Study On The Mechanism And Properties Of Grain Refinement By Ultrasonic Rolling

In the process of ultrasonic rolling,the machined surface will form a fine-grain structure layer which is different from the matrix material.The grain size of the fine-grain structure layer is significantly smaller than that of the matrix.And the formation of the fine-grain structure layer not only can affect the surface roughness and hardness of the material,but also can make an important effect on the performance of its wear resistance and corrosion resistance.Different from traditional surface processing technology,ultrasonic rolling combines the advantages of the ordinary rolling and the ultrasonic impact technology to realize the surficial compaction and smooth surface.In this process,the synergy of state of complex stress and the prodigious plastic deformation produces the surface metamorphic layer among the processing surface and the substrate,due to the frequent movement of material surface dislocation and crystal movement.The microstructure of the layer directly affects the service performance of the material.In this work,the high-strength Aluminium alloy 7075 was employed as the matrix material,the variation of the surface grain size under the different parameters was analyzed through the test of ultrasonic rolling and the MATLAB simulation.In this case,we explored the influence of the ultrasonic rolling parameters on the surficial grain refinement,and investigated the characteristic of the machined surface and its wear resistance and corrosion resistance.Firstly,the influence of ultrasonic rolling parameters on the grain refinement was analyzed using the test of ultrasonic rolling.On the basis of the mechanical property of the ultrasonic rolling,the model of impact dynamic was built through data fitting for the dynamic impact force under different parameters;the model of the surficial stress-strain was derived through simplifing the uniformly distributed load on the material surfaces as the concentrated force based on the calculation method of boussinesq;the relationship between ultrasonic rolling parameters and grain size was also derived through mechanical model of grain refinement.Besides,based on the mechanical model above,the aluminium alloy 7075 works as the researching material to conduct the MATLAB simulation,the surface stress distribution and the influence of ultrasonic rolling parameters on the material surface grain size were investigated under the impact force;applied the tools of XRD and Jade to calculate the grain size of the machined surfaces,which could be used as acertification for the results of grain size by MATLAB;the surface refining mechanism of ultrasonic burnishing was summarized through analyzed the results of theory and experiment.Finally,with the surface quality detection,through the analysis of the macro-characteristic of the machined surface to explore the influence of the ultrasonic rolling parameters on the surficial characteristic,and the macro-characteristic included the surface roughness and strain hardening.The wear resistance and corrosion resistance of the treated material were studied by friction and wear test and salt spray corrosion test,quantitative analyzed the influence of the static pressure on the performance of wear resistance and corrosion resistance,furthermore analyzed the wear mechanism from micro-perspective,and the results showed that ultrasonic rolling processing can significantly improve the surficial wear resistance and corrosion resistance.