Deformed microstructure evolution in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s−1

Deformed microstructure in AM60B Mg alloy under hypervelocity impact at a velocity of 5 km s−1 were investigated through optical microscope, scanning electron microscope and transmission electron microscope. The results show that four deformed zones around the crater can be classified based on the different deformed microstructure, including ultrafine grain zone, ultrafine grain and deformation twin zone, high and low density deformation twin zones. The dislocation slipping, deformation twins and ultrafine grains are the dominant components in the four deformed zones, and the evolution of deformed microstructure is speculated based on the deformed microstructure observed in four zones. Slipping and twinning play a critical role for the formation of the dynamic recrystallized grains, and twinning-induced rotational dynamic recrystallization mechanism is thought to be the main mechanism for the formation of ultrafine grains. The microhardness and dynamic compressive strength in different deformed zones were measured, and the high microhardness and yield strength in ultrafine grain zone should be attributed to the strain hardening and grain refining.