The Textures,Microindentation And Corrosion Properties Of Cold-rolled AA6061 Aluminum Alloy

6xxx aluminum alloy,as a kind of structural material,has great application prospect in the automobile and aerospace industries.Generally speaking,the macroscopic properties are closely related to their microstructures of material,and the length of service life of materials also depends on the inner microstructures In order to realize the controllable structure and performance and to provide certain theoretical and experimental support for the preparation of aluminum alloy sheets for the industries,it is of great importance to understand the effects of the plastic deformation on the textures,microstructures,mechanical properties and corrosion resistance and to build the quatitative relationship between the micro-textures and the macro-properties of 6xxx aluminum alloyIn this paper,the industrial AA6061 aluminum alloy sheets are selected and six aluminum sheets with different thickness reductions are prepared by cold rolling at room temperature.The microscopic morphology of AA6061 aluminum alloy is observed by optical microscope(OM)and scanning electron microscope(SEM).The texture evolution of AA6061 aluminum alloy is analyzed by X-ray neutron diffraction(XRD)and electron backscatter diffraction(EBSD).The mechanical behaviors of Vickers hardness and indentation deformation are studied by microindentation technique.The corrosion properties of aluminum alloy are tested by dynamic polarization,constant potential polarization and electrochemical impedance spectroscopy(EIS).Based on the analysis of the evolution of textures,microstructures and microindentation deformation behaviors during the plastic deformation,the quantitative relationship between the textures and Vicker Hardness of AA6061 aluminum alloy is established by combining the experiment and theory.Furthermore,the effect of plastic deformation on the corrosion performance of the AA6061 aluminum alloy is analyzed in NaCl solution.Combining the results of the effects of textures on the indentation deformation,the interconnections between the microstructures and the macroproperties is revealed during the plastic deformation.The analysis of the microstructure and macro-texture of the cold-rolled AA6061 with different thickness reductions shows that the cold rolling results in the grains elongation along the rolling direction(RD)and the texture evolution.With the increasing of the thickness reduction,there exists a slight difference between the grain size near the surface and the central part of the cold-rolled aluminum sheets,while the volume fraction of the deformation texture does not change significantly for the thickness reduction less than or equal to 30%.When the thickness reduction is larger than or equal to 50%,the differences of grain size in different regions disappear,and the volume fraction of deformation texture increases approximately linearly with the increase of the thickness reduction.Microindentation tests of the central portion of the cross-section of the cold-rolled sheets are performed.The Vickers hardness increases with the increase of the thickness reduction,and displays almost the same increase trend as the volume fraction of the deformation texture for the thickness reduction larger than and equal to 50%.The energy dissipation for a single loading-unloading cycle decreases with the increase of the thickness reduction.A simple exponential relation between the Vickers hardness and the thickness reduction is established and used to curve-fit the experimental results.The fitting result reveals the dominant role of the dislocation motion in controlling the indentation deformation of the cold-rolled AA6061 alloyThe Vickers hardness and indentation deformation of the AA6061 aluminum alloy are studied by using microindentation technique.Different indentation loads are used in different regions,and Vickers hardness is independent of indentation loads and spatial positions.As the plastic deformation degree increases,the resistance to deformation increases but the indentation depth decreases.Both the maximum indentation depth and the residual indentation depth decrease with the increasing of the thickness reduction.For the same sample,there is an exponential relationship between indentation load and the maximum indentation depth,residual indentation depth and average diagonal length of indentation.For the indentation deformation,the evolution of dislocation is related to the dislocation dynamics.The higher the plastic deformation degree,the more the dislocation density of aluminum alloy matrix under the indenter.The experimental results show that the plastic energy during indentation loading-unloading is proportional to 3/2 of the indentation loading and 3/4 of the average dislocation densityThe microtextures of the cold-rolled sheets are investigated by electron backscatter diffraction.The results show that the spatial variation of texture is relatively small through the thickness gradient.For the as-annealed sample,there exists recrystallization texture near the surface,some deformation texture in the central region and shear texture in 1/4 region and near-surface region.However,after the cold rolling,the texture of the aluminum sheets become deformation texture characterized of the typical ?-fiber.For the material with plastic deformation,the relationship between Vickers hardness Hv and ODF coefficient Wlmn is linear and also supported by experimental results.With the increasing of the thickness reduction,the<W4m0>decreases and the<W6m0>and<Hv>increase The relation between texture and Vickers hardness is mainly determined by<W4m0>.The increasing thickness reduction results in the larger plasticity anisotropy and the more negative value of the higher order term W400By measuring the corrosion behaviors of AA6061 aluminum alloy with different thickness reductions in NaCl solution,the corrosion process can be divided into three different stages:early stage,middle stage and late stage.In the early stage,the corrosion rate increases gradually which is due to the dissolving of passive film gradually caused by pitting.In the middle stage,corrosion products are continuously accumulated on the surface of the substrate and inside the pit.As a result,the reaction resistance increases gradually and the corrosion rate decreases.In the late stage,the corrosion reaction is basically at a state of fluctuating equilibrium.The electrochemical corrosion results show that plastic deformation has a harmful influence on corrosion resistance to aluminum alloy With the increase of the thickness reduction,the radius of arc resistance decreases and the corrosion potential and pitting potential gradually move negatively Meanwhile,both the increasing of corrosion current density and corrosion rate mean the decreasing of the corrosion resistance with the increase of the thickness reduction.The results of SEM and EDS show that the corrosion of aluminum alloy in NaCl solution is mainly related to the second phase with Si.The corrosion mechanism is the"small cathode-large anode"micro-battery circuit formed by second phase and the aluminum alloy matrix.The effect of thickness reduction on pitting potential Epitting,Vickers Hardness Hv and texture coefficient Wlmn is linear,which means that the different macroproperties(including mechanical and corrosion properties)induced by the different microstructures is related to texture coefficient for the AA6061 aluminum alloy.