Research On The Effect Of Laser Cladding Micropores And Reinforcing Particles On Laser Shock Processing And The Crack Propagation Behavior In Al Alloy

Laser cladding is one of the effective methods to improve the surface properties of Al alloys.However,micropores,micro-cracks and other defects are prone to appear in the cladding layer,and it is difficult to achieve the desired strengthening effect.In order to solve the problem of surface performance degradation caused by micropores in cladding layer,this paper takes Al alloy as an example,by adding reinforcing particles(SiC)in laser cladding powder,and then treated by laser shock processing(LSP).ABAQUS finite element software is used to simulate the effects of micropores and Reinforcing particles on shock wave velocity,surface plastic deformation,energy change and residual stress field during LSP.Thereafter the finite element expansion method(XFEM)is used to study and predict the effect of Reinforcing particles on fatigue crack propagation behavior after LSP.The main results are as follows:(1)The effects of micropores: The simulation results show that the micropores in laser cladding Al alloy hinders the propagation of laser shock wave.The velocity decreases once when the shock wave passes through a layer of micropores.Finally,the velocity decreases by about 3.94% through all the micropores.When the shock wave passes through the micropores,the stress decreases instantaneously,and attenuates remarkably at the beginning stage.The attenuation will weaken with the increase of the distance.At the same time,micropores changes the energy ratio in the substrate and increases the internal energy of the substrate,which is stored in the substrate in the form of more plastic strain and residual stress,significantly affecting the distribution of residual stress.After LSP,the residual compressive stress is introduced around the micropores,which is similar to shape of "four-leaf clover" and provides favorable conditions for restraining the initiation and propagation of cracks.(2)The effects of Reinforcing particles: The simulation results show that after LSP the cladding layer,the reinforcing particles make the plastic strain penetrate deeper into the substrate and introduce deeper residual stress.During the process of crack propagation,the reinforcing particles interfere with the stress field at the crack tip and reduce the stress concentration at the crack tip in the substrate.In the case of the same reinforcing particle size in the cladding layer,with the increase of particle volume fraction,the plastic strain decreases correspondingly and the ability to inhibit crack growth is improved.With the same particle volume fraction,the number of particles increases and ability to suppress crack propagation increases with the decrease of particle size.(3)The residual stress,microhardness,microstructures and fatigue crack growth life of the Al alloy are analyzed by experiments.It was verified that laser shock strengthening and strengthening particles could improve the surface properties of the substrate.The change trend of experiment and simulation is consistent.The slight difference is due to the small size of the model used in numerical simulation,which enlarges or neglects the effect of some related factors.