Improving interface joining strength of Ti6Al4V/AZ91D bimetal prepared by compound casting via Ni-coated Ti6Al4V lattice structure

The joining of titanium/magnesium (Ti/Mg) bimetals presents challenges due to the low mutual solubility and absence of metallurgical reactions between Ti and Mg. Herein we utilized the Ni-coated Ti6Al4V lattice structure to enhance the interfacial property of Ti6Al4V/AZ91D bimetal prepared by compound casting. The Box-Behnken design (BBD) was employed to optimize the lattice design. The resulting structure featured struts with a diameter ( d s ) of 2.4 mm, an aspect ratio ( l / d s ) ratio of 5.4, a tilt angle ( ω ) of 57°, and a node-to-strut diameter ratio ( d n / d s ) of 2.4. The optimized Ti6Al4V lattice structure manufactured by selective laser melting (SLM) exhibited α′ martensite with a high dislocation density, conferring exceptional tensile strength. The rough texture of the lattice surface enhanced adhesion with the Ni coating and improved wetting and reactivity between Ni and AZ91D alloy melt. This resulted in the formation of a serrated metallurgical interface with AZ91D alloy, which was primarily composed of α-Mg + Mg 2 Ni eutectic structure+τ-Ni 2 Mg 3 Al ternary phases. An impressive joining strength of 116.1 MPa was obtained under the optimized lattice structure, and the bimetal joint predominantly fails through the damage of AZ91D, aligning closely with simulated failure predictions.