Microstructure Dependence of Spall failure in Mg-Al alloys at Extreme Strain Rates

Understanding the links between microstructure and material failure is crucial for designing advanced materials in order to withstand extreme dynamic environments. Spall failure is a dynamic failure mechanism which limits material performance at high strain rates, but our understanding of the influence of microstructure on the spall strength is limited. One contradictory concept to design for spall strength lies in some models that suggest that increasing the static yield strength may improve the spall strength. However, processing steps that might increase the static yield strength may also affect the quantity of failure nucleation sites in the material, which may have deleterious effects on spall resistance. Here, we examine the spall failure of various Mg-Al systems with model microstructures through high-throughput laser-driven micro-flyer (LDMF) impact experiments. Various processing techniques are used to create eight distinct microstructures among two compositions, and the spall response of these are compared to that of their as-cast counterparts. The LDMF method allows us to detect differences in spall strength with relatively small microstructure changes. The spall strength is observed to be critically undermined by the presence of precipitates in the microstructure, as a result of processing techniques used to incrrease static yield strength.