Ultrahigh dense and gradient nano-precipitates generated by warm laser shock peening for combination of high strength and ductility

Abstract

Nanocrystalline materials generated by severe plastic deformation often come with high strength but low ductility due to the inability to accumulate dislocations and thus the low work hardening rate. In this study, a unique high strain rate deformation process – warm laser shock peening (WLSP) – is studied to generate extremely high-density nano-precipitates in precipitation hardenable alloy. Aluminum alloy (AA) 7075 was selected to evaluate the generation of ultra-high-density precipitates by WLSP and the effects on the strength and ductility. WLSP integrates the advantages of laser shock peening (LSP), dynamic strain aging (DSA) and dynamic precipitation (DP). The nanoscale precipitate particles generated by WLSP effectively block dislocations and thus increase the material strength. The precipitate–dislocation interaction has been observed by high resolution TEM (HR-TEM) and modeled by the multiscale discrete dislocation dynamic (MDDD) model. It has been demonstrated that compared with room temperature LSP, WLSP can improve material strength by 32.3% without compromising the ductility, in that elongation remains 20%. These ultra-high-density nano-precipitates greatly improve dislocation accumulation capacity and thus effectively increase ductility.