Ti/Mg bimetal composites possess the advantages of light weight and high strength, making them highly promising for various applications in lightweight field. This study enhanced the interface bonding of the TC4/AZ91D bimetal composite through fabrication of a pyramidal lattice structure on the TC4 surface. The lattice structure exhibited a high porosity and rough surface, which strengthened the interface bonding of the liquid–solid compound casting TC4/AZ91D. Finite element orthogonal analysis results indicated that the influential order of the lattice structure parameters is aspect ratio > inclined angle > node-to-strut diameter ratio. The optimal lattice structure parameters (within rod diameter range of 0.5–2 mm) were determined to be rod diameter d_s=1.7 mm, aspect ratio (l/d_s) of 5.5, inclined angle ω of 52°, and node-to-strut diameter ratio (d_n/d_s) of 2.2. Experimental verification showed a trend of increasing and then decreasing of bonding strength of the bimetal with an increasing of l/d_s. Under the optimal lattice structure parameters, bonding strength of the bimetal reached 91 MPa. Analysis of interfacial wettability revealed that the rough textured surface of the additively manufactured TC4 lattice structure enhanced the wettability between TC4 and AZ91D, resulting in a serrated interface structure, thus strengthened the mechanical bonding at the interface.