Study on the Dynamic Instantaneous Precipitation of ZK60-T4 Magnesium Alloy Under High Strain-Rate Loading

The commercial ZK60 magnesium alloy processed by solution heat treatment was dynamically loaded with a high strain rate by means of the split Hopkinson pressure bar (SHPB), and the dynamic instantaneous precipitation of second phases was investigated in the present work for the first time. TEM observations indicated that the β´₁ with average length/diameter of 68.24–19.27 nm and β′₂ phases with an average diameter of 16.15 nm precipitated within the dynamic deformation time of 180 μs at 3000 s⁻¹. The adiabatic temperature rise generated by the dynamic deformation increases the atomic diffusion coefficient of solute atoms, which contributes to the generation of precipitated phases. Therefore, the precipitation of the second phases is thermodynamically feasible. It is also feasible to kinetically accelerate the rate of atomic diffusion to eventually lead to the instantaneous precipitation of the mass of the β′₁ and β′₂ phases, due to the combined effects of adiabatic temperature rise, high deviatoric stresses, high-density dislocation (vacancies) formed by the dynamic loading, and the initial supersaturated vacancies formed by the T4 treatment. Since the high-density dislocation was generated and the numerous reinforcing phases (β′₁ and β′₂) were precipitated in the matrix during deformation, the Vickers hardness values of alloy increased from 64.4 HV to 93.1 HV.