Mold-free fs laser shock micro forming and its plastic deformation mechanism

Mold-free micro forming using a fs laser was investigated by producing micro pits on pure aluminum foil. The characteristics of the pit profiles, their forming mechanisms, and the influences of some important parameters on the pit profiles were investigated by measuring the profiles and the surface morphologies of the pits. The microstructures of the shocked aluminum foil were observed through transmission electron microscopy (TEM). Pits obtained through fs laser shock forming are composed of two regions: the directly impacted region and the plastically bending region. Diameters of the former strongly depend on laser beam sizes. The plastically bending region has a negative effect on forming precision. Shorter laser pulse width is beneficial for narrowing the range of the plastically bending region and enhancing the forming precision. Using a single-side clamping mode can also narrow the plastically bending region through buffering the local bending. Fs laser-induced microstructures are characteristic of fragmentary short dislocation lines and parallel slip lines, which are the results of the ultrafast and ultrahigh pressure loading. The localization of the fs laser shock forming induced by ultrafast loading can enhance the precision of mold-free forming. •Mold-free fs laser formed pits include: directly impacted region and bending region.•The entrance diameters of directly shocked region mainly depend on laser beam size.•Shorter laser pulse width is favorable for enhancing forming precision.•Single-side clamping also can narrow plastically bending region.•Two unique microstructures have been found in fs laser shocked aluminum foil.