Abstract: Achieving ballistic impact resistance in a lightweight magnesium (Mg) alloy is a requirement of the aerospace and military industries. However, Mg alloy has poor ballistic impact resistance, mainly attributed to its soft nature and hexagonal close-packed (HCP) crystal structure. In the current study, we reported that the die-casted Mg-Gd-Y-Zn (WEZ) alloy displayed high ballistic impact resistance against a 7.62 mm steel core projectile under both low and high-velocity impact. Most specifically, a perfect ballistic impact resistance is achieved at velocities of 344 and 605 m s^-1, having a depth of penetration of ∼ 12 and ∼25 mm, respectively. In addition, for a very high velocity of 810 m s^-1, the projectile was impeded in the sheet but at the cost of a small hole/scab on the rear face. The potential reason is the “fibrous microstructure”, comprised of profuse blocky type long period stacking order (LPSO_s), rod type LPSO_s, lamellar LPSO_s, and some rare earth (RE) enriched precipitates. These “microstructure features” act like a fiber reinforced α-Mg and play a decisive role in achieving high strength at super elevated temperature compression (500 ℃) under a high strain rate (∼ 4000 s^-1), even much higher compared to 4000 s^-1 at room temperature. As a result, this characteristic of WEZ Mg alloy leads to a high absorption capacity at elevated temperatures (90.83 ∼ MJ m^-3). This high absorption capacity due to high strength at elevated temperatures, fibrous microstructure, and hardness (∼ 80 HV) offered high resistance to impact and shock wave propagation. Consequently, the projectile experienced a high resistance against perforation, and therefore, ballistic impact resistance was achieved. Last but not least, the post-deformation features also help in understanding the stress mitigation of WEZ Mg alloy during ballistic impact, which can be advantageous while designing Mg alloys as a ballistic impact-resistant material.

Key words: WEZ Mg alloy, Ballistic impact resistance, Hardness, 7.62 mm projectile, Projectile velocity, Stress mitigation