Aluminum Alloys in Military Vehicles and Equipment

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The earliest military use of aluminum was for torpedo boats, ordered in 1892 by the French Government. The United States Army acquired aluminum picket and tent pins and aluminum canteens in 1896; in fact, Teddy Roosevelt carried an aluminum canteen in the famous charge up San Juan Hill during the Spanish-American War. Also, during the 1890`s, the United States Navy procured 94-in.-wide aluminum sheets for a large assembly, possibly a ship superstructure.
Although many military designs and materials are relatively stable, there is a strong trend toward innovation, especially in combat equipment. Thus, many products described here are likely to be changed within a short time. Design details and most applications in the development stage are omitted because of military security restrictions or uncertainty concerning final selections.

The earliest military use of aluminum was for torpedo boats, ordered in 1892 by the French Government. The United States Army acquired aluminum picket and tent pins and aluminum canteens in 1896; in fact, Teddy Roosevelt carried an aluminum canteen in the famous charge up San Juan Hill during the Spanish-American War. Also, during the 1890’s, the United States Navy procured 94-in.-wide aluminum sheets for a large assembly, possibly a ship superstructure.

The First World War generated an urgent need for aluminum in several forms and for a variety of military applications. Germany, faced with shortages in iron and steel, employed aluminum in army tanks and industrial machinery.

The Second World War added many naval uses in structural, functional, and personnel equipment aboard fighting ships. Other notable military adaptations were in bridges and pontons, walkie-talkie sets, fuel drums for air transport, aircraft landing mats, and searchlights.

Although many military designs and materials are relatively stable, there is a strong trend toward innovation, especially in combat equipment. Thus, many products described here are likely to be changed within a short time. Design details and most applications in the development stage are omitted because of military security restrictions or uncertainty concerning final selections.

Armor

Military requirements of combat vehicles establish their specifications for armor. The 5xxx series strain-hardenable alloys have been used in all aluminum military vehicles produced to date. The ballistic merit of these alloys relative to rolled homogeneous steel armor varies with the angle of impact. The 7xxx series heat treatable alloys provide improved protection at all angles. Because minimum weight for a given level of protection is essential to mobility, aluminum armor is used extensively in combat vehicles.

The ultimate selection of armor material depends also on requirements other than ballistic criteria. For vehicular applications, weldability is a primary need, because welding most economically produces structural integrity and the watertightness necessary for amphibious operation. Satisfactory machinability and formability are needed for shop fabrication. Strength must be adequate to resist service stresses, including shocks encountered in airdrops and cross-country operation.

Completed vehicles may be used or stored for long periods under extreme conditions of temperature (-80 to 165°F) and humidity. Operations also include movements through corrosive waters. Armor material must retain its mechanical and ballistic properties, and resist corrosion under such conditions. Aluminum alloy armor provides the characteristics required.

Additional advantages offered by aluminum over steel are freedom from low-temperature embrittlement and greater rigidity, resulting from thicker sections, for equal protection. Increased rigidity, up to nine times that of steel, usually eliminates the need for secondary structural support.

Production forms of aluminum alloy armor are rolled plate, extrusions, and forgings. For alloys with ballistic properties developed by strain hardening, use primarily is in the form of rolled plate.

Heat treatable aluminum alloys that can be welded effectively are being developed as weldable armor, making it possible to employ more forged and extruded armor components.

Cast aluminum armor components are being introduced for applications where requirements other than ballistic performance dictate section thicknesses greater than those necessary for wrought armor.

Vehicles

Aluminum’s greatly increased use in military vehicles in the past few decades has resulted from requirements for reduced weight for improved vehicle mobility, "swimmability", air transportability, increased payload, and ease of maintenance. Many successful, economical, commercial highway vehicles of aluminum construction have been employed by the services. However, most combat and tactical vehicles have no civilian counterparts, and their aluminum components have been developed specifically for military service.

Wheeled vehicles for general-purpose duty are used predominantly for logistics (support and supply) operations. Aluminum 5xxx series alloy sheet and 6061-T6 and 6063-T5 extrusions are employed extensively in the bodies of large buses, cargo trailers, liquid-transport tanks, and comparable vehicles.

Bus and cargo-trailer bodies usually are riveted assemblies of aluminum sheet and extrusions, whereas tankers are welded 5xxx series alloy sheet assemblies. Tanker pumps, filters, and plumbing are made of aluminum castings and tube.

Special-purpose wheeled vehicles have standard military functions or characteristics that are outside normal commercial requirements.

The Minuteman missile transporter is illustrative of single-purpose highway vehicles. Its aluminum components include: 2024-T6 alloy forged disk wheels; 2014-T6 forged front hubs, fifth-wheel control arms and cross braces, and equalizer beams in the tandem axle assemblies; 6061-T6 plate and bar stock weldments in the trailer-frame cross-assembly rear hinge structure, and in several suspension system brackets; 220- T4 alloy sand-cast support brackets for the auxiliary transmission and the gasoline tanks; welded 5052 sheet gasoline tanks; and 1100 alloy brazed tube-and-fin radiator.

Welded assemblies in the vehicle are heat treated after being welded. Where strength requirements permit, the operation is limited to artificially aging material welded in the T4 temper. In many instances, however, stock in the 0 or F temper is welded and the assembly is completely heat treated.

The adjustable-height aircraft-loading trailer, another single- purpose vehicle for use on prepared surfaces, employs forged 2014-T6 actuating beams, and several extruded 6061-T6 parts.

Others in this class of vehicle are simple, four-wheel trailers for nuclear ordnance. These are built primarily of 6061-T6 forgings, 5083 extrusions, and A356-T6 castings.

The M-I02 trail-gun-type 105-mm howitzer, a lightweight weapon carriage for rough terrain, is fabricated almost entirely of aluminum. Fusion welded box sections of 5086-H32 sheet and 5086-H112 extrusions provide structural efficiency and low weight in the trail, body, and base assemblies. Several functional extruded tubes, such as those in the cradle structure, are 5086- H32 alloy. Forged 7075-T6 and 7079-T6 structural brackets support the trunnion and cradle; ground stakes are 7075- T6 forgings, hard anodized for abrasion resistance; wheel hubs are A356-T61 castings. With a gross weight of approximately 1.6 tons, the M-102 is by far the lightest 105-mm conventional gun yet designed. Transport by helicopter for maximum tactical effectiveness takes unusual advantage of its light weight.

A family of lightweight truck designs, the XM-561, XM- 410, and XM-656, replaced the traditional group; capacities range from 11/4 to 5 tons. The combined objectives of cross country capability and lightness for maximum mobility and air transportability demand efficient structural design.

The XM-656 is a 5-ton, 8x8 truck with conventional chassis that employs 6061-T6 aluminum sheet and extrusions in cab, cargo body, and cab arctic hard-top assembly. Forged 2014-T6 alloy arms carry fore and aft thrust between axles and frame. Wheel hubs are either cast 356-T71 alloy or forged 2014-T6. The power train contains 356-T6 castings in the transfer cases and 356-T71 castings in the differential cases.

The M-116 general-purpose tracked logistics vehicle is a lightweight (5.5-ton) design, constructed principally of 5086-H34 sheet on an extruded aluminum frame, joined by welding, rivets, and bolts. Its drawn 2024-T4 plate wheels, and 6062- T6 extruded clamping plates on the track bands are characteristic of current lightweight tracked vehicles.

Earthmovers. Military tracked vehicles for other than combat or logistics are mostly earthmovers. Typical is the commercial bulldozer, where aluminum generally is limited to power-plant applications.

Amphibious vehicles of aluminum construction include the Army LARC (lighter, amphibious, resupply, cargo) group and the Navy LVH (landing vehicle, hydrofoil), both general-utility craft for ship-to-shore operation. Also included is the Army MFAB tactical bridge and ferry.

The Navy LVH is a cargo or general-utility hydrofoil boat with wheels. It differs from the LARCS by having retractable wheels, foils, and propeller. High speed and efficient performance are achieved by sophisticated structural and hydrodynamic design, and extensive use of aluminum. Sheet, plate, and extrusions of 5083 alloy in the H112 and H113 tempers are welded to form a stressed-skin hull and superstructure. The foils are hollow welded assemblies of 5083 extrusion and tube. Forged 2024- T6 wheels, cast 356- T6 power-train cases, and the normal castings, forgings, and weldments in the turboshaft engine are other aluminum applications. Land and water speeds up to 40 mph are the highest available in an amphibian.

The Army mobile floating assault bridge (MF AB) is a unique wheeled boat with a rotatable "roadway" superstructure. The MFAB can launch itself and ferry other vehicles, or form a floating bridge in conventional fashion. Hull and deck are 5456-H343 sheet, welded or riveted to 6061-T6, 2014-T6, or I5456 alloy extrusions in the framework, using 2117 or 6061 rivets. The roadway consists of 12-in.-wide ribbed 2014-T6 extrusions laid across beams welded from large 2014-T6 extruded shapes.

Ordnance

Ammunition. Lower cost and equal or better performance have led to increasing use of aluminum in recent years for parts such as projectiles (both cartridge-launched and rocket-launched), cartridges, mines, bombs, and their components.

The smallest projectiles employing aluminum are several varieties of the conventional 20-mm round. These have a conical aluminum nosepiece, machined from rod or bar of 2024-T4. Two 40-mm projectile models have machined tubular skirt of 6061-T4.

Aluminum components forged to size with extreme precision ("net" forgings, with tolerances smaller than normal even for finish machining) are economical for certain mass-produced ammunition items.

Guns and launchers utilizing aluminum range from the M-16 rifle to the superstructure of the M-474 used to transport key, equipment of the Pershing system.

One model of the M-16, with a 5.56-mm bore, has forged 7075- T6 upper and lower receivers, in addition to several smaller parts. The M-14 standard automatic rifle employs a 7075-T6 butt-plate assembly, both for light weight and capacity to accept a hard, durable anodic coating. The M-60 machine gun has several small aluminum parts, such as the bipod, that help prevent excessive over-all weight.

The M-72 recoilless rocket launcher LAW (light antitank weapon) has a 6061-T6 impact extruded chamber. A variation of the World War II "Bazooka", it is carried complete with its rocket, fired once, and discarded. Therefore, low cost is essential. An aluminum impact extrusion that is utilized as part of the shipping container and as a barrel to fire the rocket contributes greatly to the low cost, as well as to keeping maximum weight below a 4.5-lb limit. A die cast 380 alloy firing- pin housing is used for the same reasons.

Torpedoes and Mines. Torpedoes commonly are subjected to several practice firings during their service lives. They are designed with a slight net positive buoyancy to permit floating and recovery after practice runs.

Weight saved in torpedo shells or machinery can be added as instrumentation or payload. Aluminum is employed extensively, for weight reduction in the Mark 37, 44, 45, 46, and 48 torpedoes. Products vary with models, but aluminum-silicon alloy castings are used most frequently for such major parts as outer casings (aft, center, and nose sections), propellers, shroud rings, etc.

Other Military Equipment

Bridges and electronic hardware are typical of other military equipment making extensive use of aluminum. A ponton bridge, designed in World War II and still in production and use, is constructed mostly of 2014-T6 alloy extrusions. Assembly involves considerable welding, especially along the neutral axes of tubular beams made from extruded channels, of which the upper web forms the roadway. To improve traction of vehicles, the roadway face has longitudinal extruded and transverse press- formed depressions.

Several other types of aluminum ponton bridges also are in service, including a footbridge that employs extrusions and plates of 2014-T6 and 6061-T6 alloys in the superstructure. The ponton is fabricated of 6061-T6 alloy.

The armored vehicle-launched (AVL) bridge illustrates the increasing mobility of military bridging. This aluminum and steel structure is attached to the front of a modified tank, folds to ride atop the vehicle, and operates hydraulically without exposing personnel. Aluminum’s high strength-to-weight and stiffness-to-weight ratios contribute significantly toward maximum portability and mobility.

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