Study On Surface Integrity Of LY2 Aluminum Alloy Planished By Laser Shock Wave

In this paper,a metal surface planished process based on laser shock wave effect is presented(Laser shock wave planishing,LSWP).This technology has a layer of contact foil between the restraint layer and the substrate surface compared with the conventional laser shock peening.By using the laser shock wave pressure acting on the contact foil,the rough surface of metal is "planished" to become a smooth and strengthened surface.Thus this technology will solve the shortcomings of the conventional laser shock peening in the control of roughness.In this paper,the aeronautical LY2 aluminium alloy is used to study the deformation law of surface micro-feature and the planishing effect of CNC milling surface when treated by LSWP.The main results are as follows:(1)A periodic micro-groove-feature was fabricated on the surface of LY2 aluminum samples with a picosecond laser system.The profile changes of micro-feature after LSWP process with different laser energy was analyzed.The experimentally results showed that the micro-feature became a flat-top shape with upsetting deformation.The peak height of the micro-feature decreased continuously,while the bottom of the micro-feature uplifted first and then sank with the increase of laser power intensity.(2)The dynamic deformation process of micro-feature in the LSWP treatment and the influence of other process parameters were further discussed by using finite element analysis technology.It was found that the bottom of micro-feature was dragged down and extruded upward by the surrounding materials at the same time in the process of LSWP,and the final function of extrusion was greater than that of drag with the appropriate laser energy.The dynamic deformation process of micro-feature under one impact LSWP could be divided into four stages: static stage-planished stage-confined rebound stage-unconfined rebound stage.The effect of LSWP was gradually weakened with the increase of impact times due to the deformation resistance enhancement and the strain hardening effect of material in multi LSWP impacts.The thickness of the contact foil would directly affect the laser shock wave energy transmitted to the workpiece,so a appropriate thickness of the contact film was beneficial to the effect of LSWP.(3)LSWP treatment of CNC milling surface was studied experimentally.The results showed that LSWP can effectively shallow the milling cutter marks,and it was related to the smoothness of contact foil working surface,the coarser the contact foil,the higher the removal of the workpiece milling marks.For surfaces with different roughness,there was a corresponding contact foil with appropriate roughness,which could minimize the roughness of the workpiece.By selecting a contact foil of suitable roughness,LSWP could greatly reduce the NC machining surface with high initial roughness and simplify the CNC milling process.LSWP could also induce residual compressive stress and increased the surface microhardness of the workpiece.In multiple LSWPs,the surface roughness of the contact foil in the previous LSWP treatment will seriously affect the effect of the latter LSWP,so choicing a suitable roughness of the foil contact surface is particularly important.