Method for manufacturing of vehicle armor components requiring severe forming with very high bend angles with very thick gauge product of high strength heat treatable aluminum alloys

Abstract

It has been commonly believed that very thick gauge high strength aluminum alloy product such as AA2139 plate cannot be formed to the required sharp angles to form the highly protective underbody armor for the MRAP vehicles. The present process and method of manufacture provides a means for strategically combining the metallurgical process of manufacturing high strength aluminum alloys and the forming process of V shaped hull to improve the formability of the very thick gauge high strength alloy product so much that even the very thick gauge (thicker than 1 inch) plate can be formed to severe forming angles. This combined process allowed successful manufacturing of high performance V shaped hulls for the Mine Resistant Ambush Protected (MRAP) vehicles.

Description

INTRODUCTION

A Mine Resistant Ambush Protected (MRAP) vehicle is a family of armored fighting vehicles designed for the U.S. Army and United States Marine Corps with the goal of surviving IED attacks and ambushes—prompted by US deaths in Iraq.

MRAP vehicles usually have “V” shaped hulls to deflect away any explosive forces originating below the vehicle, thereby protecting the vehicle and its passenger compartment. Typically these explosions are from land mines, but they can also be IEDs (Improvised Explosive Devices).

BACKGROUND

Historically the V shaped hulls are made of welded steel plate, which is very heavy and added much more weight to the armored vehicles to slow down its mobility and limit the ammunition and personnel carrying capacity. The vehicle's weight and size severely limits its mobility off main roads, in urban areas, and over bridges (reference 1). 72 percent of the world's bridges cannot hold the MRAP. Its heft also restricts several of the vehicles from being transported by C-130 cargo aircraft or the amphibious ships that carry Marine equipment and supplies.

Instead of steel plate armor, it would be more desirable to use aluminum alloy plate to make it lighter. Unfortunately, the traditional aluminum armor alloys such as AA5083 and AA6061 are not strong enough to provide adequate protection against land mines and IED's. More recently developed high strength heat treatable aluminum alloys such as AA2139 and AA2519 among 2000 series alloys and AA7085 and AA7081 among the 7000 series alloys could meet the material property requirement for the vehicle armor components and underbody “V” hull for armored vehicles and MRAPs, respectfully. Recently, a new aluminum alloy, AA2139, has been developed by Cho et al. to provide much improved ballistic and mine blast protection compared to the traditional aluminum alloy based armor plate. The chemistry of the high strength heat treatable aluminum alloys as candidate materials for armor plate applications are listed in the TABLE 1 for AA2139, TABLE 2 for AA2519, TABLE 3 for AA2027, TABLE 4 for AA7085 and TABLE 5 for AA7081.

TABLE 1
Alloy Chemistry of AA2139
Element wt. %
Si      0.1 max
Fe      0.15 max
Cu      4.5-5.5
Mn      0.20-0.6
Mg      0.20-0.8
Cr      0.05 max
Zn      0.25 max
Ti      0.15 max
V       0.05 max
Ag      0.15-0.6

TABLE 2
Alloy Chemistry of AA2519
Element wt. %
Si      0.25 max
Fe      0.30 max
Cu      5.3-6.4
Mn      0.10-0.5
Mg      0.05-0.40
Cr      0.05 max
Zn      0.10 max
Ti      0.01-0.10
V       0.05-0.15
Zr      0.10-0.25

TABLE 3
Alloy Chemistry of AA2027
Element wt. %
Si      0.12 max
Fe      0.15 max
Cu      3.9-4.9
Mn      0.50-1.2
Mg      1.0-1.5
Cr      0.05 max
Zn      0.20 max
Ti      0.08
Zr      0.05-.25

TABLE 4
Alloy Chemistry of AA7085
Element wt. %
Si      0.06 max
Fe      0.08 max
Cu      1.3-2.0
Mn      0.04 max
Mg      1.2-1.8
Cr      0.04 max
Zn      7.0-8.0
Ti      0.06 max
Zr      0.06-0.25

TABLE 5
Alloy Chemistry of AA7081
Element wt. %
Si      0.12 max
Fe      0.15 max
Cu      1.2-1.8
Mn      0.25 max
Mg      1.8-2.2
Cr      0.04 max
Zn      6.9-7.5
Ti      0.06 max
Zr      0.06-0.25

The conventional manufacturing method of the “V” hull shaped underbody armor utilizing high strength alloys consists of welding two or more number of flat plate together by conventional welding techniques such as Gas Metal Arc Welding (GMAC) or Friction Stir welding. Such manufacturing processes increase the cost and lower the material properties drastically. For example, GMAC process on high strength, high ballistic performance aluminum alloys would lower the strength of the welded plate by as much as 70% compared to the original material properties prior to welding. Friction Stir welding process could somewhat improve the post-welding strength compared to that of GMAC process at a much higher cost and gauge limitations. Yet the post-weld mechanical properties after Friction Stir Welding (FSW) process is still lower by as much as 35% compared to the original strength of the alloy prior to welding. Therefore, the “V” shaped hull manufacturing process consists of welding processes (GMAW and/or FSW) would degrade the material properties and severely degrade the protection capability provided by the V shaped underbody armor against the land mines and IEDs, which MRAPs are designed for.

SUMMARY OF THE INVENTION

This application incorporates by reference U.S. Pat. No. 7,229,508, U.S. Pat. No. 6,972,110 and PCT Application Publication No. WO 2004/090185A1 all of which are incorporated by reference herein in their entirety. Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

One of the solution to avoid the over weight of MRAP vehicles due to the over weight of the underbody armor of the “V” shape hull is to find a manufacturing process of low weight, high performance underbody armor utilizing high strength, high ballistic performance aluminum alloys such as high strength 2000 series and 7000 series heat treatable alloys. The preferred solution is to avoid any welding processes which degrade the properties of the aluminum alloys significantly. This can be achieved by manufacturing the “V” shaped hull by forming instead of welding process. However, “V” shaped hulls for MRAP underbody armor based on high strength aluminum alloys via. forming process without welding have not been available to date because of the following reasons.

1) Highly protective Underbody armor for MRAP vehicles requires very thick gauge aluminum alloy plate
2) Forming process for highly protective underbody armor for MRAP requires severe angle of bend forming to meet the geometry requirement.
3) Forming process of very thick gauge material to sharp bend angles would require very high formability of the material
4) High strength, high ballistic performance aluminum based alloys do not have high formability.

It has been commonly believed that very thick gauge high strength aluminum alloy product such as AA2139 plate cannot be formed to the required sharp angles to form the highly protective underbody armor for the MRAP vehicles. However, it was unexpectedly discovered that strategically combining the metallurgical process of manufacturing high strength aluminum alloys and the forming process of V shaped hull could improve the formability of the very thick gauge high strength alloy product so much that even the very thick gauge (thicker than 1 inch) plate can be formed to severe forming angles. This combined process allowed successful manufacturing of high performance V shaped hulls for the Mine Resistant Ambush Protected (MRAP) vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the several views and wherein:

FIG. 1. Picture of the 2.5 inch thick 2139-T8 temper plate after a bend forming attempt. The plate was fractured at bend angle of 160 degrees;

FIG. 2; A schematic diagram of vehicle armor component of 2.5 inch thick AA2139 alloy plate which requires bend angle of 144 degrees, 140 degrees, and 135 degrees;

FIG. 3; A picture of the successfully formed a vehicle armor component of 2.5 inch thick AA2139 alloy plate by following the invented forming process. This part requires bend angle of 144 degrees, 140 degrees, and 135 degrees as shown in FIG. 2;

FIG. 4; A schematic diagram of vehicle armor component of 2.5 inch thick AA2139 alloy plate which requires bend angle of 135 degrees, 130 degrees, and 125 degrees;

FIG. 5; A picture of the successfully formed a vehicle armor component of 2.5 inch thick AA2139 alloy plate by following the invented forming procedure. This part requires bend angles of 135 degrees, 130 degrees, and 125 degrees as shown in the FIG. 4; and

FIG. 6; One example of the underbody armor component design for armored vehicles which require 125 degree and 140 degree bending of 2.5 inch thick gauge plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

By strategically combining metallurgical process of manufacturing high strength heat treatable alloys and bend forming of very thick gauge work piece, high strength heat treatable alloys can be formed into various armor components for armored vehicles even for the parts requiring very thick gauge plate and bend forming of sharp angles.

For very thick plate of 2000 series aluminum alloys such as 1 inch to 6 inch thick gauge 2139 alloy plate and 2519 alloy plate can be solution heat treated at 960° F.-980° F. and cold water quench for conditioning the work piece to be ready for forming operation. After forming the work piece to the final shape, the work piece can be age hardened to meet high ballistic and blast resistance for the armored vehicles. A cold stretch of the work piece by a small amount right after the solution heat treatment can be a part of the conditioning the work piece for forming operation. This would further improve the final mechanical properties and minimize the residual stress of the formed and age hardened work piece in the final temper condition.

For very thick plate of 7000 series aluminum alloys such as 1 inch to 6 inch thick gauge 7085 alloy plate and 7081 alloy alloy plate can be solution heat treated at 860° F.-880° F. and cold water quenched to condition the work piece to be ready for forming operation. After forming the work piece to the final shape, the work piece can be age hardened to meet high ballistic and blast resistance for the armored vehicles. A cold stretch of the work piece by a small amount right after the solution heat treatment can be a part of the conditioning the work piece for forming operation. This would further improve the final mechanical properties and minimize the residual stress of the formed and age hardened work piece in the final temper condition.

Example 1

To examine the forming capability of high strength armor alloy 2139-T8 plate, a test sample of a 2.5 inch thick×5 inch wide×18″ long sample plate was sawed from a commercially produced large parent plate of 2139-T8 plate delivered from the plate rolling mill of the Alcan Rolled Products LLC, located at Ravenswood W. Va. USA. The formability of the 2.5 inch thick 2139-T8 flat plate (180 degree) was formed by a break forming press with the 16 inch apart two supporting points in the bottom die and the 4 inch radius of the top die blade. The goal was to bend the plate to at least 144 degrees to meet the geometry requirement for the current design of the V shaped hull of an MRAP vehicle. However, the formability of the 2139-T8 plate was not robust enough to achieve the required amount of bending. As a result, the sample plate was fractured at the bending angle of 160 degrees as shown in the FIG. 1. This test result confirmed that the formability of very thick gauge 2139-T8 plate is not robust enough to produce the V shaped very thick gauge high strength aluminum alloy hull of an MRAP. It is generally known in the professional community skilled in the art that very thick gauge high strength heat treatable aluminum alloy plate are not formable.

Example 2

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenized at 980 F for 24 hours and hot rolled to 2.5 inch gauge plate in the temperature range of 800 F-900 F and subsequently followed by solution heat treated at 980 F for 3 hours and cold water quenched. After cold water quench, the plate was cold stretched by 3 percent permanent set to condition the plate to be formed by severe bending. The plate was formed to an armor component requiring of three bend angles of 144 degrees, 140 degrees and 135 degrees, to make a desirable geometry to make armored vehicle components. The schematic diagram of the intended geometry is shown in FIG. 2. FIG. 3 shows the picture of the component successfully formed to meet the geometry shown in FIG. 2. The plate is now ready to be aged to the high strength mechanical property requirement by age process known in the art. The most typical age process is to heat up the work piece to 320° F. and soak at the temperature for 36 hours. A variation of thermal procedures could be utilized at the temperature range of 250°-380° F. for durations selected appropriately to the temperatures selected.

Example 3

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenized at 980 F and hot rolled to 2.5 inch gauge plate in the temperature range of 800 F-900 F and subsequently followed by solution heat treated at 980 F for 3 hours and cold water quenched. After cold water quench, the plate was cold stretched by 3 percent permanent set to condition the plate to achieve high strength after final heat treatment, and yet be formed by severe bending. The plate was formed to an armor component requiring of three bend angles of 135 degrees, 130 degrees and 125 degrees, to make a desirable geometry to make armored vehicle components. The schematic diagram of the intended geometry is shown in FIG. 4. FIG. 5 shows the picture of the component successfully formed to meet the geometry shown in FIG. 4. The plate is now ready to be aged to the high strength mechanical property requirement by age process known in the art. The most typical age process is to heat up the work piece to 320° F. and soak at the temperature for 12-48 hours. A variation of thermal procedures could be utilized at the temperature range of 250°-380° F. for durations selected appropriately to the temperatures selected.

Example 4

FIG. 6 shows one example of the underbody armor component design for armored vehicles which require 125 degrees and 140 degrees bending of 2.5 inch thick gauge plate.

Various geometries of highly effective armor components with very thick gauge high strength aluminum alloys can be manufactured by utilizing the invented procedure of combination of material processing steps and forming processes as described above.

Example 5

An ingot of alloy AA2139 was cast in 16 inch thick ingot and homogenized at 980 F and hot rolled to 2.0 inch gauge plate in the temperature range of 800 F-900 F and subsequently followed by solution heat treated at 980 F for 3 hours and cold water quenched. After cold water quench, the plate was cold stretched by 3 percent permanent set to condition the plate to achieve high strength after final heat treatment, and yet be formed by severe bending. The plate was formed to an armor component requiring of three bend angles of 140 degrees, 160 degrees and 160 degrees, to make a desirable geometry to make armored vehicle components. The formed parts are age strengthened at 320 F for 24 hours.

Performance Characteristics of the Formed Underbody Armor

• • 1. The mechanical properties of the formed underbody armor after final heat treatment are different from those of flat plate armor. The three bent areas in the formed underbody armor are very high in strength due to the high level of cold work (as high as 22%) and provide extremely rigid structural integrity of the overall armor against the blast force, and the flat portion between the bent areas are moderately high in strength due to the moderate level of cold work (nominally 3%) and provide high rupture resistance with very high fracture toughness. Such a unique combination of mechanical properties enhances the geometrical advantage of formed underbody armor as described in above.
  • 2. The examples of the mechanical properties are listed below from the sample material processed by the identical manufacturing procedures as the above manufacturing process specifications.
    • a. Mechanical Properties of sample plate representative of the flat portion between the bent area having nominal 3% cold work

	UTS (ksi)	TYS (ksi)	El (%)	K1c (ksi-√inch)
	68.5	63.5	16	58.1
	68.0	63.3	16	54.2

• • • b. Mechanical Properties of the sample plate having 18% cold work, representative of the bent area

	UTS (ksi)	TYS (ksi)	El (%)	K1c (ksi-√inch)
	75.6	70.7	10	N.A.

These are very desirable combination of mechanical properties to ensure superior performance for armor application compared to the mechanical properties of flat rolled plate of 2139-T8 temper plate per SAE-AMS Specification No. 4468 (see below)

Mechanical Properties (L Direction) of 2139-T8 Flat Plate per SAE-AMS Spec 4468

	UTS (ksi)	TYS (ksi)	El (%)	K1c (ksi-√inch)
	66	62	9	35

MODIFICATIONS

Specific compositions, methods, or embodiments discussed are intended to be only illustrative of the invention disclosed by this specification. Variation on these compositions, methods, or embodiments are readily apparent to a person of skill in the art based upon the teachings of this specification and are therefore intended to be included as part of the inventions disclosed herein.

Reference to documents made in the specification is intended to result in such patents or literature cited are expressly incorporated herein by reference, including any patents or other literature references cited within such documents as if fully set forth in this specification.

The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom, for modification will become obvious to those skilled in the art upon reading this disclosure and may be made upon departing from the spirit of the invention and scope of the appended claims. Accordingly, this invention is not intended to be limited by the specific exemplifications presented herein above. Rather, what is intended to be covered is within the spirit and scope of the appended claims.

Claims

1. A method of manufacturing highly effective vehicle armor with very thick gauge high strength heat treatable aluminum alloys by strategically combining forming process and the metallurgical process of the alloy

a) Thick gauge aluminum alloy products comprised of the thickness range of from 1 inch to 6 inch thick product

b) High strength heat treatable aluminum alloys comprised of; i) high strength 2000 series aluminum alloys such as, but not limited to, AA2139, AA2027, and AA 2519 ii) high strength 7000 series aluminum alloys such as, but not limited to, AA7085 and AA7081

c) forming process requires solution heat treatment of the work piece at the solutionization temperature and quench the work piece to room temperature to condition the work piece to be capable of receiving severe forming process by bending or bending and stretching at various bending angles more severe than 160 degrees of bending angle to meet the geometry requirement of the vehicle armor component

d) If desired, a forming process can add a cold stretch by a small amount after quench the work piece to further improve the material properties prior to forming the work piece.

e) The formed armor components can be aged to increase the strength of the material to take advantage of age hardening characteristics of heat treatable aluminum alloys.

2. Forming process according to the claim 1, wherein forming the work piece immediately after solution heat treatment and quench step to maximize the formability during bend forming or stretch and bend forming procedure. The solution heat treatment for high strength 2000 series alloys can be conducted at the temperature range of 960° F. and 980° F. for the durations to be adjusted to the thickness of the work piece. The solution heat treatment for high strength 7000 series alloys can be conducted at the temperature range of 860° F. and 880° F. for the durations to be adjusted to the thickness of the work piece.

3. Forming process according to the claim 1, wherein forming the work piece after solution heat treatment and quench step to maximize the formability during bend forming or stretch and bend forming procedure. For very thick plate of 2000 series aluminum alloys such as 1 inch to 6 inch thick gauge 2139 alloy plate and 2519 alloy plate can be solution heat treated at 960° F.-980° F. for the duration of 30 minutes to 6 hours depending on the thickness of the work piece and cold water quench for conditioning the work piece to be ready for forming operation. For 2.5 inch thick work piece, 2-4 hours of heat treatment at the temperature arrange of 960° F.-980° F. would be most preferred After forming the work piece to the final shape, the work piece can be age hardened to meet high ballistic and blast resistance for the armored vehicles. Age hardening can be conducted at the temperature range of 250-380° F. for the duration of 6 hours to 72 hours depending on the actual age temperatures selected. This age process can be further modified if required such as need to compensate the limitation of equipment limitations to achieve the final age processing effect. A cold stretch of the work piece by a small amount right after the solution heat treatment can be a part of the conditioning the work piece for forming operation. This would further improve the final mechanical properties and minimize the residual stress of the formed and age hardened work piece in the final temper condition.

4. Forming process according to the claim 1, wherein forming the work piece after solution heat treatment and quench step to maximize the formability during bend forming or stretch and bend forming procedure. For very thick plate of 7000 series aluminum alloys such as 1 inch to 6 inch thick gauge 7085 alloy plate and 7081 alloy alloy plate can be solution heat treated at 860° F.-880° F. and cold water quenched to condition the work piece to be ready for forming operation. After forming the work piece to the final shape, the work piece can be age hardened to meet high ballistic and blast resistance for the armored vehicles. A cold stretch of the work piece by a small amount right after the solution heat treatment can be a part of the conditioning the work piece for forming operation. This would further improve the final mechanical properties and minimize the residual stress of the formed and age hardened work piece in the final temper condition.