Effect of laser energy on microstructure of Mg-3Al-1Zn alloy treated by LSP

The microstructural feature, residual stress distribution and bending degree of Mg-3Al-1Zn alloy subjected to laser shock peening (LSP) under different laser pulse energy levels were investigated. The microstructure in the deformed layer was characterized by using transmission electron microscopy (TEM). The effects of different laser pulse energies on the micro-indent, residual stress and arc height were examined by three dimensional (3D) non-contact surface profilometer, X-ray diffractometer and arc height measurements. A nanostructured layer with the depth over 25 μm was fabricated on laser peened Mg-3Al-1Zn alloy with laser pulse energy of 10.5 J. With laser pulse energy increasing, the grain size in the top surface decreased from 1.19 to 2.3 μm for 6.5 J to 0.04-0.27 μm for 8.5 J, and the depth of plastic deformation layer increased from 0.8 mm for 6.5 J to 0.95 μm for 10.5 J. Moreover, residual stress and arc height of LSPed samples increased with laser pulse energy increasing. Grain refinement process in Mg-3Al-1Zn alloy under ultra-high strain rate generated by LSP was mainly due to dislocation slip.