Effect of ablative and non-ablative Laser Shock Peening on AA7075-T651 corrosion and fatigue performance

Sanchez Araujo, Alvaro, Gonzalo, Leering, Mitchell, Glaser, Daniel, Fitzpatrick, M.E., Wharton, Julian and Reed, Philippa (2021) Effect of ablative and non-ablative Laser Shock Peening on AA7075-T651 corrosion and fatigue performance. Materials Science and Technology. (doi:10.1080/02670836.2021.1972272). (In Press)

Abstract

The fatigue performance from pre-corroded pits was studied for laser shock peening of aluminium alloy AA7075-T651 (UNS A97075) with and without a protective ablation layer. Surface and microstructural characterisation showed laser shock peening generated high residual stress fields of up to –400 MPa, limited hardness increase, and moderate surface roughness increase. The laser shock peened specimens were exposed to 3.5 wt.% sodium chloride solution for different levels of galvanostatic control. The compressive residual stresses did not significantly affect the corrosion behaviour, corrosion pit morphology or pit depth. Laser-shock-peening-induced surface roughness was shown to have the most detrimental impact on corrosion performance. Fatigue testing of pre-corroded AA7075-T651 showed pits act as stress concentrations, causing cracks to initiate shortly after dynamic loading, and causing a reduction of at least 50% of its fatigue life. The laser shock peening markedly increased fatigue life, by up to 400% compared to corroded untreated AA7075-T651, due to the residual stresses effectively counteracting the stress concentrations produced by these pits. Laser shock peened AA7075-T651, that suffers subsequent pitting corrosion, can be expected to still have fatigue performance and a lifetime equivalent or better than uncorroded unpenened AA7075-T651.

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Contributors

Author: Alvaro, Gonzalo Sanchez Araujo

Author: Julian Wharton

Author: Philippa Reed

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