In order to explore the formation mechanism of ultrasonic cavitation nanostructures in aqueous media,the morphological characteristics of ultrasonic cavitation nanostructures in different aqueous media were studied.By using the ultrasonic vibration cavitation test device,the 45 steel sample was subjected to ultrasonic cavitation experiments in four different water media.The morphology of cavitation nano products on the sample surface was analyzed by laser confocal microscope and scanning electron microscope.It is found that the nanostructures of 45 steel produced by cavitation in different water media are quite different.In deionized water and NaCl solution,the nanostructure of the cavitation pits in the ring-shaped area appears as an irregular flocculent structure,and the nano multilayer sheet structure is formed around the cavitation pits generated in tap water and Na2SO4 solution.In tap water,with the increase of ultrasonic time,the size of nano monolayer sheet structure first increases in the length direction,and then gradually superimposes into nano multilayer sheet structure,and the total thickness increases.In conclusion,the size of the nano multilayer sheet structure produced by ultrasonic cavitation erosion of 45 steel in tap water is related to the experiment time and the ions in the medium,which is caused by the coupling effect of cavitation erosion-corrosion.At the same time,SO2-4 and other ions in tap water also contribute to the assembly of lamellar nano layers.