HIGH STRENGTH ALUMINUM ALLOYS AND PROCESS FOR MAKING THE SAME

Description

Background Of The Invention

1. Field of the Invention

[0001] The present invention relates, in general, to a high strength aluminum alloy based on the Al-Zn-Mg-Cu alloy system and a process for forming the same. Although not limited thereto, the alloys are particularly suited for use in sporting goods and aerospace applications.

2. Description of the Background Art

[0002] The highest strength aluminum alloys known at this time are based on the aluminum-zinc-magnesium-copper system. Such alloys are disclosed for instance in US 2005/0056353 A1 Commercial high-strength alloys currently being produced include AA7055 (nominally 8% Zn-2% Mg-2.2% Cu-0.10% Zr), AA7068 (nominally 7.8% Zn-2.5% Mg-2.0% Cu-0.10% Zr) and a Kaiser Aluminum alloy designated K749 (nominally 8% Zn-2.2% Mg-1.8% Cu-0.14% Zr). From the published phase relationships at 860°F for an alloy containing 8% Zn, one can note that K749 is near a phase boundary, while the other two alloys are in multiple phase fields. In the latter case all the alloying elements are not in solid solution at 860°F, and are not only unavailable for age hardening, but the undissolved phases remaining after heat treatment detract from toughness. Although solution heat treating at a higher temperature than 860°F will dissolve more of the solute, care has to be taken to ensure that the alloy does not undergo eutectic melting, which is a common problem in commercially cast alloys that have locally enriched regions as a result of microsegregation that occurred during casting.

[0003] There is a need in many applications, such as sporting goods and aerospace applications, for even stronger alloys based on the aluminum-zinc-magnesium-copper system that do not sacrifice toughness. However, this requirement presents a problem because, in general, as the tensile strength of an aluminum alloy is increased, its toughness decreases.

Summary of the Invention

[0004] The present invention addresses the foregoing need in a number of ways. More particularly, there are three distinct avenues for increasing an alloy's strength while maintaining its toughness: rich alloy chemistries; processing to maximize alloying effectiveness; and preventing recrystallization. Rich alloys provide more solute, which is potentially available for age hardening to higher strength levels; effective processing ensures that the solute is available for strengthening and not out of solution as second phases, which detract from fracture toughness; and maintaining an unrecrystallized microstructure optimizes both strength and toughness.

[0005] To provide increased tensile strength without sacrificing toughness through the use of rich chemistries, the present invention comprises aluminum alloys based on the Al-Zn-Mg-Cu alloy system that preferably include high levels of zinc and copper, but modest levels of magnesium. As an option, small amounts of scandium can also be employed to prevent recrystallization. Each of the alloys preferably includes at least 8.5% Zn and 2.25% Cu by weight. Higher levels of each of these elements up to about 10.5% Zn and 3.0% Cu can be used. However, modestly lower amounts of Mg (max 1.85%) are preferably used to allow higher levels of the Cu. The ranges of all elements in the alloys include by weight, 8.5-10.5% Zn, 1.4-1.85 % Mg, 2.25-3.0% Cu, and at least one element from the group Zr, V, or Hf not exceeding about 0.5%, the balance substantially aluminum and incidental impurities. In the preferred embodiments, 0., optionally 0.03-0.10% Si and 0.03-0.12% Fe is also included in the alloys to prevent recrystallization. Additionally, it has been found that toughness decreases as the total weight percentage of magnesium and copper increases. Experiments have established that the ideal range of these two elements be between 4.1 and 4.5% combined. Still further, the total weight percent of Zn, Cu and Mg is ideally between 13.0 and 14.5%.

[0006] To maximize alloying effectiveness during formation of the alloys, a homogenization process is preferably employed after alloy ingot casting in which a slow rate of temperature increase is employed as the alloy is heated as near as possible to its melting temperature. In particular, for the last 20-30°F below the melting temperature, the rate of increase is limited to 20°F/hr. or less to minimize the amount of low melting point eutectic phases and thereby further enhance fracture toughness of the alloy. Once the ingot is formed into finished shape using extrusion and rolling steps, for example, the product is preferably solution heat treated at 870 to 900 degrees F and then artificially aged. The aging process can be carried out by exposing the product to a one, two or three step heat treatment process. In the first step, the product is exposed to a temperature range of 175-310 degrees F for 3 to 30 hours. In the optional second step, the first step is followed by heating at 310 to 360 degrees F for 2 to 24 hours. Finally, in the third optional step, the product is heated at 175 to 300 degrees F for 1 to 30 hours. As a still further option, the second and third aging steps can be used without the first aging step.

[0007] The foregoing alloys and processing operations enhance the properties of the Al-Zn-Mg-Cu alloy system, such that they can be more effectively employed in numerous applications. Specific products or items in which the subject alloys can be employed include, among others, sporting goods including baseball and soft ball bats, golf shafts, lacrosse sticks, tennis rackets, and arrows; and aerospace application including aerospace components such as wing plates, bulkheads, fuselage stringers, and structural extrusions and forgings; and ordnance parts such as sabots and missile launchers.

Brief Description of the Drawings

[0008] The features and advantages of the present invention will become apparent form the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph depicting T6 strength (YTS and UTS) as a function of the total alloy content in weight percent for a number of sample alloys formed in accordance with the preferred embodiments;

FIG. 2 is a graph depicting fracture toughness as a function of combined percentages of Cu and Mg for sample alloys formed in accordance with the preferred embodiments;

FIG. 3 is an equilibrium diagram which depicts the phase relationships at 885°F as a function of percentages of Cu and Mg for an alloy formed in accordance with the preferred embodiments that contains 9% Zn;

FIG. 4 is a graph illustrating the effect of the ratio of Mg to Cu on fracture toughness for the alloys formed in accordance with the preferred embodiments;

FIG. 5 is a graph depicting second phase volume percent as a function of heating rate in a formation process for Alloy AA7068; and

FIG. 6 is a graph illustrating the effect of scandium on strength of an Al-8% Zn-2.2% Mg-1.9% Cu alloy.

Detailed Description of the Preferred Embodiments

[0009] The following examples illustrate how alloy modifications and efficient processing operations can be used to enhance the properties of the Al-Zn-Mg-Cu alloy system in accordance with the preferred embodiments of the present invention, such that they can be more effectively utilized in sporting goods and aerospace applications.

Example 1

[0010] A heretofore unexplored region of the Al-Zn-Mg-Cu alloy system consists of compositions comprising about 9% to 10% zinc, 2.2% to 2.8% copper, and 1.6% to 2.0% magnesium. The alloy compositions listed in Table 1 were cast as 9-in. diameter billets: note that all these alloys contain about 0.05% scandium, an element which in combination with zirconium is effective in preventing recrystallization.

Table 1. Alloy compositions

	Percent by Weight
Alloy	Si	Fe	Cu	Mg	Zn	Zr	Sc
179	0.04	0.07	2.47	1.83	8.87	0.14	0.06
180	0.04	0.09	2.71	1.89	8.95	0.13	0.06
189	0.04	0.08	2.14	1.89	8.60	0.12	0.05
190	0.03	0.09	2.31	1.86	9.21	0.13	0.05
191	0.03	0.11	2.35	1.81	9.63	0.13	0.05
192	0.04	0.10	2.33	1.87	10.13	0.12	0.05
200	0.04	0.09	2.58	1.64	8.84	0.12	0.05
202	0.04	0.12	2.46	1.66	8.87	0.13	0.05
203	0.04	0.10	2.69	1.78	8.94	0.13	0.05
204	0.03	0.10	2.88	1.58	8.78	0.12	0.05
209	0.04	0.08	2.64	1.49	8.78	0.14	0.05
213	0.03	0.07	2.42	1.63	9.65	0.13	0.05
214	0.03	0.09	2.56	1.44	9.50	0.14	0.05
215	0.04	0.09	2.57	1.73	9.82	0.12	0.05
216	0.03	0.10	2.81	1.60	9.65	0.13	0.05

[0011] The billets were homogenized at 880F (F means degrees Fahrenheit) and extruded to seamless 4-in. diameter tubes with a 0.305 in. wall thickness. The extrusions were solution heat treated at 880F, quenched in cold water and "peak" aged to the T6 temper (24-hr soak at 250F). They were tested for tensile properties in the longitudinal direction and sections from all of the extrusions were cut and flattened to pieces about 12" square, which were also solution heat treated at 880F, quenched in cold water and peak aged. These flattened sections were tested for fracture toughness (ASTM B645) in the T-L orientation. The tensile and fracture toughness properties are listed in Table 2.

Table 2. Tensile and fracture toughness properties

%Zn	%Cu	%Mg	Strength (ksi)		Toughness (ksi rt.in)
			UTS	YTS	Kg	Kp
8.60	2.14	1.89	97.1	88.5	25.2	30.5
9.21	2.31	1.86	100.1	93.9	22.4	27.5
9.63	2.35	1.81	99.9	94.2	20.9	25.4
10.13	2.33	1.87	103.2	97.8	21.2	24.0
8.87	2.47	1.83	101.1	92.2	20.9	23.9
8.95	2.71	1.89	102.9	93.7	20.1	20.5
8.84	2.58	1.64	98.6	93.8	23.1	25.8
8.87	2.46	1.66	98.4	92.8	25.3	22.2
8.94	2.69	1.78	100.0	94.2	24.2	22.4
8.78	2.88	1.58	99.1	93.8	24.8	21.9
8.78	2.64	1.49	96.4	91.9	24.8	22.9
9.65	2.42	1.63	100.3	96.3	24.7	21.3
9.50	2.56	1.44	98.5	94.9	26.2	21.2
9.82	2.57	1.73	102.6	98.2	21.9	18.2
9.65	2.81	1.60	100.6	97.1	20.0	18.4

[0012] As can be seen from Table 2, tensile yield strengths well in excess of 90 ksi were obtained in most of the alloys, with two compositions achieving about 98 ksi. As shown in FIG. 1, strength correlated well with the total alloy content, with each wt. pct. adding about 4.8 ksi to the yield strength. The equilibrium phase relations at the homogenizing and solution heat treatment temperature explain the reason for this behavior. FIG. 3 shows how the compositions listed in Table 1 relate to the magnesium and copper solubility limits at 885F for alloys containing a nominal zinc level of 9%. Compositions lying below the demarcation line between the solid solution and the Al + S phase regions (i.e., the solvus) are single phase alloys, which have superior fracture toughness values for a given strength level, compared to those in the 2-phase region. The best combinations of strength and toughness are associated with alloys near the solvus line, which is why the 2.7% Cu/1.9% Mg composition has a relatively low toughness level. The preferred compositions therefore lie within the dashed lines that run approximately parallel to the solvus. These relationships are defined by controlling the total copper plus magnesium concentrations between 4.1% and 4.5%.

[0013] Although the properties described above were obtained with a "standard" T6 temper aging treatment by exposing the shaped products to heat of between 175 and 310F for 3 to 30 hours (24 hr at 250F was specifically used), as with most Al-Zn-Mg-Cu alloys, other practices may also be advantageous, depending on the desired combination of properties. For example, a tube from composition #213, when drawn to a tube 2.625" in diameter with a 0.110" wall thickness and aged by a 2-step practice of 8 hr at 250F plus 4 hr at 305F had yield and tensile strengths of 100.9 ksi and 102.6 ksi, respectively. Similarly, the subject alloy can be over aged beyond peak strength in a second step at temperatures in the 310-360F temperature range for 2 to 24 hours to provide a desirable combination of strength and corrosion resistance. Another preferred embodiment includes a final aging treatment in a third step at a lower temperature in the range 175-300F for 1 to 30 hours, which provides an additional strength benefit with no loss in corrosion properties. As yet another alternative, the alloy can be subjected only to the aforementioned second and third aging steps by skipping the first step.

Example 2

[0014] To compare the invention alloy with other commercial high-zinc alloys such as AA7036, AA7056 and AA7449, which have higher Mg/Cu ratios in the range 1.0 to 1.4, the following alloys were prepared as described in Example 1.

Table 3. Compositions of Comparative Alloys

	Percent by Weight
Alloy No.	Si	Fe	Cu	Mg	Zn	Zr	Sc
36	0.03	0.06	1.91	2.17	9.02	0.15	0.05
39	0.04	0.05	1.28	2.74	9.02	0.13	0.06
43	0.03	0.03	1.44	2.62	9.04	0.13	0.05
47	0.04	0.06	1.59	2.34	8.95	0.14	0.06

[0015] The yield strengths and toughness values for these alloys are listed in the following table.

Table 4. Mechanical Properties of Comparative Alloys

Alloy	Mg/Cu Ratio	%(Mg+Cu)	Yield Strength (ksi)	Kpmax (ksi rtin.)
36	1.14	4.08	94.9	24.5
47	1.47	3.93	93.9	22.7
43	1.77	3.99	93.9	21.3
39	2.14	4.02	92.7	20.2

[0016] FIG. 4 compares the toughness levels of these alloys on the basis of Mg/Cu ratio with the invention alloys, using those compositions that have similar strength levels (93-95 ksi) and total Mg + Cu contents (4.0-4.2%).

Example 3

[0017] As noted earlier it is important that undissolved second phases do not remain after processing so that fracture toughness can be maximized. This is especially important in alloys that are rich in alloy content, and lie near an equilibrium solvus phase boundary. To illustrate how homogenizing practice can affect the amount of such undissolved phase(s), samples of as-cast AA7068 alloy billet were heated from 850F at various rates in a differential scanning calorimeter (DSC), and the energy associated with eutectic melting, which started at about 885F was measured. This energy measurement is directly proportional to the amount of undissolved second phase remaining at the incipient melting point, and the relationship between these factors has been determined by quantitative microscopy. FIG. 5 shows how heating rate affects the amount of this phase as determined from the DSC data.

[0018] Note that a slow heating rate of about 10F/hr reduces the amount of second phase to a level below 1 vol.%. One would expect that a ∼5F/hr heating rate would reduce the "soluble" portion to near zero. We also note that for heating rates of 10-20F/hr, the volume fraction of undissolved eutectic is no greater than the amount of insoluble Fe-containing constituent (independent of heating rate or homogenization temperature) at a nominal 0.12% Fe level (approx. 1 vol.%).

Example 4

[0019] It has been recognized for a number of years that scandium in combination with zirconium is an effective recrystallization inhibitor. A Russian review article states "it is desirable to add scandium to aluminum alloys in a quantity from 0.1 to 0.3% together with zirconium (0.05-0.15%)". However, "the greatest effect.... is observed for alloys not containing alloy elements combining with scandium in insoluble phases...; with a limited copper content [scandium combines with copper] alloying with scandium together with zirconium of Al-Zn-Mg-Cu and Al-Cu-Li alloys is possible". As such, "commercial alloys based on Al-Zn-Mg-Sc-Zr (01970, 01975) have been developed".

[0020] Two potential drawbacks to scandium additions to 7XXX alloys containing about 2% copper are evident:

1) the copper level is high enough to combine with scandium, thereby rendering it ineffective, and

2) the high price of scandium; at the 0.2% level it would add about $10 a pound to the cost of the aluminum alloy.

[0021] It would therefore be economically and technically attractive if scandium levels could be effectively used below those recommended in the Russian literature.

[0022] Alloys of the compositions listed in the following table were prepared as 5" diameter billets, which were processed as described below. Although the sample alloys contained more Mg and less Cu than the preferred alloys discussed previously, it is believed that the effect of Sc addition to the alloys would be essentially the same for the preferred alloys.

	% by wt.
Alloy No.	Si	Fe	Cu	Mg	Zn	Zr	Sc
A	0.03	0.04	1.95	2.20	8.07	0.11	0.00
B	0.03	0.05	1.86	2.17	8.05	0.00	0.22
C	0.03	0.05	1.89	2.18	8.09	0.11	0.06
D	0.03	0.04	1.84	2.12	8.11	0.12	0.11
E	0.03	0.05	1.95	2.18	8.08	0.11	0.22

[0023] The ingots were homogenized at 875F using a 50F/hr heating rate and air cool, and then reheated to 800F and extruded to a 0.25" by 3" flat bar. Sections of each extrusion were annealed at 775F for 3 hr, cooled 50F/hr to 450F, held 4 hr and cooled 50F/hr to room temperature. The sections were then cold rolled to 0.040" sheet using five pass reductions (84% total reduction). The sheets were solution heat treated at 885F for 30 min, quenched in cold water, and then aged to the peak strength condition (10 hr at 305F). The as-extruded bars were also heat treated similarly and both products were tested for transverse tensile properties, as listed below. The specific effects of scandium on strength are also shown in FIG. 6.

Alloy No.	%Zr	%Sc	UTS (ksi)		Yield Strength (ksi)
			Extrusion	Sheet	Extrusion	Sheet
A	0.11	0	94.7	90.7	91.4	87.8
B	0	0.22	88.2	92.0	86.1	88.4
C	0.11	0.06	95.7	97.1	92.2	93.3
D	0.12	0.11	95.2	96.6	92.2	93.3
E	0.11	0.22	94.5	96.5	91.1	92.5

[0024] A number of points are evident from these results:

1. The strongest alloy in both extrusion and sheet form contains 0.06% Sc (with 0.11% Zr)

2. At the 0.1% Zr level, 0.06% Sc is effective in raising the strength of the sheet product by about 6 ksi.

3. 0.22% Sc in the absence of zirconium raises the strength of the sheet product by only 1 ksi, and lowers the extrusion strength by about 6 ksi. The effectiveness of only 0.06% Sc in preventing recrystallization was confirmed by comparing the microstructures of the sheet products containing (a) 0.11% Zr, (b) 0.11% Zr + 0.06% Sc, and (c) 0.22% Sc (no Zr) .

In view of the foregoing, the preferred range in the alloys for Sc is 0.05-0.30%, with a more preferred range of 0.05-0.10%.

[0025] It is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

Claims

1. An aluminum alloy product having high strength with good toughness, containing by weight, 8.5-10.5% Zn, 1.4-1.85% Mg, 2.25-3.0% Cu, and at least one element from the group Zr, V, or Hf not exceeding 0.5%, optionally 0.05-0.30% Sc, optionally 0.03-0.10% Si and 0.03-0.12% Fe, the balance aluminum and incidental impurities.

2. The alloy product of claim 1, wherein said alloy contains 0.05-0.2% Zr.

3. The alloy product of claim 1, wherein said alloy includes 0.05-0.30% Sc.

4. The alloy product of claim 3, wherein said alloy includes 0.05-0.20% Zr.

5. The alloy product of claim 1, wherein said alloy includes 0.03-0.10% Si and 0.03-0.12% Fe.

6. The alloy product of claim 1, wherein the combined weight percentages of Mg and Cu range from 4.1 to 4.5%.

7. The alloy product of claim 6, wherein the combined weight percentages of Zn, Mg and Cu range from 13.0 to 14.5%.

8. The aluminum alloy product of claim 1, wherein said product is selected from the group including sporting goods such as baseball and soft ball bats, golf shafts, lacrosse sticks, tennis rackets, and arrows; aerospace components such as wing plates, bulkheads, fuselage stringers, and structural extrusions and forgings; and ordnance parts such as sabots and missile launchers.

9. A process for making an aluminum alloy product containing 8.5-10.5% Zn, 1.4- 1.85% Mg, 2.25-3.0% Cu, and at least one element from the group Zr, V, or Hf not exceeding 0.5%, optionally 0.05-0.30% Sc the balance aluminum and incidental impurities, said method including the steps of:

casting said alloy product to form an alloy ingot; and

homogenizing said alloy ingot to minimize the amount of low melting point eutectic phases therein by heating said ingot at a heating rate of no more than 11.11°K/hr. (20°F/hr.) from a first temperature at least 11.11 (20°F) below the melting temperature of said ingot to a second temperature of about 2.78 °K (5°F) below said melting temperature.

10. The process of claim 9, wherein said first temperature is 272.04°K (30°F) below said melting temperature.

11. The process of claim 9, wherein said first temperature is selected to be 738.71°K (870°F) and said second temperature is selected to be in the range of 747.04-749.82°K (885-890°F).

12. The process of claim 9 where the alloy ingot is held at said first temperature for at least 8 hours.

13. The process of claim 9, wherein said alloy contains 0.05-0.30% Sc.

14. The process of claim 9, wherein said alloy ingot is formed into a shape of a finished product, solution heat treated at 738.71 to 755.37 degrees K (870 to 900 degrees F) and then artificially aged in a first aging step by being heated at 352.59 to 427.59 degrees K (175-310 degrees F) for 3 to 30 hours.

15. The process of claim 14, wherein said product is exposed to a second aging step by being heated at 427.59 to 455.37 degrees K (310 to 360 degrees F) for 2 to 24 hours.

16. The process of claim 15, wherein said alloy product is exposed to a third aging step by being heated at 352.59 to 422.39 degrees K (175 to 300 degrees F) for 1 to 30 hours.

17. The process of claim 9, wherein said alloy ingot is formed into a shape of a finished product, solution heat treated and then artificially aged in a first aging step by being heated at 427.59 to 455.37 degrees K (310 to 360 degrees F) for 2 to 24 hours.

18. The process of claim 17, wherein said alloy product is exposed to a second aging step by being heated at 352.59 to 422.39 degrees K (175 to 300 degrees F) for 1 to 30 hours.

Ansprüche

1. Aluminiumlegierungsprodukt mit hoher Festigkeit und guter Zähigkeit, das bezogen auf das Gewicht 8,5 bis 10,5 % Zn, 1,4 bis 1,85 % Mg, 2,25 bis 3,0 % Cu, und höchstens 0,5 % mindestens eines Elements aus der Gruppe Zr, V oder Hf, gegebenenfalls 0,05 bis 0,30 % Sc, gegebenenfalls 0,03 bis 0,10 % Si und 0,03 bis 0,12 % Fe, den Rest Aluminium und zufällige Verunreinigungen enthält.

2. Legierungsprodukt nach Anspruch 1, wobei die Legierung 0,05 bis 0,2 % Zr umfasst.

3. Legierungsprodukt nach Anspruch 1, wobei die Legierung 0,05 bis 0,30 % Sc umfasst.

4. Legierungsprodukt nach Anspruch 3, wobei die Legierung 0,05 bis 0,20 % Zr umfasst.

5. Legierungsprodukt nach Anspruch 1, wobei die Legierung 0,03 bis 0,10 % Si und 0,03 bis 0,12 % Fe umfasst.

6. Legierungsprodukt nach Anspruch 1, wobei die kombinierten Gewichtsprozentsätze von Mg und Cu im Bereich von 4,1 bis 4,5 % liegen.

7. Legierungsprodukt nach Anspruch 6, wobei die kombinierten Gewichtsprozentsätze von Zn, Mg und Cu im Bereich von 13,0 bis 14,5 % liegen.

8. Aluminiumlegierungsprodukt nach Anspruch 1, wobei das Produkt aus der Gruppe ausgewählt ist, die Sportartikel, wie beispielsweise Baseball- und Softballschläger, Golfschäfte, Lacrosse Schläger, Tennisschläger und Pfeile; Luft- und Raumfahrtkomponenten, wie beispielsweise Flügelplatten, Schotten, Rumpfstreifen und strukturelle Extrusionen und Schmiedeteile; und Militärmaterialien, wie beispielsweise Treibkäfige und Raketenwerfer, umfasst.

9. Prozess zur Herstellung eines Aluminiumlegierungsprodukts, das 8,5 bis 10,5 % Zn, 1,4 bis 1,85 % Mg, 2,25 bis 3,0 % Cu, und höchstens 0,5 % mindestens eines Elements aus der Gruppe Zr, V oder Hf, gegebenenfalls 0,05 bis 0,30 % Sc, den Rest Aluminium und zufällige Verunreinigungen enthält, wobei das Verfahren die folgenden Schritte umfasst:

Gießen des Legierungsprodukts, um einen Legierungsgussblock zu bilden;

Homogenisieren des Legierungsgussblocks, um die Menge eutektischer Phasen niedrigen Schmelzpunkts darin durch Erwärmen des Gussblocks bei einer Erwärmungsrate von höchstens 11,11 °K/Std. (20 °F/Std.) von einer ersten Temperatur von mindestens 11,11 °K (20 °F) unter der Schmelztemperatur des Gussblocks auf eine zweite Temperatur von etwa 2,78 °K (5 °F) unter der Schmelztemperatur zu minimieren.

10. Prozess nach Anspruch 9, wobei die erste Temperatur 272,04 °K (30 °F) unter der Schmelztemperatur liegt.

11. Prozess nach Anspruch 9, wobei die erste Temperatur so ausgewählt wird, dass sie 738,71 °K (870 °F) beträgt, und die zweite Temperatur so ausgewählt wird, dass sie im Bereich von 747,04 bis 749,82 °K (885 bis 890 °F) liegt.

12. Prozess nach Anspruch 9, wobei der Legierungsgussblock für mindestens 8 Stunden auf der ersten Temperatur gehalten wird.

13. Prozess nach Anspruch 9, wobei die Legierung 0,05 bis 0,30 % Sc enthält.

14. Prozess nach Anspruch 9, wobei der Legierungsgussblock zu einer Form eines Fertigprodukts geformt, bei 738,71 bis 755,37 Grad Kelvin (870 bis 900 Grad Fahrenheit) lösungsgeglüht und anschließend in einem ersten Alterungsschritt durch Erwärmen bei 352,59 bis 427,59 Grad Kelvin (175 bis 310 Grad Fahrenheit) für 3 bis 30 Stunden künstlich gealtert wird.

15. Prozess nach Anspruch 14, wobei das Produkt durch Erwärmen bei 427,59 bis 455,37 Grad Kelvin (310 bis 360 Grad Fahrenheit) für 2 bis 24 Stunden einem zweiten Alterungsschritt unterzogen wird.

16. Prozess nach Anspruch 15, wobei das Legierungsprodukt durch Erwärmen bei 352,59 bis 422,39 Grad Kelvin (175 bis 300 Grad Fahrenheit) für 1 bis 30 Stunden einem dritten Alterungsschritt unterzogen wird.

17. Prozess nach Anspruch 9, wobei der Legierungsgussblock zu einer Form eines Fertigprodukts geformt, lösungsgeglüht und anschließend in einem ersten Alterungsschritt durch Erwärmen bei 427,59 bis 455,37 Grad Kelvin (310 bis 360 Grad Fahrenheit) für 2 bis 24 Stunden künstlich gealtert wird.

18. Prozess nach Anspruch 17, wobei das Legierungsprodukt durch Erwärmen bei 352,59 bis 422,39 Grad Kelvin (175 bis 300 Grad Fahrenheit) für 1 bis 30 Stunden einem zweiten Alterungsschritt unterzogen wird.

Revendications

1. Produit en alliage d'aluminium ayant une résistance élevée et une bonne dureté, contenant en poids, de 8,5 à 10,5 % de Zn, de 1,4 à 1,85 % de Mg, de 2,25 à 3,0 % de Cu, et au moins un élément du groupe Zr, V, ou Hf n'excédant pas 0,5 %, éventuellement de 0,05 à 0,30 % de Sc, éventuellement de 0,03 à 0,10 % de Si et de 0,03 à 0,12 % de Fe, le reste étant de l'aluminium et des impuretés incidentes.

2. Produit en alliage selon la revendication 1, dans lequel ledit alliage contient de 0,05 à 0,2 % de Zr.

3. Produit en alliage selon la revendication 1, dans lequel ledit alliage contient de 0,05 à 0,30 % de Sc.

4. Produit en alliage selon la revendication 3, dans lequel ledit alliage contient de 0,05 à 0,20 % de Zr.

5. Produit en alliage selon la revendication 1, dans lequel ledit alliage contient de 0,03 à 0,10 % de Si et de 0,03 à 0,12 % de Fe.

6. Produit en alliage selon la revendication 1, dans lequel les pourcentages en poids combinés de Mg et Cu sont dans la plage de 4,1 à 4,5 %.

7. Produit en alliage selon la revendication 6, dans lequel les pourcentages en poids combinés de Zn, Mg et Cu sont dans la plage de 13,0 à 14,5 %.

8. Produit en alliage d'aluminium selon la revendication 1, dans lequel ledit produit est choisi dans le groupe comprenant les articles de sport tels que les battes de baseball et de softball, les clubs de golf, les bâtons de jeu de crosse, les raquettes de tennis, et les flèches ; les composants pour l'industrie aérospatiale tels que les plaques d'ailes, les cloisons étanches, les raidisseurs de fuselage, et les extrusions et les pièces forgées structurales ; et les pièces d'artillerie telles que les sabots et les lanceurs de missiles.

9. Procédé de fabrication d'un produit en alliage d'aluminium contenant de 8,5 à 10,5 % de Zn, de 1,4 à 1,85 % de Mg, de 2,25 à 3,0 % de Cu, et au moins un élément du groupe Zr, V, ou Hf n'excédant pas 0,5 %, éventuellement de 0,05 à 0,30 % de Sc, le reste étant de l'aluminium et des impuretés incidentes, ledit procédé comprenant les étapes de :

coulage dudit produit en alliage pour former un lingot en alliage ; et

homogénéisation dudit lingot en alliage pour réduire au minimum la quantité de phases eutectiques à bas points de fusion par chauffage dudit lingot à une vitesse de chauffage inférieure ou égale à 11,11 °K/h (20 °F/h) depuis une première température au moins 11,11 °K (20 °F) au-dessous de la température de fusion dudit lingot jusqu'à une seconde température environ 2,78 °K (5 °F) au-dessous de ladite température de fusion.

10. Procédé selon la revendication 9, dans lequel ladite première température est 272,04 °K (30 °F) au-dessous de ladite température de fusion.

11. Procédé selon la revendication 9, dans lequel ladite première température est choisie pour être de 738,71 °K (870 °F) et ladite seconde température est choisie pour être dans la plage de 747,04 à 749,82 °K (885 à 890 °F).

12. Procédé selon la revendication 9 dans lequel le lingot en alliage est maintenu à ladite première température pendant au moins 8 heures.

13. Procédé selon la revendication 9, dans lequel ledit alliage contient de 0,05 à 0,30 % de Sc.

14. Procédé selon la revendication 9, dans lequel ledit lingot en alliage est formé en fonction de la forme du produit fini, soumis à un traitement thermique de mise en solution de 738,71 à 755,37 degrés K (870 à 900 degrés F) puis artificiellement vieilli dans une première étape de vieillissement par chauffage de 352,59 à 427,59 degrés K (175 à 310 degrés F) pendant 3 à 30 heures.

15. Procédé selon la revendication 14, dans lequel ledit produit est exposé à une deuxième étape de vieillissement par chauffage de 427,59 à 455,37 degrés K (310 à 360 degrés F) pendant 2 à 24 heures.

16. Procédé selon la revendication 15, dans lequel ledit produit en alliage est exposé à une troisième étape de vieillissement par chauffage de 352,59 à 422,39 degrés K (175 à 300 degrés F) pendant 1 à 30 heures.

17. Procédé selon la revendication 9, dans lequel ledit lingot en alliage est formé en fonction de la forme du produit fini, soumis à un traitement thermique de mise en solution puis artificiellement vieilli dans une première étape de vieillissement par chauffage de 427,59-455,37 degrés K (310 à 360 degrés F) pendant 2 à 24 heures.

18. Procédé selon la revendication 17, dans lequel ledit produit en alliage est exposé à une seconde étape de vieillissement par chauffage de 352,59 à 422,39 degrés K (175 à 300 degrés F) pendant 1 à 30 heures.

Drawing