled plate exhibits markedly improved short transverse elongation, more than twice that of the conventionally hot rolled plate. The attendant significant improvements in short transverse strength are also noteworthy, the result being that the tensile properties of the preforged plate are more isotropic, or less directional, than the conventional plate. Also, not only are the longitudinal and long transverse properties unimpaired, they are slightly improved. Thus the tensile tests indicate a general upgrading of mechanical properties .in all directions but particularly the short transverse direction which is now in more 'comformance with the others. One additional item of interest observed in these tests is that the mechanical properties were not affected to any'substantial extent by alloying variations anywhere within 2024 alloy composition limits and these results would then apply, generally speaking, to the entire composition range for this alloy.

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.

As with the tensile properties, 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.

The sequence of steps in carrying out the invention is illustrated in the following example.

TABLE II.TEAR PROPERTIES IN DIFFERENT DIRE OTIONS Longitudinal Tear Strength, Ratio: Unit Propaga- K s.i. Tear Strength tion Energy Yield Strength 'l 111-) Hot rolled 59. 4 0.96 145 Forged 71. 4 1. 15 260 Long Transverse Hot rolled 54. 2 0.89 Forged 66. 6 1. 06 200 Short Transverse Hot rolled l 41. 6 0. 71 80 Forged 52. 2 0.87

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. In this case 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. Next, 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. 7 As indicated earlier in this description, 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. Generally speaking the impurity limits associated with the described type alloys preferably apply to the practice of the invention. Thus the following 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. Stated briefly 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. Within the broader range (minimum Mg=0.32 Cu) 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. yield strength for 2024 alloy. These results are based upon numerous standard accelerated tests of the alternate immersion type in a 3.5% sodium chloride aqueous solution. The results indicate that specimens within the broad alloy composition limit withstand 50% yield stress application for at least thirty days. This is considered in the art as a reliable indication of indefinite life under ordinary atmospheric conditions at this stress level, or in other Words, substantial immunity to stress corrosion. Likewise the additional 0.2% magnesium increases the permissible stress application to 75% and more of the yield stress level with substantial immunity to stress corrosion.

An important modification to the basic magnesium and copper relationship occurs where manganese exceeds 0.5%. For this relatively high manganese content, the minimum magnesium necessary to maintain substantial immunity to stress corrosion is slightly lessened. Accordingly, the following equations govern the minimum magnesium content in accordance with the invention where the stress levels do not exceed 50% of the yield strength by a substantail amount:

(1) min. Mg=0.32 Cu where Mn does not exceed 0.5 (2) min. Mg=0.2+0.32 Cu0.4 Mn Where Mn exceeds In the preferred practice of the invention where the applied stress can equal and even slightly exceed 75 of the yield stress, the equations become:

(3) min. Mg=0.2+0.32 Cu where Mn does not exceed (4) min. Mg=0.4+0.32 Cu-0.4 Mn where Mn exceeds The following example illustrates the benefit derived from controlling the alloy composition in accordance with Equations 2 and 4 emphasizing its importance in combination with the special forging operation.

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. for about 20 hours to homogenize their internal structure and prepare them for hot forging. They were then stood on end and compressed in the A direction in a large forging press at about 800 F. to form biscuits having height dimensions of 32 inches, which represented a reduction of about 70%. The temperature during this forging step did not fall significantly below 700 F. and generally ran between 750 and 800 F. The resulting biscuits were then reheated to about 800 to 850 F. and drawn down on a forging press to form elongated slabs about 150 long, 60 wide and having a thickness of about 15 inches. These elongated slabs were reheated for hot rolling to about 875 F. and rolled to a final thickness generally ranging from 3 to 4 /2 inches. 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 other plates, containing magnesium at a lower level that exhibited like results provided the applied stress did not substantially exceed 30,000 p.s.i. (50% yield).

These results may be contrasted with those obtained for plates of aluminum base alloys containing 4.2 to 4.8% copper, 1.2 to 1.5% magnesium and 0.30 to 0.45% manganese wherein the magnesium content was less than 0.32 times the copper content. The plate was produced by conventional hot rolling at 850 F., ingots about 18 inches thick, 40 to 50* inches wide and 12 feet long to the final plate thickness of about 3 to 5 inches. The parameters for homogenization prior to rolling together with the solution heat treatment and artificial aging parameters were the same as set forth earlier in this Example 11. The average short transverse mechanical properties for this plate were about 1.2% elongation and 82 in. lb./sq. in. unit propagation energy in tear resistance. The plate did, however, exhibit relatively satisfactory short transverse resistance to stress corrosion in the accelerated alternate immersion tests.

In a further test 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. In addition, 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. Additional plates of the same composition were produced in accordance with the forging and rolling procedure as taught by this invention. For this purpose, round ingots were cast, cropped and scalped to yield stock about inches in length and 37 inches in diameter. The ingots were upset at 800 to 900 F. in the A direction to form biscuits about 30 to 32 inches high which were reheated to 850 F. and drawn down into elongated slabs about 14 inches thick. These slabs were hot rolled at 850 F. to form the plate which was stretched, solution heat treated and artificially aged as set forth previously in this Example II. This plate exhibited the same markedly improved short transverse mechanical properties as did the plate first cited in this example which also was fabricated in accordance with the forging practice of the invention. However, when short transverse specimens from this plate were subjected to the accelerated alternate immersion tests, they exhibited significant susceptibility to failure by stress corrosion cracking. Many samples were found to fail in as short a time as 3 days and even less, and at applied stress levels about as low as 35% of the yield strength and even lower. Thus, both the critical fabrication cycle and the critical composition control described herein are necessary to yield satisfactory plate in accordance with the invention. Failure to follow either or both will result in inadequate short transverse properties or inadequate resistance to stress corrosion resistance or both.

At this point it may be mentioned that a considerable quantity of plate having the composition range as set forth at the outset of Example II has been produced and that this plate has consistently exhibited the desired characteristics of mechanical and stress corrosion properties and that hence this particular composition is considered preferred within the practice of the invention.

The invention has been described with particular reference to preferred embodiments; however, the invention is not limited to such. Various minor modifications will suggest themselves to those skilledin the art and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of producing improved aluminum base alloy plate comprising:

(1) providing an elongated body composed of an alloy consisting essentially of aluminum, 3 to 6% copper, 0.8 to 3% magnesium and 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 Cu-0.4 Mn where Mn is greater than 0.5%, the body having a length to base ratio of at least 2 to 1,

(2) heating said body to a temperature of at least 800" F. for a period of time sufiicient to homogenize the internal structure of said body,

(3) initially upsetting by forging, at a temperature of about 600 to 900 F., said body in an axial direction to effect an A reduction to form a biscuit having a height of not more than 40% of the original body length,

(4) further reducing the biscuit at a temperature of about 600 to 900 F. in the A direction to form an elongated slab having a thickness of not more than of the biscuit height,

(5) hot rolling at a temperature of about 600 to 900 F. said elongated slab to a final plate thickness of from 1 to 8 inches,

(6) solution heat treating the plate at a temperature of about 800 to 950 F. for a period of time sufficient to elfect substantial solution of the soluble alloy constituents and quenching the plate, and

(7) artificially aging the plate at a temperature of about 300 to 400 F. for about six to twenty-four hours,

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.

2. The method according to claim 1 wherein the minimum magnesium content is governed by the relation:

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%,

and 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.

3. The method of producing improved aluminum base alloy plate comprising:

(1) providing an elongated body composed of an alloy 10 consisting essentially of aluminum, 3.5 to 5% copper, 1 to 2% magnesium and 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 body having a length to base ratio of at least 2 to l,

(2) heating said body to a temperature of at least 800 F. for a period of time sufficient to homogenize the internal structure of said body,

(3) initially upsetting by forging at a temperature of about 600 to 900 B, said body in an axial direction to effect an A reduction to form a biscuit having a height of not more than 40% of the original body length,

(4) further reducing the biscuit at a temperature of about 600 to 900 F. in the A direction to form an elongated slab having a thickness ranging from A to /2 of the biscuit height,

(5) hot rolling said elongated slab at a temperature of about 600 to 900 F. to a final plate thickness of from 2 inches to 6 inches,

( 6) solution heat treating the plate at about 800 to 950 F. for a period of time suificient to effect substantial solution of the soluble alloy constitutents and quenching said plate,

(7) mechanically stress relieving the plate by stretching at substantially room temperature to effect a 1%% to 3% permanent stretch, and

(8) artificially aging the plate at about 300 to 400 F.

for about six to twenty-four hours, 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. N

- 4. The method according to claim 3 wherein the minimum magnesium content is governed by the relation:

Mg min.-=0.2+0.32 Cu where Mn is not greater than Mg min.=0.4+0.32 Cu0.4 Mn where Mn is greater than 0.5%,

5. The method according to claim 3 wherein the plate produced ranges in thickness from 1 inch to 8 inches.

6. The method according to claim 3 wherein the length to base ratio of the alloy body is at least 2% to 1 and the height of the biscuit is not more than 25% of the original alloy 'body length.

7. The method of producing improved aluminum base alloy plate comprising:

(1) providing an elongated body composed of alloy consisting essentially of aluminum, 4.15 to 4.60% copper, 1.45 to 1.65% magnesium, 0.5 to 0.65% manganese, up to 0.05% titanium and up to 0.002% boron, and the following maximum.- impurity levels: silicon 0.15%, iron 0.25%, chromium 0.10%, zinc 0.20% and nickel 0.05 the minimum magnesium content being governed by the relation:

Mg Min.=0.2-|-,0.32 Cu0.4 Mn, the body having a length to base ratio of at least 2 to l,

(2) heating said body to a temperature of about 900 to 925 F. for a period of time sufficient to homogenize the internal structure of said body,

(3) initially upsetting by forging said body at a temperature of about 600 to 900 F. in axial direction 11 to effect an A" reduction to form a biscuit having a height of not more than 40% of the original body length,

(4) further reducing the biscuit in the A direction at a temperature of about 600 to 900 F. to form an elongated slab having a thickness ranging from A to /2 of the biscuit height,

(6) solution-heat treating the plate at about 800 to 950 F. for a period of time sufiicient to effect substantial solution of the soluble alloy constituents and quenching said plate,

(7) stretching said plate at room temperature to effect a permanent stretch of 1 /2% to 3%, and

(8) artificially aging the plate at about 360 to 390 F.,

for about six to twenty-four hours,

8. The method as in claim 7 wherein the minimum magnesium content is governed by the relation:

Mg min. =0.4+0.32 Cu0.4 Mn, and the plate produced exhibits substantial immunity to short transverse stress corrosion at stress levels up to and exceeding 75% of the alloy yield strength.

9. The method as in claim 7 wherein the length to base ratio of the alloy body is at least 2 /2 to 1 and the height of the biscuit is not more than 25% of the original alloy body length.

10. 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:

12 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%,

5 the plate having an internal structure produced by:

(1) heating to a temperature over 800 F, for a period of time sufficient to homogenize the internal structure,

(2) initially upsetting by forging at a temperature of about 600 to 900 F. a body of said alloy having a length to base ratio of at least 2 to 1, to effect an A reduction to form a biscuit having a height of not more than 40% of the original body length,

(3) further reducing the resulting biscuit at a temperature of about 600 to 900 F. in the A direction to form an elongated slab having a thickness of not more than A of the biscuit height,

(4) hot rolling said elongated slab at a temperature of about 600 to 900 F. to form said plate,

(5) solution heat treating the plate at a temperature of about 800 to 950 F. for a period of time sufficient to effect substantial solution of the soluble alloy constituents and quenching said plate, and

(6) artificially aging the plate at a temperature of about 300 to 400 F. for about six to twenty-four hours,

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.

3/1954 Rosenkranz 148--12.7 X 8/1966 Foerster 14832.5 X

DAVID L. RECK, Primary Examiner.

CHARLES N. LOVELL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,333 ,989 August 1 1967 Melvin H. Brown t 1 It is hereby certified that error appears in the above-numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 13 for "0 .3" read .3 column 2, line 13, for "the alloy type described, this technique has produced" read the thickness of a conventional ingot from about 16 inches line 15 for "thea lloy" read the alloy colum 7 line 35 for "substantail" read substantial column 10 line 28 for "constitutents" read constituents Signed and sealed this 25th day of June 1968 (SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. THE METHOD OF PRODUCING IMPROVED ALUMINUM BASE ALLOY PLATE COMPRISING: (1) PROVIDING AN ELONGATED BODY COMPOSED OF AN ALLOY CONSISTING ESSENTIALLY OF ALUMINUM, 3 TO 6% COPPER, 0.8 TO 3% MAGNESIUM AND 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 CU-0.4 MN WHERE MN IS GREATER THAN 0.5%, THE BODY HAVING A LENGTH TO BASE RATIO OF AT LEAST 2 TO 1. (2) HEATING SAID BODY TO A TEMPERATURE OF AT LEAST 800*F. FOR A PERIOD OF TIME SUFFICIENT TO HOMOGENIZE THE INTERNAL STRUCTURE OF SAID BODY, (3) INITIALLY UPSETTING BY FORGING, AT A TEMPERATURE OF ABOUT 600* TO 900*F., SAID BODY IN AN AXIAL DIRECTION TO EFFECT AN "A" REDUCTION TO FORM A BISCUIT HAVING A HEIGHT OF NOT MORE THAN 400*F., OF THE ORIGINAL BODY LENGTH, (4) FURTHER REDUCING THE BISCUIT AT A TEMPERATURE OF ABOUT 600* TO 900*F. IN THE "A" DIRECTION TO FORM AN ELONGATED SLAB HAVING A THICKNESS OF NOT MORE THAN 3/4 OF THE BISCUIT HEIGHT, (5) HOT ROLLING AT A TEMPERATURE OF ABOUT 600* TO 900* F. SAID ELONGATED SLAB TO A FINAL PLATE THICKNESS OF FROM 1 TO 8 INCHES, (6) SOLUTION HEAT TREATING THE PLATE AT A TEMPERATURE OF ABOUT 800* TO 950*F. FOR A PERIOD OF TIME SUFFICIENT TO EFFECT SUBSTANTIAL SOLUTION OF THE SOLUBLE ALLOY CONSTITUENTS AND QUENCHING THE PLATE, AND (7) ARTIFICIALLY AGING THE PLATE AT A TEMPERATURE OF ABOUT 300* TO 400*F. FOR ABOUT SIX TO TWENTY-FOUR HOURS, 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.