Theoretical analysis of ionization of spherical aluminum alloy projectile impacting aluminum alloy target in hypervelocity impact

A two-stage light gas gun is used to accelerate the sphere 6061 aluminum projectiles to a speed range of 2.3-6.3 km/s in an almost vacuum environment. Spectrometer and pyrometer are adopted to measure the time-frequency characteristics of the collision-generated spectra when 6061 aluminum projectiles impact on 6061 aluminum targets with thicknesses varying from 1 mm to 26 mm. Based on the thermal ionization, theories of the single and the secondary collision are established. Experimental spectra show that threshold velocities of evaporation and plasma phase transition are 2.45 km/s and 4.7 km/s when spherical aluminum alloy projectile impacts on aluminum alloy target. Theoretical calculation demonstrates that neither the single impact nor the secondary impact of debris or secondary compression in the oblique direction can explain the ionization at low-speed impact. The threshold velocity of ionization, however, calculated by the combined secondary collision both in the oblique and horizontal direction during the impact of spherical projectile colliding on the target is most reasonable to explain the plasma produced by relatively low-speed hypervelocity impact.