Uncovering the combining V with Ni micro-addition alloying on the mechanical properties and multiphase transformation during solidification and homogenization of Al–Zn–Mg–Cu–Sc alloy

The ultimate tensile strength of the T6-aged Al–Zn–Mg–Cu–Sc alloy is improved by 24 MPa reached 667 MPa with the addition of 0.10 % V, 0.20 %Ni and decrease 0.1 %Sc. The thermodynamic and microalloying mechanisms of phase transformation during solidification and homogenization of Al–Zn–Mg–Cu–Sc–V–Ni alloy were clarified. The phase transformation model of Al₃Sc (V, Ni) structure induced by V and Ni addition during homogenization was established. The calculation radius showed that coherent L1₂-ordered Al₃Sc(V, Ni) nanoparticles were formed in the Al–Zn–Mg–Cu–Sc–V–Ni alloy, which had a small critical nucleation radius (22.0 nm). The large thermodynamic driving force and the high kinetic energy migration energy barrier of γ-Al₇Cu₄Ni and Al₃Sc (V, Ni) phases led to the finer microstructure of grain. V element not only promoted the formation of Al₂₁V₂ phase containing Sc but also hindered the mutual diffusion of Al and (Sc, Ni) elements in the eutectic system via segregation at the α-Al/Al₃Sc (V, Ni) interface, which improved the stability of the whole alloy. The edge nucleation of γ-Al₇Cu₄Ni phase upon its diffusion into a Sc-containing Al₂₁V₂ phase induced the formation of Al₃Sc (V, Ni) structure, whereas the segregation of V and Ni further strengthened the alloy matrix.