Interface microstructure regulation of Mg/Ti bimetals by thermal diffusion treatment of Ni-coated TC4 alloy

In the present work, solid-liquid compound casting process was used to fabricate TC4/AZ91D bimetals using thermal diffused Ni-coated TC4 alloy. The effects of thermal diffusion time of Ni-coated TC4 alloy on interface microstructure evolution and mechanical features of TC4/AZ91D bimetals were investigated. The interface microstructure has undergone the evolution of NiTi2, NiTi and Ni3Ti to NiTi2, NiTi and Ni2Ti4O (Mg) at Ni-Ti interface and (Mg2Ni + alpha-Mg) eutectic structure + Ni2Mg3Al ternary phase to eutectic-free (only Al3Ni, Al3Ti and Ni2Mg3Al) at Ni-Mg interface as the thermal diffusion time of Ni-coated TC4 alloy increased from 0.5 h to 5 h and 9 h. The maximum shear strength of 105.2 MPa was obtained for the eutectic-free interface of TC4/AZ91D bimetals when Ni-coated TC4 alloy were thermal diffused by 5 h. The rupture of TC4/AZ91D bimetals mainly takes place at (Mg2Ni + alpha-Mg) eutectic structure or between the interface of Ni3Ti layer/(Mg2Ni + alpha-Mg) eutectic structure when the thermal diffusion time of Ni-coated TC4 alloy is 0.5 h. Besides, with the thermal diffusion time increases to 5 and 9 h, the rupture occurs at the NiTi2 and Ni2Ti4O (Mg) reaction layers, respectively.