| A large number of studies have shown that fatigue failure is one of the main forms of structural materials serving in the aerospace field,accounting for more than 70%,and surface treatment of the material surface is one of the effective measures to improve its fatigue life.As a structural material widely used in the aerospace field,SiC particle-reinforced aluminum-based composite materials have been extensively studied by scholars at home and abroad,mainly focusing on material components,preparation methods and processes,plastic deformation and heat treatment.Research on surface treatment is not sufficient.Therefore,in order to improve the fatigue life of 15%SiCp/2009Al composite materials,this paper carried out experiments on the effects of three surface treatment processes,including sandblasting,vibratory grinding and shot peening on the performance of the material,to explore the mechanism and obtain the optimal process.In this paper,for the blasting process,adjust the different blasting mesh number(40 mesh,60 mesh,80 mesh),blasting pressure(0.1 MPa,0.2 MPa,0.3 MPa,0.4 MPa,0.5 MPa,0.6 MPa)on the sample surface Sandblasted.For the vibration grinding process,different grinding abrasive shapes(spherical,inclined cylinder),grinding time(10 min,20 min,30 min,40 min,50 min,1 h,2 h,3 h)were used Vibration grinding treatment.For the shot peening process,different shot peening pressures(0.1 MPa,0.2 MPa,0.3 MPa,0.4 MPa,0.5 MPa)were subjected to shot peening on the sample surface.Within the scope of the experiment,the main findings are as follows:(1)Sandblasting can significantly improve the surface roughness of the material.When the blasting time and blasting pressure are unchanged,the smaller the grit mesh,the greater the surface roughness of the sample.In order to reduce the surface roughness of the sample as much as possible,grit with a larger mesh should be used.When the blasting pressure and the number of grit meshes are fixed,as the blasting time increases,the surface roughness of the sample gradually increases,and the standard deviation of the roughness also increases.In order to make the surface roughness of the sample as low as possible,and the uniformity of the roughness as small as possible,the blasting time should be shortened.Sandblasting also has a strong cutting effect on the surface of the material.When the sandblasting pressure is greater than the minimum value of 0.073 MPa,the amount of material removed is linearly related to the sandblasting pressure.In order to ensure cutting efficiency and take into account the surface quality,a larger blast pressure and a larger grit should be used.The best parameters of the blasting process are:using 80 mesh grit,the blasting pressure is 0.6 MPa,and the blasting time can be adjusted as needed.At this time,the material surface removal rate is 7.83 mg/s,and the thickness removal rate is about 10μm/s.Sand blasting will cause the tensile strength of the tensile specimen to decrease greatly,and the roughness will increase greatly.At the same time,deep and sharp scratches will be formed on the surface.Therefore,sand blasting is not suitable as the final process,only suitable for surface pretreatment,used to eliminate obvious Defects and surface oxides.(2)Vibration grinding treatment can significantly reduce the surface roughness of the material,and change the vibration grinding time and the shape of the abrasive,which will affect the surface roughness.The surface roughness of the specimens treated with spherical abrasives and vibration grinding for 3 hours decreased from 2.46μm to 0.32μm,a reduction of 87%.Vibration grinding can increase the residual compressive stress on the surface of the material.The residual stress on the surface of the untreated sample is-55 MPa,and the residual compressive stress on the surface of the sample treated with oblique cylindrical abrasive is-166 MPa,which is a 202%increase.Vibration grinding can significantly improve the Vickers hardness of the surface of the material.The surface Vickers hardness of the samples after 3 hours of treatment with oblique cylindrical abrasives and vibration grinding was increased from 164.4 to 184.4,an increase of 12.2%.Based on the comprehensive experimental results,the best vibration process is:use oblique cylindrical abrasive,vibration grinding treatment for 3 hours.The fatigue limit of the sample treated with this process is 265 MPa,which is 10.4%higher than that of the untreated sample;the surface roughness is reduced from 2.64μm to 0.59μm,a decrease of 77.7%;the surface residual stress is increased from-55 MPa to-166 MPa,an increase of 202%;surface Vickers hardness increased from 164.4 to 184.4,an increase of 12.2%.Regardless of whether spherical abrasive or oblique cylindrical abrasive is used,vibration grinding has no significant effect on tensile strength and yield strength.Vibration grinding can greatly reduce the surface roughness of the sample and the consistency of the roughness is high,significantly improving the Vickers hardness of the surface of the material,and introducing a certain residual compressive stress,which is suitable for further processing of the pretreated sample.(3)Shot peening can greatly increase the residual compressive stress on the surface of the sample.The residual compressive stress increases with the increase of the shot peening pressure.When the shot peening pressure gradually increased from 0.2 MPa to 0.5 MPa,the surface residual compressive stress increased from-202 MPa to-252 MPa,which can be increased by up to 358.2%compared with-55 MPa before treatment.Regardless of the peening pressure used,the residual compressive stress after shot peening increases from the surface to the interior of the sample and then decreases,and reaches a maximum at a depth of 50μm.Among them,the residual compressive stress reached the maximum at a depth of 50μm with a shot peening pressure of 0.5 MPa.The value was-262 MPa,which was an increase of 376.4%compared with the untreated sample.Shot peening will slightly increase the surface roughness.The surface roughness of the specimens treated with 0.5 MPa shot peening pressure is increased from 2.46μm to 3.08μm,an increase of 25.2%.In order to increase the residual stress after shot peening as much as possible,the optimal shot peening pressure was selected as 0.5 MPa.Compared with the untreated sample treated with the best shot peening pressure,the fatigue limit was increased from 240 MPa to 315 MPa,an increase of 31.3%;the surface residual stress was increased from-55 MPa to-252 MPa,an increase of 358.2%.;Surface roughness increased from 2.46μm to 3.08μm,an increase of 25.2%.Within the range of shot peening pressure used in the experiment,the tensile strength and yield strength of the sample did not change significantly after the shot peening,the surface roughness only slightly increased,the residual compressive stress value was greatly increased,and the fatigue limit was greatly increased,suitable for the final surface Treatment process.(4)In order to comprehensively improve the fatigue limit of 15%SiCp/2009Al composite materials,a comprehensive process of sand blasting,vibration grinding,and final shot peening can be used.After the sandblasting process,there are no obvious forging defects and oxide layers on the surface of the material.After the vibration grinding process,the surface roughness of the material can be greatly reduced and the Vickers hardness of the material surface can be significantly improved.Finally,a large amount of residual pressure is introduced after the shotblasting process.Stress,at this time,the surface of the material has a lower surface roughness and a higher surface residual compressive stress,and the fatigue performance is optimal. |
