Static/dynamic Tensile Mechanical Properties And Strengthening Mechanism Of New Al-Cu-X Alloy

Selected as the basic system in this thesis,the static/dynamic tensile mechanical properties of the Al-Cu alloy under Ti,Zn and Mg microalloying were investigated.The strengthening mechanism of Al-Cu-X alloy with Ti,Zn and Mg alloying elements was discussed by analyzing the microstructure and fracture morphology of Al-Cu-X alloy.Furthermore,in order to understand the dynamic mechanical properties of the new Al-Cu-X alloy,dynamic tensile experiments were performed by use of Split Hopkinson Tie Bar for Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloy at strain rates of 1000 s^-1,1500 s^-1,2000 s^-1,and 2500 s^-1,respetively.Meanwhile,the yield strength,tensile strength,elongation,and strain energy density of this alloy were all analyzed at different strain rates.By the aid of Abaqus finite software,the dynamic tensile simulations were conducted for Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloys.The studied results were obtained as follows:（1）The strength of Al-4.8Cu-Ti alloy with adding Ti element can be improved effectively.The tensile strength and yield strength of Al-4.8Cu-1Ti alloy reaches 408.3 MPa and 300 MPa,respectively,which increases by 83.2%and 80.3%respectively,compared with those of Al-4.8Cu alloy without Ti.（2）The mechanical properties of Al-4.8Cu-1Ti alloy by addition of appropriate amounts of Zn and Mg elements can improved effectively.The tensile strength,yield strength and elongation rate of Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloy reaches 560.1 MPa,380.6 MPa and 4.2%,respectively.（3）By the results of quasi-static/dynamic tensile experiments,it can be showed that the yield strength and tensile strength of the Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloy increase with the increase of strain rate.The tensile strength had a higher rate sensitivity.But,the elongation of the alloy presented a trend of increasing firstly,and then decreasing with the increase of strain rate.Under a high strain rate,the strain energy density increases with the strain rate increasing.The strain energy density increased by 28.8%,when the strain rate was increased from 1000 s^-1 to 2000 s^-1.（4）It can been seen from microstructure analysis that the number and size of the round granular second phase Al₂Cu and the slate-like second phase Al-4.8Cu-Ti have a greater influence on the mechanical properties of the alloy.When the Ti content is 1%,the mechanical properties of the alloy were advanced remarkably,which are ascribed to the fine slate-like compound and the major round granular precipitations,the mechanical properties of the Al-4.8Cu-1Ti alloy were significantly improved by the action of these two compounds with different Ti contents.The regular equiaxed crystals and slate-like compounds were formed in the microstructure of the Al-4.8Cu-1Ti-Zn-Mg alloy.So that,the outstanding mechanical properties were obtained in this alloy.（5）By observing the fracture morphology of the dynamic tensile specimens,it can be showed that the plastic deformation capacity gradually increases with the increase of the strain rate as the tough nest-like organization inside the fracture gradually increases.When the strain rate exceeds 2500 s^-1,the plastic deformation capacity of the alloy go into droping,because of the dominant role of the dislocation value-added mode.（6）Combined with the dynamic tensile experiments datas of Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloy,the Johnson-Cook constitutive equation was educed.The dynamic tensile simulations under different strain rates were conducted by use of Abaqus finite software for Al-4.8Cu-1.8Zn-1Ti-0.6Mg alloys.It can be found that the simulation results were in agreement with that of the experimental.