Research On Surface Nanocrystallization In The Process Of Two Dimensional Ultrasonic Rolling

Ultrasonic rolling process with Longitudinal-torsional vibration is a new surface finishing strengthen technology,which is combined the two dimensional ultrasonic vibration processing technology with rolling process,to achieve complementary advantages and improve the comprehensive performance of material surface.In this thesis,the 7050 aeronautical aluminum alloy is processed with two-dimensional ultrasonic rolling(TDUR).The nano-forming mechanism of two-dimensional ultrasonic rolled aluminum alloy is studied by theoretical analysis,numerical simulation,process test and test analysis.The main work is as follows:(1)Based on the mechanism of metal material surface plastic deformation strengthening and the mechanism of metal material surface self nanocrystallization,combined with two-dimensional ultrasonic rolling process,the mechanism of surface self nanocrystallization of TDUR was studied.In the process of TDUR,the maximum stress is greater than the yield strength of aluminum alloy,material plastic deformation occurs.At the same time,under the torsional vibration,the coarse grain structure on the surface of the metal material produces strong plastic deformation in different directions,to produce high-density crystal defects,these defects interact,continue to annihilate and reorganize,so that the grain gradually refined to the nanometer level.(2)Based on the motion analysis of TDUR,the kinematic model and stress model of two-dimensional ultrasonic rolling of shaft parts were established.The trajectory of the rolling tool head is elliptical when the TDUR is performed.The internal stress produced by the specimen is not only related to the physical and mechanical properties of the rolling tool head and the specimen,but also with the ultrasonic vibration parameters and rolling parameters related(3)The surface roughness value,surface hardness and residual stress of the surface of the 7050 aluminum alloy were studied by TDUR.The surface microstructure of the sample was observed and analyzed.The results show that the surface of the specimen is formed with a smooth surface and the surface roughness value is obviously reduced after TDUR.The surface of the specimen produces a hardened layer,and the surface hardness is significantly improved.The residual stress test value is slightly larger than that of the simulation stress and the law of influence is basically the same.The surface of the aluminum alloy is plastic and the grains are extruded,elongated and refined.This research results may help to further improve the surface nanocrystallization mechanism of two-dimensional ultrasonic rolling aluminum alloy,and provide reference for the technical engineering application...