| Heat-treatable 6xxx series aluminum alloys are widely used in transportation,constructions and aerospace fields due to the medium aging strength and excellent extrusion performance.However,6xxx aluminum alloys have the "room temperature parking" effect,that is,the natural aging has an adverse effect on the subsequent conventional artificial age strengthening of the alloys(such as reducing the aging precipitation kinetics and weakening the age hardening effect).It results in the problem of excessive artificial aging peak time of 6xxx aluminum alloys,which seriously restricts the wide application of 6xxx aluminum alloys.Considering that Sn alloying and pre-deformation have the characteristics of inhibiting the natural age hardening of alloys and promoting artificial age precipitation,this paper will explore the influence of Sn alloying and pre-deformation on the precipitation behavior of a 6xxx aluminum alloys during aging,and prepare6 xxx aluminum alloys with good performance and fast aging response.Combined with hardness and tensile tests,SEM and TEM characterization,and precipitation kinetic analysis,the main conclusions are as follows:(1)There are two forms and functions of Sn element in 6xxx aluminum alloys:when the addition of Sn exceeds the maximum solid solubility in Al,Sn element exists in the form of Mg2 Sn phase.The Mg2 Sn particles can pin grain boundaries,reducing the grain size of the cast alloys;when Sn is dissolved in the Al matrix in the form of solute atoms,it affects the precipitation behavior of the alloy during aging.(2)Under the synergistic effect of Sn alloying and room temperature predeformation,the aging precipitation rate of Al-Mg-Si-Cu(6xxx)aluminum alloys increases and the aging response is enhanced: the peak aging time decreases from 12 h to 7 h;the yield strength of the peak-aged alloy increases from 285 MPa to 334 MPa.The influence of the combination of Sn alloying and room temperature pre-deformation on the aging precipitation behavior of Al-Mg-Si-Cu alloy has been revealed: the introduction of Sn element can promote the formation of Sn-containing solute atom clusters,making it easier for the clusters to transition to subsequent metastable phases(such as β? phase).The introduction of dislocations by pre-deformation can accelerate the diffusion of solute atoms and further promote the transition of Sn-containing solute atom clusters to subsequent metastable precipitated phases.(3)Under the influence of natural aging,the aging precipitation rate of Al-MgSi-Cu alloy increases under the synergistic effect of Sn alloying and room temperature pre-deformation,while the aging response is strengthened: the peak aging time decreases from 16 h to 3 h;the yield strength of the peakaged alloy increases from 260 MPa to 348 MPa.The synergistic mechanism of Sn alloying and pre-deformation on the artificial aging precipitation behavior of the alloy under the influence of natural aging has been revealed:a certain amount of Sn-containing solute atom clusters could form during the natural aging period,and this Sn-containing solute atom cluster is the same as the Sn-containing solute atom cluster in the early stage of subsequent artificial aging,so the number of Sn-containing solute atom clusters increases.At this time,dislocations can accelerate the diffusion of solute atoms,the precipitation rate of the alloy can be further increased and the number of precipitated phases increases.(4)The calculation of β? phase activation energy under different conditions shows that the synergistic effect of Sn alloying and room temperature predeformation can significantly promote the aging precipitation kinetics of alloys: that is,the synergistic effect of Sn alloying and room temperature pre-deformation reduces the activation energy of the aging precipitated phase. |
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