<p>The commercial ZK60 magnesium alloy with extruded state experienced aging heat treatment (T6) was dynamically loaded at strain rate of 3000 s⁻¹ by means of the split Hopkinson pressure bar (SHPB) in this paper. Transmission electron microscopy (TEM) observations showed that the precipitated <i>β</i>′₁ phases partially dissolved (spheroidized) with blurred interfaces within 160 µs at 3000 s⁻¹. The average length and diameter of the rod-shaped <i>β</i>′₁ phase particles were 48.5 and 9.8 nm after the T6 heat treatment; while the average diameter of the spherical <i>β</i>′₁ phases changed to 8.8 nm after loading. The deformed <i>β</i>′₁ phase generated larger lattice distortion energy than Mg matrix under high strain rate loading. Therefore, the difference of free energy (the driving force of dissolution) between the <i>β</i>′₁ phase and the matrix increased, making the instantaneous dissolution of the <i>β</i>′₁ phase thermodynamically feasible. The dissolution (spheroidization) of the <i>β</i>′₁ phase particles was kinetically promoted because the diffusion rate of the solute Zn atoms was accelerated by combined actions of adiabatic temperature rise, high density of dislocations (vacancies) and high deviatoric stresses during high strain rate loading. The increase in hardness of ZK60-T6 alloy could be attributed to solid solution strengthening, dislocation strengthening and second phase particle strengthening.</p>