Experimental Study Of Cavitation Strengthening Of Metal Specimens With Submerged Water Jet

In liquid,as the local static pressure is lowered down to be less than the corresponding saturation vapor pressure and the conditions are maintained long enough,cavitation will be triggered.In as early as late 19 century,the study of cavitation has started,but the understanding of cavitation is only in the areas of damage,such as material erosion,vibration,noise and other disadvantages.Water jet cavitation strengthening is a new type of cold processing technology.It employs cavitation bubbles,which are produced by high jet velocity.And the shock wave produced by bubble collapse acts on material surface,resulting in residual stress on the surface and subsurface.As a consequence,the surface strength and fatigue life of the material are enhanced.Compared with the traditional mechanical shot peening technology,cavitation water jet strengthening can improve the surface quality of the material and reduce the processing cost.The surface of the material strengthened by the submerged water jet cavitation is smooth,clean and low roughness,which can relieve the stress concentration in the material and improve the performance of the material.In this study,the copper alloy and aluminum alloy were tested by water jet cavitation.The microstructure and mechanical properties of the materials are compared,the mechanism of cavitation performance of water jet cavitation is analyzed,obtained the best strengthening process.The surface of copper alloy was strengthened by cavitation water jet equipment.In the experiment,the jet pressure,the time and the target distance were changed by the multi angle contrast analysis.The surface topography of the strengthened samples was scanned by three-dimensional profilometry and the metallographic microscope was observed.The results show that: with the increase of the jet pressure,the cavitation pits on the surface of the specimen become denser and larger,which indicates that the cavitation effect is related to the jet pressure.The optimum process parameters are the jet pressure 300 MPa,the strengthening time is 15 minutes,the target distance is 7cm,and the surface of the material has a better shaping deformation and integrity.The surface of aluminum alloy was strengthened by cavitation water jet equipment.In the experiment,the pressure and time of the jet were analyzed,and the surface morphology of the strengthened samples was observed by metallographic microscope.The results show that the residual stress increases with the increase of time,and the residual stress increases slowly when the reinforcement time is more than 15 minutes,when the strengthening time changes from 0 to 15 minutes.When the jet pressure is in the range of 0~40MPa,the residual stress increased with the increase of consolidation pressure sharply increases,when the jet pressure is greater than 40 MPa,with the increase of jet pressure on residual stress decreased,in strengthening the time for 20 minutes,to obtain the residual pressure of-98 MPa 40MPa stress value.The optimal process parameters are the strengthening time is 10 minutes,the jet pressure is 50 MPa,the hardness value is 399.45 HV,the surface deformation and surface smoothness are better.