| In modern industry,aluminum alloy has the advantages of small density,corrosion resistance and high specific strength,which has become the best material to replace steel in automobile industry.6xxx series aluminum alloy with relatively superior comprehensive properties has a broader application prospect in the automobile industry.In the automobile manufacturing,it is usually necessary to bend the body sheet into a certain curvature.Considering the requirements of aerodynamics,structural mechanics and aesthetics,it puts forward higher requirements for the bending performance of the sheet.The bending property of aluminum alloy is closely related to heat treatment state,forming temperature and complex process parameters.It is of great significance to master the bending deformation law of aluminum alloy sheet for improving its bending performance.In this paper,6061 aluminum alloy sheet is taken as the research object.By three-point bending experiments,the effects of different heat treatment conditions(NA,HT,ST,T6-4h and T6-8h)and deformation conditions(initial sheet temperature T,punch radius R and span between supports L)on the bending deformation of aluminum alloy sheet are studied.Under different deformation conditions,three levels of each deformation conditions are selected by single factor bending experiment.Then,based on the box Behnken response surface method with different deformation conditions,the regression models of bending angle,bending radius and springback angle are established.Finally,the sensitivity of each deformation conditions to the springback angle of aluminum alloy sheet is determined by variance analysis,and the response surface model about the springback angle is established.At the same time,using the finite element software LS-DYNA,the main stress distribution of aluminum alloy sheet under different heat treatment and high temperature conditions is further verified.The main results are as follows:(1)Under different heat treatment conditions,the deformation of T6-8h aluminum alloy sheet is the most serious,showing the minimum bending radius and thickness of 25.7mm and 1.85mm respectively.However,the bending radius of homogenized aluminum alloy sheet is the largest,which is 45.9%higher than that of natural aging aluminum alloy sheet.This is due to more materials involved in bending deformation.The bending properties of homogenized treated and solution treated aluminum alloy sheets are higher than those of natural aging and T6 aluminum alloy.With the increase of aging time,the material strength of T6 aluminum alloy can be improved,resulting in greater springback and neutral layer shift.T6-8h aluminum alloy sheet has the highest springback angle and neutral layer offset,which are 20.3°and 0.25(expressed by neutral layer coefficient).However,the springback angle and neutral layer offset of the homogenized aluminum alloy sheet are the lowest,which are 10.1°and 0.45 respectively.(2)Under different deformation conditions,the horizontal order of the sensitive factors affecting the springback angle after bending is:the initial sheet temperature,the span of the supporting column and the radius of the indenter.The bending angle of aluminum alloy sheet is 120°.The results of response surface optimization show that the optimal deformation conditions are T=317?,R=10 mm,L=119 mm,which are in line with the expected parameters,and have passed the experimental verification.The mathematical model established by regression analysis can accurately predict the bending deformation behavior of 6061 aluminum alloy sheet. |
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