| 6xxx aluminum alloy has beenwidely used as lightweight material for the automobile body structural parts,such as the energy absorbing components.The energy absorption ability and bending strength of these components can be actually improved by optimizing the aging process.For 6xxx aluminum alloy with various contents of Mg and Si,the natural aging shows different strengthening behavior to subsequent artificial aging.In this paper,in order to understand the aging strengthening behavior of alloy elements,two aluminum alloys(6063 and6061aluminum alloy)are studied to exploit the aging strengthening mechanism based on two modified models,namely the Aging process-yield strength quantification model and the Na Mo model.The two modified models are used to predict the mechanical properties of two alloys and the predicted results have a good agreement with the test results.Then the predicted parameters are introduced into the finite element simulation to predict the crushing behaviors and three-point bending properties.The effects of natural aging on mechanical properties of 6xxx aluminum alloys are studied by hardness tests.The hardness increases with the prolongation of natural aging.According to the aging precipitation kinetics,the microstructure evolution parameters of the Mg-Si clusters formed in 6xxx aluminum alloy during natural aging are calculated.The effect of alloy composition on the growth rate of clusters is negligible.However,6061 aluminum alloy has higher nucleation rate and volume fraction change rate than 6063 aluminum alloy,and the former is higher above 40%as hardness as the latter.By tensile tests and TEM detection,it is found that natural aging has a promoting effect on artificial aging of 6063 aluminum alloy.The reason is that the the rod-likeβ’phase transfers to needle-likeβ"phase and the average diameter of precipitates decreases and the quantity density increases during the artificial aging process with the prolongation of natural aging,which leads to the yield strength increasing and the strain hardening index increasing.However,natural aging has an inhibitory effect on6061 aluminum alloy.The reason is that only acicularβ"phase is produced during artificial aging,and the average diameter ofβ"phase increases,the quantity density decreases,resulting in decreasing the yield strength and strain hardening index.With the natural aging prolonging,the growth rate and volume fraction of precipitates in6063 aluminum alloy is increased,and the nucleation barrier is decreased;the growing rate of dislocation density in the plastic deformation increases,and the work hardening rate strengthens.However,prolonging the natural aging reduces the growth rate ofβ"phase in 6061 aluminum alloy,and the nucleation barrier increases;the growing rate of dislocation density in the plastic deformation decreases,and the work hardening rate weakens.Through the crushing tests,it is found that although the natural aging prolongs from 1 hour to 1 week followed by peak artificial aging,the deformation mode of two kinds of 6xxx aluminum alloy energy absorbing components remains the same.However,the absorbed energy of 6063 and 6061 aluminum alloy components increases by 2 times and 3 times respectively.With the natural aging prolonging,the crushing parameters(F_pand F_m)of peak aging 6063 and 6061 aluminum alloy energy absorption components increase and decrease,respectively.At the same natural aging,with the artificial aging prolonging,the F_pand F_mof the two kinds of 6xxx aluminum alloy energy absorption components increase continuously.But in the underage,the energy absorption of 6061 aluminum alloy energy absorption component is greater than that of 6063 aluminum alloy.At the peak aging,the energy absorption of both are equal.The three-point bending experiments show that the bending strength of the two aluminum alloys decreases with the artificial aging prolonging,and the bending strength reaches the lowest at peak aging.Two aging strengthening models are expanded and modified.First,the aging process-yield strength quantification model is modified considering the precipitate growth delay induced by the peak aging platform.And the modified calculation results are in better agreement with the experimental values.Secondly,considering that 6xxx aluminum alloy with low content of Mg and Si elements has a significant incubation period at the beginning of artificial aging,the Na Mo model is modified.During the incubation period,the strength of the alloy unchanges.The modified Na Mo model results are more consistent with the experimental results.By introducing the stress-strain curves predicted in the Na Mo model and J-C constitutive parameters into the finite element simulation,the crushing performance and three-point bending performance of two kinds of 6xxx aluminum alloy profiles are predicted.In the finite element simulation process of crushing and three-point bending,the Na Mo model and J-C model are established by combining C-L failure criteria,respectively,to simulate the mechanical properties and fracture failure behavior of 6xxx aluminum alloy in the axial crushing and three-point bending process.The simulated results are compared with the experimental results.It is verified that the errors of Na Mo+C-L model and J-C+C-L model in predicting the mechanical properties of 6xxx aluminum alloy components are within 10%. |
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