Dual-pulse arc modulation for enhanced microstructural homogeneity and mechanical isotropy in high-strength aluminum alloy additive manufacturing

Abstract

Fabricating high-strength Al-Zn-Mg-Cu alloy components via wire-arc directed energy deposition (DED) remains challenging due to inherent defects and anisotropic mechanical properties caused by uncontrolled heat input. This study introduces a dual-pulse modulated variable polarity arc additive manufacturing process as a fundamental advancement in addressing these limitations. By cyclically modulating the peak/base current ratio, the process induces periodic electromagnetic stirring and thermal oscillations in the molten pool, which fundamentally alters solidification dynamics. This innovation achieves a self-regulating cyclic microstructure of alternating fine equiaxed and columnar grains (aspect ratio reduced to 2.91), eliminates porosity (reduced to 0.65 %), and weakens the dominant <001> texture (pole density reduced from 17.47 to 9.88), thereby enhancing mechanical isotropy. Critically, the method refines grains by 50 % without altering nano-precipitate phases (η', 15–25 nm), preserving intrinsic precipitation strengthening. Post-deposition T6 heat treatment yields a tensile strength of 545.4 MPa, comparable to wrought counterparts, while retaining elongation (8.4 %). The work establishes a scalable, non-alloying strategy to suppress defects and anisotropy in high-strength aluminum alloys, advancing wire-arc DED toward aerospace-grade applications through precise arc energy modulation and molten pool control.