WO2007115617A1

WO2007115617A1 - Al-mg alloy product suitable for armour plate applications

Info

Publication number: WO2007115617A1
Application number: PCT/EP2007/001910
Authority: WO
Inventors: Stefan Moldenhauer; Ingo Günther KRÖPFL; Alfred Johann Peter Haszler; Desikan Sampath; Hormoz Ghaziary
Original assignee: Aleris Aluminum Koblenz Gmbh
Priority date: 2006-04-07
Filing date: 2007-03-06
Publication date: 2007-10-18
Also published as: FR2899598A1; WO2007115617A8

Abstract

Aluminium alloy plate having improved resistance against incoming kinetic energy projectiles, the plate having a gauge of 10 mm or more and the aluminium alloy having a chemical composition comprising, in weight percent: Mg 4.95 to 6.0; Mn 0.45 to 1.2; Zn 0.20 to 0.90; Zr 0.05 to 0.25; Cr < 0.3; Sc < 0.5; Ti < 0.3; Fe < 0.5; Si < 0.45; Ag < 0.4; Cu < 0.25; other elements and unavoidable impurities each <0.05, total <0.20, balance aluminium. The plate has an at least 5% improvement in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 30 AMP2 test according to MIL-DTL-46027J of September 1998. Furthermore, a method of use of the plate as armour plate is disclosed.

Description

Al-Mg alloy product suitable for armour plate applications

FIELD OF THE INVENTION

This invention pertains to an aluminium alloy plate product having a gauge of 10 mm or more. More particularly, this invention pertains to aluminium-magnesium alloys that are suitable for armour plate, yet have improved performance properties, particularly improved resistance against incoming kinetic energy projectiles.

BACKGROUND TO THE INVENTION

As will be appreciated herein below, except as otherwise indicated, alloy designations and temper designations refer to the Aluminum Association designations in Aluminum Standards and Data and the Registration Records, as published by the Aluminum Association

For any description of alloy compositions or preferred alloy compositions, all references to percentages are by weight percent unless otherwise indicated.

Because of their light weight, aluminium alloys have found wide use in military applications, including military vehicles such as personnel carriers The light weight of aluminium allows for improved performance and ease of transporting equipment, including air transport of military vehicles In some vehicles it is advisable to provide shielding or protection against assault, by providing armour plate to protect the occupants of the vehicle. Aluminium has enjoyed substantial use as armour plate, and there are a number of armour plate specifications for the use of different aluminium alloys.

The most relevant requirements for aluminium alloy armour plate are resistance to projectiles, good corrosion resistance, and in some applications, good weldability. Ballistic tests are often conducted with armour piercing ("AP") projectiles such as the 7.62 mm AP M2 and with fragment simulating projectiles ("FSP") such as the common 20 mm projectile. Aluminium alloys which satisfy all the requirements for armour plate are desirable, and these desires have been met to varying degrees. Aluminium alloy AA5083 is covered in the U.S. Military Specification for armour plate MIL-DTL-46027J (September 1998), and the alloy AA7039 is covered in the U.S. Military Specification MIL-DTL-46063H (September 1998). It is generally recognized that for many applications the alloy AA7039 armour plate is better than AA5083 armour plate, although the advantage is more for armour piercing ballistic performance and less so for fragment simulation performance, at least according to the military specifications. However, the alloy AA7039 can present corrosion or stress corrosion problems to a much greater degree than AA5083. The alloy AA7039 is very difficult to weld. The AA7039 alloy when used for armour plate applications is commonly in a T6 temper and the AA5083 alloy when used for armour plate applications is used in the H131 temper.

The compositional ranges for AA5083 are, in weight percent: Mg 4.0 - 4.9 Mn 0.40 - 1.0 Cr 0.05 - 0.25 Si max. 0.40 Fe max. 0.40 Cu max. 0.10 Zn max. 0.25 Ti max. 0.15 impurities each element < 0.05, total < 0.15, balance aluminium.

The nominal composition for the AA5083 alloy is about 4.4 wt.% Mg, 0.7 wt.% Mn and O.15 wt.% Cr.

The compositional ranges for AA7039 are, in weight percent: Zn 3.5 - 4.5 Mg 2.3 - 3.3 Mn 0.10 - 0.40 Cr 0.15 - 0.25 Si max. 0.30 Fe max. 0.40 Cu max. 0.10 Ti max. 0.10 impurities each element < 0.05, total < 0.15, balance aluminium. The nominal composition for the AA7039 alloy is about 4 wt.% Zn₁ 2.8 wt.% Mg, 0.25 wt.% Mn and 0.20 wt.% Cr.

Unless otherwise indicated, all composition percents in the present specification are weight percents.

The most important requirements for aluminium alloy armour plate are resistance to projectiles, good corrosion resistance and stress corrosion resistance in particular, and in modern applications, good weldability. Ballistic tests are often conducted with armour-piercing projectiles such as 0.30 inch calibre projectiles and with fragment-simulating projectiles such as the common 20 mm projectile. Aluminium alloys which satisfy all the requirements for armour plate are desirable.

Another aluminium-magnesium alloy is the AA5059 alloy registered with the Aluminum Association in June 1999. The registered compositional ranges for AA5059 are, in weight percent:

Mg 5.0 - 6.0

Mn 0.6 - 1.2

Zn 0.40 - 0.9

Zr 0.05 - 0.25

Cr max. 0.25

Si max. 0.45

Fe max. 0.50

Cu max. 0.25

Ti max. 0.20 impurities each element < 0.05, total < 0.15, balance aluminium.

This aluminium alloy is also disclosed in US-6,238,495-B2 and US-6,342,113- B2, both incorporated herein by reference in their entireties. The aluminium alloy is for the construction of large welded structures such as storage containers and vessels for marine and land transportation. The alloy has found in particular commercial usage in shipbuilding application, whereby the aluminium alloy is typically in the H321 -temper or O-temper and has a thickness or gauge of less than 20 mm. According to US-6,238,495 the H321 temper was reached by a cold rolling reduction of 40% followed by heat treating by soaking the cold rolled product at 25O⁰C for one hour. The O-temper was reached by a cold rolling reduction of 40% followed by soaking to cold rolled product at 525⁰C for a period of 15 minutes.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved 5000 series alloy that has very good weldablility, yet exhibits good corrosion performance and high resistance to incoming kinetic energy projectiles.

A further object is to provide a 5000 series alloy having improved ballistic properties compared to its AA5083-H131 counterpart.

These and other objects and further advantages are met or exceeded by the present invention concerning an aluminium alloy plate having improved resistance against incoming kinetic energy projectiles, the plate having a gauge of 10 mm or more and the aluminium alloy having a chemical composition comprising, in weight percent:

Mg about 4.95 - 6.0, preferably 5.0 - 5.7

Mn about 0.45 - 1.4, preferably 0.65 - 1.2

Zn about 0.20 - 0.90, preferably about 0.35 - 0.70

Zr about 0.05 - 0.25

Cr < 0.3

Sc < 0.5

Ti < 0.3

Fe < 0.5, preferably < 0.25

Si < 0.45, preferably < 0.2

Ag < 0.4

Cu < 0.25 other elements and unavoidable impurities each <0.05, total <0.20, balance aluminium, and wherein the plate has an at least 5% improvement in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 30 AMP2 test according to MIL-DTL-46027J of September 1998.

By an AA5083-H131 counterpart it is meant an aluminium alloy plate having a composition as defined above for AA5083, and processed and heat treated to H131 temper and having the same dimensions of length, width and thickness as the plate of the present invention to which it is compared. A typical counterpart has a composition within the elemental window of about 4.4 wt.% Mg, 0.7 wt.% Mn₁ 0.15 wt.% Cr, 0.40 wt.% Si max., 0.40 wt.% Fe max., 0.10 wt.% Cu max., 0.25 wt.% Zn max., 0.15 wt.% Ti max., impurities each element < 0.05 wt.%, total < 0.15 wt.%, and balance aluminium. A plate within the elemental composition described for the present invention having the at least 5 % improvement in the V50 limit over a single AA5083-H131 counterpart meets the feature of being a plate having an at least 5% improvement in the V50 limit compared to an AA5083-H131 counterpart. For example, a plate within the elemental composition described for the present invention having the at least 5 % improvement in the V50 limit over an AA5083-H131 counterpart, having a composition of 4.4 wt.% Mg, 0.7 wt.% Mn, 0.15 wt.% Cr, 0.2 wt.% Si, 0.2 wt.% Fe, 0.05 wt.% Cu, 0.15 wt.% Zn, 0.1 wt.% Ti, impurities each element < 0.05 wt.%, total < 0.15 wt.%, and balance aluminium, meets the feature of being a plate having an at least 5% improvement in the V50 limit compared to an AA5083-H131 counterpart.

Likewise, an AA7039-T6 counterpart is an aluminium alloy plate having a composition as defined above for AA7039 and processed and heat treated to a T6 temper and having the same dimensions of length, width and thickness as the plate of the present invention to which it is compared. A typical counterpart has a composition within the elemental window of about 4 wt.% Zn, 2.8 wt.% Mg, 0.25 wt.% Mn and 0.20 wt.% Cr, 0.30 wt.% Si max., 0.40 wt.% Fe max., 0.10 wt.% Cu max., 0.10 wt.% Ti max., impurities each element < 0.05 wt.%, total < 0.15 wt.%, balance aluminium; for example, 4 wt.% Zn, 2.8 wt.% Mg, 0.25 wt.% Mn and 0.20 wt.% Cr, 0.20 wt.% Si, 0.20 wt.% Fe, 0.05 wt.% Cu, 0.05 wt.% Ti, impurities each element < 0.05 wt.%, total < 0.15 wt.%, balance aluminium.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 and Fig. 2 show the measurement results of the mechanical properties of respectively Table 1 and 2. Fig.1 is for the LT-direction and Fig. 2 is for the Indirection. For both figures the horizontal axes defines the amount of cold work (in %), and the vertical axes the strength in MPa.

Fig. 3 shows an up-armoured Multipurpose Wheeled Vehicle, or ΗMMWV".

Fig. 4 shows a Stryker vehicle.

Fig. 5 shows a Bradley M2/M3 vehicle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an aluminium alloy plate having improved resistance against incoming kinetic energy projectiles, the plate having a gauge of 10 mm or more and the aluminium alloy having a chemical composition comprising, in weight percent:

Mg about 4.95 - 6.0, preferably 5.0 - 5.7, for example 5.2 - 5.6 Mn about 0.45 - 1.4, preferably 0.65 - 1.2, for example 0.75 - 0.9

Zn about 0.9 max., preferably about 0.20 - 0.90, preferably about 0.35 - 0.70, for example 0.45 to 0.6

Zr < 0.3, preferably about 0.05 - 0.25, for example about 0.05 - 0.15 Cr < 0.3, for example 0.08 to 0.15

Sc < 0.5, for example 0.08 to 0.45, 0.2 to 0.45, or < 0.1 , but preferably 0.05 to 0.30, 0.05 to 0.20, or 0.05 to 0.15

Ti < 0.3, for example < 0.1

Fe < 0.5, preferably < 0.25, for example < 0.14

Si < 0.45, preferably < 0.2, for example <0.14

Ag < 0.4, for example < 0.01

Cu < 0.25, for example < 0.05, other elements and unavoidable impurities each <0.05, total <0.20, balance aluminium, and wherein the plate has an at least 5%, and preferably an at least 6%, improvement in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 30 AMP2 test according to MIL-DTL-46027J of September 1998.

In an embodiment the plate has an at least 5% improvement, and preferably an at least 8% improvement, in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 20 mm FSP test according to MIL-DTL-46027J of September 1998.

The aluminium alloy plate according to the present invention offers a plate product ideally suitable for armour plate applications having significantly improved ballistic properties compared to its AA5083-H131 counterpart. The aluminium alloy plate according to the present invention offers also a plate product having ballistic properties close to its AA7039-T6 counterpart, but in combination with very good weldability and improved corrosion resistance performance, in particular in stress corrosion resistance, compared to the AA7039-T6 alloy. This combination of ballistic properties, very good weldability and corrosion resistance performance favours the alloy plate of the present invention for the application as armour plate.

An important advantage of the present invention is the improved Mass Efficiency compared to AA5083-H131 and even compared to AA7039-T6 counterparts. The alloy product according to the invention has a lower specific density measured at 2O⁰C compared to both the AA5083 and AA7039 alloys resulting in a favourable strength-to-weight ratio or specific strength (tensile strength divided by specific density). The Mass Efficiency is a measure for the FSP performance and relates also to the specific density and allows for a fair comparison of various armour plate materials of similar gauge against each other. Mass Efficiency or "E_m" is being defined as the weight per unit area of a reference material, for example an AA 5083- H131 counterpart alloy, required for defeating a given ballistic threat divided by the weight per unit area of the subject material.

It has been found that when taking AA5083-H131 as the norm, then the AA7039-T64 shows a more than 3% better Mass Efficiency, whereas the alloy product according to this invention shows a more than 5% improvement, and in the better examples an at least 7% improvement. The improvement found increased even further as the higher velocity of the impacting projectile was increased. The improved mass efficiency of the alloy product allows for the construction of a lighter vehicle while offering the same resistance against incoming projectiles. Weight saving in an armoured vehicle can translate amongst other advantages, into vehicle mobility. Alternatively, when constructing an armoured vehicle an unchanged plate thickness can be used while offering a significantly improved resistance against incoming projectiles and thereby an increased survivability.

In the alloy product according to this invention Mg content is limited to 6% because alloy products having a higher Mg content are not very easy to manufacture. Furthermore, a Mg content of more than 6% does not result in any significant strength increase, whereas the corrosion resistance, in particular the resistance against intergranular corrosion, exfoliation corrosion and stress corrosion, deteriorate very fast at higher Mg levels. If desired Mg + Mn is greater than 6.8% or Mg + Mn is less than 5.9%. The plate product preferably has a Zn content in a range of about 0.2 to 0.9 wt. % to enhance weldability and the corrosion resistance of the base plate.

The plate product preferably has a Zr content in a range of about 0.05 to 0.25%, for example >0.16 to 0.25, to further improve the weldability and the corrosion resistance of the base plate.

Ti may be purposively added up to about 0.3%, for example >0.16 to 0.3, for grain-refiner purposes during casting and/or welding.

If desired Cr and/or Ti may be absent. However, in another embodiment a further improvement of the properties, particularly the corrosion resistance, of the aluminium alloy plate product according to the invention is obtained when both Ti and Cr are present in considerable amounts within the defined range. Preferably titanium and chromium are present in equal or about equal quantities in the aluminium alloy product, and wherein Cr is in a range of about 0.08 to 0.25% and Ti is a range of about 0.1 to 0.2%. In this embodiment also Zr in the previously defined range of 0.05 to 0.25% may be present in addition to the combined presence of Ti and Cr in the defined ranges.

It has been found that for a given alloy composition with a combined addition of Cr and Ti the strength increases while the toughness is maintained at about the same level.

In an embodiment Sc may purposively be added up to 0.5%, preferably in a range of 0.05 to 0.3%, and more preferably in the range of 0.05 to 0.15%, to further increase the resistance to incoming kinetic energy projectiles.

In a preferred embodiment the aluminium alloy plate according to the present invention has a composition within the range of AA5059.

In an embodiment the alloy plate has a proof strength ("PS") of at least about 330 MPa, preferably at least about 340 MPa, and more preferably at least about 350 MPa, when measured in its L-direction. When measured in its LT direction the plate has a proof strength of at least about 310 MPa₁ preferably at least about 320 MPa, and preferably at least 330 MPa.

In an embodiment the alloy plate has a ultimate tensile strength ("UTS") of at least about 380 MPa, preferably at least about 390 MPa, and more preferably at least about 400 MPa, when measured in either in its L-direction or LT direction.

The plate according to this invention is ideally suitable as armour plate for application in armoured vehicles, in particular armoured military vehicles. The gauge range or thickness range of the aluminium alloy plate is of more than about 10 mm. A suitable upper-limit for aluminium alloy plate is about 100 mm. A preferred gauge range is of about 15 to 75 mm.

In a preferred mode of the invention the aluminium alloy plate product, having the defined chemical composition and mechanical properties rendering it in particular suitable for armour plate applications, is obtained by a manufacturing process comprising casting, preheating and/or homogenisation, hot rolling and cold working of the alloy plate product by means of a cold working operation selected from the group consisting of (i) stretching in a range of 3 to 18% and (ii) cold rolling with a total cold roll reduction in a range of 15% to less than 40%.

In a more preferred embodiment of the manufacturing process of the alloy plate, the alloy plate at final gauge after the cold working operation is not subjected to of a further heat-treatment such that no substantial recovery occurs in the alloy plate. This results in the mechanical properties at final thickness or final gauge remaining substantially unchanged, thus substantially no recovery occurs. After a cold working operation according to the present invention a heat-treatment of for example 30 min at 8O⁰C can be carried out as this merely stabilises the alloy product. Whereas a heat treatment of 30 min or 60 min at 25O⁰C to obtain an H321 temper results amongst others in an undesirable increase of the ductility. Any high temperature heat- treatment after cold rolling to final thickness is preferably to be avoided.

The alloy described herein can be ingot derived and can be provided as an ingot or slab by casting techniques including those currently employed in the art. A preferred practice is semi-continuous casting of large ingots, for instance 350 or 500 mm in thickness by about 2000 mm or more in width by about 3.5 m or more in length. Such large ingots are preferred in practicing the invention especially in making large plates for use in armour plate applications.

The aluminium alloy stock is preferably preheated or homogenized at a temperature of at least 480⁰C prior to hot rolling in single or multiple steps. In order to avoid eutectic melting resulting in possible undesirable pore formation within the ingot the temperature should not be too high, and should typically not exceed 535°C. The time at temperature for a large commercial ingot can be about 2 to 24 hours. A longer period, for example 48 hours or more, has no immediate adverse effect on the desired properties, but is economically unattractive. When using regular industrial scale furnace the heating rate is typically in a range of 30 to 40°C/hour. The alloy is hot rolled to reduce its thickness by at least about 30% of its initial (before any hot rolling) thickness, preferably by about 50% or more, for instance 60 or 65% or more of its thickness when using large commercial starting stock (for instance around 400 mm or more thick) using a reversing hot mill which rolls the metal back and forth to squeeze its thickness down. Thus, the initial hot rolling can be done in increments using different rolling mills. It can also include conventional reheating procedures at around 500⁰C or so between the rolling passes to replace lost heat.

Following the hot rolling operation the alloy product is cold worked by means of a cold working operation selected from the group consisting of (i) stretching in a range of 3 to 18% and (ii) cold rolling with a total cold roll reduction in a range of 15% to less than 40%.

The cold rolling reduction is by less than 40% of its initial (after hot rolling and before any cold rolling) thickness, preferably by at least 15%. Preferably the total reduction of cold rolling in the range of about 15% to 35%, and more preferably in the range of about 22% to 32%. The best balance in properties has been achieved using a cold rolling reduction of about 25%. The total cold rolling reduction can be achieved in one or multiple rolling stages. Where appropriate to enhance workability a heat- treatment or inter-anneal may be carried during between the various cold rolling steps as is regular in the art.

Stretching is defined as the permanent elongation in the direction of stretching, commonly in the L-direction of the plate product. The stretching is to be carried out in the range of about 3 to 18%, preferably in the range of about 8 to 18%, and more preferably in the range of about 8 to 12%. The stretching operation is preferably carried out when producing thicker gauge plate products, such as for plate products having a final gauge of 40 mm or more, and preferably of 50 mm or more.

Each of the cold rolling operation and the stretching operation can be carried out as the only cold working operation. However, these cold working steps can also be carried out in combination, for example by carrying out a 20% cold rolling operation followed by a 4% stretching operation.

The aluminium alloy plate product according to the invention can be welded by means of all regular welding techniques such as MIG and friction stir welding. After the welding operation there is no need for further heat treatment to obtain maximum properties or to recover some of the losses in mechanical properties as a resultant of the heat input during the welding operation and therefore there are less costs in the production of armoured vehicles. The aluminium plate can be welded using regular filler wires such as AA5183 or by modified filler wires having a higher Mg- and/or Mn- content.

A further aspect of the invention relates to a method of use of the aluminium alloy product as armour plate in an armoured vehicle, in particular in military vehicles such as Tracked Combat Systems, Armoured Personnel Carriers, Armoured Support Systems, Amphibious Assault Systems, Advanced Assault Amphibious Vehicles or Armed Robotic Vehicles. When applied in such armoured vehicles it will be a form of a welded configuration such that it forms integral armour. Hang-on armour plate is possible for the aluminium alloy plate according to this invention, but is not the most preferred application.

Fig. 3 shows an up-armored US Army High Mobility Multipurpose Wheeled Vehicle, or "HMMWV 110. Fig. 4 shows a Stryker vehicle 120. Fig. 5 shows a Bradley M2/M3 vehicle 130. These vehicles 110, 120, 130 can be modified in view of the present invention to have plates of the armour of the present invention applied, for example by welding, to an outer surface or other locations of the vehicle suitable for armour protection. The armour is vital protection against small arms, rocket- propelled grenades, or RPGs, and "improvised explosive devices," or IEDs. Additional information on armored vehicles is available at the website of Global Security.org, Alexandria, VA, http://www.globalsecurity.org/military/systems/ground/hmmwvua.htm, July 2006.

The invention will now be illustrated with reference to non-limiting embodiments according to the invention.

EXAMPLES Example 1

On an industrial scale by means of DC-casting several ingots of 400 mm thickness have been cast having a composition within the range of AA5059, namely, in weight percent: 5.45% Mg, 0.81% Mn, 0.51% Zn, 0.14% Zr, 0.09% Si, 0.08% Fe, 0.03% Ti, balance aluminium and unavoidable impurities. The ingots have been scalped, preheated for 8 hours at 510⁰C₁ hot rolled and cold rolled to a final gauge of 38 mm. The hot rolling practice was such that the cold rolling reduction could be varied to investigate the mechanical properties as function of the cold rolling reduction. The cold rolled plates received no further heat-treatment after the cold rolling operation. The mechanical properties (tensile strength and ultimate tensile strength) have been measured according to ASTM B557 in the LT direction and the L-direction. The mechanical properties are listed in Table 1 and illustrated in Fig. 1 and Fig. 2.

From the results of Table 1 and the Figs. 1 and 2 it can be seen that the mechanical property levels depend strongly on the amount of cold work, and that for the alloy plate according to this invention the most preferred level is at about 25% cold work.

Example 2

Alloy plate products having a composition similar to the alloy of Example 1 have been manufactured on an industrial scale analogous to Example 1 such that the final gauge of the plate was varied but all plates had a cold rolling reduction of 25%. This was to investigate the consistency of the mechanical properties as a function of plate thickness.

The results are listed in Table 2. From these results it can be seen that the plate products according to this invention show a very good consistency in their mechanical properties as function of the plate product gauge.

Example 3

This example relates to aluminium alloy plates of 38 mm gauge according to this invention, in particular the preferred embodiment of the AA5059 alloy manufactured according to the process and chemical composition of Example 1 with a 25% cold rolling reduction. Each of these plates was tested for its ballistic properties as a function of the amount of cold work by means of cold rolling and compared against its armour plate counterpart AA5083-H131 counterpart and against its AA7039-T64 counterpart.

Two ballistic tests have been carried out, namely an armour piercing test using 0.3 inch (6.72 mm) projectiles pursuant to MIL-DTL-46027J of September 1998, and with 20 mm fragment simulating projectiles pursuant to MIL-DTL-46027J of September 1998. In both tests the V50 limit in m/s is determined. The tests on the AA7039 alloy have been carried out pursuant to MIL-DTL-46063H of September 1998. The V50 limit or v50 value is defined as the arithmetic mean of the 2(3) lowest projectile velocities giving complete penetration and the 2(3) highest velocities giving partial penetration. 2(3) means two out of three. These velocities should fall within a bracket of 18.3 (27.4) m/s (MIL-DTL-46027J(MR)). The results are listed in Table 3 and Table 4.

From the results of Table 3 it can be seen that the plate product according to this invention exhibits in both type of tests a significant improvement in ballistic properties compared to its AA5083-H131 counterpart.

And from the results of Table 4 it can be seen that the plate product according to this invention exhibits a slightly lower performance for the APM2 tests but a comparable performance in the FSP test compared to its AA7039-T64 counterpart.

Example 4

The Mass Efficiency has been calculated for the alloy product according to this invention and AA7039-T64 and normalised against AA5083-H131 material for a 20 mm FSP threat at 0 deg. obliquity at three different V50 velocities (ft/sec). "FSP" means Fragment Simulating Projectiles. The results are listed in Table 5. The alloy product according to this invention had a composition within the range of AA5059 similar to the alloy of Example 1 and had been cold rolled for 25% devoid of any further heat treatments.

From the results of Table 5 it can be seen that for all V50 velocities the alloy product according to this invention has a mass efficiency which outperforms both the known AA5083-H131 and AA7039-T64 armour plate products.

Example 5

For plate material having a final thickness or gauge of 19 mm or more, the armour plate qualification requirements for the stress corrosion resistance measured according to ASTM G39 when using C-rings are for:

AA5083-H131 96 hours (4 days) at a stress level of 207 MPa. AA7039-T74 96 hours (4 days) at a stress level of 242 MPa.

Alloy plate products having a composition similar to the alloy of Example 1 have been manufactured on an industrial scale analogous to Example 1 such that the final gauge of the plate was 38 mm and the plate had a cold rolling reduction of 25%.

Six samples were tested according to ASTM G39 and all specimens were exposed for 1000 hours (45 days) without any crack formation at a stress level of 242 MPa. Thus no stress corrosion occurred.

Six specimens of 8 mm (3 taken from the outside of the plate and 3 taken from the core of the plate) from the same batch were also tested according to ASTM G39- 90 (Four-point loaded specimens). The yield strength in the LT direction of the alloy plate was 365 MPa and the applied load was consequently 292 MPa. After 1000 hours (45 days) of testing still no cracks occurred in any of the specimens.

These results show that the alloy plate according to the present invention has a significantly better resistance against stress corrosion measured according to ASTM G39 than its AA5083 and AA7039 counterparts, and together with the very good weldability makes the alloy product a favourable candidate for armour plate applications.

Example 6

AA5059 plate material according to the present invention and having been cold rolled with a reduction of 25% was tested against the same AA5059 alloy in the H321 temper as disclosed in US-6,238,495-B2 and US-6,342,113-B2 and also against its AA5083-H131 counterpart for the V50 limit with 20 mm fragment simulating projectiles at 0 deg. obliquity according to MIL-DTL-46027J of September 1998.

The AA5059-H321 showed a 2% improvement in the V50 limit compared to the AA5083-H131 counterpart, whereas the alloy plate according to the present invention showed a 5% improvement in the V50 limit. These results confirm that the alloy plate according to the present invention outperforms its AA5083-H131 counterpart, but also shows a significant improvement over the same AA5059 alloy in the H321 temper commonly used for shipbuilding applications

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the spirit or scope of the invention as herein described.

Claims

1. Aluminium alloy plate having improved resistance against incoming kinetic energy projectiles, the plate having a gauge of 10 mm or more and the aluminium alloy having a chemical composition comprising, in weight percent:

Mg 4.95 to 6.0

Mn 0.45 to 1.2

Zn 0.9 max.

Zr < 0.3

Cr < 0.3

Sc < 0.5

Ti < 0.3

Fe < 0.5

Si < 0.45

Ag < 0.4

Cu < 0.25, other elements and unavoidable impurities each <0.05, total <0.20, balance aluminium, and wherein the plate has an at least 5% improvement in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 30 AMP2 test according to MIL-DTL-46027J of September 1998.

2. Aluminium alloy plate according to claim 1, wherein the plate has an at least 6% improvement in the V50 limit compared to an AA5083-H131 counterpart, as measured by the 30 AMP2 test according to MIL-DTL-46027J of September 1998.

3. Aluminium alloy plate according to claim 1 , wherein the plate has an at least 5% improvement in mass efficiency compared to the AA5083-H131 counterpart, and preferably at least 6% improvement.

4. Aluminium alloy plate according to claim 1 , wherein the plate has a proof strength of at least about 330 MPa, and preferably of at least about 380 MPa.

5. Aluminium alloy plate according to claim 1, wherein the Mg content is in a range of 5.0 to 5.7%.

6. Aluminium alloy plate according to claim 1 , wherein the Mn content is in a range of 0.65 to 1.2%.

7. Aluminium alloy plate according to claim 1, wherein the Zn content is in a range of 0.20 to 0.90%, and preferably in a range of 0.35 to 0.70%.

8. Aluminium alloy plate according to claim 1, wherein the Zr content is in a range of 0.05 to 0.25%.

9. Aluminium alloy plate according to claim 1, wherein the Cr content is in a range of 0.08 to 0.25% and the Ti content is in a range of 0.1 to 0.2%.

10. Aluminium alloy plate according to claim 1, wherein the Sc content is in a range of 0.05 to 0.3%.

11. Aluminium alloy plate according to claim 1, wherein the chemical composition is within the range of AA5059.

12. Aluminium alloy plate according to claim 1, wherein the plate has a gauge of less than 100 mm, and preferably in the range of 15 to 75 mm.

13. Aluminium alloy plate according to claim 1 , wherein the alloy plate product is obtained by a manufacturing process comprising casting, preheating and/or homogenisation, hot rolling and cold working of the alloy plate product by means of a cold working operation selected from the group consisting of (i) stretching in a range of 3 to 18% and (ii) cold rolling with a total cold roll reduction in a range of 15% to less than 40%.

14. Aluminium alloy plate according to claim 13, wherein the cold working operation consists of cold rolling.

15. Aluminium alloy plate according to claim 13, wherein the cold working operation consists of stretching.

16. Aluminium alloy plate according to claim 13, wherein the cold working consists of a combination of stretching and cold rolling.

17. Aluminium alloy plate according to claim 13, wherein the cold rolling is carried out with a cold roll reduction in a range of 15% to less than 35%, and preferably in a range of 22% to 32%.

18. Aluminium alloy plate according to claim 13, wherein the stretching operation is in a range of 8 to 18%, and preferably in a range of 8 to 12%.

19. Aluminium alloy plate according to claim 13, wherein the manufacturing process of the alloy plate at final gauge after the cold working operation is devoid of a further heat-treatment such that no substantial recovery occurs in the alloy plate.

20. Aluminium alloy plate according to claim 1, wherein the aluminium alloy has a composition, in weight percent, consisting of:

Mg 4.95 to 6.0

Mn 0.45 to 1.4

Zn <0.9

Zr <0.3

Cr <0.3

Sc <0.5

Ti <0.3

Fe <0.35

Si <0.35

Ag <0.4

Cu < 0.25, other elements and unavoidable impurities each 0.05, total <0.20, balance ! aluminium.

21. Aluminium alloy plate according to claim 1, wherein the aluminium alloy has a composition, in weight percent, consisting of:

Mg 5.0 to 5.7

Mn 0.65 to 1.2

Zn 0.35 to 0.70

Zr 0.05 to 0.25

Cr <0.3

Sc < 0.5, preferably 0.05 to 0.5

Ti <0.3

Fe <0.35

Si <0.35

Ag <0.4 Cu < 0.25, other elements and unavoidable impurities each <0.05, total <0.20, balance aluminium.

22. A method of use comprising applying an aluminium alloy plate according to claim 1 as armour plate to an armoured vehicle.

23. The method of use of claim 22, wherein the aluminium alloy has a composition within the range of AA5059 and is welded to the armoured vehicle.

24. A vehicle comprising the armour plate of claim 1.