Bauman Moscow State Technical University, Moscow, Russia:

A. G. Grigoryants, Head of Department of Laser Technology in Mechanical Engineering
I. N. Shiganov, Professor at the Department of Laser Technology in Mechanical Engineering, e-mail: inshig@bmstu.ru
D. M. Melnikov, Associate Professor at the Department of Laser Technology in Mechanical Engineering
A. I. Misyurov, Associate Professor at the Department of Laser Technology in Mechanical Engineering

This paper examines an laser shock peening technique designed to reduce residual tensile stresses in welded aluminium joints. The technique implies bombarding the target surface with strong short duration laser pulses. A solid-state Solar LQ 829 laser with the wave length of 532 nm was used in the study. For pulse transmission, the target surface is coated with an absorbent, which helps enhance ablation and protect the surface from melting. What material should be used for coating is dictated by the substrate material, as well as by the density and speed of sound, which may create acoustic impedance. The absorbing coating should have a transparent medium with a high acoustic impedance value above it, which is essential for redirecting the shock wave energy. The laser ablation conditions create a highly directional impact, which is what causes a greater depth of peening. The authors conducted analysis and a series of tests to identify what absorbing materials and protective medium would work better. It was established that, as suggested by the results of microhardness tests, the best performance can be achieved when aluminium foil is used as an absorbent (it should be taped to the target surface with the help of flexible adhesive tape), and water — as a protective medium. Welded AlMg6 alloy joints were laser shock peened. This helped convert the after-welding tensile stresses into compressive stresses 3–4 times higher than before processing, which helps enhance the mechanical properties.
This research was funded by the Russian Science Foundation under the Grant No. 171901706.

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