Unveiling non-equilibrium metallurgical phases in dissimilar Al-Cu joints processed by vaporizing foil actuator welding

An integrated experimental and computational approach has been adopted to investigate the formation mechanism of intermetallic compounds (IMCs) in dissimilar Al-Cu joints processed by vaporizing foil actuator welding (VFAW). Aiming to understand the formation of IMCs and their transition, the present work employed first-principles calculations of thermodynamic properties as a function of temperature and pressure together with diffusivities of Al and Cu from the literature. Agreeing with experimental observations, the predicted IMC formation sequence in the low-energy welding region is as follows. θ-Al₂Cu forms first due to the fast diffusivity of Cu in the Al-matrix. θ-Al₂Cu then transforms to η₂-AlCu because of the fast diffusivities of Al/Cu in θ-Al₂Cu. In the high-energy welding region, the stable γ₁-Al₄Cu₉ and the metastable θ’’-Al₃Cu are also formed in addition to the aforementioned θ-Al₂Cu and η₂-AlCu. η₂-AlCu and considerable γ₁-Al₄Cu₉ are the major phases in the high-energy welding region. The present approach, combining experiments and calculations, is proven to be a practical way to understand non-equilibrium metallurgical processes, as demonstrated through the study of VFAW Al-Cu joints.