Study on the Formation and Regulation Mechanism of W Phase and the Improvement of Mechanical Properties in Homogenization of Cast Al–Cu-Sc-Zr Alloys: Experiments and Calculations

With the aim of elucidating W phase formation in the cast Al–Cu-Sc-Zr alloy during homogenization, its mechanism of formation was revealed using quasi in situ characterization and first principles calculations. A homogenization method was proposed to improve the mechanical properties by regulating the formation of the W phase. Based on first principles calculations, it was deduced that the Sc atoms in the Al matrix have a tendency to segregate into the GP zone and θ'' bulk phases, but cannot replace atoms in the θ′ and θ phase bulk phases. The experimental results showed that the combination of Sc atoms and vacancies during the homogenization process provides nucleation sites for the GP zone and the θ'' phase, which were transformed into the W phase by the diffusion of Sc atoms. It has been determined that the Sc atoms were precipitated in the Al matrix in the form of Al3(Sc,Zr), which can inhibit the formation of the W phase, thereby improving the strength and ductility of the alloy, and its yield strength, ultimate tensile strength, and elongation were increased by 17.9%, 16.1% and 41.8%, respectively.