ARL-TR-7807 ● SEP 2016

US Army Research Laboratory

A Limited Dynamic Investigation of 

Magnesium Alloy AZ31B in 3 Orientations

by Tyrone L Jones and John P Riegel III

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ARL-TR-7807 ● SEP 2016

US Army Research Laboratory

A Limited Dynamic Investigation of 

Magnesium Alloy AZ31B in 3 Orientations

by Tyrone L Jones

Weapons and Materials Research Directorate, ARL

John P Riegel III

R3 Technology, Inc., Springfield, Virginia

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1. REPORT DATE (DD-MM-YYYY)

September 2016

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

1 August 2014–31 December 2015

4. TITLE AND SUBTITLE

A Limited Dynamic Investigation of Magnesium Alloy AZ31B in 3

Orientations

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Tyrone L Jones and John P Riegel III

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

US Army Research Laboratory

ATTN: RDRL-WMP-E

Aberdeen Proving Ground, MD 21005-5066

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ARL-TR-7807

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The work described in this report examines the ballistic characterization of the magnesium alloy AZ31B-H24 in 3 

orientations: normal direction, transverse direction, and rolling direction. Semi-infinite impacts from penetrators in each 

direction are shown. The targets were sectioned and machined using electrical discharge machining in preparation for 

polishing and etching to determine the extent of plastic flow that can be seen.

15. SUBJECT TERMS

AZ31B, semi-infinite, penetration characterization, WAPEN, effective flow stress (EFS)

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19a. NAME OF RESPONSIBLE PERSON

Tyrone L Jones

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410-278-6223

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Contents

List of Figures iv

List of Tables iv

1. Introduction 1

2. Experimental Methodology 1

3. Ballistic Results 4

4. Conclusion and Future Considerations 7

5. References 9

Distribution List 10
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List of Figures

Fig. 1 Plate fabrication orientation...................................................................1

Fig. 2 Sketch of 7.62-mm APM2 projectile .....................................................2

Fig. 3 Setup of the ballistic experiments..........................................................2

Fig. 4 Ballistic launch view..............................................................................3

Fig. 5 Experimental target fixture with plate oriented in transverse direction 

for testing ...............................................................................................3

Fig. 6 Initial penetration trends........................................................................5

Fig. 7 Normal direction, shot no. 12688, yaw = 1.85°.....................................5

Fig. 8 Dimensionless outline of the penetrator core and target crater from 

shot no. 12688 with 1.85° of yaw ..........................................................6

Fig. 9 Rolling direction, shot no. 12685, yaw 0.93° ........................................6

Fig. 10 Shot no. 12685: penetration into normal direction channel showing 

jacket stripping and core rebound..........................................................7

Fig. 11 Transverse direction...............................................................................7

List of Tables

Table 1 Experimental data ..................................................................................4
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1. Introduction

Magnesium (Mg) is the lightest structural metal available. Historically, it has not 

been perceived to have properties suitable for armor applications. However, over 

the last decade, the US Army Research Laboratory has been examining Mg alloys 

for ballistic applications.1 This work has improved the understanding of Mg 

properties, especially strength and ductility, important factors in the application of 

Mg in lightweight armors. This report continues the effort, exploring the ballistic 

performance of Mg as a function of the plate direction. Mg is known for showing 

significant variation in properties as a function of the loading direction.2 However, 

in a search of the literature, we were unable to find work that carefully examined 

the ballistic performance as a function of plate direction. The directions evaluated 

are the rolling, also known as longitudinal, direction, normal direction, and 

transverse direction as shown in Fig. 1.

Fig. 1 Plate fabrication orientation

The goal of this effort was to develop experimental data comparing performance of 

AZ31B-H24 in the various orientations. It requires gathering experimental data to 

determine the variation in penetration as a function of the orientation of the target 

material relative to the rolling, normal, and transverse directions. 

2. Experimental Methodology

The specific ballistic threat used to test the Mg alloy plate samples was the 

7.62-mm APM2 armor-piercing projectile,3 shown in Fig. 2. The projectile was 

fired at each face of the Mg AZ31B-H24 targets. The size of the targets were 

609.6 × 76.2 × 76.2 mm thick.
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Fig. 2 Sketch of 7.62-mm APM2 projectile

Target impact with a total yaw less than one-half degree was desired. The pitch and 

yaw for each shot were determined by using orthogonal flash X-rays. The total yaw 

values obtained were typically between 1° and 2°. The potential degradation in 

penetration as a function of yaw has been previously discussed by Riegel4 and

Yaziv et al.

5 In short, the critical yaw angle is a function of the penetration crater 

diameter relative to the projectile diameter. For rigid penetration, the ratio of the 

crater diameter to the projectile diameter goes to 1. That translates to a critical total 

yaw of 0°. In practice, the amount of degradation depends on the material properties 

of the target, the shape of the projectile nose, and other factors, making it impossible 

to assume a simple relationship between penetration obtained with an unyawed 

projectile and that of a yawed projectile. Figure 3 illustrates the setup of the ballistic 

experiments.

Fig. 3 Setup of the ballistic experiments

The distance from the muzzle of the gun barrel for the 7.62-mm APM2 projectile 

and the target face was 4.52 m (15 ft). The primary velocity measurement tool for 

the 7.62-mm APM2 projectile was 2 sets of orthogonal 150-kV flash X-rays in front 

of the target strike face. The spacing between the striking face X-rays was 254 mm 
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(10 inches) from center to center. The spacing from the center of the closest striking 

X-ray and the target face was 381 mm (15 inches). The flash X-rays capture 

orthogonal images of the projectile at 2 times. The images can be corrected to 

determine the actual distance traveled during the time interval between X-ray 

flashes. Analysis of the X-ray images includes the projectile orientation relative to 

the shot line in addition to locating the center of mass of the projectile in each 

image. These data determine the projectile velocity as well as the projectile pitch 

and yaw. The ballistic launch view is shown in Fig. 4. The experimental target 

fixture is shown in Fig. 5.

Fig. 4 Ballistic launch view

Fig. 5 Experimental target fixture with plate oriented in transverse direction for testing
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Three Oehler Model 57 IR screens near the muzzle of the gun barrel were used as 

a backup system for the projectile velocity measurements. These instruments 

optically detect the passage of a projectile across a plane that is normal to the shot 

line. The separation between the light planes, coupled with the time that the light is 

interrupted, permits the projectile velocity to be computed but does not provide a 

method for determining pitch or yaw. Since the X-ray system worked for all tests, 

the data from this backup system were not used. 

Semi-infinite penetration occurs when the projectile is fired into a target where the 

thickness is such that the rear surface is not deformed. The target is sectioned, and 

the penetration normal to the original impact face is measured. For each shot, the 

impact velocity, projectile pitch, projectile yaw, and depth of penetration into the 

AZ31B-H24 targets were recorded. 

3. Ballistic Results

This first set of data was intended to be at a constant velocity of 457 m/s to capture 

the rigid mode of the penetrator. In practice, the impact velocities varied from 440 

to 473 m/s. The desired limit for total yaw was 0.5°. The measured total yaw values 

ranged from 0.93 to 1.85°. Table 1 shows the data for this series of shots.

Table 1 Experimental data

Shot ID Direction Velocity

(m/s)

Penetration

(mm) Yaw

12684 RD 444 21.5 1.28

12685 RD 458 26.2 0.93

12686 TD 473 27.7 1.39

12687 TD 440 23.5 1.22

12688 ND 466 24.3 1.85

Notes: RD = rolling direction, TD = transverse direction, and ND 

= normal direction.

It is interesting to note the difference in slope between the transverse direction shots 

and the rolling shots, as shown in Fig. 6.
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Fig. 6 Initial penetration trends 

The highest-penetration rolling direction shot impacted at a total yaw of 0.93. The 

lower penetration rolling direction shot had a yaw of 1.28, and the 2 transverse 

direction shots had yaws of 1.28 and 1.22. From this data set, there is not sufficient 

data to draw conclusions regarding the role that yaw plays.

Figure 7 shows the sectioned target for shot no. 12688, fired in the normal direction 

orientation followed by Fig. 8, which shows an outline of the target crater and 

projectile core profiles. The outlines more clearly indicate that the crater is not 

symmetric, with a larger crater in the yaw direction. This is a direct indication that 

the loading on the projectile is not symmetric. For rigid projectiles impacting 

relatively soft low-density targets, this can result in shallower penetrations as the 

projectile deviates from the shot line. Riegel4 showed how repeatable penetrations 

can be obtained with yawed impacts that are substantially shorter than penetrations 

with zero yaw impacts. Unlike eroding projectiles that form a crater in the target, 

rigid penetration results in a crater that is in contact with the projectile body.

Fig. 7 Normal direction, shot no. 12688, yaw = 1.85°
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Fig. 8 Dimensionless outline of the penetrator core and target crater from shot no. 12688 

with 1.85° of yaw

The sectioned target for shot no. 12685 is shown in Fig. 9. That shot was fired in 

the rolling direction and was at the lowest yaw, 0.93°, obtained during the series. 

Figure 9 illustrates that the jacket is being stripped in a more symmetric manner 

than seen in shot no. 12688 and shows that the core has rebounded from the point 

of maximum penetration. The cross section implies that the projectile had a lower 

yaw, consistent with the yaw measurement. The targets were sectioned along the 

shot line so the depth of penetration could be more clearly visualized.

Fig. 9 Rolling direction, shot no. 12685, yaw 0.93°

Figure 10 is an etched optical image of shot no. 12685, indicating the depth of 

plastic deformation or flow. The region is relatively constant, extending beyond the 

projectile.
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Fig. 10 Shot no. 12685: penetration into normal direction channel showing jacket stripping 

and core rebound

Figure 11 is the view of the penetration produced when the Mg was shot in the 

transverse direction. The jacket is being stripped in a more symmetric manner than 

seen in shot no. 12688, and the core has rebounded from the point of maximum 

penetration.

Fig. 11 Transverse direction

4. Conclusion and Future Considerations

The experiments conducted in this report are an examination into the effects of 

grain orientation on ballistic penetration. From our results, the following 

conclusions can be deduced:

• Yaw reliability was limited in consistently firing a small-arms projectile at 

0.5° or less. There were not sufficient data to determine the effect of yaw 

on the penetration in the semi-infinite blocks. 
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• The shots fired here were intended to be replicated at the same velocity to 

establish the repeatability of the shots and determine the difference in 

penetration as a function of the material orientation. There was slightly 

more scatter than desired in the impact velocities.

For future considerations, impacts over a wider velocity regime should be 

considered to capture the spectrum of failure from the projectile into the semiinfinite Mg plate. The higher-velocity regimes will also provide data regarding how 

yaw affects penetration at those velocities.

Improvements to the experimental methodology or the use of a gas gun may be 

considered to control the variability of the yaw. Capturing the plastic flow fields in 

the microstructural analysis at the penetration zone will provide the extent of the 

material damage and will be the basis of future work. 
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5. References

1. Jones TL, DeLorme RD, Burkins MS, Gooch WA. Ballistic evaluation of 

magnesium alloy AZ31B. Aberdeen Proving Ground (MD): Army Research 

Laboratory (US); 2007 Apr. Report No.: ARL-TR-4077.

2. Powers B, Dwivedi A, Walter T, Williams C, Meredith C, Ligda J, Schuster 

B, Casem D. AMX602 – fundamental penetration experiments and basic 

mechanical characterization. Proceedings of AMX602 Interest Group 

Workshop; 2014 Oct; Aberdeen Proving Ground, MD.

3. Jones TL. Development of a ballistic specification for magnesium alloy

AZ31B. Aberdeen Proving Ground (MD): Army Research Laboratory (US);

2008 Dec. Report No.: ARL-TR-4664.

4. Riegel JP III. The analysis and reporting of V50 – should we do better? 

Proceedings of the 27th International Symposium on Ballistics; 2013 Apr; 

Freiburg, Germany.

5. Yaziv D, Rosenberg Z, Riegel JP III. Penetration capability of yawed long rod 

penetrators. Proceedings of the 12th International Symposium on Ballistics;

29 Oct–1 Nov 1990; San Antonio, TX.
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