IT8520694A1 - COMPOSITE ELEMENT IN THE FORM OF A THREE-LAYER PLATE IN ALUMINUM ALLOYS - Google Patents

Description

Description of an industrial invention entitled "Eemenocomposonomadpiat

-aluminum alloy layers

DESCRIPTION

The present invention relates to a composite element in the form of a multi-layered plate made of aluminium alloys for use in armoured devices, particularly armoured vehicles.

The growing interest in armour elements made of aluminium alloys is well known, especially in relation to the need to reduce the weight of said armour as much as possible.

It is also known that an armour element must satisfy several (and sometimes conflicting) requirements, such as in particular a high resistance to penetration by projectiles and hard bodies, a low tendency to form splinters, good weldability, as well as good mechanical properties.

H.P.Georae et al. (US Patent No. 3,042,5551 describes a plate approximately 12-13 mm thick made of 7075 alloy (according to the Aluminum Association-USA designation) consisting of 5.6% Zn, 2.5% Mg, 1.6% Cu, 0.22% Cr, 0.30% Mn (maximum), 0.40% Si (maximum), 0.50% Fe (maximum), 0.20% Ti (maximum) and the remainder being substantially 100% Al, or of 7178 alloy consisting of 6.8% Zn, 2.7% Mg, 2% Cu, 0.22% Cr, 0.30% Mn (maximum), 0.40% Si (maximum), 0.50% Fe (maximum), 0.20% Ti (maximum) and the remainder being substantially 100% Al, substantially Al, said plate being subjected, limited to the "rear" face (i.e. opposite to the duel of impact of the projectiles) to an aging treatment, which makes said rear face less sensitive to the formation of shards, while the "front" face maintains good resistance to penetration. The process for obtaining the above-mentioned plate is however very difficult to control (and consequently it is difficult to achieve the desired optimal levels of resistance).

available in the form of wide plates, as required by industrial uses.

An aluminum alloy commonly used in single-layer armor elements (plates) is 7039, as it represents a good compromise between resistance to detonation and resistance to the formation of splinters. This alloy (typically made up of:

4.0% Zn; 2.8% Mg; 0.20% Cr; 0.25% Mn; remainder 100% Al+impurities) does not appear to be completely satisfactory in relation to its low ballistic resistance to conventional and armour-piercing projectiles hitting the plate at angles of approximately 35 to 55° with respect to a perpendicular line.

for IT 80 armor at the same weight per unit of surface area. Furthermore, for high thicknesses, the 7039 alloy plates show a tendency to give rise to the formation of spalls. Similar considerations can be made for the 7020 alloy (4.5% ZrI; 1.5% Mg; Or; Mn; Zr) and for other known alloys. M.C. FETZER et al. (US Patent 3,649,227) describe two-layer composite plates, in which the "front" layer, featuring high penetration resistance properties, is made of a alloy consisting of: 4.0-7.0% Zn; 1.5-5.0% Mg; up to 3% Cu-100% Al+impurities, while the "back" layer, resistant to the formation of splinters (as it is more tenacious), is made up of a layer consisting of:

4.0-6.0% Zn; 0.5-3.5% Mg; up to 3% Cu: remainder at 10% Al+impurities. The front and back layers have a tensile strength of 446-618 N/mm2 and 309-480 N/mm2 (Newton per mm) respectively, and in any case the back layer has a tensile strength lower than that of the front layer by at least 15 N/mm. The support of the back layer also represents 4-20% of the total support of the double-layer plate. This plate, DL? having a ballistic behavior superior to that of single-layer plates in alloy 7039 (or other known alloys), however suffers from limitations and welding drawbacks (brittleness of the welded joint and/or susceptibility to stress corrosion cracking).

The aim of the present invention is therefore to provide a composite element in the form of a multi-layered plate made of aluminium alloys for use as a component of fixed or mobile armour, said plate being equipped with high resistance characteristics both to the penetration of conventional and armour-piercing projectiles as well as hard bodies in general, and to the formation of splinters, and being such that it can be effectively assembled to other similar plates by means of welded joints, without any problems.

Another aim of the invention is to provide the composite element mentioned above which has improved characteristics of resistance to stress corrosion cracking and fatigue compared to the prior art. The above-mentioned aims and others which may become apparent to a person skilled in the art from the following description are achieved by a composite element in the form of a plate made of aluminium alloys treated with an "artificial solubilisation-tempering-aging" process. This plate, according to the present invention, comprises:

- a "central" component in leaa consisting of 6 - 8% Zn; 2 - 3% Mo; Cu; 0.25-1% of addition elements selected from Mn, Cr, Zr, Ti: the remainder at 100% being impurities, said central component possessing high mechanical resistance and hardness, having a tensile strength between 540 and 750 N/mm;

- a "frontkle" component and a "rearkle" component in an alloy consisting of 4-6% Zn;

Mg; 0-0.15% Cu; 0.25-1% addition elements selected from Mn, Cr, Zr, Ti; the remainder being 100% pure Al, said two front and rear components possessing good toughness and weldability characteristics and having a tensile strength of between 290 and 550 N/mm, said two front and rear components being in mutual contact with said central component in an overlapping position and welded together at their respective interfaces, said central component representing 25-70% of the total thickness of the composite plate element, such total thickness being between 10 and 100 mm, and said front and rear components each having a thickness of between 15 and 32.5% of said total thickness.

The content of impurities represented by Fe and Si in the above-mentioned alloys is, according to the invention, lower than 0.30% and 0.25% respectively, preferably lower than 0.15% and 0.10% respectively, with said chemical elements having a negative effect on fracture toughness.

All quantities of chemical elements which enter into the alloys indicated in this description and in the related claims are expressed in % by weight, and the names of the alloys themselves are according to the designations of the Aluminum Association-USA {Unless otherwise specified).

In the continuation of the description which follows, further detailed information of the present invention, with reference to the single unit, is given in the drawing plate where figure 1 shows, in skeptical view, two composite plates, according to the invention, assembled together similarly by welding.

A preferred, but not exclusive, embodiment of the invention is one which provides the central layer (1 in figure 1) in 7010 type alloy (approximately 6.2% Zn; approximately 2.3% Ma; approximately 8% Cu; approximately 0.35% of addition elements selected from Mn, Cr, Zr, Ti; remainder 100% Al+ impurities) and two other layers, respectively the front (2, figure 1) and the rear (3, figure 1), both in an alloy which, according to the invention, is herein referred to as Cp41-S, has the following composition: approximately 5.0% Zn; approximately 2.0% Ma; approximately 0.13% Cu; approximately 0.5% of addition elements selected from Mn, Cr, Zr, Ti; remainder 100% Al+ impurities. This alloy has (in the T6 state) a tensile strength (Rm) of approximately 517 N/mm, while the aforementioned 7010 alloy (if in the T6 state) has Rm equal to approximately 634 N/mm. Naturally, the invention can be realized using, respectively, for the front layer and Der, the rear layer, two alloys that are equal to each other or different from each other, but always falling, in terms of composition, within the limits indicated above.

Fundamental requirement in choosing De leahe

whether (based on the knowledge known to a person skilled in the art) they respond effectively to the same heat treatment (discussed further below) in relation to the fact that said treatment is to be applied to the composite plate. The (face-to-face) joint between the three components 1, 2, and 3 (Figure 1) constituting the plate is created with known processes, such as hot rolling or welding.

(usually after preheating to 300-480°C in a normal or inert atmosphere), the joining can be carried out by direct contact between the three components or, preferably, by pre-plating (according to the known lamination plating techniques) the three said components in correspondence with one or both of the respective contact surfaces of the components themselves in the composite plate, using for said plating aluminium laminates (99.0-99.99% title) or aluminium alloys usually used in the plating of light alloys.

The thickness of the layer of said plating on each of the plated surfaces is of the order of 25-3% of the thickness of the relevant composite surface, while the total thickness of the said plating layers does not usually exceed 5% of the total thickness of the composite plate.

The total thickness reduction in the above hot rolling operation shall be not less than 40%, preferably greater than RO?.

The heat treatment to which the composite plates of the present invention are subjected is carried out with known processes and consists of a complete cycle of "solubilization-tempering-artificial aging". More specifically, for this heat treatment, the solubilization temperatures are between 350 and 530°C with a duration of residence at steady state ranging from 30 minutes to 5 hours; the artificial aging is carried out in a single stage (isothermal) at 120-180°C for times varying from 4 to 48 hours, or in two successive stages (di-isothermal), the first of which is at 90-120°C for 6-15 hours and the second at 90-120°C for 6-15 hours. According to the present invention, the penetration of projectiles from heavy weapons is resistant.

caliber - or fragments of explosive projectiles and a resistance to the formation of splinters superior (at a rate of weight per unit of surface, substantially at the same thickness) to those of homogeneous metal plates currently industrially produced made of Al-Zn-Mq leds, in particular 7020 and 7039, widely used in the construction of armor.

The above-mentioned superior ballistic properties result from the specific geometric-mechanical structure and the chemical-structural characteristics of the plates which are the object of the present invention, in particular the "front component" performing a pre-absorption action of the energy of the projectile, this action facilitating the function of the "central component", which is to prevent or in any case hinder the penetration of the projectile itself, and the "rear component" specifically performing the function of avoiding the formation of splinters.

The compositions and structure of the composite plates of the invention also allow for the easy creation of mechanically and ballistically highly resistant plate-to-plate joints.

said plates, assembled in armored systems and

resistance to fatigue and stress corrosion cracking. Particularly important for the applications of the composite plates mentioned in this invention are their good weldability characteristics, substantially linked to the chemical composition of the alloys constituting the front component and the rear component respectively, and to the functional geometry of the welded joint.

ra 1, in which the two welding beads 4 a are made using an electric arc process with inert gas current.

To better highlight the advantages of the present invention, examples of some embodiments of plates according to the invention are described below, compared with both single-layer and double-layer plates of the known type, with reference to what has already been said and specified above. These embodiments are given by way of example and are not intended to limit the invention.

EXAMPLE 1.

In this example, single-layer plates of a known type and three-layer composite plates according to the invention are described and compared, first providing technical data and information relating to said plates and then data and results of ballistic tests carried out on the plates themselves.

Single-layer plates of three known types (numbered 1 to 3) and composite plates according to the present invention of different types (numbered FS to 6) are produced.

The three single-layer plates (made respectively of alloys 5083, 7020, and Cp 41-S (7017), currently the most widely used for armor plating on armored vehicles) are produced using known methods and, except for alloy 5083 (produced in the well-known typical state H 115, being a work-hardening alloy), are subjected to the same solution annealing, tempering, and aging treatment as the composite plates described below, which ensures that all of the plates have optimal mechanical strength and hardness characteristics. The three-layer composite plates numbered 5 and 6 are obtained by creating the joint

After the above-mentioned joining operation, the resulting three-layer composite plates, together with the single-layer plates of types No. 2 and No. 3, are subjected to a known heat treatment (TS) comprising a solubilization phase at a temperature of 460-470°C for approximately 2 hours, a water heating phase at room temperature, and finally an artificial diisote aging phase.

first stage at 100-105?C for approximately 9 hours and second stage at 130-135?C for approximately 24 hours, this last stage ensuring that all the alloys making up the said plates reach the optimum values of the aforementioned single-layer and composite tristra plates.

plates with a total thickness of 20 mm (this angle represents the value of the inclination angle of the projectile's trajectory - with respect to the line normal to the plane of the plate hit by the projectile - for values greater than which the perforation of the plate itself no longer occurs);

- the "thickness of the plate's narrow perforation for a fixed angle of attack equal to the projectile's trajectory normal to the plate; this thickness is determined using plates with a total thickness between 20 and 30 mm in the tests;

? the weight per unit of surface expressed in N/m2 of plate corresponding to the said "thickness of the perforation";

- the "tendency to form splinters" on the surface opposite to the impact surface of the projectile, i.e. the tendency of the material to cause its fragments to detach from the surface behind it.

These characteristics are reported in Table 2, from which it is evident that the three-layer composite plates - according to the present invention - have a better ballistic behaviour (evaluated on the basis of the resistance to penetration of the projectile and the tendency to form splinters) than the single-layer plates of known type; this better ballistic behaviour is particularly evident for the

By means of mechanical and thermal processes similar to those adopted for the aforementioned three-layer composite plates) with total thicknesses between 20 and 30 mm; the plate itself has the rear component

plating layers of total thickness) equal to approx. The chemical compositions and mechanical characteristics of the alloys constituting the two front and rear components of the said double-layer composite plate (subjected to a T6 heat treatment similar to that adopted for the three-layer composite plates!) are reported in Table 1.

In accordance with what is indicated in the above-mentioned patent, the type of alloy used for the front component was chosen with the criterion of ensuring the maximum mechanical resistance characteristics for said component combined with the possibility of welding the component itself, while the type of alloy constituting the rear component was chosen with the criterion of ensuring, in addition to good weldability characteristics, high toughness characteristics.

The said double-layer composite plate was subjected to the same ballistic tests as in example 1, and the related results are reported in Table 2, from which the improved ballistic behaviour of the three-layer composite plates according to the present invention can be seen.

It should be noted that the double-layer composite plate N? 4, in comparison with the single-layer plate N? 3 in CD 41-S-T6 lead, offers, for the reasons above,

As illustrated, difficulties in industrial application arise due to the high susceptibility to stress corrosion cracking of the front component, especially in the welded joint areas, which can only be avoided by adopting very advanced artificial ageing processes, which also degrade the ballistic resistance of the assembled plate itself.

Example 3

On single-layer plates of known type, no. 1, 2 and 3 and three-layer no. 6 according to the present invention, already described in Example 1, ballistic tests were conducted according to the German specification TL 2350-004 Ed. 1-76 which provides for the following shooting conditions: - light automatic rifle (F.A.L.) FN cal. 7.62 NATO mounted on a rigid support

- FNP 80 (NATO) cartridge equipped with a 9.75 q "armour piercing" bullet with a 3.6 o steel core

- projectile velocity: 816 15 m/s measured at 5 m from the muzzle

- shooting distance; 30 m

In these tests (as in Example 1) the angle of attack for narrow drilling on plates of total thickness 32 mm was determined, obtaining the values listed in Table 3.

From the data reported, it can be deduced that the three-layer plate of the present invention offers a clear superiority in terms of resistance to the kinetic impact of the projectile compared to conventional materials.

Example 4.

Ballistic tests were conducted on plates of variable thickness of known types, Nos. 1, 2 and 3 and trilayer No. 6 according to the present invention, according to the procedures indicated in Example 3, to determine the advantages achievable in weight reduction per unit of surface area with the same ballistic performance, from the use of the trilayer plate compared to known materials.

This characteristic is expressed by the ratio (RM = merit ratio) between the weight per unit of surface area of the single-layer plates and the weight per unit of surface area of the three-layer plate n? 6, at a given ballistic behaviour. The results obtained relate to an angle of attack

1. Composite element in the form of a con-

made from aluminium alloys treated with "solution-tempering" procedures instead of artificial hardening, characterised by the fact that it includes

- a "central" component _ (1) in an alloy consisting of 6-8% Zn: 2-3% Ma; 1-2.3% Cu; 0.25-1% of addition elements selected from Mn. Cr. Zr. Ti;

the rest is 100% Al+impurities, the central component having very high mechanical resistance, having a tensile strength between 540 and 750 N/mm;

- a "front" component (2) and a "rear" component (3) in an alloy consisting of 4-6% Zn;i-2 5% Ma;0-0.15% Cu; 0.25-1% of addition elements selected from Mn. Cr. Zr. Ti: the remainder being 100% Al+irr, said two front and rear components having good characteristics of both toughness and weldability and having a tensile strength between 290 and 550 N/mm, said two front and rear components being mutually in contact with said central component in an overlapping position and welded together at their respective interfaces, said central component representing 35-70% of the total thickness of the composite plate element, such total thickness being between 10 and 100 mm, and said front and rear components each having a thickness between 15 and 32.5% of said total thickness.

I give claim 1, characterized in that: said central component is made of an alloy

Claims (1)

that the two front and rear layers are both made of an alloy consisting of approximately 5.0% Zn; approximately 2.0% Mg; approximately 0.13% Cu; approximately 0.50% of addition elements selected from Mn, Cr, Zr, Ti; the remainder 100% Al+impurities. 3. Composite element in the form of a plate according to one of the preceding claims, characterised in that the impurities in Fe and Si contained in said alloys