Study On Mechanical Properties And Microstructure Morphology Of 2024-T4 Aluminum Alloy By Pulsed Current Assisted Laser Shock Processing

With the continuous development of the industry,higher requirements are put forward for the comprehensive performance of aluminum alloy components.However,traditional strengthening technologies,including mechanical shot peening,cold extrusion,heat treatment,etc.,have problems such as long processing cycles,complicated technological processes,and unsatisfactory strengthening effects.Laser shock processing is an effective surface strengthening method.It can form a deeper residual compressive stress layer near the surface area of the strengthened component and can refine the crystal grains.However,when the workpiece is thick,the strengthening effect is limited.The pulse current assisted machining(PECM)technology can input a variety of energy coupling fields(thermo-electro-mechanical)into the material in a very short time,which can change the microstructure of the material and reduce the flow stress.Therefore,the current will form a larger residual compressive stress and a thicker plastic deformation layer,and then improve the strengthening effect.This paper mainly focuses on the experiment,and combines the theoretical analysis and numerical simulation method,first of all,analyzes the feasibility of the electric assisted reinforcement,then analyzes the distribution of thermal power field by the method of coupling numerical simulation and test of thermal power field.Finally,the mechanical properties and microstructure of 2024-T4 aluminum alloy components are studied after pulse current assisted laser shock,and the analysis is explored The strengthening mechanism is also discussed.The main contents and relevant conclusions are as follows:(1)The model of thermo-electric coupling is established by ANSYS numerical analysis software,and the influence of pulse current with different parameters on thermo-electric field distribution is analyzed by combining with the experimental results of actual temperature measurement.The results show that the skin effect,temperature rise rate,final stable temperature and temperature stable time will increase with the increase of peak current,duty cycle and frequency.The peak temperature and temperature rise efficiency will increase with the increase of frequency,when the frequency is higher,the skin effect will be more obvious,and the current density on the surface will be significantly higher than that of the inside of the sample,and the difference between the current density of the surface and the inside of the sample will increase as the frequency increases.(2)Pulse current assisted laser shock processing tests were performed on 2024-T4 aluminum alloy samples under different methods and different current densities,and the microhardness,residual stress distribution and tensile properties of the 2024-T4 aluminum alloy under different processes were studied.The results show that compared with the single laser shock processing,the two treatment methods of pre-energization and cooperative energization assisted strengthening have obtained higher microhardness and residual stress,and the cooperative processing has improved more,and the post-energized assisted strengthening has a smaller negative gain.Compared with single laser shock processing,the tensile strength of pulse current assisted laser shock processing is obviously improved,and the elongation is not significantly reduced.(3)Through the observation of the microstructure of the material,it is found that the average size of the crystal grains on the surface of the material is reduced to 50?m(LSP)and30?m(LSP-DAE)from 75?m of the untreated sample,and the laser shock processing during applying electropulsing(LSP-DAE)treatment,obvious recrystallized fine grains appeared on the surface of the material;after LSP-DAE treatment,depth of the grain refinement layer in the thickness direction reached 510?m,and the grain size was also significantly smaller than that of untreated and single laser shock processing sample.By analyzing the XRD patterns,it is found that the FWHM of(200)peak of LSP-DAE treated samples is larger than that of LSP and untreated samples.(4)Through the fatigue test,it is found that after LSP-DAE and LSP treatment,the fatigue life is increased by 119.19% and 79.96% respectively compared with the untreated sample;because LSP-DAE forms a deeper residual compressive stress layer and grain refinement layer in the near surface area than single LSP treatment.The deeper grain refinement layer and residual compressive stress layer causes the growth rate of fatigue cracks to decrease,and the main crack growth area is also restricted to a smaller area.A great part of the main propagating crack is confined to the middle region of the specimen.It grows for a distance perpendicular to the thickness direction and approximately parallel to the water flow,and then spreads to the surface in a fan shape.According to the theoretical analysis,it is revealed that the LSP-DAE treatment is due to the introduction of a variety of energy fields at the same time and the laser shock wave acting on the sample,so as to improve the comprehensive properties of the material.