Effect Of Shot Peening Treatment On Microstructure And Properties Of CuZnAl Alloy

Nanocrystalline metal materials have high strength,but their plasticity is limited.Lu Ke et al.used the gradient nanocrystalline copper prepared by surface nanocrystallization technology to limit the strain localization of the surface nanocrystals through the large crystal grains of the bottom layer,so that the nanocrystals exhibit large plastic deformation with the elastic strain less than 0.5%,which is much lower than the theoretical elastic strain limit of the metal crystal(10%).In our previous studies,Nb nanowires exhibite large elastic strains in Ni Ti memory alloys by matching the elastic strain of Nb nanowires to the lattice shear strain of memory alloys.Inspired by this,when the memory alloy is treated by surface nano-technology,the elastic deformation behavior of the surface nanocrystals is worthy of study.In this paper,we choose Cu Zn Al memory alloy as research object.Firstly,the effect of heat treatment on the microstructure of Cu Zn Al alloy sheet was studied.Secondly,the effect of shot peening on the microstructure and properties of Cu Zn Al alloy was studied.Finally,the elastic deformation behavior of nanocrystals on the surface of Cu Zn Al memory alloy was studied by synchrotron radiation high energy X-ray technique.The study found that when the heat treatment temperature is lower than 800°C,with the increase of heat treatment temperature and holding time,the content of ? phase decreases while the content of ? phase increases in Cu Zn Al alloy.The grain size inside the Cu Zn Al alloy increases from 4 ?m to 12 ?m,and the elongation and tensile strength decreased.When the heat treatment temperature is higher than 800°C,the structure of the alloy is mainly martensite.After air-cooling at 750°C for 10 min,the structure of Cu Zn Al alloy is mainly ? phase at room temperature,and the elongation and yield strength are 10.53% and 171.31 MPa respectively.After air-cooling at 750°C for 20 min,the structure of Cu Zn Al alloy is mainly ? phase at room temperature,and the elongation and yield strength are 8.38% and 286.16 MPa respectively.After water quenching at 800°C for 5 min,the structure of Cu Zn Al alloy is martensite at room temperature,and the elongation and yield strength are 11.43% and 250.84 MPa respectively.After shot peening,the surface structure of these three kinds of Cu Zn Al alloy above were transformed into ? phase.When the shot peening time extends,the degree of surface deformation and the thickness of deformed layer are both increased,while the grain size gradually is decreased.After 5 min of shot peening,the grain size of ?-Cu Zn Al alloy surface is 24.36 nm.Compared to the matrix,the microhardness,the elongation and the yield strength have been increased by 72.94%,51.28% and 89.57% respectively;the grain size of ?-Cu Zn Al alloy surface is 22.68 nm.Compared to the matrix,the microhardness,the elongation and the yield strength have been increased by 52.63%,69.14% and 37.36% respectively;the grain size of M-Cu Zn Al alloy surface is 34.81 nm.Compared to the matrix,the microhardness,the elongation and the yield strength have been increased by 20.60%,55.56% and 14.19% respectively.The high-energy X-ray diffraction of synchrotron radiation shows that the elastic strain of the surface nanocrystals of M-Cu Zn Al alloy after shot peening reached 3.20%,which was significantly higher than that of ?-Cu Zn Al alloy surface nanocrystals (1.74%).