Study On Deformation Uniformity And Bending Control Of Aluminum Thick Plate During Gradient Temperature Shear Rolling

Hot rolling is a key process for preparing high-performance aluminum alloy thick plates.The demand for aluminum alloy thick plates is increasing in the fields of aerospace,rail transportation and the automotive industry.In this process,the large deformation of the plate can be eliminated,the casting defects of the thick plate can be eliminated,the grains can be refined,and the performance of the thick plate can be improved.With the development of the aerospace industry,more demanding requirements have been imposed on the performance of aluminum alloy thick plates(such as the strength of aluminum plates even exceeding 700 MPa and the thickness even exceeding 250 mm).However,the conventional symmetrical rolling results in inhomogeneity distribution of large deformation on the surface and small deformation in the central,which leads to inhomogeneity microstructure and performance.In order to overcome this challenge,this paper adopts a new method of gradient temperature shear rolling,which combined speed ratio and temperature gradient,under this technology,the core deformation of the thick plate can be effectively promoted,in addition,the problem of serious bending of thick plate bending in asynchronous rolling is solved.The main work is as follows:(1)To study the rheological properties of 7055 aluminum alloy in the rolled state,aluminum alloy experimental parts were isothermally compressed on the Gleeble-3180 thermal simulation test machine,the stress-strain curves at different strain rates and temperatures were obtained,and the least square method is used to solve the constitutive model.(2)Firstly,the spray quenching model was established to obtain the temperature distribution law of the thick gradient of the rolled plate.The model of gradient temperature shear rolling is established.Deformation characteristics of rolled plate under this rolling pattern were analyzed.The influence of process parameters such as gradient temperature and speed ratio on strain distribution and uniformity was studied.Equivalent and shear strain sensitivity equations were fitted(3)Shear action can be introduced by the speed ratio to effectively promote the core deformation of the rolled plate,but the problem of the rolled plate bending is caused.The asymmetry coefficient and bending value of the rolled plate were defined,and the effect of different process parameters on the deformation asymmetry of the rolled plate was quantitatively analyzed.The variation of the bending degree of the rolled plate was analyzed and the bending control equation was fitted.The bending degree of the rolled plate can be reduced by adjusting the temperature difference between the upper and lower surfaces of the rolled plate.The bending control equation was obtained by regression fitting.Based on different process parameters,the reasonable temperature difference between the upper and lower surfaces was calculated by this formula,so that the bending degree of the rolled plate was effectively regulated.(4)The experiments of symmetrical rolling and gradient temperature shear rolling were carried out.The deformation of rolled plate was measured by "grid method" and the deformation characteristics of rolled plate were obtained.The results show that the rolled plate will be introduced with strong shear due to the temperature difference between the upper and lower surfaces and the speed ratio,and the shear deformation of the center layer of the rolled plate is further increased under the combined action of the two.(5)The effects of symmetrical rolling and gradient temperature shear rolling on microstructure and properties of rolled plate were studied by Optical Micrographs and hardness test.The results show that the grain size of the central layer of the plate under gradient temperature shear rolling are refined by 33.5% compared with the symmetrical rolling.From the microscopic point of view,it is proved that the deformation is more favorable to the depth of the core than the symmetrical rolling.In addition,the thick-directional hardness of the rolled plate was increased by gradient temperature shear rolling,and the average hardness value increased from 88.8HV to 97.7HV...