EP2796827B1 - Composite panel for vehicle armour - Google Patents

Description

The invention relates to the production of shielding panels for protecting vehicles vis-à-vis the piercing projectiles and fragments projected during an impact.

Generally, a shield comprises a metal panel, typically made of steel, aluminum, titanium or their alloys. Such panels generally have excellent kinetic energy absorption capacity of the piercing projectile during an impact. However, particularly if they are made of steel or titanium alloy, such panels are heavy and therefore have a low efficiency in terms of energy absorption when it is related to the weight carried by a vehicle. Titanium alloy panels usually give the best shielding protection but they are very expensive and heavy.

The shield panel has a shock-exposed face and a back face. During an impact on a metal armor panel, the piercing projectile can be perfectly stopped in the panel but the damage to the panel on its rear face can result in the formation of fragments which, when violently ejected from the panel (towards the inside of the vehicle) can become more dangerous than the projectile stopped by the panel.

Composite panels have been developed which have greater projectile arresting capability and less susceptibility to fragmentation, thus providing better performance relative to the weight carried by the vehicle. However, these are composite products comprising ceramic products placed on the shock-exposed face of a support plate, itself composite, generally based on carbon, glass and high molecular weight polymers. Such products are very expensive.

To characterize their effectiveness, the shielding panels are generally subjected to two types of tests. The first test is intended to quantify their ability to stop piercing projectiles. It is designated by the acronym "AP"("ArmorPiercing") and characterizes the resistance to perforation. The second test is intended to quantify their ability to withstand the impacts of fragmented debris. This second type of test is designated by the initials "FSP"("Fragment simulated projectiles"). During these tests, the shielding panels are the target of projectiles of different shapes (spindle shape for the AP test, larger projectile, more compact shape for the FSP tests). In each type of test, several projectile geometries are used depending on the thickness of the panel tested and the nature of the threats that said shielding panel is intended to protect.

For both tests, the ability to stop the projectiles, to absorb their kinetic energy without emitting dangerous debris, is quantified by a speed V50, which is defined for example in the MIL-STD-662 standard: it is a question of the average of the velocities achieved by the projectiles during the impact obtained by taking an equal number of results having the highest partial penetration speeds and results with the lowest complete penetration rates, the velocity being imposed within a specified domain.

In general, the material constituting the shielding panel, whether it is a ceramic, a steel, an aluminum alloy or titanium, rarely presents a good compromise AP-FSP. When it shows good performance in the resistance to perforation, it is often average FSP resistance. Conversely, a material with good performance at the FSP resistance is often found to be average in AP resistance.

The patent application US2011 / 0252956 discloses metal shielding panels consisting of at least two layers of different aluminum alloys which are metallurgically bonded together. The intimate metallurgical bond between these two layers typically results from transformation ranges such as co-rolling, multi-layer casting, or casting to obtain in the thickness of the plate a controlled concentration gradient of one layer. element such as magnesium. The alloys are selected and located in the thickness of the plate so that one gives the assembly good puncture resistance and the other good FSP resistance. The production of such panels, however, requires the implementation of complex and expensive processes.

The patent application US 2001/053645 A1 , which forms a starting point for claim 1, thus describes a composite shielding panel.

The applicant has sought to develop a shielding system particularly suitable for fast vehicles such as military vehicles, typically equipped with wheels, which has a better efficiency in terms of protection AP and FSP, compared to the weight carried, which is easier to achieve and less expensive than known products.

1. a) ledit alliage d'aluminium a la composition chimique suivante, exprimée en pourcentages pondéraux: $$\mathrm{7,5}\%\le \mathrm{Zn}\le \mathrm{9,7}\%$$
   
   $$\mathrm{1,5}\%\le \mathrm{Mg}\le \mathrm{2,9}\%$$
   
   $$\mathrm{1,2}\%\le \mathrm{Cu}\le \mathrm{2,1}\%$$
   
   $$\mathrm{Si}\le \mathrm{0,4}\%$$
   
   $$\mathrm{Fe}\le \mathrm{0,5}\%$$
   
   $$\mathrm{Mn}\le \mathrm{0,3}\%$$
   
   $$\mathrm{Cr}\le \mathrm{0,28}\%$$
   
   $$\mathrm{Ti}\le \mathrm{0,2}\%$$
   
   $$\mathrm{Zr}\le \mathrm{0,15}\mathrm{}\%$$
   
   reste aluminium et impuretés inévitables, chaque élément ayant un teneur pondérale inférieure à 0,05 %, la somme étant inférieure à 0,15 %;
2. b) la dite plaque comprend une face orientée face aux projectiles et une face qui est opposée à ladite face orientée face aux projectiles et qui est revêtue d'une couche de renfort composite comprenant des fibres ou des bandes de renfort présentant une haute performance mécanique qui leur confère une capacité de protection balistique élevée. De telles fibres ou bandes de renfort à capacité de protection balistique élevée peuvent être en un ou plusieurs matériaux appartenant au groupe regroupant:
   • les verres à haute performance mécanique, tels que les verres R, H, S ou , de préférence, S2;
   • les aramides, de préférence les para-aramides tels que le Kevlar ® ;
   • les polyéthylènes à haute performance (HPPE) ou les polyéthylènes à ultra-haut poids moléculaire (UHMWPE ou UHMW), qui sont des polyéthylènes fortement orientés se présentant sous forme de fibres, de fils ou bandes, par exemple le Tensylon®.

A first object of the invention is a shielding panel comprising an aluminum alloy plate and characterized in that:

1. a) said aluminum alloy has the following chemical composition, expressed in percentages by weight: $$7.5\%\le \mathrm{Zn}\le 9.7\%$$
   
   $$1.5\%\le \mathrm{mg}\le 2.9\%$$
   
   $$1.2\%\le \mathrm{Cu}\le 2.1\%$$
   
   $$\mathrm{Yes}\le 0.4\%$$
   
   $$\mathrm{Fe}\le 0.5\%$$
   
   $$\mathrm{mn}\le 0.3\%$$
   
   $$\mathrm{Cr}\le 0.28\%$$
   
   $$\mathrm{Ti}\le 0.2\%$$
   
   $$\mathrm{Zr}\le 0.15\mathrm{}\%$$
   
   remains aluminum and unavoidable impurities, each element having a weight content of less than 0.05%, the sum being less than 0.15%;
2. b) said plate comprises a face facing the projectiles and a face which is opposed to said face facing the projectiles and which is coated with a composite reinforcing layer comprising fibers or reinforcing strips having a high mechanical performance which gives them a high ballistic protection capability. Such reinforcing fibers or bands with high ballistic protection capacity may be in one or more materials belonging to the group comprising:
   • high performance mechanical glasses, such as R, H, S or, preferably, S2;
   • aramids, preferably para-aramids such as Kevlar®;
   • high performance polyethylenes (HPPE) or ultra high molecular weight polyethylenes (UHMWPE or UHMW), which are highly oriented polyethylenes in the form of fibers, yarns or strips, for example Tensylon®.

Advantageously, said composite reinforcing layer comprises one or, preferably, several unidirectional webs or woven from yarns comprising fibers with high ballistic protection capacity.

The yarns or strips are preferably impregnated with a thermoplastic or thermoset resin, typically a PVB modified phenolic resin (polyvinyl butiral). The canvases can be made by weaving in several frames (unidirectional, braided, plain weave, etc ...). The composite reinforcing layer is obtained for example by stacking the webs on each other and compressing them hot.

By plate means a flat product, typically a sheet ("sheet") or a thick plate ("flat"), with a thickness greater than 5 mm, preferably greater than 20 mm, typically close to 20-30 mm. The width / thickness ratio of the plate is preferably but not necessarily greater than 10. The composite panel has a thickness typically of less than 50 mm, preferably less than 40 mm and has a surface density of less than 125 kg / m ² , preferably less than 110 kg / m ² , more preferably less than 100 kg / m ² . The interest of such shielding panels is to provide the best possible AP and FSP protection with the lowest possible surface density. Thus, a composite panel according to the invention which has a surface density of less than 90 kg / m ² , or even less than 85 kg / m ² , can be expected to reach the level of protection defined in STANAG 4569 (V50 FSP = 960 m / s with 20 mm projectile fired at 25 m).

The aluminum alloy plate includes a projectile-facing face, which can be directly impacted or otherwise protected, for example by ceramic tiles. It comprises a face opposite to said face facing the projectiles which is covered by a composite reinforcing layer without necessarily having a continuous connection over the entire contact surface, for example with the aid of an adhesive binder. For example, it suffices for the composite reinforcing layer to be secured to the plate at the periphery thereof by gluing or any other fixing means, typically mechanical.

We performed AP and FSP tests on aluminum alloy plates coated or not with a composite reinforcement layer comprising aramid fibers. AP perforation tests use 7.62mm and 35.6mm long projectiles, referred to as "0.30 cal AP M2", which have a steel core, an intermediate lead layer and a copper ogival envelope. . For the panels according to the invention and the panels having For comparative tests, FSP tests use 23 mm long steel projectiles, the cylindrical part of which has a diameter of 20 mm, called "20 mm FSP".

Firstly, we found that in the target density range (50 to 125 kg / m2), with the panel structures tested (19 to 46 mm thick plates, panels between 30 and 50 mm, weight ratio composite reinforcing layer / total panel weight less than 25%), the results of the perforation tests depended essentially on the alloy of the plate and the average density of the composite panel: a panel made of a given alloy uncoated gives a result (expressed by the speed V50) almost identical to that of a panel made of the same alloy but thinner and coated with a composite reinforcement layer whose thickness is such that the assembly has the same density surface. There has even been a slight degradation of the AP properties when weight ratio composite reinforcement layer / total weight of the lower panel is of the order of 22%. Thus, on the sole criterion of resistance to perforation, an uncoated plate has a significant economic advantage and a smaller footprint for the same or even greater performance. Among the tested materials, the aluminum alloys of the 7xxx series gave, at comparable surface density, better results than the 5xxx and 6xxx series alloys as well as the steels.

The results of the FSP tests led to a different and surprising finding. The Applicant has indeed found that if the plates are covered with a composite reinforcing layer comprising fibers or reinforcing strips with high ballistic protection capacity, for example aramid fibers, whose surface density is greater than 0, 5 kg / m ² , preferably 1 kg / m ² , more preferably 2 kg / m ² , the gain, in terms of increasing the V 50 as a function of the increase in the surface density of the shielding panel, is significantly superior for aluminum alloys and in particular for alloys of the 7xxx series.

• 7,5 % ≤ Zn ≤ 9,7 %, de préférence 7,5 % ≤ Zn ≤ 8,7 %,
• 1,5 % ≤ Mg ≤ 2,9 %, de préférence 1,8 % ≤ Mg ≤ 2,7 %,
• 1,2 % ≤ Cu ≤ 2,1 % , de préférence 1,4 % ≤ Cu ≤ 2,1 %
• Si ≤ 0,4 %, de préférence Si ≤ 0,12 %
• Fe ≤ 0,5 %, de préférence Fe ≤ 0,15 %
• Mn ≤ 0,3 %, de préférence Mn ≤ 0,2 %
• Cr ≤ 0,28 %, de préférence Cr ≤ 0,05%
• Ti ≤ 0,2 %, de préférence Ti ≤ 0,05 %
• Zr ≤ 0,15 %, de préférence Zr ≤ 0,05 %
• autres éléments ≤ 0,05 % individuellement et ≤ 0,15 % au total.

The best AP-FSP compromise is achieved, however, with alloys from the 7xxx series that have a high enough zinc and copper content. Thus, the 7039 and 7020, if they present, in combination with a layer of composite reinforcement of aramid fibers, significantly improved FSP performance, remain poor performance in the perforation tests AP. Thus, the alloy of the plate according to the invention has the following composition, where the contents are expressed in weight percentages:

• 7.5% ≤ Zn ≤ 9.7%, preferably 7.5% ≤ Zn ≤ 8.7%,
• 1.5% ≤ Mg ≤ 2.9%, preferably 1.8% ≤ Mg ≤ 2.7%,
• 1.2% ≤ Cu ≤ 2.1%, preferably 1.4% ≤ Cu ≤ 2.1%
• If ≤ 0.4%, preferably Si ≤ 0.12%
• Fe ≤ 0.5%, preferably Fe ≤ 0.15%
• Mn ≤ 0.3%, preferably Mn ≤ 0.2%
• Cr ≤ 0.28%, preferably Cr ≤ 0.05%
• Ti ≤ 0.2%, preferably Ti ≤ 0.05%
• Zr ≤ 0.15%, preferably Zr ≤ 0.05%
• other elements ≤ 0.05% individually and ≤ 0.15% in total.

Preferably, these alloys are processed to obtain a state having not only high instantaneous mechanical characteristics (resistance R _m , conventional yield strength R _p0,2 , elongation at break A%) but also good toughness. Advantageously, a solution, quenching and tempering treatment will be carried out making it possible to obtain conditions such that T6 (maximum R _m ), T64 (tempered state slightly under-tempered) or, preferably, T651 (quenched stress relieved by moderate traction controlled and income) or alternatively T7651 (hardened stress relieved by controlled moderate traction and over-tempering).

The surface density of the composite reinforcing layer is in practice between 2 and 25 kg / m ² . It is preferably less than 20 kg / m ² , more preferably less than 15 kg / m ² mainly because of the cost.

The effect of this composite reinforcing layer on the improvement of the FSP properties is all the more accentuated that the surface density of the composite reinforcing layer is high, but this is remarkable with the aluminum alloy plates, in particular those consisting of the alloy according to the invention is that this effect is strongly manifest even if the composite reinforcing layer is thin, with a surface density of the order of 1 kg / m ² , it is that is, typically as soon as the panel is coated with three or four aramid woven canvases.

When the surface density is less than 90 kg / m ² , aluminum alloys such as 7xxx have lower FSP performance than shielding steel, such as HHS ("high hardness steel"). However, when these alloys are combined with a composite reinforcing layer comprising aramid fibers, the FSP results rapidly exceed those of the steel, even if it is also covered with the same type of composite reinforcement layer, with comparable surface density. . For example, to obtain on a steel plate the same improvement in FSP performance that is observed on 7xxx plates with a composite reinforcement layer with a surface density of only 2 kg / m ² , it is necessary, other things being equal. associating with said steel plate a composite reinforcing layer between 4 and 6 times thicker.

The effect of the composite reinforcing layer on the improvement of the FSP properties is particularly remarkable when the plate is 7449 T651.

Among the various composite reinforcement layers tested, that consisting of a stack of fabrics woven from Kevlar® 129 yarn gave good results, regardless of the type of weaving made. The Kevlar ® 129 grade is known for its lightness and high mechanical performance, especially its high toughness.

These are the 7449 T651 sheets covered with layers of fabrics woven from Kevlar ® 129 yarns that have the best AP and FSP performance. This alloy makes it possible to obtain, for the FSP test, a V50 greater than 950 m / s with a shielding panel whose overall surface density is less than 95 kg / m ² , or even less than 90 kg / m ² .

The figure 1 represents the results of AP tests carried out on shielding panels consisting of metal plates coated or not with a composite reinforcing layer comprising aramid fibers.

The figure 2 represents the results of FSP tests carried out on shielding panels consisting of 7xxx series aluminum alloy plates and steel, coated or not with a composite reinforcing layer comprising aramid fibers.

The figure 3 represents, for several materials, the improvement of the properties FSP, in terms of relative variation of V50, as a function of the relative increase of surface density.

The figure 4 represents, for several materials, the improvement of the properties FSP, in terms of increase of V50 as a function of the surface density increase due to the composite reinforcing layer.

EXAMPLE

Shield plates were made from thick plates of different alloys. They have been machined to different thicknesses between 25 and 40 mm. Table 1 groups together the main constituents of their chemical compositions. Table 1 Alloy Type Yes Fe Cu mg Zn AT 7449 0.05 0.07 1.9 2.1 8.5 B 6061 0.62 0.4 0.26 1.0 0.00 VS 7020 0.13 0.12 0.13 1.22 4.69 D 0.05 0.07 1.7 2.0 9.4

Table 2 summarizes the state, the thickness and the average mechanical characteristics of these plates (traction, long transverse direction) Table 2 Alloy State Thickness Rp0.2 (MPa) Rm (MPa) AT% AT T651 30 583 651 11 B T6 30 295 330 12 VS T651 30 360 420 12 D MS 472 ° C-quenching -6h120 ° C + 7h135 ° C 25 694 707 11.5

Some plates have been coated with a composite reinforcement layer, comprising a stack of a greater or lesser number of Kevlar® 129 fiber-based yarns with a linear density of 1330 dtex, coated with polyvinyl resin butiral (PVB), each fabric having a surface density of 275 g / m ² approximately. Composite reinforcement layers of different thicknesses were produced by stacking a greater or lesser number of webs and then hot pressing the stack thus produced in a press.

Ballistic perforation tests ("AP tests")

Table 3 groups the results of the "0.30 cal AP M2" tests carried out on thick plates coated or not with a composite reinforcing layer. When it exists, it has been placed on the opposite side to the projectile. The surface density of the stack of Kevlar® yarn woven fabrics 129 is given in the fourth column of Table 3 below.

The figure 1 illustrates the different results obtained and situates them in relation to the known results on other materials (5083 H131 (MIL-DTL-46027), RHA Steel (MIL-A-12560), 7039 T64 (MIL-DTL-46063), 6061 T651 (MIL-DTL-32262)

It can be seen that for surface densities typically less than 100 kg / m ² , the alloys 5083 and 6061 are less efficient than steels such as RHA Steel, which is less efficient than the 7449. The sheets in 7039 exhibit AP performance. relative to the surface density barely higher than those of steel and significantly lower than those in 7449. The known AP tests on alloy 7020 were carried out with a different projectile and the results are not directly comparable. However, they show that the 7020's AP performance is no better, rather lower than that of 7039.

Once coated with woven Kevlar® yarn 129, thick plates in 7449 have, at equal density area, a similar behavior, or even slightly less effective, than thick uncoated sheets. Table 3 Ech Alloy thickness (mm) Stacking woven layers from Kevlar® yarn 129 Density per unit area (kg / m ² ) Glue Density area (kg / m2) V50 (m / s) 1-1 7449 T651 30 0 0 85.5 805 1-2 7449 T651 30 0 0 85.5 815 1-3 7449 T651 30 16.7 1 102 862 1-4 7449 T651 30 10.7 1 96 844 1-5 7449 T651 30 10.7 0 96 845 1-6 7449 T651 30 22.9 0 108 876 1-7 7449 T651 39.3 0 0 112 948 1-8 7449 T651 39.9 0 0 114 944 1-9 7449 T651 39.9 0 0 114 936 1-10 7449 T651 39.9 0 0 114 877 1-11 7449 T651 25.5 0 0 73 724 1-12 7449 T651 19 0 0 55 612 1-13 6061 T6 30 0 0 81 641 1-14 6061 T6 30 16.7 1 98 702 1-15 6061 T6 30 22.9 1 104 767

FSP tests

Table 4 groups together the results of the "20 mm FSP" tests carried out on thick plates coated or not with a composite reinforcing layer. When it exists, it has been placed on the opposite side to that intended to receive the impact of the projectile.

The figure 2 illustrates the different results obtained on the 7020, the 7449 and a high-hardness steel (HHS), with a Brinell hardness between 420 and 480 HB. These results are compared to results obtained on other materials (7039 T64 (MIL-DTL-46063), RHA Steel (MIL-A-12560)). The figure 2 also allows to compare the results between plates, coated or not, in 7xxx and plates, coated or not, steel.

The figure 2 shows that uncoated steel plates are more efficient for FSP tests than aluminum alloy plates as long as the surface density remains below about 100 kg / m ² . Table 4 Ech Alloy thickness (mm) Composite reinforcement layer Surface density (kg / m2) Glue Surface density V50 (m / s) 2-1 7449 T651 30 0 0 85.5 534 2-2 7449 T651 39.3 0 0 112 827 2-3 7449 T651 39.9 0 0 114 842 2-4 7449 T651 39.9 0 0 114 884 2-5 7449 T651 39.9 0 0 114 877 2-6 7449 T651 30 3.9 1 89.4 837 2-7 7449 T651 30 7.7 1 93.2 942 2-8 7449 T651 30.8 10.7 1 98.5 1102 2-9 7020 T651 28.5 0 0 79.1 534 2-10 7020 T651 30.75 0 0 85.3 600 2-11 7020 T651 30.75 3.9 1 89.2 834 2-12 HHS 10 10.7 1 89.3 812 2-13 HHS 10 0 0 78.6 585

The experimental points obtained with the uncoated 7449 T651 show a trend curve substantially parallel to that of the 7039 T64, but with slightly lower FSP performance. The experimental points obtained with the 7020 T651 are also placed on a trend curve substantially parallel to that of the 7039 T64 but with slightly higher FSP performance. The experimental point of the uncoated HHS steel plate is slightly below the trend curve of "RHA Steel" steel.

The points relating to 7449 T651 plates coated with a composite reinforcing layer comprising aramid fibers are located significantly above the curve which groups together the FSP results of the uncoated plates. The difference, significant even with a thin layer, is even more important than the composite reinforcing layer is thick. Thus, the combination of a 7449 T651 plate and a composite reinforcing layer comprising Kevlar® 129 fibers having a surface density of 10.7 kg / m 2 makes it possible to reach a V50 greater than 1100 m / s.

The results for the coated 7020 T651 plate also show a significant influence of the composite backing layer. This, however, appears to be weaker than that observed on the plates in 7449. Furthermore, the known AP results on the alloy 7020 lead to the belief that copper-poor alloys such as 7020 and 7039, even associated with a composite reinforcing layer comprising aramid fibers, do not allow to obtain a good compromise AP-FSP.

The FSP results relating to the coated steel plate also show an influence of the composite reinforcing layer, but this is much less important.

Table 5 shows the FSP results obtained on the plates of coated aluminum alloys and gives the gains obtained compared with the uncoated plates. For each composite panel, the results obtained on the uncoated plate A made of the same material as the core of the composite panel and having the same thickness as the latter and 7 ^th column estimated values were labeled in the ^6th column for an uncoated plate B made of the same material as the core of the composite panel and having the same surface density as the composite panel. It is found that the gain due to the presence of the composite reinforcing layer, expressed in terms of increase of V50, is multiplied by a coefficient of between 4.8 and 7.8 for aluminum alloys. For the same thickness of the composite reinforcing layer, this coefficient is of the order of 6.6 for the aluminum alloy and only 4.5 for the steel.

The figure 3 shows these same results in the form of the relative increase of V50 as a function of the relative increase in surface density. The thick curves are associated with 7449. Curve (I), which is substantially straight and has a slight slope, represents the effect of increasing the thickness of uncoated plates on the relative increase of V50. Curve (II) represents the effect of increasing the thickness of the composite reinforcement layer in the composite panels on the relative increase of V50. Table 5 Ech soul (mm) surf density. panel (kg / m ² ) V50 (m / s) surf density. soul (kg / m ² ) V50 A (m / s) V50 B (m / s) Gain V50 B - A (m / s) Gain V50 composite - A (m / s) Coefficient 2-6 30 89.4 837 85.5 534 577 43 303 7.0 2-7 30 93.2 942 85.5 534 620 86 408 4.8 2-8 30.8 98.5 1102 87.8 603 679 76 499 6.6 2-11 30.8 89.2 834 85.3 600 641 41 234 5.7 2-13 10 89.3 812 78.6 585 635 50 227 4.5

For example, in figure 3 that a relative increase of 10% of the density of the armor board in 7449 T651, leads to a relative increase in FSP performance of about 20% if we just increase the thickness of the panel and the order of 80% if it is associated with a composite reinforcement layer comprising aramid fibers. The FSP performance of composite panels having a 7020 core are also notable. When the core of the panel is steel, the performance is more modest (dotted line).

The figure 4 shows the gain in V50 as a function of the increase in surface density. The effect of the composite reinforcing layer on the improvement of the FSP properties is strongly manifest even if the composite reinforcing layer is thin, as soon as the surface density of said composite reinforcing layer is greater than a value of the order of magnitude. 1 kg / m ² , which typically corresponds to the stacking of less than five aramid yarn woven fabrics. We also see that, to obtain on a steel plate the same improvement in FSP performance that is observed on 7xxx plates with a composite reinforcement layer with a surface density of only 2 kg / m ² , it is necessary, all things being equal moreover, associating with said steel plate a composite reinforcing layer between 4 and 6 times thicker.

Finally, the analysis of these results leads to the conclusion that it is possible to obtain a level of protection 5 as defined in STANAG 4569 [V50 greater than 960 m / s for FSP 20 mm tests], with an aluminum alloy composite panel having the composition covered with a composite backing layer comprising aramid fibers having a surface density of less than 95 kg / m ² .

Claims (13)

1. Armor panel comprising an aluminium alloy slab:

   a) said aluminium alloy having the following chemical composition, expressed as a percentage by weight: $$7.5\%\le \mathrm{Zn}\le 9.7\%$$

   

   $$1.5\%\le \mathrm{Mg}\le 2.9\%$$

   

   $$1.2\%\le \mathrm{Cu}\le 2.1\%$$

   

   $$\mathrm{Si}\le 0.4\%$$

   

   $$\mathrm{Fe}\le 0.5\%$$

   

   $$\mathrm{Mn}\le 0.3\%$$

   

   $$\mathrm{Cr}\le 0.28\%$$

   

   $$\mathrm{Ti}\le 0.2\%$$

   

   $$\mathrm{Zr}\le 0.15\mathrm{}\%$$

   

   b) said plate comprises a surface oriented to face projectiles and a surface opposite said face oriented to face projectiles and that is coated with a composite reinforcing layer comprising reinforcing fibres or strips with high mechanical performances that confer a strong ballistic protection on them.
2. Armor panel according to claim 1, characterised in that the reinforcing fibres or strips with a high ballistic protection capacity can be made of one or several materials belonging to the group including:

   - high mechanical performances glass, such as R, H, S glass or preferably S2 glass;

   - aramids, preferably para-aramids;

   - high performance polyethylenes (HPPE) or ultra high molecular weight polyethylenes (UHMWPE or UHMW).
3. Armor panel according to claim 1 or 2, characterised in that said composite reinforcing layer comprises one or several single-directional or woven fabric sheets made from yarn composed of fibres with a high ballistic protection capacity.
4. Armor panel according to claim 3, characterised in that said composite reinforcing layer comprises fabric sheets woven from para-aramid yarn impregnated with resin.
5. Armor panel according to claim 4, in which said resin is a modified PVB (polyvinyl butyral) phenolic resin.
6. Armor panel according to any one of claims 1 to 5, in which the composite reinforcing layer is a stack of hot compressed stacked fabric sheets.
7. Armor panel according to any one of claims 1 to 6, characterised in that its thickness is more than 5 mm and less than 50 mm, and its mass per unit area is less than 125 kg/m².
8. Armor panel according to claim 7, characterised in that its thickness is more than 20 mm and less than 40 mm, and its mass per unit area is less than 110 kg/m² and preferably less than 100 kg/m².
9. Armor panel according to any one of claims 1 to 8, characterised in that the mass per unit area of the composite reinforcing layer comprising aramid fibres accounts for less than 25%, and preferably less than 15%, of the total mass per unit area of the panel.
10. Armor panel according to any one of claims 1 to 9, characterised in that the mass per unit area of the composite reinforcing layer comprising aramid fibres is more than 0.5 kg/m², preferably more than 1 kg/m² and even more preferably 2 kg/m².
11. Armor panel according to any one of claims 1 to 10, characterised in that the mass per unit area of the composite reinforcing layer comprising aramid fibres is less than 25 kg/m², preferably less than 20 kg/m² and even more preferably 15 kg/m².
12. Armor panel according to any one of claims 1 to 11, characterised in that said plate is made of a 7449 alloy, preferably in the T651 state.
13. Armor panel according to any one of claims 1 to 12, characterised in that said composite reinforcing layer comprises fabric sheets woven from Kevlar ® 129 yarn coated with phenolic resin - polyvinyl butyral (PVB) .

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