晶粒尺寸对高纯铝板材层裂特性的影响

采用不同热处理工艺制备了3种晶粒尺寸（60、100、500 μm）的高纯铝板材，利用平板撞击实验研究了其层裂行为。通过改变飞片击靶速度，在靶板中实现初始层裂状态和完全层裂状态。基于自由面速度时程曲线和微损伤演化及断口显微形貌分析，讨论了晶粒尺寸对高纯铝板材层裂特性的影响规律。实验结果显示:（1）晶粒尺寸对高纯铝板材层裂特性的影响强烈依赖于冲击加载应力幅值，在低应力条件下，层裂强度与晶粒尺寸之间表现出反Hall-Petch关系，而在高应力条件下，晶粒尺寸对层裂强度几乎没有影响；（2）随着晶粒尺寸的增大，靶板损伤区微孔洞的尺寸和分布范围均增大，但数量显著减少，在微孔洞周围还发现比较严重的晶粒细化现象；（3）随着晶粒尺寸的增大，层裂微观机制从韧性沿晶断裂向准脆性沿晶断裂转变，且在断口上观察到少量随机分布的小圆球，归因于微孔洞长大和聚集过程中严重塑性变形引起的热效应。

Effects of grain size on the spall behaviors of high-purity aluminum plates

High-purity (HP) aluminum plates were cold rolled and heat treated to produce recrystallized samples with average grain sizes of 60, 100 and 500 μm, respectively. The effects of grain size on the spall response of HP aluminum plates were investigated by plate impact experiments including real-time measurements of the free surface velocity profiles by a compact all-fiber displacement interferometer system for any reflector, and post-impact fractography of soft-recovered samples by optical microscopy and scanning electron microscopy. The effect of grain size on the spall strength depends on the amplitude of peak stress. At lower peak stress loading, the dependence of the spall strength on the grain size is an inverse Hall-Petch relationship, but at higher peak stress loading, the spall strength is nearly constant with little effect of grain size. With the increase of grain size, the distribution range and size of micro-voids in the damaged sample increase, but the number of micro-voids decreases, and the grain refinement caused by the shock compression process is observed. On the other hand, with the increase of grain size, the mechanism of spallation changes from ductile intergranular fracture to quasi-brittle intergranular fracture. Some randomly distributed small metal balls are observed on the fracture surface, which is attributed to the thermal effect due to the serious plastic deformation during the growth and coalescence of micro-voids.