First Principles Investigation Of The Effects Of Solute And Solute Cluster On The Strength And Ductility Of Al-Cu Alloys

In aluminum alloys,the acquisition of high strength is usually accompanied by a loss of plasticity.To obtain aluminum alloys with both high strength and high plasticity,the first principle method based on density functional theory(DFT)is urgently required to reveal the influence mechanism of solute atoms and clusters on the local strength and plasticity of aluminum alloys from the atomic and electronic levels.On the basis of previous experimental research,this paper predicts four different stacking sequence interfaces configuration(001)α-Al//(001)θ’-Al2Cu of Al-Cu alloys at the atomic and electronic scale by the First-principles calculations based on density functional theory(DFT).The results indicate that the interface configuration with HCP as the stacking sequence is the most stable.As the coverage of Sc or Zr increases at the interface,the segregation energy on the α-Al side decreases.As the coverage of Cd increases,the segregation energy at all positions of the interface increases.As the coverage of Si increases,the segregation energy at all positions of the interface decreases.The segregation behavior of Sc,Zr,Si,and Cd on the side of the α-Al matrix at the(001)α-Al//(001)θ’-Al2Cu and(010)α-Al//(010)θ’-Al2Cu interfaces is only related to the interactions between solute atoms and host atoms,while the influence of interface structure distortion can be ignored.The segregation behavior of Si,Sc,and Zr solute atoms on the side of θ’-Al2Cu at the(001)α-Al//(001)θ’-Al2Cu and(010)α-Al//(010)θ’-Al2Cu interfaces is related to interactions between solute atoms and host atoms.In addition,the effect of the interface structure distortion can not be ignored.The segregation behavior of Cd on the side of θ’-Al2Cu at(001)α-Al//(001)θ’-Al2Cu interface is not only related to interactions between solute atoms and host atoms but also to interface structure distortion.However,the segregation behavior of Cd on the side of θ’-Al2Cu at(010)α-Al//(010)θ’-Al2Cu interface is only related to the interaction between solute atoms and host atoms,while the influence of interface structure distortion can be almost ignored.In addition,the effects of the solute atoms on interface strength and ductility are also investigated.Results show that the solute atoms Sc or Zr have a strengthening effect on the interface,mainly attributed to the strong interaction between the solute atoms Sc or Zr and the host atom Al.As the coverage increases,the strengthening effect becomes more obvious.The weakening effect of solute atom Cd on the interface is mainly attributed to the weak interaction between solute atom Cd and host atom Al.The strengthening or weakening behavior of solute atoms Sc,Zr and Cd on the interface comes from chemical contributions,while mechanical contributions can be ignored.The influence of solute atom Si on interface mechanical properties is relatively small.Compared to the interface without solute atom and interface with the solute atoms Si and Cd,the ratio of the Griffith work of fracture of interface with the solute atoms Sc or Zr to the dislocation nucleation work is larger,indicating that Sc or Zr can improve interfacial ductility.The introduction of vacancies does not change the most energetically favorable position of solute atoms at the interface.Vacancies strengthen the strengthening effect of solute Sc and Zr on the interface and reduce the weakening effect of solute atom Cd on the interface.It is attributed to the introduction of vacancies that lead to stronger covalent bonds near solute atoms at the interface.The solute atoms Sc,Zr,and Cd have a blocking effect on the passage of vacancies through the interface,and the blocking effect of Cd is the most obvious,which can be attributed to the maximum binding energy between Cd and vacancies at the interface.Effects of the segregation of the solute atoms on the homogeneous nucleation of the θ’-Al2Cu precipitation phase from solid solution α-Al are studied.Results show that the segregation of the solute atoms Sc or Zr at the interface(001)α-Al//(001)θ’-Al2Cu leads to a decrease in interface energy,resulting in a decrease in homogeneous critical nucleation work and critical nucleation radius ofθ’-Al2Cu precipitation phase.The segregation of Cd at the interface(001)α-Al//(001)θ’-Al2Cu causes an increase in interface energy,leading to an increase in homogeneous critical nucleation work and critical nucleation radius of θ’-Al2Cu precipitation phase.Si enters the θ’-Al2Cu precipitation phase,homogeneous critical nucleation work and critical nucleation radius of θ’-Al2Cu precipitation phase are related to the concentration of Si.Compared with the homogeneous nucleation of the θ’-Al2Cu precipitation phase from solid solution α-Al,the heterogeneous nucleation of θ’-Al2Cu precipitates attached to the dispersed phase Al3Sc is attributed to the smaller(001)θ’-Al2Cu//(001)Al3Sc interface energy and interface mismatch and its greater interface binding energy(chemical affinity).Compared to the dispersed phase Al3Sc,the heterogeneous nucleation of θ’-Al2Cu is dependent on the dispersed Al3(Sc,Zr),which has stronger nucleation ability due to the smaller(001)θ’-Al2Cu//(001)Al3Zr interface energy and greater interface binding energy(chemical affinity).Effects of solute clusters on the local strength and ductility in both Al and Cu alloys are studied.The calculations of elastic properties and the first-principles ideal strength calculation show that the chemical short-range ordering cluster L12-Al3Zr with a volume fraction of 3/27 not only leads to an increase in the strength of the Al alloy matrix(stress from 10.48 GPa to 12.15 GPa)but also leads to an increase in the ductility of the Al alloy matrix(strain from 34%to 40%).The reinforcement increase is attributed to the strong interaction between Zr atoms and host atoms Al.The improvement in ductility is attributed to the larger ratio of the Griffith work of fracture to the dislocation nucleation work.Compared with Cu-25%Sn-12.5%Zn solid solution,after 1/27 volume fraction of chemical short-range ordering cluster fcc-Fe is introduced into Cu-25%Sn-12.5%Zn solid solution,the strength and ductility increase simultaneously,which is consistent with the experimental results.This paper has important guiding significance for designing Al-Cu alloys that possess both high strength and high ductility through both theoretical calculations and experimental methods by adjusting the composition.