Study On The Effect Of Ultrasonic Rolling On The Microstructure And Mechanical Properties Of 7075 Aluminum Allo

7075 aluminum alloy is widely used in aerospace and other fields due to its high specific strength and low density.Therefore,it is of great significance to study the relationship between microstructure and mechanical properties of 7075 aluminum alloy for the safe application of aerospace structural components.In this paper,7075 aluminum alloy was taken as the research object,and the mechanical properties of7075 aluminum alloy were optimized by ultrasonic surface rolling(USRP)and low temperature aging.The contribution of fine grain strengthening,precipitation strengthening,dislocation strengthening and synergistic strengthening to the strength was quantitatively analyzed,and the influence of precipitation phase on the microstructure evolution was analyzed,which provided data support and theoretical guidance for the application of high strength aluminum alloy components in this system.The main contents of this paper are as follows:(1)Through the USRP and low temperature aging treatment,the MGNS layer was constructed on the alloy surface,The tensile strength(692 MPa)of the specimen with MGNS is about 63% higher than that of the coarse-grained specimen(425 MPa),which realizes a good combination of strength and plasticity.(2)The evolution mechanism of grain size of 7075 aluminum alloy during USRP was systematically studied.It was found that the grain size gradient structure originated from the dislocation slip induced grain refinement to form the gradient structure during USRP;the gradient distribution of precipitates originates from the fact that dislocations and crystal boundaries are the nucleation sites of precipitates during aging,which makes the density and size of precipitates in different regions change in gradient.(3)The strength increment of MGNS sample compared with CG sample originates from grain boundary strengthening,precipitation strengthening,dislocation strengthening and synergistic strengthening.Meanwhile,normalized strain hardening rate curves and the EBSD-KAM maps show that the MGNS can improve the ductility of nanomaterials.(4)Layered gradient nanostructure(LGNS)was introduced on the surface of T4(solid solution)and T6(peak aging)7075 aluminum alloy under the same USRP condition.Surface grain refinement can improve the microhardness of the sample,but T4-7075 aluminum alloy can obtain a deeper gradient deformation layer,indicating that the softer alloy is more conducive to the introduction of gradient nanostructure.(5)The precipitated phase dissolves and consumes part of the deformation energy during the deformation process,so the deformation energy used to refine the grain decreases,resulting in the grain refinement of T4-7075 is more obvious than that of T6-7075 aluminum alloy under the same strain condition.