Study On Surface Strengthening And Fatigue Behavior Of 7075 Aluminum Alloy By Ultrasonic Rolling Treatment

Aluminum alloys are widely used in aerospace,automobile,vessel field due to the excellent properties as its low density,excellent corrosion resistance,fatigue resistance and high specific strength.With the rapid development of aerospace,the resistance fatigue performance of aluminum alloy has put forward higher demands.Improving the surface properties of materials play an significant role in wear resistance,corrosion resistance,fatigue life.The specialty of various surface treatments were analysed and compared,ultrasonic rolling strengthening(URS)is supposed to be an ideal surface treatments technology.7075 aluminum alloy was applied to URS,the surface properties of surface roughness,surface microhardness,surface microstructure and surface residual stress and the fatigue behavior of fatigue life,fatigue fracture morphology,fatigue fracture regularities were investigated before and after the URS.After URS,the result indicates surface roughness of the specimens had been dropped four grades,and their smoothness were close to mirror surface,surface microhardness had been increased by 12.69%.The surface grain of the UB specimens was considerably refined compared to the central grain.The original residual tensile stress of surface changes to compressive stress,and the residual compressive stress layer was 1.75 mm deep.This could effectively prevent the initiation and development of fatigue crack.Under the 280 MPa stress level,the fatigue life of specimens had been almost enhanced by 7 times.The fatigue fracture were all composed of fatigue source,fracture growth and final rupture.The fatigue crack sources removed to the central position from surface or near-surface.Abundant strength phase were exposed during the final rupture area.The URS mechanism were investigated based on the theory and method of finite element,element modeling of the URS were established.By comparing the residual of specimens receiving experiment and simulation,the result found the distribution characteristic of residual stress are almost the same.The maximum value of compressive stress appeared on the surface,and their error between experiment and simulation is 11.6%.These findings could provide comprehensive basis for the development of aluminum alloy life.