Study On The Effect Of External Stress On The Aging Precipitation Behavior Of Al-Cu-X Alloy Single Crystal

Due to the non-uniform precipitation response of strengthening phase under external stress field,the preferred orientation precipitation behavior,namely stress orientation effect,which is one of the key basic problems involved in creep aging forming of 2000 series aluminum alloy.Therefore,in this paper,macro coarse grains of centimeter grade Al-Cu-Mg-Ag and Al-Cu-Li-(Mg-Ag)alloys were prepared by cyclic strain-high temperature annealing process,The influencing factors and growth mechanism of abnormal grain growth of alloy during single crystal preparation were studied.Based on single crystal,the effects of stress loading orientation on the precipitation characteristics and mechanical properties of precipitates during single crystal aging of Al-Cu-Mg-Ag alloy were studied by EBSD,TEM,HADDF-STEM,DSC,Vickers hardness and other analytical methods.The effects of solute elements and dislocation introduced by predeformation on the precipitation characteristics and mechanical properties of Al-Cu-Li-(Mg-Ag)alloy during aging were investigated.The main research results are as follows:(1)The number of strain annealing,pre-drawing strain and annealing temperature have great influence on the grain growth of the alloy during cyclic pre-drawing strain-annealing.Under certain annealing temperature,there is a critical value of pre-stretching strain,which makes the abnormal grain growth of Al-Cu-Li alloy reach the maximum grain size after strain annealing.The optimal strain-annealed single crystal preparation process was that the alloy was annealed at 540°C for 48 h after 0.8%pre-stretching strain,and the cycles were 2-3 times.(2)Al-Cu-Mg-Ag alloy has different precipitation characteristics in the stress aging samples loaded along different directions.The size distribution of?(Al₂Cu)phase in the samples loaded along Al direction is more uniform than that in the samples loaded along Al direction,and both samples have high-density?precipitates.On the contrary,the precipitation of?phase is significantly inhibited in the samples loaded along Al direction,and the precipitation of?phase is very little.The loading direction significantly affects the precipitation characteristics of the precipitated phases.The hardness of the stress-aged samples loaded along the<111>_Al direction is lower than that of the stress-aged samples loaded along the<001>_Al and<011>_Al directions.The precipitation of?phase in Al-Cu-Mg-Ag alloy system can be adjusted by controlling the loading direction during creep aging or stress aging.(3)The precipitation phase in Al-Cu-Li alloy is dominated by?'(Al₂Cu)phase with high density.The addition of trace Mg and Ag solute elements makes the precipitation of Al-Cu-Li-Mg-Ag alloy dominated by T₁(Al₂Cu Li)phase.The promotion of pre-deformation on the precipitation of Al-Cu-Li-Mg-Ag alloy is the combined action of trace solute elements and dislocations,and also promotes the precipitation of T₁ phase and?'phase.In the range of 0-3%pre-deformation,with the increase of pre-deformation,the number density of T₁ phase in Al-Cu-Li-Mg-Ag alloy increases from 3.189×102?m^-3 to 3.389×102?m^-3,while the average size of T₁ phase decreases from 240 nm to 160 nm,and the size of T₁ phase becomes more uniform.