Study On Severe Plastic Deformation Behavior Of Thin Metals Under Ultrasound Effect

In modern society,manufacturing is of great significance to social economic development and social stability.With the advancement of technology,the manufacturing field has put forward higher requirements on the operational performance and the life span of mechanical structures and mechanical parts.The smaller the average grain size of metal materials,the better the strength and toughness of metal materials,high performance metal materials can improve the comprehensive performance mechanical parts.Severe plastic deformation(SPD)is a technology that refines the grains of materials by introducing severe plastic strains into metal materials.At present,various SPD methods are mainly aimed at macroscopic materials above the millimeter level,but there is little work in the field of SPD reinforcement for micro-sized materials.In view of this,represented by ultrasonic impact and ultrasonic rolling technology,this subject systematically explores the severe plastic deformation behavior and mechanism of ultrasonic vibration in micro-sized thin-layer metal.The application potential of ultrasonic SPD method in the field of severe plastic strengthening of micro-sized materials was verified.we carried out following conclusions:First,the dynamic simulation analysis of the fixed-point ultrasonic impact process shows that when the impact ball bottom is always in contact with the surface of the strip,the sample quickly enters the elastic vibration equilibrium stage after a short period of plastic deformation.When the ball and strip are periodically separated,the ultrasonic dynamic shock effect dominates,and plastic deformation always exists.On the basis of deriving the motion and stress conditions,the conversion criterion formulas for two different dynamic behavior modes are given,namely the ultrasonic volume effect mode and the ultrasonic dynamic impact effect mode.Through the measurement experiment of plastic deformation under ultrasonic rolling impact,with the change of static pressure,amplitude and other factors,the obvious sudden phenomenon corresponding to the conversion of different dynamic behavior modes.The validity of the theoretical model is verifiedSecond,the ABAQUS numerical simulation was used to perform ultrasonic fixed-point impact and single-pass ultrasonic rolling simulation on T2 copper strips with different thicknesses.We found that as the thickness of the copper strip decreases,when the thickness of the copper strip decreases to the influence range of ultrasonic elastoplastic waves,the distribution of PEEQ begins to change from a gradient structure to a uniform integration.The PEEQ value increases exponentially with the decrease in sheet thickness.The simulated plastic strain and the measured plastic strain showed a similar exponential increasing trend with the decrease of thickness.The rigid-wall reflection effect of elastoplastic waves is used to explain this phenomenon.Obviously,the exponential growth and uniform distribution of PEEQ indicate that ultrasonic vibration has good application potential in the field of severe plastic deformation strengthening of micro-sized materials.Under the effect of size effect and ultrasonic volume effect,the measured strain value is larger than the simulated strain value.Third,EBSD and TEM characterizations were performed on the different local areas of the surface layer and center of the 100?m and 200?m copper strip sections processed by single-pass ultrasonic rolling.The EBSD results show that the single-pass ultrasonic rolling has obtained a large reduction in the grain size and a uniformly distributed ultra-fine grain structure in the copper strip,which is consistent with the PEEQ simulation results.A large number of small-angle grain boundaries change to large-angle grain boundaries under large plastic strain,which is a typical in-situ or continuous dynamic recrystallization.TEM results showed that a large number of various types of dislocation structures existed at the boundary of IDBs and GNBs,indicating that the recrystallization process is dominated by the fine crystal mechanism of dislocation activity.Some findings that characterize the microstructure of the SPD structure to reach the minimum grain size indicate that the recrystallization and recovery have reached a balance during the SPD process,indicating the high efficiency of the ultrasonic rolling process applied to the SPD of micro-sized copper tape.