Study On Surface Modification Of 7075 Aluminum Alloy By Ultrasonic Shot Peening

Ultrasonic shot peening(USP)technology makes the ultrasonic vibration as the energy source,driving shots to impact the metal material with high speed.As a kind of severe plastic deformation,USP can achieve the material surface modification or deformation.Compared with the traditional shot peening technology,USP has many advantages,such as high precision,good surface quality,easy to control and so on.When dealing with different materials with USP technology,the changes of the process parameters affect the structure and properties of material surface films.Therefore,it is of great theoretical and engineering significance to study the influence of USP parameters on the materials microstructure and properties.This paper studied on surface modification of 7075 aluminum alloy(Al 7075)by USP technology,through changing the peening duration,shot diameter,peening distance,sonotrode amplitude and other process parameters.The changes of microstructure of surface grain,and the influence of electrochemical corrosion resistance of materials surface were studied by USP.The changes of surface hardness and surface roughness with USP parameters were analyzed.Combining the USP technology with the tensile test,the mechanical properties of the samples were tested.The main work included:The Al 7075 USP experiment was carried out,so the effects of peening duration,shot diameter,peening distance and sonotrode amplitude on the thickness of fine grain layer were obtained.Based on the experimental study,the microscopic structure of the sample surface grain was analyzed,and the reasons for the formation of nanometer crystal(NC)on the sample surface were summarized.A1 7075 samples after USP were treated by solid solution and aging,the surface hardness and microstructure of the samples were analyzed before and after heat treatment.The effects of USP on the surface hardness of the samples were studied,and the influence rules of different process parameters on the hardness and average hardening rate of the samples were analyzed.The best combination of performance parameters was found.According to the sample surface contour plan and stereogram,the diameters of the pits on the sample surface by USP were measured,and the internal mechanism of sample surface roughness variation was revealed.The changes of arithmetic mean deviation,mean square deviation and contour height with process parameters were studied,the relationship between USP process parameters and sample surface roughness was summarized.The effects of USP on the electrochemical corrosion resistance of the samples were studied.According to electrochemistry corrosion polarization curve,impedance spectrum and corrosion morphology,the influence of Al 7075 surface electrochemistry corrosion by USP was analyzed.The electrochemical corrosion process by USP was compared to explain the internal mechanism of the electrochemical corrosion of the materials.The effects of USP on the mechanical property of the samples were studied.The tensile stress-strain curves of samples with different parameters were obtained by tensile test.The effects of USP parameters on the tensile strength,yield strength,elongation and fracture morphology were researched.The influence rules of different USP parameters on the mechanical properties and microstructure were obtained,the relationship between the materials mechanical properties and the USP parameters was analyzed.