| Electrically assisted laser shock composite strengthening is a new strengthening method.Compared with laser shock processing(LSP),the introduction of pulse current can reduce the flow stress of the material,enhance the plasticity of the material in the deformation process,resulting in deeper hardening layer,higher surface hardness and residual compressive stress after composite strengthening,which makes the strengthening effect more significant.At present,there are few researches on the electrically assisted laser shock composite strengthening,so the influence of composite strengthening and its related process parameters on the strengthening effect of materials is worthy of further study.This paper takes 2024-T4 aluminum alloy as the research object.The parameters of Johnson-Cook(JC)constitutive model were obtained by uniaxial tensile and split Hopkinson pressure bar(SHPB)test.Based on the combination of theoretical analysis,numerical simulation and experimental research,the influence of composite strengthening on the distribution of residual stress was explored,and the influence of composite strengthening process parameters on the strengthening effect was analyzed.The following are contents and conclusions of this paper:(1)The stress-strain curves of 2024-T4 aluminum alloy under the action of pulse current and high strain rate were obtained by uniaxial tensile test without the electricity assistance at room temperature,uniaxial tensile test with electricity assistance and SHPB with high strain rate.The results show that the flow stress decreases and the elongation increases with the increase of current density,duty ratios and current frequency.The material has obvious strain hardening characteristics and the strain rate sensitivity effect is not significant at room temperature.According to the experimental results,the parameters of JC constitutive model coupling electrical parameters were obtained.(2)The finite element model of electrically assisted laser shock composite strengthening was established with JC constitutive model paraments obtained from experiments.The residual stress distribution of 2024-T4 aluminum alloy under different strengthening processes was analyzed,and the effect of composite strengthening process parameters on residual stress distribution was studied.Compared with LSP,the residual stress distribution of composite strengthening is more uniform and gentle,the depth of action layer is deeper,and the stress distribution is obviously better than that of LSP.The change of power density and pulse width affect the stress distribution after composite strengthening.The current density has a great influence on the stress distribution,and the depth of the interaction layer increases with the increase of the current density,but when the current density is too large,the surface residual compressive stress decreases.The change of the duty ratio will affect the distribution of the residual stress after the composite strengthening.(3)According to the above simulation study on parameters,the reasonable technological parameters were selected to strengthen 2024-T4 aluminum alloy samples.And the residual stress,microstructure and microhardness of the strengthened samples were tested.The results are as follows: The distribution of residual stress under different current density is the same as that obtained by numerical simulation.The significance test of difference between simulated and measured residual stress was in progress.The results show that there is no significant difference between the two groups of data,which verifies the reliability of the composite reinforcement numerical simulation.The current density has a significant influence on the microstructure of the composite strengthened specimen.With the increase of current density,the deeper the grain refinement layer is.The microhardness of the sample increases with the increase of current density,and the depth of hardened layer also increases. |
PDF Full Text Request