Armour aluminium

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The primary considerations used in selecting aluminium alloys as armour aluminum are their ballistic protection, weldability and corrosion resistance.

1 Metallic armour materials

Armored vehicles, whether wheeled or tracked, serve a variety of different functions on the battlefield: as reconnaissance, ambulance, infantry delivery vehicles. The design of armour system of the vehicles depends on the size of the vehicle, the threat or threats the vehicle is likely to encounter and the weight of the armour that the vehicle can handle. Metal is the primery armour material used for large combat vehicle. The table of Figure 1 gives selected examples of such materials and their applications.

Figure 1 – The examples of metallic armour materials [1]

2 Armour aluminium

Sixty years ago, the U.S. military started using armored personnel carriers with aluminium plate. One of the first of these was the M113, a true workhorse that provided speed, agility, and safety during the Vietnam War. Aluminium made the M113 lighter than previous military vehicles yet still strong enough to protect its crew and passengers [2].

There are several benefits that make aluminum an material in many kinds of armor plating [2, 3]:

Aluminum has light (about one third that of steel).
Aluminium offers a high strength-to-weight ratio.
Ballistic performance must be balanced with light weight for vehicles that need to be transported by air, such as troop carriers.
High corrosion resistance.

3 Ballistic protection requirements

The primary considerations used in selecting alloys for aluminum armour plate are

ballistic protection,
weldability and
corrosion resistance.

Ballistic protection is measured with a couple of different metrics:

the ability to resist penetration by an armor piercing (AP) projectile with a pointed leading end such as a .30 caliber; and
the ability to resist spallation by a fragment stimulating (FS) projectile with a blunt leading end such as a 20 mm. Spallation is the fragmentation of the back side of an armored plate opposite the point of projectile impact caused by a compressive wave.

Figure 2 – Armor-Piercing (AP) Projectiles [4]

Figure 3 – Fragment-Simulating (FSP) Projectiles [4]

Figure 4 – Examples of armour test projectiles:
20 mm fragment simulator (a), .50 caliber AP round (b), and .30 caliber M2AP (c) [5]

4 Armour aluminium alloys

Figure 5 – Common Al-armor alloys according to [4]

Figure 6 – Conventional armour aluminium alloys and tempers according to [5]

Figure 7 – Military specifications of armour aluminium alloys [11]

5xxx aluminium armour

Many of the most used alloys in armour plating come from the 5xxx series. These non-heat treatable alloys use magnesium as the primary alloying agent and are recognized for having the highest strength of the alloys that can’t be heat-treated. These alloys are also well suited for welding.

Substantial increases in magnesium offer benefits of substantially improved strength and ballistics performance. However, increasing the level of magnesium introduces problems in stress corrosion cracking where significant amounts of cold work are imparted to the sheet or plate product. A preferred minimum for magnesium is about about 6.6%. A preferred maximum for magnesium is about 7.4% [5].

5456
5083
5059

6xxx aluminium armour

The 6xxx series of alloys are frequently used directly as plate in applique armour systems, such as the “up-armouring” programs that were employed to improve the protection of the military’s High-Mobility Multipurpose Wheeled Vehicle (HMMWV or Humvee) against improvised explosive devices.

6061 is the most frequently used armour alloy from this family [7].

7xxx aluminium armour

The 7xxx family of alloys have high strength and durability. These heat treatable alloys use zinc as the primary alloying element. Not all the alloys in this category are easily weldable.

7017
7029
7039
7056
7075
7085

2xxx aluminium armour

2195
2060
2139
2519

5 Aluminium armour plates specifications

The most widely accepted aluminum alloys for armored plate applications are 5083 and 7039:

5083 meets the requirements of U.S. Military Specification MIL-A46027F
7039 meets U.S. Military Specification MIL-A46063E.

While 7039 is more effective in AP performance, 5083 fares better in FS applications. The improved ballistic characteristics of 7039 are offset by its lower corrosion resistance and difficulty in welding.

Some new alloys improve the weldability, corrosion resistance and ballistic performance of approved grades, for example [5]:

5059 shows improved blast protection to 5083
7017 has shown a reduction in spallation as compared to the 7039 alloy.

6 Some aluminium armoured vehicles

6.1 Bradley

Housing parts up to 44 mm thick are made of 5083 and 5086 alloys.
The frontal projection is protected from 12,7 mm bullets, other surfaces from normal caliber.
Modern BMP M2 Bradley is also built from aluminum alloys 7039 and 5083.
The forehead and side are reinforced with steel screens (Figure 5) [5].

6.2 RG-33

The aluminum alloy 5059 offers greater ballistic and blast protection for armored hull-type vehicles.
Alloy 5059 can be readily welded and offers superior corrosion resistance.
US Army used AA5059 in the RG-33 Mine Resistant Ambush Protected (MRAP) vehicle that was deployed in Iraq (Figure 6).

6.3 HMMWV

The Monocoque Aluminum Cab Structure for Light Tactical Vehicle is comprised of all 5083-H131 Aluminum alloy armor plates with various thicknesses [7]:

1/2” Inner Floor
1” Roof & B-Pillar Gussets
1.5” Tunnel Side Walls
2” Underbody Outer Structure, Front, Rear and Side Walls, Tunnel Top “V”

6.4 AMX-10 RC

Aluminium alloy 7050 (AMS 4050A):

Hull (front/side/back) – 45/20/25 mm
Turret (front/side/back) – 42/420/25 mm

6.5 Light tank M8 AGS

Welded aluminium alloy 5083 [9]

6.6 Scorpion and Scimitar

Scorpion and Scimitar are protected by aluminium-zinc-magnesium 7017 alloy armour, which keep the vehicle weight down below 7,8 tons. Scorpion is usually fitted with a 76 mm cannon. Scimitar is basically the same vehicle as Scorpion but fitted with a 30 mm cannon instead of the 76 mm cannon.

The armour give adequate protection against 12,7 mm heavy machine gun rounds in the frontal arc and against 7,92 mm elsewhere, as well as against high-explosive shell splinters. The driver’s position is further protected by additional aluminium alloy armour against mines [10].

Figure 8 – Bradley [5]