RU2102241C1 - Aluminium-based sandwich plate for armour - Google Patents

Abstract

FIELD: manufacture of laminated products. SUBSTANCE: applicable in constructions subjected to impulse loads of a high intensity (bullet, shell, mine blasting, etc.) so as to enhance the level armour resistance by 6 to 9% as compared with the known sandwich aluminium plates. EFFECT: enhanced level of armour resistance. 5 dwg, 3 tbl

Description

 The invention relates to special mechanical engineering (civil and military) and can be used in other areas of technology that require protection of structures from the effects of concentrated concentrated and distributed loads of high intensity (grenade fragments, mine detonation, bullet, shell, etc.).

 The materials used for these purposes are called armor. As armored aluminum alloys, the welded alloys of the Al-Zn-Mg system are currently widely used, which increases almost linearly with the total content of the main alloying elements (N + Mg) (see Fig. 1, as well as Fig. 72 in the book of Elagin V. I. Doping of wrought aluminum alloys with transition metals. M: Metallurgy, 1975).

 Currently, there is no published information on aluminum armor alloys used in domestic engineering. Of the armor alloys used in foreign products, alloys 7039 (USA), E74S (7017) (England), 7020 (France), and others are known. The maximum content (Zn + mg) of these alloys is 8.8, respectively; 7.8; 6.4% (weight), which provides them with a sufficiently high hardness (HB = 135) (see the journal "Aluminum", 1977, j. 53, H7, p. 241-426).

 A comparative analysis of the chemical composition of domestic alloys 1901, 1903, 1931 shows that these alloys are similar to alloys 7017 and 7039 (see Table 1). Therefore, all of the arguments below regarding the properties of alloys 7017 and 7039 will be valid for domestic alloys if they are used as armor alloys.

 A further increase in the hardness of plates made of alloys of the type 7039, 7017 due to an increase in the total content (Zn + Mg) does not lead to an increase in the level of armor properties due to spallations formed on the back side and splits of the plate due to a decrease in the plastic properties of the alloys (Fig. 2 )

 To ensure an increased level of armor properties, an aluminum composite armor was developed, including a front layer with a hardness of 150 units. according to Brinell (HB = 150) from a welded alloy of the Al-Zn-Mg system with a thickness of 20% of the thickness of the armor (plate); the middle layer with a hardness of 180 units according to Brinell (HB = 180), made of a non-weldable alloy of the Al-Zn-Mg-Cu system, 55% of the thickness of the plate, and a back layer with a hardness of 150 HB, 20% of the thickness of the plate, made of the welded alloy of the Al-Zn system -Mg. Between these layers are thin (2.5% of the thickness of the armor) layers of technically pure aluminum (Fig. 3).

 The developed composite armor has an advantage in the level of armor resistance over armor from homogeneous alloys 7017, 7039, 7020 by 4-20% depending on the test conditions (see the journal "International Defense Review", 188, v. 21, n, 12, p. 1657-1658 (prototype)).

The disadvantages of the considered composite armor include:
1. Use as the front and back layers of the alloy system Al-Zn-Mg with a hardness of HB = 150 units and, therefore, the content of (Zn + Mg) of more than 6.5% (weight) (Fig. 1) reduces their corrosion resistance under the action of mechanical stresses (especially in welded structures) (see V. Elagin V. Zakharov V. V. Drits A.M. Alloy structure of the Al-Zn-Mg system. M: Metallurgy, 1982, p. 9).

The use of a high-strength non-weldable, but corrosion-resistant alloy of the Al-Zn-Mg-Cu system as the middle layer (55% of the armor thickness) leads to:
to complicate the design of welded joints. Static and dynamic stresses arising from the action of internal and external forces are perceived through the outer layers (front and back) made of welded alloys. This leads to an increased level of stresses in them, a decrease in resistance to corrosion damage, and, accordingly, a decrease in the operational reliability of the welded structure.

 to ensure satisfactory strength of the welded joint, layers of materials to be welded should have a relatively large thickness (often thicker than necessary for reasons of ensuring maximum armor resistance of the plate).

 An increase in the thickness of the welded layers (less durable) occurs due to a decrease in the thickness of the middle (more durable) layer, which leads to a decrease in the average strength of the plate and, accordingly, to a decrease in the level of its armor resistance.

 3. To further increase the level of armor resistance of a laminated plate, it is necessary to increase its hardness, which can be achieved by increasing the hardness of the individual layers that make up the plate, in particular the outer ones. However, when testing such plates for bulletproof resistance when approaching a bullet (acute-headed) to the back surface of the plate, even if it does not penetrate, through cracks with a depth of up to 10% of the thickness of the plate are formed (Fig. 5). Such cracks are a defective sign for armor. In this case, an increase in the hardness of the back layer does not lead to an increase in the level of armor resistance of such a layered plate. It should be noted that the initiation of cracks in the back layer occurs from its outer surface.

 4. At a high intensity of pulsed loading, for example, when tested with a blunt-headed projectile, the nature of the destruction of the laminated plate changes compared to the destruction when tested by a bullet. As a result of such loads, the depth of the rear spalls with an insufficient supply of plasticity reaches half the thickness of an aluminum homogeneous plate (Fig. 2). In a laminated plate, the nature of the formation of the back spall due to the presence of a highly plastic intermediate layer varies significantly (Fig. 3). Its main part is “blocked” by a plastic layer.

 However, due to the high intensity of loading with an insufficient supply of plasticity, a spall is formed in the back layer (Fig. 3). The ductility margin of aluminum alloys of the Al-Zn-Mg system decreases with increasing hardness (due to heat treatment). Thus, an increase in the hardness of the back layer can lead to a decrease in the level of armor properties of the layered plate.

 The aim of the invention is to provide high armor and corrosion resistance of a laminated plate of aluminum alloys with minimum weight, as well as ensuring high operational reliability of welded structures made using laminated aluminum plates.

 An increase in the corrosion resistance of a layered aluminum plate is achieved by applying thin layers of technically pure aluminum of a layer and sublayer, respectively, with a thickness of (0.01-0.03) H, where H is the thickness of the armor, on the surface of the front and back layers. Technically pure aluminum has high corrosion resistance and protects the underlying layers from corrosion.

Increasing the level of armor resistance of a laminated plate is achieved:
by reducing the thickness of the front layer to (9 ± 5%) of the thickness and, accordingly, increasing the thickness of the middle (more durable) layer, which leads to an increase in the average strength (hardness) of the plate;
by eliminating the possibility of the formation of through cracks (spalls) from the back layer due to the application of an aluminum sublayer on its outer surface. Due to the high plasticity, this sublayer prevents the initiation of cracks from the back surface under various types of stresses from the front layer of the slab;
by increasing the ductility of the back layer while maintaining (or increasing) its hardness. The increase in ductility of the back layer is achieved by introducing into its middle a layer with a thickness of 1-3% of the thickness of a plate made of aluminum. The introduction of such a layer inhibits the development of cracks (spalls) in this layer, which leads to a significant increase in its ductility. So, the impact strength of samples a _n with a soft intermediate layer, depending on the place of application of the incision, is 2-6 times higher than that of samples without a soft layer. Due to the increase in the plasticity of the back layer, back spalls are not formed and, accordingly, the level of armor resistance increases. The thickness of the back layer is reduced to 15 ± 8% of the plate thickness. Tolerances on layer thicknesses of ± 5% for the front and ± 8% for the back are technological.

 The use of welded alloys in both the front and back layers eliminates any complications compared with monometallic plates in the manufacture of welded structures.

 This makes it possible to manufacture them with a favorable distribution (low level) of voltage across the plate thickness, thereby increasing its resistance to corrosion damage and thus increasing the operational reliability of welded structures.

 In FIG. Figure 1 shows the dependence of the hardness of plates from alloys of the Al-Zn-Mg system as a function of the total content (Zn + Mg).

 In FIG. 2-5 diagrams of the destruction of homogeneous and layered plates during their interaction with a sharp-headed striker (bullet) (Fig. 5) and a blunt-headed striker (projectile) with high loading intensity (Fig. 4).

 From the FIG. 1 dependence HB = f (Zn + Mg) shows that the alloys of the system Al = Zn = Mg with hardness HB more than 140 have a total content (Zn + Mg) of more than 7.0 wt. Such alloys have a reduced resistance to corrosion damage under the action of stresses and to ensure their reliable operation in stressed structures require the development of measures aimed at improving corrosion resistance.

 From those shown in FIG. Figure 2-5 shows that during the interaction of projectile 1 (blunt projectile) with a monometallic barrier, rear spalls are formed, the depth of which reaches half the thickness of the plate (Fig. 2).

 The nature of the destruction of the laminated plate (Fig. 3, prototype) when interacting with similar drummers changes significantly. So, due to the presence of a highly plastic intermediate layer 3 in the laminated plate, cases of plate splitting are practically excluded, since the facial cracks formed upon impact of the projectile are inhibited by this layer. At the same time, a crack 8 in the middle layer 4 (Fig. 3) cannot form a deep back spall due to its inhibition by layer 5.

 At the same time, a back spall 7 is formed in the back layer 6, the depth of which reaches more than half the thickness of the back layer.

 When passing through the considered layered barrier of an acute-headed striker (bullet), a back crack 2 is often formed (Fig. 5). This crack, as noted earlier, is formed on the outer surface of the back layer.

 The introduction of a plastic aluminum layer into the plate in the middle of the back layer, as well as thin plastic layers on the outer surfaces of the laminated plate, changes the nature of the formation of cracks in the laminated plate (Fig. 4): when tested with a blunt-headed projectile, rear spalls do not form, and when tested by a bullet, they do not form cracks from the back layer.

 For a comparative assessment of the corrosion and armor properties of the proposed plates, two types of experimental plates with a nominal thickness of 40 mm were manufactured: type 1 three-layer plates (analogue of the proposed plates); type 2 three-layer plates (analogue of the prototype).

 An alloy of grade 1931 was used as the main (middle) layer of both types. As the front and back layers, alloy 1901 was used for plates of type 1 and 1903 for type 2 (Table 1).

 An alloy of the A5 grade was used as intermediate and outer layers.

The armor properties were determined by shelling the plates with a B32 bullet, cal.7.62 mm normal (the angle between the bullet’s flight path and the normal to the plate α = 0) with determining the maximum speed of conditioned lesions (V _pkp ), as well as when firing shells (dull-headed) BS 30 mm caliber at an angle of 68 ^o (angle between the trajectory of the projectile and the normal to the plate a = 68 ^o ) with the definition of the speed of conditioned lesions (V _PCP ).

 The corrosion properties of the plates were evaluated by periodically immersing the samples in seawater, followed by an assessment of the nature of the corrosion damage.

Из приведенных в табл. 3 результатов испытаний видно, что наличие в предлагаемых плитах поверхностных слоев из алюминия существенно повышает их сопротивление коррозионным разрушениям.From the above table. 2 test results shows that the proposed armor has an advantage over the known level of armor properties when tested as a bullet (1) and a projectile (2):

From the above table. 3 of the test results shows that the presence in the proposed plates of surface layers of aluminum significantly increases their resistance to corrosion damage.

 Thus, the use of the proposed plates as armor will increase the level of armor properties of products while increasing their level of corrosion resistance, and due to the use of only weldable alloys in them, increase the level of their operational reliability.

Claims (1)

 An aluminum-based laminated plate for armor, including the front and back layers made of welded aluminum alloy, the middle layer, as well as intermediate layers of technically pure aluminum, characterized in that it is additionally provided with a layer located above the face layer and a sublayer located under the back layer made of technically pure aluminum with a thickness of 1 3% of the plate thickness, while the front layer is 4 13% of the plate thickness, the middle layer is made of a welded aluminum alloy t with a verity of not less than 165 HB, and the back layer is made with a thickness of 7 23% of the plate thickness and is equipped with an additional middle layer of technically pure aluminum with a thickness of 1 3% of the plate thickness.

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