METHOD FOR IMPROVED MANUFACTURING OF THICK ALUMINIUM-COPPER ROLLED PRODUCTS

Abstract

The invention relates to a method for manufacturing a product comprising an AlCu alloy comprising (weight per cent): Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25 Cr<0.05 Zr<0.10, Ti<0.15 others <0.05, remainder aluminium. In an embodiment the method comprises naturally aging the product forming in at least one process, such as stretch forming, drawing, flow spinning, and/or bending and artificial aging at a temperature from 280 to 340° F. (138 to 171° C.) for a duration from 6 to 36 hours. The method is particularly useful to make armor products.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Patent Application Ser. No. 61/419,050 filed Dec. 2, 2010 the contents of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to aluminum-copper alloy products, and more specifically such products optionally in the form of thick rolled products (ie with a thickness of a thickness of for example, from 0.5 to 8 inches) intended to produce armored products.

2. Description of Related Art

Aluminum alloys have been widely used in light and medium armored vehicles since the 1950s because of their superior ballistic performance-weight balance combined with their good weldability, their ease of fabrication and their availability in a large range of product forms. With the recent conflicts, new threats appeared which made necessary to significantly improve the ballistic resistance of any materials used for armor plates, including aluminum alloys, as well as to develop new materials with enhanced specific protection.

2139 has been identified as a promising alloy for high ballistic performance, see for example, Lee W. M.—Dynamic Microstructural Characterization of High Strength Aluminum Alloys—Masters Thesis—2008.

Products related to AA2139 are known for example from U.S. Pat. No. 7,229,508.

For certain parts of armored vehicles, in particular the underbelly, the shape of the armoured plate can often be complicated and this may necessitate employing a difficult shaping operation.

SUMMARY OF THE INVENTION

It was therefore a purpose of the present invention to provide a method which enables forming thick Al—Cu wrought products suitable for armored vehicles and even improve armored performance such as ballistic performance and blast resistance of armored products, such as products made of AA2139.

An object of the invention was to provide a method for manufacturing a product comprising an AlCu alloy, said method comprising:

a) casting an ingot comprising (weight percent):

Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25 Cr<0.05 Zr<0.10, Ti<0.15, optionally one or more of Hf, Sc and/or V, others <0.05, remainder aluminum,

b) optionally homogenizing the ingot at a temperature from 890 to 1010° F. (477 to 543° C.) for 2 to 48 hrs, and preferably at a temperature from 950 to 990° F. (510 to 532° C.) for a duration of 12 to 36 hrs,

c) hot working the ingot to a product with a thickness from 0.5 to 8 inches, preferably from 1 to 7 inches, and most preferably from 2 to 6 inches,

d) solution treating the product from 930 to 1010° F. (499 to 543° C.), for a duration from 5 min to 10 hr,

e) rapidly cooling the product,

f) optionally cold working the product by cold rolling and/or stretching,

g) naturally aging the product,

wherein said method is optionally conducted in the order a-g.

A plate obtained by a method of the invention can advantageously undergo a forming operation to obtain a complicated shape and be artificially aged to obtain advantageous armor properties, such as ballistic properties and blast resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. 20 mm FSP/0.3 cal AP performance balance for the tested alloys (the performance index is calculated as the relative difference between impact velocity and residual velocity, a performance of 100% means projectile stopped.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Unless specified otherwise, all the indications relating to the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. The alloys are named in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The definitions of metallurgical tempers are given in the European standard EN 515, and those are incorporated herein by reference as if written.

Unless specified otherwise, the static mechanical properties, in other words the fracture strength R_m, the yield strength at 0.2% elongation Rp_0.2 (“yield strength”) and the elongation at fracture A, are determined by means of a tensile test as per EN 10002-1, the sampling and direction of the test being defined by the standard EN 485-1 and these are are also incorporated herein by reference in their entirety.

Unless specified otherwise, the definitions as per the standard EN 12258 (incorporated herein by reference) apply.

According to the present invention, there is provided a method to make a wrought product.

The method comprises successively casting an ingot comprising (weight percent):
Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25 Cr<0.05 Zr<0.10, Ti<0.15, others <0.05, remainder aluminium. AA2139 is an example of the cast composition.
Advantageously, the Ti content is from 0.02 to 0.13 wt. % and preferably from 0.08 to 0.12 wt. %.
Preferably, the Cu content is from 4.4 to 5.2 wt. %.
The Mg content is preferably from 0.3 to 0.6 wt. %.
Preferably the Mn content is from 0.3 to 0.5 wt. %.
Advantageously, the alloy further includes at least one selected from Hf 0.1-1.0 wt. %, Sc 0.03-0.6 wt. % and V 0.05-0.15 wt. %

Optionally the method comprises homogenizing the ingot at a temperature from 890 to 1010° F. (477 to 543° C.) for 2 to 48 hrs, and preferably at a temperature from 950 to 990° F. (510 to 532° C.) for a duration of 12 to 36 hrs.

The ingot is then hot worked to a product with a thickness from 0.5 to 8 inches, preferably from 1 to 7 inches, and most preferably from 2 to 6 inches. In a preferred embodiment the thickness of the product is from 1 to 4 inch.

Hot working may be carried out by rolling, forging or extruding. In a preferred embodiment, hot working is carried out by rolling.

The product is then solution heat treated from 930 to 1010° F. (499 to 543° C.), for a duration from 5 min to 10 hr and rapidly cooled.

Optionally the product is cold worked by cold rolling and/or stretching.

In an embodiment of the invention cold working is done solely by cold rolling from 0.5 to 10% and preferably from 1 to 5%. In another more preferred embodiment of the invention cold working is done solely by stretching from 0.5 to 10% and preferably from 1 to 5%. In yet another embodiment of the invention cold working is done by a combination of cold rolling from 0.5 to 5% and stretching from 0.5 to 5%.

Finally the product is naturally aged. The final temper obtained after natural aging comprises advantageously T3, T351, T3511, T36, T38, T39 or F.

The product obtained after natural aging can advantageously be formed to a complicated shape.

Advantageously, the method of the invention further comprises successively forming in at least one process, such as stretch forming, drawing, flow spinning, and/or bending, and artificial aging at a temperature from 280 to 340° F. (138 to 171° C.) for a duration from 6 to 36 hours.

Artificial aging may be carried out in one or several steps. The final temper obtained after artificial aging may be referred to as T8, T83, T851, T8511, T86, T852, T87, or T89.

Products obtained by the method of the invention have after artificial aging an even improved armor performance compared to products of similar composition in a T8 temper which was obtained without the steps of natural aging and forming to a complicated shape.

Although they are not bound to a specific theory, the present inventor believe that the “dual cold working” of some embodiments of the method of the invention: that is cold working before natural aging and forming after natural natural aging contribute the high armor performance of the products of the invention.

An armor product comprising a product made by the method of the invention is particularly advantageous.

EXAMPLES

Example 1

The ballistic performance of a selection of aluminium alloys has been tested: 5083-H131, 6061-T6, 7020-T6, 7449-T6, and 2139-T8. Two types of projectiles were used: 0.3 cal AP and 20 mm FSP. Projectile velocities were selected to guarantee the full perforation of the plates for standard alloys and the residual velocities were measured by X-Ray flashes behind the tested plates.

The ballistic performances of alloys were compared in terms of residual velocity and number of projected fragments. The AP-FSP performance balances of the tested materials are compared in FIG. 1. Post-mortem optical and electronic sectional observations of the perforated plates were performed and the failure mechanisms were classified as follows:

• • Low to medium strength alloys (5xxx and 6xxx) failed by ductile hole growth. The residual velocities measured on these alloys were quite high but only a few fragments were projected behind the specimen.
  • High strength 7xxx alloys failed by discing (rear plate failure) causing high spalling behind the armor plate and Adiabatic Shear Band (ASB) initiation, propagation and finally shear cracking.
  • Alloy 2139 exhibited the better AP-FSP balance with a ductile bulging failure mode.

Example 2

A slab made of AA2139 was cast, homogenized, hot rolled to 2.5 inch thick plate, solution heat treated, stretched 3% and naturally aged to a T351 temper.

The plate was then stretched formed and artificially aged to a T8 temper.

Ballistic performance was excellent, even improved compared to a T8 temper obtained without intermediate T351 temper and stretched forming.

Claims

1. A method for manufacturing a product comprising an AlCu alloy, said method comprising:

a) casting an ingot comprising (weight percent):

Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25 Cr<0.05 Zr<0.10, Ti<0.15, others <0.05, remainder aluminum,

b) optionally homogenizing the ingot at a temperature from 890 to 1010° F. for 2 to 48 hrs, for a duration of 12 to 36 hrs,

c) hot working the ingot to a product with a thickness from 0.5 to 8 inches,

d) solution treating the product from 930 to 1010° F., for a duration from 5 min to 10 hr,

e) rapidly cooling the product,

f) optionally cold working the product by cold rolling and/or stretching,

g) naturally aging the product,

wherein said method is optionally conducted in the order a-g.

2. A method of claim 1, wherein a final temper of the product comprises T3, T351 T3511, T36, T38, T39 or F.

3. A method of claim 1, wherein said cold working f) is done solely by cold rolling from 0.5 to 10%.

4. A method of claim 1, wherein said cold working f) is done solely by stretching from 0.5 to 10%.

5. A method of claim 1, wherein said cold working f) is done by a combination of cold rolling from 0.5 to 5% and stretching from 0.5 to 5%.

6. A method of claim 1, wherein the product is further transformed by

i) forming comprising at least one process optionally comprising stretch forming, drawing, flow spinning, and/or bending,

j) artificial aging at a temperature from 280 to 340° F. for a duration from 6 to 36 hours.

7. A method according to claim 6, wherein a final temper after said artificial aging comprises T8, T83, T851, T8511, T86, T852, T87, or T89.

8. A method of claim 6, wherein the Ti content is from 0.02 to 0.13 wt. %.

9. A method of claim 6, wherein Cu is present in an amount from 4.4 to 5.2 wt. %.

10. A method of claim 6, wherein Mg is present in an amount from 0.3 to 0.6 wt. %.

11. A method of claim 6, wherein Mn is present in an amount from 0.3 to 0.5 wt. %.

12. A method for manufacturing a product comprising an AlCu alloy, said method comprising:

a) casting an ingot comprising (weight percent):

Cu: 3.8-5.5 Mg: 0.2-0.8 Mn: 0.2-0.6 Ag 0.2-0.5 Si<0.15 Fe<0.20 Zn<0.25 Cr<0.05 Zr<0.10, Ti<0.15, at least one selected from Hf 0.1-1.0 wt. %, Sc 0.03-0.6 wt. % and V 0.05-0.15 wt. %, others <0.05, remainder aluminum,

b) optionally homogenizing the ingot at a temperature from 890 to 1010° F. for 2 to 48 hrs, for a duration of 12 to 36 hrs,

c) hot working the ingot to a product with a thickness from 0.5 to 8 inches,

d) solution treating the product from 930 to 1010° F., for a duration from 5 min to 10 hr,

e) rapidly cooling the product,

f) optionally cold working the product by cold rolling and/or stretching,

g) naturally aging the product,

wherein said method is optionally conducted in the order a-g, and wherein

wherein the product is further transformed by

i) forming comprising at least one process optionally comprising stretch forming, drawing, flow spinning, and/or bending,

j) artificial aging at a temperature from 280 to 340° F. for a duration from 6 to 36 hours.

13. An aluminium alloy product obtained by a method of claim 1.

14. A product according to claim 13, wherein the product is a rolled product.

15. A product according to claim 13, wherein the product is an extruded product.

16. A product according to claim 13, wherein the product is a forged product.

17. An aluminium alloy product obtained by a method of claim 6.

18. A product according to claim 17, wherein the product is a rolled product.

19. A product according to claim 17, wherein the product is an extruded product.

20. A product according to claim 17, wherein the product is a forged product.

21. An armour product comprising a product of any one of claim 17.