| Since the 6xxx aluminum alloy sheet has advantages of good formability and excellent corrosion resistance as well as highly bake-hardening properties by using painting bake process,it is an ideal lightweight automotive body sheet material.However,the production costs of traditional 6xxx aluminum alloy automotive body sheet is much higher,which hinders its wide application and promotion.The Sn element is rich in storage and prices low,and the effect of microalloying is remarkable.Compared with the higher priced elements such as In,toxic elements such as Cd and other elements,which has greater use value,thus,in recent years,the researchers have been greatly concerned it.However,some problems still exist in the process of research in Sn-microalloyed 6xxx series aluminum alloy,focused on the role of Sn elements in alloy and reasonable aging process and performance of the control in Sn-microalloyed 6xxx series aluminum allo.To this end,this paper studies the aging performance of Snmicroalloying 6xxx aluminum alloy,and has important practical guiding significance for the development and promotion of aluminum alloy.In this paper,we designed four kinds of 6xxx aluminum alloy plates with different trace Sn,after a solution treatment at 550? for 20min,then separately subjected at room temperature by 14 d NA+AA(T4),90? by 5 h PA(T4P)+ AA and AA(Qc),to study the effect of Sn on the natural aging properties of 6xxx alloy,and the effect of Sn on 170? to 210? artificial aging properties and the influence of the main reinforcement phase precipitation kinetics of 6xxx alloy in T4 state&T4P state&Qc state.The main conclusions obtained in the research are as follows:1.With the content increased from 0.03%to 0.08%of Sn,the inhibition of natural aging increased from 250min to 15h.Due to the addition of Sn,the formation of the initial GP zone in the initial period of natural aging of the 6xxx alloy was significantly inhibited,it is therefore impossible to make the alloy fast aging and delay the natural aging of the alloy.2.During low temperature presaging,Sn will decrease the rate of pre-aging in early stage,but it has no significant effect on the aging.At the high temperature artificial-aging stage,the addition of Sn will accelerate the hardening speed of the initial period,and it will delay the time of peak hardness of the alloy.In short-aging state,a large number of diffuse distribution of atomic cluster and GP zone are found.In peak-aging state,the atomic cluster disappear entirely under the peak-ageing state,GP zone are dispersed in the matrix,and their size gradually increased.Meanwhile,a large number of ?" phase and pre?" phase are distributed.In over-aging stage,the size of the GP zone and the needle precipitation phase increased,and the short rod precipitated phase are found.With the increase of the artificial-aging temperature,the process of the change of aging in the substrate is also accelerating.3.The hardening rate of T4?T4P state alloy was significantly reduced at the initial stage of secondary aging.With the increase of Sn content of elements,the early stage of the aging hardening rate is increasing,at the same time T4,T4P state ?" phase precipitation activation energy can be increased,and reduce the peak hardness of the alloy at the same time,it appears the baking paint softing.The activation energy of ?" phase in T4 state alloy is lower,and the activation energy of ?' phase in T4P state alloy is lower.The 190? treatment' peak aging time of the T4 state alloy less than the T4P state alloy.When the Sn content is greater than 0.08%,the activation energy of ?' phase in pre-aging state alloy can be significantly improved,the formation and growth of ?' phase are prevented. |
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