Residual Stress And Material Performance Of 8090 Aluminum-lithium Alloy By Cavitation Water Jet Peening

Cavitation water jet peening(CWJP)is a new surface strengthening method with the energy released from cavitation clouds collapse,which is generated in a submerge water to impact the surface of metal parts The CWJP technology also has many advantages such as good surface quality,environmental protection,and high versatility.In CWJP technology,the selections of standoff distance,time,and incident pressure are its bases.At the same time,the optimization of multi-process parameters and the strengthening mechanism is less studied.To promote the further development and application of this technology,this paper has carried out systematic research on the above problems.The main contents and conclusions of this paper are as followsBased on the theoretical analysis method,the bubble dynamic model of the single cavitation bubble in the submerged cavitation water jet was established and then solved by MATLAB,by which the variation of motion characteristics and pressure pulsation were obtained.Based on FLUENT,the numerical simulation of the collapse of the near-wall cavitation bubble was carried out.The effects of the distance from the cavitation bubble to the solid wall,the morphology,and mechanical actions of the bubble collapse were obtained.Based on FLUENT,the numerical simulation of cavitating water jet under different incident pressures(P)and nozzle diameters(d)were carried out.The results confirm that the cavitation performance of the jet increases with the increase of the incident pressure,but the further increase of the incident pressure has little effect on the cavitation performance of the jet when P=30MPa to 40MPa.The increase in nozzle diameter also promotes the occurrence of cavitation,but the sum of the vapor volume shows a small decrease at d=1.8mm.Combined with the high-speed photography experiment,the dynamic evolution process of the bubble cloud and the concentrated collapse range of cavitation bubbles were studied.The results show that the cavitation cloud has obvious periodicity including incubation,developing,shedding,and collapse phases in one cycle;the ratio of the concentrated collapse range of cavitation bubbles to the nozzle diameter is approximately the same under same incident pressure.Finally,the ranges of the process parameters related to CWJP were determinedTaking Aluminum lithium Alloy 8090A1-Li as an example,the factors and evaluating indicators involved in optimizing the process parameters of CWJP were introduced.The effects of nozzle diameter,incident pressure,dimensionless standoff distance,and peening time on surface residual stress,surface microhardness,and surface roughness were studiedThe cavitation water jet peening(CWJP)was used to improve the fatigue life N/cycle of 8090A1-Li compared to the unpeened sample.The results confirmed that surface morphology,compressive residual stress,and the micro hardness with CWJP pressure of 30MPa peened region increases to 4.699?m,-147MPa,and 173HV.The CWJP induced the CRS in the 8090A1-Li which increases its operative stress intensity factors of fatigue crack growth(FCG)propagation,fatigue crack initiation(FCI),fatigue striation,and also reduces the size of the dimple.The fatigue life N/cycle of 8090A1-Li was increased by 61.9965%,91.89%,and 111.74%when the impacted pressure increases from 20 to 25 and 30MPaA high dislocation density is formed in the cavitation area of the work-piece which leads to surface hardening.The cavitation effect happens in the collapse area.The results confirm that grain size,micro-strain,and erosive effect of the alloy are significantly affected by different shot peening(SP)pressures Also,the micro-crystalline structure decreases in the cavitation treatment areaThen,the surface integrity of 8090A1-Li alloy by CWJP and the strengthening mechanism were studied The results show that the transition zone of the concave-convex morphology formed by CWJP has the characteristics of continuous smoothness,while the surface roughness is only 3.04?m under high peening strength.The plastic deformation depth reaches the saturation value of 50-55?m.Deformation twins are formed in coarse ?-phase grains.With the increase of peening strength,the surface grains are refined and crystallized,while the average micro-strain increases gradually.The depth of the microhardness field and the residual stress field of the sample can reach-162?m.Except for the over peening condition,the maximum values of the residual compressive stress all appear on the sample surfaces.When the sample is under the over peening condition,cavitation erosion occurs on the sample surface,which leads to a sharp increase in surface roughness and average macroscopic strain,while the surface microhardness increases and surface residual stress decrease greatly.