Full wave profiles were monitored by the laser interferometry method by means of a VISAR laser Doppler velocimeter under shock-wave loading of samples of AMg6 aluminum alloy. Analysis of these profiles was used to study the laws of elastic precursor formation and its amplitude variation during elastic–plastic transition front propagation in samples loaded by a shock wave of variable intensity. Critical stresses leading to the spall fracture of samples were determined as dependent on the strain rate under unloading.