Study On The Effect Of Contact Film On The Surface Integrity Of LY2 Aluminum Alloy Planished By Laser Shock Wave

Given in the difficulty of controlling the surface topography of aero-engine compressor blades by laser shock processing(LSP),laser shock wave planishing(LSWP)technology is proposed,which is originated from LSP,only a layer of contact film is added between the absorbing layer and the workpiece,and the smooth bottom surface of the contact film is closely attached to the surface of the workpiece.Under the action of the high-pressure shock wave,the micro peaks and valleys on the surface of the workpiece are flattened by the contact film and plastic deformation occurs,thereby achieving the performance of smoothing and strengthening.In this thesis,LY2 duralumin alloy is taken as the research object,the effect of the contact film material on the deformation law of surface microfeatures in the LSWP technology and the effect of the contact film thickness on the surface integrity of the milled sample are explored.The results are as follows:(1)ABAQUS is used to simulate the deformation law of surface micro features under the LSWP with four different contact film materials.It is found that the smaller the contact film density is,the better the flattening effect of micro peaks is.The higher the strength of contact film is,the better the lifting effect of micro valley is.The contact film with high elastic modulus is also conducive to the uplift of micro valley.(2)Picosecond laser was used to fabricate the same micro features on the surface of LY2 aluminum alloy,and the two-dimensional cross-section deformation of micro features after LSWP with four contact film materials was analyzed.The results showed that the top of micro features is upset and deformed,showing a flat top shape,but the change of bottom of micro features was different.When high strength contact film was used,the micro concave valley rose,while when low strength contact film was used,the micro concave valley sank.The experimental results are consistent with the simulation results.(3)The effect of contact film thickness and surface roughness on the milled surface processed by LSWP technology is comprehensively studied.The results show that LSWP can effectively remove the milling marks on the workpiece surface,and the removal rate of milling marks is closely related to the thickness of contact film.The thinner the contact film is,the higher the removal rate of the milling marks is.However,the contact film is too thin to decrease surface roughness.For the milling surface with smaller surface roughness,using thin contact film would cause ‘collapse' of the workpiece surface and the surface profile would be damaged.Therefore,each kind of roughness of the milling surface must correspond to the appropriate contact film thickness,which can not only reduce the surface roughness to the minimum,but also maintain the surface accuracy.In multiple LSWP,it is found that when the surface roughness of the milling surface matches the contact film thickness,the surface roughness of the milling surface decreases with the increase of LSWP times;otherwise,the surface roughness increases.The results show that if the thickness of contact film is appropriate,the edge effect will be suppressed in overlapping LSWP.In addition,the micro convex peaks and micro concave valleys on the surface of the workpiece squeeze each other,resulting in the residual stress on the surface of the workpiece.At the same time,the microhardness also increases due to the deformation hardening.