A hybrid heat input strategy for enhancing as-built mechanical performance and geometric uniformity in stainless steel-aluminum bimetallic wire-arc directed energy deposition

Wire-arc directed energy deposition (DED) enables fabrication of large-scale bimetallic structures, but stainless steel–aluminum (SS-Al) direct-transition interfaces remain challenging because the thermal conditions required to improve surface wetting and prevent defects such as undercuts, lack of fusion, and edge cracking also accelerate formation of brittle Fe–Al intermetallic compounds (IMCs). To address this challenge, we present a hybrid heat-input (Hybrid HI) strategy that treats the first Al layer deposited on stainless steel as a distinct interface-forming step, followed by a uniform low-heat-input (LHI) setting for subsequent layers. In tall SS316L-Al4043 bimetallic builds, Hybrid HI improved interface quality relative to an All LHI build strategy, achieving 19% lower interface contact angle and 43% higher MBL while maintaining a thin IMC layer (≤10 µm) and improving wall-width uniformity by 87%. Slow strain rate testing in air on as-built coupons showed that Hybrid HI increased peak load-bearing capacity by 2.64 times and displacement at failure by 3.33 times, with fracture surfaces exhibiting a higher fraction of ductile failure. These results show that improving the mechanical performance and geometric uniformity of as-built SS–Al wire-arc DED structures requires layer-targeted heat-input design based on first-layer wetting and bonded footprint, rather than IMC minimization alone.