Effect Of Ultrasonic Vibration On The Two-stage Creep Age Forming Of 7075 Aluminum Alloys

The aging forming technology which is the effective technique to ensure the integral panel forming quality and increase the service life.Aiming at the modern aircraft manufacturing requires high performance,low cost and the design concepts of modern aircraft structure.In this paper we focus on 7075-T651 Aluminum alloy for research,which used ultrasonic vibration technology and two-stage aging forming technology as a combined process,based on theoretical analysis and process test methods.By using macro and micro analysis,explore the effect of ultrasonic vibration on the comprehensive performance of 7075 aluminum alloy two-stage aging forming,and test the changes of various process parameters on the mechanical properties and microstructure of 7075 aluminum alloy.In order to obtain better comprehensive performance,the effects of ultrasonic application time and second-stage aging temperature on the properties of materials in two-stage aging forming were studied.Results show that(1)By comparing the springback,strength,elongation and hardness after the ultrasonic application time is 0,4,6,8,and 10 hours in the first-stage aging process,it is found that with the extension of the ultrasonic application time,the springback decreases first and then increases,the lowest value is 40.2%.The strength decreases first and then increases.The elongation rate increases,with a range of about 1%.The hardness decreases first,then increases to a certain value and then decreases.(2)By comparing the springback,strength,elongation,and hardness after secondary aging forming temperature of 180,190,200,210,and 220°C,and the ultrasonic application time for 6 hours.It was found that as the secondary aging temperature increased,the springback gradually decreases,reaching a minimum value of 33.6%at 220°C;the strength gradually decreases,the minimum tensile strength is 335.63MPa and the yield strength is 287.56MPa at 220°C;the elongation gradually increases,and the highest reaches 6.61%;and the hardness gradually decreases,the lowest value is 98HV.In order to better explain the changes in mechanical properties,the precipitated phases were analyzed by metallographic observation and transmission electron microscopy.Comparison of microstructures with and without ultrasonic application,single-stage aging and dual-stage aging,and different ultrasonic application time and the results show that(1)Insoluble second particles in the metallographic structure of the sample without ultrasonic wave are coarser,while insoluble second phase particles in the metallographic structure of the sample after ultrasonic wave are smaller in size;The second-phase particles in the metallographic structure after single-stage aging are small in size and uniformly distributed,while the second-phase particles in two-stage aging are coarse and unevenly distributed.As the ultrasonic application time is extended,the second phase particles are gradually refined and distributed more uniformly.(2)In the sample without ultrasonic wave,the precipitated phase within grains was mainly spherical GP zones,with a small amount of short rod-shaped?phase and elliptical??phase.The composition of the precipitated phase within grains is MgZn₂.The grain boundary precipitate is continuously distributed,and there is no obvious precipitation-free zone.After the application of ultrasonic waves,the precipitated phases within grains are mainly?phase and??phase.The composition of the precipitated phase within grains is a ternary phase composed of Mg-Zn-Cu.There is no precipitation band,and the width is about 100 nm.