High-speed impact behavior of a casting AM80 magnesium alloy under various deformation temperatures

Abstract

Split-Hopkinson pressure bar tests were conducted on a solution-treated cast AM80 Mg alloy at 298, 423 and 523 K with strain rates (SRs) ranging from 1100 s−1 to 5000 s−1. The effects of the SR and temperature on the high-speed impact behavior and corresponding microstructure evolution were investigated. The results indicate that the flow stress behavior of the studied alloy strongly depends on the applied SR and deformation temperature. At all temperatures, the SR sensitivity (SRS) changes from positive to negative values as the applied SRs increase to their critical values. Several adiabatic shear bands (ASBs) appear at 298 K with a SR of 5000 s−1. At elevated temperatures of 423 and 523 K, mechanical twins and dislocations are gradually replaced by dynamically recrystallized grains with increasing SR. A fully recrystallized microstructure forms as the applied SR increases to 5000 s−1. The Dynamic recrystallization (DRX) is mainly induced by twinning that preferentially nucleates at the twin boundaries and intersections between the twin boundaries and grain boundaries. The adiabatic temperature rise and corresponding microstructure evolution, including the ASBs and DRX, are attributed to the negative SRS of the studied alloy because the applied SRs exceed their critical values.