Strength enhancement of high-strength aluminum alloy oscillation laser–arc hybrid welded joints via TiC nanoparticles

High-strength aluminum alloys are attractive for lightweight structures, but their weldability in fusion processes is limited by coarse grains and brittle grain-boundary intermetallics. In this work, TiC nanoparticles were incorporated into the fusion zone during oscillating laser–arc hybrid welding to tailor the microstructure and mechanical response of a high-strength aluminum alloy. TiC addition refined weld grains and promoted a columnar-to-equiaxed transition; at 1.0 wt. % TiC, the average weld grain size decreased from 60.23 to 37.27 μm and a nearly fully equiaxed morphology formed. TiC nanoparticles within grains and along grain boundaries transformed grain-boundary θ-Al2Cu/η-MgZn2 from continuous strips into reticular and particulate products, whereas 1.5 wt. % TiC caused nanoparticle agglomeration and higher porosity. As a result, joint properties showed a nonmonotonic dependence on TiC content: at 1.0 wt. % TiC, the weld microhardness increased by about 17 HV, the ultimate tensile strength rose from 288 to 341 MPa, and the elongation improved from 3.16% to 5.73%. Orowan strengthening from dispersed TiC nanoparticles, assisted by Hall–Petch grain refinement and defect reduction, mainly accounted for the strength increment. These findings demonstrate an efficient route to strengthen high-strength aluminum alloy welds via TiC nanoparticle-assisted oscillating laser–arc hybrid welding.