Research On Size Effect Of The Flow Stress Of Cu3Ag0.5Zr Alloy Sheet

In recent years,with the rapid development of electronic industry and precision machinery instruments,sheet metal plays an increasing important part in the application of electronics,medical equipment,and MEMS.At the same time,it sets higher demands for the material such as lightweight,miniaturization and integration.Copper alloys,because of its excellent electrical conductivity,thermal conductivity and nice strength,are widely used in every walk of life.However,when the geometry of sheet metal is downscaled to micro-scale,its forming law will be quite different from the macro one due to size effect which restricts the development of micro-scale alloy sheet.Therefore,it is necessary to explore the size effect of flow stress of sheet metal under micro-scale and investigate the effect of grain size on tensile mechanical properties and springback.To explore and predict the flow stress of microplasticity forming on the basis of traditional plastic forming theory.It is of great significance to promote the development of copper alloys sheet micro plastic forming.This paper explored the microstructural evolution of materials under solid solution,recrystallization annealing treatment and aging treatment of Cu-3wt.%Ag-0.5wt.%Zr(Cu3Ag0.5Zr)alloy sheet.Recrystallization annealing treatment was carried out at 945? to control grain size of the alloy sheet;The aging treatment was carried out at 475? to control the content of precipitates.And the grain growth equation and the aging precipitation kinetic equation were obtained.Through uniaxial tensile test,the influence of grain size and precipitation on the flow stress of the alloy sheet was analyzed as well as work hardening law and fracture mechanism.It was found that the flow stress of the material increased with the decrease of grain size and the increase content of precipitates.When the portion of surface grain increases,since there are basically 3 or 5 grains over the thickness of alloy sheet,the flow stress decreased markedly,because that the free surface has no hindrance to the dislocation.And the size effect showed visibly.On the basis of surface layer model,traditional Hall-Petch formula was revised,taking the grain boundary strengthening,solid solution strengthening and precipitation strengthening into consideration.The tensile constitutive model of Cu3Ag0.5Zr alloy sheet considering the size effect was established and verified.The flow stress constitutive model have a good capacity of prediction and evaluation.On the basis of the size effect mode of flow stress,the bending springback of alloy sheet was also explored.With the theoretical analysis of three points bending test including bending force,bending moment,springback angle,the bending springback model considering the size effect of flow stress was established.And the influence of grain size and precipitation on the bending properties was analyzed through three points bending test at room temperature.It was found that the bending stress of the alloy sheet increases with the decrease of the grain size and increase the content of precipitates which was consistent with the theoretical result.What's more,the springback angel also showed inflection point law of size effect similar to the flow stress.