Study Of Aluminum Nanocrystallization By Vibration-assisted Burnishing

Marine engineering equipment is the main carrier for human development,utilization,and protection of marine resources,energy,and marine transportation.It is a concrete manifestation of the level of manufacturing in marine development.The forerunner of marine engineering development is material,and the use of marine engineering materials is diversified.Among them,aluminum alloys have been widely used because of their light weight and good weldability.However,in the face of harsh and complex marine environments,the oxide film on the surface of aluminum alloy is easily damaged due to corrosion and wear,which greatly reduces its service life.Ultrasonic rolling is a kind of surface modification technology,using external force to induce strong plastic deformation on the surface of metal materials,to prepare a gradient nano/ultra-fine crystal surface layer.The structure of the grain size gradient distribution is conducive to improving the surface hardness,wear resistance and fatigue resistance of the aluminum alloy.In order to prepare surface nano/ultra-fine crystallized materials,study the effect of surface nano/ultra-fine crystallizing on 7075 aluminum alloy materials,the main work and results of this paper are as follows:(1)On the basis of the vertical milling machine,we independently designed and manufactured a new type of plane burnishing tool and ultrasonic vibration auxiliary system to provide experimental conditions for ultrasonic burnishing of aluminum alloy.(2)Using the finite element analysis method to establish a simplified model of ultrasonic rolling processing,and analyzes the elasto-plastic variation law of aluminum alloy workpiece during processing.At the same time,the energy distribution and processing efficiency of the whole model were obtained.(3)On the basis of ultrasonic burnishing process,an orthogonal experiment table was designed to study the influence of rolling pressure,ultrasonic amplitude,spindle speed,and infeed speed on the surface quality of the aluminum alloy,and to optimize the process parameters.(4)A variety of material characterization methods were used to compare the differences in microstructure and properties of aluminum alloys before and after ultrasonic burnishing.The results show that the surface roughness of aluminum alloy after ultrasonic rolling is reduced by about 7 times;the surface is formed a gradient nano/ultrafine crystal surface layer;the hardness of the material changes along the depth direction;on the condition of dry friction,the friction coefficient and wear depth of ultrasonic rolling aluminum alloy are smaller than that of the original sample.In this paper,a self-designed and manufactured ultrasonic rolling experimental device was used to successfully prepare the surface layer of gradient nano/ultrafine crystal on the surface of 7075 aluminum alloy,which changed the microstructure of the surface layer of the material,improved the mechanical properties and friction and wear properties of the material.This paper provides theoretical guidance and experimental evidence for further research and application.