Liquid immiscibility and core-shell morphology formation in ternary Al–Bi–Sn alloys

• The liquid demixing, morphology and microstructure in Al–Bi–Sn alloys were studied.
• Three types of morphology were classified and discussed.
• The conditions for formation of the core-shell morphology were obtained.
• The phase transition behaviors agree with the microstructure characterization.
• The Al/Sn–Bi core-shell particles show promise for use in electronic packaging.

The effects of composition on liquid immiscibility, macroscopic morphology, microstructure and phase transformation in ternary Al–Bi–Sn alloys were investigated. Three types of morphology, the core-shell type, the stochastic droplet type and uniform dispersion type, of Al–Bi–Sn particles prepared by a jet breakup process were distinguished, and the relationships between which were discussed. The phase transformation behaviors of the Al–Bi–Sn alloys were studied by thermal analysis, in agreement with the microstructural observation and microanalysis. The liquid immiscibility and formation of the core-shell morphology in Al–Bi–Sn alloys are easily achieved when the composition lies in the liquid miscibility gap. The particles exhibit a high melting point Al-rich core with a low melting point Sn–Bi-rich solder shell, showing promise for application as high-density electronic packaging materials.