Magnesium alloys are an attractive material system for protection applications due to their high specific strength and stiffness, but exhibit low ductility in these applications. The potential to address this shortcoming through materials-based-design has motivated the Center for Materials in Extreme Dynamic Environments (CMEDE) to focus on improving Mg systems over the past decade. The plastic anisotropy from the low-symmetry hexagonal-close-packed crystal structure of Mg, as well as defects in the microstructure such as voids and precipitates, may all play roles in spall (dynamic tensile failure at high strain rates), but experimental data assessing the effect of individual microstructure features on spall remains challenging to obtain. We begin the present study by reviewing spall investigations on pure and alloyed Mg from the literature, and then present a large number of spall experiments performed with a laser-driven micro-flyer apparatus on Mg-9Al (wt.%) thin foil specimens with various precipitate morphologies in order to address this shortcoming. The model Mg-9Al binary alloy is warm-rolled and processed in two conditions: (a) fully solutionized with no precipitates, and (b) peak-aged to generate high aspect-ratio precipitates (Mg₁₇Al₁₂ second phase particles/inclusions) with nm-scale thickness and $\mathrm{\mu }$m-scale length on the basal plane. The loading direction is varied between the normal-to and transverse-to rolling directions of the specimen in order to interrogate the effects of both plastic anisotropy of the matrix material and geometric anisotropy of the precipitates on the spall strength. Bayesian analysis of the results enables us to account for instrument uncertainty and microstructure variation in our study. We compare the experiments to numerical simulations using realistic precipitate geometries and spacings from electron microscopy observations, finding a significant decrease in spall strength in the Mg-9Al with precipitates despite the expected increase in quasi-static yield strength.

镁合金由于其高比强度和刚度而成为用于保护应用的有吸引力的材料系统，但在这些应用中表现出低延展性。通过基于材料的设计解决这一缺陷的潜力促使极端动态环境材料中心 (CMEDE) 在过去十年中专注于改进镁系统。Mg 的低对称性六方密堆积晶体结构的塑性各向异性，以及微观结构中的缺陷，如空隙和析出物，都可能在剥落（高应变率下的动态拉伸破坏）中起作用，但实验数据评估单个微观结构特征对剥落的影响仍然具有挑战性。我们通过回顾文献中对纯镁和合金镁的剥落研究来开始本研究，然后展示了使用激光驱动的微型飞行器在具有各种沉淀形态的 Mg-9Al (wt.%) 薄箔样品上进行的大量剥落实验，以解决这一缺点。模型 Mg-9Al 二元合金在两种条件下进行温轧和加工：(a) 完全固溶，没有析出物，和 (b) 峰时效以生成高纵横比的析出物 (Mg₁₇ Al ₁₂第二相颗粒/夹杂物），具有纳米级厚度和$\mathrm{\mu }$基面上的 m 尺度长度。加载方向在试样的垂直和横向于滚动方向之间变化，以询问基体材料的塑性各向异性和析出物的几何各向异性对剥落强度的影响。结果的贝叶斯分析使我们能够解释我们研究中的仪器不确定性和微观结构变化。我们将实验与使用真实沉淀几何形状和电子显微镜观察间距的数值模拟进行比较，发现尽管准静态屈服强度预期增加，但含有沉淀的 Mg-9Al 的剥落强度显着降低。