Effect Of Microalloying Element Doping On Intermetallic Compounds In Al-Zn-Mg-Cu Alloy

Al-Zn-Mg-Cu alloy has many kinds of alloy elements and various intermetallic compounds,which will not only affect the microstructure of the alloy,but also have a great influence on the properties of the alloy.In recent years,the addition of trace elements to Al-Zn-Mg-Cu alloy is an important way to strengthen and toughen the alloy.The added trace elements may enter into the alloy phase to form doping phase and thus affect the overall properties of the alloy.At present,the influence of the addition of trace elements on the stability and mechanical properties of the intermediate phase of the alloy is still unclear.Therefore,the effects of microalloying elements on the properties of intermetallic compounds were studied by the combination of first-principles calculation and experimental methods.In this paper,the first-principles method based on density functional theory was used to calculate the influence of the doping of trace alloy elements Zr,Ti or Nb on the stability and mechanical properties of??Al2Cu?,S?Al2CuMg?and??MgZn2?phases in Al-Zn-Mg-Cu.And the effect of Ti or Nb doping on the stability and mechanical properties of the L12 structural Al3Zr phase was calculated.This is to supplement the relevant theoretical calculation of the influence of the addition of trace elements on the phase of the high-strength aluminum alloy,and at the same time provide theoretical guidance for the design of the type and content of trace elements in the high-strength aluminum alloy.Combination study of calculation with experimental research was used to investigate the existence of trace elements Zr and Ti in the Al-Zn-Mg-Cu alloy.The main conclusions obtained in this article are as follows:The formation energy of?,S and?phases doped with Zr or Ti decreases with the increase of the content of doped atoms,which can improve the structural stability of each phase.Nb-doped?,S,and?phase formation energies all increase,and phase stability decreases.The doping of S and?phases with Zr and Ti makes the Young's modulus of the precipitated phase increase and the anisotropy value decreases,which can enhance the alloy.When Ti is doped with L1₂ structure,the formation energy of the system decreases linearly with the increase of the doping atomic concentration and then increases.In a certain concentration range,the doping of Ti atoms enhances the stability of the L12metastable phase,which is beneficial to improve the stability of the L1₂-Al₃Zr metastable phase.The increase of Young's modulus of the Ti-doped Al₃Zr phase and the decrease of the anisotropy value are all beneficial to the improvement of the alloy strength.Combined with the theoretical calculation results,it is found that when Zr and Ti are added together,the two elements will combine with Al to form an Al-Zr-Ti complex ternary compound with the L1₂ structure and D0₂₃3 structure.The experimental results show that when Ti is doped in the L1₂-Al₃Zr phase,the measured lattice constant becomes larger,which is in good agreement with the theoretical calculation results and is likely to occupy the position of Al atoms.This finding provides a theoretical basis for correcting the long-held belief that Ti occupies the Zr position in the L12-Al3Zr phase.