To meet the demand for efficient joining of dissimilar materials in aerospace

this study explores interface regulation mechanisms during ultrasonic welding of TC4 titanium alloy to carbon fiber-reinforced polyphenylene sulfide (CF/PPS) composites. A multiscale physicochemical interface engineering strategy is proposed

combining silane coupling agent functionalization with laser microtexturing. We systematically examined how welding parameters

energy director design

and interface modifications affect joint performance. Composite modification through titanium-surface laser engraving and energy-director coatings shifted the interfacial bonding mechanism from mechanical interlocking to a mechanochemical synergy. Under shallow-depth constraints

the linear microtextures achieved optimal shear strength (32.03 MPa)

representing a 70.2% increase over deep-depth conditions (18.82 MPa). Without depth restrictions

circular arrays showed superior stability

with an average shear strength of 24.26 MPa

23.7% higher than grid patterns. Fractography revealed cohesive

interfacial

and mixed failure modes

clarifying the mechanisms behind the strength improvement. This work provides both theoretical and practical insights for dissimilar-material joining in aerospace applications.